U.S. patent application number 16/042294 was filed with the patent office on 2019-06-27 for systems and methods for real-time, transcranial monitoring of blood-brain barrier opening.
This patent application is currently assigned to The Trustees of Columbia University in the City of New York. The applicant listed for this patent is The Trustees of Columbia University in the City of New York. Invention is credited to Vincent P. Ferrera, Elisa E. Konofagou, Fabrice Marquet, Tobias Teichert, Yao-Sheng Tung, Shih-Ying Wu.
Application Number | 20190192112 16/042294 |
Document ID | / |
Family ID | 52584182 |
Filed Date | 2019-06-27 |
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United States Patent
Application |
20190192112 |
Kind Code |
A1 |
Konofagou; Elisa E. ; et
al. |
June 27, 2019 |
SYSTEMS AND METHODS FOR REAL-TIME, TRANSCRANIAL MONITORING OF
BLOOD-BRAIN BARRIER OPENING
Abstract
Systems and techniques for real-time, transcranial monitoring of
safe blood-brain barrier opening include determining an approach
angle for targeted blood-brain barrier opening proximate a
predetermined region in a brain of a patient, and positioning an
ultrasound transducer to generate a focused ultrasound signal at
the determined approach angle to the predetermined region in the
brain.
Inventors: |
Konofagou; Elisa E.; (New
York, NY) ; Teichert; Tobias; (Pittsburgh, PA)
; Ferrera; Vincent P.; (New York, NY) ; Marquet;
Fabrice; (Bordeaux, FR) ; Tung; Yao-Sheng;
(Redmond, WA) ; Wu; Shih-Ying; (New York,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Trustees of Columbia University in the City of New
York |
New York |
NY |
US |
|
|
Assignee: |
The Trustees of Columbia University
in the City of New York
New York
NY
|
Family ID: |
52584182 |
Appl. No.: |
16/042294 |
Filed: |
July 23, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14476543 |
Sep 3, 2014 |
10028723 |
|
|
16042294 |
|
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61873310 |
Sep 3, 2013 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G16H 50/30 20180101;
A61N 7/02 20130101; A61B 2090/378 20160201; A61B 8/5223 20130101;
A61B 8/4281 20130101; A61N 2007/0052 20130101; A61N 2007/0091
20130101; A61N 2007/0039 20130101; A61B 8/0808 20130101; A61B 8/481
20130101 |
International
Class: |
A61B 8/08 20060101
A61B008/08; A61N 7/02 20060101 A61N007/02; A61B 8/00 20060101
A61B008/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH
[0002] This invention was made with government support from the
National Institutes of Health under Grant Nos. R01AG038961 and
R01EB009041. The government has certain rights in the invention.
Claims
1. A system for real-time, transcranial monitoring of safe
blood-brain barrier opening, comprising: an ultrasound transducer;
and a targeting component, coupled to the ultrasound transducer and
configured to: determine an approach angle for targeted blood-brain
barrier opening proximate a predetermined region in a brain of a
patient, and position the ultrasound transducer to generate a
focused ultrasound signal at the determined approach angle to the
predetermined region in the brain.
2. The system according to claim 1, wherein the ultrasound
transducer operates at an intermediate frequency of 500 kHz.
3. The system according to claim 1, wherein the targeting component
is configured to target the predetermined region of the brain
without use of a magnetic resonance image monitoring.
4. The system according to claim 1, wherein the targeting component
comprises a stereotactic manipulator to target the predetermined
region in the brain.
5. The system according to claim 1, further comprising a real-time
monitoring component configured to monitor opening of the
brain-blood barrier by the ultrasound transducer,
6. The system according to claim 1, wherein the real-time
monitoring component monitors using a frequency of a backscattered
acoustic signal generated in response to the targeting by the
ultrasound transducer.
7. The system according to claim 6, wherein the real-time
monitoring component comprises a passive cavitation detector.
8. A method for real-time, transcranial monitoring of safe
blood-brain barrier opening, comprising: providing an ultrasound
transducer; determining an approach angle for targeted blood-brain
barrier opening proximate a predetermined region in a brain of a
patient; and positioning the ultrasound transducer to generate a
focused ultrasound signal at the determined approach angle to the
predetermined region in the brain.
9. The method according to claim 8, further comprising operating
the ultrasound transducer at an intermediate frequency of 500
kHz.
10. The method according to claim 8, further comprising targeting
the predetermined region of the brain without use of a magnetic
resonance image monitoring.
11. The method according to claim 8, further comprising targeting
the predetermined region in the brain using a stereotactic
manipulator.
12. The method according to claim 8, further comprising monitoring
the opening of the brain-blood barrier using the ultrasound
transducer.
13. The method according to claim 12, wherein the monitoring is
performed using a frequency of a backscattered acoustic signal
generated in response to the targeting by the ultrasound
transducer.
14. The method according to claim 12, wherein the monitoring is
performed using a passive cavitation detector.
15. The method according to claim 12, wherein the monitoring
comprises detecting an occurrence of the blood-brain barrier
opening.
16. The method according to claim 8, wherein the patient is
anesthetized during the blood-brain barrier opening.
17. The method according to claim 8, wherein the patient is awake
during the blood-brain barrier opening.
18. The method according to claim 8, further comprising:
administering microbubbles to the patient; generating the focused
ultrasound signal at the determined approach angle to the
predetermined region in the brain; and monitoring an occurrence of
the blood-brain barrier opening.
19. The method according to claim 18, wherein the monitoring is
performed using PCD.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/476,543, filed Sep. 3, 2014, now allowed, which claims the
benefit of U.S. Provisional Application No. 61/873,310, filed Sep.
3, 2013, each of which is incorporated by reference herein in its
entirety.
BACKGROUND
[0003] In certain techniques for targeted blood-brain barrier
opening, including using focused ultrasound (FUS), it can be
desirable to increase targeting accuracy while decreasing the time
and effort necessary for accurate targeting. Systems and techniques
for blood-brain barrier opening using FUS are described in U.S.
Patent Application Publication No. 2009/0005711, which is
incorporated by reference herein in its entirety.
[0004] Targeting accuracy can be reduced by aberrations of the
ultrasound beam caused by the skull. The discrepancy between the
high speed of sound through the skull and the low speed through the
underlying brain tissue, alone or along with attenuation of
ultrasound waves through the skull bone, can distort the beam
shape, including at higher frequencies. Moreover, the trabecular
layer of the skull can induce heterogeneities in both speed of
sound and density, which can lead to phase aberrations of the
acoustic beam. At higher frequencies, the defocusing effect of the
skull can be increased as the wavelength can reach the size of
local skull bone heterogeneities (for example, the trabeculae can
be around 1 mm). The phase aberrations can be reduced by reducing
the ultrasound frequency. However, the size of the focal region can
likewise increase, which can increase the likelihood of undesirable
inertial cavitation.
[0005] In therapeutic ultrasound, it can also be desirable to have
real-time monitoring and treatment efficiency verification. A
passive cavitation detector ("PCD") can be used to transcranially
acquire the acoustic emissions stemming from the microbubble. The
frequency analysis of backscattered signals can be relevant to
characterize undesirable bubble-capillary interaction.
SUMMARY
[0006] Systems and techniques for transcranial monitoring of safe
blood-brain barrier opening in real time are disclosed herein.
[0007] In one embodiment of the disclosed subject matter, an
example system for real-time, transcranial monitoring of safe
blood-brain barrier opening can include an ultrasound transducer
and an ultrasound transducer; and a targeting component, coupled to
the ultrasound transducer and configured to determine an approach
angle for targeted blood-brain barrier opening proximate a
predetermined region in a brain of a patient, and position the
ultrasound transducer to generate a focused ultrasound signal at
the determined approach angle to the predetermined region in the
brain.
[0008] In some embodiments, for example and without limitation, the
system can include the ultrasound transducer can operate at an
intermediate frequency of 500 kHz. The ultrasound transducer can be
configured to operate without use of a magnetic resonance image
monitoring and can include a stereotactic manipulator for
performing targeting of the predetermined region in the brain.
[0009] In some embodiments, the system can also include a real-time
monitoring component for monitoring opening of the brain-blood
barrier by the ultrasound transducer. The monitoring component can
perform monitoring using a frequency of a backscattered acoustic
signal generated in response to the targeting by the ultrasound
transducer. The real-time monitoring component can include passive
cavitation detector.
[0010] In some embodiments, computer program products are provided
that comprise non-transitory computer readable media storing
instructions, which when executed by at least one data processor of
one or more computing systems, cause at least one data processor to
perform operations disclosed herein. Similarly, computer systems
are also described that can include, for example, one or more data
processors and a memory coupled to the one or more data processors.
The memory can temporarily or permanently store instructions that
cause at least one processor to perform one or more of the
operations disclosed herein. In addition, methods can be
implemented by one or more data processors either within a single
computing system or distributed among two or more computing
systems.
[0011] Certain variations of the subject matter disclosed herein
are set forth in the accompanying drawings and further description
below. Other features and advantages of the subject matter
described herein will be apparent from the description and
drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates an exemplary system for real-time,
transcranial monitoring of safe blood-brain barrier opening,
according to the disclosed subject matter.
[0013] FIGS. 2A and 2B are diagrams illustrating an exemplary
technique for sonication with subsequent MRI-based verification
according to the disclosed subject matter.
[0014] FIGS. 2C and 2D are cranial ultrasound scans for purpose of
illustration and confirmation of the disclosed subject matter.
[0015] FIGS. 3A-3D together illustrate a quantification of
targeting accuracy according to the disclosed subject matter.
[0016] FIG. 4 is a series of diagrams illustrating targeting
accuracy according to the disclosed subject matter.
[0017] FIG. 5 is a series of diagrams illustrating targeting
accuracy according to the disclosed subject matter.
[0018] FIG. 6 is a series of diagrams illustrating targeting
accuracy according to the disclosed subject matter.
[0019] FIG. 7 is an exemplary series of diagrams illustrating
harmonic ("HEI") and broadband ("BE1") energy increase according to
the disclosed subject matter.
[0020] FIGS. 8A and 8B are exemplary diagrams illustrating BBB
opening volume as a function of pressure and the average harmonic
energy increase according to the disclosed subject matter.
[0021] FIG. 9 is two exemplary magnetic resonance ("MR") images
illustrating T2-weighted (left) and SWI (right) MR images
corresponding to the technique of FIG. 2.
[0022] FIG. 10 is an exemplary series of coronal (left row) and
sagittal (right row) T1-weighted MR slices illustrating BBB opening
volume over time according to the disclosed subject matter.
[0023] FIG. 11 is an exemplary diagram illustrating BBB closing
over time for a single low-pressure sonication illustrated in FIG.
10.
[0024] FIG. 12 illustrates another embodiment of a system for
real-time, transcranial monitoring of safe blood-brain barrier
opening, according to the disclosed subject matter.
[0025] FIGS. 13A-13D are diagrams illustrating in vitro cavitation
monitoring: spectrograms. (a) Sonicating water without the skull in
place. (b) Sonicating microbubbles without the skull in place. (c)
Sonicating microbubbles with the macaque skull in place. (d)
Sonicating microbubbles with the human skull in place. (i), (ii),
(iii), and (iv) represents 50 kPa, 150 kPa, 200 kPa, and 450 kPa,
respectively. The colorbar illustrates the intensity of the
spectra, with a dynamic range of 25 dB and 15 dB for macaque and
human skull examples, respectively, from the preamplification
(macaque: 20 dB, human: 10 dB).
[0026] FIGS. 14A-14D are exemplary B-mode images in transverse
plane after the sonication. (a) Without the skull in place using
100 cycles. (b) With the macaque skull in place using 100 cycles.
(c) With the human skull in place using 100 cycles. (d) Without the
skull in place using 5000 cycles. (i), (ii), (iii), and (iv)
represents 50 kPa, 150 kPa, 200 kPa, and 450 kPa, respectively. The
arrows indicate the spot losing echogenicity.
[0027] FIGS. 15A-15I are diagrams illustrating additional
characteristics according to the disclosed subject matter of (a)
SCD.sub.h, (b) SCD.sub.u, and (c) ICD for the macaque skull
examples using 100-cycle pulses. (d) SCD.sub.h, (e) SCD.sub.u, and
(f) ICD for the human skull examples using 100-cycle pulses. (g)
SCD.sub.h, (h) SCD.sub.u, and (i) ICD without the skull in place
using 100- and 5000-cycle pulses. The error bar shows the standard
deviation. *: p<0.05. Green *: comparison made in the cases
without the skull in place. Red *: comparison made in the cases
with the skull in place.
[0028] FIGS. 16A-16C are diagrams illustrating additional
characteristics according to the disclosed subject matter (a)
without the skull in place using 100-cycle pulses, (b) without the
skull in place using 5000-cycle pulses, (c) with the macaque skull
in place using 100 cycles, and (d) with the human skull in place
using 100 cycles. The error bar shows the standard deviation. The
dash lines in (a) represent the transcranial detection threshold
(macaque: 15.2 dB, human: 34.1 dB).
[0029] FIGS. 17A-17C are diagrams illustrating additional
characteristics according to the disclosed subject matter of in
vivo cavitation doses using 100 and 5000 cycles. (a) SCD.sub.h. (b)
SCD.sub.u. (c) ICD. *: p<0.05. The error bar shows the standard
deviation.
[0030] FIGS. 18A-18B are diagrams illustrating additional
characteristics according to the disclosed subject matter of in
vivo cavitation SNR using (a) 100-cycle and (b) 5000-cycle pulses.
The error bar shows the standard deviation.
[0031] FIGS. 19A-19D are diagrams illustrating in vivo BBB opening
according to the disclosed subject matter at (a) 275 kPa, (b) 350
kPa, (c) 450 kPa, and (d) 600 kPa in the thalamus (orange arrow)
and the putamen* (green arrow). The upper and middle rows show the
post-contrast T1-weighted images in axial and coronal view
respectively, in which the colormap shows the enhancement ratio as
compared to the pre-contrast images. The opening volume was 338.6,
223.8, 213.4, and 262.5 mm.sup.3, respectively. The bottom row
shows the realtime monitoring of SCD.sub.h, SCD.sub.u, and ICD for
sonicating the thalamus, and that for the putmen was similar and is
not shown.
[0032] FIGS. 20A-20D are diagrams illustrating exemplary safety
assessment using MRI according to the disclosed subject matter at
(a) 275 kPa, (b) 350 kPa, (c) 450 kPa, and (d) 600 kPa. The upper
row shows the T2-weighted images (coronal view) for detecting the
edema, which is lighter if occurred. The lower row shows the SWI
(coronal view) for detecting the hemorrhage, which is darker if
occurred.
DETAILED DESCRIPTION
[0033] According to aspects of the disclosed subject matter,
systems and techniques for real-time, transcranial monitoring of
safe blood-brain barrier opening include an ultrasound transducer
and a targeting component configured to target the ultrasound
transducer for targeted blood-brain barrier opening by targeting a
predetermined region in a brain of a patient from a predetermined
approach angle.
[0034] With reference to FIG. 1, an exemplary system 100 for
real-time, transcranial monitoring of safe blood-brain barrier
opening is illustrated. A subject 102 can be positioned in a
stereotaxic frame under general anesthesia. For example and not
limitation, a 500-kHz ultrasound transducer 104 can be attached to
a Kopf stereotaxic manipulator 114 to enable targeting of the
ultrasound focus in stereotactic coordinates, as described herein.
Negative control sonications can be performed in the absence of
microbubbles, as illustrated in FIG. 2 and discussed further
herein. For example and not limitation, monodisperse 4-5 11 m
microbubbles can be IV injected and size-isolated using
differential centrifugation. The subject 102 can be sonicated for
about 2 minutes with focal maximum pressures ranging between about
0.20 and about 0.30 MPa. Post-sonication controls in the presence
of microbubbles can be performed, and the location of the BBB
opening can be determined, for example using contrast-enhanced TI
images, as discussed herein.
[0035] With continued reference to FIG. 1, the attenuation in the
subject 102 scalp can be considered around -0.9 dB/em and the
thickness can be about 0.5 em. Attenuation in the subject 102 brain
tissue can be determined to be about -0.5 dB/em and the thickness
can be about to 2 em. As such, the emission amplitude can be raised
by 7.15 dB (approximately a factor 2.28) compared to the
calibration measurements in water to compensate for the energy loss
along the path. For example and without limitation, a flatband,
spherically focused hydrophone 106 (Y-107, Sonic Concepts, WA, USA)
can be positioned through the center hole of the FUS transducer
102. The two transducers 104, 106 can be aligned so that their
focal regions overlapped within the confocal volume. The hydrophone
106, which can be connected for example and without limitation to a
digitizer 108 (Gage Applied Technologies, Inc., Lachine, QC,
Canada) through a 20-dB amplification 110 (5800, Olympus NDT,
Waltham, Mass., USA), can monitor real-time acoustic emissions from
microbubbles (referred to herein as passive cavitation detection or
PCD).
[0036] Still referring to FIG. 1, the top image illustrates a large
view of the operating room. As embodied herein, the PC and
amplifiers can be used to drive the transducer-hydrophone assembly.
The degassing system 112 (vacuum pump+water circulation pump) can
provide a constant flow of degassed water for acoustic coupling. As
embodied herein, the transducer-hydrophone assembly can be mounted
on a manipulator with 5 degrees of freedom (x, y, and z position of
the focus, as well as two approach angles: azimuth and elevation).
The bottom image illustrates an enlarged view. The membrane 116 can
be inflated to regulate the water flow using the degassing system
112, which can provide a maximal acoustic transmission in the
subject 102.
[0037] Individualized targeting of the ultrasound focus to a
particular brain region can be performed. The targeting can include
T1 weighted stereotactically aligned structural images acquired for
all animals (Tt sequence as discussed further herein). For
targeting in stereotactic coordinate frames, an R-based (R
Development Core Team 2009) software package (stereotax.R) can be
utilized to convert a particular setting of the stereotactic
manipulator (Kopf) into stereotactic coordinates. The setting of
the stereotactic manipulator can be determined by one or more of
the following free parameters: the setting of the media-lateral
drive (ml), the position of the manipulator on the stereotactic arm
along the anterior-posterior direction (ap), the setting of the
dorso-ventral drive (dv), the rotation of the manipulator around
the z-axis (azimuth), the tilt of the manipulator (elevation angle)
that can occur either around the ml- or ap-axis (elevation
setting), the position of the manipulator on the left or right
stereotactic arm (arm), the relative alignment of the ml and dv
stereotax drives, i.e., the ml drive positioned anterior or
posterior to the dv drive (stereo), and a degree of freedom that
determined the attachment of the ultrasound transducer on the
stereotactic manipulator (finger). Based at least in part on the
setting of the stereotactic manipulator, the software can determine
the focal point and the axis from the focal point to the ultrasound
transducer (angle of approach). For visualization purposes, the
predicted region of BBB opening around the ultrasound focus can
then be projected onto an individual stereotactically aligned T1
image, as illustrated for example in FIG. 2. The software can also
invert this procedure, that is, for any desired sonication target
(including a desired approach angle) that can be specified in
stereotactic coordinates, the software can determine up to eight
different settings of the stereotactic manipulator to target this
neural structure from the specified approach angle, and an optimal
approach angle can then be determined. As embodied herein, the
approach angle can be set to provide a close to perpendicular
incidence angle between ultrasound beam and skull.
[0038] The BBB opening can be verified, for example and as embodied
herein, with contrast-enhanced MRI. T2 and T2 FLAIR images can be
taken of the subject 102 to detect any potential damage caused by
the sonication. The integrity of the BBB can be tested using a T1
contrast agent gadodiamide (Omniscan.TM.) that can be used to
visualize the break-down of the BBB in neurological disease. A
high-resolution structural T1 image can be recorded prior to the
injection of gadodimide (T1 Pre; 3D Spoiled Gradient-Echo,
TRITE=20/1.4 ms; flip angle: 30.degree.; NEX=2; in-plane
resolution: 1.times.1 mm2; slice thickness: 1 mm with no interslice
gap). 30 min after injection of 0.15 ml/kg gadodiamide IV, another
T1 image can be acquired using similar scanning parameters (T1
Post). As gadodiamide typically not cross the intact BBB, increased
T1 signal strength can be found in vessels or regions with
increased BBB permeability. As embodied herein, a 3D T2-weighted
sequence (TRITE=3000/80 ms; flip angle: 90.degree.; NEX=3; spatial
resolution: 400.times.400 mm2; slice thickness: 2 mm with no
interslice gap) and a 3D Susceptibility-Weighted Image (SWJ)
sequence can be applied (TRITE=19/27 ms; flip angle: 15.degree.;
NEX=1; spatial resolution: 400.times.400 mm2; slice thickness: 1 mm
with no interslice gap).
[0039] T1 pre and T1 post images can be registered to the
individual stereotactically aligned T1 image using FSL's FLIRT
routine. To estimate gadodiamide concentration [Gd]c, the post T1
image can be divided by the pre T1 image to obtain a post/pre
image. The post/pre image can highlight regions of increased T1
contrast following the injection of gadodiamide. This can include
regions of interest where the BBB was opened, but also can include
vessels or other regions with high blood volume such as the pial
surface. The post/pre image can be flipped such that the left
hemisphere overlaid the right hemisphere. The un-flipped image can
be divided by the flipped image. This procedure can reduce or
remove activations due to high [Gd]c in voxels with high
blood-volume, in symmetric regions between the hemispheres. The
resulting image can highlight increased [Gd]c in the sonicated
region, as well as some residual artificial activation, which can
be due to asymmetric vasculature.
[0040] To assess the targeting accuracy, the resulting image can be
rotated and shifted into a new coordinate frame, where the origin
can be defined as the predicted location of the ultrasound focus,
and the z-axis can correspond to the approach angle, as shown for
example in FIG. 3. FIGS. 3A-3D form a series of illustrations
showing a quantification of targeting accuracy. After calculating
the raw result image that provides a normalized estimate of the
increase in T1 contrast (as shown in FIG. 3A), the image was
shifted and rotated in to a new coordinate frame (as shown in FIG.
3B) whose origin was defined by the coordinates of the intended
target, and the z-axis corresponded to the approach angle. A voxel
was considered opened if its T1 value was enhanced by about 10%.
The in-plane targeting accuracy was assessed by averaging the
fraction of opened voxels across the z-axis (as shown in FIG. 3C).
Targeting in the depth axis along the ultrasound beam was
quantified by collapsing across the x and y-axis (as shown in FIG.
3D).
[0041] A region of interest around the origin was selected
corresponding to .+-.7.5 mm in the x- and y-direction, and -5 to
+12 mm along the z-axis. A voxel can be considered "opened" when
the T1-enhancement exceeds a threshold of 10%. The total volume of
the BBB opening can be quantified as the volume of the opened
voxels in the region of interest around the sonication target. The
fraction of opened voxels can be averaged across the z-axis. The
region of the opening can be defined on the two-dimensional x-y map
as pixels with more than an average of 35% of opened voxels (black
contour line). The observed center of the sonication in the
x-y-plane can be defined as the center of mass of the region of the
opening (illustrated as a black dot in FIGS. 4-6). The targeting
error in the x-y plane can be defined as the difference of the
observed position of the opening from the theoretical position of
the geometric focus. Similarly, targeting accuracy along the axis
of propagation of the ultrasound can be assessed by averaging the
fraction of opened voxels across the x- and y-axis. The averaging
can be performed on voxels within a square region of .+-.2 mm
around the observed xy-center of the sonication. The center of the
sonication along the z-axis can be defined as the center of gravity
of the bins with more than 35% opened voxels. The targeting error
along the z-axis can be defined as the difference between the
observed center of the sonication along the z-axis and the
predicted focal depth. The predicted focal depth can be determined
to be the geometric focal depth plus 5 mm due to the focal shift
induced by the skull.
[0042] FIG. 4 forms a series of plots illustrating targeting
accuracy for 6 (4+2 for two monkeys 0 and N) sonications of caudate
nucleus. The panels in the first row show the color-coded fraction
of activated voxels (>10% enhancement of T1 signal) as a
function of medio-lateral and anteroposterior deviation from the
intended focal point in the x-y-plane. The panels collapsed across
voxels that are between -5 mm and 10 mm in depth from the intended
depth. In all instances, the opening of the BBB either overlapped
with or was in immediate vicinity of the intended target. To
quantify targeting accuracy along the direction of the ultrasound
propagation, panels in the second row show the fraction of
activated voxels collapsed around a 2 mm by 2 mm square region
around the measured focal point (block dots in panels in A). The
dotted horizontal line corresponds to the depth of the geometric
ultrasound focus. The actual focal depth (solid horizontal line)
shifted about 5 mm towards the ultrasound transducer. Panels in the
third row depict the backscattered acoustic energy of the
microbubbles excited in the ultrasound focus as a function of time
from injection of the microbubbles. The blue line to the desired
harmonic oscillations of the microbubbles (HEY) associated with
safe BBB opening. The black line corresponds to inertial cavitation
(BE1) that has been linked to extravasation of red blood cells and
tissue damage. The red line corresponds to the BE1 detection
threshold.
[0043] FIG. 5 forms a series of plots illustrating targeting
accuracy and PCD responses for 6 sonications of putamen in animal
one. The PCD for sonication 12 06 23 shows immediately elevated HEI
values because by accident, the microbubbles were injection before
sonication onset.
[0044] FIG. 6 forms a series of plots illustration targeting
accuracy and PCD responses for 5 sonications of putamen in the
second animal.
[0045] As embodied herein, real-time monitoring can be performed
using the evolution of the frequency content of the backscattered
acoustic signal. Bubble oscillations along the acoustic excitation
can be non-linear (stable cavitation), and the PCD can thus detect
harmonic modes in the frequency spectrum. Bubble collapse and jet,
more generally described herein as inertial cavitation, can induce
broadband noise. As such, detection of broadband response can be
considered a signature of inertial cavitation. Using 4-5-f,lm
monodisperse microbubbles, the BBB can be opened without inertial
cavitation. Additionally, stable cavitation alone has not been
associated with any tissue damage. The frequency spectra of
backscattered acoustic emissions can be used to infer the
cavitation-behavior of the micro-bubbles in the focal region. To
remove the harmonic (nf, n=1, 2, . . . , 6), sub-harmonic (f/2) and
ultra-harmonic (nf/2, n=3, 5, 7, 9) frequencies produced by stable
cavitation, the response within a 300-kHz bandwidth around each
harmonic and 100-kHz bandwidth of each sub- and ultra-harmonic
frequency can be filtered out in order to obtain the broadband
signal. This can be performed within the 0.6-5.2 MHz frequency band
to reduce or inhibit perturbation induced by the fundamental
frequency and to account for the growing attenuation of the signal
along the frequency. From the sets of two spectra, both the
broadband and total energies (respectively 0.sup.broadband and
0.sup.total) can be determined by summing the spectral amplitudes
(s) on the defined frequency range as follows:
.epsilon..varies..intg..sub.f=0.6 MHz.sup.5.2 MHz{tilde over
(s)}.sup.2(f)df (1)
[0046] Two metrics can be represented as indications of inertial or
stable cavitation by analyzing the differences between
backscattered with and without bubbles. The broadband energy
increase ("BEJ") from the negative control level (without
microbubbles) can be monitored as an indication of inertial
cavitation and can be represented as follows:
BEI = 10 log ( bubble broadband control broadband ) ( 2 )
##EQU00001##
[0047] The harmonic energy can be obtained by subtracting the
broadband energy to the total energy. The harmonic energy increase
("HEI") can be an indication of stable cavitation and can be
represented as follows:
HEI = 10 log ( bubble total - bubble broadband control total -
control broadband ) ( 3 ) ##EQU00002##
[0048] The energy increase of the control signals can be
represented as the average value of the 2 second long negative
control sonication taken before injecting the bubbles but otherwise
used the same ultrasound parameters as the treatment
sonication.
[0049] For purpose of illustration and not limitation, as embodied
herein, immediately after the treatment sonication, a series of
2-sec positive control sonications can be performed while
microbubbles are still in circulation. The positive controls can
use pressures between 0.05 and 0.35 MPa. Except for the shorter
duration and variable pressures, the same sonication settings can
be applied for the treatment sonication. The positive controls can
be used to describe the relationship between ultrasound pressure
and the harmonic/broadband energy increase. As discussed further
herein, for purpose of illustration and confirmation of the
disclosed subject matter, 8 testing sets were performed. The mean
HEI over the entire sonication can be calculated to relate stable
cavitation to the observed size of the BBB opening.
EXAMPLE 1
[0050] For purpose of illustration and confirmation of the
disclosed subject matter, exemplary experimental results were
obtained according to the techniques disclosed herein. The
experimental results included, for example, results of a series of
17 sonications targeting the caudate nucleus (6) and the putamen
(11) in the left hemispheres of two macaque monkeys. The analyses
are focused on targeting accuracy, the relationship between PCD
response and BBB opening volume as well as safety of the procedure.
In addition, one exploratory study examined the duration for which
the BBB remains open after the sonication.
[0051] FIGS. 2A-2B together illustrate timelines of sonication
experiment with subsequent MRI-based verification. Briefly, the
animals were sonicated for two minutes using a 500 kHz focused
ultrasound transducer following the systemic injection of
microbubbles. The opening location was then analyzed using
contrast-enhanced T1 images (as shown in FIG. 2D) for details.
Additional clinical scans were performed to detect potential
damage. FIG. 2C illustrates a geometric ultrasound focus overlaid
on a T1 structural scan in stereotaxic coordinate frame. Due to the
geometry of the ultrasound transducer, the focal region was
elongated along the axis of ultrasound propagation. The ultrasound
was applied at an angle of 26.degree. from the upper right to
provide a close to normal incidence angle of the ultrasound and
skull. FIG. 2D illustrates a T1 structural scan in stereotaxic
coordinate grame and illustrates increased blood-brain barrier
(BBB) permeability for the T1 contrast agent gadodiamide following
a single sonication of left caudate. Brighter colors indicate
regions where gadodiamide was able to diffuse across the BBB into
the brain tissue. The remaining regions of increased T1 signal
indicate asymmetric vasculature. Note the close alignment between
intended (as shown in FIG. 2C) and actual location (as shown in
FIG. 2D)) of the BBB opening. The axial shift in location of the
BBB opening towards the transducer is close to the value predicted
from in-vitro experiments.
[0052] FIGS. 2C-2D illustrates an exemplary result of BBB
disruption using T1-weighted MR imaging and gadodiamide MR contrast
agent. The image on the left depicts the theoretical position of
the ultrasound focus. The image on the right renders regions where
the T1 contrast agent gadodiamide was able to diffuse to the brain
parenchyma as a result of BBB opening (as described herein). FIGS.
2C-2D thus highlight the good qualitative agreement between the
intended target of the ultrasound focus and the actual region of
increased BBB permeability.
[0053] To quantify the targeting accuracy of the method, the
processing shown in FIG. 3 was performed for each experiment (as
described herein). The individual plots for lateral and axial
targeting accuracy are depicted in FIG. 4 for caudate targets of
both animals. FIGS. 5 and 6 provide identical plots for the putamen
sonications in the two animals, respectively. These results
illustrate the reproducibility and targeting precision of the FUS
technique. First, the targeting accuracy was quantified by
averaging the relative focal position for all sonications and
animals. The mean focal point was 0.2.+-.1.0 mm posterior to the
intended target (all results are reported as mean.+-.standard
deviation in mm). This difference did not reach significance
(t-test, p>0.05). The observed focal point was significantly
ventral to the intended target (1.9.+-.1.7 mm; t-test p<0.05).
Further, the mean focal point was shifted towards the ultrasound
transducer (1.4.+-.1.4 mm, t-test, p<0.05). Predicted focal
depth was defined as the depth of the geometric ultrasound focus
plus 5 mm (i.e., shifted towards the ultrasound transducer). The 5
mm shift was added to account for the shift of focal depth that was
measured in vitro with immersed skull plates. Hence, the results
demonstrate the correspondence between the in vitro and in vivo
measurements. However, a stronger focal shift was observed in the
in vivo experiments.
[0054] The reliability of the sonication procedure was assessed as
the mean targeting error (absolute distance from intended target).
The mean targeting error over all sonications in the lateral plane
was 2.5.+-.1.2 mm. Mean targeting error in the axial direction was
1.5.+-.1.3 mm. Combined lateral and axial error averaged 3.1.+-.1.3
mm.
[0055] During experiments, and according to some embodiments, the
system was further configured to dissociate random errors due to
day-to-day fluctuations from systematic targeting errors that could
be specific to a particular animal and/or target. To quantify the
systematic targeting error the location of the focal point for both
targets and both animals were averaged separately. The mean
systematic lateral targeting error was 1.8 mm. Mean systematic
axial targeting error was 1.4 mm. Combining the lateral and axial
error resulted in a mean systematic targeting error of 2.7 mm
across all four targets (2 targets in 2 animals). An analysis of
variance was utilized to test whether targeting accuracy differs as
a function of the four different groups of sonications (two targets
in two animals). Neither anterior-posterior nor axial position
(relative to the intended target) differed as a function of the
sonication group. However, dorso-ventral position depended on
sonication group (ANOV A, p<O.OS). This can be due at least in
part to the difference between the two caudate and the two putamen
targets. In both animals, the sonications to putamen exhibited a
systematic targeting error in the along the dorso-ventral axis. No
such systematic targeting error was found in the caudate
sonications.
[0056] Random error was further quantified, i.e., the absolute
distance of the observed focus from the mean focal point over all
repetitions with the same target in the same animal. The mean
random lateral error was 1.2.+-.0.6 mm. The mean random axial error
was 0.6.+-.0.6mm. Combining lateral and axial error, a mean random
error of 1.5.+-.0.7 mm was found.
[0057] The size of the region in which the permeability of the BBB
was increased was quantified. Averaged over all sonications, the
volume of the BBB opening was estimated at 115.+-.44 mm3. Larger
openings were observed at higher sonication pressures (e.g., 0.30
MPa). Moderate openings were observed at lower pressures (0.20 or
0.25 MPa). One sonication at 0.25 MPa failed to elicit any opening
(as shown in FIG. 5). Another sonication at 0.20 MPa only elicited
a minimal opening (as shown in FIG. 4).
[0058] HEI and BE1 monitoring were performed for each experiment in
real time. The lower rows in FIGS. 5-7 render the recorded
real-time monitoring for the corresponding sonications. In all but
one of the sonications, HEI increased by at least 15 dB during the
sonication. This was indicative of stable cavitation of the bubbles
in the focal region. The lack of an increase in broadband energy
indicated the absence of potentially harmful inertial cavitation. A
6 dB threshold, corresponding approximately to two times average of
the negative controls, had been set as a limit of potential damage
and was never surpassed.
[0059] To characterize the dynamic range of the HEI and BE1
responses, acoustic emissions as a function of ultrasound pressure
were measured using a series of brief ultrasound pulses of a wide
range of pressures (as described herein). FIG. 7 illustrates HEI
and BE1 as a function of ultrasound pressure. As expected, the HEI
starts increasing for lower pressures (0.15 MPa). In contrast, the
BE1 remains unchanged at 0 dB for pressures up to 0.35 MPa. The HEI
seems to reach an asymptote of approximately 10 dB for pressures at
and above 0.25 MPa. It is lower than what is shown in the real-time
PCD monitoring since this PCD testing was done after the treatment
sonication and part of the circulating bubbles were degraded. This
analysis defines a window between 0.15 and 0.35 MPa that leads to a
reliable increase of harmonic energy while avoiding potentially
harmful broad-band energy increase. In this study, pressures were
well within this window and ranged between 0.20 and 0.30 MPa.
[0060] FIG. 7 forms a series of graphs illustration harmonic (HEI)
and broadband (BE1) energy increase plotted as a function of
ultrasound pressure. Data was acquired using a series of brief
pulses of ultrasound after the main sonication while micro-bubbles
were still circulating. The blue dash line corresponds to the
lowest pressure at which BBB opening was achieved, and the. The
light blue area highlights the pressure range used in this study.
The red line corresponds to the ultrasound pressure that would
cause BE1 to rise above levels that were found to be safe in the
current set of sonications.
[0061] Online PCD monitoring was tested to determine suitability to
predict the success of the sonication and the size of the ensuing
BBB opening. To that aim, size of the BBB opening as a function of
the mean HEI during the 2-minute sonication period were plotted
(e.g., FIG. 8B). The results showed that stronger HEI responses are
not indicative of larger BBB opening volume. However, in all but
two cases, the presence of HEI went along with a successful BBB
opening.
[0062] FIGS. 8A and 8B are graphs illustrating BBB opening volume
as a function of pressure (as shown in FIG. 8A) and the average
harmonic energy increase, HEI (as shown in FIG. 8B). Two targets in
the putamen and the caudate for two animal subjects (0 and N) were
marked separately. FIG. 8A illustrates the relationship between
ultrasound pressure and opening size (r=0.41). Due to the narrow
range of pressures and low number of sonications, this effect does
not reach significance. The dashed line shows the mean value with
standard deviation. As shown in FIG. 8B, there is no apparent
relationship between average HEI and opening volume.
[0063] Additional MR imaging sequences (T2-weighted and SWI, as
described herein) were used to assess potential brain damage after
the ultrasound procedure. In line with the observed stable
cavitation indicative of safe in situ ultrasound pressures, neither
T2 nor SWI images detected any damage such as edema or hemorrhage
in all experiments described herein. FIG. 9 illustrated coronal
slices of T2-weighted and SWI images corresponding to the
Tl-weighted coronal slices rendered in FIG. 2.
[0064] FIG. 9 illustrates two MR images illustrating an example of
T2-weighted (left) and SWI (right) MR images corresponding to the
experiment from FIG. 2. Edemas appear brighter in T2-weighted
images; hemorrhages, as well as large vessels appear in black in
SWI images. No damage was detected on any of the experiments
performed.
[0065] A preliminary experiment to investigate the closing timeline
was also performed. Gadodiamide IV injections along with pre- and
post-T 1-weighted MR sequences were repeated 1, 2, and 4 days after
the initial ultrasound treatment. Coronal and sagittal slices of
these experiments are illustrated in FIG. 10. Standard T1 contrast
enhanced imaging and subsequent analyses indicate a clearly
visible, average-sized (126 mm3) BBB opening. FIG. 11 illustrates
the opening volume decreased with time. The BBB was almost
completely restored two days after sonication. Experiments in mice
have shown that the duration of the BBB opening depends on acoustic
and microbubble parameters.
[0066] FIG. 10 illustrates a series of coronal (left row) and
sagittal (right row) T1-weighted MR slices showing the evolution of
the BBB opening volume along time. The area with contrast agent
diffusion is overlaid in blue. The BBB is restored between day 2
and 4.
[0067] FIG. 11 illustrates a timeline of BBB closing for a single
low-pressure sonication depicted in FIG. 10. Voxels with a
normalized pre-post enhancement of more than 10% were classified as
"opened." The total volume of opened voxels decreases as a function
of time from the sonication. The opened volume in the
contra-lateral control region is constant and close to the one
predicted by a false detection rate of 5%.
[0068] Some of the above discussed experiments were aimed at
testing whether a single spherical transducer at an intermediate
frequency of 500 kHz can be used for accurate, repeatable and
localized blood-brain barrier disruption in deep subcortical
structures. The observed targeting error was sufficiently small (as
embodied herein, 2.5.+-.1.2 mm laterally, 1.5.+-.1.3 mm along
depth-axis, 3.1.+-.1.3 total) to enable the specific targeting of
substructures of the basal ganglia such as the associative or
oculomotor caudate.
[0069] To further reduce the targeting error potential sources of
the error were analyzed. Three potential factors for error include:
errors due to deviation of the geometric focus from the intended
target (geometric errors), errors due to the analysis of the focal
position (analysis errors), and errors due to deviation of actual
ultrasound focus from the geometric focus (ultrasound aberration
errors).
[0070] Over the course of the experiments, the stereotactic
manipulator and the targeting routine were repeatedly calibrated.
For these calibrations, a metal rod was used that was attached to
the stereotaxic manipulator in the same way as the ultrasound
transducer. The length of the rod was chosen to match the focal
length of the transducer and hence its tip corresponded to the
location of geometric ultrasound focus (assuming there were no
ultrasound aberrations). This setup enabled targeting of various
known positions, such as the interaural point of the stereotax.
These measurements routinely found deviations from the intended
target about 1-2 mm. Geometric error arises when the setting on the
stereotactic manipulator that determines geometric focus is off.
The position of the geometric focus can be determined by the 9
degrees of freedom of the stereotactic manipulator. Some of these
settings are continuous and prone to error. The ml, ap, and dv
settings have 1 mm scales in combination with a vernier scale to
enable accuracy on the order of a tenth of a millimeter. The
azimuth and elevation scales, however, are divided in steps of 5
and 2 degrees, respectively, without an additional vernier scale.
This can enable accuracy of about 1 to 2 degrees. Even small
angular deviations can have a big effect on the final position of
the geometric focus.
[0071] The elevation setting should be correct for an additional
reason: If the approach angle deviates from vertical, gravitational
forces perpendicular to the approach angle will grow stronger.
These gravitational forces can introduce systematic errors for
angled approach vectors. The mislocalization in the dorso-ventral
direction was strongest for the putamen target, and this target
utilized a more angled approach. The ventral mislocalization
decreases over time (as shown for example in FIGS. 7 and 8). As
such, over the time-course of the experiments described herein,
more force was used to fasten the set-screws to maintain the
elevation angle against gravitational pull.
[0072] Further, the analysis pipeline used to infer the observed
focal point can induce additional small errors. The analysis
depends on alignment of pre- and post-contrast-enhanced T1 images
to a stereotactically aligned reference image. Small errors can
arise during the registration process of the pre- and post-images
to the reference. Similarly, the alignment of the reference image
can fail to perfectly match the intended stereotactic alignment. In
addition, the actual position of the animal in the stereotax can
vary slightly on a day-by-day basis. Together these factors can
contribute up to 1 mm of the random and/or systematic targeting
error. Further, the fractional enhancement of the post-relative to
the pre-image can be based on noisy T1 MRI images, which can
contribute to the overall targeting error.
[0073] Mislocalization in the axial direction can occur due to
ultrasound aberrations based on in vitro measurements with immersed
skull plates. The results herein correspond to the in vitro
findings. On average, a 6.5 mm focal shift was observed, compared
to the predicted 5 mm focal shift. The additional 1.5 mm can be due
at least in part to different ultrasound aberrations in vivo or can
be due to geometric and analysis error.
[0074] Real-time monitoring based on the frequency content of the
backscattered signal was performed to classify the cavitation
behavior and hence establish the success and safety of the
sonication. Measuring the cavitation spectrum can verify that the
microbubbles are correctly excited in situ, i.e., non-linear
resonance along the ultrasonic frequency without broadband noise
signature of bubbles collapsing or micro-jet streaming (inertial
cavitation). This can correspond to a significant HEI (between 15
dB and 25 dB) and no BET. During all experiments performed,
(pressures at or below 0.3 MPa) only stable cavitation was
observed. Therefore, the PCD monitoring indicated that the
procedure can be considered safe and successful. In addition, the
HEI can be indicator of the success of the BBB opening in these
initial findings. For the cases with an average HEI higher than 5
dB, there was 94% (15/16) of success. The correlation between the
HEI and the opening volume in FIG. 8B was not high since the focus
was on a small range of pressures (0.20-0.30 MPa).
[0075] Focused ultrasound can be used to temporarily disrupt the
integrity of the blood brain-barrier in specifically targeted brain
regions of rodents and monkeys. Focused ultrasound can also allow
clinicians to deliver drugs to specific neural targets. However,
certain clinical ultrasound setups can include multiphased
ultrasound transducer arrays located inside an MR scanner. This can
restrict the use of ultrasound to highly specialized clinical
settings. Here, a low-tech single-element 500 kHz spherical
transducer ultrasound setup was used that can overcome this
challenge. The system is portable, and can use a stereotactic
targeting technique independent of MR guided targeting. The systems
and techniques of the disclosed subject matter can thus use
independent of an MR scanner. The stereotactic targeting procedure
is accurate and reliable, and for purpose of illustration and
confirmation, the success of the sonication can reliably be
inferred using real-time passive cavitation spectral analysis.
While successful sonications were usually accompanied by a 10-15 dB
HEI, no correlation was found between HEI and opening volume.
[0076] As such, the systems and techniques according to the
disclosed subject matter can be used to open the BBB in specific
brain regions of a subject, largely independent of MRI-guided
targeting and/or verification. Hence, in operation, the systems and
techniques can provide noninvasive targeted brain-drug delivery to
a subject in less specialized clinical settings (e.g., outpatient
clinics; community hospitals). Targeting accuracy can be increased
by using an individual stereotactically aligned T1 image. However,
subsequent sonications can be performed completely independent of
MRI.
[0077] The results and analyses outlined described herein
illustrate that the single-element FUS systems and techniques can
be used to accurately and reliably target sub-structures of the
basal ganglia. Additionally, it can be desirable to know how long
the BBB will stay open before it regenerates and prevents the
passage of molecules from the blood to the brain. This can be
desirable for at least the following two reasons: the window of
opportunity during which drugs can be delivered can be determined
and, how long the brain region in question will be exposed to other
substances that usually would not cross the intact BBB can also be
determined. The duration of the BBB opening can depend at least in
part on the precise sonication parameters such as ultrasound
pressure and microbubble size. The duration of the BBB opening can
range between 12 hours and 5 days. First, the time course of the
BBB closing for a single sonication in one of the macaque subjects
was measured. Due to the closer similarity between brain structures
of the macaque and human species, these measurements can correspond
to a time course expected in the human brain. The results from a
single exploratory analysis indicated that an average-sized BBB
opening (-126 mm.sup.3) with moderate in situ ultrasound pressures
(0.30 MPa) and 4-5 monodisperse microbubbles takes between 2 and 4
days to close.
EXAMPLE 2
[0078] For purpose of further illustration and confirmation of the
disclosed subject matter, additional exemplary experimental results
were obtained according to the techniques disclosed herein. The
experimental results included, for example, results of a series of
17 sonications targeting the caudate nucleus (6) and the putamen
(11) in the left hemispheres of two macaque monkeys. The analyses
are focused on targeting accuracy, the relationship between PCD
response and BBB opening volume as well as safety of the procedure.
In addition, one exploratory study examined the duration for which
the BBB remains open after the sonication.
[0079] Both in vitro macaque and human skull techniques as well as
in vivo skull effects and realtime monitoring in BBB opening of
macaques were performed in this example. Three types of cavitation
doses and the cavitation SNR were quantified and used to address
the characteristics of cavitation, skull attenuation, and detection
threshold. The stable cavitation dose (SCD) representing the
overall extent of stable cavitation can be represented as the
cumulative harmonic or ultraharmonic emission. The inertial
cavitation dose (ICD) can represent the overall extent of inertial
cavitation, and can be represented as the cumulative broadband
acoustic emission. The cavitation SNR can be represented as the
ratio of post- to pre-microbubble administration cavitation
doses.
[0080] FIG. 12 illustrates an alternative embodiment of a system
200 for real-time, transcranial monitoring of safe blood-brain
barrier opening. A single-element FUS transducer (H-107, Sonic
Concepts, WA, USA) operated at 0.5 MHz with a -6-dB focal width by
length equals to 5.85 mm by 34 mm and a geometric focal depth of
62.6 mm was used for sonication. A spherically focused, flatband
hydrophone (Y-107, Sonic Concepts, WA, USA; -6-dB sensitivity: 10
kHz-15 MHz) was coaxially and confocally aligned with the
transducer and served as the passive cavitation detector. A PC work
station (model T7600, Dell) with a customized program in
MATLAB.RTM. (Mathworks, Mass., USA) was developed to automatically
control the sonication through a function generator (model 33220A,
Agilent Technologies, CA, USA) followed by a 50-dB amplifier (A075,
ENI, N.Y., USA). The PCD signal acquisition was performed at a
14-bit analog-to-digital converter (Gage Applied Technologies, QC,
Canada) (sampling rate: 100 MHz and 50 MHz in vitro and in vivo,
respectively). A 20-dB amplification was applied throughout the
macaque experiments, while 10 dB was applied for the human skull,
due at least in part to increased reflection. All PCD signals in
vivo including the frequency spectra and cavitation doses were
monitored in real time.
[0081] The desiccated macaque skull was obtained from Skull
Unlimited (Macaca mulatta, Okla., USA) and sectioned to keep the
cranial part (including frontal bone, parietal bones, and occipital
bone), as shown for example in FIG. 12. The averaged thickness in
the ultrasound beam path was 3.09 mm using a caliper at five points
of the skull lined in a cross below the transducer, and was
degassed for 24 hours prior to use. The desiccated human skull was
obtained from The Bone Room (CA, USA), and sectioned, as shown for
example in FIG. 12, to keep the frontal and the parietal bones with
an averaged thickness of 4.65 mm using the same measuring method
described above. The skull was degassed for 48 hours prior to use.
The pressures at the focus of the FUS transducer with and without
the skulls were calibrated using a bullet hydrophone.
[0082] For purpose of illustration an not limitation, a number of
sonications performed was summarized in Table 1. In-house,
lipid-shell, monodisperse microbubbles (median diameter: 4-5 .mu.m)
were diluted to 2.times.105 bubbles/mL and injected to the
4-mm-in-diameter channel in the acrylamide phantom before and after
placing the skull. The channel was roughly 45 mm and 25 mm below
the macaque and the human skull, respectively. The PCD with the
hydrophone and the diagnostic B-mode imaging system (Terason,
Mass., USA) were separately used to monitor the sonication (peak
negative pressure (PNP): 50-450 kPa, pulse length: 100 cycles (0.2
ms) and 5000 cycles (10 ms), pulse repetition frequency (PRF): 10
Hz, duration: 2 s) in order not to interfere the PCD. B-mode images
of bubble disruption were acquired to ensure the FUS focusing at
the channel, which was performed through a linear array transducer
(10L5, Terason, Mass., USA; center frequency: 5.1 MHz) placed
transversely to the FUS beam.
TABLE-US-00001 TABLE 1 Number of in vitro sonications. Without With
microbubbles microbubbles Skull effect Macaque No skull 41 49 (100
cycles) Skull 33 46 Human No skull 60 60 Skull 70 81 Pulse length
effect No skull 20 20 (5000 cycles)
[0083] The in vitro configuration was implemented similarly to the
in vivo conditions in terms of targeting through the skull. That
is, FUS was applied through the parietal bone next to the sagittal
suture, corresponding to the position for targeting the thalamus,
putamen, and caudate nucleus. The 4-mm channel was chosen to
accommodate the area of bubble disruption at the highest pressure
(450 kPa). The low microbubble concentration was chosen in order to
reduce or minimize the bubble-bubble interaction (the mean distance
between bubbles is 58.5 mm) while being captured for B-mode
visualization. Sonication using 5000-cycle pulses without the skull
in place was also performed.
[0084] Four male rhesus macaques (Macaca mulatta) weighing between
6-11 kg were used to perform in vivo techniques according to the
disclosed subject matter. Two separate sets of experiments, i.e.,
one set for the in vivo skull effect and another for BBB opening in
non-human primates were performed, and the number of sonications
was summarized in Table 2. Microbubbles were intravenously
injected, and the total number of microbubbles administered was
determined based on the animal's weight. For the purpose of BBB
opening, a bolus of microbubbles (2.5.times.108 bubbles/kg) was
injected and the sonication (PNP: 250-600 kPa, pulse length: 10 ms,
PRF: 2 Hz, duration: 2 min) started at the beginning of injection.
To study the in vivo skull effect, a bolus of microbubbles
(1.25.times.108 bubbles/kg) were injected after the BBB opening
sonication. Ten seconds after the injection when the microbubbles
perfused to the brain, a consecutive sonication at ramp-up
pressures was started (PNP: 50-700 kPa, pulse length: 100 cycles
(0.2 ms) or 5000 cycles (10 ms), PRF: 2 Hz, duration: 10 s). The
targeted regions were thalamus and putamen.
TABLE-US-00002 TABLE 2 Number of in vivo sonications. Without With
Pulse length microbubbles microbubbles Skull effect 100 cycles 8*
8* 5000 cycles 14** 14** BBB opening 5000 cycles 40 40 *6 at 700
kPa. **12 at 700 kPa.
[0085] Magnetic Resonance Imaging (3T, Philips Medical Systems, MA,
USA) was performed 0.5 h after the sonication to confirm BBB
opening and assess safety. Spoiled Gradient-Echo T1-weighted
sequence (TR/TE=20/1.4 ms; flip angle=30.degree.; NEX=2; spatial
resolution: 500.times.500 .mu.m2, slice thickness: 1 mm with no
interslice gap) before and 40 min after intravenously injecting the
contrast agent gadodiamide (Omniscan.RTM., GE Healthcare, NJ, USA;
dosage: 0.2 mL/kg), was used to visualize the opening, with the
analysis described in the following paragraph. T2-weighted sequence
(TR/TE=3000/80 ms; flip angle=90.degree.; NEX=3; spatial
resolution: 400.times.400 .mu.m2, slice thickness: 2 mm with no
interslice gap) was performed for detecting edema.
Susceptibility-weighted imaging (SWI, TR/TE=19/27 ms; flip
angle=15.degree.; NEX=1; spatial resolution: 400.times.400 .mu.m2,
slice thickness: 1 mm with no interslice gap) was performed for
detecting hemorrhage.
[0086] Analysis for the opening volume across the experiments
included image re-alignment, enhancement evaluation, and volume
calculation. The pre-contrast and post-contrast images were aligned
to the individual stereotactically aligned T1-weighted images
acquired using FSL's FLIRT to ensure the alignment of the pre- to
post-contrast images. The ratio of the post- to the pre-contrast
images was taken and normalized by setting 0 and 1 to the mean of
the contralateral region oppose to the sonicated region (a circle
of 6.25 mm in diameter in the horizontal slice) and the anterior
cerebral artery (a circle of 1.75 mm in diameter in the horizontal
slice), respectively, and the opening region was thresholded by
three times standard deviation of the contralateral (unsonicated)
region. The volume was represented as the accumulated voxels over
the threshold in the sonicated region times the voxel size.
[0087] The PCD signals, frequency spectra, and spectrograms
(8-cycle Chebyshev window, 98% overlap, 4096-point Fast Fourier
Transform) were used to monitor the cavitation using MATLAB.RTM..
To quantify the cavitation level--time derivative of the cavitation
dose, the harmonic, ultraharmonic, and the broadband signals in the
spectra for each pulse were separately filtered. The stable
cavitation level based on harmonics only (dSCDh) was represented as
the root-mean squared amplitude of the harmonic signals in a single
pulse, with the harmonic signals defined as the maxima in the
20-kHz (-6-dB width) range around the harmonic frequency (0.5 f*n)
in the frequency spectrum. The stable cavitation level from
ultraharmonics only (dSCDu) was represented as the root-mean
squared amplitude of the ultraharmonic signals in a single pulse,
with the ultraharmonic signals defined as the maxima in 20 kHz
around the ultraharmonic frequency (0.5 f*n+0.25 f) in the
frequency spectrum. The inertial cavitation level (dICD) was
represented as the root-mean squared amplitude of the frequency
spectrum after excluding the harmonics (360 kHz around the harmonic
frequency) and ultraharmonics (100 kHz around the ultraharmonic
frequency).
[0088] The cavitation dose for each sonication was represented as
the cumulative sum of the cavitation level in 1.25-5.00 MHz for
every pulse; the cavitation SNR, the ratio of post- to
pre-microbubble administration cavitation doses.
Cavitation dose (CD)=.SIGMA._(t=0-T)dCD_t=.SIGMA._(t=0-T) ((SA
2).sup.-)_t (4)
Cavitation SNR=20 log (CD_post/CD_pre) (5)
[0089] where t can represent the time for each pulse; T, the
sonication duration; CD, the cavitation dose (SCD.sub.h, SCDu, and
ICD for harmonics, ultraharmonics, and broadband emissions,
respectively); dCD_t, the cavitation level for the pulse at time t
(dSCD.sub.h, dSCDu, and dICD for harmonics, ultraharmonics, and
broadband emissions, respectively); ((*S 2).sup.-)_t the root-mean
squared amplitude of the harmonic/ultraharmonic/broadband signals
in the frequency spectrum for the pulse at time t; CD_post, the
post-microbubble administration cavitation dose; CD_pre, the
pre-microbubble administration cavitation dose.
[0090] The frequency range used to quantify the cavitation level
was 1.25-5.00 MHz to cover the strong harmonics, ultraharmonics,
and broadband emission, while reducing the linear and nonlinear
scattering from the tissue and the skull. The quantification of the
SCDh and the SCDu was based at least in part on the acoustic
emissions generated by the stable cavitation, including harmonics
and ultraharmonics. The harmonics and ultraharmonics were
quantified separately due at least in part to a difference of the
spectral amplitudes. Furthermore, the harmonics can be considered a
result of volumetric oscillation, and the ultraharmonics and
subharmonics can relate to nonspherical bubble oscillation. To
quantify the ICD, the width of the spectral window for the
broadband signals was chosen in order to reduce or minimize both
the electronic noise and the increase due to the harmonic peaks
(i.e., the window width is large enough to reduce or minimize the
electronic noise by averaging and not to cover the broadening part
of harmonic peaks).
[0091] In the in vitro techniques, for purpose of illustration and
confirmation of the disclosed subject matter, an unpaired
two-tailed Student's t-test was used to determine if the treatment
(post-microbubble administration) was significantly higher than the
control (pre-microbubble administration) for each pressure. In the
in vivo skull effect techniques, for purpose of illustration and
confirmation of the disclosed subject matter, a paired two-tailed
Student's t-test was used to determine if the treatment
(post-microbubble administration) was significantly higher than the
control (pre-microbubble administration) for each pressure in each
animal.
[0092] FIGS. 13A-13D illustrate exemplary PCD spectrograms before
and after placing the skull. Before placing the skull, the
amplitude of harmonics, ultraharmonics as well as the broadband
signals increased significantly with pressure after microbubble
administration (FIG. 13B) when compared to the control (FIG. 13A),
in which the second harmonic became significant at and above 150
kPa. The broadband signals increased mostly within the range of 3-5
MHz according to the results at 150 kPa and 200 kPa in FIG. 13B.
After placing the macaque skull (FIG. 13C), the high frequency
components were attenuated, while the signals remained detectable
at the lowest pressure (50 kPa). After placing the human skull
(FIG. 13D), the frequency components below 3 MHz were detected only
at and above 100 kPa.
[0093] B-mode cine-loops were also used to monitor the cavitation
separately. FIGS. 14A-14D shows the images of the microbubbles in
the channel phantom after sonication. The microbubbles were found
to collapse at and above 200 kPa evidenced by the loss of
echogenicity in the focal region in cases without the skull (FIG.
14A), with the macaque skull (FIG. 14B), with the human skull (FIG.
14C), and using longer pulses without the skull (5000 cycles in
FIG. 14D). The mean diameter of the hypoechogenic area at 200 kPa
and 450 kPa was 1.3 mm and 4 mm, respectively.
[0094] FIGS. 15A-15I are diagrams illustrating cavitation doses
with and without the skull in place using 100-cycle pulses. In the
macaque skull examples (FIGS. 14A-14C), the SCDh, the SCDu, and the
ICD without placing the skull were significantly higher (p<0.05)
than the control at and above 50 kPa, which also increased
monotonically with pressure. After placing the macaque skull, the
SCDh was detectable (p<0.05) at all pressures, whereas the
detection pressure threshold for both the SCDu and the ICD
increased to 150 kPa. In the human skull examples (FIGS. 15D-15F),
the SCDh was detectable at and above 100 kPa after placing the
skull. For the SCDu, the detection pressure threshold increased to
250 kPa. For the ICD, it became 350 kPa. The SCDh at and above 400
kPa was undetected at least in part because the control signal with
the human skull was strong. While the detection pressure threshold
changed slightly after placing the macaque and the human skull, the
sensitivity of cavitation doses to pressure changes remained the
same.
[0095] The pulse length effect on the cavitation dose was also
examined. FIGS. 15G-15I illustrate the cavitation doses with
100-cycles and 5000-cycle pulse lengths. The SCDh using 100-cycle
pulses increased monotonically with pressure increase, whereas the
SCDh with 5000-cycle pulses reached a maximum at 300 kPa and
started to decrease at pressures above 300 kPa. The SCDu using
100-cycle pulses increased monotonically with pressure, while the
SCDu using 5000-cycle pulses reached a plateau at 250 kPa and
started to decrease at higher pressures. The ICD using 100-cycle
and 5000-cycle pulses both increased monotonically with pressure
increase, and the latter increased at a faster rate. All of the
cavitation doses of 5000-cycle pulses were higher than that of
100-cycle pulses.
[0096] FIGS. 16A-16D are diagrams illustrating the cavitation SNR,
illustrating the sensitivity of PCD using pulse lengths, the
detection limit, and skull attenuation. Before placing the skull,
the cavitation SNR for the SCDh, SCDu, and ICD using 100-cycle
pulses (FIG. 16A) ranged within 28.6-49.1 dB, 2.1-38.9 dB, and
3.1-37.0 dB, respectively. Followed by the SCDu and the ICD, the
cavitation SNR for the SCDh was the highest. The cavitation SNR for
the SCDh, SCDu, and ICD using 5000-cycle pulses (FIG. 16B) ranged
within 24.8-54.6 dB, 2.2-54.8 dB, and 2.9-41.9 dB, respectively.
Both the cavitation SNR for the SCDh, SCDu reached a plateau at 250
kPa, while it increased monotonically for the ICD.
[0097] FIGS. 16C-16D illustrate the cavitation SNR using 100-cycle
pulses through the skull. The cavitation SNR through the macaque
skull (FIG. 16C) corresponding to the statistically significant
SCDh, SCDu, and ICD through the macaque skull (FIGS. 15A-15C)
ranged within 9.7-29.4 dB, 1.6-15.6 dB, and 1.1-14.1 dB,
respectively. The cavitation SNR through the human skull (FIG. 16D)
corresponding to the statistically significant SCDh, SCDu, and ICD
through the human skull (FIGS. 15D-15F) ranged within 2.4-6.2 dB,
1.4-3.0 dB, and 1.2-1.9 dB, respectively. For the cavitation SNR
with the skull lower than 1 dB, the corresponding cavitation doses
were lower. As such, 1 dB can be represented as the detection
threshold (or SNR threshold), meaning that the PCD signals were
more reliable when the cavitation SNR exceeded 1 dB.
[0098] As described above, by correlating the cavitation SNR with
the skull (FIGS. 16C-16D) to the cavitation doses with the skull
(FIGS. 15A-15F), when the cavitation SNR exceeded 1 dB--defined as
the detection threshold for PCD--the transcranially acquired
cavitation doses were statistically significant. In order to assess
the skull attenuation, the cavitation SNR without the skull (FIG.
14A) was then compared with the cases with the skull surpassing the
1-dB SNR limit (FIGS. 14C-14D). The SNR without the skull was above
15.2 dB and 34.1 dB in order to be detected through the macaque and
the human skull, respectively. The skull attenuation was determined
by dividing by the skull thickness: 4.92 dB/mm and 7.33 dB/mm for
the macaque and human, respectively.
[0099] For purpose of illustration and confirmation of the
disclosed subject matter, in vivo skull effects at different
pressures and different pulse lengths were examined and compared
with those of the in vitro techniques. FIGS. 17A-17C are diagrams
illustrating the cavitation doses using 100- and 5000-cycle pulses.
When applying 100-cycle pulses, the SCDh, SCDu, and ICD were
significantly higher than the control at and/or above 300 kPa, 700
kPa, and 600 kPa, respectively. When applying 5000-cycle pulses,
the SCDh, SCDu, and ICD were significant at pressure lower than
that for the 100-cycle pulses: at and above 100 kPa, at 200 kPa and
700 kPa, and at and above 250 kPa, respectively. The cavitation
dose when applying 5000-cycle pulses was higher than that with
100-cycle pulses. As such, the cavitation doses increased
monotonically with pressure increase. The SCDh using 100-cycle
pulses at 450 kPa, the SCDh using 5000-cycle pulses at 150 kPa, and
the ICD using 5000-cycle pulses at 300 kPa (0.05<p<0.06)
showed higher variability.
[0100] FIGS. 18A-18B are diagrams illustrating the cavitation SNR
for the skull effect using 100- and 5000-cycle pulses. When
applying 100-cycle pulses (FIG. 18A), the cavitation SNR for SCDh,
SCDu, and ICD ranged within 1.2-9.8 dB, 2.3 dB, and 0.7-2.1 dB,
respectively. The cavitiation SNR increased monotonically for the
SCDh and ICD, and fluctuated for the SCDu. When applying 5000-cycle
pulses (FIG. 18B), the cavitation SNR for the SCD.sub.h, SCDu, and
ICD ranged within 3.8-13.3 dB, 1.4-3.5 dB, and 1.0-6.1 dB,
respectively, reached a plateau for the SCDh at 250 kPa, and
started to decrease at 400 kPa. For the SCD.sub.h, the cavitation
SNR fluctuated at low pressures and increased monotonically at and
above 400 kPa. For the ICD, the cavitation SNR increased
monotonically without fluctuating or reaching a plateau. The
cavitation SNRs for pressures where significant cavitation signals
were detected were all above the 1-dB SNR threshold, with the
exception for SCDu (57% of the measurements passing the detection
threshold were statistically insignificant).
[0101] Realtime PCD monitoring during BBB opening according to the
disclosed subject matter was performed. FIGS. 19A-19D illustrate
four cases of PCD monitoring and the corresponding opening results
in MRI at different pressures. The MRI showed BBB opening in two
macaques in the thalamus and the putamen at pressures ranging from
250 kPa to 600 kPa, with the opening volume of 338.6, 223.8, 213.4,
and 262.5 mm3, respectively. The volume increased with pressures in
the same macaque (FIGS. 19B-19D) in general, and the range varied
across animals. The dSCDh reached a plateau in 10-30 seconds after
injecting microbubbles and was kept at the same level for the rest
of sonication duration. The dSCDu remained generally undetected.
The dICD increased by 3.18 dB at 350 kPa and 0.19 dB at 450 kPa
from the end of the sonication to the beginning, and remained
unchanged at 275 kPa and 600 kPa.
[0102] For purpose of illustration, FIGS. 20A-20D illustrate an
exemplary safety assessment technique using T2-weighted MRI and SWI
corresponding to the four BBB opening cases in FIGS. 19A-19D. In
each example, no edema or hemorrhage was detected, corresponding to
the PCD monitoring results for which little or no ICD increase was
seen during sonication.
[0103] For purpose of illustration and confirmation of the
disclosed subject matter, as embodied herein, to investigate the
sensitivity, reliability, and the transcranial cavitation detection
limit in macaques and humans, both in vitro macaque and human skull
techniques as well as in vivo techniques for the skull effect and
BBB opening in macaques were performed.
[0104] The transcranial PCD was found sensitive to detect
cavitation signals at pressures as low as 50 kPa. The transcranial
detection threshold (1-dB SNR threshold) served as a guide to
determine reliable detection. Realtime PCD monitoring was performed
during BBB opening, in which safe opening and reliable detection
was achieved using long pulses.
[0105] B-mode imaging was used to visualize the cavitation, to
ensure the focal alignment to the channel and the pressure in situ.
The imaging visualized cavitation by the maintenance or loss of
echogenicity, representing stable or inertial cavitation,
respectively, and confirmed good focal alignment to the channel
before and after placing the skull by detecting the bubble collapse
at the center of the channel. The pressure in the channel was
confirmed after placing the skull since the loss of echogenicity
became detectable at 200 kPa.
[0106] The PCD was utilized as an indirect monitoring tool. The PCD
was shown to be more sensitive than B-mode imaging at least in part
because PCD detected inertial cavitation at 50 kPa, lower than the
lowest pressure losing echogenicity (200 kPa). Detecting bubble
destruction in B-mode imaging can be affected by its spatial and
contrast resolution, which can be unable to detect a smaller amount
of bubble destruction at pressures lower than 200 kPa. As such,
B-mode imaging was used to supplement to the PCD results rather
than to determine the inertial cavitation threshold. The inertial
cavitation occurred at 50 kPa due at least in part to low
excitation frequency, long pulse lengths, and low stiffness of the
in-house microbubbles with a 4-5 .mu.m diameter.
[0107] The pulse length affected the characteristics of the
cavitation doses (FIGS. 15A-15I). Using 100-cycle pulses, the
cavitation doses increased monotonically with pressure increase as
the magnitude of bubble oscillation increased. Furthermore, using
long pulses (5000 cycles) was found to generate higher cavitation
doses. The ICD still increased monotonically with pressure
increase, while the SCDh and the SCDu reached a plateau at 250 kPa.
Under a long-pulse excitation, a larger number of microbubbles
underwent stable and inertial cavitation, and stable cavitation
reached a plateau and started to decrease when most microbubbles
were undergoing inertial cavitation and collapse immediately
without contributing to stable cavitation. The microbubbles
undergoing stable cavitation diffused faster using longer pulses
and failed to enhance the SCDh.
[0108] Through the skull the change of cavitation doses to pressure
change remained the same, while the pressure threshold for the
cavitation doses becoming detectable varied depending on the type
of cavitation doses and the skull (FIGS. 15A-15I). The monotonical
increase of cavitation doses to pressure increase remained the same
after placing the macaque and the human skull for signals surpassed
the skull attenuation. The pressure threshold to detect the SCDh
through the macaque skull was unchanged, while it increased for the
SCDh and ICD; for the human skull, the threshold increased for the
three types of cavitation doses. For all types of cavitation doses,
the pressure threshold for the SCDh was the lowest, followed by the
SCDu and ICD. The SCDh remained detectable through the skull at 50
kPa and 100 kPa for macaques and 100 kPa, respectively. For the
SCDu and ICD, the pressure threshold increased to 150 kPa and 350
kPa for macaques and human respectively due at least in part to low
signal intensity, and the ultraharmonics and the broadband
emissions occurred at 50 kPa.
[0109] With respect to the in vivo techniques, using 100-cycle and
5000-cycle pulses, the SCDh as well as the ICD generally increased
monotonically with pressure. The SCDh for the 5000-cycle pulse did
not reach a plateau, which can be due at least in part to nonlinear
scattering from the skull and/or air trapped between the transducer
and the animal's skin. The SCDu from the less frequent
ultraharmonics can be attributed to the biological environment such
as blood, capillary, and blood vessel. The varying blood pressure
can also contribute to variation in the SCDu. The inertial
cavitation was detected at and above 250 kPa, though microbubble
collapse can occur at lower pressures.
[0110] The cavitation SNR was determined and used to investigate
the sensitivity and reliability of PCD under different conditions
such as varied pressures and pulse lengths, and corresponding skull
effects. In this manner, the transcranial detection threshold (1-dB
SNR threshold), the skull attenuation, and other parameters can be
determined. To achieve reliable PCD, the cavitation SNR can be
increased in any or all of three ways: increasing the pressure, the
pulse length, and/or the number of microbubble injected. Using long
pulse lengths was found effective in increasing the cavitation SNR
at low pressures, while the cavitation SNR for the SCDh decreased
at high pressures due to the cavitation characteristics and
nonlinear skull scattering. Increasing the number of microbubbles
injected can also improve the cavitation SNR, at least in part
because the inertial cavitation can be detected at low pressures
(250 kPa) in the in vivo skull effect examples after a second bolus
injection of microbubbles.
[0111] The cavitation signals can be considered reliable through
the skull, particularly where the cavitation SNR was above 1 dB,
such that the signals were strong enough to surpass skull
attenuation. The 1-dB SNR threshold was determined in the in vitro
study and confirmed in the in vivo study. As in both studies, the
cavitation doses generally showed statistical significance when
using this guide. The transcranial detection threshold can also
provide an indication of inertial cavitation detected, and can
indicate reliable PCD for all types of cavitation doses.
[0112] As described herein, the attenuation by the human skull was
higher than that for macaque, which can be due at least in part to
higher skull density, stronger nonlinear ultrasound transmission,
stronger reflections and/or different extents of mode conversion.
The cavitation SNR can be increased to surpass the detection
threshold, for example and without limitation, by increasing the
pressure, the pulse length, or the number of microbubbles injected
as described herein. The in situ cavitation strength can be
estimated by combining the transcranial PCD measurements exceeding
the transcranial detection threshold with the skull attenuation
acquired from simulation or ex vivo measurement to assess the
treatment outcome.
[0113] Nonlinear ultrasound scattering due at least in part to the
skull can also affect the detection of harmonics. Nonlinear
scattering from the human skull was appared above 450 kPa (FIG.
15D), affecting the detection of the harmonics (SCDh) generated by
the microbubble cavitation. Higher pressure was applied in order to
compensate for the 80% of pressure attenuation through the human
skull, which can create or increase nonlinear scattering. The FUS
focus was 25 mm below the human skull, can increase nonlinear
effects compared to deeper focus. Trapped air can also be present.
Nonlinear effects can affect the detection of the SCD.sub.h, which
can lead to overtreatment based on the monitoring.
[0114] Realtime monitoring of the cavitation doses was performed
during BBB opening using 5000-cycle pulses, providing the
information of bubble perfusion and the cavitation level.
Furthermore, the use of long pulses facilitated reliable PCD
monitoring and opening at low pressures. By monitoring the
SCD.sub.h, the time for microbubbles perfuse to the sonicated
region as well as the microbubble persistence during the entire
treatment can be monitored at pressures as low as 250 kPa. By
monitoring the ICD, the safety of the treatment can be determined
in real time at least in part because low or no inertial cavitation
was detected in the cases of safe BBB opening. Low or no ICD
obtained during BBB opening experiments (FIGS. 19A-19D) compared to
the in vivo skull effect (FIG. 17A-17C) was due at least in part to
lower number of microbubbles circulating during BBB opening, at
least in part because increase of ICD was obtained in the same
animal after a second bolus injection of microbubbles for in vivo
skull effect.
[0115] Safe BBB opening was achieved at low pressures (250-600 kPa)
in both the putamen and the thalamus (FIGS. 19A-19D). No
differences were observed in the putamen and the thalamus in terms
of cavitation doses or opening threshold, as described herein. The
opening volume varied across animals, and increased with pressure
in the same macaque comparing the 350-kPa example (FIG. 19B) with
the 600-kPa example (FIG. 19D). The 450-kPa case had a smaller
opening volume than the 350-kPa case from the slightly decreasing
SCD.sub.h, which can be due at least in part to the animal's
physiological effect to the circulating microbubbles. The average
SCDh at different pressures was at the same level, which can be due
at least in part to the cavitation characteristics using long
pulses and the high variation between examples, as illustrated for
example in FIGS. 16A-16C.
[0116] For purpose of illustration, as embodied herein, the
positive correlation of the ICD to pressure can be considered
independent of the pulse length, which can affect cavitation
characteristics. The ICD in the examples herein was not affected by
the nonlinear ultrasound scattering due to the skull (as
illustrated for example in the human skull results in FIGS.
15D-15F. The ICD can also provides a safety assessment. Improved
ICD detection can be achieved by increasing the cavitation SNR.
Additionally or alternatively, passive cavitation mapping,
including spatial information of cavitation, can improve estimation
of opening volume and safety assessment using both the SCDh and
ICD.
[0117] The foregoing merely illustrates the principles of the
disclosed subject matter. Various modifications and alterations to
the described embodiments will be apparent to those skilled in the
art in view of the teachings herein. It will thus be appreciated
that those skilled in the art will be able to devise numerous
techniques which, although not explicitly described herein, embody
the principles of the disclosed subject matter and are thus within
its spirit and scope.
* * * * *