U.S. patent application number 14/048089 was filed with the patent office on 2014-02-20 for method and device for real time mechanical imaging of prostate.
This patent application is currently assigned to Artann Laboratories, Inc.. The applicant listed for this patent is Artann Laboratories, Inc.. Invention is credited to Souren Airapetian, Vladimir Egorov, Sergiy Kanilo, Armen P. Sarvazyan.
Application Number | 20140052027 14/048089 |
Document ID | / |
Family ID | 40161458 |
Filed Date | 2014-02-20 |
United States Patent
Application |
20140052027 |
Kind Code |
A1 |
Sarvazyan; Armen P. ; et
al. |
February 20, 2014 |
METHOD AND DEVICE FOR REAL TIME MECHANICAL IMAGING OF PROSTATE
Abstract
The present invention relates to a method for real time
mechanical imaging of a prostate with a transrectal probe. In the
method, generating a composite two- and three-dimensional prostate
mechanical image from a plurality of partial mechanical images
extracted from pressure response data and a probe orientation data
starts with examining the prostate by pressing a probe head
pressure sensor array against it at various overlapping locations.
Merging of partial mechanical images together is accomplished by
analyzing an overlap between each subsequent and previous partial
mechanical image. Finding the prostate is assisted with a
supplemental pressure response data indicating the location of a
sphincter known to be about 4-5 cm away from the prostate. Data
processing is improved by including probe orientation data to
further increase the accuracy and sensitivity of the method. The
probe is equipped with a two-dimensional head pressure sensor
array, a supplemental shaft sensor array and orientation tracking
sensors including a three-axis magnetic sensor and a two-axis
accelerometer sensor for calculating elevation, rotation and
azimuth angles of the probe.
Inventors: |
Sarvazyan; Armen P.;
(Lambertville, NJ) ; Egorov; Vladimir; (Princeton,
NJ) ; Kanilo; Sergiy; (Lawrenceville, NJ) ;
Airapetian; Souren; (Levittown, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Artann Laboratories, Inc. |
Trenton |
NJ |
US |
|
|
Assignee: |
Artann Laboratories, Inc.
Trenton
NJ
|
Family ID: |
40161458 |
Appl. No.: |
14/048089 |
Filed: |
October 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13005401 |
Jan 12, 2011 |
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14048089 |
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11123999 |
May 6, 2005 |
7922674 |
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13005401 |
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Current U.S.
Class: |
600/587 |
Current CPC
Class: |
A61B 2562/046 20130101;
A61B 5/1077 20130101; A61B 5/72 20130101; A61B 2562/0247 20130101;
A61B 5/4381 20130101; A61B 5/6847 20130101; A61B 5/7425 20130101;
A61B 5/11 20130101 |
Class at
Publication: |
600/587 |
International
Class: |
A61B 5/107 20060101
A61B005/107; A61B 5/00 20060101 A61B005/00 |
Goverment Interests
REFERENCE TO GOVERNMENT-SPONSORED RESEARCH
[0002] This invention was made with government support under SBIR
Grant 2 R44 CA82620-02A1 awarded by the National Institutes of
Health, National Cancer Institute. The government has certain
rights in this invention.
Claims
1. A method for mechanical imaging of a palpable organ through a
natural body opening comprising the steps of: (a) providing a probe
equipped with a two-dimensional pressure sensor array adapted to
obtain pressure response data when pressed against said palpable
organ, (b) conducting examination of said palpable organ by
inserting said probe through said natural body opening and pressing
said probe against said palpable organ at various locations about
thereof to obtain said pressure response data, each subsequent
location overlapping a previous location, (c) obtaining a plurality
of partial mechanical images from said pressure response data, each
subsequent and previous partial mechanical image corresponding to
the respective location of pressing of said probe against said
palpable organ, (d) comparing each subsequent partial mechanical
image with the previous partial mechanical image to find an overlap
therebetween, and (e) constructing a composite mechanical image of
said palpable organ from said plurality of partial mechanical
images using overlaps between each subsequent and previous partial
mechanical image to merge them together, whereby the entire
mechanical image of said palpable organ is obtained with said
two-dimensional pressure sensor array irrespective of the movements
of said organ during examination.
2. The method as in claim 1, wherein said palpable organ is a human
prostate gland and said natural body opening is a rectum.
3. The method as in claim 1, wherein said probe is further equipped
with a supplemental pressure sensor array located in a known
geometrical relationship to said pressure sensor array along said
probe, said step (b) further including obtaining supplemental
pressure response data from said second pressure sensor array.
4. The method as in claim 3, wherein said step (b) further includes
identifying a preliminary position of said palpable organ at a
predetermined distance from a supplemental reference organ as
detected from said supplemental pressure response data.
5. The method as in claim 1, wherein said probe is further equipped
with orientation tracking means, said step (c) further includes
obtaining orientation data, and said step (e) further including
constructing said composite image of said palpable organ using said
orientation data and said overlaps to merge said partial images
together.
6. The method as in claim 1, wherein said step (e) further includes
constructing at least one two-dimensional composite image of said
palpable organ.
7. The method as in claim 1, wherein said step (e) further includes
constructing a three-dimensional composite image of said palpable
organ.
8. The method as in claim 1 further including a step (f) of
displaying said composite image.
9. The method as in claim 1 further including a step (f) of
calculating geometrical parameters of said palpable organ and
mechanical parameters of its inner structure.
10. The method as in claim 9 further including a step (g) of
displaying said composite image, said geometrical parameters, and
said mechanical parameters of the inner structure of said palpable
organ.
11. A device for mechanical imaging of a palpable organ through a
natural body opening comprising: a probe head sized to fit through
said natural body opening, said probe head equipped with a
two-dimensional head pressure sensor array adapted to obtain a
pressure response data when pressed against said palpable organ, an
electronic unit connected to said probe head and adapted to
receiving said pressure response data from said probe head, and a
processing and display means connected to said electronic unit,
said processing and display means further including a means for
calculating a plurality of partial mechanical images, each partial
mechanical image calculated from said pressure response data when
said probe is pressed against said palpable organ, a means for
comparing each subsequent partial mechanical image with a previous
partial mechanical image to determine an overlap therebetween, and
a means for constructing a composite image of said palpable organ
from said plurality of partial images by merging them together
using said overlap.
12. The probe as in claim 11, wherein said palpable organ is a
prostate gland.
13. The probe as in claim 11, wherein said probe head pressure
sensor array includes a plurality of individual pressure sensors,
said sensor selected from a group consisting of capacitive pressure
transducer, piezoelectric pressure transducer, resistive pressure
transducer, and MEMS pressure transducer.
14. The probe as in claim 13, wherein the number of said individual
sensors in said plurality exceeds 60.
15. The probe as in claim 11, wherein said probe head further
includes a shaft equipped with a shaft pressure sensor array spaced
away from the head pressure sensor array and adapted to obtain a
supplemental pressure response data.
16. The probe as in claim 11, wherein said probe head further
includes orientation tracking means adapted to provide positional
data of the location of said probe.
17. The probe as in claim 16, wherein said orientation tracking
means including a three-axis magnetic sensor and a two-axis
accelerometer sensor.
18. The probe as in claim 17, wherein said processing and display
means further includes means for calculating elevation, rotation
and azimuth angle of said probe from data provided by said
three-axis magnetic sensor and said two-axis accelerometer
sensor.
19. The probe as in claim 11, wherein said means for constructing
said composite image further includes means for calculating
geometrical parameters of said palpable organ and mechanical
parameters of its inner structure.
Description
CROSS-REFERENCE DATA
[0001] This application is a continuation of a co-pending U.S.
patent application Ser. No. 13/005,401 filed 12 Jan. 2011, which in
turn is a continuation of the patent application Ser. No.
11/123,999 filed 6 May 2005, now abandoned, all of which are
incorporated herein by reference in their respective
entireties.
BACKGROUND OF THE INVENTION
[0003] The present invention relates generally to medical devices.
More specifically, it relates to a mechanical imaging system and
process for examining, mapping, and diagnosing diseases of a
palpable organ such as a prostate gland in a male patient,
especially the prostate cancer. It is also applicable more
generally to mechanical imaging of palpable tissues, including but
not limited to, through natural body openings in a human being,
i.e. mouth, ear(s), rectum, and other body cavities. It is also
applicable to determination of a relative stiffness or elasticity
of tissues. The term "patient" includes humans and animals, both
alive and dead that can be subject for mechanical imaging.
[0004] The high incidence of prostate cancer, as well as benign
prostatic hyperplasia (BPH), especially among the older male
population, dictates the need for effective means of early
detection. Prostate cancer is the cause of death in about 30,000
men each year, making it the number two cancer killer of men in the
United States, second only to lung cancer. However, if prostate
cancer is detected early and treated effectively, the chance of
survival of one afflicted with this disease improves significantly.
Current methods of early diagnosis of prostate cancer include
digital rectal examination (DRE), measurement of serum levels of
prostate specific antigen (PSA), and transrectal ultrasound (TRUS)
examination.
[0005] The following discussion provides useful overview of various
methods described in the prior art and applicable to prostate
examination and imaging. Substantial prior art is accumulated
describing various devices and techniques using ultrasound for the
imaging of the prostate. U.S. Pat. No. 6,561,980 by Gheng describes
the methods of processing ultrasound images to cause automatic
segmentation of prostate, rectum, and urethra once the transverse
cross-sectional image of prostate is acquired by ultrasound means.
U.S. Pat. No. 6,824,516 by Batten describes a sophisticated system
for examining, mapping, diagnosing, and treating prostate diseases
based on ultrasonic imaging, this patent is incorporated herein in
its entirety by reference. U.S. Pat. No. 6,778,690 by Ladak
describes a method of processing 2D and 3D ultrasound images to
determine the prostate boundaries and is also incorporated herein
by reference in its entirety as it provides useful image processing
methodology.
[0006] Unfortunately, to date the experience with TRUS as a means
of prostate cancer screening and staging has been disappointing. It
adds little to screening by DRE and PSA, and the small improvement
in prostate cancer detection does not justify its cost. As a
screening test, TRUS has a low specificity and a high false
positive rate. Evaluation of pathologic specimens shows that a
significant fraction of tumors are isoechoic and thus
indistinguishable from surrounding tissue, while many palpable
tumors could not be visualized by TRUS.
[0007] The most sensitive single test for prostate cancer is
measurement of serum PSA levels. However, its positive predictive
value is limited. The DRE alone is even less useful. However,
combining the two modalities nearly doubles the cancer detection
rate. Large-scale studies of systematic screening for prostate
cancer using PSA, DRE and TRUS concluded that combining PSA and DRE
provided the highest sensitivity and specificity for prostate
cancer diagnosis. Therefore, the combination of the two methods for
prostate cancer screening is currently recommended by the AUA and
American Cancer Society, and has been approved by FDA for patients
between the ages of 50 and 75 years.
[0008] At the present time, digital rectal examination is the most
widely used method of prostate cancer screening. Approximately
30-50% of palpable prostate nodules prove to be malignant upon
pathologic evaluation. Screening trials have demonstrated that 70%
of men with abnormal DRE undergoing radical prostatectomy have
organ-confined cancer. A strong association between abnormal DRE
and prostate cancer mortality has been demonstrated and it was
suggested that screening DRE could prevent as many as 50-70% of
deaths due to prostate cancer. DRE also has been shown to be the
most cost efficient prostate screening method, especially when
combined with PSA.
[0009] The main disadvantage of DRE is its high degree of
subjectivity. The user has to instinctively relate what he or she
senses by the finger to previous DRE experience. There may not be a
sufficient number of skilled users available for large-scale mass
prostate screenings. Another limitation of DRE is that a physician
performing the examination cannot objectively record the state of
the examined prostate. Therefore, it is difficult to objectively
compare the results of consecutive examinations of the same
prostate.
[0010] A new method of prostate imaging based on principles similar
to those of manual palpation has been developed by Sarvazyan et al.
and described in the U.S. Pat. Nos. 6,569,108; 6,142,959;
5,922,018; 5,836,894; 5,785,663; and 5,524,636, all incorporated
herein in their entirety by reference. This method, termed
Mechanical Imaging, provides the ability to "capture the sense of
touch" and store it permanently for later temporal correlation and
trending. The essence of mechanical imaging is measurement of the
stress pattern on the surface of the compressed tissue and
analyzing the changes of that pattern while moving the sensor array
over the examined tissue. Temporal and spatial changes in the
stress pattern provide information on the mechanical structure of
the examined tissue and enable 3D reconstruction of internal
structures and mechanical heterogeneities in the tissue. Mechanical
imaging is free of many of the disadvantages of DRE. Mechanical
imaging has been shown to exceed substantially the limits of lesion
size and depth detectable by conventional manual palpation
techniques [Weiss R., Hartanto V, Perrotti M, Cummings K, Bykanov
A, Egorov V, Sobolevsky S. "In vitro trial of the pilot prototype
of the prostate mechanical imaging system", Urology, V.58, No. 6,
2001, p. 1059-1063].
[0011] Recently, the American Urological Association issued
recommendations to help physicians confirm the diagnosis of
prostate cancer. According to these recommendations, a biopsy
should be considered for any patient with an abnormal DRE and
elevated PSA. The effectiveness and reliability of DRE are highly
dependent on the skill of the user, since the finger does not
provide a quantitative or objectively verifiable assessment. Thus,
there is a great need for a new technology and a device to enable
general practitioners and urologists alike to perform a reliable,
accurate, sensitive, and quantitative assessment of the prostate
using a computerized palpation-imaging device. Moreover, such
accurate assessment of prostate size, shape, and elasticity is also
important for diagnosing and monitoring of prostate cancer and BPH.
Mechanical imaging technology and the low cost, prostate imaging
device should improve significantly the ability of minimally
trained individuals in primary care settings to assess, screen, and
monitor prostate pathology in a reliable and valid manner in a male
human, with a minimum of physical and mental discomfort.
[0012] While prior art mechanical imaging devices provided for data
collection, the ability to recreate the 2D and 3D images of the
prostate were limited by the insufficiently accurate information
about the position of transrectal probe with regard to the examined
prostate in the course of examination. One reason for this is
because the prostate can shift from its original place during the
procedure. Therefore, the prior art methods have a fundamental
disadvantage in that as the examination progresses, no means are
available to properly compensate for the probe position and
orientation relative to the moving prostate. Inaccuracies in the
evaluation of the location of the prostate with respect to the
probe head during the course of examination may result in low
quality of obtained images and introduce various artifacts.
[0013] The need exists therefore for a prostate examination means
and methods of use designed to eliminate the distortion in the
position data of the prostate probe and make it independent of the
internal movements of the prostate organ.
SUMMARY OF THE INVENTION
[0014] Accordingly, it is an object of the present invention to
overcome these and other drawbacks of the prior art by providing a
novel method and device for mechanical imaging of a palpable organ
such as a prostate gland through a natural body opening, this
method and device having the ability to generate real time 2D and
3D depiction of the organ and automatic detection of suspicious
areas within thereof.
[0015] It is another object of the present invention to provide a
mechanical imaging device for examination of prostate capable of
automatically compensating for the internal shifts of the prostate
during the examination.
[0016] It is another object of the present invention to provide a
mechanical imaging device for examination of prostate capable of
merging at least two independently obtained mechanical images of
prostate using commonly identified features of the prostate image
from an overlap between these two images.
[0017] It is a further object of the present invention to provide a
probe for prostate examination equipped with a two-dimensional
pressure array sensor capable of providing mechanical images with
the ability to recognize the overlap between these two images.
[0018] The method of the invention is based on a method for real
time mechanical imaging of the palpable organ with a probe inserted
through a natural body opening. According to one aspect of the
method of the invention, generating a two- or three-dimensional
prostate mechanical image from a plurality of pressure response
data and probe orientation data comprises the steps of: [0019]
locating the prostate under the transrectal probe head pressure
sensor array, [0020] examining the prostate by the probe head
two-dimensional sensor array by pressing it repeatedly against the
prostate at various locations such that each subsequent location
overlaps the previous location, [0021] incorporating newly acquired
mechanical prostate information from each location where the probe
is pressed against the prostate into a partial two-dimensional
normalized mechanical image of the prostate, [0022] comparing each
subsequent partial mechanical image with the previous partial
mechanical image to find an overlap therebetween, and [0023]
constructing a composite mechanical image of the prostate from the
entire plurality of partial mechanical images using overlaps
between each subsequent and previous partial mechanical image to
merge them together.
[0024] Importantly, the processing of data obtained from the probe
head pressure sensor array allows moving the probe relative to the
prostate while maintaining the common identified features of each
obtained partial mechanical image. In other words, every time the
probe is moved from one location to the next, the processing means
of the device are adapted to follow certain identifiable features
from the overlap between the previous partial mechanical image to
the next one such that a complete 2D or 3D image may be
constructed. That way, there is less or even no need for knowing
the absolute position in space of both the prostate and the probe
in order to accurately relate each successive mechanical image to a
certain part of the prostate.
[0025] In the preferred embodiment, the device comprises: a probe
shaft pressure sensor array for collecting pressure response data
in the vicinity of the sphincter; a probe head pressure sensor
array for collecting data in the vicinity of the prostate volume; a
probe orientation tracking sensors for collecting a probe
orientation data; a processing apparatus for processing the
pressure response and orientation data to generate mechanical image
data and calculate prostate parameters; and a display device for
representation of at least a two-dimensional image of the
prostate.
[0026] Preferably, in order to further increase the accuracy of the
results, the probe head orientation and its position relative to
examined prostate is calculated from orientation data recorded from
3D magnetic sensors and a 2D accelerometer sensor, and combined
with the pressure response data recorded from the head pressure
sensor array and the shaft pressure sensor array.
[0027] As opposed to the devices of the prior art, the present
invention takes advantage of combining three independent sources of
positioning information: [0028] using the prostate itself as a
reference object by examining the overlap between each previous and
subsequent partial mechanical image of the prostate, [0029] having
more than one pressure sensor arrays working together in an
integrated manner to take advantage of locating the prostate in its
relationship to a nearby organ, which is more stable in its
position such as sphincter, and finally [0030] calculating of probe
head position from probe orientation data.
[0031] Combining all these sources of information, the device of
the invention provides calculations including both the orientation
and pressure response data.
[0032] The device and method of the present invention are created
with a design philosophy to create a patient-friendly system, which
is easy and intuitive to use by the examining physician.
[0033] As a result, the present invention advantageously provides
for: [0034] early prostate cancer detection; [0035] quantitative
classification of prostate geometrical and mechanical parameters;
[0036] automatic identification of what has changed between
successive examinations; [0037] tracking and trending treatment
impact for certain treatment modalities; [0038] matching the system
output with pathology findings as proof of system performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] A more complete appreciation of the subject matter of the
present invention and the various advantages thereof can be
realized by reference to the following detailed description in
which reference is made to the accompanying drawings in which:
[0040] FIG. 1 is a schematic diagram illustrating the functional
structure of the system in accordance with the present
invention,
[0041] FIG. 2 is a side view of the probe with a two-dimensional
head pressure sensor array, a shaft pressure sensor array, and
orientation sensors,
[0042] FIGS. 3A and 3B are cross-sectional views of the probe head
and the probe shaft respectively in accordance with the present
invention,
[0043] FIG. 4 is a diagram of an orientation tracking system used
in the preferred embodiment of the present invention,
[0044] FIG. 5 represents an electronic unit schematic diagram of
the device,
[0045] FIG. 6 is a flow chart describing steps for obtaining
diagnostic information,
[0046] FIG. 7 is a perspective view of the transrectal probe
relative to an examined prostate, illustrating a reference
coordinate system having three orthogonal axes and probe
orientation angles,
[0047] FIG. 8 is a flow chart describing steps for composition of
two-dimensional and three-dimensional prostate mechanical images
and calculating prostate parameters,
[0048] FIG. 9 is an illustration of real time two-dimensional
prostate image and sphincter area mechanical image with relative
probe positioning to guide the use of the probe during prostate
examination, and
[0049] FIG. 10 is an illustration of a three-dimensional prostate
mechanical image composition.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
[0050] A detailed description of the present invention follows with
reference to accompanying drawings in which like elements are
indicated by like reference letters and numerals.
[0051] Referring now to the drawings, FIG. 1 is a schematic view of
a preferred embodiment of a device for generating a mechanical
image of a three-dimensional prostate volume from pressure response
data corresponding to a scan of the prostate. The device comprises
the following major elements: [0052] a transrectal probe 3 with
incorporated two-dimensional head pressure sensor array 1 for
receiving pressure response data for the prostate 4 and shaft
pressure sensor array 2 for receiving supplemental pressure
response data for a sphincter area 5, [0053] electronic unit 6, and
[0054] a processing and displaying means 7, which may be for
example incorporated into a compact personal computer.
[0055] The prostate examination is performed using the following
general steps. The patient is instructed to take off all clothes
below the waist. The examination is preferably performed in the
standing position by bending the patient over the examination table
to form a 90-degree angle at the waist. Patient' chest is placed on
the table and patient's weight is applied to the table surface so
that leg muscles are free from any tension. Optionally, the patient
can also be examined while positioned on his side, with his knees
bent toward his chest. The probe is preferably covered with a
disposable lubricated cover. During the insertion into the rectum,
pressure applied to the anal sphincter should be monitored in order
to minimize the level of patient' discomfort. Pressure response
data obtained from a supplemental pressure array may be optionally
used for that purpose. Gentle posterior pressure is applied as the
probe is slowly inserted with the sensor surface down. Allowing a
few seconds for the external and internal sphincter to relax will
avoid patient discomfort. Scanning begins in the sagitall plane by
first optionally imaging the sphincter used as a supplemental
reference organ. Then, the probe is inserted deeper until the
bladder is visualized. Next, by sliding the probe backwards, the
prostate is detected at about 4-5 cm from the sphincter and the
probe is positioned in a way that enables the device to display the
prostate gland surface in the center of the screen. Once the probe
is properly positioned, evaluation of prostate is performed through
a set of multiple pressings on the median sulcus and lateral lobes
of the prostate. Each location of compression of the prostate is
done such that it overlaps the previous location of such
compression. In certain cases, change in an elevation angle of the
probe is required to visualize the prostate.
[0056] FIG. 2 is a side view of the preferred embodiment of the
transrectal probe 3 with the head pressure sensor array 1 installed
on a probe head 21, and with the shaft pressure sensor array 2
installed on a probe shaft 22 attached to the probe handle 24. The
optional elastic disposable cover (not shown) is envisioned to
envelop the entire surface of the probe head 21, probe shaft 22,
and partly the probe handle 24. The probe handle 24 further
comprises orientation tracking means consisting of a three-axis
magnetic sensor 25 and a two-axis accelerometer sensor 26. The
probe also includes an examination "start-stop" button 23. Of note
here is the offset of the probe head 21 relative to the probe shaft
22. It is designed such that the probe better fits with the anatomy
of a human patient, so that compression of the prostate does not
cause loading the sphincter with a side force. Both the shaft and
the head pressure sensor arrays are better adapted to visualize the
prostate and the sphincter respectively.
[0057] FIG. 3A is a preferred cross-sectional view of the oblong
probe head 21 with surface installed pressure sensors 31 in
accordance with the present invention. The probe of the invention
is equipped with a two-dimensional pressure sensor array with over
60 individual sensors arranged in a two-dimensional array, for
example 8.times.16 or 16.times.16. Importantly, the number of
sensors, their density, and array configuration is selected to
provide sufficient pressure response data to obtain two-dimensional
pressure data in each pressing of the probe against the palpable
organ. When each subsequent location in which the probe is pressed
against the prostate overlaps the previous location, resolution of
the pressure array should be sufficient to identify such overlap
between the partial mechanical images corresponding to a previous
and subsequent location, as discussed in more detail below.
Previously known devices of this type were not capable of obtaining
a two-dimensional pressure patterns after a single pressing since
they were equipped with just a linear array of sensors or had
limited number of sensors. That was insufficient for obtaining
useful two-dimensional patterns by making just a single pressing of
the pressure sensing array. A plurality of pressure sensors 32
constitutes the pressure sensing array of the head pressure sensor
array 1 as shown in FIG. 2. The two-dimensional pressure sensor
array 1 serves the following three main purposes: [0058] providing
pressure response data in the course of examination of the
prostate, [0059] providing information on changes in the probe head
position relative to the prostate deploying a mechanical image
recognition technique, and [0060] guiding the user during prostate
examination by displaying a real time complete two-dimensional
pressure pattern of the head pressure sensor array.
[0061] Size, grid, and sensor quantity in the head pressure sensor
array may very. Preferably, the head pressure sensor array has a
pressure sensitive area of about 12 to 20 mm wide by 30 to 50 mm
long, and includes over 60 individual pressure sensors. The
curvature radius of the probe head may vary too, but preferably the
curvature radius should be about 10 to 20 mm to provide a uniform
stress pattern while pressing against the prostate. Individual
pressure sensors may be designed to be a piezoelectric, resistive,
or MEMS pressure transducer, possibly using micro-machined parts or
nano-technologies. Preferably though, each pressure sensor
comprises a capacitive pressure transducer covered by an elastic
compound.
[0062] FIG. 3B is a preferred cross-sectional view of the probe
shaft 22 with surface installed supplemental pressure sensors 32 in
accordance with the present invention. A plurality of supplemental
pressure sensors 32 constitutes the shaft pressure sensor array 2
as shown in FIG. 2. This shaft pressure sensor array serves two
main purposes: [0063] receiving supplemental pressure data from the
sphincter area needed to guide the user during prostate examination
by displaying a real time complete two-dimensional pressure pattern
of the shaft pressure sensor array, and [0064] assisting the user
in estimating a most probable location of the prostate being
typically at a distance of about 4-5 cm away from the location of
the sphincter. As with the head pressure sensor, the size, grid,
design, and sensor quantity in the supplemental shaft pressure
sensor array may very. In the most basic case, it can be a simple
linear array of sensors. Preferably, the shaft pressure sensor
array has a pressure sensitive area all the way around the probe
shaft sized to be about 40 mm long and include over 600 individual
pressure sensors. A shaft diameter may vary too, but preferably the
shaft diameter is about 12.5 mm. Each individual pressure sensor
may be a piezoelectric, resistive, or MEMS pressure transducer, but
in the preferred embodiment it is a capacitive transducer, similar
to that of the head pressure sensor array.
[0065] FIG. 4 is a diagram of an orientation tracking sensor means
used in the preferred embodiment of the present invention. The
orientation tracking means includes a three-axis magnetic sensor 25
with orthogonal sensitivity axes M.sub.x, M.sub.y, M.sub.z, and a
two-axis acceleration sensor 26 having sensitivity axes A.sub.x,
A.sub.y accordingly. Importantly, A.sub.x-axis is parallel to the
M.sub.x-axis and A.sub.y-axis is parallel to the M.sub.y-axis. Both
the magnetic sensor 25 and the acceleration sensor 26 are mounted
on a platform 41 so that X and Y axes are parallel thereto, which
in turn is parallel to the probe head pressure sensing surface.
Preferably, platform 41 is incorporated inside the probe handle to
be in the vicinity of the sphincter during prostate examination.
Magnetic sensor readings give sensor orientation relative to
Earth's magnetic field. To compensate the magnetic sensor reading
for a platform tilt relative to a horizontal plane, which is
perpendicular to Earth's gravity vector, it is necessary to know
the platform tilt angles. The two-dimensional accelerometer sensor
is used here as a tilt sensor to provide elevation (.phi.) and
rotation (.theta.) readings. The X, Y, Z magnetic readings can be
traced back to the horizontal plane by applying the rotational
equations shown below:
Xh=X*cos(.phi.)+Y*sin(.theta.)*sin(.phi.)-Z*cos(.theta.)*sin(.phi.)
(1)
Yh=Y*cos(.theta.)+Z*sin(.theta.) (2)
where Xh and Yh are Earth's magnetic vector projections to the
horizontal plane. Once Xh and Yh are known, it is possible to
calculate an azimuth angle as:
azimuth=arcTan(Yh/Xh) (3)
[0066] To facilitate the use of the accelerometer sensor as a tilt
sensor, a known low-pass filter may be applied.
[0067] In use, upon pressing the "start" button on the probe
handle, the processing means 7 is supplied with all angle readings
and calculates current azimuth angle to set this azimuth angle as a
azimuth reference angle equaling to zero. At the same time, an
orientation closeness of azimuth angle discontinuity to this
azimuth reference angle is calculated. In case this closeness
exceeds a predetermined threshold, axes X and Y are mutually
changed in equations (1), (2) to move away the azimuth angle
discontinuity from a probe operation range. All azimuth angles
thereafter and during prostate examination procedure are calculated
relative to that azimuth reference angle so that the user may
observe in real time all probe orientation angles: azimuth,
elevation, and rotation.
[0068] FIG. 5 represents a schematic diagram of an electronic unit
6 of the device in accordance with the present invention. A
plurality of pressure sensors 31 forming the head pressure sensor
array 1, and a plurality of pressure sensors 32 forming the shaft
pressure sensor array 3 are shown on the diagram. A pressure
sensing circuit inside the electronic unit 6 comprises an analog
switching unit 45, amplifier 46, converter and/or integrator 49,
designed to amplify and convert respective electrical signals
generated by each pressure sensor for detecting a pressure imposed
on each sensor during prostate examination. Analog-to-digital
converter 48 transforms analog input signal into a digital signal
and sends it to a processor 52. A plurality of amplifiers 43
amplify signals generated by accelerometer sensor 25 and magnetic
sensor 26 described above for detecting the probe orientation
during pressing against the prostate and movement of the probe from
one pressing site to another. The amplified signals from amplifiers
43 are sent to multiplexer 47. Multiplexed signals are converted to
digital signals by analog-to-digital converter 51 and sent to
processor 52. A set/reset circuit 44 controlled by the processor 52
generates set/reset pulses supplied to magnetic sensor 26 to
optimize the magnetic domains for most sensitive performance.
Structure and functional characteristics of set/reset circuit 44
are determined by the type of magnetic sensor used for the design
of the probe and by recommendations of specific magnetic sensor
manufacturer. A control button 23 mounted on the transrectal probe
handle is connected to the processor 52 through a driver 50 for
controlling the prostate examination process and providing at least
a stop/start function. Processor 52 communicates with
analog-to-digital converters 48 and 51, multiplexers 45 and 47, and
a communication port 54 to support data exchange with external
processing and displaying means 55. Preferably, the external
processing and displaying means 55 is a compact laptop computer.
Data storage unit 53 may be used in electronic unit 6 for storing
prostate examination data and intermediate information needed for
proper functioning thereof, for example orientation sensor
calibration data, pressure sensor calibration and tuning data, etc.
The processing means is designed to automatically detect pressure
sensors malfunction such as for example excessive noise and
impaired sensitivity and excludes any defect sensor data from
acquired pressure data frames.
[0069] The external processing and displaying means 55 is intended
to serve for examination data processing. It is adapted to perform
the following functions: [0070] calculate the position of each
pressure sensor during prostate examination, [0071] approximate and
correct partial mechanical images of the prostate and surrounding
tissues, [0072] separate and analyze the prostate partial
mechanical images, [0073] determine the prostate geometrical
parameters and mechanical parameters of prostate inner structures
such as lesions, nodules, stiffer tissue and the like, and [0074]
prepare the prostate images for visualization, as described
below.
[0075] The displaying means 55 preferably has a touch screen
functions to communicate with the device during prostate
examination.
[0076] FIG. 6 is a flow chart describing steps for obtaining
diagnostic information in accordance with the present invention.
Head pressure signal is first acquired from the probe head pressure
sensor array and then transformed into head pressure response data
61 expressed for example in kPa according with the sensor
calibration characteristics. After temporal and two-dimensional
spatial filtering in block 62, the data is displayed for the user
(in block 63) in real time during prostate examination. It allows
the user to guide the probe helping in detection of any abnormal or
suspicious sites in the examined prostate. Shaft pressure signal is
acquired from the probe shaft pressure sensor array and transformed
into a shaft pressure response data 65 expressed for example in kPa
according to the sensor calibration characteristics. After a
temporal and two-dimensional spatial filtering in block 66, it is
also displayed (block 67) in real time during prostate examination.
This allows visualizing a part of sphincter area to guide the user
in finding prostate and assisting in the probe navigation.
Orientation data 70 is acquired from the probe orientation sensors.
Further, after calculation of azimuth, elevation and rotation
angles in block 71, these angles are displayed (block 72) in real
time during the prostate examination to guide the user in probe
navigation.
[0077] After locating the prostate under the probe head pressure
sensor array, the user presses the examination start/stop button on
the probe handle to start a real time prostate mechanical image
composition algorithm (block 68). Description of this algorithm is
given below in explanations of FIG. 9. The two-dimensional prostate
mechanical image is composed and displayed in block 73.
Simultaneously, the prostate examination data including that
pressure response and probe orientation data are accumulated in
block 64. All operations in block 60 take place in real time during
prostate examination.
[0078] After completing the prostate examination, the user presses
again the examination start/stop button on the probe handle to stop
the real time prostate mechanical image composition algorithm, and
to go to examination data saving procedure in block 74. A
three-dimensional prostate mechanical image composition algorithm
in block 75 is running automatically as described in detail below.
The composed three-dimensional mechanical prostate image may be
visualized in block 77. Prostate geometrical parameters and
mechanical parameters are calculated in blocks 76 and 78
respectively. Printout of the prostate examination results (block
79) includes a series of prostate mechanical images representing
the most distinctive prostate findings and quantitative prostate
data such as a size, symmetry, medium groove, lesion detection
classifier outputs and alike.
[0079] FIG. 7 is a perspective view of a probe relative to an
examined prostate illustrating a reference coordinate system having
three orthogonal axes and probe orientation angles. A processing
means defines the reference coordinate system X, Y, Z at the moment
of first capturing a prostate mechanical image when a total
pressure prostate signal exceeds a predetermined threshold after
pressing the start examination button on the probe handle. The
following instant orientation angles are defined as reference
angles for the reference coordinate system X, Y, Z: elevation (80),
azimuth (81), and rotation (82). All subsequent probe orientation
angles relative to the reference system X, Y, Z are calculated
relative to these reference angles. The probe head 21 is pressed
against the prostate 4, when the first capturing a prostate
mechanical image occurs. In a preferred method of the invention, a
probe rotation angle should be maintained close to zero. Despite of
the presence of the probe head pressure sensing surface curvature,
the mechanical image projection along X-coordinate on X, Y-plane is
done without taking into account that curvature. The probe head
mechanical image is acquired as a 2D image and used for prostate
image reconstruction inside a defined three-dimensional prostate
volume. For the simplicity of real time calculations, the two axes
X and Y of the reference coordinate system X,Y,Z are positioned in
the mechanical image plane of the probe head pressure sensor array,
while the third reference or Z-coordinate is perpendicular to the
mechanical image plane.
[0080] FIG. 8 is a flow chart describing the steps necessary for
composition of a two-dimensional and a three-dimensional prostate
mechanical image and calculating prostate parameters. These
algorithms can be activated in real time during prostate
examination as marked by dashed line 83 or after the examination is
complete when all examination records are available (block 64). The
first step includes extraction of continuous pressure data sequence
from the head pressure sensor array by means for calculating a
plurality of partial mechanical images of the prostate. One partial
mechanical image is calculated each time when the prostate is
located under the probe head, so that this data will be used later
in prostate image composition. The purpose of this extraction is to
exclude sphincter signals from the head pressure data during the
probe insertion into the rectum.
[0081] Detection of prostate partial mechanical image in pressure
response data recorded from the head pressure sensor array is done
in block 84 by using an algorithm, which estimates the probability
that mechanical image has a pressure signal increase in its central
part. The possibility that some sensors could produce an erroneous
signal, as well as that some rows and column in the sensor array
could have incorrect tuning or calibrating are taken into account.
Such column and row errors may cause false pressure jumps or gaps
in the pressure data. For each interior row or column of the sensor
array, the detection algorithm calculates a pressure signal value
relative to the linear interpolation based on the boundary
pressure. A predetermined number of points with highest and lowest
pressure values are discarded. The positive or negative sign of the
sum of remaining values defines the sign of the entire line. Each
line (row or column) is assigned a certain weight, the highest for
the central lines, and the lowest for boundary lines. If the sum of
the weights for all lines with corresponding signs is greater than
a predefined value, it is considered that the mechanical image
contains the prostate imprint. The sum is then normalized to a
predetermined range, using two scale parameters, which gives a
quantitative estimation of the presence of a prostate imprint in
the mechanical image. If no prostate pressure signal was detected
inside the analyzed pressure data frame, this data frame is
discarded. On the opposite, if the prostate pressure signal was
detected, the next procedure in block 85 activates extraction of
only the prostate pressure response data (pixels) inside analyzed
pressure response data frame.
[0082] The procedure for isolation of a partial prostate image
consists of separation of one or several relatively big coherent
zones containing a relatively high pressure signal. Another purpose
of this procedure is to reduce the influence of boundary effects
and suppression of pressure peaks in the top and bottom parts of
the sensor array corresponding to the sphincter and bladder
pressure signals. This procedure starts with quadrupling the number
of pixels in the image using two by two interpolations between
neighboring sensors. The binary image of the pressure pattern is
created by setting all pixels for which the pressure is higher than
average to black. At the same time, the pixels for which the
pressure is lower than average are set to white. Two types of
filtering are applied thereafter to the binary image. The expanding
filtering calculates the number of black pixels adjacent to each
white point. If the number is higher than the predetermined value,
it turns the white point into a black point in order to enlarge the
black regions and cover small white holes. The squeezing filtering
is applied next to achieve the same but opposite effect for black
points. It calculates the number of white pixels adjacent to each
black point. If that number is higher than the predetermined value,
it turns it to the white point in order to squeeze black zones and
smooth their edges. A sequence of expanding and squeezing removes
or significantly reduces small boundary defects, eliminates the
inner white holes, combines and rounds large inside zones. The
resulting black zone is mapped back to the pressure sensor array,
and only the pressure sensors, which belong to the black zone, are
allowed to participate in the next phase of prostate image
analysis.
[0083] Important advantage of the present invention is its ability
to use the prostate itself as a reference object. After
determination of prostate partial images earlier in the sequence,
this is accomplished in the next few steps by the means 86 for
constructing of the composite prostate image. Specifically, in the
block 86 the first n-frames of pressure response data are captured
to construct a first pass two-dimensional mechanical prostate
structure. This capture is occurring when the total pressure
prostate signal exceeds a predetermined threshold. After averaging,
the captured first pass prostate structure is transferred into a
two-dimensional composite prostate image 91. After that, each
subsequent pressure response data carrying the prostate partial
mechanical image is analyzed in means for comparing partial
mechanical images 90 to find an overlap area with the previous
partial mechanical image. Subsequently, means for constructing the
composite image 94 are used for placing new partial mechanical
image into the composite two-dimensional prostate mechanical image.
Block 90 runs a matching algorithm trying to find best fit of a
current prostate partial mechanical image inside the
two-dimensional composite prostate mechanical image. Preferably,
the best fit is calculated by maximizing a functional F
F ( n , m ) = i , j = 0 i = k , j = l S i , j * P n + i , m + j for
n ( - k / 4 , + k / 4 ) , m ( - l / 4 , + l / 4 ) ( 4 )
##EQU00001##
where k and l are quantities of horizontal and vertical pixels
inside the pressure frame with the current prostate mechanical
image, n and m are maximum possible image shift in pixels relative
to a previous fitted mechanical image, S.sub.i,j is current
pressure response signal of i,j pixels, and P.sub.n+i,m+j is a
pressure signal of n+i,m+j pixel inside the two-dimensional
composite prostate image.
[0084] After the best fit is found, each pixel of a current partial
mechanical prostate image is placed into the two-dimensional
composite prostate image with a predetermined weighted factor if
its current value exceeds respective pixel value inside the
two-dimensional composite prostate image (block 94). Preferably,
all calculations in blocks 86, 90, 91, and 94 are implemented with
normalized pixels, so that each pixel value of the prostate
mechanical image is divided by a modified average of analyzed
pressure data frame calculated inside block 87. The modified
average S is calculated according to equation (5) after removing a
predetermined quantity (b) of pressure pixels S.sup.max having
maximum values.
S = ( i , j = 0 i = k , j = l S i , j - q = 0 q = b S q max ) / ( k
* l - b ) ( 5 ) ##EQU00002##
where k and l are quantities of horizontal and vertical pixels
inside the pressure response frame with the analyzed prostate
mechanical image, S.sub.i,j is an instant pressure signal of i,j
pixels.
[0085] Azimuth, elevation, and rotation angles calculated for the
instant pressure response data frame in block 93, and evaluated
Y-coordinate from shaft pressure data in block 89 are used in
finding a frame local reference position inside the two-dimensional
mechanical image space to start matching algorithm in the
accordance with equation (4). Simultaneously, a procedure 95 of
removing image distortion and procedure 96 of correction of the
two-dimensional mechanical image 91 are run during prostate
examination. The procedure 95 smoothes any distortions above a
predetermined threshold in the calculated a two-dimensional
gradient field inside the image 91. Procedure 96 corrects a
prostate form if prostate form distortion exceeds the bounds of an
acceptable prostate form variety.
[0086] Each pressure response data carrying a partial mechanical
image of a prostate is included into a three-dimensional composite
mechanical prostate image 92 in accordance with positioning in
X,Y-plane as calculated in block 90 and Z-coordinate, which is
considered proportional to the calculated in block 87 modified
average for current frame 87. More detailed description of the
three-dimensional image composition algorithm of this block is
given below in the description for FIG. 10.
[0087] After prostate examination is complete, a procedure 97 of a
final smoothing and three-dimensional interpolation is applied to
current mechanical image 92. The final two-dimensional and
three-dimensional mechanical prostate images are then prepared in
block 98 representing a plurality of contour, slices, iso-surfaces
and alike for a better visual perception. Such prostate parameters
as prostate gland size (small/medium/large) 102, medium groove
(absent/present) 103, prostate shape (symmetrical/asymmetrical) 104
are calculated directly from the final prostate image by testing
these value to a predetermined acceptance criteria.
[0088] A nodule classifier includes three nodule detectors. First
of them, shown in block 99, analyzes a signal distribution for
prostate pressure data to detect specific features typical for a
positive nodule presence. Second nodule detector, shown in block
100, applies a series of predetermined convolution filters to each
two-dimensional prostate mechanical image to detect a nodule from a
variety of possible nodule forms. Preferably, a form of a
convolution filter corresponds to what is being looked for in a
nodule form. A third nodule detector, shown in block 101, applied a
series of three-dimensional convolution filters to the final
three-dimensional prostate image in block 98. Presence of specific
three-dimensional objects inside a filtered prostate image signals
a possible nodule presence and its location.
[0089] FIG. 9 is an illustration of a sample real time
two-dimensional prostate and sphincter area mechanical imaging with
a relative probe positioning designed to guide the user during
prostate examination. Multiple pressings of probe head 21 against
the prostate 4 allow the head pressure sensor array to obtain
pressure response data for the prostate. Each location when the
probe is pressed against the prostate overlaps the previous such
location. The pressure response data is then transformed into a
composite two-dimensional mechanical prostate image 109 as
described in FIG. 8 (block 91). At the same time, the shaft
pressure sensor array provides supplemental mechanical data for the
sphincter area, which is visualized in the same image frame 106 as
a two-dimensional sphincter mechanical image 110. Using procedures
in blocks 89, 90, and 93 described in FIG. 8, current coordinates
107, 108 of a probe head center 111 in the reference coordinate
system X, Y, Z, as well as probe azimuth angle 113, and distance
112 between a sphincter center and the probe center 111 are then
calculated. Combined visualization of the prostate image 109, the
sphincter image 110 and the probe head position facilitates the
prostate probe navigation and provides efficient feedback to the
user.
[0090] FIG. 10 is an illustration of a three-dimensional prostate
mechanical image composition in accordance with the method of the
present invention. The three-dimensional prostate mechanical image
114 (see also the description of block 92 in FIG. 8 above),
includes a plurality of two-dimensional mechanical prostate images
115, 117, 120 placed inside planes 116, 118, 119 accordingly.
During prostate scanning by multiple pressings of probe head 21
against the prostate 4, the head pressure sensor array provides
pressure response data for the prostate. Each new portion of
pressure response data is transformed into a two-dimensional
partial mechanical prostate image in the accordance with procedure
85 and X, Y-frame coordinates for example 107, 108 as calculated by
procedure 90 and Z-coordinate as calculated by procedure 87 from
FIG. 8. Each pixel of this pressure response data is then placed
inside a two-dimensional mechanical prostate image 117 with a
predetermined weighted factor if its current pixel value exceeds a
threshold value inside the two-dimensional prostate image 117.
Preferably, two different three-dimensional mechanical prostate
images are constructed: one image includes only normalized pressure
response pixels (each pixel value of the prostate mechanical image
is divided by a modified average of analyzed pressure response data
frame), while another image includes only absolute pressure
response pixels.
[0091] Although the invention herein has been described with
respect to particular embodiments, it is understood that these
embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *