U.S. patent application number 10/596113 was filed with the patent office on 2007-11-29 for ultrasonic diagnostic imaging system with automatic control of penetration, resolution and frame rate.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS N.V.. Invention is credited to Jing-Ming Jong.
Application Number | 20070276236 10/596113 |
Document ID | / |
Family ID | 34700042 |
Filed Date | 2007-11-29 |
United States Patent
Application |
20070276236 |
Kind Code |
A1 |
Jong; Jing-Ming |
November 29, 2007 |
Ultrasonic diagnostic imaging system with automatic control of
penetration, resolution and frame rate
Abstract
An ultrasonic diagnostic imaging system and method are presented
in which the balance between image resolution and frame rate
(Res/Speed) and the balance between image resolution and
penetration (Pen/Gen/Res) are automatically adjusted in response to
image content. A motion detector analyzes the relative motion
between successive images. If the motion content is relatively
high, the imaging parameters are changed in favor of relatively
greater frame rate and reduced resolution. A low motion content
causes the opposite adjustment. The electronic noise between
successive images is also computed with a relatively high noise
content (low correlation) in the far field resulting in an
adjustment to penetration as by lowering the transmit frequency. A
relatively low noise content causes an adjustment in favor of
increased resolution.
Inventors: |
Jong; Jing-Ming; (Seattle,
WA) |
Correspondence
Address: |
PHILIPS MEDICAL SYSTEMS;PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3003
22100 BOTHELL EVERETT HIGHWAY
BOTHELL
WA
98041-3003
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS
N.V.
Eindhoven
NL
5621 BA
|
Family ID: |
34700042 |
Appl. No.: |
10/596113 |
Filed: |
December 7, 2004 |
PCT Filed: |
December 7, 2004 |
PCT NO: |
PCT/IB04/52697 |
371 Date: |
May 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60529782 |
Dec 16, 2003 |
|
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|
Current U.S.
Class: |
600/437 |
Current CPC
Class: |
G01S 7/52038 20130101;
A61B 8/465 20130101; A61B 5/11 20130101; A61B 8/5276 20130101; A61B
8/585 20130101; G01S 7/52046 20130101; G01S 7/52073 20130101; G01S
7/52039 20130101; G01S 7/52041 20130101; A61B 8/00 20130101 |
Class at
Publication: |
600/437 |
International
Class: |
A61B 8/00 20060101
A61B008/00 |
Claims
1. A method for automatically adjusting the relationship between
image resolution (Res) and real time frame rate (Speed) of an
ultrasound system comprising: acquiring a plurality of ultrasound
images over time; sensing the relative motion between temporally
different ultrasound images; and increasing the image resolution
and decreasing the frame rate in response to relatively less sensed
motion or decreasing the image resolution and increasing the frame
rate in response to relatively greater sensed motion, wherein the
ultrasound system includes a Res/Speed display of the relationship
between image resolution and frame rate; and further comprising
automatically adjusting Res/Speed display in correspondence with a
change made to the image resolution and/or frame rate.
2. The method of claim 1, wherein sensing comprises calculating the
correlation of the pixel content of temporally different ultrasound
images, wherein a relatively high correlation corresponds to
relatively less motion and a relatively low correlation corresponds
to relatively greater motion.
3. The method of claim 1, wherein sensing comprises sensing
relative motion with a probe motion sensing device.
4. The method of claim 1, wherein sensing comprises sensing
relative motion by analyzing the image content of successive
ultrasound images.
5. (canceled)
6. The method of claim 1, wherein the Res/Speed display includes a
user adjustable setting which enables a user to manually balance
the relationship between image resolution and frame rate of the
ultrasound system.
7. The method of claim 6, wherein manual adjustment of the
Res/Speed display adjusts the manner in which subsequent automatic
adjustments to the balance between image resolution and frame rate
will be made.
8. The method of claim 1, wherein the frame rate is changed by
changing at least one of the transmit beam density, multiline
order, number of focal zones, or number of transmit pulses.
9. The method of claim 8, wherein the image resolution is changed
by changing the spatial sampling of the image field.
10. A method for automatically adjusting the relationship between
image resolution (Res) and the depth of penetration (Pen) of an
ultrasound system comprising: acquiring a plurality of ultrasound
images over time; calculating the electronic noise between
temporally different ultrasound images; and increasing the image
resolution in response to relatively less electronic noise or
increasing the penetration in response to relatively greater
electronic noise.
11. The method of claim 10, wherein calculating the electronic
noise comprises calculating the decorrelation of electronic noise
between regions of successively acquired images.
12. The method of claim 11, wherein calculating the electronic
noise further comprises comparing the correlation of far field
signals with the correlation of signals elsewhere in the
images.
13. The method of claim 12, wherein when the comparison shows a
relatively low correlation in the far field and a relatively high
correlation elsewhere, the operating frequency of the ultrasound
system is automatically decreased, and when the comparison shows a
relatively high correlation in the far field and elsewhere, the
operating frequency of the ultrasound system is automatically
increased.
14. The method of claim 10, wherein increasing the image resolution
comprises increasing at least one of the transmit or receive
frequency of the ultrasound system, and wherein increasing the
penetration comprises decreasing at least one of the transmit or
receive frequency of the ultrasound system.
15. The method of claim 10, further comprising aligning the
temporally different ultrasound images prior to calculating the
electronic noise.
16. The method of claim 10, wherein the ultrasound system includes
a Pen/Gen/Res display of the relationship between image resolution
and depth of penetration; and further comprising automatically
adjusting Pen/Gen/Res display in correspondence with a change made
to the balance between resolution and penetration.
17. The method of claim 16, wherein increasing the image resolution
comprises increasing an operating frequency of the ultrasound
system; wherein increasing the penetration comprises decreasing an
operating frequency of the ultrasound system; and wherein
automatically adjusting the Pen/Gen/Res display comprises adjusting
the display toward Pen when the operating frequency is decreased
and adjusting the display toward Res when the operating frequency
is increased.
18. The method of claim 17, wherein automatically adjusting the
Pen/Gen/Res display comprises adjusting the display toward Pen when
fundamental frequency operation is performed and adjusting the
display toward Res when harmonic operation is performed.
19. The method of claim 17, wherein the operating frequency
comprises at least one of the transmit frequency or the receive
frequency.
20. The method of claim 16, further comprising manually adjusting
the Pen/Gen/Res display to adjust the manner in which automatic
adjustments to the balance between resolution and penetration will
be made.
21. An ultrasonic diagnostic imaging system comprising: a probe
including an array transducer; a transmitter coupled to apply drive
signals to the array transducer; a receiver coupled to process
signals received by the array transducer; a display coupled to the
receiver which displays received ultrasound images; a sensor
coupled to the probe which senses relative motion in the image
field; a Res/Speed display responsive to the sensor which is shown
on the display to depict the relative balance between image
resolution and frame rate, wherein the transmitter is responsive to
the sensor for adjusting the frame rate of the ultrasound
images.
22. An ultrasonic diagnostic imaging system comprising: a probe
including an array transducer; a transmitter coupled to apply drive
signals to the array transducer; a receiver coupled to process
signals received by the array transducer; a display coupled to the
receiver which displays received ultrasound images; a sensor
coupled to the probe which senses electronic noise in the image
field; a Pen/Gen/Res display responsive to the sensor which is
shown on the display to depict the relative balance between image
resolution and penetration, wherein the transmitter is responsive
to the sensor for adjusting the penetration of transmitted drive
signals.
Description
[0001] This invention relates to medical diagnostic imaging systems
and, in particular, to diagnostic imaging systems which
automatically control ultrasonic imaging for optimal tissue
penetration, imaging frame rate, and image resolution.
[0002] Ultrasonic diagnostic imaging applications can differ widely
in the imaging conditions encountered. When imaging the fetal heart
for instance a high frame rate of display is required to accurately
image the detail of a rapidly beating heart. In other applications
such as the diagnosis of tumors in the liver, a high frame rate is
not necessary but a high image quality (resolution) is generally
preferred. In some cases the pathology being diagnosed may be deep
within the patient's body. In other cases the pathology may be just
beneath the skin. These widely differing conditions mean that the
sonographer frequently has to change a wide variety of settings on
the ultrasound system in order to acquire the best images for a
given examination. It would be desirable to minimize the number of
ultrasound system settings which need to be manipulated in order to
set up the system for a new exam. In particular, it would be
desirable for many of the manual settings of an ultrasound system
to be automated when possible so that the ultrasound system would
automatically optimize the operational settings of the system on
the basis of the examination being performed.
[0003] In accordance with the principles of the present invention,
an ultrasonic diagnostic imaging system is described which
automates two of the most frequently used user settings, the
Res/Speed control and the Pen/Gen/Res control. The Res/Speed
control adjusts the trade-off between image quality (resolution)
and frame rate (speed) by varying imaging parameters such as image
line density, multiline order, and number of focal zones. The
Pen/Gen/Res control adjusts the trade-off between image resolution
and the depth of penetration of ultrasound through control of
imaging parameters such as the transmit and receive frequencies. In
an illustrated embodiment the setting of these controls is
automated by sensing the amount of motion and/or noise in the
anatomy being imaged. In response to the sensed image motion and/or
noise, the relevant image parameters are automatically varied to
obtain images which are a sensible balance of these competing
factors.
[0004] In the drawings:
[0005] FIG. 1 illustrates in block diagram form an ultrasonic
diagnostic imaging system constructed in accordance with the
principles of the present invention.
[0006] FIG. 2 illustrates an implementation of a Res/Speed control
on an ultrasound system and a Pen/Gen/Res control on an ultrasound
system.
[0007] FIG. 3 illustrates an ultrasound sector image which has been
divided into image sub-regions for motion analysis.
[0008] FIG. 4 illustrates a methodology for analyzing motion in
successive ultrasound images.
[0009] FIG. 5 illustrates the correlation of types of information
in successive ultrasound images.
[0010] Referring first to FIG. 1, an ultrasonic diagnostic imaging
system constructed in accordance with the principles of the present
invention is shown in block diagram form. An ultrasonic scanhead 12
includes an array 14 of ultrasonic transducers that transmit and
receive ultrasonic pulses. The array may be a one dimensional
linear or curved array for two dimensional imaging, or may be a two
dimensional matrix of transducer elements for electronic beam
steering in three dimensions. The ultrasonic transducers in the
array 14 transmit ultrasonic energy and receive echoes returned in
response to this transmission. A transmit frequency control circuit
20 controls the transmission of ultrasonic energy at a desired time
and at a desired frequency or band of frequencies through a
transmit/receive ("T/R") switch 22 coupled to the ultrasonic
transducers in the array 14. The times at which the transducer
array is activated to transmit signals may be synchronized to an
internal system clock (not shown), or may be synchronized to a
bodily function such as the heart cycle, for which a heart cycle
waveform is provided by an ECG device 26. When the heartbeat is at
the desired phase of its cycle as determined by the waveform
provided by ECG device 26, the scanhead is commanded to acquire an
ultrasonic image. The ultrasonic energy transmitted by the scanhead
12 can be relatively high energy (high mechanical index or MI)
which destroys or disrupts contrast agent in the image field, or it
can be relatively low energy which enables the return of echoes
from the contrast agent without substantially disrupting it. The
frequency and bandwidth of the ultrasonic energy generated by the
transmit frequency control circuit 20 is controlled by a control
signal f.sub.tr and the times at which individual elements in the
array are actuated to steer and focus an ultrasonic beam in a
desired direction is controlled by a control signal T.sub.st. Both
control signals are generated by a central controller 28.
[0011] Echoes from the transmitted ultrasonic energy are received
by the transducers in the array 14, which generate echo signals
that are coupled through the T/R switch 22 and digitized by analog
to digital ("A/D") converters 30 when the system uses a digital
beamformer. Analog beamformers may also be used. The A/D converters
30 sample the received echo signals at a sampling frequency
controlled by a signal f.sub.s generated by the central controller
28. The desired sampling rate dictated by sampling theory is at
least twice the highest frequency of the received passband, and
might be on the order of at least 30-40 MHz. Sampling rates higher
than the minimum requirement are also desirable.
[0012] The echo signal samples from the individual transducers in
the array 14 are delayed and summed by a beamformer 32 to form
coherent echo signals in a desired beam steering direction
specified by a control signal R.sub.st. The digital coherent echo
signals are then filtered by a digital filter 34. In this
embodiment, the transmit frequency and the receiver frequency are
individually controlled so that the beamformer 32 is free to
receive a band of frequencies which is different from that of the
transmitted band. The digital filter 34 bandpass filters the
signals, and can also shift the frequency band to a lower or
baseband frequency range. The digital filter could be a filter of
the type disclosed in U.S. Pat. No. 5,833,613.
[0013] Filtered echo signals from tissue are coupled from the
digital filter 34 to a B mode processor 36 for conventional B mode
processing. The B mode image may also be created from microbubble
echoes returning in response to nondestructive ultrasonic imaging
pulses.
[0014] Filtered echo signals of a contrast agent, such as
microbubbles, are coupled to a contrast signal processor 38. The
contrast signal processor 38 preferably separates echoes returned
from harmonic contrast agents by the pulse inversion technique, in
which echoes resulting from the transmission of multiple pulses to
an image location are combined to cancel fundamental signal
components and enhance harmonic components. A preferred pulse
inversion technique is described in U.S. Pat. No. 6,186,950, for
instance. The detection and imaging of harmonic contrast signals at
low MI is described in U.S. Pat. No. 6,171,246.
[0015] The filtered echo signals from the digital filter 34 are
also coupled to a Doppler processor 40 for conventional Doppler
processing to produce velocity and power Doppler signals. The
outputs of these processors may be displayed as planar images, and
are also coupled to a 3D image rendering processor 42 for the
rendering of three dimensional images, which are stored in a 3D
image memory 44. Three dimensional rendering may be performed as
described in U.S. Pat. No. 5,720,291, and in U.S. Pat. Nos.
5,474,073 and 5,485,842, all of which are incorporated herein by
reference.
[0016] The signals from the contrast signal processor 38, the
B-mode processor 36 and the Doppler processor 40, and the three
dimensional image signals from the 3D image memory 44 are coupled
to a Cineloop.RTM. memory 48, which stores image data for each of a
large number of ultrasonic images. The image data are preferably
stored in the Cineloop memory 48 in sets, with each set of image
data corresponding to an image obtained at a respective time. The
sets of image data for images obtained at the same time during each
of a plurality of heartbeats are preferably stored in the Cineloop
memory 48 in the same way. The image data in a group can be used to
display a parametric image showing tissue perfusion at a respective
time during the heartbeat. The groups of image data stored in the
Cineloop memory 48 are coupled to a video processor 50, which
generates corresponding video signals for presentation on a display
52. The video processor 50 preferably includes persistence
processing, whereby momentary intensity peaks of detected contrast
agents can be sustained in the image, such as described in U.S.
Pat. No. 5,215,094.
[0017] In accordance with the principles of the present invention a
motion/noise processor 46 is provided to detect the motion of
objects and/or noise in the image field. This is done in the
illustrated embodiment by a correlation process such as a Pearson's
correlation which will be discussed more fully below. The criteria
against which the results of the correlation process are compared
are determined by the setting of either a Res/Speed control or a
Pen/Gen/Res control or both by user adjustment of a control on a
user interface 150 as discussed below. The results of the detection
of motion and/or noise in the image field are used to automatically
adjust the settings of either or both of the Res/Speed control and
the Pen/Gen/Res control. The adjustments optimize the operation of
the ultrasound system to provide clearer, better resolved images by
adjustment of imaging parameters in response to the outcome of the
detection of motion and/or noise.
[0018] Examples of a Res/Speed control and a Pen/Gen/Res control
are shown in FIG. 2. While these controls may be hardware knobs or
sliders on a control panel, in this embodiment the controls are
display controls generated by software on the screen of the
ultrasound display 52. The controls may be displayed as dials or
meters or other graphics displayed in various shapes and colors,
and may have either qualitative or quantitative settings. In this
embodiment both are qualitative bar displays 60. The Res/Speed
control 62 is variable between "Res" (maximum resolution) and
"Speed" (maximum frame rate) and proportions of these maximum
settings therebetween. The Pen/Gen/Res control 64 is variable
between "Pen" (maximum penetration) and "Res" (maximum image
resolution) and proportions of these maximum settings therebetween
centered around a nominal general setting "Gen". The effect of the
current setting of each control is shown by a marker 66 in the bar,
which is positioned in accordance with the effective setting
currently applied to the ultrasound images. An arrow 68 can be
adjusted by a user pointing device such as a trackball or key or
mouse on the control panel 150 to manually set a control
setting.
[0019] The Res/Speed control and the Pen/Gen/Res control can be
independently set for either manual control or automatic control.
When a control is set for manual control its setting can only be
adjusted by manual manipulation of the user. When a control is set
for manual control its marker 66 is greyed out and moves in tandem
with the constantly aligned arrow 68 as the user adjusts the arrow
to vary the control setting. When a control is set for automatic
operation its marker 66 is brightly displayed and the arrow 68 and
the marker can move independently. When the user manually adjusts
the arrow 68 in the automatic mode, the image will vary in response
to the manual variation and the marker 66 will align with the last
setting of the arrow. Once manual control of the arrow is released,
automatic operation commences. As the motion and/or noise
characteristic of the image field is detected and used to determine
appropriate automatic settings for the Res/Speed control and/or the
Pen/Gen/Res control, the marker 66 will move automatically to show
the current setting resulting from automatic control. The user can
see at a glance how the automatic setting has changed from his or
her last manual setting, and can see the response of the control
setting to the motion and noise detected in the image field.
[0020] If the user is dissatisfied with the response of the
automatic operation of a control, the user can reset the position
of the arrow 68 of the control. Resetting the arrow during
automatic operation will reset the balance of the respective
performance factors of the control and will also adjust the manner
in which the automatic adjustments discussed below are made. For
instance, if the user resets the arrow toward more resolution
(Res), the subsequent automatic adjustments can more greatly favor
changes in the direction toward a greater Res setting. Resetting
the manual adjustment arrow of the controls can thus adjust the
degree to which the automatic system balances the competing effects
of resolution, frame rate, and depth of penetration.
[0021] Motion-detecting capabilities are often found in ultrasound
systems for a variety of purposes. Various sensors have been used
to detect the motion of an ultrasound probe, such as those
described in U.S. Pat. No. 5,529,070 (Augustine et al.) and U.S.
Pat. No. 5,538,004 (Bamber). Motion may also be sensed by comparing
successive real time images as described in U.S. Pat. Nos.
6,299,579 (Peterson et al.); 6,238,345 (Wissler et al.); 6,117,081
(Jago et al.); 5,782,766 (Weng et al.); 5,575,286 (Weng et al.);
5,566,674 (Weng); 5,899,861 (Freimel et al.); 5,910,114 (Nock et
al.); and WO 00/24316 (Hossack et al.) The motion sensing or image
alignment techniques described in these patents are used for
purposes such as aligning individual images to create a panoramic
image or to remove motional distortion from images. Any one of
these techniques can be used in an automated system of the present
invention. In an embodiment of the present invention the motion or
alignment information is used to adjust the Res/Speed setting.
Higher image quality and a lower frame rate setting is employed
when motion is relatively low, and lower image quality and a higher
frame rate is employed when motion is relatively high.
[0022] An embodiment of an automated control of the present
invention can start with a sequence of ultrasound images such as
image 70 in FIG. 3. Each image is analytically divided into a
plurality of blocks 72 of a predetermined pixel size, such as 8
pixels by 8 pixels or 16 pixels by 16 pixels. For a rectangular
image the blocks may be oriented in a rectilinear grid pattern. For
a sector image such as image 70 of FIG. 3 the blocks can be
arranged in a curve-linear fashion according to the curvature of
the sector. Motion is then computed between corresponding blocks of
successive images, as shown in FIG. 4. In this illustration a block
82 of pixels in Img 1 acquired at one point in time is compared
with the neighborhood of a corresponding block 84 of an image Img 2
acquired at a different point in time. The next motion computation
uses the block 84 in Img 2 and a corresponding block 86 in image
Img 3 acquired at another point in time. For each block a motion
vector can be derived by finding the maximal Pearson correlation
between the two pixel patterns. The formula for this computation
is: .rho. = x , y .times. ( I t .times. .times. 1 .function. ( x ,
y ) - I _ t .times. .times. 1 ) .times. ( I t .times. .times. 2
.function. ( x + d x , y + d y ) - I _ t .times. .times. 2 ) x , y
.times. ( I t .times. .times. 1 .function. ( x , y ) - I _ t
.times. .times. 1 ) 2 .times. x , y .times. ( I t .times. .times. 2
.function. ( x + d x , y + d y ) - I _ t .times. .times. 2 ) 2
##EQU1##
[0023] where I(x,y) is the pixel intensity at coordinates (x,y),
the indices t1 and t2 indicate image frames at different time
point, I is the average intensity in the pixel block, and
(d.sub.x,d.sub.y) is the magnitude (distance) and direction of the
local motion between two image frames. The correlation value .rho.
indicates the reliability of the motion vector
(d.sub.x,d.sub.y).
[0024] The motion vectors and/or correlation coefficients for a
plurality of blocks are then examined. The motion vectors and/or
correlation coefficients for all of the blocks can be examined, or
only a selected set of blocks can be used such as those in the
center of the image 70. If the magnitude of the motion vectors is
large for most blocks, or the correlation value .rho. is low for
most blocks, the frame rate is increased by incrementing the
setting of the Res/Speed control from Res toward Speed. The
resultant command from the motion/noise processor 46 to the central
controller 28 causes the central controller to change the commands
to the probe 12 in a manner which increases the frame rate. One way
to do this is to increase the angle or spacing of the beam steering
between adjacent beams through a change to the beam steering
parameter T.sub.st. With the beams more widely spaced, fewer beams
will be transmitted in the area or volume scanned by the probe
which causes the frame rate to increase. That is, with fewer beams
to transmit and receive to acquire a frame or volume, the image
area can be scanned in less time. The increase in the beam spacing
decreases the spatial sampling of the image area or volume, causing
a corresponding decrease in image resolution. Another way to do
this is to increase the multiline order: instead of receiving one
or two receive beams in response to a transmit beam, the point
spread function can be changed to receive two or four receive beams
in response to each of a lesser number of transmit beams. Yet
another possibility is to reduce the number of focal zones of the
image. For instance, each pair of consecutive focal zones can be
combined into one focal zone, with the focus set at the boundary of
the two original zones. Thus, the Res/Speed setting has been
adjusted in a direction which tends to increase frame rate (Speed)
but with decreased image resolution (Res).
[0025] Correspondingly, if the magnitude of the motion vectors is
small for most blocks, or the correlation value .rho. is high for
most blocks, indicating little motion between images, the image
quality is increased by changing the setting from Speed to Res. The
command from the motion processor 46 to the central controller 28
now effects an increase in the beam density by changing the beam
steering parameter T.sub.st to transmit a greater number of more
closely spaced transmit beams which are properly received by a
change of the receive beam parameter R.sub.st. The multiline order
can also be decreased from four to two or two to one, for instance,
for a greater number of transmit beams. The number of focal zones
can also be increased by splitting one or more current focal zones
into two. These changes will all effect an adjustment of the
Res/Speed setting in a direction which tends to increase image
resolution (Res) with a decrease in the frame rate (Speed).
[0026] As these adjustments are made the position of the marker 66
is changed accordingly in the Res/Speed bar 62. This is generally
done by changing the value for the marker which is sent from the
motion/noise processor 46 to a graphics processor (not shown) which
processes the graphic overlay of the Res/Speed control for display
with the ultrasound image.
[0027] A similar approach can be used to automatically adjust the
Pen/Gen/Res control 64 setting as a function of image signal/noise.
FIG. 5 illustrates the decorrelation of pure speckle images with
motion. This plot is made of the change in correlation as a planar
imaging probe travels in the elevational direction. As it does so
and the image plane moves in the elevational direction, the speckle
information begins to decorrelate over the entire image. In FIG. 5
the X-axis is the distance of travel of the probe in mm and the
Y-axis is the correlation between images. The different curves
represent the change in correlation at different image depths shown
by the legends in box 94. It can be seen that the correlation
changes at different rates, depending upon image depth. The solid
line curves indicated at 90 for near and mid-field depths show a
smooth decline in correlation as the image plane travels, gradually
decreasing with increasing distance. However, the dashed curves
indicated at 92 for the far field (greater depths) are marked by a
sharp drop with a small change in distance, followed by a more
gradual decrease. This large initial drop in correlation is
believed to be caused by the decorrelation of electronic noise
(signal/noise) in the far field and directly related to imaging
penetration. A response to a sharp drop in correlation is an
adjustment of the Pen/Gen/Res setting toward increased penetration
(Pen), as for example by decreasing the transmit frequency or
switching from harmonic frequency reception to fundamental
frequency reception. See, by comparison, U.S. Pat. No. 6,458,083
(Jago, et al.) and U.S. Pat. No. 6,283,919 (Roundhill et al.) By
aligning consecutive image frames through motion compensation and
computing the image decorrelation, an appropriate adjustment can be
made to the Pen/Gen/Res control to render the best image resolution
with optimal imaging penetration. This feature is particularly
useful when the clinician is frequently changing the imaging depth
during scanning.
[0028] Turning again to FIGS. 3 and 4, the correlation is computed
for a plurality of pixel blocks 72 of consecutive images. The
correlation in the far field is compared with the correlation in
the near and/or mid field or the correlation for the entire image.
If the correlation is relatively low in the far field and the
correlation is relatively high elsewhere, the penetration is
increased by adjusting the Pen/Gen/Res control from Res or Gen
toward Pen. This effects a command from the motion/noise processor
46 to the central controller 28 which causes the central controller
to command a change in the operating frequency. This can be
effected by changing the transmit frequency parameter f.sub.tr to a
lower transmit frequency, reducing the passband of the digital
filter 34, or a combination of the two. If blended
fundamental/harmonic information is used in the far field, the
blending ratio of the two types of signal content can be adjusted
in favor of more fundamental signal frequency content.
Alternatively, more pulses can be transmitted in each beam
direction and greater signal averaging employed. Corresponding, the
marker 66 of the Pen/Gen/Res control bar 64 is adjusted toward the
Pen end of the control on the displayed graphic.
[0029] Similarly, if the correlation is relatively high throughout
the image, that is, is not particularly low in the far field, the
operating frequency can be increased to increase resolution, and
the Pen/Gen/Res control is adjusted from Pen or Gen toward Res. The
motion processor commands the central controller 28 to increase the
operating frequency by increasing the value of the transmit
frequency parameter f.sub.tr, increasing the passband of the
digital filter 34, or both. If blended fundamental/harmonic
information is used in the far field, the blending ratio of the two
types of signal content can be adjusted in favor of more harmonic
signal frequency content. A corresponding adjustment toward Res is
made to the marker 66 displayed in the Pen/Gen/Res control 64.
[0030] In an embodiment of the present invention, more efficient
computation may be obtained by using fewer pixel blocks 72 and the
sum of absolute difference (SAD) algorithm. See U.S. Pat. No.
6,442,298 (Olsson et al.) Corresponding pixel blocks of successive
images can be compared to compute the motion (displacement) vector
from block to block over the time interval between the two images.
Then, using this vector, one of the image is warped (aligned) with
the other on either a local or global basis. See U.S. Pat. No.
5,566,674 (Weng). This alignment reduces the decorrelation between
images due to probe or tissue motion, leaving the signal/noise
(electronic noise) factor as a decorrelative effect. The number of
pixel blocks used in the alignment computation can be fewer than
the number used in the subsequent correlation analysis to reduce
computation time, if desired. The correlation of the aligned or
warped images is then computed as described above to automatically
adjust the Pen/Gen/Res control setting.
* * * * *