U.S. patent application number 13/491602 was filed with the patent office on 2012-09-27 for ultrasonic signal processor for a hand held ultrasonic diagnostic instrument.
This patent application is currently assigned to SONOSITE, INC.. Invention is credited to Terrence R. Doherty, Juin-Jet Hwang, Geoffrey H. Jones, Lauren S. Pflugrath.
Application Number | 20120243367 13/491602 |
Document ID | / |
Family ID | 27538769 |
Filed Date | 2012-09-27 |
United States Patent
Application |
20120243367 |
Kind Code |
A1 |
Hwang; Juin-Jet ; et
al. |
September 27, 2012 |
Ultrasonic Signal Processor for a Hand Held Ultrasonic Diagnostic
Instrument
Abstract
A hand held ultrasonic instrument is provided in a portable unit
which performs both B mode and Doppler imaging. The instrument
includes a transducer array mounted in a hand-held enclosure, with
an integrated circuit transceiver connected to the elements of the
array for the reception of echo signals. A digital signal
processing circuit performs both B mode and Doppler signal
processing such as filtering, detection and Doppler estimation, as
well as advanced functions such as assembly of multiple zone
focused scanlines, synthetic aperture formation, depth dependent
filtering, speckle reduction, flash suppression, and frame
averaging.
Inventors: |
Hwang; Juin-Jet; (Mercer
Island, WA) ; Jones; Geoffrey H.; (Seattle, WA)
; Doherty; Terrence R.; (Snohomish, WA) ;
Pflugrath; Lauren S.; (Seattle, WA) |
Assignee: |
SONOSITE, INC.
Bothell
WA
|
Family ID: |
27538769 |
Appl. No.: |
13/491602 |
Filed: |
June 8, 2012 |
Related U.S. Patent Documents
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12692483 |
Jan 22, 2010 |
8216146 |
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13491602 |
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11762019 |
Jun 12, 2007 |
7740586 |
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12692483 |
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10745827 |
Dec 24, 2003 |
7604596 |
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11762019 |
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10151583 |
May 16, 2002 |
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10745827 |
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09630165 |
Aug 1, 2000 |
6416475 |
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10151583 |
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09167964 |
Oct 6, 1998 |
6135961 |
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09630165 |
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08863937 |
May 27, 1997 |
5817024 |
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09167964 |
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08826543 |
Apr 3, 1997 |
5893363 |
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08863937 |
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08672782 |
Jun 28, 1996 |
5722412 |
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08826543 |
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Current U.S.
Class: |
367/7 ; 367/138;
367/87 |
Current CPC
Class: |
A61B 2560/0456 20130101;
A61B 8/4455 20130101; A61B 8/5269 20130101; G10K 11/345 20130101;
G01S 15/8915 20130101; G01S 7/52033 20130101; G01S 7/52079
20130101; G01S 7/52034 20130101; G01S 7/5208 20130101; G01S 15/8979
20130101; G01S 7/5206 20130101; G10K 11/004 20130101; A61B 8/462
20130101; A61B 8/461 20130101; A61B 8/56 20130101; G01S 7/52028
20130101; A61B 8/4472 20130101; G01S 15/899 20130101; A61B 8/00
20130101; A61B 8/06 20130101; G01S 15/892 20130101; A61B 8/4494
20130101; A61B 8/13 20130101; A61B 8/4427 20130101; G01S 7/52026
20130101; A61B 8/467 20130101; G01S 7/52071 20130101; G01S 7/529
20130101; A61B 8/54 20130101; G01S 7/52068 20130101; A61B 8/46
20130101; G01S 7/52085 20130101; A61B 8/145 20130101; A61B 8/14
20130101; A61B 8/488 20130101 |
Class at
Publication: |
367/7 ; 367/138;
367/87 |
International
Class: |
G01S 15/89 20060101
G01S015/89; H04B 1/02 20060101 H04B001/02; G03B 42/06 20060101
G03B042/06 |
Claims
1. A system comprising: a transducer enclosure comprising: an array
transducer; a sampled data beamformer configured to delay and
combine samples of echo signals received by elements of said array
transducer; a cable configured to connect said hand-held transducer
enclosure to a second unit, said cable configured to propagate
beam-formed signals between said hand-held transducer enclosure and
said second unit, said second unit configured to accept and process
beam-formed signals and to output an ultrasound image.
2. The system of claim 1 wherein said cable is further configured
to convey power to said hand-held transducer.
3. The system of claim 1 wherein said beam-formed signals
propagated on said cable are digital beam-formed signals.
4. The system of claim 1 wherein said second unit comprises a back
end ASIC.
5. The system of claim 1 wherein said back end ASIC implements scan
conversion and outputs a video signal.
6. The system of claim 5 further comprising a display device
configured to accept and display said video signal.
7. An ultrasound transducer apparatus comprising: an array
transducer; a sampled data beamformer configured to delay and
combine samples of echo signals received by elements of said array
transducer; and a connection means configured to connect said
hand-held transducer enclosure to a second unit via a connection
link, said connections means configured to propagate beam-formed
signals between said transducer apparatus and said second unit.
8. The ultrasound transducer apparatus of claim 7 wherein said
connection link is a cable.
9. The ultrasound transducer apparatus of claim 8 wherein said
connection means is configured to receive power which is conveyed
by said cable.
10. The ultrasound transducer apparatus of claim 7 wherein said
connection link is a modem.
11. The ultrasound transducer apparatus of claim 7 wherein said
beam-formed signals are digital beam-formed signals.
12. An ultrasound system comprising: a transducer unit comprising a
sampled data beamformer configured to delay and combine samples of
echo signals received by elements of said array transducer; and a
separate control unit configured to receive beam-formed signals
from said transducer unit via a connection link.
13. The ultrasound system of claim 12 wherein said separate
hand-held control unit further comprises a display device.
14. The ultrasound system of claim 12 wherein said connection link
is a cable.
15. The ultrasound system of claim 14 wherein said beam-formed
signals are digital beam-formed signals.
16. The ultrasound system of claim 14 wherein said separate
hand-held control unit further comprises a power source configured
to provide power to said transducer unit via said cable.
17. The ultrasound system of claim 12 wherein said separate
hand-held control unit comprises a back end ASIC.
18. The ultrasound system of claim 17 wherein said back end ASIC
implements scan conversion and outputs a video signal.
19. The ultrasound system of claim 12 wherein said separate
hand-held control unit further comprises user controls configured
to control ultrasound imaging.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 11/762,019, filed on Jun. 12, 2007, which is a continuation of
U.S. application Ser. No. 10/745,827, filed on Dec. 24, 2003, which
is a continuation of U.S. application Ser. No. 10/151,583, filed on
May 16, 2002, which is a continuation of U.S. application Ser. No.
09/630,165, filed on Aug. 1, 2000, which is a continuation-in-part
of U.S. application Ser. No. 09/167,964 (U.S. Pat. No. 6,135,961),
filed on Oct. 6, 1998, which is a continuation-in-part of U.S.
application Ser. No. 08/863,937 (U.S. Pat. No. 5,817,024), filed on
May 27, 1997, which is a continuation-in-part of U.S. application
Ser. No. 08/826,543 (U.S. Pat. No. 5,893,363), filed on Apr. 3,
1997, which is a continuation-in-part of U.S. application Ser. No.
08/672,782 (U.S. Pat. No. 5,722,412), filed on Jun. 28, 1996, the
full disclosures of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to medical ultrasonic diagnostic
systems and, in particular, to a fully integrated hand held
ultrasonic diagnostic instrument.
BRIEF SUMMARY OF THE INVENTION
[0003] As is well known, modern ultrasonic diagnostic systems are
large, complex instruments. Today's premium ultrasound systems,
while mounted in carts for portability, continue to weigh several
hundred pounds. In the past, ultrasound systems such as the ADR
4000 ultrasound system produced by Advanced Technology
Laboratories, Inc., assignee of the present invention, were
smaller, desktop units about the size of a personal computer.
However, such instruments lacked many of the advanced features of
today's premium ultrasound systems such as color Doppler imaging
and three dimensional display capabilities. As ultrasound systems
have become more sophisticated they have also become bulkier.
[0004] However, with the ever increasing density of digital
electronics, it is now possible to foresee a time when ultrasound
systems will be able to be miniaturized to a size even smaller than
their much earlier ancestors. The physician is accustomed to
working with a hand held ultrasonic scanhead which is about the
size of an electric razor. It would be desirable, consistent with
the familiar scanhead, to be able to compact the entire ultrasound
system into a scanhead-sized unit. It would be further desirable
for such an ultrasound instrument to retain as many of the features
of today's sophisticated ultrasound systems as possible, such as
speckle reduction, color Doppler and three dimensional imaging
capabilities.
[0005] In accordance with the principles of the present invention,
a diagnostic ultrasound instrument is provided which exhibits many
of the features of a premium ultrasound system in a hand held unit.
These premium system features are afforded by a digital signal
processor capable of performing, both greyscale and Doppler signal
processing including their associated filtering, compression, flash
suppression and mapping functions, as well as advanced features
such as synthetic aperture formation, multiple focal zone imaging,
frame averaging, depth dependent filtering, and speckle reduction.
In a preferred embodiments the digital signal processor is formed
on a single integrated circuit chip. This sophisticated ultrasound
instrument can be manufactured as a hand held unit weighing less
than five pounds.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates in block diagram form the architecture of
a hand-held ultrasound system of the present invention;
[0007] FIGS. 2a and 2b are front and side views of a hand-held
ultrasound system of the present invention which is packaged as a
single unit;
[0008] FIGS. 3a and 3b are front and side views of the transducer
unit of a two-unit hand-held ultrasound system of the present
invention;
[0009] FIG. 4 illustrates the two units of a hand-held ultrasound
system of the present invention in a two-unit package;
[0010] FIG. 5 is a block diagram of the digital signal processing
ASIC of the ultrasound system of FIG. 1;
[0011] FIG. 6 is a flowchart of B mode processing by the digital
signal processing ASIC;
[0012] FIG. 7 is a flowchart of Doppler processing by the digital
signal processing ASIC; and
[0013] FIG. 8 is a chart of the user controls of the ultrasound
system of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Referring first to FIG. 1, the architecture of a hand-held
ultrasound system of the present invention is shown. It is possible
to package an entire ultrasound system in a single hand-held unit
only through judicious selection of functions and features and
efficient use of integrated circuit and ultrasound technology. A
transducer array 10 is used for its solid state, electronic control
capabilities, variable aperture, image performance and reliability.
Either a flat or curved linear array can be used. In a preferred
embodiment the array is a curved array, which affords a broad
sector scanning field. While the preferred embodiment provides
sufficient delay capability to both steer and focus a flat array
such as a phased array, the geometric curvature of the curved array
reduces the steering delay requirements on the beamformer. The
elements of the array are connected to a transmit/receive ASIC 20
which drives the transducer elements and receives echoes received
by the elements. The transmit/receive ASIC 20 also controls the
active transmit and receive apertures of the array 10 and the gain
of the received echo signals. The transmit/receive ASIC is
preferably located within inches of the transducer elements,
preferably in the same enclosure, and just behind the transducer. A
preferred embodiment of the transmit/receive ASIC is described in
detail in U.S. Pat. No. 5,893,363 for ULTRASONIC ARRAY TRANSDUCER
TRANSCEIVER FOR A HAND HELD ULTRASONIC DIAGNOSTIC INSTRUMENT.
[0015] Echoes received by the transmit/receive ASIC 20 are provided
to the adjacent front end ASIC 30, which beamforms the echoes from
the individual transducer elements into coherent scanline signals.
The front end ASIC 30 also controls the transmit waveform timing,
aperture and focusing of the ultrasound beam through control
signals provided for the transmit receive ASIC. In the illustrated
embodiment the front end ASIC 30 provides timing signals for the
other ASICs and time gain control. A power and battery management
subsystem 80 monitors and controls the power applied to the
transducer array, thereby controlling the acoustic energy which is
applied to the patient and minimizing power consumption of the
unit. A memory device 32 is connected to the front end ASIC 30;
which stores data used by the beamformer. A preferred embodiment of
the front end ASIC is described in detail in U.S. Pat. No.
5,817,024 for HAND HELD ULTRASONIC DIAGNOSTIC INSTRUMENT WITH
DIGITAL BEAMFORMER.
[0016] Beamformed scanline signals are coupled from the front end
ASIC 30 to the digital signal processing ASIC 40. The digital
signal processing ASIC 40 filters the scanline signals, processes
them as B mode signals, Doppler signals, or both, and in the
preferred embodiment also provides several advanced features
including synthetic aperture formation, frequency compounding,
Doppler processing such as power Doppler (color power angio)
processing, and speckle reduction as more fully detailed below. The
ultrasound B mode and Doppler information is then coupled to the
adjacent back end ASIC 50 for scan conversion and the production of
video output signals. A memory device 42 is coupled to the back end
ASIC 50 to provide storage used in three dimensional power Doppler
(3D CPA) imaging. The back end ASIC also adds alphanumeric
information to the display such as the time, date, and patient
identification. A graphics processor overlays the ultrasound image
with information such as depth and focus markers and cursors.
Frames of ultrasonic images are stored in a video memory 54 coupled
to the back end ASIC 50, enabling them to be recalled and replayed
in a live Cineloop.RTM. realtime sequence. Video information is
available at a video output in several formats, including NTSC and
PAL television formats and RGB drive signals for an LCD display 6.0
or a video monitor.
[0017] The back end ASIC 50 also includes the central processor for
the ultrasound system, a RISC (reduced instruction set controller)
processor 502. The RISC processor is coupled to the front end and
digital signal processing ASICs to control and synchronize the
processing and control functions throughout the hand-held unit. A
program memory 52 is coupled to the back end ASIC 50 to store
program data which is used by the RISC processor to operate and
control the unit. The back end ASIC 50 is also coupled to a data
port configured as an infrared transmitter or a PCMCIA interface
56. This interface allows other modules and functions to be
attached to or communicate with the hand-held ultrasound unit. The
interface 56 can connect to a modem or communications link to
transmit and receive ultrasound information from remote locations.
The interface can accept other data storage devices to add new
functionality to the unit, such as an ultrasound information
analysis package.
[0018] The RISC processor is also coupled to the user controls 70
of the unit to accept user inputs to direct and control the
operations of the hand-held ultrasound system.
[0019] Power for the hand-held ultrasound system in a preferred
embodiment is provided by a rechargeable battery. Battery power is
conserved and applied to the components of the unit from the power
subsystem 80. The power subsystem 80 includes a DC converter to
convert the low battery voltage to a higher voltage which is
applied to the transmit/receive ASIC 20 to drive the elements of
the transducer array 10.
[0020] FIGS. 2a and 2b illustrate a one piece unit 87 for housing
the ultrasound system of FIG. 1. The front of the unit is shown in
FIG. 2a, including an upper section 83 which includes the LCD
display 60. The lower section 81 includes the user controls as
indicated at 86. The user controls enable the user to turn the unit
on and off, select operating characteristics such as the mode (B
mode or Doppler), color Doppler sector or frame rate, and special
functions such as three dimensional display. The user controls also
enable entry of time, date, and patient data. A four way control,
shown as a cross, operates as a joystick to maneuver cursors on the
screen or select functions from a user menu. Alternatively a mouse
ball or track pad can be used to provide cursor and other controls
in multiple directions. Several buttons and switches of the
controls are dedicated for specific functions such as freezing an
image and storing and replaying an image sequence from the Cineloop
memory.
[0021] At the bottom of the unit 87 is the aperture 84 of the
curved transducer array 10. In use, the transducer aperture is held
against the patient to scan the patient and the ultrasound image is
displayed on the LCD display 60.
[0022] FIG. 2b is a side view of the unit 87, showing the depth of
the unit. The unit is approximately 20.3 cm high, 11.4 cm wide, and
4.5 cm deep. This unit contains all of the elements of a fully
operational ultrasound system with a curved array transducer probe,
in a single package weighing less than five pounds. A major portion
of this weight is attributable to the battery housed inside the
unit.
[0023] FIGS. 3 and 4 illustrate a second packaging configuration in
which the ultrasound system is housed in two separate sections. A
lower section 81 includes the transducer array, the electronics
through to a video signal output, and the user controls. This lower
section is shown in FIG. 3a, with the curved transducer array
aperture visible at the bottom. The lower section is shown in the
side view of FIG. 3b. This lower section measures about 11.4 cm
high by 9.8 cm wide by 2.5 cm deep. This unit has approximately the
same weight as a conventional ultrasound scanhead. This lower
section is connected to an upper section 83 as shown in FIG. 4 by a
cable 90. The upper section 83 includes an LCD display 82 and a
battery pack 88. The cable 90 couples video signals from the lower
unit 81 to the upper unit for display, and provides power for the
lower unit from the battery pack 88. This two part unit is
advantageous because the user can maneuver the lower unit and the
transducer 84 over the patient in the manner of a conventional
scanhead, while holding the upper unit in a convenient stationary
position for viewing. By locating the battery pack in the upper
unit, the lower unit is lightened and easily maneuverable over the
body of the patient.
[0024] Other system packaging configurations will be readily
apparent. For instance, the front end ASIC 30, the digital signal
processing ASIC 40, and the back end ASIC 50 could be located in a
common enclosure, with the beamformer of the front end ASIC
connectable to different array transducers. This would enable
different transducers to be used with the digital beamformer,
digital filter, and image processor for different diagnostic
imaging procedures. A display could be located in the same
enclosure as the three ASICs, or the output of the back end ASIC
could be connected to a separate display device. Alternatively, the
transducer array 10, transmit/receive ASIC 20 and front end ASIC 30
could be in the transducer enclosure and the balance of the system
in the battery and display unit. The configuration of FIG. 4 could
be changed to relocate the user controls onto the display and
battery pack unit, with the ultrasound ASICs located in the unit
with the transducer array.
[0025] Referring to FIG. 5, a detailed block diagram of the digital
signal processing ASIC 40 is shown. Scanline signals from the front
end ASIC 30 are received by a normalization circuit 410, where they
are multiplied by a variable coefficient supplied by coefficient
memory 408 to normalize the received signals for aperture
variation. When the transducer is receiving signals along the
scanline from shallow depths, a relatively small aperture, such as
four or eight transducer elements, is used to receive echo signals.
As the reception depth along the scanline increases, the aperture
is incrementally increased so that the full 32 element aperture is
used at maximum depths. The normalization circuit 410 will multiply
the received scanline signals by appropriate coefficients over the
range of aperture variation, such as factors of four or eight, to
normalize the signals for this aperture variation effect.
[0026] When the ultrasound system is operated in the B mode to form
a structural image of tissue and organs, the digital signal
processor is operated as shown by the flowchart of FIG. 6. The
normalized echo signals follow two paths in FIG. 5, one of which is
coupled to a four multiplier filter 412 and the other of which is
coupled by a multiplexer 422 to a second four multiplier filter
414. Each multiplier filter includes a multiplier and an
accumulator which operate as an FIR (finite impulse response)
filter. Scanline echo signals are shifted sequentially into a
multiplier, multiplied by coefficients supplied by the coefficient
memory 408, and the products are accumulated in the accumulator at
the output of the multiplier. The coefficients for the filter 412
are chosen to multiply the echo signals by a cosine function and
the coefficients for the filter 414 are chosen to multiply the echo
signals by a sine function, preparatory for I and Q quadrature
signal detection. The four multiplier filters produce accumulated
signals at a rate which is less than the input rate to the
multipliers, thereby performing decimation band pass filtering.
When the signal bandwidth exceeds the display bandwidth of the
display monitor, the image lines will flicker due to an abasing
condition. The decimation filtering is designed to reduce the
signal bandwidth as well as the data rate to match the display
bandwidth of the monitor. By applying a succession of input signals
and coefficients to a multiplier and accumulating intermediate
products, the effective length of the filter can be increased. For
instance, input signals 1-8 can be sequentially weighted by the
fourth multiplier and the products accumulated in the fourth
accumulator; input signals 3-10 can be weighted by the third
multiplier and the products accumulated in the third accumulator;
input signals 5-12 can be weighted by the second multiplier and the
products accumulated in the second accumulator; and input signals
7-14 can be weighted by the first multiplier and the products
accumulated in the first accumulator. The data rate has thereby
been decimated by two, and each multiplier and accumulator is
effectively operated as an eight tap filter. Thus it is seen that
the effective number of taps of the filter is a product of the
number of multipliers (four in this example) and the decimation
rate (two in this example).
[0027] Additionally, this filter reduces r.f. noise and
quantization noise through its bandwidth limiting effects. I and Q
echo signal samples are produced at the outputs of filters 412 and
414, amplified if desired by the multipliers of gain stages 416 and
418, then stored in the r.f. memory 420. The Q samples are coupled
to the r.f. memory by a multiplexer 426.
[0028] When a synthetic aperture image is to be formed, partially
summed scanlines from a portion of the full aperture are acquired
following separate pulse transmissions, then combined to form full
aperture scanlines. When the synthetic aperture is formed from two
pulse transmissions, the I and Q samples from the scanline of the
first half of the aperture are stored in the r.f. memory 420 until
the I and Q samples from the other half of the aperture are
received. As the samples from the second half of the aperture are
received, they are combined with their spatially corresponding
counterparts by an adder 424. The size of the r.f. memory is kept
to a minimum by storing the aperture signals after decimation
filtering, which reduces the size of the memory required to store
the scanline signal samples.
[0029] After the I and Q samples for the full aperture have been
formed, the echo samples are coupled from the adder 424 to a
detection and compression circuit 428. This circuit includes two
shift registers and a multiplier arranged to form a CORDIC
processor for performing envelope detection of the form
(I.sup.2+Q.sup.2).sup.1'2. See, for instance, "The CORDIC
Trigonometric Computing Technique, by J. E. Volder, IRE Trans. on
Elect. Computers, (Sep. 30, 1959). The detected signal is
compressed and scaled to map the detected signals to a desired
range of display gray levels.
[0030] Following detection and compression mapping, the grayscale
signals are lowpass filtered in an FIR filter 432, then stored in
an image frame memory 430. If the selected scanning mode utilizes a
single transmit focal point, the grayscale signals are transmitted
to the back end ASIC 50 for scan conversion. Prior to leaving the
ASIC 40, the greyscale signals can be frame averaged by an infinite
impulse response (IIR) filter 436 which utilizes image frame memory
430 as a frame buffer and incorporates one multiplier and two
adders to perform frame to frame averaging of the form
F.sub.out=(1-.alpha.)F.sub.out-1+.alpha.F.sub.new=F.sub.out-1+.alpha.(F.-
sub.new-F.sub.out-1)
where the multiplier coefficient is a. If the coefficient is a
binary number (e.g., 0.5, 0.25, 0.125) F.sub.out can be obtained
with an add-shift-add operation.
[0031] If multiple focal zones are used, each received scanline
segment is stored in the r.f. memory 420 until scanline segments
from the entire display depth have been received. Preferably the
scanline segments for one complete focal zone are acquired before
transmitting and receiving segments from another focal zone. When
all segments for a scanline have been acquired, each complete
scanline is then read out of the r.f. memory and filtered by the
FIR filter 432, which smoothes the boundaries between the segments
for a more pleasing, artifactfree image.
[0032] If both multiple zone focusing and synthetic aperture are
used, the scanline segments of both halves of the aperture are
received over the full focal zone and assembled in the r.f. memory
420. Corresponding scanline segments are then received from other
focal zones and joined with the segments from the first received
focal zone. The completed scanlines are then filtered by FIR filter
432 to smooth the boundaries between segments.
[0033] The user may choose to process the grayscale image with
certain image enhancement features, such as depth dependent
filtering or speckle reduction such as the frequency compounding
technique described in U.S. Pat. No. 4,561,019. These optional
processing techniques necessitate the use of the filters 412 and
414 for separate bandpass filtering of the scanline signals and
absolute value detection rather than quadrature detection. In the
case of depth dependent filtering the received echo signals are
multiplied by cosine functions in both of filters 412 and 414, but
with coefficients chosen so that one filter produces output signals
in a high passband and the other produces output signals in a low
passband. The output signals produced by the two filters are of the
form I.sub.1=h.sub.1(t) cos .omega..sub.Ht and I.sub.2=h.sub.2(t)
cos .omega..sub.Lt. These two output signals are amplified in gain
stages 416 and 418 by complementary time varying gain control
functions. The high frequency passband signals I.sub.1 are
initially amplified strongly, then the gain is decreased as echo
signals are received from increasing depths along the scanline. In
a complementary manner the low frequency passband signals I.sub.2
are initially at a low level, then amplified in an increasing
manner with depth as the high frequency gain is rolled off. Thus,
signals at shallow depths will exhibit a relatively high passband,
and signals from greater depths will pass through a relatively
lower passband which reduces high frequency noise at the greater
depths. Detection in the CORDIC processor of circuit 428 is
performed by absolute value detection by squaring I.sub.1, and
I.sub.z, then summing the results. Following summation the signals
are log compressed to the desired grayscale mapping characteristic.
Alternatively, the signals passed by the separate passbands are
summed by the adder 424, then detected by absolute value detection
in the detection and compression circuitry 428 and mapped.
[0034] The same processors can be used to provide speckle reduction
by frequency compounding. The coefficients of one of the filters
412, 414 are chosen to filter the received signals by a high
frequency passband, and the coefficients of the other filter are
chosen to filter the received signals by a contiguous low frequency
passband. The coefficients of the gain stages 416, 418 are chosen
to equalize the responses of the two passbands. The signals of the
high and low passbands are coupled to the detection and compression
circuitry where the passbands are separately detected through
absolute value detection as described above, then the detected
signals are log compressed to the desired grayscale mapping
characteristic and summed on a spatial basis.
[0035] The processing of Doppler echo signals for power Doppler
(CPA) display is shown in FIG. 5 together with the flowchart of
FIG. 7. Each scanline vector is scanned repetitively, for instance
eight times, to assemble an ensemble of Doppler information along
the vector. Each received scanline of echo signals is normalized by
the normalization circuit 410 and undergoes decimation band pass
filtering in the filter 412. Each scanline of the ensemble is
stored in the r.f. memory 420 until a complete ensemble has been
accumulated. The scanlines of each ensemble are coupled by the
multiplexer 422 to the four multiplier filter 414, which performs
wall filtering and Doppler power estimation through matrix
filtering. Wall filtering is performed by selection of appropriate
multiplier coefficients and the matrix filtering is of the form
[ Y 1 Y 2 Y 3 Y n ] = [ a 11 a 12 a 13 a 1 n b 11 b 12 b 13 b 1 n c
11 c 12 c 13 c 1 n z 11 z 12 z 13 z 1 n ] * [ x 1 x 2 x 3 x n ]
##EQU00001##
where x.sub.1 . . . x.sub.n are spatially aligned signals from the
ensemble of scanlines and Y.sub.1 . . . Y.sub.n are output Doppler
values. In a preferred embodiment a four multiplier filter is used
for matrix filtering, and the filtering is performed sequentially
and incrementally. Intermediate products are accumulated as
described above, thereby extending the filter length. For example,
in processing the above matrix with a four multiplier filter, the
intermediate products
a.sub.11x.sub.1+a.sub.12x.sub.2+a.sub.13x.sub.3+a.sub.14x.sub.4 are
formed initially and summed in the accumulator. Then products
a.sub.15x.sub.5+a.sub.16x.sub.6+a.sub.17x.sub.7+a.sub.18x.sub.8 are
formed by the multipliers and summed in the accumulator with the
previously computed intermediate products. By accumulating
intermediate products in this manner the four multipliers and
accumulator can be extended to a filter of any desired length,
restricted only by the maximum processing time available. The
Doppler values are coupled to the detection and compression
circuitry 428 through the gain stage 418 and the multiplexer 426,
where the Doppler signal amplitude at each echo location along the
scanline is detected through absolute value detection of the
form
Y = n 1 - n Yn 2 ##EQU00002##
[0036] The Doppler values Y are compressed and scaled using the
CORDIC processor of the detection and compression circuitry
428.
[0037] Once the Doppler signal amplitude values have been detected
and filtered by FIR filter 432, the resulting values are spatially
stored and image clutter is removed by a flash suppression
processor 434, which eliminates large frame to frame variations in
the displayed signals. Flash suppression processor 434 may operate
by any of a number of known flash suppression techniques, such as
frame to frame comparison and elimination or the notch filtering
technique of U.S. Pat. No. 5,197,477. A preferred technique for
flash suppression processing is min-max filtering as described in
detail in the parent, U.S. Pat. No. 5,722,412.
[0038] The image frame memory 430 is capable of storing either a
gray scale frame or a power Doppler frame. Each frame can be
temporally filtered by the IIR filter 436, which performs frame
averaging on a point-by-point basis as described above. The
temporally filtered image information is then provided to the back
end ASIC 50 for scan conversion and display.
[0039] The sequences of operating the digital signal processing
ASIC 40 for B mode (two dimensional) echo and Doppler processing,
respectively, are outlined in the flowcharts of FIGS. 6 and 7,
respectively. The number in each flowchart block of FIGS. 6 and 7
refers to the numbered processor in the ASIC block diagram of FIG.
5.
[0040] The image frame memory 430 of the digital signal processing
ASIC 40 shares a common architecture and implementation technology
with the frame buffer memory of the back end ASIC 50. To take
advantage of this commonality and the resultant efficiency in ASIC
fabrication and density, the image frame memory 430 and its
associated flash suppression processor 434 and IIR filter 436 can
be located on the back end ASIC 50, thereby partitioning the
digital signal processing ASIC and the back end ASIC at the output
of FIR filter 432. Thus, the digital signal processing function of
FIG. 5 up through the output of FIR filter 432, or all of the
functions shown in FIG. 5 can be fabricated on a single integrated
circuit chip, depending upon this partitioning choice and other
integrated circuit layout considerations.
[0041] The back end ASIC 50 is the location of the RISC processor
502, which is used to coordinate the timing of all of the
operations of the handheld ultrasound system. The RISC processor is
connected to all other major functional areas of the ASICs to
coordinate, process timing and to load buffers and registers with
the data necessary to perform the type of processing and display
desired by the user. Program data for operation of the RISC
processor is stored in a program memory 52 which is accessed by the
RISC processor. Timing for the RISC processor is provided by clock
signals from the clock generator located on the front end ASIC 30.
The RISC processor also communicates through a PCMCIA and/or
infrared transmitter interface, by which the processor can access
additional program data or transmit image information remotely. The
interface can connect to a telemetry link or a modem for the
transmission of ultrasound images from the handheld unit to a
remote location, for instance.
[0042] The RISC processor is operated under user control by
commands and entries made by the user on the user control 70. A
chart showing control functions, the type of controls, and their
description is shown in FIG. 8. It will be appreciated that a
number of functions, such as patient data entry, Cineloop
operation, and 3D review, will operate through menu control to
minimize the number of key or button controls on the small handheld
unit. To further simplify the unit a number of operating functions
are preprogrammed to specific diagnostic applications and will
operate automatically when a specific application is selected.
Selection of B mode imaging will automatically invoke frequency
compounding and depth dependent filtering on the digital signal
processing ASIC 40, for instance, while a four multiplier filter
will automatically be set up as a wall filter on the DSP ASIC when
Doppler operation is selected. The menu selection of specific
clinical applications can automatically invoke specific feature
settings such as TGC control characteristics and focal zones, for
example.
* * * * *