Method and apparatus for compensating for inoperative elements in ultrasonic transducer array

A method and an apparatus for compensating for fully or partially inoperative elements in an ultrasonic transducer array. The inoperative elements are compensated for by "bridging" or "shorting" them to fully operative elements. This compensation technique can be applied to one-dimensional or multi-dimensional transducer arrays. A bridge between a fully or partially inoperative element and an adjacent fully operative element can be achieved by physically shorting the elements somewhere in the signal chain or by electrically connecting the elements via switches, e.g., of a multiplexer. The state of the multiplexer switches (i.e., open or closed) is controlled by loading MUX State control data into a flash memory located on-board the probe. This MUX State control data includes switch settings for connecting a defective element to an adjacent fully functional element in the transducer array.

FIELD OF THE INVENTION 
This invention generally relates to ultrasound imaging, primarily clinical 
ultrasound images as well as industrial ultrasonic images. In particular, 
the invention relates to methods of compensating for inoperative elements 
in an ultrasonic transducer array. 
BACKGROUND OF THE INVENTION 
Conventional ultrasound imaging systems comprise an array of ultrasonic 
transducer elements which are used to transmit an ultrasound beam and then 
receive the reflected beam from the object being studied. For ultrasound 
imaging, a one-dimensional array typically has a multiplicity of 
transducer elements arranged in a line and driven with separate voltages. 
By selecting the time delay (or phase) and amplitude of the applied 
voltages, the individual transducer elements can be controlled to produce 
ultrasonic waves which combine to form a net ultrasonic wave that travels 
along a preferred vector direction and is focused at a selected point 
along the beam. Multiple firings may be used to acquire data representing 
the same anatomical information. The beamforming parameters of each of the 
firings may be varied to provide a change in maximum focus or otherwise 
change the content of the received data for each firing, e.g., by 
transmitting successive beams along the same scan line with the focal 
point of each beam being shifted relative to the focal point of the 
previous beam. By changing the time delay and amplitude of the applied 
voltages, the beam with its focal point can be moved in a plane to scan 
the object. 
The same principles apply when the transducer array is employed to receive 
the reflected sound (receiver mode). The voltages produced at the 
receiving transducers are delayed and summed so that the net signal is 
indicative of the ultrasound reflected from a single focal point in the 
object. As with the transmission mode, this focused reception of the 
ultrasonic energy is achieved by imparting a separate time delay (and/or 
phase shift) and gain to the signal from each receiving transducer. 
A phased-array ultrasound transducer consists of an array of small 
piezoelectric elements, with an independent electrical connection to each 
element. In most conventional transducers the elements are arranged in a 
single row, spaced at a fine pitch (one-half to one acoustic wavelength on 
center). As used herein, the term "1D" array refers to a single-row 
transducer array having an elevation aperture which is fixed and a focus 
which is at a fixed range; the term "1.5D" array refers to a multi-row 
array having an elevation aperture, shading, and focusing which are 
dynamically variable, but symmetric about the centerline of the array; and 
the term "2D" array refers to a multi-row transducer array having an 
elevation geometry and performance which are comparable to azimuth, with 
full electronic apodization, focusing and steering. Electronic circuitry 
connected to the elements uses time delays and perhaps phase rotations to 
control the transmitted and received signals and form ultrasound beams 
which are steered and focused throughout the imaging plane. For some 
ultrasound systems and probes, the number of transducer elements in the 
probe exceeds the number of channels of beamformer electronics in the 
system. In these cases an electronic multiplexer is used to dynamically 
connect the available channels to different (typically contiguous) subsets 
of the transducer elements during different portions of the image 
formation process. 
With the advent of multidimensional probes and the high element counts 
required to create this type of diagnostic imaging device, the problems 
associated with the manufacture of ultrasonic transducer arrays are 
mounting. The problem of "dead" (i.e., fully inoperative) or "weak" (i.e., 
partially inoperative) elements is of particular concern as the industry 
moves toward the manufacture of two-dimensional arrays having element 
counts exceeding 1,000. Process or material errors are often responsible 
for the creation of a probe without all elements fully functional. Because 
the specifications regarding element functionality are quite tight, there 
is little tolerance for dead or weak elements in current probe 
manufacturing. These requirements focus particular attention on the 
performance of the manufacturing processes and directly control the amount 
of manufacturing scrap. Dead element specifications are tight because the 
effect of this defect on the image quality can be significant, 
particularly in the near field of the image where a fewer number of 
elements are used to form the beam. In this case a dead or weak element 
becomes a significant part of the aperture used to create the image, 
resulting in an intensity loss at the acoustic line in question. 
Currently, probe technology is delivering element counts on the order of 
200 or less with processes providing reasonable manufacturing yields. 
However, new technology is demanding probes with element counts greater 
the 1,000. Utilizing current production processes, the dead or weak 
element probability delivers unacceptable yield at this element density. 
Other than developing new or tighter tolerance manufacturing processes, 
there are two solutions to this problem. The first is to develop a 
compensation scheme within the system to detect the presence of the dead 
element and adjust the beamforming parameters to compensate for the loss. 
One such technique is disclosed in U.S. Pat. No. 5,676,149 to Yao. The 
second is to detect the failure during or after the manufacturing process 
and connect the missing element with a functional one, thereby reducing or 
eliminating the effect of the failure. 
SUMMARY OF THE INVENTION 
The present invention is a method and an apparatus for compensating for 
fully or partially inoperative elements in an ultrasonic transducer array. 
The inoperative elements are compensated for by "bridging" or "shorting" 
them to fully operative adjacent elements. This compensation technique can 
be applied to one-dimensional or multi-dimensional transducer arrays. 
While this technique is not the optimal solution from the imaging 
standpoint, it enables the loosening of manufacturing tolerances, thereby 
providing more cost-efficient manufacturing. 
In accordance with the preferred embodiment of the invention, an ultrasonic 
probe is provided with multiplexer switches for connecting adjacent 
transducer elements as required, on-board flash (nonvolatile) memory for 
storing MUX State control data for controlling the state of the 
multiplexer switches and a dedicated microcontroller which loads and 
retrieves the MUX State control data into and from the flash memory. In 
response to detection of dead or weak elements by the master controller, 
new MUX State control data is sent from a flash memory programmer in the 
system to the microcontroller on-board the probe. The flash memory 
programmer in turn receives the new MUX State control data from the master 
controller after the latter has performed a diagnostic routine to identify 
any dead or weak elements in the transducer array. The flash memory 
programmer reconfigures the new MUX State control data into the format 
required for loading into the flash memory on-board the probe. 
In accordance with the preferred embodiment, a bridge between a fully or 
partially inoperative element and an adjacent fully operative element is 
achieved by electrically connecting the elements via a switch of the 
multiplexer. Transducer elements which are not fully operative can be 
detected by analyzing the signals produced by each transducer element. If 
an element produces a weak or no signal, it is assumed that the transducer 
element is not fully operative. The on-board microcontroller uses the new 
MUX State control data to set the multiplexer switches so as to compensate 
for any detected dead or weak elements in the transducer array. This 
arrangement allows for automatic compensation of elements which are made 
defectively or become defective after manufacture. 
Alternatively, a bridge between a fully or partially inoperative element 
and an adjacent fully operative element can be achieved by physically 
shorting the elements somewhere in the signal chain. A conventional 
ultrasonic probe comprises a transducer package which is supported within 
a probe housing. The transducer package comprises an array of transducer 
elements made of piezoelectric ceramic material. Typically, each 
transducer element has a metallic coating on opposing front and back 
faces. The metallic coating on the front face serves as the ground 
electrode. The ground electrodes of the transducer elements are all 
connected to a common ground. The metallic coating on the back face serves 
as the signal electrode. The signal electrodes of the transducer elements 
are connected to respective conductive traces formed on a flexible printed 
circuit board. Thus, adjacent elements can be shorted by connecting either 
the signal electrodes or the conductive traces associated with the 
adjacent elements. This repair operation can be performed following 
diagnostic testing performed during the production process or in the 
field. 
The present invention is of use in two scenarios. The first is on the 
manufacturing line, where the ability to improve the performance of the 
probe in the presence of dead or weak elements may lead to an increased 
yield and lower cost during the production cycle. A secondary benefit may 
be achieved through the ability to calibrate the probes after field use, 
either in the field, at the factory, or at a remote service location.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 depicts an ultrasound imaging system consisting of four main 
subsystems: a beamformer 2, processors 4 (including a separate processor 
for each different mode), a scan converter/display controller 6 and a 
kernel 8. System control is centered in the kernel, which accepts operator 
inputs through an operator interface 10 and in turn controls the various 
subsystems. The master controller 12 performs system level control 
functions. It accepts inputs from the operator via the operator interface 
10 as well as system status changes (e.g., mode changes) and makes 
appropriate system changes either directly or via the scan controller. The 
system control bus 14 provides the interface from the master controller to 
the subsystems. The scan control sequencer 16 provides real-time (acoustic 
vector rate) control inputs to the beamformer 2, system timing generator 
24, processors 4 and scan converter 6. The scan control sequencer 16 is 
programmed by the host with the vector sequences and synchronization 
options for acoustic frame acquisitions. The scan converter broadcasts the 
vector parameters defined by the host to the subsystems via scan control 
bus 18. 
The main data path begins with the analog RF inputs to the beamformer 2 
from the transducer 20. The beamformer 2 outputs data to a processor 4, 
where it is processed according to the acquisition mode. The processed 
data is output as processed vector (beam) data to the scan 
converter/display controller 6. The scan converter accepts the processed 
vector data and outputs the video display signals for the image to color 
monitor 22. 
Referring to FIG. 2, a conventional ultrasound imaging system includes a 
transducer array 24 comprised of a plurality of separately driven 
transducer elements 26, each of which produces a burst of ultrasonic 
energy when energized by a pulsed waveform produced by a transmitter (not 
shown). The ultrasonic energy reflected back to transducer array 24 from 
the object under study is converted to an electrical signal by each 
receiving transducer element 26 and applied separately to beamformer 2. 
The echo signals produced by each burst of ultrasonic energy reflect from 
objects located at successive ranges along the ultrasonic beam. The echo 
signals are sensed separately by each transducer element 26 and the 
magnitude of the echo signal at a particular point in time represents the 
amount of reflection occurring at a specific range. Due to the differences 
in the propagation paths between an ultrasound-echo-producing sample 
volume and each transducer element 26, however, these echo signals will 
not be detected simultaneously and their amplitudes will not be equal. 
Beamformer 2 amplifies the separate echo signals, imparts the proper time 
delay to each, and sums them to provide a single echo signal which 
accurately indicates the total ultrasonic energy reflected from the sample 
volume. Each beamformer channel 28 receives the analog echo signal from a 
respective transducer element 26. 
To simultaneously sum the electrical signals produced by the echoes 
impinging on each transducer element 26, time delays are introduced into 
each separate beamformer channel 28 by a beamformer controller 30. The 
beam time delays for reception are the same delays as the transmission 
delays. However, the time delay of each beamformer channel is continuously 
changing during reception of the echo to provide dynamic focusing of the 
received beam at the range from which the echo signal emanates. The 
beamformer channels also have circuitry (not shown) for apodizing and 
filtering the received pulses. 
The signals entering the summer 32 are delayed so that when they are summed 
with delayed signals from each of the other beamformer channels 28, the 
summed signals indicate the magnitude and phase of the echo signal 
reflected from a sample volume located along the steered beam. A signal 
processor or detector 34 converts the received signal to display data. In 
the B-mode (gray-scale), this would be the envelope of the signal with 
some additional processing such as edge enhancement and logarithmic 
compression. The scan converter 6 receives the display data from detector 
34 and converts the data into the desired image for display. This 
scan-converted acoustic data is then output for display on display monitor 
22, which images the time-varying amplitude of the envelope of the signal 
as a gray scale. 
A typical one-dimensional linear or convex transducer array and multiplexer 
is shown schematically in FIG. 3. The beamformer 2 has 128 beamformer 
channels, but the transducer array 24 has significantly more elements 
(typically 192 to 256). The multiplexer 36 allows any set of up to 128 
contiguous transducer elements 26 to be simultaneously connected to the 
beamformer channels 28 via coaxial cable bundles 38. By closing switches 
connected to elements 0 through 127, the beamformer 2 is connected to the 
left end of the transducer array and focused beams of ultrasound may be 
transmitted and received to acquire data for the corresponding edge of the 
image. As the point of origin of successive ultrasound beams steps along 
the transducer array 24 to the right, it becomes advantageous to shift the 
active aperture so that the origin of the ultrasound beam is centered 
within it. To shift the aperture from the extreme left end of the array by 
one element toward the right, the multiplexer switch connected to element 
0 is opened and the switch connected to element 128 is closed. This shifts 
beamformer channel 0 from the left end to the right end of the active 
aperture, while leaving all other channels and elements connected as 
before. The time delays and other beamforming parameters are changed by 
the software to correspond to the new multiplexer state and one or more 
additional image vectors are acquired. Then the aperture is stepped 
further to the right, by opening the switch connected to element 1 and 
closing the switch connected to element 129, leaving the multiplexer 36 in 
the state shown in FIG. 3. In this manner the active aperture can be 
stepped sequentially from one end of the transducer array 24 to the other. 
Alternatively, the same multiplexer hardware may be used to scan the 
active aperture more rapidly across the array by switching several 
transducer elements per step. In some imaging modes, successive apertures 
may be selected non-sequentially, jumping back and forth between the left 
and right ends of the transducer array. The state of multiplexer 36 is 
controlled by a multiplexer control board 40. The multiplexer control 
board 40 receives a MUX State command from the master controller 12 (see 
FIG. 1) and uses data stored in on-board memory (ROM or EEPROM) to set 
every switch in multiplexer 36 to the open or closed position required for 
the commanded multiplexer state. 
During the process of manufacturing an ultrasonic transducer array, it is 
possible to detect weak or dead elements during the testing cycle. At this 
time, using known soldering or electrical connection techniques, it is 
possible to directly electrically connect weak or dead elements to 
adjacent fully operative elements in order to compensate for the defect. 
As a result of this arrangement, each of the beamformer receive channels 
corresponding to the electrically connected transducer elements will 
receive a signal which is the sum of the signals produced by the 
electrically connected transducer elements. The electrical connection 
might take the form of a bridge wire on a flex circuit or a solder or 
conductive epoxy bridge on the ceramic. Alternatively, the electrical 
connection could be established in the system connector. This methodology 
can be applied to any one-dimensional or multi-dimensional (including 
1.25D, 1.5D, 1.75D and 2D) arrays. 
FIG. 4 shows a plurality of adjacent elements 26a-26d of a 1D transducer 
array 24A. For the purpose of discussion, it will be assumed that element 
26b is fully or partially inoperative, while elements 26a, 26c and 26d are 
fully operative. 
In accordance with a preferred embodiment of the invention shown in FIG. 5, 
the defective element 26b can be compensated for by establishing a direct 
electrically conductive connection 42 between fully operative element 26a 
and defective element 26b. Alternatively, defective element 26b could be 
directly electrically connected to fully operative element 26c. 
In accordance with a variation of the above-described preferred embodiment 
shown in FIG. 6, the defective element 26b can be compensated for by 
establishing a direct electrically conductive connection 42 between fully 
operative element 26a and defective element 26b as well as a direct 
electrically conductive connection 44 between fully operative element 26c 
and defective element 26b. 
An alternative technique for implementing the invention is to design a 
multiplexing circuit for use alone or in combination with an existing 
multiplexer such that the bridging option can be controlled electronically 
based on the results of diagnostic testing. In accordance with a further 
preferred embodiment, the master controller monitors the operative status 
of each transducer element and automatically compensates for a detected 
defective element by causing one or more associated switches of the 
multiplexer to be closed. For example, the compensation function can be 
implemented by providing a multiplexer having a bank of selectively 
controllable (i.e., electronically controlled) switches, each multiplexer 
switch being arranged to bridge a respective pair of adjacent transducer 
elements when the switch is closed. FIG. 7 shows an exemplary arrangement 
wherein a first multiplexer switch 46a selectively electrically connects 
elements 26a and 26b; a second multiplexer switch 46b selectively 
electrically connects elements 26b and 26c; and a third multiplexer switch 
46c selectively electrically connects elements 26c and 26d. It should be 
appreciated that this arrangement can be extended in the azimuth direction 
indefinitely, i.e., for any number of transducer elements. 
FIG. 8 depicts the situation wherein a defective transducer element 26b has 
been compensated for by closing multiplexer switch 46a, thereby 
electrically connecting element 26b to fully operative transducer element 
26a. (Multiplexer switch 46a could also be closed in response to detection 
that element 26a, instead of element 26b, was defective.) As an 
alternative to closing multiplexer switch 46a to compensate for element 
26b being defective, multiplexer switch 46b could be closed, thereby 
electrically connecting element 26b to fully operative transducer element 
26c instead of element 26a. 
The same techniques used for compensating for the loss of the elements in 
the azimuth direction (i.e., the one-dimensional case) are applicable in 
the two-dimensional case. Now a defective element can be directly 
connected to one of four contiguous neighbors, effectively reducing the 
amplitude differential between the elements. However, in order to maintain 
the peak performance in the azimuthal plane, the preferred embodiment is 
to connect elements in the elevation direction only, not in the azimuth 
direction. This results in an effective element which has the same 
azimuthal dimension as the other elements, limiting the difference to the 
elevation plane. 
FIG. 9 shows a 3.times.3 subarray of adjacent elements of a 2D transducer 
array 24B, with elements of the second column being designated 26a, 26b 
and 26c. Again it will be assumed that element 26b is fully or partially 
inoperative, while elements 26a and 26c are fully operative. Each of 
elements 26a-26c is electrically connected to the system connector (not 
shown) via respective conductors 48a-48c. 
In accordance with another preferred embodiment of the invention shown in 
FIG. 10, the defective element 26b can be compensated for by establishing 
a direct electrically conductive connection 50a between conductors 48a and 
48b or a direct electrically conductive connection 50b between conductors 
48b and 48c or both. The connection 50a shorts defective element 26b to 
fully operative element 26a, while the connection 50b shorts defective 
element 26b to fully operative element 26c. When conductors 48a and 48b 
are electrically connected by connection 50a, the beamformer former 
channels corresponding to elements 26a and 26b each receive the sum of the 
receive signals from those two elements. During transmission, elements 26a 
and 26b will receive the same transmit pulse waveform. Similarly, when 
conductors 48a, 48b and 48c are electrically connected by connections 50a 
and 50b, the beamformer channels corresponding to elements 26a, 26b and 
26c each receive the sum of the receive signals from those three elements. 
Again during transmission, elements 26a-26c will receive the same transmit 
pulse waveform. 
Although FIG. 10 depicts the connection of a defective transducer element 
26b to adjacent transducer elements in the elevation direction, it will be 
appreciated that, in the alternative, transducer element 26b could be 
connected to adjacent transducer elements in the azimuth direction. 
In accordance with an alternative preferred embodiment, the electrical 
conductors corresponding to adjacent transducer elements in the elevation 
direction can be selectively connected using multiplexer switches. For 
example, multiplexer switches could be incorporated in place of 
connections 50a and 50b in FIG. 10 and also could be used to selectively 
connect the conductors associated with adjacent transducer elements in 
other columns. 
FIG. 11 shows a 3.times.3 subarray of adjacent elements of a 1.5D 
transducer array 24C, with elements of the second column again designated 
26a, 26b and 26c, and element 26b being in the center row of the 1.5D 
array. In a 1.5D array, the transducer elements in each row other than the 
center row are electrically linked to the corresponding transducer 
elements in the symmetrically arranged row on the other side of the center 
row, e.g., element 26a is electrically linked to element 26c via 
electrical conductors 52a and 52c in FIG. 11. The junction connecting 
conductors 52a and 52c is in turn connected to the system connector via an 
electrical conductor 52d, while element 26b of the center row is connected 
to the system connector via an electrical conductor 52c. Again it will be 
assumed that element 26b is fully or partially inoperative, while elements 
26a and 26c are fully operative. 
In accordance with the preferred embodiment of the invention shown in FIG. 
11, the defective element 26b can be compensated for by establishing a 
direct electrically conductive connection 54 between conductors 52c and 
52d. The connection 54 shorts defective element 26b to fully operative 
elements 26a and 26c. When conductors 52c and 52d are electrically 
connected by connection 54, the beamformer channels corresponding to 
elements 26a, 26b and 26c each receive the sum of the receive signals from 
those three elements. During transmission, elements 26a-26c will receive 
the same transmit pulse waveform. 
In accordance with an alternative preferred embodiment for use with 1.5D 
arrays, the electrical conductor associated with the element in the center 
row and the i-th column can be connected to the electrical conductor 
linking the elements in the i-th column adjacent to the center row element 
in the i-th column by means of a multiplexer switch. For example, FIG. 12 
shows three multiplexer switches 46a-46c associated with respective 
columns of a 1.5D array. Switch 46b is closed to compensate for the 
defective element 26a, i.e., by electrically connecting element 26a to 
linked fully operative elements 26a and 26c. Electrical control means must 
be provided to the switches in order to configure the probe either on the 
production line or in the field if elements fail during normal use of the 
product. 
A preferred embodiment of the invention can be configured as shown in FIG. 
13. An ultrasonic probe comprising an array 24 of ultrasonic transducer 
elements is connected to an ultrasound imaging system by a probe/system 
connector 54. The probe/system connector comprises a multiplicity of 
electrically conductive connections connected at one end to respective 
transmit/receive (T/R) switches (not shown) of a beamformer 2 and at the 
other end to various subsets of multiplexer switches 36. In addition to 
switches for connecting transducer elements to beamformer receive 
channels, the multiplexer 36 includes switches for connecting adjacent 
transducer elements to each other. 
The beamformer 2 is operated under control of the master controller 12, 
which provides apodization weighting factors and time delays to the 
beamformer in both the transmit and receive modes. Under the direction of 
the master controller 12, the transmit beamformer drives transducer array 
24 such that the ultrasonic energy is transmitted as a directed focused 
beam. To accomplish this, respective time delays are imparted to a 
multiplicity of pulsers (not shown) incorporated in beamformer 4. The 
master controller determines the conditions under which the acoustic 
pulses will be transmitted. With this information, the transmit beamformer 
will determine the timing and the amplitudes of each of the transmit 
pulses to be generated by the pulsers. The pulsers in turn send the 
transmit pulses to each of the elements of the transducer array 24 via the 
T/R switches, the probe/system connector 54 and the multiplexer switches 
36. By appropriately adjusting the transmit focus time delays and the 
apodization weightings in a conventional manner, an ultrasonic beam can be 
directed and focused to form a transmit beam. 
The echo signals produced by each burst of ultrasonic energy reflect from 
objects located at successive ranges along each transmit beam. The echo 
signals are sensed separately by each transducer element. Due to the 
differences in the propagation paths between a reflecting point and each 
transducer element, the echo signals will not be detected simultaneously 
and their amplitudes will not be equal. The receive beamformer amplifies 
the separate echo signals in each receive channel. Under the direction of 
the master controller 12, the receive beamformer tracks the direction of 
the transmitted beam, sampling the echo signals at a succession of ranges 
along each beam. The receive beamformer imparts the proper time delays and 
receive apodization weightings to each amplified echo signal and sums them 
to provide an echo signal which accurately indicates the total ultrasonic 
energy reflected from a point located at a particular range along one 
ultrasonic beam. 
As seen in FIG. 13, the probe further comprises a flash (nonvolatile) 
memory 58 for storing MUX State control data for controlling the state of 
the multiplexer switches 36 and a CPU 56 which serves as a dedicated 
microcontroller for loading and retrieving MUX State control data into and 
from the flash memory. The CPU 56 interfaces with a flash memory 
programmer 66 via the probe/system connector 54. In accordance with the 
present invention, new MUX State control data containing switch settings 
for connecting a defective transducer element to an adjacent fully 
functional element is output to CPU 56 by flash memory programmer 66. The 
flash memory programmer in turn receives new MUX State control data from 
the master controller 12, albeit in a format not suitable for loading into 
the flash memory 58. The flash memory programmer 66 reconfigures the new 
MUX State control data into the format required by flash memory 58. The 
master controller 12 computes new MUX State control data after performing 
a diagnostic routine which detects dead or weak elements in the transducer 
array 24. 
In accordance with a preferred embodiment of the invention, a MUX State 
control signal is output by the master controller 12 to a state control 
device 64. The MUX State control signal configures the probe with a 
desired aperture. In response to the MUX State control signal, the state 
control device 64 sets a register on the probe/system connector 54. The 
CPU 56 reads that register to determine the desired MUX State and then 
retrieves the MUX State control data corresponding to that state from the 
flash memory 58. The multiplexer switches 36 are then set by the 
corresponding MUX State control signals output from CPU 60. Alternatively, 
the CPU 56 can provide address signals and a read signal which allow the 
MUX State control signals to be sent directly from the flash memory 58 to 
the multiplexer 36. 
The probe system also includes an element calibration memory 60, which 
stores the individual transducer element performance data, i.e., amplitude 
and phase information. This amplitude and phase information characterizes 
the particular probe being used. When the probe is connected to an 
ultrasound imaging system (as shown in FIG. 13), the serial bus control 
device 62 reads the element amplitude and phase information from memory 60 
and outputs it to the master controller, which uses that information to 
calibrate the beamformer 2 for amplitude and phase differences between 
elements. 
The flash memory 58 and element calibration memory 60 are both initially 
loaded on the probe manufacturing line. Reprogramming of one or both 
memories can be done on the manufacturing line or in the field. In 
accordance with a preferred embodiment, the flash memory 62 can be 
reprogrammed to compensate for dead or weak elements in the transducer 
array 24. If dead or weak elements are detected during quality control 
inspections on the manufacturing line, the flash memory is reprogrammed at 
a programming station. After this process, calibration of the transducer 
elements is completed and the element calibration data is loaded into the 
element calibration memory 64. Alternatively, if dead or weak elements are 
detected in the field using a diagnostic program run by the master 
controller, the flash memory is reprogrammed by the master controller via 
flash memory programmer. Then the element calibration memory 60 is 
reprogrammed via the bus control device 62. In either case, the 
reprogramming of the flash memory 58 enables the CPU 60 to close 
multiplexer switches 36 of the type shown in FIGS. 7, 8 and 12 in order to 
electrically connect a dead or weak element to an adjacent fully operative 
element. 
As the element count in two-dimensional probes increases dramatically, the 
difficulties associated with delivering a "no dead element" probe from 
manufacturing are daunting. However, with the increased element count 
comes some redundancy and, in some cases, some latitude with respect to 
dead elements. In simple terms, increasing the element count by a factor 
of 4 or 5 means that a single dead element constitutes a smaller 
percentage of the total number of elements. While this view holds in the 
case of full aperture imaging, it does not support the case where the 
aperture used for imaging is the same size as that of the one-dimensional 
case. This occurs at close range where the aperture size is reduced in 
both elevation and azimuth. Thus there is a need for a technique by which 
dead or weak transducer elements can be compensated for. That need is 
satisfied by the present invention. 
The foregoing preferred embodiments have been disclosed for the purpose of 
illustration. Variations and modifications will be readily apparent to 
persons skilled in the art. For example, it will be apparent to a person 
skilled in the art that a defective transducer element could be connected 
to a diagonally located element, instead of a contiguous element in the 
same row or same column of the array. All such variations and 
modifications are intended to be encompassed by the claims set forth 
hereinafter.