Digital Ultrasonic Array Data Capture
Customer Case
A customer possesses a commercial medical diagnostic ultrasonic system. The ultrasonic sensing head consists of an ultrasonic generator transducer and an 8′ x 8′ two-dimensional array of receiver transducers. The sensing head is pressed against the tissue under study and the generation transducer is periodically excited so that it emits a burst of ultrasonic energy. After each burst, the receiver array registers ultrasonic echoes reflected off tissue structures from each transducer element. In normal operation, digitized array data from each element is numerically processed and combined to construct a display image of the tissue.
The customer wants to process the data in a way different from that which is built into the system by the manufacturer. Custom processing will provide more resolved information about certain tissue features in which the customer is interested. The data stream in the existing system must somehow be diverted to the customer’s PC for the alternate analysis.
The customer has determined that the best place at which to tap the data is after the 64 ADCs in the system that simultaneously digitize the transducer array data. These 64 ADCs output 8-bit data at 20 MHz during a ~200 us time interval at an adjustable repetition rate of several kHz. The customer also has access to both the 20 MHz data clock and to the trigger signal that begins the 200 us bursts of data from all 64 ADCs. The requirement is to capture as much data as possible at the highest possible rate.
GaGe Case Solution
Three GaGe solutions were proposed to this customer, who decided on the solution which best fit their needs.
Solution 1: The simplest solution initially proposed to the customer was twenty-two CompuScope 8012/DIM24 boards with several Megabytes of memory on each board. The CS8012/DIM24 is a 24-bit Digital Input Module for the ISA bus, which can acquire 24-bit digital data at rates up to 40 MS/s in dual-channel mode.
Each 24-bit DIM board would capture 8-bit data from three transducers so that the data from all 64 ADCs could be captured (3 * 22 = 66). Since each ultrasonic record consists of 20 MB/s * 200 us = 4 KB of data, the several MB of memory on each board could hold thousands of records. After the board memory was full, all the data would be downloaded through the ISA bus to PC RAM for later processing. However, the customer determined that this solution, while complete, exceeds the budget for this project.
Solution 2: The next proposed solution was to wire the 64 ADCs to sixty-four 8-bit, deep memory shift registers. During the 200 us data bursts, the digital data would be clocked into each shift register. After one or more repetitions, the stored data would be individually clocked out of the shift registers and read by a single CS8012/DIM through a 64-channel multiplexer (MUX). This solution, which involves complicated control circuitry to drive the shift registers, was deemed to be beyond what the customer could reasonably request of their engineering resources.
Solution 3: The GaGe solution that the customer decided upon is illustrated below and consists of one CompuScope 8012/DIM24/PCI and three high-speed 8-bit 22-channel multiplexers (MUXs). The CS8012/DIM24/PCI is a Digital Input Module (DIM) which can acquire 24-bit digital data at rates of up to 40 MHz in dual-channel mode, twice the required rate for this application. The CS8012/PCI is externally triggered by the trigger signal from the ADCs and has an optional input to externally clock the DIM with the ADC clock.
The input channels of the three MUXs are connected to ADCs {#1, #4, #7…#64}, ADCs {#2, #5, #8…#62}, and ADCs {#3, #6, #9…#63}, respectively. The channel is of each MUX is selected by the same digital address generated by the PC printer port. After each acquisition of data from three ADCs by the DIM, the MUX address is changed to switch the DIM input to the next three transducers. After 22 MUX channel switchings, data from all 64 transducers will have been captured, although not simultaneously. The external circuit consists of only three MUXs controlled by the printer port. The customer knows that this circuit can easily be constructed.
The PCI bus is a 32-bit wide, 33 MHz bus. GaGe engineers have measured sustained data transfer rates of 25 MHz for 32-bit data (and 100 MHz for 8-bit data). Since the customer’s 24-bit wide data is captured at only 20 MHz, it can be continuously transferred through the PCI bus with no overflow, even if there are no breaks in the data. The CS8012/DIM24/PCI will therefore be operated in PCI Real-Time Transfer Mode, in which captured data is not stored in on-board memory, but is immediately transferred to PC RAM for later processing. The amount of data that the customer can capture, therefore, is limited only by the amount of PC RAM.
Let us assume that the MUX switching time is zero and that the ADC trigger repetition rate is increased so that triggers occur right after the end of the previous record capture. With a 200 us record capture time, all 64 transducers could therefore be polled in 22 * 200 us = 4.4 ms to create a complete data frame.
Fortunately, the customer is not looking at, say, a live heart where tissue motion during this 4.4 ms would lead to image blurring. The theoretical maximum frame refresh rate is 1 / 4.4 ms, or 230 Hz. The customer will process the data into display images that will later be replayed in real time. With a fast MUX, the customer should be able to achieve the 30 Hz frame refresh rate necessary to trick the human eye into perceiving continuous motion.
If this preliminary project succeeds, the customer may be able to procure the funds for the 22 CS8012/DIM24/PCI board solution and increase the time resolution of the system by a factor of 22.
The described solution shows how, with a GaGe ultra-fast data acquisition card and a little bit of home-made circuitry, the customer was able to construct a cost-effective, custom system to meet their specific data acquisition needs.
GaGe Case Recommended Products
- CS8012/DIM24/PCI
- 24-bit, 40 MS/s Dual-Channel Digital Input Module for PCI Bus
Industrial Application Request
We encourage you to contact us and discuss your industrial application in more detail with our engineering team. GaGe can provide tailored custom data acquisition hardware and software solutions to meet specific application requirements.