Case Studies

Ultrasound Imaging

THE PROBLEM

This customer's application involves capturing ultrasound echoes from a medical imaging system, to be used in bedside monitors, defibrillators, intervascular ultrasound, ECG, etc.

The live imaging rate is 30 frames per second (fps). Each image frame depicts a full 360-degree circular section. A frame is 240 echoes, so the pulse repeat frequency (PRF) is 7200 Hz, or one echo every 140 us.

The customer anticipates signals at 50 MHz with a 50% bandwidth (the passband must extend to at least 75 MHz). The echo duration is 15 us; the signal size is roughly +/- 70 mV.

To support this application, the system would have to capture echoes from 60 consecutive triggers, ignore the next 180 triggers, then capture the next 60 triggers, etc. The customer predicts the need to construct an external interface to block the unwanted triggers. Available signals include triggers for frame-start and line-start, as well as the 8 bit line number.

The customer will be working with LabVIEW under Windows NT.

Data Rate Considerations:

GAGE'S SOLUTION

CompuScope 8500 is an ideal solution for this customer.

The CompuScope 8500 has a bandwidth of 250 MHz, which is far more than the 75 MHz the customer needs. As such, bandwidth is not an issue.

As the maximum sample rate of the CompuScope 8500 is 500 MSPS, sampling at 250 MSPS is not a problem. In fact, the Signal to Noise Ratio at 250 MSPS will be even better.

Finally, the customer must capture 4096 points in 15 us, leaving 125 us to offload the data to the PC RAM (as the Pulse Repeat Interval is 140 us). At a data transfer rate of 100 MB/s, the customer will be able to accomplish that in approximately 40 us. Even after allowing another 20 us of overhead for non-optimized code, the customer still has 65 us left over.

The timing diagram for this application is shown below.

It is clear from the problem description above that the effective data transfer rate to the storage medium is 30 MB/s, which is not attainable with normal SCSI disk drives. If only partial frames are stored (60 through 120 degrees only), the customer will be able to reduce the effective transfer rate to one-sixth that rate (5 MB/s).

This rate is now achievable using a fast SCSI disk such as the Barracuda, working under an Adaptec 2940/UW SCSI controller.

PRODUCT RECOMMENDED

CompuScope 8500 - 8 bit, 500 MSPS A/D card for the PCI Bus
LabVIEW Drivers for Windows NT

This application note is provided "as is" without any warranties of any kind, either expressed or implied, including but not limited to the implied warranties of merchantability or fitness for a particular purpose. Gage Applied Technologies further does not warrant the accuracy and completeness of the material contained herein. Gage Applied Technologies may make changes to this material, or to the products described in it, at any time without notice.

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