Medical sonography refers to the use of reflected ultrasonic echoes to image a patient's internal organs. A customer has a commercial medical diagnostic ultrasound system. During its operation, an external probe is placed upon the patient. An ultrasonic transducer within the probe head mechanically scans in a linear frame pattern at a rate of approximately 22 frames/sec. The transducer generates a sharp ultrasonic pulse into the patient and the same transducer detects reflected echoes from various tissue interfaces. In normal operation, the system processes the ultrasonic echoes in a prescribed fashion and displays a two-dimensional sonogram that is continuously updated in time.
The customer wants to analyze the data in a fashion not afforded by the standalone commercial system. Consequently, the customer wants to capture the analog ultrasonic data with a separate digitizer and perform alternative analysis off-line. The customer has previously constructed a digitizer system around a CompuScope 8012A-4M ISA board with which single frames of data were captured.
The purpose of the improved CompuScope 8012A/PCI-1M system is to capture as many successive data frames as possible so that time-dependent behavior of cardiac tissue may be studied.
A diagram of the experimental setup is shown below. The customer has access to three signal lines tapped from the standalone system. The first is the RF signal which is the analog ultrasonic waveform from the moving transducer. Secondly, the SYNC signal is a TTL pulse synchronized with the ultrasonic generation. Finally, the FRAME signal is a TTL pulse that goes high while the transducer is scanning.
FRAME goes low when the frame is finished and the transducer quickly returns to its initial position to prepare for the next frame. The SYNC signal runs continuously when FRAME is high with a nearly constant pulse repeat interval that is always greater than 300 us. A frame consists of 121 ultrasonic generations that occur over 40 ms. Subsequently, the FRAME signal goes low for 5 ms during preparation for the next frame. The ultrasonic A/D acquisition is done at 50 MS/s over 100 us for a total record length of 5 kS.
The earlier CS8012A-4M ISA system digitizes the RF signal in single channel mode and is triggered by the SYNC signal. The SYNC signal is gated by the FRAME signal in a home-made circuit box that the customer wanted to replace. The board is operated in Multiple Record mode where the digitizer is quickly rearmed in hardware after successive captures until the entire 4 MS of on-board memory is filled. Since a frame consists of 121 x 5 kS, which is approximately equal to 0.6 MS, the board can store more than 6 frames of data. Only the first frame is considered and subsequent frames are ignored.
The new GaGe system consists of a CS8012A/PCI-1M and a 512 MB MMD 5400 PCI memory board installed in a GaGePC 586 with 18 GB of disk storage. A removable drive and a network connection provide convenient methods for off-loading data. The 8012A/PCI streams data over the PCI bus to the MMD board. With 2 bytes per 12-bit sample, the 512 MB MMD board is able to store 256 MS of data. At 0.6 MS per frame, the MMD board will be able to store 256/0.6 = 426 frames. At 22 frames per second, this corresponds to 424/22 = 19 seconds worth of data - several heartbeats. After the acquisition, the contents of the MMD board will be downloaded to the disk. If the customer wants to capture more frames in future, he can purchase up to 2 GB on an MMD 5400 board.
To replace the home-made gating circuit, the customer has specified the Trigger Enable Input Option for the CompuScope 8012A/PCI board. With this option, the EXTERNAL TRIGGER input passes through a high speed switch gated by the ENABLE. The customer connects the RF, SYNC and FRAME lines tapped from the standalone system to CHANNEL A, EXTERNAL TRIGGER and ENABLE inputs on the CS8012A/PCI, respectively. The ENABLE input is configured so that the SYNC line is passed to the CS8012A/PCI triggering circuitry only while the FRAME signal is high. Furthermore, upon arming, the ENABLE input does not pass to the EXTERNAL TRIGGER until the next rising edge of the FRAME signal. This feature ensures that when the overall sequence of frame captures begins, the CS8012A/PCI does not start capturing in the middle of a frame.
There are various ways to perform data capture with CompuScope boards. In Memory Mode, the CS8012A/PCI digitizes data directly into on-board memory. The customer will work in PCI Real-time Multiple Record Mode, where data samples are not stored in on-board memory but are routed directly to the PCI bus and are transferred directly to the MMD board. This mode of operation is called PCI bus-mastering and requires no CPU intervention during the transfer. The PCI bus in a GaGePC 586 can continuously sustain a 100 MB/s PCI transfer rate. Consequently, for 12-bit samples, it can maintain the 50 MS/s=100 MB/s required by the customer's application. Between captures, the board is quickly hardware re-armed for the next capture with no software intervention as in conventional Multiple Record Mode. Since in PCI Multiple Record Mode data transfer is simultaneous with data capture, the transfer time is zero and the CS8012A/PCI can keep up with triggers whose repeat intervals are less than 200 us. This leaves a healthy margin for the customer's 300 us requirement.
Sequential frames are captured by executing TESTPCIW.EXE, GaGe's 32-bit standalone PCI transfer utility. An RSP file passes parameters to TESTPCIW.EXE, which runs in batch-like operation. Sequential frame data are captured and transferred to the MMD board. After acquisition is complete, all data from the MMD board is stored to disk using GaGe's efficient Multiple Record SIG file format.
The system was developed and tested with a GaGe CompuGen 1100 arbitrary waveform generator installed in a separate GaGePC. The customer's RF, SYNC and FRAME signals were simulated with the CG1100. The CG1100 memory was loaded with a pattern of 121 distinct pulses, each separated by 300 us. Looped repeatedly, this pattern was captured with the CS8012A/PCI until the MMD board memory was filled. Several parts of the resulting 512 MB of data were checked. Any observed variation in the captured pattern from the known generated pattern would have indicated missed triggers. No such variations were observed, so that the GaGe system integrity was firmly established before shipment to the customer. The customer has since used data collected with the GaGe system to generate a 19 second image sequence of a human heart beating.
We encourage you to contact us and discuss your medical application in more detail with our engineering team. GaGe can provide tailored custom data acquisition hardware and software solutions to meet specific application requirements.