Ultrasound processing spurs color flow images

By: 
June 08, 1998

Issaquah, WA--Imagine a doctor waving a magic wand over a limb or organ and being able to see the vascular flows or movement within. That's what Siemens Ultrasound Group has given sonographers thanks to its Crescendo(TM) Multidimensional Image Processor. Capable of four billion operations a second, the device, developed in concert with the University of Washington (Seattle), allows wide-field-of-view imaging of large volumes in real time, as opposed to assembling an overall view from individual smaller images. The latest available extension of the company-developed SieScape(TM) software provides color images that detail organ fluid flows and anatomical movements within and around complete internal structures. "Clinical trials suggest that the most promising applications of Color SieScape will be mapping blood vessels and demonstrating pathology (the effects of diseases)," according to Paul Jones,the company's clinical evaluation manager.

Panoramic imaging allows clinicians to collect more extensive data, for example, in assessing blood flow in carotid arteries, looking for aortic aneurysms, and determining the success of bypass-operation vessel grafts. Other applications include imaging blood flow to and through organs, tumors, and other masses in a single image. Expanded views allow for comparisons--such as including both lobes of the thyroid or both testicles in one scan--and viewing enlarged organs and large abdominal wall masses. "Neither traditional ultrasound, with its limited field of view, nor CT (computed tomography) scans, which are limited to certain scan planes, allow you to perceive the extent of an extensive leg hematoma nor directly measure its length," notes Eric Sauerbrei of Kingston (Ontario, Canada) General Hospital. And comprehensive panoramic imaging can eliminate the need for additional tests to verify conclusions from a series of smaller images.

Previous ultrasound systems were complex, hardware-based devices using articulated arms to mount scanners and producing low-resolution images. For each application, such as grayscale, color flow, or Doppler, to be added to a system, engineers would need to design a new processing board. Siemens began its collaboration with the University of Washington to develop a programmable image processor in 1992. The first SieScape applications were released in late 1996.

Siemens Crescendo processor at the heart of SieScape imaging use the Texas Instruments (Austin, TX) C-80 multimedia video processor (MVP) chip. The image processor is a general purpose board that can run many programs without specialized hardware. Programmability permits rapid development and testing of new applications, paring time to market.

Imaging is based on pixel-by-pixel pattern recognition that compares individual ultrasound images and sequentially aligns them in anatomical context. Thus, as a clinician sweeps a hand-held transducer across a patient's body, a panoramic image is presented on a screen in real time. The supercomputer-power processor must handle these images at a data rate more than 1,000 times that of conventional still CT x-ray or magnetic resonance imaging (MRI). For example, a typical 10-minute ultrasound scan generates enough data to fill 6,000 CD-ROMs.

The recent extension showing flows in color is based on the Doppler effect on ultrasound--blood moving toward the transducer shifts the ultrasound frequency up, while that flowing away shifts it lower. Two different display colors indicate different directions. Such flow direction knowledge is vital in investigating heart valve problems that can cause blood to flow the wrong way. A "power Doppler" mode generates a non-directional overall view indicating flow volume (see image).

Other SieScape applications include obstetrics and gynecological uses. The former encompass not only fetal orientation and placental localization but evaluation of surrounding anatomy fluid pockets. The latter include looking at large pelvic masses and anatomical variations in one image.

Siemens is looking for the Crescendo processor to enable future ultrasound developments, such as contrast imaging and 3D imaging.

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