Reflex Transmission Imaging (RTI)

SRI has developed a novel method of scanning and signal processing that permits orthographic transmission images to be made with a modified conventional pulse-echo ultrasound scanner. Using a bidirectional scan probe with a large, annular-array transducer, the system detects echoes from a range increment beyond the transducer focus and averages them to form each pixel value. This work is supported by the National Cancer Institute. A commercial B-scanner is now being adapted for clinical trials. For one of its licensees, SRI has adapted RTI for use in a commercial kidney-stone/gallstone extracorporeal lithotripter. It promises to be more effective than conventional ultrasound for monitoring stone disintegration.

Ultrasonic Camera

Under a grant from the National Institute of General Medical Sciences, the SRI ultrasonic camera was developed to the point at which clinical application could be demonstrated in several areas of medical diagnosis. The latest version of this transmission imaging system was installed in West Germany. The camera combines the advantages of two X-ray techniques-laminography and fluoroscopy-and allows risk-free visualization of tendons, ligaments, muscle, cartilage, blood vessels, and organ tissues, as well as bone silhouette. It has also been used successfully to demonstrate breast disease.

Transmission Imaging System for Basic Research

Sponsored by the National Cancer Institute, we developed a computer-controlled imaging system using a pair of confocal PVDF transducers, one of which was a 17-element transmitting array. This slow-scan system produces excellent orthographic transmission images.

Ultrasonic Arteriography System

SRI developed a high-resolution, real-time, B-scan imaging system for detecting carotid atherosclerosis. This instrument produces images of a 3- by 4-cm field, delineating tissue structure with unprecedented clarity. In addition, it superimposes on the image the pulsating velocity profiles of blood flowing in the vessels. This work, which was supported by the National Heart, Lung and Blood Institute, included the development of dynamically focused annular-array technology. SRI also developed a commercial prototype of this instrument for its licensee (it became the Microview®) and, in a project for a European clinic, we developed an advanced version that provides quantitative volume-flow-rate graphs as well. For this version we developed the first 10-MHz, six-ring, annular-array transducer, using voltage-variable, analog delay lines for transient-free dynamic control.

Ultrasonic Endoscope

To improve early detection of pancreatic cancer, SRI developed a unique instrument: a high-resolution, real-time ultrasonic scanner with a linear-array transducer integrated into the tip of a fiber-optic gastric endoscope. The physician visually guides the instrument into the stomach or duodenum; the transducer section rests against the intestinal wall. A television screen displays a cross section of the wall and adjacent organs, including the pancreas, spleen, liver, kidneys, heart, and abdominal vessels. The unique dynamic focusing method and transducer technology developed for this application have also been used in conventional ultrasonic-scanning applications. This work was sponsored by the National Cancer Institute. SRI built subsequent versions for a licensee.

Segmented Annular-Array Imaging System

For the National Heart, Lung and Blood Institute, SRI developed a very sophisticated scanner incorporating a 4-MHz, 21-element segmented-annular-array, high-speed A/D converter in each channel, and digital delay and summation. SRI pioneered the use of dynamic refractive-aberration correction for use in this instrument.

Ultrasonic Eye Scanner

For a commercial client, SRI developed a sophisticated prototype ophthalmological scanner that provides B-scan images, A-scans, and measurements using screen cursors and built-in lens-computation algorithms.

System Component Development

SRI has frequently developed subsystems and special components for its commercial clients; an example is a Doppler spectrum analyzer and a high-performance mechanical scan probe with interchangeable transducers and domes for general and cardiological use.

Industrial Applications

SRI conducts research in nondestructive evaluation, on imaging composite aircraft structural materials, including honeycomb and solid materials of metal, and carbon-reinforced laminates. Both transmission and reflection C-scans are made on our computer-controlled research scanner. A wide variety of transducers and fixtures is available for evaluating various imaging modalities. Research in sonochemistry is directed to the decomposition of environmental toxins. SRI is also investigating applications of ultrasound in the food industry.

Computer Modeling, Design, Simulation, and Image Processing

Many of SRI's ultrasonic programs involve computer modeling of wave propagation, transducer response, and array performance. We often simulate imaging modalities on the computer prior to building a prototype system. We make extensive use of computer image enhancement and we synthesize stereographic ultrasonic images from transmission and echo signals.

Ultrasonic Biophysics

SRI studies the bioeffects of ultrasound by using a highly automated exposure facility developed at SRI under an NIH grant. Members of the Ultrasonics Program and other biomedical scientists have combined their efforts to evaluate the bioeffects of ultrasound on cells, tissues, and organs. Other studies, both short- and long-term, have investigated the possibility of cytotoxic or cytogenetic effects of ultrasound as well as determining possible effects on reproductive physiology in mice. SRI also develops instrumented phantoms to measure heat flow during ultrasound hyperthermia and conducts studies to determine the ultrasonic properties of normal and pathological tissues.