Biomedical subjects
Publications and source records attributed to C R Merritt.
For screening patients suspected of having portal vein thrombosis, the ultrasound examination is simple to perform, noninvasive, and can be accomplished rapidly. Three patients were studied in whom ultrasound examination revealed portal vein thrombosis that was subsequently confirmed by angiography or surgery. Ultrasonic findings in a series of 100 randomly selected patients are summarized.
A characteristic sonographic pattern that suggests a bowel lesion is pathologically significant in over 90% of patients with this pattern. The authors call this pattern the "pseudokidney sign" because it superficially resembles the ultrasonic appearance of the kidney. Although found occasionally in normal persons, this characteristic pattern should always lead the sonographer to consider a bowel lesion. Additional radiographic examinations, such as an upper-gastrointestinal series, small-bowel studies, and barium-enema examinations, are advised for definitive diagnosis.
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By simultaneous processing of frequency, phase, and amplitude information in the backscattered ultrasound signal, new instruments now permit the real-time display of high-resolution grey scale images of tissue combined with the simultaneous display of flow data from vessels within the scan plane. Doppler Color Flow Imaging, or DCFI, using such processing, permits blood flow direction and relative velocity to be detected and displayed in a color encoded display from throughout the ultrasound image. We have tested a new Doppler color flow imaging system over a period of two years to evaluate the carotid arteries, peripheral arteries and veins, and dialysis fistulas. In the abdomen and pelvis we have imaged blood flow to the liver, spleen, kidneys, uterus and renal transplants. Our experience in over 500 patients leads us to conclude that DCFI has significant advantages over conventional duplex Doppler sonography for blood flow evaluation. For examination of carotid and peripheral vessels, we have found DCFI to permit more rapid assessment in both normal and abnormal states. Areas of vessel narrowing or turbulent flow may be identified rapidly and accurately, and vessel orientation may be determined precisely, allowing accurate calculation of blood flow velocity from Doppler frequency shifts. The system we have used has adequate penetration and sensitivity to allow imaging of hepatic and renal blood flow and is extremely promising as a method of imaging organ perfusion and in the detection of abnormalities of perfusion that accompany disease, such as transplant rejection. Tumor vascularity may also be identified with DCFI, opening the possibility of additional clinical applications.
Conventional portal films taken with high-energy x rays are severely impaired by poor image quality, and many attempts have been made to overcome this problem. A new technology, computed radiographic imaging, has been investigated as a means of producing images taken with 6-and 10-MV x rays. The computed radiographic imaging (CRI) system is based on the principle of laser-stimulated luminescence induced in an image receptor plate exposed to ionizing radiation, and direct conversion of the light into digital form. Image processing using contrast enhancement and unsharp masking yields images at least as good as the best portal films obtainable with conventional commercial radiotherapy cassettes. Additionally, CRI offers advantages of reduced image size and digital storage. The system is capable of producing normal film densities over an extremely wide range of exposure.