SPRINT: A Stationary Detector Single Photon Ring Tomograph for Brain Imaging

During the last two decades, various Doppler methods have been successfully used to screen patients with significant cerebral and peripheral vascular disease. In general terms, the principal advantages of Doppler ultrasound techniques in the evaluation of atherosclerotic lesions are that they: 1) are noninvasive, 2) are nontraumatic, 3) are relatively inexpensive, 4) provide anatomical and physiological data, and 5) provide direct and dynamic measurements. Nevertheless, the general limitations of the techniques are of equal importance: 1) the techniques are difficult in some subjects due to obesity and anatomical variations; 2) the technique cannot examine tissues surrounded by air or bone; 3) the techniques require operator skill and a thorough knowledge of human anatomy and cardiovascular dynamics; 4) the techniques have finite spatial resolutions which may compromise the important measurement of vessel diameter, ulceration, and percent stenosis; and 5) the techniques have finite velocity measuring capabilities which may compromise some measurements of highly disturbed blood velocities outside the range of 2-200 cm/sec. As clinical demands for the early diagnosis and quantification of vascular lesions increased, improvements in Doppler ultrasonics and spectra analysis significantly increased the technical and clinical capabilities of existing simple, inexpensive instruments. Presently, both anatomical and physiological images along with quantitative Doppler spectra from superficial and deep-lying vessels can be obtained. Consequently, the ability of Vascular Laboratory, Clinical Research Division; Lovelace Medical Foundation, and the University of New Mexico School of Medicine, Albuquerque, New Mexico 87108 Manuscript received at IEEE April 30, 1982. new expensive imaging equipment to quantitate atherosclerotic lesions using spectral analysis techniques compares favorably with the interpretational precision of standard invasive or intravenous digital angiography. New data suggest that unique hemodynamic information which reflects the effects of cardiac output and vascular input impedance on the hemodynamic consequences of an anatomical lesion can also be obtained. This paper will 1) briefly discuss the general considerations of Doppler ultrasonics; 2) critique the specific characteristics and utility of standard clinical Doppler units; and 3) discuss the ability of new, multipurpose equipment to quantitate (both anatomically and physiologically) atherosclerotic lesions throughout the cardiovascular system.