Recent developments in instrumentation for emission computed tomography

Equipment for emission tomography is currently undergoing a rapidly changing stage of development, both for single-gamma detection and for tomography using positron emitters. For single-gamma longitudinal tomography, the 7-pinhole collimator has won wide acceptance because of it simplicity and rapid reconstruction times. However, rotating slant-hole collimators overcome some of the disadvantages of the 7-pinhole method and may eventually be used more widely. For transverse single-gamma imaging, rotating gamma cameras are currently attracting the most interest and offer the best prospects for wise-spread application, since such instruments can be used also for routine studies. In the field of positron tomography, development of new positron cameras has moved from the research center to the commerical area, with at least four manufacturers now marketing tomographic units, all of the multiple-ring design. Small cyclotrons suitable for in-hospital use also are being offered by these companies. Most of the new positron tomographic units employ BGO crystals, which offer substantial advantages over Nal for this purpose. However, the recent introduction of cesium fluoride (CsF) as a detector for tomographic cameras offers the exciting possibility of using time-of-flight techniques for positron detection. This should substantially improve the attainable resolution, which presently is slightly less than 1 cm FWHM. The number of institutions involved in research using positron tomography has suddenly increased, in part because of the recent award of substantial research grants from NIH. Thus, a field which has grown very slowly over the past decade has taken a sudden spurt, and we can anticipate further growth during the coming decade as clinical utility improves.