The DSR: A high temporal resolution volumetric roentgenographic CT scanner

The dynamic spatial reconstructor (DSR) is a high temporal resolution volumetric roentgenographic computor tomographic scanner. Specifically for the heart, it promises to yield accurate, non-invasive, three-dimensional representations throughout the cardiac cycle at a high enough repetition rate and with sufficient spatial and contrast resolution to be able to delineate and measure the endocardium, epicardium and coronary vessels. Optimal imaging properties, characterized by the temporal, spatial and contrast resolution, represent the basis of the system's capability to produce stop-action images of the left ventricular wall during systole which moves at about 10 cm/s maximum speed requiring an aperture time of approximately 0.01 second to maintain the 1 mm spatial resolution. Modern technology has enabled development of the essential components consisting of: a rotating scanner with 28 X-ray tubes, positioned at intervals of 6° over 162° of the rotating structure, which are pulsed sequentially at a peak input power of 100 KW for approximately 350 μs every 1/60 of a sec; a hemicylindrical, rare earth, fluorescent screen with superior signal intensity build-up and decay lag characteristics, extending around 184° at a radius of 58 cm for image formation; video cameras with geometric circuits associated with the sweep circuitry permitting correction of total geometric distortion in the image from all sources to approximately 0.25%; an 8-bit microprocessor for control of the system, and a multiplex system for composite imaging of the images from groups of four cameras, 4:1, into 60 video lines from each of the four. Functionally there are three modes of normal operation: scanning with subsequent transfer of the video images to a video disc system for temporary storage; reconstruction, augmented by special hardware to enhance high speed computation, on a slice for slice basis after digital conversion of the video data from the discs, and analysis of the unit volume from stop-action frames throughout the cycle from which it is possible to mathematically produce new sets of cross sections at any desired arbitrary slice angle. The DSR system thus promises potential applicability for a wide variety of biomedical problems. For reseach purposes, the DSR offers the possibility of delineating the precise extent of anatomical structures and the ability to make accurate geometric measurements throughout the cardiac cycle which may used to provide an indirect means for assessing the length/tension relationship in a normal or diseased functioning heart. The ability to visualize and measure variations in shape, size and density will permit mathematical assessment of specific structures for detection of abnormalities such as congenital heart disease or, in conjunction with peripheral injections of roentgenographic contrast material, localized reduction of luminal diameter in major branches of coronary vessels. In addition, the possibility of measuring temporal variation of roentgen density promises to be very useful for studies of pulmonary ventilation and, with respect to density measurements as a function of time when using an intravenous injection of contrast agent, perfusion studies will be enabled. The DSR is currently in a period of performance evaluation during which potential improvements, in video camera objective, inclusion of an anti-scatter grid, incorporation of an electronic line averager and employment of logarithmic amplifiers on each video signal, are being addressed before the system achieves operational status. It is anticipated that the DSR is going to provide new insights into the study of moving organs and three-dimensional structure in living animal and humans. Preliminary studies with the single source prototype have given a hint of what can be expected, but the true potential of the DSR will probably first be recognized when the system is operational.