? Present computed tomography systems provide limited temporal resolution. Large spatial coverage requires sequential acquisition of slices as the patient table passes through a narrow region of exposure. This is true for helical CT scanners as well as electron beam CT (EBCT). There are several consequences of this. For contrast enhanced angiographic studies or studies of tumor contrast uptake, there is little dynamic information available at any anatomical location and the timing of the acquisition relative to the contrast arrival can be variable from patient to patient. For coronary artery imaging the need to acquire substantial sectors of angular data during the acquisition of each slice as the table moves past the source leads to coronary artery motion during acquisition times on the order of fifty milliseconds, even when EBCT is used. Failure to properly advance the sector in sequential heartbeats can lead to inadequate angular sampling and technically unacceptable examinations. ? ? Recently, several groups have begun to investigate volume CT systems using conventional x-ray tubes rotated in a single circular path with an opposed flat panel X-ray detector in conjunction with table motion. Although this increases the useful detection solid angle it does not provide optimal source trajectories for dynamic imaging over large fields of view. ? ? We propose to investigate the feasibility of an advanced CT system in which the x-ray focal spot is rapidly varied along the length (Z dimension) of the patient during gantry rotation (Z-Scan). This will be accomplished by means of a scanning electron beam or a linear array of discrete focal spots producing a flexible distribution of cone beam sources opposed by large detector arrays. Source trajectories can be optimized for particular clinical applications. The availability of arbitrary source trajectories wilt permit large volume dynamic time resolved detection of contrast material dynamics without significant table motion and, for coronary artery imaging, will permit a short exposure times in each cardiac phase. ? ? We will investigate the extension to X-ray CT of MRI acquisition schemes that have enabled us to acquire contrast-enhanced MR images with speeds up to a factor of forty faster than with conventional Cartesian MRI. ? ? In the R21 phase, the potential performance of systems based on the proposed approach will be studied using simulations. Measurements and image reconstructions wilt be generated using an X-ray test bed in which a conventional source will be moved to simulate the contemplated source trajectories. In the R33 phase a source test bed employing scanned electron beam technology or distributed pulsed sources will be developed. ? ? Potential applications of the contemplated scanner include dynamic studies of tumor contrast uptake, time resolved CT angiography, and coronary artery imaging. We will focus on the latter two applications and, based on the proposed studies, will develop a design for an optimized scanner based on the Z-Scan principle. ? ?
