oving Beam Helical CT Scanning

Images generated with helical scanning are degraded by partial volume artifacts caused by an increased slice thickness when compared to conventional computed tomography (CT) scanning. The slice thickness for a helical scan is proportional to the sum of the thickness of the fan of radiation and the distance the patient moves during data acquisition. We present a method called moving beam helical scanning (MBHS) which significantly reduces the partial volume artifacts caused by h e l i d scanning. The key element of MBHS is a rotatable collimator that is placed between the X-ray source and the patient. As the patient is translated, the collimator is used to aim the fan on a fixed position in the patient. Once sufficient data are obtained to reconstruct a slice, the collimator is quickly reset to scan a target in the next slice. We examined the performance of MBHS by scanning wires and phantoms on a modified scanner. The full-width-at-tenth-maximum of the slice profile at iso-center for MBHS is identical to conventional CT versus a 59% increase for conventional helical scanning. We conclude that MBHS can be used to obtain the scan rate advantages of helical scanning with image quality comparable to conventional scanning.