Kevin Franklin King

Computed tomography scanning with simultaneous patient translation

This paper deals with methods of reducing the total time required to acquire the projection data for a set of contiguous computed tomography (CT) images. Normally during the acquisition of a set of slices, the patient is held stationary during data collection and translated to the next axial location during an interscan delay. We demonstrate using computer simulations and scans of volunteers on a modified scanner how acceptable image quality is achieved if the patient translation time is overlapped with data acquisition. If the concurrent patient translation is ignored, structured artifacts significantly degrade resulting reconstructions. We present a number of weighting schemes for use with the conventional convolution/backprojection algorithm to reduce the structured artifacts through the use of projection modulation using the data from individual and multiple slices. We compare the methods with respect to structured artifacts, noise, resolution and to patient motion. Review of preliminary results by a panel of radiologists indicates that the residual image degradation is tolerable for selected applications when it is critical to acquire more slices in a patient breathing cycle than is possible with conventional scanning.

A unified description of NMR imaging, data-collection strategies, and reconstruction

In nuclear magnetic resonance (NMR) imaging by the zeugmatographic methods, there is a common and unified theoretical description. All forms of two-dimensional and three-dimensional imaging involve NMR data which trace various geometric representations, in reciprocal transform space, of the subjects spatially blurred effective spin density. The effective density is proportional to the physical density modulated spatially by the several factors of receiver coil (B/I) ratio, rf pulse excitation terms, T1-relaxation terms, and T2-relaxation terms. These factors depend upon the rf pulse sequence and field-gradient modulation sequence,and they may be calculated according to some model or directly measured. From this viewpoint, all different imaging modes appear as variations in data-collection and image-reconstruction strategies. The results are used here to describe slice-oriented polar and Cartesian strategies, three-dimensional Cartesian and two forms of spherical strategies, and multiecho strategies of the planar-echo type.