Method and system for high resolution nutated slice reconstruction using quarter detector offset

摘要

A method and system are provided for generating high resolution CT images. The NSR# method improves on the AMPR method, by increasing the in-plane image resolution of CT scanners, in the helical scanning mode. The provided method uses the quarter detector offset and interleaving of complementary data to achieve in plane image resolution that is similar to the high resolution axial scanning mode utilizing quarter detector offset and interleaving. The method includes several ways of choosing the data to be interleaved, like NSR# with two planes, NSR# with 3 planes, NSR# with multiple planes. The interleaved data are used to create high resolution tilted slices. The NSR# method optimizes the untilting filter to create a mix of high and low resolution tilted slices to achieve the desired in-plane image resolution-image artifact balance required for the imaging task. In one embodiment in the untilting process one may use only high resolution tilted slices, for maximum resolution benefit. In another embodiment one may mix high resolution tilted slices with standard resolution tilted slices resulting from data that did not go through interleaving. This creates unfilled slices of higher resolution than the standard and with lower artifacts. In another embodiment for scans with pitch lower than ⅔ one may reduce the collimation to reduce the dose to the patient.

主权项

1. A helical CT scanner for scanning an object, comprising:
an x-ray source constructed so as to define a focal spot, and a detector array comprising a plurality of detectors positioned to rotate with the source about an axis of rotation, wherein the source and detector array are arranged to rotate about a rotation axis with the object moving relative to and between the source and detector array in a direction parallel to the rotation axis during a helical scan; and a processor operative to process data acquired by the detector array during the helical scan, and based on the data, construct tilted slices with respect to the rotation axis, wherein each of the tilted slices are defined by an angle γ with respect to the rotating X-axis and an angle δ with respect to the rotating Y-axis; wherein the angle γ is chosen as a function of the pitch of the helical scan, so as to minimize the distance of the focal spot to the tilted slice for a center ray over all views used to reconstruct a tilted slice; wherein the angle δ is determined by the phase of the slice and a predetermined number of slices passing through each attachment point for each possible scan pitch; wherein the processor is further operative to interleave samples from pairs of complementary tilted slices to form combined slices, then reconstruct an image from each combined slice, and then untilt each image to form an untitled image that is perpendicular to the axis of rotation; wherein two tilted slices are complementary if they satisfy the following conditions: (1) respective attachment points of those tilted slices are separated by half a rotation of the x-ray source, and (2) planes intersect along a line which connects the two attachment points; wherein the x-ray source is constructed so as to define a fixed focal spot with respect to the detector array during the helical scan, and the detectors of the array are positioned relative to the source and axis of rotation during rotation so as to provide a quarter detector offset so that rays from 180° apart during rotation are interleaved.