Weighted ray projection imaging for mr angiography

Abstract

A magnetic resonance imaging apparatus (A) applies appropriate magnetic fields, magnetic field gradients, and radio frequency pulses across an examination region to generate magnetic resonance signals or views indicative of the properties of a volume of a subject examined in the examination region. The views are reconstructed (B) into voxel values V(x,y,z) and stored in a volumetric image memory (C). A relative angle and position of a viewing plane (10) relative to the image volume are selected. A plurality of rays (14), each corresponding to a pixel P(i,j) of a resultant projection image, are projected from the viewing plane into the volumetric image data. Each ray retrieves a corresponding vector of voxel values V.sub.1, V.sub.2, V.sub.3, . . . V.sub.n. Bright voxel values indicate blood. Dark pixel values indicate non-blood tissue. Intermediate voxel values have a greater uncertainty whether the pixel value represents blood or non-blood tissue. Probability ranges are determined (30) and used to select powers or exponents N which are used to expand the dynamic range of the voxel values non-linearly. The normalized partial sums of each ray are weightedly averaged (56 ) to produce the corresponding angiographic projection pixel value for storage in an image memory (F).