Background darkening of magnetic resonance angiographic images

Abstract

A magnetic resonance imaging system (A) examines a region of a patient and generates a plurality of views which are reconstructed (B) into a volumetric image representation and stored in a volume image memory (C). A ray projector (D) projects a plurality of rays (14) from a selectable viewing plane (10) into the volume data and retrieves a plurality of data values that lie along each ray. A maximum intensity projection system (E) selects the brightest pixel along each ray to become the corresponding pixel value of an uncorrected projection angiographic image which is stored in an image memory (F). The uncorrected angiographic image represents blood as bright or white values and non-blood tissues as dark or black values. Noise, some tissue types, regions with fine capillaries, and the like, cause the background non-blood regions of the image to appear hazy or gray rather than black. Each pixel value from the uncorrected angiographic image is processed by a transfer function (30) to generate corresponding pixel values of a background darkened angiographic image. The transfer function is linear (32) above a threshold brightness value (34) such that the bright or blood pixels have the same brightness in both the uncorrected and background darkened images. Pixels below the threshold (34) are lowered in brightness along a parabolic curve segment (36) such that the background appears darker.