Contrast-to-noise ratio manipulation with linear filters

A common practice in MR imaging is to obtain several different images of the same body section. Given these images, a linear filter can produce an image in which the contrast-to-noise ratio (C/N) between pathologic and normal tissues is greater than in any of the initial images. When the abnormality must be separated from more than one tissue, the filter should optimize the set of C/Ns between the abnormalities and each of the tissues. The optimal filter will provide the largest value for the minimum C/N in the set. One can predict the C/N for each possible filter and use this to determine the optimal filter. To separate the abnormality from two other tissues, the optimal filter is often the one that sets the appropriate C/N equal. The filtered image then has a solid background, effectively highlighting the pathologic tissue. The filters were implemented on a General Electric Signa MR imaging system and evaluated in a sequence of ten patients. Significant improvement was seen in the selective portrayal of musculoskeletal tumors when MR images were processed in this manner. Other possible applications include the detection of meningiomas with MR imaging and dual-energy x-ray CT scans of spinal abnormalities