Interactive MR image synthesis

In MR tomography the contrast in images made with the spin-echo method or the inversion-recovery method depends greatly on the time parameters of the r.f. pulses that are applied to obtain signals. The user of MR equipment cannot, however, always indicate the contrast values - the parameters required - beforehand. Once a single MR exposure has been made, the grey levels of points in the MR image can be recalculated to give grey levels for other pulse parameters. The use of a RAM look-up table enables the computer to perform this calculation in real time. The user can thus see the result of a different choice of pulse parameters on the monitor screen immediately. Because small numbers of bits have to be used for the digital values of the proton density and the two relaxation times the quantization noise in the image is increased, but the application of a modified Floyd-Steinberg algorithm prevents the occurrence of 'interference patterns' in the image. The definitive image, which takes rather longer to calculate, is free from quantization noise, however, since it is obtained by using the original numbers of bits. Refinementsof the method are the addition of colour to the image and a procedure for maximizing the contrast between areas in the image indicated by the user. (Auth.)