Filtered backprojection and spectral width of MR signal

Reconstructed images obtained by filtered backprojection are altered when the projections are distorted by an attenuation of the high frequency components of the demodulated magnetic resonance (MR) signal. This attenuation occurs if the spectral width of the MR signal is reduced by the bandwidth of the receiver radiofrequency coil as well as by the use of imperfect refocusing pulses. This signal spectrum has to be wide when the sampling bandwidth is wide, because the sampling time is very short, for instance in the case of very short interpulse delay such as 6 ms. A short interpulse delay is needed when many images are required, to enable the transverse magnetization decay of each pixel to be recorded accurately. This paper presents an analysis of backprojection reconstruction for such a case and demonstrates a contamination of each pixel by surrounding pixels. The consequence on the results of T2 measurement and biexponential decomposition of transverse magnetization decay curves are discussed. A method for correction of such artifacts is described.