Gated cardiac imaging using low-field NMR

Both techniques considered have major disadvantages for anatomical studies: inversion recovery images suffer from a low signal level in general, not giving much signal from blood; saturation recovery images do not give differentiation between tissue and blood, whilst being sensitive to flow effects. It appeared that the best image is a combination of a higher contrast SR image (with a Tsub(R) of about 200 ms) and a rectified IR image (with Tsub(R)=Tsub(H)) to delineate the heart walls. The two types of functional study considered are the cine of SR images (van Dijk 1985) and the phase-encoded motion image (van Dijk 1984, O'Donnell 1984). Collecting multiple SR images was generally less technically demanding than phase-encoded imaging, though a relatively simple, though limited method of the latter has been proposed by Wedeen et al (1985). Acquisition times for the methods are comparable but the cine of SR images requires more sophisticated display hardware. Phase-encoded imaging may have the advantage of yielding quantitative information on blood flow and heart wall motion. (U.K.)