NMR Microscopy by Radiofrequency Field Gradients

Quasi-Immunity ofB1Gradient NMR Microscopy to Magnetic Susceptibility Distortions

“…It can be noted internal B 0 gradients. It has been shown previously (6) that that a quantitative account (not developed here) could be such effects should be partly compensated by a sort of averprovided by means of the theoretical treatment of Callaghan aging process because nutation encoding generally involves a large number of periods. However, the compensation is far from being perfect and the resulting spurious effects are examined in detail below.…”

“…The experiment involves the acquisition of a series of ever, as soon as paramagnetic centers are present, large disprojections (in practice by rotating the sample in a stepped tortions may ultimately make image alterations untenable, manner) which yield a two-dimensional image through a as already recognized by Kinchesh et al (2). dedicated filtered back-projection algorithm (6,8). Because In order to have at hand some reference images obtained nutation rather than precession is involved for each projecby conventional B 0 gradient techniques, we have repeated tion, no effect arising from internal B 0 gradients (thus from experiments of the same kind as those reported in Ref.…”

“…ents) (6,7). The method has been described previously in These distortions arise from internal B 0 gradients which necdetail (6) and we just recall its salient features with regard essarily exist between zones of different magnetic susceptibilities.…”

Fast NMR Imaging withB1Gradients

“…It time can be substantially reduced by acquiring the spatially encoded NMR signal between pulses of B 1 gradient is easy to understand that the duration of gradient pulses determines the field-of-view and must therefore be adapted ( 7 -9 ) , producing an image within a very short period is still a challenge. This may be of some interest in the to the size of the object under examination (5). Finally, we purposely leave aside the problem of slice selection (along context of the microscopic observation of systems evolving on a very short time scale, and ideally, one would the Z direction of the laboratory frame), and for the sake of the present study, the object will be physically limited in like to devise a procedure similar to EPI, which is capable of sampling the so-called k space ( the reciprocal space ) thickness.…”

“…The idea for lowering this waiting time is that Let us first recall how our standard imaging experiment with B 1 gradients works (5). A single-turn coil generates a radiofrequency field whose amplitude varies linearly across the object under investigation; we shall denote by X the spatial direction along which the B 1 gradient is applied.…”