Magnetic gradient requirements for diffusion weighted imaging of the central nervous system

Diffusion weighted imaging, in which image intensity primarily depends on the extent to which NMR visible spins are free to undergo translational diffusion, is beginning to find wide application in neuroradiology of the central nervous system. In order to achieve sufficient contrast for clinical diagnosis, this form of imaging requires large magnetic field gradients to be applied over extended periods of time, placing great demands on both gradient coils and amplifiers. The simplest technique used employs balanced gradient pulses on either side of the 180° refocusing pulse of a spin echo. For example a typical diagnostic sequence employing gradients capable of a maximum amplitude of 10 mT/m requires pulses of 45 msec duration. The minimum echo time for this sequence is about 120 msec. Nontheless clinically useful diffusion weighted images can be produced on standard commercial whole body scanners, although multi-slice capabilities may be impaired