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Radial diffusion coefficient mapping

CRC Clinical Magnetic Resonance Research Group and Joint Department of Physics, Institute of Cancer Research and Royal Marsden Hospital, Sutton, Surrey SM2 5PT, UK

The two-dimensional mapping of the effective diffusion coefficient of water in tissues may provide a useful method of tissue characterization to complement T₁ and T₂ relaxation time studies for diagnostic purposes. Current diffusion techniques rely on the application of large gradient strengths and long echo times to achieve the required sensitivity. This, in turn, limits the applicability of the technique to tissues having long T₂s with rapid water diffusion. In addition, the inherent directionality of these methods results in only the partial encoding of diffusion information. A modified diffusion sequence is presented, radial diffusion mapping (RAD), which provides enhanced sensitivity diffusion maps by employing gradient sensitization in three orthogonal directions. Results in both phantoms and volunteers are presented, together with an investigation of the effects of T₂ on the measurement accuracy. Using RAD, a two- to five-fold improvement in sensitivity was achieved, thus significantly enhancing the dynamic range of the method and allowing more accurate in vivo diffusion measurements to be carried out.

Key Words: Diffusion • Nuclear magnetic resonance • IVIM • In vivo diffusion

Received for publication February 4, 1991. Accepted for publication March 26, 1992.