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Multi-component apparent diffusion coefficients in human brain

1999; Wiley; Volume: 12; Issue: 1 Linguagem: Inglês

10.1002/(sici)1099-1492(199902)12

1099-1492

Robert V. Mulkern, Hákon Guðbjartsson, Carl‐Fredrik Westin, Hale Pınar Zengingönül, Werner Gartner, Charles R.G. Guttmann, Richard L. Robertson, Walid E. Kyriakos, Richard B. Schwartz, David Holtzman, Ferenc A. Jólesz, Stephan E. Maier,

MRI in cancer diagnosis

The signal decay with increasing b-factor at fixed echo time from brain tissue in vivo has been measured using a line scan Stejskal–Tanner spin echo diffusion approach in eight healthy adult volunteers. The use of a 175 ms echo time and maximum gradient strengths of 10 mT/m allowed 64 b-factors to be sampled, ranging from 5 to 6000 s/mm2, a maximum some three times larger than that typically used for diffusion imaging. The signal decay with b-factor over this extended range showed a decidedly non-exponential behavior well-suited to biexponential modeling. Statistical analyses of the fitted biexponential parameters from over 125 brain voxels (15 × 15 × 1 mm3 volume) per volunteer yielded a mean volume fraction of 0.74 which decayed with a typical apparent diffusion coefficient around 1.4 µm2/ms. The remaining fraction had an apparent diffusion coefficient of approximately 0.25 µm2/ms. Simple models which might explain the non-exponential behavior, such as intra- and extracellular water compartmentation with slow exchange, appear inadequate for a complete description. For typical diffusion imaging with b-factors below 2000 s/mm2, the standard model of monoexponential signal decay with b-factor, apparent diffusion coefficient values around 0.7 µm2/ms, and a sensitivity to diffusion gradient direction may appear appropriate. Over a more extended but readily accessible b-factor range, however, the complexity of brain signal decay with b-factor increases, offering a greater parametrization of the water diffusion process for tissue characterization. Copyright © 1999 John Wiley & Sons, Ltd.