Diffusion tensor MR imaging of the brain: effect of diffusion weighting on trace and anisotropy measurements.

BACKGROUND AND PURPOSE In human brain, the relationship between MR signal and b value is complicated by cerebral perfusion, restricted diffusion, anisotropy, cellular membrane permeability, and active cellular transport of water molecules. Our purpose was to evaluate the effect of the number and strength of diffusion-sensitizing gradients on measured isotropic apparent diffusion coefficients (ADCi), fractional anisotropy (FA), and their respective SD in different anatomic locations of the brain. METHODS Quantitative apparent diffusion coefficients and diffusion anisotropy brain maps were obtained from 10 healthy volunteers by using six different levels of diffusion weighting (b0 = 0, bl = 160, b2 = 320, b3 = 480, b4 = 640, and b5 = 800 s/mm2), applied sequentially in six different directions (Gxx, Gyy, Gzz, Gxy, Gxz, Gyz) and coupled to a single-shot spin-echo echo-planar (2,045/115 [TR/TE]) MR imaging technique. ADCi, FA, eigenvalues (lambda1, lambda2, lamdba3)1 of the principal eigenvectors, and their respective SD were measured from seven different anatomic locations in the brain. Repeated measures analysis of variance was used to evaluate for the existence of significant differences in the average and SD of the calculated ADCi and FA as a function of the number and strength of b values. When a difference existed, the Bonferroni t method was used for paired comparisons of the groups. RESULTS The measured ADCi was affected by the number and strength of b values (P < .05). The SD of the ADCi was affected by the strength (P < .05) but not the number of b values (P > .05). The measured FA was unaffected by the number and strength of b values (P > .05). The SD was affected by the number and strength of b values (P < .05). CONCLUSION The number and strength of b values do influence measures of diffusion and anisotropy. Attention to the choice of diffusion sensitization parameters is important in decisions regarding clinical feasibility (acquisition time) and normative measures.

[1]  K Minematsu,et al.  Diffusion‐weighted magnetic resonance imaging , 1992, Neurology.

[2]  T. Chenevert,et al.  Anisotropic diffusion in human white matter: demonstration with MR techniques in vivo. , 1990, Radiology.

[3]  A. Snyder,et al.  Normal brain in human newborns: apparent diffusion coefficient and diffusion anisotropy measured by using diffusion tensor MR imaging. , 1998, Radiology.

[4]  E. Akbudak,et al.  Encoding of anisotropic diffusion with tetrahedral gradients: A general mathematical diffusion formalism and experimental results , 1996, Magnetic resonance in medicine.

[5]  D. Norris,et al.  Biexponential diffusion attenuation in various states of brain tissue: Implications for diffusion‐weighted imaging , 1996, Magnetic resonance in medicine.

[6]  J. Pekar,et al.  MR color mapping of myelin fiber orientation. , 1991, Journal of computer assisted tomography.

[7]  E. Hsu,et al.  Analytical expressions for the NMR apparent diffusion coefficients in an anisotropic system and a simplified method for determining fiber orientation , 1995, Magnetic resonance in medicine.

[8]  T. L. Davis,et al.  Hyperacute stroke: evaluation with combined multisection diffusion-weighted and hemodynamically weighted echo-planar MR imaging. , 1996, Radiology.

[9]  J. Tsuruda,et al.  Diffusion-weighted MR imaging of anisotropic water diffusion in cat central nervous system. , 1990, Radiology.

[10]  Y Tamagawa,et al.  Adult and neonatal human brain: diffusional anisotropy and myelination with diffusion-weighted MR imaging. , 1991, Radiology.

[11]  P van Gelderen,et al.  Restricted and anisotropic displacement of water in healthy cat brain and in stroke studied by NMR diffusion imaging , 1991, Magnetic resonance in medicine.

[12]  P. V. van Zijl,et al.  Orientation‐independent diffusion imaging without tensor diagonalization: Anisotropy definitions based on physical attributes of the diffusion ellipsoid , 1999, Journal of magnetic resonance imaging : JMRI.

[13]  Mark Doran.  Diffusion and Perfusion Magnetic Resonance Imaging: Applications to Functional MRI , 1996 .

[14]  H. Lutsep,et al.  Clinical utility of diffusion‐weighted magnetic resonance imaging in the assessment of ischemic stroke , 1997, Annals of neurology.

[15]  D. Le Bihan,et al.  Separation of diffusion and perfusion in intravoxel incoherent motion MR imaging. , 1988, Radiology.

[16]  B. Siewert,et al.  Acute human stroke studied by whole brain echo planar diffusion‐weighted magnetic resonance imaging , 1995, Annals of neurology.

[17]  R R Edelman,et al.  Time course of the apparent diffusion coefficient (ADC) abnormality in human stroke , 1997, Neurology.

[18]  John Crank,et al.  The Mathematics Of Diffusion , 1956 .

[19]  J. Pekar,et al.  Echo-planar imaging of intravoxel incoherent motion. , 1990, Radiology.

[20]  M E Moseley,et al.  Comparison of diffusion‐ and T2‐weighted MRI for the early detection of cerebral ischemia and reperfusion in rats , 1991, Magnetic resonance in medicine.

[21]  P. Petrozza.  Diffusion-weighted MRI in acute subcortical infarction , 1998 .

[22]  Gottfried Schlaug,et al.  Ischemic lesion volumes in acute stroke by diffusion‐weighted magnetic resonance imaging correlate with clinical outcome , 1997, Annals of neurology.

[23]  P. Basser,et al.  Toward a quantitative assessment of diffusion anisotropy , 1996, Magnetic resonance in medicine.

[24]  R Luypaert,et al.  A method for myelin fiber orientation mapping using diffusion-weighted MR images. , 1994, Magnetic resonance imaging.

[25]  A. Snyder,et al.  Quantitative diffusion-tensor anisotropy brain MR imaging: normative human data and anatomic analysis. , 1999, Radiology.

[26]  T. L. Davis,et al.  Human acute cerebral ischemia: detection of changes in water diffusion anisotropy by using MR imaging. , 1999, Radiology.

[27]  J. Kurhanewicz,et al.  Diffusion-weighted MR imaging of acute stroke: correlation with T2-weighted and magnetic susceptibility-enhanced MR imaging in cats. , 1990, AJNR. American journal of neuroradiology.

[28]  J. E. Tanner,et al.  Spin diffusion measurements : spin echoes in the presence of a time-dependent field gradient , 1965 .

[29]  Wei Li,et al.  Fast magnetic resonance diffusion‐weighted imaging of acute human stroke , 1992, Neurology.

[30]  J V Hajnal,et al.  Normal and abnormal white matter tracts shown by MR imaging using directional diffusion weighted sequences. , 1990, Journal of computer assisted tomography.

[31]  P. Basser,et al.  Estimation of the effective self-diffusion tensor from the NMR spin echo. , 1994, Journal of magnetic resonance. Series B.

[32]  P van Gelderen,et al.  Water diffusion and acute stroke , 1994, Magnetic resonance in medicine.

[33]  R N Bryan,et al.  Absolute quantitation of diffusion constants in human stroke. , 1997, Stroke.

[34]  K Sakurai,et al.  Differentiation of dys- and demyelination using diffusional anisotropy. , 1997, Pediatric neurology.

[35]  T Nakagawa,et al.  Diffusional anisotropy of the human brain assessed with diffusion-weighted MR: relation with normal brain development and aging. , 1994, AJNR. American journal of neuroradiology.

[36]  P. Basser,et al.  Diffusion tensor MR imaging of the human brain. , 1996, Radiology.