BACKGROUND AND PURPOSE: Animal studies have shown that MR diffusion imaging can outline acute ischemic regions before irreversible damage (infarction) occurs. To study evolution of ischemic lesions in humans, it is therefore important to quantify absolute diffusion constants (D values), but quantitation has not been reproducible among different clinics. These problems are explained, and a method for reproducible quantitation is suggested. METHODS: Diffusion-weighted and absolute diffusion images were acquired, and the absolute apparent diffusion constants in three orthogonal spatial directions (Dxx, Dyy, and Dzz) were measured. These were combined to calculate images of the orientation-independent apparent diffusion parameter Dav = 1/3 Trace[D] = 1/3(Dxx + Dyy + Dzz). Values of the individual diffusion constants and Dav were evaluated in 6 patients and 6 normal volunteers. RESULTS: Patient data show that comparison of diffusion constants between contralateral and ipsilateral hemispheres after ischemia may give results varying by more than 100% depending on orientation. Findings in normal-appearing regions containing a mixture of gray and white matter in patients (n = 5) and in normal volunteers (n = 6) show that Dav = (0.92+/-0.11) x 10(-3) mm2/s, with a small intersubject variation, whereas Dxx, Dyy, and Dzz vary strongly. Hemispheric ratios (ipsilateral/contralateral [I/C]) in these subjects were (I/C)Dav = 1.00+/-0.05, (I/C)Dxx = 1.02+/-0.15, (I/C)Dyy = 1.07+/-0.24, and (I/C)Dzz = 0.96+/-0.28. The individual subjects in this group all had an (I/C)Dav within 10% of unity, while the other three ratios showed intersubject variations as large as 100%. CONCLUSIONS: (I/C)Dav ratios are a reliable means to quantitate changes in absolute diffusion constants for the study of stroke evolution independent of tissue orientation, gradient orientation, and diffusion time. The use of these ratios will enable reproducible intersubject and interclinic quantitation.
BACKGROUND AND PURPOSE: Animal studies have shown that MR diffusion imaging can outline acute ischemic regions before irreversible damage (infarction) occurs. To study evolution of ischemic lesions in humans, it is therefore important to quantify absolute diffusion constants (D values), but quantitation has not been reproducible among different clinics. These problems are explained, and a method for reproducible quantitation is suggested. METHODS: Diffusion-weighted and absolute diffusion images were acquired, and the absolute apparent diffusion constants in three orthogonal spatial directions (Dxx, Dyy, and Dzz) were measured. These were combined to calculate images of the orientation-independent apparent diffusion parameter Dav = 1/3 Trace[D] = 1/3(Dxx + Dyy + Dzz). Values of the individual diffusion constants and Dav were evaluated in 6 patients and 6 normal volunteers. RESULTS:Patient data show that comparison of diffusion constants between contralateral and ipsilateral hemispheres after ischemia may give results varying by more than 100% depending on orientation. Findings in normal-appearing regions containing a mixture of gray and white matter in patients (n = 5) and in normal volunteers (n = 6) show that Dav = (0.92+/-0.11) x 10(-3) mm2/s, with a small intersubject variation, whereas Dxx, Dyy, and Dzz vary strongly. Hemispheric ratios (ipsilateral/contralateral [I/C]) in these subjects were (I/C)Dav = 1.00+/-0.05, (I/C)Dxx = 1.02+/-0.15, (I/C)Dyy = 1.07+/-0.24, and (I/C)Dzz = 0.96+/-0.28. The individual subjects in this group all had an (I/C)Dav within 10% of unity, while the other three ratios showed intersubject variations as large as 100%. CONCLUSIONS: (I/C)Dav ratios are a reliable means to quantitate changes in absolute diffusion constants for the study of stroke evolution independent of tissue orientation, gradient orientation, and diffusion time. The use of these ratios will enable reproducible intersubject and interclinic quantitation.
Authors: Bennett A Landman; Alan J Huang; Aliya Gifford; Deepti S Vikram; Issel Anne L Lim; Jonathan A D Farrell; John A Bogovic; Jun Hua; Min Chen; Samson Jarso; Seth A Smith; Suresh Joel; Susumu Mori; James J Pekar; Peter B Barker; Jerry L Prince; Peter C M van Zijl Journal: Neuroimage Date: 2010-11-20 Impact factor: 6.556
Authors: Jonathan A D Farrell; Bennett A Landman; Craig K Jones; Seth A Smith; Jerry L Prince; Peter C M van Zijl; Susumu Mori Journal: J Magn Reson Imaging Date: 2007-09 Impact factor: 4.813
Authors: T J Loher; C L Bassetti; K O Lövblad; F P Stepper; M Sturzenegger; C Kiefer; K Nedeltchev; M Arnold; L Remonda; G Schroth Journal: Neuroradiology Date: 2003-06-27 Impact factor: 2.804
Authors: J Ricardo Carhuapoma; Peter B Barker; Daniel F Hanley; Paul Wang; Norman J Beauchamp Journal: AJNR Am J Neuroradiol Date: 2002-09 Impact factor: 3.825