Determination of optimum combination of voxel size and b-value for brain diffusion tensor imaging

Optimum combination of voxel size resolution and b-value for whole brain imaging has been determined. Data images were acquired using a 1.5T magnetic resonance imaging (MRI) system (GE Signa HDxt). Diffusion tensor imaging (DTI) scan was performed on phantom and a human volunteer. Six protocols which consist of various combination of voxel size and b-value were evaluated. Measurement of signal-to-noise ratio (SNR) and DTI parameter indices were carried out for both phantom and in-vivo studies. Due consideration was given to a combination of parameters yielding sufficient SNR with DTI values comparable to those obtained from previous reported studies. For the phantom study, SNR ≥ 20 was found in all of the protocols except for a combination of voxel size of 2.0 × 2.0 × 2.0 mm3 with b-value of 1200 s/mm2 (V2.0 B1200) and that of voxel size of 2.0 × 2.0 × 2.0 mm3 with b-value of 1000 s/mm2 (V2.0 B1000). For in-vivo study, all protocols presented SNR > 20. It was found that a combination of voxel size of 2.5 × 2.5 × 2.5 mm3 with b-value of 1000 s/mm2 (V2.5 B1000) and that of voxel size of 2.5 × 2.5 × 2.5 mm3 with b-value of 700 s/mm2 (V2.5 B700) displayed the most comparable ADC and FA values with references. In terms of anatomic coverage, V2.5 B700 was found better than V2.5 B1000 as it assures coverage of the whole brain. In conclusion, a combination of voxel size of 2.5 × 2.5 × 2.5 mm3 with b-value of 700 s/mm2 was considered as optimum parameters for brain DTI

Relationship between volume of leukoaraiosis spot and degree of tissue damage: a quantitative diffusion tensor imaging study

Diffusion tensor imaging (DTI) offers parameter indices, namely, mean diffusivity (MD) and fractional anisotropy (FA). Leukoaraiosis is a brain white matter hyperintensity as observed on fluid-attenuated inversion recovery (FLAIR) images. In this study, we attempt to assess leukoaraiosis at its specific spot using a new parameter, namely, lesion-to-normal appearing white matter ratio (LNR). LNR was then used to investigate the relationship between the volume of leukoaraiosis spot and the degree of tissue damage. This study involved 49 leukoaraiosis subjects who altogether contributed to 274 leukoaraiosis spots. The MD, FA, and volume were measured at each spot. LNR was calculated by comparing the MD values of the spot with those of the surrounding normal-appearing white matter (NAWM). The correlation between MD, FA, and LNR with leukoaraiosis volume was then analysed. The leukoaraiosis tissues generally exhibited higher MD (103.97 ± 12.32 × 10-5 mm2/s) and lower FA (0.31 ± 0.08) values than the NAWM tissues (79.30 ± 4.76 × 10-5 mm2/s and 0.41 ± 0.09, respectively). LNR values were found to range from 0.04 to 1.63. The results showed an insignificant association between the leukoaraiosis volume and LNR [r = −.055, p = .368], whereas a very weak association was shown with MD [r = −.196,p =.001] and FA [r = .268, p < .001]. The volume of the leukoaraiosis spot does not necessarily indicate the degree of tissue damage. By using LNR instead of MD, an accurate analysis was performed since the variability of MD for NAWM surrounding the lesion is taken into account