Background: Diffusion tensor imaging (DTI) is increasingly used in various diseases as a clinical tool for assessing\r\nthe integrity of the brainââ?¬â?¢s white matter. Reduced fractional anisotropy (FA) and an increased apparent diffusion\r\ncoefficient (ADC) are nonspecific findings in most pathological processes affecting the brainââ?¬â?¢s parenchyma.\r\nAt present, there is no gold standard for validating diffusion measures, which are dependent on the scanning\r\nprotocols, methods of the softwares and observers. Therefore, the normal variation and repeatability effects on\r\ncommonly-derived measures should be carefully examined.\r\nMethods: Thirty healthy volunteers (mean age 37.8 years, SD 11.4) underwent DTI of the brain with 3T MRI.\r\nRegion-of-interest (ROI) -based measurements were calculated at eleven anatomical locations in the pyramidal\r\ntracts, corpus callosum and frontobasal area. Two ROI-based methods, the circular method (CM) and the freehand\r\nmethod (FM), were compared. Both methods were also compared by performing measurements on a DTI\r\nphantom. The intra- and inter-observer variability (coefficient of variation, or CV%) and repeatability (intra-class\r\ncorrelation coefficient, or ICC) were assessed for FA and ADC values obtained using both ROI methods.\r\nResults: The mean FA values for all of the regions were 0.663 with the CM and 0.621 with the FM. For both\r\nmethods, the FA was highest in the splenium of the corpus callosum. The mean ADC value was 0.727 Ã?â??10-3 mm2/s\r\nwith the CM and 0.747 Ã?â??10-3 mm2/s with the FM, and both methods found the ADC to be lowest in the corona\r\nradiata. The CV percentages of the derived measures were < 13% with the CM and < 10% with the FM. In most of\r\nthe regions, the ICCs were excellent or moderate for both methods. With the CM, the highest ICC for FA was in the\r\nposterior limb of the internal capsule (0.90), and with the FM, it was in the corona radiata (0.86). For ADC, the\r\nhighest ICC was found in the genu of the corpus callosum (0.93) with the CM and in the uncinate fasciculus (0.92)\r\nwith FM.\r\nConclusions: With both ROI-based methods variability was low and repeatability was moderate. The circular\r\nmethod gave higher repeatability, but variation was slightly lower using the freehand method. The circular method\r\ncan be recommended for the posterior limb of the internal capsule and splenium of the corpus callosum, and the\r\nfreehand method for the corona radiata.
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