الفهرس 
Introduction and aim of the workOnly 14 pages are availabe for public view
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Abstract
Recent technological advances in Magnetic Resonance instrumentation allow acquisition of whole-brain diffusion-weighted MR scans with b-values greater than 1000 s/mm2 without prohibitive signal-to-noise degradation. Our purpose was to demonstrate the DROP in the apparent diffusion coefficient (ADC) measurements in brain from low to high b-values, and to establish references for the signal intensity characteristics of normal human brains. In the present work, the precision of measurements of ADC was studied by diffusion-weighted Magnetic Resonance Imaging (MRI). This precision was calculated as signal-to-noise ratio (SNR) and described in the resultant ADC in terms of a diffusion-to-noise ratio (DNR). Brain MRI was taken for all subjects including diffusion-weighted echo-planar imaging in axial direction with four b-values of (0, 500, 1000, and 1500 s/mm2) at 1.5 T unit. In this acquisition, a 2-point technique at a b-value of 0 & b-values of 500, 1000, and 1500 s/mm2 was considered. Increasing b-values result in a progressive decrease in the signal intensity ratio of gray to white matter, and also decrease in ADC value. Attention to the reversal of gray-white signal intensity ratio and the dependence of ADC on the b-value are important in avoiding erroneous assignment of pathologic abnormalities to normal regions. In the present work, Results show an irregular decrease in the signal intensity, and also in ADC value. Thus, we tend to study the effect of other parameters on ADC value, and signal intensity. Few studies have concerned the effect of aging, gender, and laterality on ADC values in the normal human brain. Therefore, our purpose was to determine whether the average ADC (ADCav) values in the various regions of the brain differ with age, sex, or hemisphere (left or right). Our results show that, as for any age or any sex, the ADCav values were highest in the gray matter, and lowest in the white matter. The ADCav values in the left side of white matter were higher than that in the right side, and vice versa in gray matter. In the comparison between men and women, the men showed higher ADCav values than the women. Finally, the data obtained from the present study may be helpful, and significant, and the ADCav values can be used for reference in future diffusion investigations performed at high b-values and in clinical settings.