Zhiyue J Wang1, Jonathan M Chia2, Shaheen Ahmed3, Nancy K Rollins3. 1. Department of Radiology, Children's Medical Center, Dallas, Texas 75235 and Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390. 2. Clinical Science, Philips Healthcare, Cleveland, Ohio 44143. 3. Department of Radiology, Children's Medical Center, Dallas, TX 75235 and Department of Radiology, University of Texas Southwestern Medical Center, Dallas, TX 75390.
Abstract
PURPOSE: To describe a quantitative method for determination of SNR that extracts the local noise level using a single diffusion data set. METHODS: Brain data sets came from a multicenter study (eight sites; three MR vendors). Data acquisition protocol required b=0, 700 s/mm2, fov=256×256 mm2, acquisition matrix size 128×128, reconstruction matrix size 256×256; 30 gradient encoding directions and voxel size 2×2×2 mm3. Regions-of-interest (ROI) were placed manually on the b=0 image volume on transverse slices, and signal was recorded as the mean value of the ROI. The noise level from the ROI was evaluated using Fourier Transform based Butterworth high-pass filtering. Patients were divided into two groups, one for filter parameter optimization (N=17) and one for validation (N=10). Six white matter areas (the genu and splenium of corpus callosum, right and left centrum semiovale, right and left anterior corona radiata) were analyzed. The Bland-Altman method was used to compare the resulting SNR with that from the difference image method. The filter parameters were optimized for each brain area, and a set of "global" parameters was also obtained, which represent an average of all regions. RESULTS: The Bland-Altman analysis on the validation group using "global" filter parameters revealed that the 95% limits of agreement of percent bias between the SNR obtained with the new and the reference methods were -15.5% (median of the lower limit, range [-24.1%, -8.9%]) and 14.5% (median of the higher limits, range [12.7%, 18.0%]) for the 6 brain areas. CONCLUSIONS: An FT-based high-pass filtering method can be used for local area SNR assessment using only one DTI data set. This method could be used to evaluate SNR for patient studies in a multicenter setting.
PURPOSE: To describe a quantitative method for determination of SNR that extracts the local noise level using a single diffusion data set. METHODS: Brain data sets came from a multicenter study (eight sites; three MR vendors). Data acquisition protocol required b=0, 700 s/mm2, fov=256×256 mm2, acquisition matrix size 128×128, reconstruction matrix size 256×256; 30 gradient encoding directions and voxel size 2×2×2 mm3. Regions-of-interest (ROI) were placed manually on the b=0 image volume on transverse slices, and signal was recorded as the mean value of the ROI. The noise level from the ROI was evaluated using Fourier Transform based Butterworth high-pass filtering. Patients were divided into two groups, one for filter parameter optimization (N=17) and one for validation (N=10). Six white matter areas (the genu and splenium of corpus callosum, right and left centrum semiovale, right and left anterior corona radiata) were analyzed. The Bland-Altman method was used to compare the resulting SNR with that from the difference image method. The filter parameters were optimized for each brain area, and a set of "global" parameters was also obtained, which represent an average of all regions. RESULTS: The Bland-Altman analysis on the validation group using "global" filter parameters revealed that the 95% limits of agreement of percent bias between the SNR obtained with the new and the reference methods were -15.5% (median of the lower limit, range [-24.1%, -8.9%]) and 14.5% (median of the higher limits, range [12.7%, 18.0%]) for the 6 brain areas. CONCLUSIONS: An FT-based high-pass filtering method can be used for local area SNR assessment using only one DTI data set. This method could be used to evaluate SNR for patient studies in a multicenter setting.
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