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WE‐G‐18C‐02: Estimation of Optimal B‐Value Set for Obtaining Apparent Diffusion Coefficient Free From Perfusion in Non‐Small Cell Lung Cancer
Author(s) -
Karki K,
Hugo G,
Ford J,
Olsen K,
Saraiya S,
Groves R,
Weiss E
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4889521
Subject(s) - intravoxel incoherent motion , effective diffusion coefficient , nuclear medicine , perfusion , coefficient of variation , diffusion mri , medicine , magnetic resonance imaging , nuclear magnetic resonance , mathematics , radiology , physics , statistics
Purpose: Diffusion‐weighted MRI (DW‐MRI) is increasingly being investigated for radiotherapy planning and response assessment. Selection of a limited number of b‐values in DW‐MRI is important to keep geometrical variations low and imaging time short. We investigated various b‐value sets to determine an optimal set for obtaining monoexponential apparent diffusion coefficient (ADC) close to perfusion‐insensitive intravoxel incoherent motion (IVIM) model ADC (ADCIVIM) in nonsmall cell lung cancer. Methods: Seven patients had 27 DW‐MRI scans before and during radiotherapy in a 1.5T scanner. Respiratory triggering was applied to the echo‐planar DW‐MRI with TR=4500ms approximately, TE=74ms, pixel size=1.98×1.98mm 2 , slice thickness=4–6mm and 7 axial slices. Diffusion gradients were applied to all three axes producing traceweighted images with eight b‐values of 0–1000μs/μm 2 . Monoexponential model ADC values using various b‐value sets were compared to ADCIVIM using all b‐values. To compare the relative noise in ADC maps, intra‐scan coefficient of variation (CV) of active tumor volumes was computed. Results: ADCIVIM, perfusion coefficient and perfusion fraction for tumor volumes were in the range of 880‐1622 μm 2 /s, 8119‐33834 μm 2 /s and 0.104–0.349, respectively. ADC values using sets of 250, 800 and 1000; 250, 650 and 1000; and 250–1000μs/μm 2 only were not significantly different from ADCIVIM(p>0.05, paired t‐test). Error in ADC values for 0–1000, 50–1000, 100–1000, 250–1000, 500–1000, and three b‐value sets‐ 250, 500 and 1000; 250, 650 and 1000; and 250, 800 and 1000μs/μm 2 were 15.0, 9.4, 5.6, 1.4, 11.7, 3.7, 2.0 and 0.2% relative to the reference‐standard ADCIVIM, respectively. Mean intrascan CV was 20.2, 20.9, 21.9, 24.9, 32.6, 25.8, 25.4 and 24.8%, respectively, whereas that for ADCIVIM was 23.3%. Conclusion: ADC values of two 3 b‐value sets (250, 650 and 1000; and 250, 800 and 1000μs/μm 2 ) approached ADCIVIM, with relative noise comparable to that of ADCIVIM. These sets may be used to obtain perfusion‐insensitive ADC values in lung tumors. E. Weiss: Funding through Varian Medical Systems and Philips Oncology Systems, UpToDate royalties. G. Hugo: NIH R01CA166119, P01 CA116602, NHMRC Project Grant.