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Estimation of Optimal B-Value Set for Obtaining Apparent Diffusion Coefficient Free From Perfusion in Non-Small Cell Lung Cancer

K Karki

K Karki¹*, G Hugo¹ , J Ford¹ , K Olsen² , S Saraiya¹ , R Groves² , E Weiss¹ , (1) Radiation Oncology, Virginia Commonwealth University, Richmond, VA, (2) Radiology, Virginia Commonwealth University, Richmond, VA

Presentations

WE-G-18C-2 Wednesday 4:30PM - 6:00PM Room: 18C

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 (ADC_IVIM) in non-small 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=1.98X1.98mm², slice thickness=4-6mm and 7 axial slices. Diffusion gradients were applied to all three axes producing trace-weighted images with eight b-values of 0-1000μs/μm². Monoexponential model ADC values using various b-value sets were compared to ADC_IVIM 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: ADC_IVIM, perfusion coefficient and perfusion fraction for tumor volumes were in the range of 880-1622 μm²/s, 8119-33834 μm²/s and 0.104-0.349, respectively. ADC values using sets of 250, 800 and 1000; 250, 650 and 1000; and 250-1000μs/μm² only were not significantly different from ADC_IVIM(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/μm² were 15.0, 9.4, 5.6, 1.4, 11.7, 3.7, 2.0 and 0.2% relative to the reference-standard ADC_IVIM, respectively. Mean intra-scan CV was 20.2, 20.9, 21.9, 24.9, 32.6, 25.8, 25.4 and 24.8%, respectively, whereas that for ADC_IVIM was 23.3%.

Conclusion: ADC values of two 3 b-value sets (250, 650 and 1000; and 250, 800 and 1000μs/μm²) approached ADC_IVIM, with relative noise comparable to that of ADC_IVIM. These sets may be used to obtain perfusion-insensitive ADC values in lung tumors.

Funding Support, Disclosures, and Conflict of Interest: E. Weiss: Funding through Varian Medical Systems and Philips Oncology Systems, UpToDate royalties. G. Hugo: NIH R01CA166119 , P01 CA116602, NHMRC Project Grant. There are no conflicts of interest.


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