Hybrid [18F]-FDG PET/MRI including non-Gaussian diffusion-weighted imaging (DWI): Preliminary results in non-small cell lung cancer (NSCLC)

PurposeTo assess the feasibility of non-Gaussian DWI as part of a FDG-PET/MRI protocol in patients with histologically proven non-small cell lung cancer.Material and methods15 consecutive patients with histologically proven NSCLC (mean age 61 ± 11 years) were included in this study and underwent whole-body FDG-PET/MRI following whole-body FDG-PET/CT. As part of the whole-body FDG-PET/MRI protocol, an EPI-sequence with 5 b-values (0, 100, 500, 1000 and 2000 s/mm2) was acquired for DWI of the thorax during free-breathing. Volume of interest (VOI) measurements were performed to determine the maximum and mean standardized uptake value (SUVmax; SUVmean). A region of interest (ROI) was manually drawn around the tumor on b = 0 images and then transferred to the corresponding parameter maps to assess ADCmono, Dapp and Kapp. To assess the goodness of the mathematical fit R2 was calculated for monoexponential and non-Gaussian analysis. Spearman's correlation coefficients were calculated to compare SUV values and diffusion coefficients. A Student's t-test was performed to compare the monoexponential and non-Gaussian diffusion fitting (R2).ResultsT staging was equal between FDG-PET/CT and FDG-PET/MRI in 12 of 15 patients. For NSCLC, mean ADCmono was 2.11 ± 1.24 × 10−3 mm2/s, Dapp was 2.46 ± 1.29 × 10−3 mm2/s and mean Kapp was 0.70 ± 0.21. The non-Gaussian diffusion analysis (R2 = 0.98) provided a significantly better mathematical fitting to the DWI signal decay than the monoexponetial analysis (R2 = 0.96) (p < 0.001). SUVmax and SUVmean of NSCLC was 13.5 ± 7.6 and 7.9 ± 4.3 for FDG-PET/MRI. ADCmono as well as Dapp exhibited a significant inverse correlation with the SUVmax (ADCmono: R = −0.67; p < 0.01; Dapp: R = −0.69; p < 0.01) as well as with SUVmean assessed by FDG-PET/MRI (ADCmono: R = −0.66; p < 0.01; Dapp: R = −0.69; p < 0.01). Furthermore, Kapp exhibited a significant correlation with SUVmax (R = 0.72; p < 0.05) and SUVmean as assessed by FDG-PET/MRI (R = 0.71; p < 0.005).ConclusionSimultaneous PET and non-Gaussian diffusion acquisitions are feasible. Non-Gaussian diffusion parameters show a good correlation with SUV and might provide additional information beyond monoexponential ADC, especially as non-Gaussian diffusion exhibits better mathematical fitting to the decay of the diffusion signal than monoexponential DWI.