PT  - JOURNAL ARTICLE
AU  - Adams, Lisa C.
AU  - Bressem, Keno K.
AU  - Brangsch, Julia
AU  - Reimann, Carolin
AU  - Nowak, Kristin J.
AU  - Brenner, Winfried
AU  - Makowski, Marcus R.
TI  - Quantitative 3D assessment of <sup>68</sup>Ga-DOTATOC PET/MRI with diffusion-weighted imaging to assess imaging markers for gastroendopancreatic neuroendocrine tumors: Preliminary results
AID  - 10.2967/jnumed.119.234062
DP  - 2019 Dec 01
TA  - Journal of Nuclear Medicine
PG  - jnumed.119.234062
4099  - http://jnm.snmjournals.org/content/early/2019/12/20/jnumed.119.234062.short
4100  - http://jnm.snmjournals.org/content/early/2019/12/20/jnumed.119.234062.full
AB  - 68Ga-DOTATOC-PET/MRI (68Gallium-DOTATOC-positron emission tomography/magnetic resonance imaging) combines the advantages of PET in the acquisition of metabolic-functional information with the high soft tissue contrast of MRI. Standardized uptake values (SUV) in tumors were suggested as a measure of somatostatin receptor expression. A challenge with receptor ligands is, that the distribution volume is confined to tissues with tracer-uptake, potentially limiting SUV quantification. In this study, different functional, three-dimensional (3D) SUV, apparent diffusion coefficient (ADC) parameters and arterial tumor enhancement were tested for the characterization of gastroendopancreatic neuroendocrine tumors (GEP-NET). Methods: For this single-center, cross-sectional study, 22 patients with 24 histologically confirmed GEP-NET lesions (15 men/7 women; median, 61 years, range, 43-81 years), who received hybrid 68Ga-DOTA-PET/MRI examinations at 3T between January 2017 and July 2019 met eligibility criteria. SUVs, tumor-to-background ratios (TBR), the total functional tumor volume (TFTV), ADCmean and ADCmin were measured based on volumes of interest (VOI) and examined with receiver operating characteristic analysis to determine cut-off values for differentiation between low and intermediate grade GEP-NET. Spearman’s rank correlation coefficients were used to assess correlations between functional imaging parameters. Results: The ratio of PET-derived SUVmean and diffusion-weighted imaging (DWI)-derived ADCmin was introduced as a combined variable to predict tumor grade, outperforming single predictors. Based on a threshold ratio of 0.03 to be exceeded, tumors could be classified as grade 2 with a sensitivity of 86% and specificity of 100%. SUV and functional ADC values as well as arterial contrast enhancement parameters showed non-significant and mostly negligible correlations. Conclusion: As receptor density and tumor cellularity appear to be independent, potentially complementary phenomena, the combined PET/MRI ratio SUVmean/ADCmin may be used as a novel biomarker, allowing to differentiate between grade 1 and 2 GEP-NET.