Quantitative differentiation of minimal-fat angiomyolipomas from renal cell carcinomas using grating-based x-ray phase-contrast computed tomography: an ex vivo study

Background The differentiation of minimal-fat--or low-fat--angiomyolipomas from other renal lesions is clinically challenging in conventional computed tomography. In this study, we have assessed the potential of grating-based phase-contrast computed tomography imaging (GBPC-CT) for visualization and quantitative differentiation of minimal-fat angiomyolipomas (mfAMLs) and oncocytomas from renal cell carcinomas (RCCs) on ex vivo renal samples. Materials and methods Laboratory GBPC-CT was performed at 40 kVp on 28 ex vivo kidney specimens including five angiomyolipomas with three minimal-fat (mfAMLs) and two high-fat (hfAMLs) subtypes as well as three oncocytomas and 20 RCCs with eight clear cell (ccRCCs), seven papillary (pRCCs) and five chromophobe RCC (chrRCC) subtypes. Quantitative values of conventional Hounsfield units (HU) and phase-contrast Hounsfield units (HUp) were determined and histogram analysis was performed on GBPC-CT and grating-based attenuation-contrast computed tomography (GBAC-CT) slices for each specimen. For comparison, the same specimens were imaged at a 3T MRI scanner Results We have successfully matched GBPC-CT images with clinical MRI and histology, as GBPC-CT allowed for improved soft tissue contrast compared to absorption-based images revealing more histological details in the same sections. GBPC-CT images revealed a significant (p<0.05) difference between mfAML samples (58{+/-}4 HUp), hfAML (-58{+/-}17 HUp) and RCCs (clear cell RCCs: 40{+/-}12 HUp; papillary RCCs: 43{+/-}9 HUp; chromophoe RCCs: 40{+/-}7 HUp) in contrast to corresponding laboratory attenuation-contrast CT and clinical MRI. Due to the heterogeneity and lower signal of oncocytomas (44{+/-}10 HUp), quantitative differentiation of the samples based on HUp or in combination with HUs was not possible. Conclusions Our GBPC-CT results allowed quantitative differentiation of minimal-fat angiomyolipomas from oncocytomas and RCCs in contrast to absorption-based imaging and clinical MRI.