Pseudoenhancement in Cystic Renal Lesions – Impact of Virtual Monoenergetic Images of Photon-Counting Detector CT on Lesion Classification

Abstract

To investigate the impact of virtual monoenergetic images (VMI) from photon-counting detector CT (PCD-CT) on the enhancement and classification of renal cysts. Adults with renal cysts (≥7mm) who received a triphasic examination on a clinical PCD-CT (120kVp; IQ level 68) between July 2021 and March 2022 were retrospectively identified. Only non-enhancing cysts (enhancement<10HU between unenhanced and venous phase at 70keV) were included. VMI from 40 to 190keV with increments of 10keV were reconstructed from the venous phase. Enhancement was measured to classify each lesion as non-enhancing (<10HU), equivocally enhancing (10-19HU), and definitely enhancing (≥20HU). Classification changes as a function of VMI were assessed. Pearson correlation coefficient, the Kruskal-Wallis and the Chi-square test were used. A total of 86patients (mean age, 74±9 years; 74 male) with 160 non-enhancing renal cysts (17.6±10mm) were included. CT attenuation of the cysts increased from higher to lower VMI levels with a mean attenuation of 4±11HU at 190keV to 36±17HU at 40keV. Mean attenuation of the renal parenchyma was 43±4HU at 190keV and 414±71HU at 40keV. No cyst exhibited enhancement from 70keV to 190keV. At 40, 50, and 60keV, 35% (56/160), 29% (47/160) and 9% (15/160) of cysts showed equivocal and 46% (74/160), 10% (16/160), and 0% (0/160) definite enhancement, respectively. There was no significant influence of size (P=.13), cyst location (P=.9) and BMI (P=.19) on enhancement classification. VMI has a relevant impact on enhancement and classification of renal cysts with misclassification in a large number of cases at energy levels below 70keV.