In 86 patients with 160 non-enhancing renal cysts, the study assessed how PCCT virtual monoenergetic image (VMI) energy level affects apparent renal cyst enhancement and therefore lesion classification.
Low-keV VMI substantially increased apparent cyst attenuation: mean attenuation rose from 4 ± 11 HU at 190 keV to 36 ± 17 HU at 40 keV.
This produced marked pseudoenhancement at low energies: at 40 keV, 35% of cysts appeared equivocally enhancing and 46% definitely enhancing; at 50 keV, these rates were 29% and 10%, respectively. At 60 keV, 9% were equivocal but none definitely enhancing.
Importantly, no cyst was classified as enhancing at 70–190 keV, indicating that ≥70-keV VMI provides substantially more reliable assessment of true renal cyst enhancement.
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Practical PCCT takeaway:
Low-keV reconstructions are attractive for increasing iodine conspicuity, but they should not be used uncritically for HU-based renal lesion characterization. For renal cyst enhancement, 70 keV appears to be a safer reference reconstruction in this study.
The observed misclassification was not significantly dependent on cyst size, location, or patient BMI, suggesting that the VMI energy itself is the dominant issue.
Protocol:
Clinical PCCT, 120 kVp, image-quality level 68; triphasic examination. Venous-phase VMIs were reconstructed from 40–190 keV in 10-keV increments. Only cysts ≥7 mm confirmed as non-enhancing (<10 HU difference between unenhanced and venous 70-keV images) were analyzed.
Source: Schade KA, Mergen V, Sartoretti T, Alkadhi H, Euler A. Pseudoenhancement in Cystic Renal Lesions – Impact of Virtual Monoenergetic Images of Photon-Counting Detector CT on Lesion Classification. Academic Radiology. 2023;30(Suppl 1):S305-S313. doi:10.1016/j.acra.2023.04.005. Published online May 5, 2023.
