The diagnostic value of virtual unenhanced spectral CT images in acute pancreatitis: a comparison with true unenhanced images

To investigate whether virtual unenhanced (VUE) images generated from spectral CT using the rapid kVp switching technique can serve as a substitute for true unenhanced (TUE) images in the assessment of acute pancreatitis (AP). This retrospective study included 90 patients diagnosed with AP according to the Revised Atlanta Classification who underwent unenhanced non-spectral CT scan and dual-phase spectral CT scans of the abdomen. VUE images for the arterial (AP-VUE) and venous phases (VP-VUE) were reconstructed using material decomposition techniques. Objective and subjective assessments were conducted on TUE, AP-VUE, and VP-VUE images. The objective evaluation included CT attenuation, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). The subjective evaluation was performed by three readers independently and assessed image quality, lesion identification, severity grading of pancreatitis, and diagnostic confidence. CT attenuations differences between the TUE and VUE images were not significant for AP lesion (P = 0.110 (Pancreatitis) & 0.052 (Peripancreatic effusion)), with over 76.67% of anatomical regions showing differences within 10 HU. Compared with VP-VUE and AP-VUE images, TUE images demonstrated higher SNR and CNR overall. Diagnostic confidence scores were comparable across TUE, AP-VUE, and VP-VUE (confidence scores from 5(4, 5) to 5(5, 5), P from 0.439 to 1.000) and the diagnostic conclusions showed no significant differences as well (P > 0.05). The Balthazar CT grading system (A–E) demonstrated high concordance (Intraclass correlation coefficients > 0.8) across all image types, with no difference in AP severity assessment (P > 0.05). The diagnostic value of VUE images in AP is comparable to that of TUE images, suggesting that VUE images can serve as an alternative to reduce radiation exposure.