Better Imaging, Less Stress: Virtual Non-Contrast CT Proves Effective in Rabbits

Evaluation of virtual non-contrast detector-based spectral CT images in comparison to true unenhanced images in 20 rabbits

Manon Mikić, Philipp Lietz, Julie-Ann Dierig, Sebastian Meller, Michael Pees, Kristina Merhof

Background
Spectral detector computed tomography (SDCT) allows for the generation of virtual non-contrast (VNC) images from post-contrast scans by subtracting iodine, potentially reducing radiation exposure and scan time in high-risk patients like rabbits. While VNC techniques have been validated in dogs and humans, their performance in rabbits remained unexplored. This study aimed to assess the reliability of VNC images in comparison to true unenhanced (TUE) images for evaluating abdominal organs in 20 rabbits scanned without sedation.

Methods
This retrospective study included 20 client-owned rabbits that underwent abdominal SDCT scans with both TUE and post-contrast series. VNC images were reconstructed and compared to TUE images using 219 regions of interest (ROIs) across multiple organs. Quantitative equivalence was assessed using two one-sided t-tests (TOST) with thresholds of ≤5, ≤10, and ≤15 Hounsfield Units (HU). A qualitative evaluation of image quality and iodine subtraction was performed using 5-point Likert scales by two observers in consensus.

Results
The attenuation difference between VNC and TUE images was ≤15 HU in 72.1% of ROIs, ≤10 HU in 60%, and ≤5 HU in 30.7%. Statistically significant equivalence was demonstrated for the spleen at ≤5 HU, and additionally for the liver, musculature, and renal cortices at ≤10 and ≤15 HU. VNC image quality was rated high, with an average score of 4.2/5, and iodine subtraction was nearly complete (mean score 4.4/5). Best performance was observed in the liver, spleen, musculature, and caudal vena cava, with lower agreement in fat, bladder, and aorta due to biological and technical factors.

Limitations
Limitations include the small sample size, retrospective design, and the absence of histopathological confirmation to ensure true organ health. Motion artifacts from conscious scanning may have affected image alignment, and discrepancies in manual contrast injection timing could influence enhancement phases. The exclusion of patients with abnormal imaging findings also limits applicability to diseased tissues.

Conclusions
VNC images generated via SDCT in rabbits provided clinically acceptable alternatives to TUE scans for most abdominal structures, especially the spleen, liver, renal cortex, and musculature. This approach offers a promising means to reduce scan time, radiation exposure, and motion artifacts in sensitive patients. However, further studies involving pathological tissues are required to validate VNC application in diagnostic settings.

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