Purpose: To evaluate the feasibility of helical computed tomography (CT) as an imaging modality for depicting active colonic hemorrhage in a swine model.
Materials and methods: Controlled extravasation of contrast material-enhanced blood (CEB) from 140 to 180 HU and at varying rates (0.3-1.0 mL/min) was performed during a 30-second period by using a microcatheter system placed within the descending colon of 14 swine. CEB was immediately followed by extravasation of unopacified blood at the same location and rate during serial helical CT imaging of the extravasation site. Region-of-interest analysis allowed quantification of the dilution of extravasated CEB as a function of time that was then modeled mathematically based on iodine mass and volume balances. Nonlinear least squares analysis was performed to optimize fitting of the model to experimental data, with a maximum regression value (R2) of 1.0 indicating a perfect fit. This model enabled the computer simulation of CT imaging of multiple combinations of bleeding rates and CEB attenuation to determine the sensitivity of helical CT for depicting active colonic bleeding.
Results: Sixteen swine examinations yielded 16 CEB dilution curves. An excellent fit of the model to each dilution curve was achieved, as indicated by a mean R2 value of 0.8402. Swine examinations alone showed that targeted CT could depict CEB as low as 111 HU extravasating at a rate of 0.3 mL/min. Simulations that were based on helical CT images with 5-mm collimation reconstructed every 3 mm and that used the model indicated bleeding rates below 0.4 mL/min are detectable, provided peak aortic enhancement reaches 100 HU.
Conclusion: Conservatively, helical CT has the potential to depict active colonic hemorrhage at rates of 0.5 mL/min or less.