Quantifying lower extremity blood flow using low-dose CT perfusion: validation in a swine model.

Background: Quantitative assessment of blood flow in peripheral extremities in conjunction with simultaneous CT angiography measurements can improve risk assessment and provide a critical decision-making tool for patients across a wide spectrum of vascular disease severity.

Purpose: This study assessed the reproducibility and accuracy of lower extremity blood flow measurements with a low-dose first-pass analysis CT perfusion technique.

Materials and methods: This prospective study utilized 16 Yorkshire Swine to obtain lower extremity blood flow CT measurements at baseline and under induced femoral stenosis using a vascular occluder. Thirty-three pairs of CT measurements evaluated reproducibility, and 43 CT measurements assessed accuracy against ultrasound flow probe references. Contrast agent and saline chaser were both injected peripherally at a rate of 5 mL/s. Bolus tracking was used, and a pre-contrast and post-contrast helical scan were acquired at the base and approximately the peak of the femoral enhancement (CT angiogram), respectively. The acquired data were then used as analytical inputs into a first-pass analysis model to derive perfusion in mL/min/g. The reproducibility and accuracy of lower extremity perfusion measurements were assessed via Mixed model regression and Bland-Altman analysis.

Results: Calculated CT perfusion measurements derived from first-pass analysis technique (P _CT), and the reference standard ultrasound perfusion measurements (P _ref) were related by P _CT = 1.06 P _ref + 0.00 (r ² = 0.90, Root-Mean-Square Error [RMSE] = 0.01 mL/min/g). The first (P ₁) and second (P ₂) CT perfusion measurements were related by P ₂ = 0.98 P ₁ + 0.02 (r = 0.97, RMSE = 0.11 mL/min/g). The average effective dose of perfusion measurement using first-pass analysis technique was calculated to be only 2.13 mSv.

Conclusion: The low-dose quantitative CT perfusion technique can accurately measure lower extremity perfusion (mL/min/g) using only 2 helical scans. The CT angiogram and perfusion measurements can be used as a comprehensive technique for morphological and physiological assessment of limb ischemia.