Myocardial Capillary Permeability to Iohexol

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Abstract
The accuracy and sensitivity of fast x-ray computed tomography (CT) for estimating myocardial capillary permeability to iohexol was evaluated. The long-term goal is to quantitate capillary integrity. Anesthetized pigs were scanned during coronary infusion of adenosine and an aortic root injection of iohexol. The CT images were used to compute myocardial perfusion (F) and capillary extraction factor (E). The permeability-surface area product (PS) was calculated as follows: PS = -F.ln(1-E). Accuracy of the PS value was evaluated with catheter-sampled dual-dilution curves (DDC) resulting from simultaneous injection of cobalt-58 EDTA and iodine-125 albumin. A second group of pigs was scanned while bradykinin (5, 10 or 20 ng/kg/min) was infused into the coronary artery. The DDC and CT-based PS values (mean +/- standard deviation) were as follows: 0.149 +/- 0.107, 0.125 +/- .067; 0.127 +/- 0.072, 0.129 +/- 0.053; and 0.132 +/- 0.043, 0.190 +/- 0.111 for 350, 230, and 175 mg iodine/mL, iohexol respectively. The regression was PS = 0.22 [bradykinin] + 0.083, r = .845. Dual-dilution curve-obtained and CT-obtained PS values are well correlated. The data show that concentration of iohexol has little (P > .1) impact on the calculated PS value and the bradykinin data suggest good sensitivity.

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