MEASUREMENT OF ABSOLUTE BLOOD IODINE CONCENTRATION DURING DIGITAL SUBTRACTION VENTRICULOGRAPHY

A system to measure the absolute iodine concentration (mg iodine/milli liter blood) in the left ventricle (LV) during digital subtraction ven triculography has been developed. The technique uses a catheter to dra w blood from the LV through a detection cell. This occurs as the iodin e bolus passes through the heart. The cell determines iodine concentra tion by measuring x-ray attenuation as the iodinated blood passes betw een a low-power x-ray tube and a diode detector. In vitro and in vivo testing of the system was conducted. The system response was linear (r = 0.99) with respect to iodine concentration. This response was indep endent of hematocrit. Dispersion of contrast medium in the catheter ca used distortion of the shape of the time-concentration curve. The impu lse response of the system was measured and found to be independent of hematocrit. A correction algorithm based on Wiener filter deconvoluti on was developed. In vitro testing using simulated time-concentration curves demonstrated that the rms error in the iodine measurement after dispersion correction did not exceed 4% over the region of the time-c oncentration curve extending from the peak to the point on the tail wh ere the signal fell to 50% of its peak value. Cardiac output was measu red from the time-concentration curve via the indicator-dilution metho d in an animal model. This cardiac output measurement (CO(I)) agreed c losely with cardiac output measured simultaneously with an aortic flow probe (CO(P)), namely, CO(I) = 1.02 CO(P)-0.03 L/min, r = 0.95, SEE = 10%, p < 0.001. The application of the blood iodine concentration mea surement to the densitometric measurement of absolute LV volume from d igital subtraction angiography (DSA) images is discussed.