The Application of Catheter-type Semiconductor Radiation Detector (CASRAD) to the Pulmonary Function Studies

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Abstract
A new approach to the measurement of pulmonary function was attempted by the use of catheter-type semiconductor radiation detector (CASRAD). When Kr85 dissolved in normal saline solution is injected as a bolus intravenously, the maximum counting rate obtained in a particular bronchus is a reflection of the amount of pulmonary blood flow and the subsequent washout rate, that of ventilatory efficiency of that lobe. From the basic and model experiments, it is concluded that the ratio of Kr85 counting rates in different bronchi measured by CASRAD can be compared as the concentration ratio of Kr85 if these bronchi are similar in size. Three dogs were used for animal experiments. Kr85 solution was injected as a bolus into the right side of the heart and the counting rate was measured in the upper and the lower lobe bronchus where CASRAD was placed respectively. The maximum counting rates were essentially the same in the upper and the lower lobe bronchus for the supine position, while they tended to get higher in the lower lobe for the head-up position. This phenomenon was explained by the increase of perfusion to the dependent zone of the lung due to the gravity. The approximation of the perfusion ratio between the upper and the lower lobe by the ratio of the maximum counting rate was also attempted. When washout rates of Kr85 in the upper and the lower lobe were compared, there was no significant difference between them whether the dogs were placed supine or head-up. As a preliminary study for the clinical application, CASRAD was used for the measurement of ventilatory efficiency, lobar function, and for the bronchospirometry. The clinical applicability was confirmed. The advantages and limitations were discussed comparing CASRAD with the external counting method.

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