Noninvasive Determination of Arterial Input of 15O Tracers, Using a Dual Cutaneous β-Detector Set above the Radial Artery

As the clinical use of positron emission tomography technology grows, so does the demand for noninvasive measurement of cerebral blood flow (CBF). This chapter presents the development of a compact radiation monitor composed of dual β-detectors suitable for the detection of radiation from superficial tissue. One detector is placed over the wrist above the radial artery to monitor arterial radioactivity, whereas another was placed on an adjacent skin area to measure the background. The monitor worked fairly well except on obese subjects, for whom an arterial count curve was not recoverable. A model has been developed to restore the arterial input function comparing the two-detector response with time that incorporated the superficial tissue flow, mainly of skin and the subcutaneous tissue. Twenty-four studies on five normal volunteers are conducted with [ 15 O]-water slow bolus injections, which are controlled by an automatic injection system. A significant correlation is obtained between the calculated CBF using restored input function by the system and the CBF using an actual arterial input curve by arterial cannulation. Further, refinement of the procedures that include the calibration of restored arterial input to well counter and accurate correction of dispersion in the restored arterial input may increase the accuracy of this noninvasive method.