Calibration of X-ray Fluorescence Thyroid Imaging System

X-ray fluorescence (XRF) has been used for in vivo measurement and imaging of intra-thyroidal stable iodine (¹²⁷I) for more than 25 years. Methodological problems limit the accuracy of non invasive measurement of iodine contained in large glands and glands with very low thyroid iodine content (TIC). Inaccuracy results from difficulties in correcting for spatial variations in the shape of the irradiating field, the fluorescent x-ray emission distribution, the detector response profile and the effects of attenuation as well as variations in the size, shape and location of the thyroid gland. We report a method which takes geometry and sensitivity factors into account in the calibration of the TIC measurement system. In this report, we present results of a pilot study utilizing detailed information on the XRF system spatial response characteristics. We use knowledge of the size, shape and location of the thyroid gland obtained from other means such as ultrasound to illustrate how the method can be used clinically.