Thyroid exposure in brain CT-scan and skull X-ray, using different levels of mA and Kvp with and without thyroid shield

Nowadays, thyroid exposure is a major concern in skull radiological imaging. The aim of this study was to evaluate thyroid exposure in brain CT-scan and skull X-ray, using different levels of Kvp (Kilovoltd peak) and mA, with and without thyroid shield. In this descriptive- analytic study, 350 outpatients were selected randomly. Two TLD-100 chips (Thermo Luminescence Dosimeter) were placed on the thyroid of each patient. Three levels of mA were applied in brain CT-scan (210 patients) and two levels of Kvp were used in routine skull X-rays (140 patients). The experiments were performed with and without thyroid shield. The TLDs were read and the statistical analysis was performed using student-t test. During brain CT-scan, decreasing current intensity from 150 to 125 mA, significantly decreased the thyroid exposure from 101±9.38 to 82.2±8.04 mili rem (P<0.01). Using a thyroid shield extremely reduced the thyroid exposure to 29±5.83 mili rem (P<0.01). In routine skull x-rays, increasing voltage from 60 to70 Kvp, significantly decreased the thyroid exposure from 72.6±7.74 to 67±8.41 mili rem (P<0.05). Moreover, using the thyroid shield remarkably reduced the thyroid exposure to 19.6±1.82 mili rem (P<0.05). Using lower levels of mA in brain CT-scans and higher levels of Kvp in skull X-rays, decrease thyroid exposure. Furthermore, using thyroid shield during X-ray examinations of the skull remarkably reduces thyroid exposure.