The radiation dose to patients from EMI brain and body scanners

Absorbed doses throughout the head of a Rando standard man phantom have been measured with lithium borate thermoluminescent dosimeters during simulated neurological examinations with the EMI Mk 1 brain scanner and the second generation CT1010 brain scanner. Similar measurements have been made with the CT 5005 which have also included scans through thoracic and abdominal sections of the phantom. Results are reported for both the standard and high accuracy scan speed options on the two scanners where this choice is available. Maximum skin doses varied from 30 to 50 mGy (3.0 to 5.6 rad) being highest for the CT 1010 scanner. Use of the high accuracy scan option increased the energy imparted and the maximum skin dose by a factor of about five, while providing much enhanced tissue density discrimination. The values of energy imparted are compared with those associated with conventional radiographs. Recent work by EMI involving further refinements to the collimation system has reduced the dose levels by typically 50%. Some preliminary results with this new system are included to indicate the likely degree of improvement. (author)