Preoperative radiographic evaluation of implant sites by computed tomography. Radiation dose profiles.

The purpose of the present study was to compare radiation dose profiles for one and two mm slice thicknesses typically used for preoperative computed tomographic examination of potential implant sites. A Siemens Somatom DRH CT-system was used. A single two mm slice absorbed only 29% of the integral dose and a single one mm slice, absorbed only 17% of the integral dose. This is because the radiation beam was unchanged between the two different examinations. The integral dose is therefore identical for a single one mm slice and for a single two mm slice. When 10 consecutively two mm thick slices were exposed, approximately 50% of the integral dose was absorbed within the examined region. When 20 one mm thick slices were exposed, slightly less of the integral dose was absorbed within the examined region. This difference may be explained by uncertaines in the measuring instruments. The integral dose is, with the 10 two mm thick slices, half the integral dose compared to a serie of 20 one mm slices. In spite of a well restricted beam, more than half of the integral dose is absorbed outside the examined part. Consequently, during examination the thyroid gland, the eyes lens and the pituitary gland will be exposed to some irradiation.