CTDI

Tratto dall'articolo: CT Dosimetry: Comparison of Measurement Techniques and Devices 

John A. Bauhs, PhD ● Thomas J. Vrieze, RT(R) ● Andrew N. Primak, PhD ● Michael R. Bruesewitz, RT(R) ● Cynthia H. McCollough, PhD

RadioGraphics Volume 28 • Volume 1 • January-February 2008

The CTDI is a simple, standardized measure of the dose output of a CT scanner that can be used to compare different scan techniques on a single scanner or between scanners. CTDI is an averaged dose to a standard phantom from a multiple scan examination where the patient table is incremented between scans. Besides the ionization chamber measurement method, equivalent methods have been developed that use alternative dosimeters, including an OSL probe and a solid-state, real-time dosimeter. Variations of CTDI have been developed to represent the CTDI averaged over the field of view (CTDIw) and corrected for overlaps or gaps between scans (CTDIvol).

Because the CTDI is an averaged dose to a homogeneous cylindrical phantom, the measurements are only an approximation of patient dose.

Another limitation is that CTDI overestimates dose for scans where the patient table is not incremented, such as in interventional and perfusion CT. For these CT applications, the CTDI can overestimate peak dose by a factor of two. Therefore, point dose measurements made with dosimeters with small active volumes are necessary to determine skin doses from interventional and perfusion examinations.