2017 Imaging for Physicists Coursebook

CTDI

CTDI

vol

Now we have to take into account the fact that the table (for spiral examinations) is

actually moving. We define CTDI

vol

as:

CTDI

vol

reflects the dose that a 32 cm or 16 cm water phantom would absorb with the

specific scan settings.

Patient size plays an important role in estimating the effectively absorbed dose and

should be taken into account.

One way of doing it is to calculate the effective diameter of the patient and estimate the

aborbed dose via a proportion with the diameter of the phantom.

Effective dose is calculated as DLP*w, where the weight w depends on the body region

and the DLP is the CTDI multiplied by the scan lenght.