Estimation of radiation exposure for brain perfusion CT: standard protocol compared with deviations in protocol.

Objective: The purpose of this study was to measure the organ doses and estimate the effective dose for the standard brain perfusion CT protocol and erroneous protocols.

Materials And Methods: An anthropomorphic phantom with metal oxide semiconductor field effect transistor (MOSFET) detectors was scanned on a 64-MDCT scanner. Protocol 1 used a standard brain perfusion protocol with 80 kVp and fixed tube current of 200 mA. Protocol 2 used 120 kVp and fixed tube current of 200 mA. Protocol 3 used 120 kVp with automatic tube current modulation (noise index, 2.4; minimum, 100 mA; maximum, 520 mA).

Results: Compared with protocol 1, the effective dose was 2.8 times higher with protocol 2 and 7.8 times higher with protocol 3. For all protocols, the peak dose was highest in the skin, followed by the brain and calvarial marrow. Compared with protocol 1, the peak skin dose was 2.6 times higher with protocol 2 and 6.7 times higher with protocol 3. The peak skin dose for protocol 3 exceeded 3 Gy. The ocular lens received significant scatter radiation: 177 mGy for protocol 2 and 435 mGy for protocol 3, which were 4.6 and 11.3 times the dose for protocol 1, respectively.

Conclusion: Compared with the standard protocol, erroneous protocols of increasing the tube potential from 80 kVp to 120 kVp will lead to a three- to fivefold increase in organ doses, and concurrent use of high peak kilovoltage with incorrectly programmed tube current modulation can increase dose to organs by 7- to 11-fold. Tube current modulation with a low noise index can lead to doses to the skin and ocular lens that are close to thresholds for tissue reactions.