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

Area of Science:

• Radiology
• Medical Physics
• Radiation Dosimetry

Background:

• Computed tomography (CT) is crucial for brain imaging.
• Optimizing CT protocols is essential for minimizing radiation exposure.
• Brain perfusion CT protocols require careful parameter selection to balance diagnostic image quality and patient safety.

Purpose of the Study:

• To quantify organ and effective doses for a standard brain perfusion CT protocol.
• To estimate radiation doses for two erroneous brain perfusion CT protocols.
• To compare dose differences between standard and erroneous protocols.

Main Methods:

• Utilized an anthropomorphic phantom equipped with metal oxide semiconductor field effect transistor (MOSFET) detectors.
• Scanned the phantom using a 64-MDCT scanner.
• Evaluated three protocols: standard (80 kVp, 200 mA), high kVp (120 kVp, 200 mA), and high kVp with automatic tube current modulation (120 kVp, noise index 2.4).

Main Results:

• Protocol 2 (120 kVp) increased effective dose 2.8-fold compared to the standard protocol.
• Protocol 3 (120 kVp with auto-mA) increased effective dose 7.8-fold.
• Peak skin dose in Protocol 3 exceeded 3 Gy, and ocular lens doses were significantly elevated (up to 11.3 times higher).

Conclusions:

• Increasing tube potential from 80 kVp to 120 kVp in brain perfusion CT can increase organ doses three- to fivefold.
• Combining high peak kilovoltage with improperly programmed automatic tube current modulation can amplify organ doses seven- to 11-fold.
• Low noise index settings in tube current modulation may lead to skin and ocular lens doses approaching thresholds for tissue reactions.