Answer to Question #8455 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
- Which modality has the highest leakage radiation—fluoroscopy at 2.58 × 10-5 coulomb per kilogram per hour (C h kg-1) at 1 meter (m) or computed tomography (CT)?
- Is CT dose measured by CT dose index (CTDI), CTDI volume (CTDIvol), or effective dose?
- All x-ray tubes are restricted to a leakage radiation limit of < 2.58 × 10-5 C h kg-1 at 1 m from the tube housing.
- With the advent of multidetector CT (MDCT), adding table translation into the equation, we now have to consider "pitch" as a contributing factor to dose, either overscanning (pitch <1) or underscanning (pitch >1). Without pitch, the CT dose is the weighted CTDI or (CTDIw), which is just [(2 × peripheral exposure)/3] + (central exposure/3). But with helical scanning the CT dose is CTDIw/pitch.
Kishor M. Patel, PhD, DABR
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