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
Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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