Answer to Question #13118 Submitted to "Ask the Experts"

Category: Medical and Dental Patient Issues — Diagnostic X Ray and CT

The following question was answered by an expert in the appropriate field:

Q

I want to better understand information I received from a computed tomography (CT) scan I had recently. I went to the emergency room for possible kidney stones. A CT was ordered. At the top of the image, it said "multiplanar + VRT (act. series) other series." The report indicates the procedure did not include a "scout scan." The report provided a CTDIvol, and DLP then says "phantom CM of body 32." I am not sure what "multiplanar + VRT," "scout," or "phantom CM of body 32" mean.

A

The terms "multiplanar" and "VRT" are associated with creating a 3-D image. When CT is used to confirm kidney stones, not only is it possible to tell whether they exist, but it is also possible to tell their composition and possible treatment (e.g., susceptibility to ultrasonic lithotripsy), and any underlying kidney disease or damage. This additional information, however, requires higher radiation output of the CT scanner. An analogy is a digital camera—under low light conditions, the image resolution is much grainier than when there is more light reaching the image receptor.

A "scout scan" is a low dose scan to find the best places to start and stop the actual diagnostic scan. 

The term "CTDIvol" stands for CT dose index volume. The "phantom CM of body" means that the CTDIvol was measured in a 32 cm diameter acrylic phantom which is standard for representing CT scans of the body. A 16 cm diameter phantom is used to represent the adult head and pediatric bodies. 

Kent Lambert, CHP, FHPS

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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