Answer to Question #13560 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment and Shielding — Equipment

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

Q

I wanted to ask about diagnostic reference levels (DRLs) for computed tomography (CT) scans. Are the DRLs preset by manufacturers, like Siemens CT scanners have protocols for each scan? Are the computed tomography dose index (CTDI) values preset while considering DRLs? What is the role of manufacturers in these preset protocols? I read somewhere that Siemens keeps the CTDI values at almost 50% of the most conservative DRLs. What is your take on this?

A

Many modern CT scanners come with preset DRLs, which are typically obtained from current professional publications.

CTDI values are a result of the scan parameters and are not directly related to the DRLs. However, the average CTDI would always be less than a given DRL because the DRLs serve as informal thresholds at which the adequacy of the settings should be investigated and/or verified. For example, an obese patient would require an abdomen/pelvis scan with a justifiably much higher CTDI (that perhaps exceeds the abdomen/pelvis DRL) than an average-sized patient.

Manufacturers play a role in establishing scan parameters by performing initial "first draft" optimization of the dose vs. image quality of the scanner utilizing its capabilities. Further, fine tuning is always performed at each individual site to meet the needs of the radiologist, typically with input from medical physicists and technologists.

Michael Cox, DABR
Harjinder Khaira, DABR

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