Successful dose-reduction strategy possible for neuroradiology CT exams

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The use of dose-modulation techniques for neuroradiology CT examinations affords significant dose reduction while image quality is maintained, according to a retrospective study in the May issue of Radiology.

Alice B. Smith, MD, from the department of radiology and neuroradiology, at the University of California, San Francisco, and colleagues undertook the study to quantify the effect of systematic use of a tube’s current modulation for neuroradiology CT protocols on patient dose and image quality.

The authors noted that their HIPAA-compliant study had institutional review board approval with a waiver of informed consent.

The researchers evaluated the effect of dose modulation on four types of neuroradiologic CT studies: brain CT performed without contrast material in adult patients, unenhanced brain CT in pediatric patients, adult cervical spine CT, and adult cervical and intracranial CT angiography.

For each type of CT study, three series of 100 consecutive studies were reviewed: 100 studies performed without dose modulation, 100 studies performed with z-axis dose modulation and 100 studies performed with x-y-z–axis dose modulation. For each exam, the researchers measured and recorded the weighted volume CT dose index (CTDIvol) and dose-length product (DLP); and each study was also reviewed for image quality.

The investigators compared continuous variables (CTDIvol, DLP, noise) by using t tests, and compared categorical variables (image quality) by using Wilcoxon rank-sum tests.

For unenhanced CT of adult brains, Smith and colleagues found that the CTDIvol and DLP, respectively, were reduced by 60.9 percent and 60.3 percent, respectively, by using z-axis dose modulation and by 50.4 percent and 22.4 percent by using x-y-z–axis dose modulation.

The researchers also observed significant dose reductions for pediatric unenhanced brain CT, cervical spine CT, and adult cervical and intracranial CT angiography performed with each dose modulation technique.

The authors noted that image quality and noise were unaffected by the use of either dose modulation technique.

“Implementation of dose modulation requires a fine-tuning process to identify optimal signal-to-noise level for each type of CT study performed,” Smith and colleagues wrote.