Lowering the Dose in Head CT Using Adaptive Statistical Iterative Reconstruction

To avoid increased radiation exposure and subsequent long-term risk of cancer, iterative reconstruction is a means of lowering the dose on CT studies. Here, the authors compared head CT scans obtained via standard dose with low-dose (31% less) iterative reconstruction. Signal-to-noise and contrast-to-noise ratios as well as image noise, sharpness, artifacts, and diagnostic acceptability were assessed. Overall these parameters were judged to be better in the standard-dose CT, but those obtained with the lower dose and iterative reconstruction were judged acceptable. Thus, iterative reconstruction appears to be useful in adult head CT examinations. (Editor's Note: This technique would be ideal in children where radiation dosage is of utmost concern. At my institution we use it for all head and neck studies, but not for temporal bone or paranasal sinus studies as we have found that bone detail may be less than optimal.) BACKGROUND AND PURPOSE: While CT has found wide use in medical practice, it is also a substantial source of radiation exposure and is associated with an increased lifetime risk of cancer. There is an urgent need for new approaches to reduce the radiation dose in CT. In this regard, ASIR is an alternative method to FBP. We assessed the effect of ASIR on dose reduction in adult head CT. MATERIALS AND METHODS: We retrospectively evaluated a sample of 149 adult head CT examinations that were divided into 2 groups, STD and LD. We lowered the tube current and used ASIR in the LD group. SNR and CNR were analyzed. Dose parameters were recorded while subjective image noise, sharpness, diagnostic acceptability, and artifacts were graded. The Student t test, the Mann-Whitney U test, and κ statistics were used for statistical analyses. RESULTS: We achieved a dose reduction of 31% in the LD group (STD, 2.3 ± 0.1 mSv; LD, 1.6 ± 0.1 mSv; P < .001). There was no significant difference in the noise measured in the air between the 2 comparison groups (P = .273). Noise in the CSF was higher in the STD group (P < .001), while the noise in the WM was higher in the LD group (P < .001). Differences in the CNR between groups were insignificant, but the STD group displayed better SNR values. There was no significant difference in the modal scores of diagnostic acceptability (P = .062) and the artifacts (P = .148) between the 2 groups. Better scores for subjective image noise (P < .001) and sharpness (P = .04) were observed in the STD group. CONCLUSIONS: ASIR appears to be useful in reducing the dose in adult head CT examinations. While the effect of ASIR on noise reduction observed in the present study of head CT is less than that reported previously in abdomen and chest CT, these findings encourage further prospective studies in larger patient samples.