Correct Patient Centering Increases Image Quality without Concomitant Increase of Radiation Dose during Adult Intracranial Computed Tomography.

PURPOSE: To evaluate the impact of patient centering and radiation dose during intracranial computed tomography (ICT) on quantitative and qualitative image quality.

MATERIALS AND

METHODS

A total of 500 consecutive patients who underwent ICT were retrospectively reviewed using a 128-slice CT scanner (Definition AS+, Siemens, Germany). Patients were subjected in equal numbers to one of two positioning protocols: group A, poorly centered; and group B involved accurate centering before imaging. Gray-white matter (GWM) conspicuity, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) in each group were calculated. Qualitative image quality in terms of GWM differentiation, distinctness of posterior fossa contents, and overall diagnostic acceptability were evaluated by 2 neuroradiologists. The dose length product, CNR, SNR, and noise were measured between each group and data generated were compared using Mann-Whitney U nonparametric statistics. Visual grading characteristic and Kappa analyses were performed.

RESULTS

The mean noise index was significantly lower in group B (2.61 ± 0.29) compared with A (2.66 ± 0.21; P < .02). The mean attenuation of GWM, SNR, and CNR in the frontal lobe (A, 1:0.77, 0.84, 8.70 ± 1.36; and B, 1:0.65, 0.85, 15.32 ± 1.21; P < .02), occipital lobe (A, 1:1.10, 1.18, 10.79±2.11; and B, 1:0.94, 0.64, 14.41 ± 3.09; P < .04), and cerebellum (A, 1:0.79, 0.90, 12.56 ± 4.08; and B, 1:0.82, 0.87, 14.07 ± 2.28; P < .04) were significantly higher in group B compared with A, while the globus pallidus, caudate nucleus, and optic track in the basal ganglia demonstrated no difference in each group (P > .05). Mean dose length product demonstrated no significance between each group (A, 1312.03 ± 133.92; B, 1298.11 ± 130.61). The qualitative analyses demonstrated significant increases in visual grading characteristic for each reader (P < .02) and interobserver agreement was significantly increased in protocol B (k = 0.81) compared with A (k = 0.62).

CONCLUSIONS

Correct patient centering increases the CNR and SNR in both GWM in the left and right hemispheres of the brain during ICT.