Fig. 7

Increase in image noise for brain ULD CT with pure IR. a Two-level axial (3-mm slice thickness) computed tomography images acquired using standard dose and ULD in the same patient. Although discrimination of the ventricles is achieved on ULD CT with pure IR, subjective noise is high and image contrast is poor. b Image noise and SNRs in the standard dose and ULD CT with pure IR brain study from the same patients were compared. Difference in means for image noise and signal-to-noise ratio was assessed using a Wilcoxon matched-pairs signed rank test and paired samples t-test, respectively. Data represent the mean and standard deviation. A p-value < 0.05 was considered statistically significant. ****p < 0.001, **p = 0.004. c Comparison of contrast-to-noise ratios between the two techniques was performed using a paired samples t-test. Caudate: CSF *p = 0.021; PLIC: CSF **p = 0.004; cerebellar GM: CSF **p = 0.010. Cerebellar WM: CSF *p = 0.039. GM (caudate): WM (PLIC) p = 0.236. CT Computed tomography, CSF Cerebrospinal fluid, IR Iterative reconstruction, PLIC Posterior limb of internal capsule, GM Grey matter, WM White matter, ULD Ultralow dose