Radiation intensity (CTDIvol) and visibility of anatomical structures in head CT examinations

Assessment of patient dose and noise level of clinical CT images: automated measurements

We investigated comparisons between patient dose and noise in pelvic, abdominal, thoracic and head CT images using an automatic method. 113 patient images (37 pelvis, 34 abdominal, 25 thoracic, and 17 head examinations) were retrospectively and automatically examined in this study. Water-equivalent diameter (Dw), size-specific dose estimates (SSDE) and noise were automatically calculated from the center slice for every patient image. The Dw was calculated based on auto-contouring of the patients' edges, and the SSDE was calculated as the product of the volume CT dose index (CTDIvol) extracted from the Digital Imaging and Communications in Medicine (DICOM) header and the size conversion factor based on the Dw obtained from AAPM 204. The noise was automatically measured as a minimum standard deviation in the map of standard deviations. A square region of interest of about 1 cm² was used in the automated noise measurement. The SSDE values for the pelvis, abdomen, thorax, and head were 21.8 ± 7.3 mGy, 22.0 ± 4.5 mGy, 21.5 ± 4.7 mGy, and 65.1 ± 1.7 mGy, respectively. The SSDEs for the pelvis, abdomen, and thorax increased linearly with increasing Dw, and for the head with constant tube current, the SSDE decreased with increasing Dw. The noise in the pelvis, abdomen, thorax, and head were 5.9 ± 1.5 HU, 5.2 ± 1.4 HU, 4.9 ± 0.8 HU and 3.9 ± 0.2 HU, respectively. The noise levels for the pelvis, abdomen, and thorax of the patients were relatively constant with Dw because of tube current modulation. The noise in the head image was also relatively constant because Dw variations in the head are very small. The automated approach provides a convenient and objective tool for dose optimizations.

RADIATION DOSE AND IMAGE QUALITY IN PEDIATRIC HEAD CT

Our goal was to define a pediatric head CT protocol able to provide images of diagnostic quality, using the least amount of radiation, in children <10 years of age, while using a filtered back projection reconstruction algorithm. Image quality of 119 pediatric head CTs was assessed using a 5-point scoring system. Exams with scores ≥2.5 were considered of sufficient diagnostic quality. The contrast-to-noise ratio (CNR) was also measured. For children <1 year and 1-9 years, all studies performed with CTDIvol ≥ 20.1 mGy (range: 9-46 mGy) and CTDIvol ≥ 27.5 mGy (range: 15-60 mGy) yielded images of diagnostic quality. All diagnostic studies had a minimum CNR of 1.4. These CTDIvol values represent a good balance between image quality and radiation burden. This information can be helpful in designing pediatric head CT protocols with further dose-reduction, namely, iterative reconstruction algorithms and automated exposure control.