Radimetrics

The effective radiation dose was estimated using the software package Radimetrics (Radimetrics Enterprise Platform, Bayer Pharma, Leverkusen, Germany). Effective radiation dose was calculated for every CT independent of the study protocol and separately for each region (hip, knee, ankle). The total effective dose is defined as the sum of radiation doses of all organs in the scan range. All organ doses were weighted by tissue weighting factors from the International Commission on Radiological Protection (ICRP103) and were directly calculated using Monte Carlo simulations.

Radiation doses were reported as effective dose (ED) for the different scan ranges, as defined by the International Commission on Radiological Protection publication 103 [17 ], and were calculated by a Monte Carlo simulation on a phantom matched to the acquired CT using commercial software (Radimetrics, Bayer Pharmaceuticals). It accounts for patient size by choosing an appropriately sized phantom; it implicitly considers ECG gating by using the CTDI_vol readings.
ED was also calculated based on CTDI_vol and scan length to compare the more complex Monte Carlo simulation values with a more straightforward estimation. For this, the formula $ED={\mathit{CTDI}}_{\mathit{vol}}\times \mathit{scanLength}\times k$ was used, where $k$ is a conversion factor mainly depending on the scanned body part. Following Trattner et al [18 (link)], $k$ was set to 0.026 mSv/(mGy × cm). The ED for females were corrected by a factor of 0.045 mSv/(mGy × cm) to account for the breast [19 (link)].

We assessed the radiation dose of the full range as well as the virtual reduced range CT in terms of whole body effective dose and organ doses. These were calculated using a commercially available dose monitoring and tracking software (Radimetrics, Bayer Healthcare, Leverkusen, Germany). Based on anthropomorphic phantoms and Monte Carlo simulations, this software provides effective dose and organ dose values of the original full range CT scan according to the weighting factors published in the International Commission on Radiation Protection 103 report. By using an interactive tool which allows to manually adjust the superior and inferior border of the scan range, we additionally obtained effective dose and organ dose values for the virtual reduced range CT in a second step. Besides the whole body effective dose, we recorded the dose values for the following organs: adrenals, colon, esophagus, gall bladder, heart, kidneys, liver, lungs, muscle, pancreas, red marrow, skeleton, skin, small intestine, spleen, stomach and urinary bladder. Furthermore, the organ dose of breasts, ovaries and uterus was recorded in female subjects as well as the testicle dose in males.

Patient data were collected at three different sites of one radiological institution (site I: University Hospital Essen, Essen, Germany; site II: Elisabeth Hospital, Essen, Germany; site III: St. Marien-Hospital, Mülheim an der Ruhr, Germany) between March and April 2021. Collection was performed consecutively, until around 50 patients were included. Patients were considered eligible if they underwent a routine head CT scan without contrast. Examinations were identified using the DICOM header-based dose monitoring software Radimetrics (Bayer AG, Leverkusen, Germany) and the local picture archiving and communications system (PACS). Studies were excluded if brain pathology significantly affected the objective assessment of image quality (e.g., severe cerebral edema or hemorrhage). Incomplete CT scans or repeated scans of the same patient during the study period were also excluded. CT scans that were incompletely post-processed by the DLID software or where no post-processed images were generated on the axial reconstructed CT images were also excluded.