Computed Tomography Dose Index CTDIvol Research Articles

Evaluation of X-ray doses in paediatrics multislice computed tomography

The present paper aims to examine the doses delivered to children at the paediatric Computer Tomography (CT) unit in the radiology service of the Mother and Child Hospital (MCH) in the Mohammed VI University Hospital Centre (Med VI UHC) of Marrakech, Morocco, and to compare our values with the dosimetric data of the published literature. This investigation included 440 CT examinations of the head, chest, and abdomen-pelvis in paediatric patients whose ages ranged from 1 to 5 yr (AG1y­5y), 5 to 10 yr (AG5y­10y), and 10 to 15 yr (AG10y­15y). We estimated the 75th percentile values of the Volume Computed Tomography Dose Index CTDIvol (mGy) and the Dose-Length-Product DLP (mGy.cm). The obtained results showed that the calculated 75th percentile of DLP for head CT are less than the National Diagnostic Reference Levels (DRLs) observed in Japan, Belgium, Germany, French, United Kingdom, United State, and China. However, the proposed DRLs for the abdomen-pelvis, and chest CT are significantly higher compared with international DRLs.

Radiation exposure during pelvimetry CT procedures in Ibn Sina Children's Hospital of Rabat

PurposeThe goal of this pilot study was to estimate the doses delivered during of pelvimetry Computed Tomography (CT) procedures in order to establish local diagnostic reference level (DRL) of Ibn Sina Children's Hospital of Rabat. Materials and methodsThis study consisted of examining a total of 30 patients. All CT examinations were performed with a SIEMENS Somatom Sensation 64 CT with Automatic Exposure Control System. The data that collected for each diagnostic exam chosen included scanner acquisition parameters, number of series, use of the contrast medium, and rotation time as well as slice thickness, the displayed CT dose index (CTDIvol) and the Dose Length Product (DLP). Effective dose and DRL were evaluated using the International Commission on Radiological Protection (ICRP) conversion factor. ResultsThe average age of women who have benefited from the pelvimetry CT scan is equal to 25.10 ± 4.75 years. Tube voltage (kV), tube current and rotation time were 110 (kV), 30 (mA) and 0,8 (s) respectively. The average displayed CT dose index CTDIvol were 2.15 ± 0.02 mGy. The average dose length product (DLP) was (55.97 ± 0.25) mGy cm. The average effective dose received by women pregnant during a pelvimetry CT scan was 0.84 ± 0.01 mSv. The foetal dose was 2.36 ± 0.02 mGy. The local DRL for this procedure was equal to 56.66 ± 2.15 mGy cm. ConclusionOur values are higher than the standards of some European countries. This first ever survey of CT practice in Ibn Sina Children's Hospital of Rabat confirmed the need to improved training of health professionals involved in computed tomography on factors affecting image quality and dose and protocols optimization.

Improved dose calculation accuracy for low energy brachytherapy by optimizing dual energy CT imaging protocols for noise reduction using sinogram affirmed iterative reconstruction

The goal of this study was to evaluate the noise reduction achievable from dual energy computed tomography (CT) imaging (DECT) using filtered backprojection (FBP) and iterative image reconstruction algorithms combined with increased imaging exposure. We evaluated the data in the context of imaging for brachytherapy dose calculation, where accurate quantification of electron density ρe and effective atomic number Zeff is beneficial.A dual source CT scanner was used to scan a phantom containing tissue mimicking inserts. DECT scans were acquired at 80 kVp/140Sn kVp (where Sn stands for tin filtration) and 100 kVp/140Sn kVp, using the same values of the CT dose index CTDIvol for both settings as a measure for the radiation imaging exposure. Four CTDIvol levels were investigated. Images were reconstructed using FBP and sinogram affirmed iterative reconstruction (SAFIRE) with strength 1,3 and 5. From DECT scans two material quantities were derived, Zeff and ρe. DECT images were used to assign material types and the amount of improperly assigned voxels was quantified for each protocol. The dosimetric impact of improperly assigned voxels was evaluated with Geant4 Monte Carlo (MC) dose calculations for an 125I source in numerical phantoms.Standard deviations for Zeff and ρe were reduced up to a factor ∼2 when using SAFIRE with strength 5 compared to FBP. Standard deviations on Zeff and ρe as low as 0.15 and 0.006 were achieved for the muscle insert representing typical soft tissue using a CTDIvol of 40 mGy and 3mm slice thickness. Dose calculation accuracy was generally improved when using SAFIRE. Mean (maximum absolute) dose errors of up to 1.3% (21%) with FBP were reduced to less than 1% (6%) with SAFIRE at a CTDIvol of 10 mGy. Using a CTDIvol of 40mGy and SAFIRE yielded mean dose calculation errors of the order of 0.6% which was the MC dose calculation precision in this study and no error was larger than ±2.5% as opposed to errors of up to -4% with FPB.This phantom study showed that the SAFIRE image reconstruction algorithm provided reduced standard deviations of Zeff and ρe in uniform regions of interest while preserving mean Zeff and ρe values. This resulted in improved material type assignment. The use of SAFIRE improved brachytherapy dose calculations for the materials from the phantom investigated in this study using 125I.