Iterative reconstruction reduces abdominal CT dose.

OBJECTIVE: In medical imaging, lowering radiation dose from computed tomography scanning, without reducing diagnostic performance is a desired achievement. Iterative image reconstruction may be one tool to achieve dose reduction. This study reports the diagnostic performance using a blending of 50% statistical iterative reconstruction (ASIR) and filtered back projection reconstruction (FBP) compared to standard FBP image reconstruction at different dose levels for liver phantom examinations. METHODS: An anthropomorphic liver phantom was scanned at 250, 185, 155, 140, 120 and 100 mAs, on a 64-slice GE Lightspeed VCT scanner. All scans were reconstructed with ASIR and FBP. Four readers evaluated independently on a 5-point scale 21 images, each containing 32 test sectors. In total 672 areas were assessed. ROC analysis was used to evaluate the differences. RESULTS: There was a difference in AUC between the 250 mAs FBP images and the 120 and 100 mAs FBP images. ASIR reconstruction gave a significantly higher diagnostic performance compared to standard reconstruction at 100 mAs. CONCLUSION: A blending of 50-90% ASIR and FBP may improve image quality of low dose CT examinations of the liver, and thus give a potential for reducing radiation dose.

Dose levels from thoracic and pelvic examinations in two pediatric radiological departments in Norway - a comparison study of dose-area product and radiographic technique.

BACKGROUND: pediatric doses expressed in dose-area product (DAP) can be retrieved from only a few publications; most of which correlate DAP to patient size or large age spans. In clinical practice age is often the only available parameter describing the patient, and thus, evaluation of dose levels in pediatric radiology on the basis of DAP related to age alone would be useful in optimization work. PURPOSE: to provide comparable data on age-related DAP from thoracic and pelvic radiological examinations of children, and evaluate the usefulness of comparing age-related DAP and radiographic technique between systems to identify areas with potential for optimization. MATERIAL AND METHODS: DAP, age, and radiographic technique were registered for 575 thoracic examinations and 371 pelvic examinations of children from newborn up to 14 years of age in groups with an age span of 1 year, performed with two digital flat-panel systems and one computed radiography system. RESULTS: DAP varies from 2.2 to 54.0 mGycm(2) for thoracic examinations, and from 4.6 to 532.5 mGycm(2) for pelvic examinations. There are significant differences in DAP between systems and departments due to differences in technique, equipment, and staff. CONCLUSION: this study provides comparable data on age-related DAP from thoracic and pelvic radiological examinations of children, which could be used as an input to estimate diagnostic reference levels. The comparison between systems of DAP and radiographic technique has proven useful in identifying areas where there may be a potential for optimization.

Improved image quality of low-dose thoracic CT examinations with a new postprocessing software.

In 2008 a phantom study indicated that there is a potential for reducing the CT doses when using a new postprocessing filter. The purpose of this study was to test this new postprocessing filter clinically for low-dose chest CT examinations, to assess whether the diagnostic performance is the same or improved. A standardized clinical chest CT protocol was used on patients with colorectal cancer. Only mA settings changed between patients according to patient size. One standard and one low-dose chest protocol were performed for all patients. The low-dose images were postprocessed with a new software filter, which provides context-controlled restoration of digital images by using adaptive filters. Three radiologists assessed randomly all the images independently. A total of 24 scan series were evaluated with respect to image quality according to quality criteria from the European guidelines for chest CT using a five-point scale; 576 details were assessed. Overall mean score is the average score for all details rated for all three readers for all full-dose series, low-dose series and low-dose enhanced series, respectively. The statistical methods used for comparison were paired sampled t-test and intraclass correlation coefficient. The postprocessing filter improved the diagnostic performance compared to the unenhanced low-dose images. Mean score for full-dose, low-dose and low-dose enhanced series were 3.8, 3.0 and 3.3, respectively. For all patients the full-dose series gave higher scores than the low-dose series. Intraclass correlation coefficients were 0.2, 0.1 and 0.3 for the full-dose, low-dose and low-dose enhanced series, respectively. There is a potential for improving diagnostic performance of low-dose CT chest examinations using this new postprocessing filter.

[Radiation protection of childrens' chest during high resolution CT of the lungs]. / Strålebeskyttelse av barns bryst ved høyoppløselig CT av lungene.

BACKGROUND: The Norwegian Radiation Protection Authority recommends bismuth to protect radiosensitive surface organs during CT imaging. A study based on the use of phantoms was therefore initiated to investigate the usefulness of this protection on the breasts of young girls undergoing high-resolution computed tomography (HRCT) of the chest. MATERIAL AND METHODS: Shields covered with one, two or three layers of bismuth were placed on a homogenous phantom. CT numbers (pixel values in the images which describe the density of the tissue imaged), noise and artifacts were evaluated from the images of the phantom. Dosimeters were used for dose measurements in an anthropomorphic phantom of a child. RESULTS: Areas close to the shield in the images of the phantom had CT numbers up to 33 % higher with two and three layers of bismuth than in the images without shielding. With one layer the CT numbers were up to 8 % higher. Noise in the same area was up to 56 % higher with two and three layers of bismuth than without, and up to 14 % higher with one layer. The surface dose in the breast region was reduced with 30 % with one layer of bismuth, 45 % with two and 75 % with three layers of bismuth. INTERPRETATION: Shielding with one layer of bismuth seems to have little effect on the CT images. The Department of pediatric radiology at Ullevaal University Hospital now uses bismuth protection with one layer as a routine during HRCT of girls up to 16 years of age.