Improving practice in radiology: a quality-improvement project examining CT colonography patient dose and scanning technique.

AIM: To audit scanning technique and patient doses for computed tomography (CT) colonography (CTC) examinations in a large UK region and to identify opportunities for quality improvement. MATERIALS AND METHODS: Scanning technique and patient dose data were gathered for both contrast-enhanced and unenhanced CTC examinations from 33 imaging protocols across 27 scanners. Measurements of patient weight and effective diameter were also obtained. Imaging protocols were compared to identify technique differences between similar scanners. Scanner average doses were calculated and combined to generate regional diagnostic reference limits (DRLs) for both examinations. RESULTS: The regional DRLs for contrast-enhanced examinations were volume CT dose index (CTDIvol) of 11 and 5 mGy for the two scan phases (contrast-enhanced and either delayed phase or non-contrast enhanced respectively), and dose-length product (DLP) of 740 mGy·cm. For unenhanced examinations, these were 5 mGy and 450 mGy·cm. These are notably lower than the national DRLs of 11 mGy and 950 mGy·cm. Substantial differences in scan technique and doses on similar scanners were identified as areas for quality-improvement action. CONCLUSION: A regional CTC dose audit has demonstrated compliance with national DRLs but marked variation in practice between sites for the dose delivered to patients, notably when scanners of the same type were compared for the same indication. This study demonstrates that the national DRL is too high for current scanner technology and should be revised.

Improving the quality of computed tomography brain images in the presence of cochlear implant induced metal artefacts through the additional use of tissue mimicking materials alongside metal artefact reduction software.

INTRODUCTION: Metal artefact reduction software (MAR) can be used to improve Computed Tomography (CT) image quality in the presence of implanted metalwork; however, this software is not effective for superficial metallic structures such as cochlear implants (CI). This study aimed to investigate whether the effectiveness of MAR software could be improved for brain scans with CI present through the use of tissue mimicking materials (TMM) placed exteriorly to the implant. METHODS: In this two-part study, a CI was positioned on the surface of water and anthropomorphic phantoms and imaged using a helical CT brain protocol. Three TMM, Superflab, Sure Thermal heat packs, and Bart's Bolus, were utilised and images were acquired to assess the resulting artefact reduction in terms of CT numbers, noise and artefact index (Aind). Changes in CTDIvol were assessed for the anthropomorphic phantom scans. RESULTS: In the water phantom, statistically significant reductions in CT number (p = 0.038) and noise (p = 0.033) were observed for Superflab, whilst the heat packs produced similar significant reductions in CT number (p < 0.001) and noise (p = 0.001) for the anthropomorphic phantom images. Aind values were significantly reduced through the use of Superflab (p = 0.009) and the heat packs (p < 0.001). No significant effects were observed for Bart's Bolus. CTDIvol increases of generally less than 5% were observed for scans with TMM in place. CONCLUSION: The additional use of TMM alongside MAR software yielded statistically significant reductions in CI induced metal artefacts on both water and anthropomorphic phantom scans with minimal dose increases. IMPLICATIONS FOR PRACTICE: The extent of metal artefacts in clinical head scans with CI in place could be significantly reduced through combined use of TMM and MAR software, consequently providing greater diagnostic confidence in the images.

Synthesis of a Vocal Sound from the 3,000 year old Mummy, Nesyamun 'True of Voice'.

The sound of a 3,000 year old mummified individual has been accurately reproduced as a vowel-like sound based on measurements of the precise dimensions of his extant vocal tract following Computed Tomography (CT) scanning, enabling the creation of a 3-D printed vocal tract. By using the Vocal Tract Organ, which provides a user-controllable artificial larynx sound source, a vowel sound is synthesised which compares favourably with vowels of modern individuals.

Assessment of tube current modulation in pelvic CT.

An anatomically shaped polymethylmethacrylate (PMMA) phantom was used to assess the effect of the Siemens CARE Dose mA modulation system on pelvic CT scans. The effect of the system on absorbed dose to air, image percentage noise and the signal to noise ratio of clinically relevant details was assessed. The signal to noise ratio was calculated using Polytetrafluoroethylene (PTFE) and distilled water inserts; PTFE was used to represent bony structure and distilled water was used to represent soft tissue abscess. Pelvis protocols identified from local hospitals and the UK CT Dose Survey (2002), were assessed and compared with those provided by Siemens Medical (UK). These protocols were tested on a Siemens Sensation 4 CT scanner, both with and without CARE Dose. Results were obtained which showed that dose savings were possible with no significant increase in image noise. Dose reductions were 8% in the lateral positions in the phantom and 42% in the centre, top and bottom. The calculated "CTDIvol" was 32% lower with CARE Dose than without CARE Dose. This is slightly greater than the 25% change in the effective mAs values that was found. This implies that the reduction in the effective mAs values is a reasonable predictor of the total reduction in absorbed dose to air, whilst slightly underestimating the actual change. The results also showed a non-significant trend towards decreased signal to noise ratios for clinically relevant CT numbers when CARE Dose was activated. This suggests that tube current modulation may detrimentally affect signal detection due to changes in image noise.

Organ and effective dose reduction in adult chest CT using abdominal lead shielding.

OBJECTIVES: The purpose of this study was to evaluate and compare organ and effective dose savings that could be achieved using conventional lead aprons and a new, custom-designed shield as out-of-plane shielding devices during chest CT scans. METHODS: Thermoluminescent dosimeters were used to measure doses throughout the abdomen and pelvis during CT scans of the chest of a RANDO phantom. Dose measurements were made with no shielding, with lead aprons and with the new shield around the abdomen and pelvis in order to quantify the achievable organ and effective dose reductions. RESULTS: Average dose savings in the 10 phantom sections ranged from 5% to 78% with the highest point dose saving of 93% being found in the mid-pelvis. When shielding was used, the maximum measured organ dose reduction was a 72% dose saving to the testes. Significant dose savings were found throughout the abdomen and pelvis, which contributed to an effective dose saving of 4% that was achieved over and above the dose savings obtained through conventional optimisation strategies. This could yield significant population dose savings and reductions in collective radiation risk. CONCLUSION: In this study significant organ and effective dose reductions have been achieved through the use of abdominal shielding during chest CT examinations and it is therefore recommended that out-of-plane patient shielding devices should be used for all chest CT scans and potentially for every CT scan, irrespective of body part.

Modelling the effect of lead and other materials for shielding of the fetus in CT pulmonary angiography.

The aim of this work is to construct and validate a model to describe the variation in fetal dose as a function of the thickness of abdominal lead shielding used during CT pulmonary angiography and to determine the optimal shielding material. An anthropomorphic phantom was modified to contain a 15 cm(3) ionization chamber at the site of the uterus. Fetal dose was measured with varying thicknesses of lead shielding at four values of tube potential (kV(p)). Data generated by the proposed model were compared with experimental data to determine the validity of the model. The effect of lead shielding has been modelled accurately and results have shown that, although alternative materials could be used, lead is an effective and practical shielding material. In conclusion, lead remains a suitable shielding material and a pair of conventional lead aprons provides significant shielding for the fetus; we recommend that aprons should be reserved specifically for this purpose. However, it is possible that a dedicated and specifically designed lead shield could reduce fetal dose more effectively whilst also reducing patient discomfort.

Investigation into the effects of lead shielding for fetal dose reduction in CT pulmonary angiography.

This work aims to determine whether lead shielding can be used to decrease the radiation dose to the fetus during CT scans for the diagnosis of pulmonary embolism during early stage pregnancy. An anthropomorphic phantom was modified to contain a 15 cc ionization chamber at the site of the uterus to enable fetal dose to be measured. The effects of a range of scan parameters, positioning of lead and thicknesses of lead were investigated. Fetal dose was lower with lower values of kV(p) and mAs. An increasing thickness of lead decreased the radiation dose to the uterus, as did increasing the proportion of the patient covered by the lead shielding. Fetal dose increased exponentially as the edge of the scan volume moved closer to the point of measurement. In no experiment was the dose to the fetus increased by the presence of the lead. It was found that the fetal radiation dose from a CT scan following a pulmonary embolism protocol can be effectively reduced by the use of lead shielding.