Evaluation of X-ray table mattresses for radiation attenuation and impact on image quality.

INTRODUCTION: Mattresses in the radiology department tend to be an overlooked aspect of imaging equipment. This paper evaluates the radiation attenuation characteristics of mattresses and the effect they have on image quality. METHODS: Thirteen mattresses (from new to 20 years of age) were evaluated. Incident air kerma (IAK) was measured in two conditions, with and without mattress over a range of exposure factors using a digital dosimeter. Image quality was assessed by calculating the inverse image quality factor (IQFinv) using a commercially available phantom (CDRAD) for the same exposure factors. The correlation of age and attenuation and image quality was calculated. RESULTS: Measured IAK and image quality was affected by the addition of a mattress with older mattresses having greater attenuation; there is a moderate/large correlation (0.38-0.51) between age and IAK. IQFinv deteriorated with the addition of a mattress but there was no correlation with age (-0.41 to 0.16). Clinically, there is no impact of any mattress in the study as changes to the exposure factors to account for the attenuation are smaller than the increments in mAs available on X-ray equipment. CONCLUSION: The results indicate that while the presence of a mattress does impact on transmitted radiation and the quality of the image, the clinical impact is insignificant. Attenuation correlates with age but with no clinical significance. There is no correlation between age and image quality. IMPLICATIONS FOR PRACTICE: Quality control tests for attenuation and impact on image quality are not required in clinical practice. The method could be used by manufacturers to test new materials and mattresses and could provide users with specifications of new products.

Development and validation of a bespoke phantom to test accuracy of Cobb angle measurements.

INTRODUCTION: Adolescent idiopathic scoliosis (AIS) is a spinal deformity that causes the spine to bend laterally. Patients with AIS undergo frequent X-ray examinations to monitor the progression of the disorder by through the measurement of the Cobb angle. Frequent exposure of adolescents poses the risk of radiation-induced cancer. The aim of this research was to design and build a bespoke phantom representing a 10-year-old child with AIS to allow optimisation of imaging protocols for AIS assessment through the accuracy of Cobb angle measurements. METHODS: Poly-methyl methacrylate (PMMA) and plaster of Paris (PoP) were used to represent human soft tissue and bone tissue, respectively, to construct a phantom exhibiting a 15° lateral curve of the spine. The phantom was validated by comparing the Hounsfield unit (HU) of its vertebrae with that of human and sheep. Additionally, comparisons of signal-to-noise ratio (SNR) to those from a commercially available phantom. An assessment of the accuracy of the radiographic assessment of the Cobb angle measurement was performed. RESULTS: The HU of the PoP vertebrae was 628 (SD = 56), human vertebrae was 598 (SD = 79) and sheep vertebra was 605 (SD = 83). The SNR values of the two phantoms correlated strongly (r = 0.93 (p = 0.00)). The measured scoliosis angle was 14°. CONCLUSION: The phantom has physical characteristics (in terms of spinal deformity) and radiological characteristics (in terms of HU and SNR values) of the spine of a 10-year-old child with AIS. This phantom has utility for the optimisation of x-ray imaging techniques in 10 year old children. IMPLICATIONS FOR PRACTICE: A phantom to investigate new x-ray imaging techniques and technology in the assessment of scoliosis and to optimise currently used protocols.

The accuracy of Cobb angle measurement on CT scan projection radiograph images.

INTRODUCTION: Adolescent idiopathic scoliosis (AIS) is a spinal deformity that can affect young children. It requires frequent exposure to X-rays to monitor the deformity, which can lead to the development of radiation-induced cancer later in life. The aim of this study is to test the accuracy of using scan projection radiography (SPR) in computed tomography (CT) scans for AIS assessment. This scanning mode delivers low radiation compared with conventional radiography. METHOD: A bespoke phantom with a 14° scoliotic spine was scanned in CT SPR mode using 18 imaging acquisitions. These images were visually evaluated against set criteria to determine their suitability for Cobb angle measurements Those deemed of insufficient quality were excluded from the study (n = 8, excluded). Cobb angle measurements were then performed on the remaining images (n = 10, included) by 13 observers. RESULTS: On average, the difference between the measured Cobb angle and the known angle was -2.75° (SD 1.46°). The agreement between the observers was good (p = 0.861, 95% CI 0.70-0.95) and comparable to similar studies on other imaging modalities which are used for Cobb angle estimation. CONCLUSION: CT SPR images can be used for AIS assessment with the 5° margin of error that is clinically acceptable. IMPLICATIONS FOR PRACTICE: The outcome is promising for patients and health providers because it provides an opportunity to reduce patient dose, achieve clinically acceptable Cobb angle measurements whilst using existing (CT) technology that is available in most hospital.

Impact of gonad shielding for AP pelvis on dose and image quality on different female sizes: A phantom study.

INTRODUCTION: In clinical practice AP pelvis standard protocols are suitable for average size patients. However, as the average body size has increased over the past decades, radiographers have had to improve their practice in order to ensure that adequate image quality with minimal radiation dose to the patient is achieved. Gonad shielding has been found to be an effective way to reduce the radiation dose to the ovaries. However, the effect of increased body size, or fat thickness, in combination with gonad shielding is unclear. The goal of the study was to investigate the impact of gonad shielding in a phantom of adult female stature with increasing fat thicknesses on SNR (as a measure for image quality) and dose for AP pelvis examination. METHODS: An adult Alderson female pelvis phantom was imaged with a variety of fat thickness categories as a representation of increasing BMI. 72 images were acquired using both AEC and manual exposure with and without gonad shielding. The radiation dose to the ovaries was measured using a MOSFET system. The relationship between fat thickness, SNR and dose when the AP pelvis was performed with and without shielding was investigated using the Wilcoxon signed rank test. P-values < 0.05 were considered to be statistically significant. RESULTS: Ovary dose and SNR remained constant despite the use of gonad shielding while introducing fat layers. CONCLUSION: The ovary dose did not increase with an increase of fat thickness and the image quality was not altered. IMPLICATIONS FOR PRACTICE: Based on this phantom study it can be suggested that obese patients can expect the same image quality as average patients while respecting ALARA principle when using adequate protocols.

Scoliosis imaging: An analysis of radiation risk in the CT scan projection radiograph and a comparison with projection radiography and EOS.

INTRODUCTION: Scoliosis is defined as a deformity of the spine with lateral curvature in the coronal plane. It requires regular X-ray imaging to monitor the progress of the disorder, therefore scoliotic patients are frequently exposed to radiation. It is important to lower the risk from these exposures for young patients. The aim of this work is to compare organ dose (OD) values resulting from Scan Projection Radiograph (SPR) mode in CT against projection radiography and EOS® imaging system when assessing scoliosis. METHODS: A dosimetry phantom was used to represent a 10-year old child. Thermoluminescent dosimetry detectors were used for measuring OD. The phantom was imaged with CT in SPR mode using 27 imaging parameters; projection radiography and EOS machines using local scoliosis imaging procedures. Imaging was performed in anteroposterior, posteroanterior and lateral positions. RESULTS: 17 protocols delivered significantly lower radiation dose than projection radiography (p < 0.05). OD values from the CT SPR imaging protocols and projection radiography were statistically significant higher than the results from EOS. No statistically significant differences in OD were observed between 10 imaging protocols and those from projection radiography and EOS imaging protocols (p > 0.05). CONCLUSION: EOS has the lowest dose. Where this technology is not available we suggest there is a potential for OD reduction in scoliosis imaging using CT SPR compared to projection radiography. Further work is required to investigate image quality in relation to the measurement of Cobb angle with CT SPR.

Radiation protection value to the operator from augmented reality smart glasses in interventional fluoroscopy procedures using phantoms.

INTRODUCTION: Smart glasses can be adapted to display radiographic images to allow clinician's gaze not to be directionally fixed or predetermined by computer monitor location. This study presents an analysis of eye lens dose during interventional fluoroscopy guided procedures, comparing fixed monitor positions against the use of smart glasses. METHODS: Using a head phantom (simulating the clinician), thermoluminescent dosimeters and lead shielded glasses, the dose to the eye was measured for different head 'rotations and tilts' for: gaze directed towards the main scattering source (patient/primary beam) to represent potential gaze direction if smart glasses are used; gaze directed to a range of potential computer monitor positions. An anthropomorphic pelvis phantom was utilised to simulate the patient. Accumulated dose rates (µGy s-1) from five 10-second exposures at 75 kV 25.2 mAs were recorded. RESULTS: An average DAP reading of 758.84 cGy cm2 was measured during each 10 second exposure. Whilst wearing lead shielded glasses a 6.10 - fold reduction in dose rate to the lens is possible (p < 0.05). Influence of the direction of gaze by the clinician demonstrated a wide range of dose rate reduction from 3.13% (p = 0.16) to 143.69% (p < 0.05) when the clinician's gaze was towards the main scattering source. Increased dose rate to the clinician's eyes was received despite wearing lead shielded glasses, as the angle of gaze moved 45° and 90° from 0°. CONCLUSION: If the clinician's gaze is directed towards the main scattering source a potential exists for reducing eye lens dose compared with fixed location computer monitors. Introduction of lead lined smart glasses into interventional radiology may lead to improvements in patient care, reducing the need for the clinician to look away from the patient to observe a radiographic image.

Effective lifetime radiation risk for a number of national mammography screening programmes.

BACKGROUND AND PURPOSE: The performance of mammography screening programmes is focussed mainly on breast cancer detection rates. However, when the benefits and risks of mammography are considered, the risk of radiation-induced cancer is calculated for only the examined breast using Mean Glandular Dose (MGD). The risk from radiation during mammography is often described as low or minimal. This study aims to evaluate the effective lifetime risk from full field digital mammography (FFDM) for a number of national screening programmes. MATERIAL AND METHODS: Using an ATOM phantom, radiation doses to multiple organs were measured during standard screening mammography. Sixteen FFDM machines were used and the effective lifetime risk was calculated across the female lifespan for each machine. Once the risks were calculated using the phantom, the total effective lifetime risk across 48 national screening programmes was then calculated; this assumed that all these programmes use FFDM for screening. RESULTS: Large differences exist in effective lifetime risk, varying from 42.21 [39.12-45.30] cases/106 (mean [95% CI]) in the Maltese screening programme to 1099.67 [1019.25-1180.09] cases/106 for high breast cancer risk women in the United States of America. These differences are mainly attributed to the commencement age of screening mammography and the time interval between successive screens. CONCLUSIONS: Effective risk should be considered as an additional parameter for the assessment of screening mammography programme performance, especially for those programmes which recommend an early onset and more frequent screening mammography.

Analysis of effective and organ dose estimation in CT when using mA modulation: A single scanner pilot study.

INTRODUCTION: Effective dose (ED) estimation in CT examinations can be obtained by combining dose length product (DLP) with published ED per DLP coefficients or performed using software. These methods do not account for tube current (mA) modulation which is influenced by patient size. The aim of the work was to compare different methods of organ and ED estimation to measured values when using mA modulation in CT chest, abdomen and pelvis examinations. METHOD: Organ doses from CT of the chest, abdomen and pelvis were measured using digital dosimeters and a dosimetry phantom. ED was calculated. Six methods of estimating ED accounting for mA modulation were performed using ImPACT CTDosimetry and Dose Length Product to ED coefficients. Corrections for the phantom mass were applied resulting in 12 estimation methods. Estimated organ doses from ImPACT CTDosimtery were compared to measured values. RESULTS: Calculated EDs were; chest 12.35 mSv (±1.48 mSv); abdomen 8.74 mSv (±1.36 mSv) and pelvis 4.68 mSv (±0.75 mSv). There was over estimation in all three anatomical regions. Correcting for phantom mass improved agreement between measured and estimated ED. Organ doses showed overestimation of dose inside the scan range and underestimation outside the scan range. CONCLUSION: Reasonable estimation of effective dose for CT of the chest and abdomen can be obtained using ImPACT CTDosimetry software or k-coefficients. Further work is required to improve the accuracy of ED estimation from CT of the pelvis. Accuracy of organ dose estimation has been shown to depend on the inclusion or exclusion of the organ from the scan range.

Does collimation affect patient dose in antero-posterior thoraco-lumbar spine?

INTRODUCTION: The purpose of this study is to determine the effect of collimation on the lifetime attributable risk (LAR) of cancer incidence in all body organs (effective risk) in patients undergoing antero-posterior (AP) examinations of the spine. This is of particular importance for patients suffering from scoliosis as in their case regular repeat examinations are required and also because such patients are usually young and more susceptible to the effects of ionising radiation than are older patients. METHODS: High sensitivity thermo-luminescent dosimeters (TLDs) were used to measure radiation dose to all organs of an adult male dosimetry phantom, positioned for an AP projection of the thoraco-lumbar spine. Exposures were made, first applying tight collimation and then subsequently with loose collimation, using the same acquisition factors. In each case, the individual TLDs were measured to determine the local absorbed dose and those representing each organ averaged to calculate organ dose. This information was then used to calculate the effective risk of cancer incidence for each decade of life from 20 to 80, and to compare the likelihood of cancer incidence when using tight and loose collimation. RESULTS: The calculated figures for effective risk of cancer incidence suggest that the risk when using loose collimation compared to the use of tight collimation is over three times as high and this is the case across all age decades from 20 to 80. CONCLUSION: Tight collimation can greatly reduce radiation dose and risk of cancer incidence. However collimation in scoliotic patients can be necessarily limited.

Effect of reconstruction methods and x-ray tube current-time product on nodule detection in an anthropomorphic thorax phantom: A crossed-modality JAFROC observer study.

PURPOSE: To evaluate nodule detection in an anthropomorphic chest phantom in computed tomography (CT) images reconstructed with adaptive iterative dose reduction 3D (AIDR(3D)) and filtered back projection (FBP) over a range of tube current-time product (mAs). METHODS: Two phantoms were used in this study: (i) an anthropomorphic chest phantom was loaded with spherical simulated nodules of 5, 8, 10, and 12 mm in diameter and +100, -630, and -800 Hounsfield units electron density; this would generate CT images for the observer study; (ii) a whole-body dosimetry verification phantom was used to ultimately estimate effective dose and risk according to the model of the BEIR VII committee. Both phantoms were scanned over a mAs range (10, 20, 30, and 40), while all other acquisition parameters remained constant. Images were reconstructed with both AIDR(3D) and FBP. For the observer study, 34 normal cases (no nodules) and 34 abnormal cases (containing 1-3 nodules, mean 1.35 ± 0.54) were chosen. Eleven observers evaluated images from all mAs and reconstruction methods under the free-response paradigm. A crossed-modality jackknife alternative free-response operating characteristic (JAFROC) analysis method was developed for data analysis, averaging data over the two factors influencing nodule detection in this study: mAs and image reconstruction (AIDR(3D) or FBP). A Bonferroni correction was applied and the threshold for declaring significance was set at 0.025 to maintain the overall probability of Type I error at α = 0.05. Contrast-to-noise (CNR) was also measured for all nodules and evaluated by a linear least squares analysis. RESULTS: For random-reader fixed-case crossed-modality JAFROC analysis, there was no significant difference in nodule detection between AIDR(3D) and FBP when data were averaged over mAs [F(1, 10) = 0.08, p = 0.789]. However, when data were averaged over reconstruction methods, a significant difference was seen between multiple pairs of mAs settings [F(3, 30) = 15.96, p < 0.001]. Measurements of effective dose and effective risk showed the expected linear dependence on mAs. Nodule CNR was statistically higher for simulated nodules on images reconstructed with AIDR(3D) (p < 0.001). CONCLUSIONS: No significant difference in nodule detection performance was demonstrated between images reconstructed with FBP and AIDR(3D). mAs was found to influence nodule detection, though further work is required for dose optimization.

Comparison of effective dose and lifetime risk of cancer incidence of CT attenuation correction acquisitions and radiopharmaceutical administration for myocardial perfusion imaging.

OBJECTIVE: To measure the organ dose and calculate effective dose from CT attenuation correction (CTAC) acquisitions from four commonly used gamma camera single photon emission CT/CT systems. METHODS: CTAC dosimetry data was collected using thermoluminescent dosemeters on GE Healthcare's Infinia™ Hawkeye™ (GE Healthcare, Buckinghamshire, UK) four- and single-slice systems, Siemens Symbia™ T6 (Siemens Healthcare, Erlangen, Germany) and the Philips Precedence (Philips Healthcare, Amsterdam, Netherlands). Organ and effective dose from the administration of (99m)Tc-tetrofosmin and (99m)Tc-sestamibi were calculated using International Commission of Radiological Protection reports 80 and 106. Using these data, the lifetime biological risk was calculated. RESULTS: The Siemens Symbia gave the lowest CTAC dose (1.8 mSv) followed by the GE Infinia Hawkeye single-slice (1.9 mSv), GE Infinia Hawkeye four-slice (2.5 mSv) and Philips Precedence v. 3.0. Doses were significantly lower than the calculated doses from radiopharmaceutical administration (11 and 14 mSv for (99m)Tc-tetrofosmin and (99m)Tc-sestamibi, respectively). Overall lifetime biological risks were lower, which suggests that using CTAC data posed minimal risk to the patient. Comparison of data for breast tissue demonstrated a higher risk than that from the radiopharmaceutical administration. CONCLUSION: CTAC doses were confirmed to be much lower than those from radiopharmaceutical administration. The localized nature of the CTAC exposure compared to the radiopharmaceutical biological distribution indicated dose and risk to the breast to be higher. ADVANCES IN KNOWLEDGE: This research proved that CTAC is a comparatively low-dose acquisition. However, it has been shown that there is increased risk for breast tissue especially in the younger patients. As per legislation, justification is required and CTAC should only be used in situations that demonstrate sufficient net benefit.