Development of a randomised contrast detail digital phantom for observer detectability study

The accuracy and the efficacy of radiological diagnosis depend, to a large extent, on the conditions under which radiographs and images are viewed. This mainly involves the luminance of the display devices and the ambient room illumination. We report a perceptual study to investigate the relationship between detectability and monitor luminance as well as ambient illuminance. A statistical test pattern was used in this study, and the test pattern was developed using Microsoft® Visual Basic 6. The test pattern contained a set of randomised contrast detail objects, that is, disks of different diameters (0.7, 1.0, 1.4, and 2.0 mm) and contrasts against a black background (2.7, 3.9, 5.5, and 7.8%), simulating lesions in digital images. The receiver operating characteristic (ROC) analysis was used in this study. The results indicated that a set of optimal viewing conditions exists and that it has a significant effect on detectability performance

A novel method for comparing radiation dose and image quality, between and within different X-ray units in a series of hospitals

Objectives: To develop a novel method for comparing radiation dose and image quality (IQ) to evaluate adult chest X-ray (CXR) imaging among several hospitals. Methods: CDRAD 2.0 phantom was used to acquire images in eight hospitals (17 digital X-ray units) using local adult CXR protocols. IQ was represented by image quality figure inverse (IQFinv), measured using CDRAD analyser software. Signal to noise ratio (SNR), contrast to noise ratio (CNR) and conspicuity index (CI) were calculated as additional measures of IQ. Incident air kerma (IAK) was calculated using a solid-state dosimeter for each acquisition. Figure of merit (FOM) was calculated to provide a single estimation of IQ and radiation dose. Results: IQ, radiation dose and FOM varied considerably between hospitals and X-ray units. For IQFinv, the mean (range) between and within the hospitals were 1.42 (0.83-2.18) and 1.87 (1.52-2.18), respectively. For IAK, the mean (range) between and within the hospitals were 93.56 (17.26 to 239.15) µGy and 180.85 (122.58-239.15) µGy, respectively. For FOM, the mean (range) between and within hospitals were 0.05 (0.01 to 0.14) and 0.03 (0.02-0.05), respectively. Conclusions: The suggested method for comparing IQ and dose using FOM concept along with the new proposed FOM, is a valid, reliable and effective approach for monitoring and comparing IQ and dose between and within hospitals. It is also can be beneficial for the optimisation of X-ray units in clinical practice. Further optimisation for the hospitals /X-ray units with low FOM are required to minimise radiation dose without degrading IQ

A new standard in testing mattresses for use in x-ray imaging : developing, validating and using a novel method to test x-ray mattresses for pressure ulcer development, radiation dosimetry and image quality

Background In hospitals, patients often undergo X-ray imaging while lying on a mattress. Therefore, mattresses must have low X-ray attenuation properties to minimise radiation dose to the patient. Mattresses should create no artifacts within the X-ray image, as this may compromise image quality and diagnosis. Finally, mattresses should be constructed in such a way that interface pressure (IP) is minimized, limiting the chance of pressure ulcer formation. Aim For evaluating X-ray imaging table mattresses, this thesis has three aims (1). to develop and validate an anthropomorphic-phantom-based method of assessing X-ray table mattress IP as an index of mattress performance; (2) to assess X-ray table mattress pressure redistribution properties; and (3) to evaluate mattress radiation attenuation characteristics and their impacts on image quality. Methods and Materials An anthropomorphic phantom, simulating adult head, pelvis, and heels, was 3D-printed from X-ray computed tomography (CT) image data. Dry sand was added to represent 5 human weights and XSensor technology was used to assess pressure distribution. Phantom mattress IP characteristics were compared for the 5 weights against 27 sets of human mattress IP data to achieve phantom validation. Twenty-four X-ray table mattresses, 21 thinner and 3 thicker were assessed. Anthropomorphic phantom and Xsensor mattress interface pressure measurements were conducted for head, pelvis and heels, with and without X-ray table mattresses. Image quality and radiation attenuation were also assessed. Incident air kerma (IAK) was measured, with and without mattress, over a range of exposure factors using a digital dosimeter. Inverse image Quality Factor (IQFinv) was calculated to assess image quality using a commercially available phantom (CDRAD). Results The anthropomorphic phantom proved suitable for use in this thesis - based on correlation coefficient R values, there was a good correlation for the 5 phantom weights between the phantom and human pressure data. (R values: head =0.993, pelvis =0.997, and heels =0.996). There were statistically significant differences (p<0.05) between peak pressure values with and without X-ray table mattress for head, pelvis and heels. Additionally, there were statistically significant differences (p<0.05) between the IP ratio values with and without X-ray table mattresses. The type and age of the mattresses also had an impact on peak pressure values and IP ratios. IAK and image quality measures were impacted by mattress addition. IAK values decreased because of attenuation, with IQFinv having worse image quality. There was a negative correlation between mattress age and IAK, meaning that older mattresses had higher attenuation properties. The clinical impact of this finding, for the potential for radiation increase, was insignificant. No correlation was found between image quality and age. Conclusion A novel method for testing X-ray mattress IP was established and validated in this thesis. This method could be valuable for aiding mattress design and development and subsequent testing when in clinical use. For new mattresses, peak pressure values and IP ratios were greatly reduced, compared with older ones. The impact mattresses had on radiation attenuation and image quality are clinically insignificant

A comparative study evaluating the performance of diagnostic radiography units and protocols for paediatric and adult chest radiography examinations

Purpose: Little is known about the variations in image quality (IQ) and radiation dose for paediatric and adult chest radiography (CXR), between and within hospitals. Large variations in IQ could influence the diagnostic accuracy, and variations in radiation dose could affect the risk to patients. This thesis aims to develop, validate and then use a novel method for comparing IQ and radiation dose for paediatric and adult CXR imaging examinations and report variation between a series of public hospitals. Method: A Figure of Merit (FOM) concept was used for the purposes of comparing IQ and radiation dose, between and within hospitals. Low contrast detail (LCD) detectability, using the CDRAD 2.0 phantom, was utilised as the main method for IQ evaluation. The validity of utilising LCD detectability, using CDRAD 2.0 phantom, for evaluating visual IQ, simulated lesion visibility (LV) and CXR optimisation studies, was investigated. This was done by determining the correlation between the LCD detectability and visual measures of IQ and LV for two lesions with different locations and visibility in the Lungman chest phantom.The CDRAD 2.0 phantom and two anthropomorphic phantoms (adult Lungman and the neonatal Gammex phantom) were used to simulate the chest region. Radiographic acquisitions were conducted on 17 X-ray units located in eight United Kingdom (UK) public hospitals within the North-west of England using their existing CXR protocols. The CDRAD 2.0 phantom was combined with different thicknesses of Polymethyl methacrylate (PMMA) slabs to simulate the chest regions of 5 different age groups: neonate, 1, 5, 10 years and adults. A Lungman phantom, with and without the fat jacket, was used to simulate average and larger sized patients. IQ was evaluated using a number of methods, including: 1) physically, by calculating LCD detectability as represented by an image quality figure inverse (IQFinv) using the CDRAD analyser software; 2) using images acquired from the anthropomorphic phantoms – for this, a relative visual grading analysis (VGA) method was used. Additionally, signal to noise ratios (SNR), contrast to noise ratios (CNR) and conspicuity indices (CI) were calculated for all phantom image data in this study. Incident air karma (IAK) was measured using a solid-state dosimeter. Results: Regarding the validation of utilising LCD detectability for evaluating visual IQ and LV, and CXR optimisation studies, a strong positive correlation (r = 0.91; p < 0.001) was observed between IQFinv and the visual IQ scores from the Lungman phantom. A good correlation was observed between IQFinv and visual LV from the Lungman phantom for both lesions (lesion 1 (with low visibility) (r = 0.79; p < 0.001); lesion 2 (with high visibility) (r =0.68; p < 0.001), respectively). Considerable variation in standard imaging protocols/techniques, radiation dose, IQ and FOM were observed between the hospitals, while within hospital variation was lower. A weak correlation between IQ and radiation dose was observed across most of the age groups studied. Conclusion: A novel method has been established to evaluate and compare IQ and radiation dose between and within hospitals based on an FOM concept. This combines IQ and radiation dose into a single factor and is the first of its kind to reported within the field of medical imaging. It can be confirmed that LCD detectability using the CDRAD 2.0 phantom is valid for evaluating visual IQ and LV and can be of use within routine quality assurance and optimisation studies in digital radiography. Further radiation dose optimisation for the paediatric age groups and adult group, especially in hospitals /X-ray machines with low IQ and high IAK, are required