Relationship between body habitus and image quality and radiation dose in chest X-ray examinations: A phantom study

Effects of body part thickness on low-contrast detail detection and radiation dose during adult chest radiography

INTRODUCTION

Differences in patient size often provide challenges for radiographers, particularly when choosing the optimum acquisition parameters to obtain radiographs with acceptable image quality (IQ) for diagnosis. This study aimed to assess the effect of body part thickness on IQ in terms of low-contrast detail (LCD) detection and radiation dose when undertaking adult chest radiography (CXR).

METHODS

This investigation made use of a contrast detail (CD) phantom. Polymethyl methacrylate (PMMA) was utilised to approximate varied body part thicknesses (9, 11, 15 and 17 cm) simulating underweight, standard, overweight and obese patients, respectively. Different tube potentials were tested against a fixed 180 cm source to image distance (SID) and automatic exposure control (AEC). IQ was analysed using bespoke software thus providing an image quality figure inverse (IQFinv ) value which represents LCD detectability. Dose area product (DAP) was utilised to represent the radiation dose.

RESULTS

IQFinv values decreased statistically (P = 0.0001) with increasing phantom size across all tube potentials studied. The highest IQFinv values were obtained at 80 kVp for all phantom thicknesses (2.29, 2.02, 1.8 and 1.65, respectively). Radiation dose increased statistically (P = 0.0001) again with increasing phantom thicknesses.

CONCLUSION

Our findings demonstrate that lower tube potentials provide the highest IQFinv scores for various body part thicknesses. This is not consistent with professional practice because radiographers frequently raise the tube potential with increased part thickness. Higher tube potentials did result in radiation dose reductions. Establishing a balance between dose and IQ, which must be acceptable for diagnosis, can prevent the patient from receiving unnecessary additional radiation dose.

Method of determining technique from weight and height to achieve targeted detector exposures in portable chest and abdominal digital radiography

This study presents a methodology to develop an X-ray technique chart for portable chest and abdomen imaging which utilizes patient data available in the modality worklist (MWL) to reliably achieve a predetermined exposure index (EI) at the detector for any patient size. The method assumes a correlation between the patients' tissue equivalent thickness and the square root of the ratio of the patient's weight to height. To assess variability in detector exposures, the EI statistics for 75 chest examinations and 99 abdominal portable X-ray images acquired with the new technique chart were compared to those from a single portable unit (chest: 3877 images; abdomen: 200 images) using a conventional technique chart with three patient sizes, and to a stationary radiography room utilizing automatic exposure control (AEC) (chest: 360 images; abdomen: 112 images). The results showed that when using the new technique chart on a group of portable units, the variability in EI was significantly reduced (p < 0.01) for both AP chest and AP abdomen images compared to the single portable using a standard technique chart with three patient sizes. The variability in EI for the images acquired with the new chart was comparable to the stationary X-ray room with an AEC system (p > 0.05). This method could be used to streamline the entire imaging chain by automatically selecting an X-ray technique based on patient demographic information contained in the MWL to provide higher quality examinations to clinicians by eliminating outliers. In addition, patient height and weight can be used to estimate the patients' tissue equivalent thickness.

PATIENT DOSE ASSESSMENT AND OPTIMISATION OF PELVIC RADIOGRAPHY WITH COMPUTED RADIOGRAPHY SYSTEMS

Digital radiography systems can reduce radiation dose, this capability was harnessed to explore dose and image quality (IQ) optimisation strategies. Entrance surface dose (ESD), effective dose (ED) and organ doses were determined by the indirect method for patients undergoing pelvic anteroposterior X-ray examinations with computed radiography systems. The IQ of patients' radiographs was assessed in terms of signal-to-noise ratio (SNR). An anthropomorphic phantom was exposed with varying tube potential (kVp), tube current-time product (mAs), and focus-to-detector distance (FDD) to determine phantom-entrance dose for the optimisation studies. SNR of each phantom radiograph was determined. Patients' mean ESD of 2.38 ± 0.60 mGy, ED of 0.25 ± 0.07 mSv and SNR of 8.5 ± 2.2 were obtained. After optimisation, entrance dose was reduced by 29.2% with 5 cm increment in FDD, and 5 kVp reduction in tube potential. kVp and/or mAs reduction with an increment in FDD reduced entrance dose without adversely compromising radiographic-IQ.

Evaluation of image quality and patient exposure in fluoroscopy using a phantom: Is there any clinical relevance?

OBJECTIVE

To investigate the impact of X-ray preset acquisition protocol settings on fluoroscopy image quality (IQ) and radiation exposure.

MATERIALS & METHODS

A quality control (QC) phantom was imaged with a modern digital C-arm system, using various preset fluoroscopy protocols. IQ was assessed using human observers and in-house software for automated evaluation, based on contrast-to-noise ratios of details and their background. Patient radiation exposure was evaluated using the displayed Incident Air-Kerma and Kerma-Area Product values.

RESULTS

Protocol selection affects radiation exposure by a factor of about 3. IQ evaluation showed that acquisition protocols produce images with quite different characteristics. The visual IQ evaluation method was time consuming and cumbersome. The automated method, utilized the visual IQ evaluation results for calibration of detection thresholds. However, it failed to reproduce these results for all images and details types. In some images, digital image processing created artifacts which affected the pixel value distributions around details in a way that could be handled only by the human vision.

CONCLUSION

Manufacturers provide many preset protocols designated for specific clinical uses, which have large impact on IQ characteristics and radiation exposure. However, protocol settings' selection rationale is essentially a "black box" for the end user. Though QC phantoms are currently used for IQ evaluation, they are not appropriate for drawing firm conclusions concerning the expected performance of each protocol in clinical practice. Currently, there is no consensus on the optimum technical characteristics of preset protocols for specific procedures. More work is needed in this area.

LOW BMI PATIENT DOSE IN DIGITAL RADIOGRAPHY

In this study, the radiation dose received by 364 low body mass index (BMI) adult patients undergoing chest, abdomen, lumbar spine, kidneys and urinary bladder (KUB) and pelvis X-ray examinations in an X-ray room with a digital radiography system was evaluated. The patients' kerma area product (KAP) values were recorded, and the entrance surface air kerma (ESAK) was calculated based on the X-ray tube output, exposure parameters and technical data. The 75th percentiles of the distribution of ESAK and KAP values were also estimated. The dose values were compared with the corresponding values for normal patients obtained from a previous survey in our hospital, as well as with the national and UK diagnostic reference levels (DRLs). The correlation of dose values with patient size metrics (mass, height, BMI) was also investigated. A statistically significant difference was found in KAP and the ESAK values between low BMI and normal patients (Mann-Whitney test, p < 0.05), for all examinations studied. The percentage difference for chest PA, chest LAT, abdomen PA, lumbar spine AP, lumbar spine LAT, pelvis AP and KUB AP examinations was 40, 36, 48, 68, 57, 46 and 67% for median KAP and 26, 43, 52, 48, 19, 44 and 51% for median ESAK, respectively. The corresponding 75th percentiles for low BMI patients were 0.065, 0.349, 0.683, 1.54, 3.92, 1.11, 0.67 mGy and 0.042, 0.218, 0.450, 0.280, 0.598, 0.597, 0.267 Gycm2 in terms of ESAK and KAP values, respectively. They were 74-90% lower compared to the national diagnostic reference levels (DRLs), 35-84% and 58-82% compared to the UK DRLs, for ESAK and KAP values, respectively. Regarding the gender of the patients, no statistically significant difference was found in the dose values between female and male patients (Mann-Whitney test, p > 0.05), for all examinations studied. A statistically significant correlation was found between ESAK and KAP values with BMI for KUB AP, pelvis AP, lumbar spine AP, lumbar spine LAT and chest PA, while for chest LAT examinations, only the ESAK were significantly correlated with BMI. They also significantly correlated with the mass for KUB AP, lumbar spine LAT, abdomen PA and chest PA examinations, while no significant correlation was found between the dose values and patients' height. It can be concluded that the low BMI patients received a significantly reduced radiation dose compared to normal patients. Additional studies need to be conducted for these patient groups, which could contribute to the further development of a radiation protection culture in diagnostic radiography.

Neonatal chest radiography: Influence of standard clinical protocols and radiographic equipment on pathology visibility and radiation dose using a neonatal chest phantom

INTRODUCTION

Little is known about the variations in pathology visibility (PV) and their corresponding radiation dose values for neonatal chest radiography, between and within hospitals. Large variations in PV could influence the diagnostic outcome and the variations in radiation dose could affect the risk to patients. The aim of this study is to compare the PV and radiation dose for standard neonatal chest radiography protocols among a series of public hospitals.

METHODS

A Gammex 610 neonatal chest phantom was used to simulate the chest region of neonates. Radiographic acquisitions were conducted on 17 X-ray machines located in eight hospitals, utilising their current neonatal chest radiography protocols. Six qualified radiographers assessed PV visually using a relative visual grading analysis (VGA). Signal to noise ratios (SNR) and contrast to noise ratios (CNR) were measured as a measure of image quality (IQ). Incident air kerma (IAK) was measured using a solid-state dosimeter.

RESULTS

PV and radiation dose varied substantially between and within hospitals. For PV, the mean (range) VGA scores, between and within the hospitals, were 2.69 (2.00-3.50) and 2.73 (2.33-3.33), respectively. For IAK, the mean (range), between and within the hospitals, were 24.45 (8.11-49.94) μGy and 34.86 (22.26-49.94) μGy, respectively.

CONCLUSION

Between and within participating hospitals there was wide variation in the visibility of simulated pathology and radiation dose (IAK).

IMPLICATIONS FOR PRACTICE

X-ray units with lower PV and higher doses require optimisation of their standard clinical protocols. Institutions which can offer acceptable levels of PV but with lower radiation doses should help facilitate national optimisation processes.

Calculating the target exposure index using a deep convolutional neural network and a rule base

PURPOSE

The objective of this study is to determine the quality of chest X-ray images using a deep convolutional neural network (DCNN) and a rule base without performing any visual assessment. A method is proposed for determining the minimum diagnosable exposure index (EI) and the target exposure index (EIt).

METHODS

The proposed method involves transfer learning to assess the lung fields, mediastinum, and spine using GoogLeNet, which is a type of DCNN that has been trained using conventional images. Three detectors were created, and the image quality of local regions was rated. Subsequently, the results were used to determine the overall quality of chest X-ray images using a rule-based technique that was in turn based on expert assessment. The minimum EI required for diagnosis was calculated based on the distribution of the EI values, which were classified as either suitable or non-suitable and then used to ascertain the EIt.

RESULTS

The accuracy rate using the DCNN and the rule base was 81%. The minimum EI required for diagnosis was 230, and the EIt was 288.

CONCLUSION

The results indicated that the proposed method using the DCNN and the rule base could discriminate different image qualities without any visual assessment; moreover, it could determine both the minimum EI required for diagnosis and the EIt.