Pediatric digital chest radiography, comparison of grid versus non-grid techniques

Introduction

The usefulness of anti-scatter grid in digital pediatric chest radiography was investigated by a phantom study assessing image quality using subjective evaluations and dose measurements.

Method

A contrast detail study was undertaken. Images were taken with and without anti-scatter grids (grid ratio 15:1), for PMMA phantom thickness ranging from 1 to 15 cm. Fourteen radiographers, experienced in digital pediatric and/or skeletal radiography, read 96 images. At each thickness, the image with and without grid technique was read three times, and in random order. Correct Observation Ratio (COR) and Image Quality Figures (IQF) were calculated. Dose Area Products were measured with DAP-meter.

Results

The COR and IQF values indicated statistically significant (p < 0.05) enhanced image quality when using anti-scatter grid for all thicknesses 5 cm and more. The DAP values increased significantly by grid techniques (p = 0.01).

Conclusions

Grid techniques may be beneficial to image quality for PMMA objects over 5 cm, but this leads to a higher dose. Although the magnitude of dose may be low, the dose should be kept at a minimum. In conclusion, improving image quality should be based on optimizing post-processing settings and image evaluation conditions.     

An option for optimising the radiographic technique for horizontal beam lateral (HBL) hip radiography when using digital X-ray equipment

AimTo investigate the optimum technique for the horizontal beam lateral (HBL) hip projection considering image quality and radiation dose.MethodsUsing digital radiography equipment an anthropomorphic phantom was positioned for a HBL projection of the hip. Radiographic exposures were undertaken across a range of acquisition parameters (tube potentials, source to image distances, object to detector distances, with and without an anti-scatter radiation grid/additional copper filtration). Each acquisition combination was imaged three times and the dose area product (DAP) and post-AEC mAs recorded. 168 images were acquired. A single observer evaluated five anatomical areas on all images using a two-alternative force choice technique. The reference image was selected based on the current locally accepted technique. 50 images out of the original 168 were independently assessed by a further four observers to ensure reliability of the results.ResultsImage quality, when comparing all the images to the reference, was improved on in two cases; however the radiation dose had increased. 18 images had equal image quality with some having an 80% reduction in the DAP. In terms of the diagnostic acceptability, 51 were considered acceptable with a lower radiation dose.ConclusionBy optimising acquisition factors for the HBL hip projection the radiation dose to the patient can be reduced. Based on the findings the factors proposed for HBL hip projections are 90 kVp, 135 cm SID, 45 cm ODD, grid and 0.1 mm copper filtration.     

Optimisation of the AP abdomen projection for larger patient body thicknesses

IntroductionThis study aims to identify optimal exposure parameters, delivering the lowest radiation dose while maintaining images of diagnostic quality for the antero-posterior (AP) abdomen x-ray projection in large patients with an AP abdominal diameter of >22.3 cm.MethodologyThe study was composed of two phases. In phase 1, an anthropomorphic phantom (20 cm AP abdominal diameter) was repetitively radiographed while adding 3 layers (5 cm thick each) of fat onto the phantom reaching a maximum AP abdominal diameter of 35 cm. For every 5 cm thickness, images were taken at 10 kVp (kilovoltage peak) intervals, starting from 80 kVp as the standard protocol currently in use at the local medical imaging department, to 120 kVp in combination with the use of automatic exposure control (AEC). The dose area product (DAP), milliampere-second (mAs) delivered by the AEC, and measurements to calculate the signal to noise ratio (SNR) and contrast to noise ratio (CNR) were recorded. Phase 2 included image quality evaluation of the resultant images by radiographers and radiologists through absolute visual grading analysis (VGA). The resultant VGA scores were analysed using visual grading characteristics (VGC) curves.ResultsThe optimal kVp setting for AP abdominal diameters at: 20 cm, 25 cm and 30 cm was found to be 110 kVp increased from 80 kVp as the standard protocol (with a 56.5% decrease in DAP and 76.2% in mAs, a 54.2% decrease in DAP and 76.2% decrease in mAs and a 29.2% decrease in DAP and 59.7% decrease in mAs, respectively). The optimal kVp setting for AP abdominal diameter at 35 cm was found to be 120 kVp increased from 80 kvp as the standard protocol (with a 50.7% decrease in DAP and 73.4% decrease in mAs). All this was achieved while maintaining images of diagnostic quality.ConclusionTailoring the exposure parameters for large patients in radiography of the abdomen results in a significant reductions in DAP which correlates to lower patient doses while still maintaining diagnostic image quality.Implications for clinical practiceThis research study and resultant parameters may help guide clinical departments to optimise AP abdomen radiographic exposures for large patients in the clinical setting.     

Optimisation of the lateral lumbar spine projection using an air-gap technique

IntroductionLumbar spine radiography is considered as having a high radiation dose compared to other planar radiography examinations. The aim of this study was to investigate the feasibility of replacing an antiscatter grid with an air gap technique to achieve dose reduction for lateral lumbar spine radiography while maintaining image quality on a direct digital radiography (DDR) system.MethodsIn phase 1, an experimental study using an anthropomorphic phantom identified the optimal airgap technique. In phase 2, lateral projections of the lumbar spine were performed on 50 patients randomly assigned equally into a control group (using the antiscatter grid) and an experimental group (using the airgap technique). The dose area product (DAP) was recorded, keeping other variables constant. Image quality evaluation was performed by 5 radiologists performing Absolute Visual Grading Analysis (VGA) using an image quality score tool, with resultant scores analysed using Visual Grading Characteristics (VGC).ResultsA 10 cm airgap in conjunction with a source to image distance (SID) of 121 cm was found as the optimal airgap technique. The clinical application of this technique resulted in a statistically significant (p < 0.05) reduction in DAP of 72%. Image quality scores were higher for the antiscatter grid but variation between the two techniques was not significant (p > 0.05).ConclusionReplacing the antiscatter grid with an airgap technique in lateral lumbar spine digital radiography, provides a significant dose reduction whilst still maintaining diagnostic image quality.Implications for practiceThe airgap technique is a simple and easy technique to implement and radiographers should find no difficulties in applying it, as It involves no additional cost and no additional equipment.     

Evaluating the use of higher kVp and copper filtration as a dose optimisation tool in digital planar radiography

IntroductionTo identify the potential of beam hardening techniques, specifically the use of higher kilo voltage (kV) and copper (Cu) filtration, to optimise digital planar radiographic projections. The study assessed the suitability of such techniques in radiation dose reductions while maintaining diagnostic image quality for four common radiographic projections: antero-posterior (AP) abdomen, AP-knee, AP-lumbar spine, and lateral lumbar spine.MethodsAnthropomorphic phantom radiographs were obtained at varying kVp (standard kVp, +10 kVp, and +20 kVp) and varying Cu filtration thickness (0 mm, 0.1 mm, and 0.2 mm Cu). The Dose Area Product (DAP), mAs and time (s) were recorded as an indication of the emitted radiation dose. Image quality was assessed objectively via Contrast-Noise-Ratio (CNR) calculations and subjectively via Visual Grading Analysis (VGA) performed by radiographers and radiologists.ResultsOptimised exposure protocols were established for the AP-abdomen (100 kVp with 0.2 mm Cu), AP-knee (85 kVp, and 0.1 mm Cu), AP-lumbar spine (110 kVp and 0.2 mm Cu), and lateral lumbar spine (110 kVp and 0.2 mm Cu). This strategy resulted in respective DAP reductions of 71.98%, 62.50%, 64.51% and 71.85%. While CNR values decreased as beam hardening techniques were applied, VGA demonstrated either a lack of statistical variation or improved image quality between the standard and the optimised exposure protocols.ConclusionsDAP reductions without compromising image quality can be achieved through beam hardening for the AP-abdomen, AP-knee, AP-lumbar spine, and lateral lumbar spine projections.Implications for practiceBeam hardening techniques should be considered as an optimisation strategy in medical imaging departments. Research into the applicability of this strategy for other radiographic projections is recommended.     

Effects of tube potential and scatter rejection on image quality and effective dose in digital chest X-ray examination: An anthropomorphic phantom study

ObjectivesThe purpose of this study was to investigate the effects of tube potential and scatter rejection techniques on image quality of digital posteroanterior (PA) chest radiographs.Methods: An anthropomorphic phantom was imaged using a range of tube potentials (81–125 kV_p) without scatter rejection, with an anti-scatter grid, and using a 10 cm air gap. Images were anonymised and randomised before being evaluated using a visual graded analysis (VGA) method.ResultsThe effects of tube potential on image quality were found to be negligible (p > 0.63) for the flat panel detector (FPD). Decreased image quality (p = 0.031) was noted for 125 kV_p relative to 109 kV_p, though no difference was noted for any of the other potentials (p > 0.398) for computed radiography (CR). Both scatter rejection techniques improved image quality (p < 0.01). For FPD imaging the anti-scatter grid offered slightly improved image quality relative to the air gap (p = 0.038) but this was not seen for CR (p = 0.404).ConclusionsFor FPD chest imaging of the anthropomorphic phantom there was no dependence of image quality on tube potential. Scatter rejection improved image quality, with the anti-scatter grid giving greater improvements than an air-gap, but at the expense of increased effective dose.CR imaging of the chest phantom demonstrated negligible dependence on tube potential except at 125 kV_p. Scatter rejection improved image quality, but with no difference found between techniques. The air-gap resulted in a smaller increase in effective dose than the anti-scatter grid and would be the preferred scatter rejection technique.     

Optimisation of the CT pulmonary angiogram (CTPA) protocol using a low kV technique combined with high iterative reconstruction (IR): A phantom study

IntroductionThis study aims to optimise the current CTPA protocol at a public general hospital in Malta using lower kV combined with high Iterative Reconstruction (IR) (>50%).MethodsThe research consisted of a 2-phase anthropomorphic phantom study. Phase 1: radiation dose evaluation of 6 experimental protocols consisting of the low kV technique and high IR values and comparison with the current protocol. Phase 2: image evaluation. Objective image quality was evaluated in terms of contrast to noise ratio (CNR) and signal to noise ratio (SNR). Subjective image quality evaluation was performed by 3 radiologists undertaking Absolute Visual Grading Analysis (VGA). Resultant image quality scores were analysed using Visual Grading Characteristics (VGC).ResultsAll experimental protocols achieved significant (p < 0.05) dose reductions. SNR and CNR improved in almost all protocols, however, differences were not significant (p > 0.05). In subjective image quality analysis, the current protocol provided significant superior image quality (AUC > 0.5; p < 0.05) when compared to the experimental protocols consisting of 80 kV with 70%, 80%, 90% and 100% IR. The only two experimental protocols yielding comparable image quality to the current protocol were 80 kV with 50% IR (AUC: 0.195; p: 0.137) and 80 kV with 60% IR (AUC: 0.554; p: 0.624). The protocol yielding the greatest decrease in radiation dose being 80 kV with 60% IR.ConclusionsThe optimal IR value was 60%. When applying the optimal experimental protocol (80 kV combined with 60% IR), a significant dose reduction was achieved while maintaining diagnostic image quality.Implications for practiceThe low kV technique combined with high IR parameter is easily implemented and involves no additional cost and equipment.     

To repeat or not to repeat: Radiologists demonstrated more decisiveness than their fellow radiographers in reducing the repeat rate during mobile chest radiography

IntroductionRadiologists and radiographers play a complementary role in providing an optimal image quality with decrease radiation dose and proper diagnosis during chest radiographs. We aim Investigate years of experience among radiologists and radiographers on perception of image quality and its impact on repeat rate when evaluating portable pediatric chest radiographs.MethodsIRB approved retrospective study consisted of randomly selected images (n = 131) of pediatric portable chest radiographs. Images were blindly assessed by four radiologists and four radiographers. Readers were asked to assess qualitative and quantitative image quality by rating: image quality, decision to repeat and image technique. All data was compared employing Pearson's Correlation, Visual grading characteristic (VGC) and Cohens' kappa analyses.ResultsImage quality: Radiologists (88.4%) rated images as excellent significantly more than radiographers (11.6%), and radiographers (90.1%) as poor significantly more than radiologists (9.9%) (p < 0.05). Repeat: Radiologists (57%) decided not to repeat images significantly more than radiographers (43%) (p < 0.05). Image technique: Radiologists rated images as acceptable (65%) and excellent (97.7%) significantly more than radiographers (35% and 2.3% respectively) (p < 0.05), whereas radiographers (84%) assessed image technique as poor significantly more than radiologists (16%) (p < 0.05). VGC: radiographers had slightly better qualitative evaluation of image quality than radiologists. An association between image quality (p < 0.002) and repeat decision (p < 0.044) with years of experience was established when comparing years of experience with image assessment rubric, while no association was noted with image technique (p < 0.9).ConclusionRadiologists demonstrated more decisiveness than their fellow radiographers in reducing the repeat rate of portable pediatric chest radiographs. Interestingly, years of experience only seem to affect image technique and image quality assessment among radiologists.Implications for practiceContinuous education of radiographers and close collaboration with radiologists is crucial to achieve optimal image quality and low radiation doses.     

Metal artefact reduction in low-dose computed tomography: Benefits of tin prefiltration versus postprocessing of dual-energy datasets over conventional CT imaging

IntroductionThe purpose of this study was to determine the potential for metal artefact reduction in low-dose multidetector CT as these pose a frequent challenge in clinical routine. Investigations focused on whether spectral shaping via tin prefiltration, virtual monoenergetic imaging or virtual blend imaging (VBI) offers superior image quality in comparison with conventional CT imaging.MethodsUsing a third-generation dual-source CT scanner, two cadaveric specimens with different metal implants (dental, cervical spine, hip, knee) were examined with acquisition protocols matched for radiation dose with regards to tube voltage and current. In order to allow for precise comparison, and due to the relatively short scan lengths, automatic tube current modulation was disabled. Specifically, the following scan protocals were examined: conventional CT protocols (100/120 kVp), tin prefiltration (Sn 100/Sn 150 kVp), VBI and virtual monoenergetic imaging (VME 100/120/150 keV). Mean attenuation and image noise were measured in hyperdense and hypodense artefacts, in artefact-impaired and artefact-free soft tissue. Subjective image quality was rated independently by three radiologists.ResultsObjectively, Sn 150 kVp allowed for the best reduction of hyperdense streak artefacts (p < 0.001), while VME 150 keV and Sn 150 kVp protocols facilitated equally good reduction of hypodense artefacts (p = 0.173). Artefact-impaired soft tissue attenuation was lowest in Sn 150 kVp protocols (p ≤ 0.011), whereas all VME showed significantly less image noise compared to conventional or tin-filtered protocols (p ≤ 0.001). Subjective assessment favoured Sn 150 kVp regarding hyperdense streak artefacts and delineation of cortical bone (p ≤ 0.005). The intraclass correlation coefficient was 0.776 (95% confidence interval: 0.712–0.831; p < 0.001) indicating good interrater reliability.ConclusionIn the presence of metal implants in our cadaveric study, tin prefiltration with 150 kVp offers superior artefact reduction for low-dose CT imaging of osseous tissue compared with virtual monoenergetic images of dual-energy datasets. The delineation of cortical boundaries seems to benefit particularly from spectral shaping.Implications for practiceLow-dose CT imaging of osseous tissue in combination with tin prefiltration allows for superior metal artefact reduction when compared to virtual monoenergetic images of dual-energy datasets. Employing this technique ought to be considered in daily routine when metal implants are present within the scan volume as findings suggest it allows for radiation dose reduction and facilitates diagnosis relevant to further treatment.     

10 kVp rule – An anthropomorphic pelvis phantom imaging study using a CR system: Impact on image quality and effective dose using AEC and manual mode

PurposeThis study aims to investigate the influence of tube potential (kVp) variation in relation to perceptual image quality and effective dose (E) for pelvis using automatic exposure control (AEC) and non-AEC in a Computed Radiography (CR) system.Methods and materialsTo determine the effects of using AEC and non-AEC by applying the 10 kVp rule in two experiments using an anthropomorphic pelvis phantom. Images were acquired using 10 kVp increments (60–120 kVp) for both experiments. The first experiment, based on seven AEC combinations, produced 49 images. The mean mAs from each kVp increment were used as a baseline for the second experiment producing 35 images. A total of 84 images were produced and a panel of 5 experienced observers participated for the image scoring using the two alternative forced choice (2AFC) visual grading software. PCXMC software was used to estimate E.ResultsA decrease in perceptual image quality as the kVp increases was observed both in non-AEC and AEC experiments, however no significant statistical differences (p > 0.05) were found. Image quality scores from all observers at 10 kVp increments for all mAs values using non-AEC mode demonstrates a better score up to 90 kVp. E results show a statistically significant decrease (p = 0.000) on the 75th quartile from 0.37 mSv at 60 kVp to 0.13 mSv at 120 kVp when applying the 10 kVp rule in non-AEC mode.ConclusionUsing the 10 kVp rule, no significant reduction in perceptual image quality is observed when increasing kVp whilst a marked and significant E reduction is observed.     

Scatter dose calculation for anti-scatter linear grids in mammography

Monte Carlo simulations were used to optimize the geometry of a mammography anti-scatter linear grid to achieve minimum scatter-to-primary ratio (SPR) for different X-ray tube voltages. A single optimum design of the grid with 0.9 mm septa height, 12 μm septa thickness and 100 μm interspace thickness was found for breast phantom thicknesses between 30 and 80 mm. The optimal grid has 0.153–0.330 scatter-to-primary ratio, a Bucky factor (BF) less than 2.5 and a contrast improvement factor (CIF) of 1.3.     

The combined application of the contrast-to-noise index and 80 kVp for cardiac CTA scanning before atrial fibrillation ablation reduces radiation dose exposure

IntroductionTo compare the radiation dose, diagnostic accuracy, and the resultant ablation procedures using 80 and 120-kVp cardiac computed tomography angiography (CCTA) protocols with the same contrast-to-noise ratio in patients scheduled for atrial fibrillation (AF) ablation.MethodsThis retrospective study was performed following institutional review board approval. We divided 140 consecutive patients who had undergone CCTA using a 64-MDCT scanner into two equal groups. Standard deviation (SD) of the CT number was set at 25 Hounsfield units (HU) for the 120-kVp protocol. To facilitate a reduction in radiation dose it was set at 40 HU for the 80 kVp protocol. We compared the two protocols with respect to the radiation dose, the diagnostic accuracy for detecting left atrial appendage (LAA) thrombi, matching for surface registration, and the resultant ablation procedures.ResultsAt 120 kVp, the dose length product (DLP) was 2.2 times that at 80 kVp (1269.0 vs 559.0 mGy cm, p < 0.01). The diagnostic accuracy for thrombus detection was 100% using both protocols. There was no difference between the two protocols with respect to matching for surface registration. The protocols did not differ with respect to the subsequent time required for the ablation procedures and the ablation fluoroscopy time, and the radiation dose (p = 0.54, 0.33, and 0.32, respectively).ConclusionFor the same CNR, the DLP at 80 kVp (559.0 mGy cm) was 56% of that delivered at 120 kVp (1269.0 mGy cm). There was no reduction in diagnostic accuracy.Implications for practiceMaintaining CNR allows for a reduction in the radiation dose without reducing the image quality.     

Radiography of the knee joint: A comparative study of the standing partial flexion PA projection and the standing fully extended AP projection using visual grading characteristics (VGC)

ObjectivesTo compare the diagnostic information in detection and assessment of knee pathology from knee radiographs using either the PA standing with partial flexion projection or AP fully extended standing projection.MethodA set of 32 knee radiographs was retrospectively compiled from 16 adult patients imaged using both projections over a 2-year period (PA: n = 16 and AP: n = 16). Repeat radiographs (n = 6) were added to the image set facilitating inter and intra observer reliability. Image evaluation was performed by 5 orthopaedic surgeons performing Absolute Visual Grading Analysis assessing image quality based on 6 anatomical image quality criteria specifically developed to evaluate and compare the two projections. The resulting image quality scores were analysed using Visual Grading Characteristics.ResultsImage quality scores were higher for the PA projection but variation between the two projections was not significant (p > 0.05). The PA projection was significantly (p < 0.05) better in the visualization of 2 anatomical image quality criteria involving the joint space width and tibial spines.ConclusionBoth projections can be used for general evaluation of the knee joint, however the PA partial flexion projection is preferred for the investigation of specific knee pathology. Recommendations for minimizing variations in radiographic positioning technique are also highlighted.     

Fact or fiction: An analysis of the 10 kVp ‘rule’ in computed radiography

PurposeTo determine whether increasing the tube voltage by 10 kVp whilst reducing the tube current by 50% (10 kVp ‘rule’) produces similar perceptual image quality.Method391 matched pairs of anthropomorphic chest phantom X-ray images were produced on a computed radiography (CR) system. Five experienced clinicians graded the images using a 2 alternative forced choice comparison method. Based on acquisition parameters and dose area product (DAP) readings, effective dose (E) was calculated for all images using dose calculation software.ResultsPerceptual image quality scores prior to and following application of the 10 kVp ‘rule’ were found have no statistical difference (p > 0.1), indicating that the increase in kVp and reduction in mAs had limited impact on the perceptual image quality. In all cases E reduced, with an average 36% (s.d 7%) after the ‘rule’ had been applied (p < 0.001).ConclusionResults demonstrate that application of the 10 kVp ‘rule’ significantly reduces E, with no significant reduction in perceptual image quality. Further research should be conducted for a range of examinations using CR and digital radiography (DR) systems.     

降低儿童16层螺旋CT检查辐射剂量的研究

目的论证CT扫描参数kVp和mAs与剂量和图像噪声的关系,在不影响临床诊断的基础上,修正并验证一种基于成人扫描参数的安全可行的儿童16层螺旋CT检查的扫描参数。方法利用16层螺旋CT,采用标准CT剂量指数(CTDI)测试仪、100mm笔型电离室,分别测量16cm和32cm直径模体在2mm×5mm准直宽度时不同kVp和mAs的CTDI;采用20cm标准水模,测量单一感兴趣区域(ROI)标准偏差值SD代表噪声水平。以成人扫描参数的不同百分比修正为不同年龄段儿童CT扫描的参数供临床验证。结果随着kVp和mAs的增加,CTDI随之增加,并与mAs呈线性关系;16cm直径模体的表面CTDI要高于32cm模体58%;实际的加权CTDIw值高于CT扫描仪显示的CTDIw;mAs相同时,kVp越高,图像噪声SD值越低,在kVp固定时,随着mAs的增加,图像噪声SD随之减少,当mAs增加到一定程度后,图像噪声趋向平稳。结论在不影响临床诊断的图像噪声水平下,根据年龄和体型特点,儿童16层CT检查mAs可以比成人降低10%～85%。     

Comparison of image quality and patient dose for chest x-ray examinations on conventional and low cost computed radiography systems

PurposeThe aims of this study were to assess if clinical chest radiographs taken at two computed radiography (CR) facilities fulfill standard quality criteria on conventional display monitor and the status of patient doses.MethodsTwenty-five adult patients were x-rayed at 102–109 kVp using Fuji type C image plates and low cost Philips PCR digitizer. Another group of 25 patients were x-rayed at 120 kVp using CRMD 4.0 image plates and conventional Agfa 75 CR digitizer. All 50 radiographs were independently assessed by four radiologists on conventional display monitor (model HP M70) with image software using six standard quality criteria. Entrance surface air kerma (ESAK) was determined using the measured incident air kerma values and exposure parameters.ResultsThe results show that the differences in visualization of anatomical structure in terms of image quality criteria were comparable (p > 0.05), with the exception of the visualisation of intervertebral disc spaces. However, the ESAK values for Philips PCR were higher than those for Agfa CR 75 (p < 0.001).ConclusionImages from a low cost CR system can display anatomic details comparably to conventional CR system but at the cost of higher radiation dose. Optimisation of variables that effect patient dose is desirable when using low cost CR systems.     

Manual or auto-mode: Does this affect radiation dose in digital mammography without compromising image quality?

IntroductionIn current practice, auto-filter exposure mode is used for most screening mammography examinations. However, with better understanding of the side effects of radiation, it is important to examine exposure parameters and practises to minimise radiation dose to patients. The purpose of this phantom study is to investigate the impact that different exposure modes (manual, auto-time and auto-filter) have on radiation dose, while maintaining images of diagnostic quality.MethodsThis study was conducted in three stages. In the first stage, 125 images were taken using a Gammex 156 phantom with polymethyl methacrylate blocks to reflect varying thicknesses (4.5, 5.0, 5.5, 6.0 and 6.5 cm). In the second stage, three mammographers independently assessed image quality and assigned scores based on the number of distinct fibers, masses and speck groups visible. Images with acceptable quality were further investigated in the third stage by comparing their average glandular dose (AGD) using the Kruskal–Wallis H test and Dunn's post-hoc pairwise analysis.ResultsSignificant differences in AGD were shown between the auto-filter mode and manual mode techniques for 6.0 cm, and between auto-time mode and manual mode techniques for 6.5 cm (p < 0.05).ConclusionFor 4.5, 5.0 and 5.5 cm phantoms, as AGD was not significantly different among the different modes, the auto-filter may remain the most practical option. However, significant reductions in AGD were obtained for the 6.0 and 6.5 cm phantoms when manual mode techniques were used.Implications for practiceManual mode techniques can potentially provide dose-saving opportunity in 6.0 and 6.5 cm breast thickness though future work on human breast should be done to confirm this. Results from this study will support future research based on patient data.     

Patient-based low dose cone beam CT acquisition settings for prostate image-guided radiotherapy treatments on a Varian TrueBeam linear accelerator

Objective:To evaluate the performance of low dose cone beam CT (CBCT) acquisition protocols for image-guided radiotherapy of prostate cancer.Methods:CBCT images of patients undergoing prostate cancer radiotherapy were acquired with the settings currently used in our department and two low dose settings at 50% and 63% lower exposure. Four experienced radiation oncologists and two radiation therapy technologists graded the images on five image quality characteristics. The scores were analysed through Visual Grading Regression, using the acquisition settings and the patient size as covariates.Results:The low dose acquisition settings have no impact on the image quality for patients with body profile length at hip level below 100 cm.Conclusions:A reduction of about 60% of the dose is feasible for patients with size below 100 cm. The visibility of low contrast features can be compromised if using the low dose acquisition settings for patients with hip size above 100 cm.Advances in knowledge:Low dose CBCT acquisition protocols for the pelvis, based on subjective evaluation of patient images.     

Can the anode heel effect be used to optimise radiation dose and image quality for AP pelvis radiography?

IntroductionA study was conducted to determine whether the anode heel effect can be used to influence optimisation of radiation dose and image quality (IQ) for AP pelvis radiography.MethodsATOM dosimetry phantom and an anthropomorphic phantom were positioned for AP pelvis. Using a CR system, images were acquired and doses were measured with phantom feet toward anode and then feet toward cathode. Exposure factors (kVp, mAs and SID) were systematically generated using a factorial design. Images were scored visually for quality using relative visual grading together with a 3 point Likert scale. Signal to noise ratio was also calculated as a physical measure of image quality. Dosimetry data were collected for the ovaries and testes.ResultsThe optimum technique for male, which resulted in lower dose and suitable image quality, was with feet positioned toward the anode (0.80 ± 0.03 mGy; SNR of 38 ± 2.9; visual IQ score 3.13 ± 0.35). The optimum technique for female was with feet toward anode (0.23 ± 0.02 mGy; SNR of 34.7 ± 2.6; visual IQ score 3.15 ± 0.26). kVp had the biggest effect on both visual and physical image quality metrics (p < 0.001) for both tube orientations, whereas SID had the lowest effect on both visual and physical image quality metrics compared with mAs and kVp (p < 0.001). The effect of SID on the SNR was not significant (p > 0.05) with feet toward anode.ConclusionPositioning the patient with feet toward the anode, as opposed to the cathode, has no adverse effect on visual image quality assessment but it does have an effect on physical image quality.Implications for practiceThis study would add a new clinical concept in positioning of AP pelvis radiography especially for male positioning.     

Image quality and dose analysis for a PA chest X-ray: Comparison between AEC mode acquisition and manual mode using the 10 kVp ‘rule’

PurposeTo compare the image quality and effective dose applying the 10 kVp rule with manual mode acquisition and AEC mode in PA chest X-ray.Method68 images (with and without lesions) were acquired using an anthropomorphic chest phantom using a Wolverson Arcoma X-ray unit. These images were compared against a reference image using the 2 alternative forced choice (2AFC) method. The effective dose (E) was calculated using PCXMC software using the exposure parameters and the DAP. The exposure index (lgM provided by Agfa systems) was recorded.ResultsExposure time decreases more when applying the 10 kVp rule with manual mode (50%–28%) when compared with automatic mode (36%–23%). Statistical differences for E between several ionization chambers' combinations for AEC mode were found (p = 0.002). E is lower when using only the right AEC ionization chamber. Considering the image quality there are no statistical differences (p = 0.348) between the different ionization chambers' combinations for AEC mode for images with no lesions. Considering lgM values, it was demonstrated that they were higher when the AEC mode was used compared to the manual mode. It was also observed that lgM values obtained with AEC mode increased as kVp value went up. The image quality scores did not demonstrate statistical significant differences (p = 0.343) for the images with lesions comparing manual with AEC mode.ConclusionIn general the E is lower when manual mode is used. By using the right AEC ionising chamber under the lung the E will be the lowest in comparison to other ionising chambers. The use of the 10 kVp rule did not affect the visibility of the lesions or image quality.