Low-dose lung CT: Optimizing diagnostic radiation dose – A phantom study

Radiation dose reduction is essential in paediatric lung computed tomography (CT). Advances in energy-integrating detector CT and deep-learning reconstruction may enable ultra-low-dose imaging comparable to photon-counting CT. To evaluate the radiation dose and performance of an ultra-low-dose lung CT protocol using a wide-detector energy-integrating CT system in paediatric patients, focusing on effective radiation dose and diagnostic image quality. A total of 277 low-dose lung CT scans from 106 paediatric patients (age range, 113days to 17.85years) were retrospectively analysed. All scans were acquired in axial mode using a 256-slice-multidetector CT scanner with deep learning image reconstruction and attenuation-based Auto Prescription. Radiation dose parameters, including volume CT dose index, dose-length product, size-specific dose estimate, and effective dose, were calculated. Signal-to-noise ratio and contrast-to-noise ratio were assessed in standardised anatomical regions. Patients were stratified by age, and statistical analysis was conducted to evaluate dose trends and image quality metrics. There were significant differences between all age groups for all dose parameters (Kruskal-Wallis test, P<0.05). The median effective dose increased with age, ranging from 0.12mSv (interquartile range (IQR) 0.09-0.14mSv) in the 0-5-year group to 0.23mSv (IQR 0.21-0.25mSv) in adolescents aged 15 years to <18years. Contrast-to-noise ratio and signal-to-noise ratio exhibited age-dependent variation with a small increase in older age groups. One-sided non-inferiority testing demonstrated that the signal-to-noise ratio and contrast-to-noise ratio in the youngest age group (0-5years) were not significantly inferior to those in the ≥15-year group (P<0.05). All examinations were deemed diagnostically sufficient by board-certified paediatric radiologists. Non-disruptive artefacts such as cardiac motion and step artefacts occurred frequently but did not impair interpretation. Ultra-low-dose lung CT using wide-detector energy-integrating CT with deep-learning image reconstruction allows for routine diagnostic imaging in children at radiation doses ranging from 0.12mSv to 0.23mSv, comparable to those reported for newer photon-counting CT systems. This approach provides a robust, clinically viable strategy for minimizing radiation exposure while maintaining diagnostic image quality.

Introduction CT coronary angiography (CTCA) is widely applied in coronary artery disease. It is therefore important that imaging protocols are optimised to obtain diagnostic images at the lowest possible radiation dose. We aimed to establish the feasibility of single heart-beat imaging in 320-multidetector CTCA, and assess variables that affect image quality. Methods Consecutive patients (n=249, 38% male) underwent contrast enhanced prospective electrocardiogram-gated single heart-beat CTCA. We assessed images before and after the introduction of sublingual glyceryl trinitrate to the CTCA protocol. Tube current and voltage were selected based on body-mass index (BMI) and acquisition window was selected based on heart rate (70–80% or 30–80% if the heart rate was below or above 65 beats/min respectively). Images were assessed by two trained observers and image quality was graded on a 4-point scale (1, excellent; 4, poor). Obstructive disease was defined as a stenosis of greater than 70% diameter. Results The mean heart rate was 60 beats/min (95% CI 59 to 62), BMI 29 kg/m2 (28, 30), age 58 years (56, 59) and dose-length product 283 mGy cm (266, 301). During scanning, 133(51%) received sublingual glyceryl trinitrate (GTN), 9(4%) had ectopic beats, and 12(5%) had atrial fibrillation. Diagnostic image quality was obtained in 99% with mean image quality 1.4 (1.3, 1.5). For patients with a BMI of 30 or above (n=111) diagnostic image quality was obtained in 109 scans (98%) and excellent image quality was obtained in 78 scans (70%). For patients with a heart rate above 65 bpm (n=58) diagnostic image quality was obtained in 98% (57 scans) and excellent image quality was obtained in 36% (21 scans). The mean dose-length product was 283 mGy cm (266, 301). An increase in heart rate led to an increase in radiation dose to 377 mGy cm (286, 268) for patients with a heart rate of greater than 80 beats/min (p&lt;0.001). A higher radiation dose was also associated with a BMI above 30 (DLP 231 (213, 248) vs 353 (330, 377), p&lt;0.001) and the presence of arrhythmia (DLP 275 (259, 290) vs 384 (301, 467), p 0.013). Age, sex, atrial fibrillation, ectopics, diabetes mellitus (12%) and the presence of obstructive coronary disease were not related to image quality. In multivariate regression analysis a lower heart rate and GTN were associated with improved image quality (β 0.439, p&lt;0.001 and β −0.199, p=0.001 respectively). Figure 1 The effect of heart rate, BMI and arrhythmia on the proportion of CTCA with diagnostic image quality. Conclusions Optimal image quality in single heart-beat 320-multidetector CTCA is achievable at low radiation doses in 99% of unselected patients. Image quality is further improved by lower heart rate and sublingual GTN. This study has established the use of half-segment reconstruction in all patients undergoing wide volume CTCA irrespective of heart rate, ectopic beats and the presence of atrial fibrillation. A widened window of acquisition can be used to improve image quality in patients with a heart rate greater than 65 beats per minute. In addition we have established that the use of GTN improves image quality in 320 multidetector CTCA.

The present clinical trial was intended to clarify whether subjective assessments of diagnostic X-ray image quality achieved via hand-held (HH) Nomad Pro 2 (KaVo Kerr, Brea, CA, USA) X-ray device is non-inferior that of the wall-mounted (WM) KaVo Focus (KaVo Dental, Bieberich, Germany). A prospective, cross-over, and in vivo non-inferiority clinical trial was conducted to compare these two diagnostic modalities. Based on sampling calculations, 205 patients were selected for study, generating 410 paired bitewing radiographs in randomized sequence. The films were assessed independently, engaging three observers blinded to modality for random, side-by-side-comparisons. Diagnostic image quality was rated as follows: no preference, HH preference, or WM preference. Observer judgements were combined accordingly to reach a majority. Collective observer ratings indicated no preference for diagnostic image quality in 63.9% of cases, with WM preference at 16.6% and HH preference at 19.5%. The difference in HH and WM preferences (19.5%-16.6% = 2.9%) was within the expected 95% confidence interval. Majority agreement was reached in 82.7%. Subjectively assessed diagnostic image quality in bitewing radiographs acquired by HH and WM devices did not differ significantly. The hand-held device is thus non-inferior to the WM in this regard. Our data set of paired bitewing radiographs may subsequently aid in future research.

The exposure to ionizing radiation has raised concerns about coronary CT angiography (CCTA). Recently, prospective ECG-triggered sequential scan technique has been introduced in CCTA to significantly reduce radiation exposure. The purpose of this study was to analyze our experience with the sequential scan technique on a dual-source CT system with respect to image quality and radiation dose. Qualitative and quantitative image quality as well as radiation dose were assessed in 514 consecutive patients undergoing CCTA either with sequential or spiral image acquisition technique on dual-source CT. The selection of the applied scan technique was at the discretion of an experienced coronary CT angiographer. A multivariate logistic regression analysis was applied to identify predictors of diagnostic image quality. Diagnostic CCTA image quality was found in 1,395/1,429 (97.6%) versus 4,664/4,782 (97.5%) of the coronary segments in patients studied with sequential versus spiral scanning (P = 0.82). While the application of betablockers for CCTA was an independent factor for improved image quality in the multivariate regression analysis, heart rate variability and body mass index were indepentently associated with a deterioriated image quality. The scan technique had no independent impact on diagnostic image quality. Mean estimated radiation dose was reduced by 63% in patients studied with sequential scan technique (3.4 ± 2.2 vs. 7.6 ± 5.0 mSv, P < 0.01). In patients with a low and stable heart rate, the sequential scan technique is a promising method to effectively reduce radiation exposure in dual-source CCTA. Due to the comparable image quality in sequential and spiral dual-source CCTA, the sequential scan technique should be considered as the primary scan protocol in appropriate patients.

In CT scanning, image quality has many components and is influenced by many technical parameters. While image quality has always been a concern for the physics community, clinically acceptable image quality has become even more of an issue as strategies to reduce radiation dose — to all patients, but especially to pediatric patients— has become a focus in many radiology practices.The purpose of this presentation will be to first describe several of the components of CT image quality — noise, slice thickness (Z‐axis resolution), low contrast resolution and high contrast resolution— as well as radiation dose and to describe how each of these may be affected by technical parameter selection. This presentation will pay particular attention to the tradeoffs that exist between different aspects of image quality, especially when the reduction of radiation dose is one of the objectives.The presentation will then explore several mechanisms that can be used to reduce radiation dose in CT exams and the implications for the diagnostic image quality of the exam. Specifically, the implications of varying the tube current*time product (mAs), pitch or tablespeed (or for axial imaging, the table increment), slice thickness, beam energy (kVp), patient (or phantom) size and dose reduction options (such as tube current modulation) will be described for both radiation dose and diagnostic image quality. Finally, this presentation will emphasize that the tradeoffs between radiation dose and image quality are clinical‐task dependent; that is, the goals of the clinically indicated exam dictate what aspect of image quality may be emphasized for that exam (low contrast resolution or high contrast spatial resolution, etc.) and this will have implications for the amount of radiation dose reduction that is acceptable. This will be illustrated with examples from selected diagnostic imaging exams.Educational Objectives:1. Understand key components of image quality in CT scanning as well as reinforce CT radiation dose concepts.2. Understand the impact that technical parameter selection has on the various aspects of image quality and radiation dose.3. Examine the tradeoffs between various aspects of image quality and radiation dose.4. Examine the impact of these tradeoffs on a few clinical imaging protocols and illustrate the task‐dependence of image quality requirements.

Late gadolinium-enhanced (LGE) MRI has become a widely used technique to non-invasively image the left atrium prior to catheter ablation. However, LGE-MRI images are prone to variable image quality, with quality metrics that do not necessarily correlate to the image's diagnostic quality. In this study, we aimed to define consistent clinically relevant metrics for image and diagnostic quality in 3D LGE-MRI images of the left atrium, have multiple observers assess LGE-MRI image quality to identify key features that measure quality and intra/inter-observer variabilities, and train and test a CNN to assess image quality automatically. We identified four image quality categories that impact fibrosis assessment in LGE-MRI images and trained individuals to score 50 consecutive pre-ablation atrial fibrillation LGE-MRI scans from the University of Utah hospital image database. The trained individuals then scored 146 additional scans, which were used to train a convolutional neural network (CNN) to assess diagnostic quality. There was excellent agreement among trained observers when scoring LGE-MRI scans, with inter-rater reliability scores ranging from 0.65 to 0.76 for each category. When the quality scores were converted to a binary diagnostic/non-diagnostic, the CNN achieved a sensitivity of and a specificity of . The use of a training document with reference examples helped raters achieve excellent agreement in their quality scores. The CNN gave a reasonably accurate classification of diagnostic or non-diagnostic 3D LGE-MRI images of the left atrium, despite the use of a relatively small training set.

Impact of a Reduced Tube Voltage on CT Angiography and Radiation Dose: Results of the PROTECTION I Study

This study investigates dose distribution due to kV cone-beam computed tomography (CBCT) for the patients undergoing CBCT-based image-guided radiation therapy (IGRT). The kV-CBCT provides an efficient image-guidance tool for acquiring the latest volumetric image of a patient's anatomy, and has been being routinely used in clinics for an accurate treatment setup. Imaging radiation doses resulting from six different acquisition protocols of the on-board imager (OBI) were calculated using a Geant4 Application for Tomographic Emission (GATE) Monte Carlo simulation toolkit, and the absorbed doses by various organs were analyzed for the adult and pediatric numerical XCAT phantoms in this study. The calculated organ doses range from 0.1 to 24.1 mGy in the adult phantom, and from 0.1 to 36.8 mGy in the pediatric one. The imaging organ doses to the pediatric phantom turn out to be consistently higher than those to the adult phantom. It is believed that our results would provide reliable data to the clinicians for their making better decisions on CBCT scanning options and would also provide a platform for developing a new kV-CBCT scanning protocol in conjunction with a low-dose capability.

To evaluate the diagnostic performance, image quality, artifacts, and radiation doses of virtual non-contrast (VNC) images, relative to true non-contrast (TNC) images, in patients with surgically clipped aneurysms. Seventy-six patients who underwent unenhanced computed tomography (CT) and dual-energy (DE)-CT angiography after surgical clipping of 85 intracranial aneurysms were included in the study. Diagnostic performances of VNC and TNC images were compared with respect to sensitivity, specificity, and positive and negative predictive values. The results of quantitative and qualitative analyses were compared between VNC and TNC images. Radiation doses were also compared between VNC and TNC images. Diagnostic performance of VNC images was lower than that of TNC images; however, addition of contrast-enhanced images improved diagnostic performance. Image noise and mean attenuation of VNC images were significantly higher than those of TNC images in the centrum semiovale, cerebellum, and pons. The quality of VNC images was excellent or sufficient (85.5% for observer 1, 85.5% for observer 2), and complete acceptance of VNC images was achieved in 64.5% for observer 1 and in 71.0% for observer 2; however, the addition of contrast-enhanced images increased the level of acceptance (92.0% for observer 1, 90.9% for observer 2). Clip artifacts were significantly lower in VNC images than in TNC images. CT dose index, dose-length product, and effective dose were significantly lower without TNC images. VNC images showed lower diagnostic performance and image quality, and higher image noise than TNC images; however, VNC images could reduce clip artifacts and radiation doses.

Computed tomography radiation dose optimization for the diagnosis of acute rib fractures in infants investigated for suspected physical abuse: An experimental animal study.

Objective To investigate the feasibility of coronary CT angiography in single cardiac cycle and to analyze the image quality and radiation dose in patients with high heart rate(HR) using 256-row detector CT. Methods Ninety-two consecutive patients between October and November 2015 who were suspected coronary artery disease underwent coronary CT angiography (CCTA) were enrolled, which was performed with a 256-row detector CT (Revolution CT, GE Healthcare) using prospective ECG-triggered volume CCTA within a single cardiac cycle with snapshot freeze (SSF) technique. The patients were grouped by HR during CT scans: group A (80—89 bpm, n=56), group B (90—99 bpm, n=20), and group C (≥100 bpm, n=16). Image quality was compared before and after using SSF technique reconstructions in seventy-four patients. The image quality of coronary artery was evaluated blindly by 2 experienced radiologists using a four-point scale based on the 18-segment model according to the Society of Cardiovascular Computed Tomography guidelines. The differences in age, body mass index, heart rate and CT dose index volume, effective dose(ED) among the three groups were compared by using ANOVA analysis or Kruskal-Wallis test, the image quality and interpretability using χ2 test. Comparisons of image quality between standard and SSF were performed with paired Wilcoxon rank sum test. Kappa coefficient was used to test inter-observer agreement. Results A total of 1 065 coronary artery segments, 98.97% (1 054/1 065) met the requirements for diagnosis. No significant difference was found (χ2=1.274, P=0.563) for the diagnostic image quality of coronary artery segments among the 3 groups with 98.64% (651/660), 99.57%(232/233), 99.42% (171/172), respectively. Significant difference (χ2=68.811, P 0.05). Conclusions Single cardiac cycle scan is feasibility for coronary CT angiography in patients with high heart rate using 256-row detector CT. This scan mode can maintain the diagnostic image quality with low radiation dose. SSF technique can improve the image quality. Key words: Heart rate; Coronary vessel; Tomography, X-ray computed; Radiation dosage

This study aimed to evaluate image quality of coronary artery imaging on non-electrocardiography (ECG)-gated high-pitch dual-source computed tomography (DSCT) in children with congenital heart disease (CHD) and to assess factors affecting image quality. We retrospectively reviewed the records of 142 children with CHD who underwent non-ECG-gated high-pitch DSCT. The subjective image quality of the proximal coronary segments was graded using a five-point scale. A score <3 represented a non-diagnostic image. Age, body weight, and heart rate were compared between the two groups: patients with good diagnostic image quality in all four segments and patients with at least one segment with non-diagnostic image quality. Predictors of image quality were assessed by multivariate logistic regression, including age, body weight, and heart rate. Four-hundred-fifty-seven of the 568 segments (80.5%) had diagnostic image quality. Patients with non-diagnostic segments were significantly younger (21.6±25.5months), had lower body weight (7.82±5.00kg), and a faster heart rate (123±23.7 beats/min) (each p<0.05) than patients with diagnostic image quality in all four segments (30.6±20.7months, 10.3±4.00kg, and 113±21.6 beats/min, respectively; each p<0.05). The multivariate logistic regression revealed that body weight (odds ratio 1.228; p=0.029) was a significant predictor of image quality. Non-ECG-gated high-pitch DSCT provided adequate image quality of the proximal coronary segments in children with CHD. Lower body weight was a factor that led to poorer image quality of the coronary arteries.

Background: Pain is the most common side effect of hysterosalpingography (HSG) and partly arises from vulsellum placement on the cervix and cervical traction. Objective: To study the effect of conducting HSG without grasping the cervix with vulsellum forceps on the time taken to complete the procedure, pain experienced by the participants and diagnostic quality of HSG images produced.Materials and Methods: A randomized controlled trial of 64 consenting adult women referred to the Radiodiagnostic department for HSG from July to December 2020 was carried out. The women were consecutively selected and randomly distributed into two groups: Group 1 - no cervical grasp and Group 2 – with cervical grasp with vulsellum forceps. HSG was done using a fluoroscopy machine, following the standard hospital protocol with speculum, Leech Wilkinson cannula and Urografin 76%. Procedure time, procedure pain using the visual analog scale and diagnostic quality of images were assessed. Data analysis was done using Microsoft Excel and SPSS software version 22.Results: The overall mean duration of the procedure was 12.59 minutes. There was no significant difference in the procedure duration between both groups. The overall mean pain scores immediately and 15 minutes after the procedure were 4.83 and 2.23 respectively. Significant differences in pain scores were seen in the immediate post procedure 3.94 (group 1) versus 5.72 (group 2) and 15 minutes post procedure 1.75 (group 1) versus 2.72 (group 2). After adjusting for confounders, the pain score was noted to be significantly related to the HSG technique with vulsellum use associated with the higher immediate post HSG pain score. No significant difference was seen in the diagnostic image quality between group I and IIConclusion: The elimination of vulsellum forceps during hysterosalpingography was associated with reduced pain in the immediate and 15 minutes after the procedure, without significantly increasing the procedure duration. It had no deleterious effect on the image quality.

BackgroundWhen using an anti‐scatter grid, a decrease in receptor dose caused by its X‐ray absorption seems to lead to the misperception that radiation dose needs to be increased even in digital radiography (DR).ObjectiveTo demonstrate that there is no need to increase radiation dose in DR with a grid, based on a visual evaluation using an adult and a pediatric abdomen phantom (PAD and PPD, respectively).Materials and methodsPhantom images with and without a grid were obtained with exposure parameters determined based on a preliminarily measured signal‐to‐noise ratio improvement factor (SIF), an index for potential dose reduction when using a grid. In visual evaluation, four radiologists compared phantom images with a grid applied at different dose reduction rates (0% [no reduction], 18%, 36%, and 59% for PAD and 0% and 11% for PPD) against an image without a grid at the baseline dose (as the reference). They graded the overall image quality of the former relative to that of the latter (reference) on a 3‐point scale (3 = better, 2 = almost equal, 1 = worse).ResultsThe mean scores for dose reduction rates of 0%, 18%, 36%, and 59% were 3.00, 3.00, 2.75, and 1.00, respectively, for PAD; those for 0% and 11% were 2.13 and 1.63, respectively, for PPD. These results support the validity of our view that no dose increase is necessary when using an anti‐scatter grid. Actually, there is even a potential for improvement in image quality with dose reduction rates of ≤36% for PAD.ConclusionIt is worth reconsidering the necessity of increasing radiation dose in the DR imaging of the adult and pediatric abdomens with an anti‐scatter grid.

Balancing the tradeoff between radiation dose, acquisition duration and diagnostic image quality is essential for medical imaging modalities involving ionizing radiation. Lower administered activities to the patient can reduce absorbed dose, but can result in reduced diagnostic image quality or require longer acquisition durations. In pediatric nuclear medicine, it is desirable to use the lowest amount of administered radiopharmaceutical activity and the shortest acquisition duration that gives sufficient image quality for clinical diagnosis. However, diagnostic image quality is a complex function of patient factors including body morphometry. In this study, we present a digital population of 90 computational anatomic phantoms that model realistic variations in body morphometry and internal anatomy. These phantoms were used to generate a large database of projection images modeling pediatric SPECT imaging using a 99mTc-DMSA tracer. We used an analytic projection code that models attenuation, spatially varying collimator-detector response, and object-dependent scatter to generate the projections. The projections for each organ were generated separately and can be subsequently scaled by parameters extracted from a pharmacokinetics model to simulate realistic tracer biodistribution, including variations in uptake, inside each relevant organ or tissue structure for a given tracer. Noise-free projection images can be obtained by summing these individual organ projections and scaling by the system sensitivity and acquisition duration. We applied this database in the context of 99mTc-DMSA renal SPECT, the most common nuclear medicine imaging procedure in pediatric patients. Organ uptake fractions based on literature values and patient studies were used. Patient SPECT images were used to verify that the sum of counts in the simulated projection images was clinically realistic. For each phantom, 384 uptake realizations, modeling random variations in the uptakes of organs of interest, were generated, producing 34 560 noise-free projection datasets (384 uptake realizations times 90 phantoms). Noisy images modeling various count levels (corresponding to different products of acquisition duration and administered activity) were generated by appropriately scaling these images and simulating Poisson noise. Acquisition duration was fixed; six count levels were simulated corresponding to projection images acquired using 25%, 50%, 75%, 100%, 125%, and 150% of the original weight-based administrated activity as computed using the North American Guidelines (Gelfand et al 2011 J. Nucl. Med. 52 318–22). Combined, a total number of 207 360 noisy projection images were generated, creating a realistic projection database for use in renal pediatric SPECT imaging research. The phantoms and projection datasets were used to calculate three surrogate indices for factors affecting image quality: renal count density, average radius of rotation, and scatter-to-primary ratio. Differences in these indices were seen across the phantoms for dosing based on current guidelines, and especially for the phantom modeling the newborn. We also performed an image quality study using an anthropomorphic model observer that demonstrates that the weight-based dose scaling does not equalize image quality as measured by the area under the receiver-operating characteristics curve. These studies suggest that a dosing procedure beyond weight-based scaling of administered activities is required to equalize image quality in pediatric renal SPECT.