Effect of tube current on diagnostic image quality in paediatric cerebral multidetector CT images

Effect of tube current on computed tomography radiomic features

Variability in the x-ray tube current used in computed tomography may affect quantitative features extracted from the images. To investigate these effects, we scanned the Credence Cartridge Radiomics phantom 12 times, varying the tube current from 25 to 300 mA∙s while keeping the other acquisition parameters constant. For each of the scans, we extracted 48 radiomic features from the categories of intensity histogram (n = 10), gray-level run length matrix (n = 11), gray-level co-occurrence matrix (n = 22), and neighborhood gray tone difference matrix (n = 5). To gauge the size of the tube current effects, we scaled the features by the coefficient of variation of the corresponding features extracted from images of non-small cell lung cancer tumors. Variations in the tube current had more effect on features extracted from homogeneous materials (acrylic, sycamore wood) than from materials with more tissue-like textures (cork, rubber particles). Thirty-eight of the 48 features extracted from acrylic were affected by current reductions compared with only 2 of the 48 features extracted from rubber particles. These results indicate that variable x-ray tube current is unlikely to have a large effect on radiomic features extracted from computed tomography images of textured objects such as tumors.

Influence of adaptive statistical iterative reconstruction algorithm on image quality in coronary computed tomography angiography

Background

Coronary computed tomography angiography (CCTA) requires high spatial and temporal resolution, increased low contrast resolution for the assessment of coronary artery stenosis, plaque detection, and/or non-coronary pathology. Therefore, new reconstruction algorithms, particularly iterative reconstruction (IR) techniques, have been developed in an attempt to improve image quality with no cost in radiation exposure.

Purpose

To evaluate whether adaptive statistical iterative reconstruction (ASIR) enhances perceived image quality in CCTA compared to filtered back projection (FBP).

Material and Methods

Thirty patients underwent CCTA due to suspected coronary artery disease. Images were reconstructed using FBP, 30% ASIR, and 60% ASIR. Ninety image sets were evaluated by five observers using the subjective visual grading analysis (VGA) and assessed by proportional odds modeling. Objective quality assessment (contrast, noise, and the contrast-to-noise ratio [CNR]) was analyzed with linear mixed effects modeling on log-transformed data. The need for ethical approval was waived by the local ethics committee as the study only involved anonymously collected clinical data.

Results

VGA showed significant improvements in sharpness by comparing FBP with ASIR, resulting in odds ratios of 1.54 for 30% ASIR and 1.89 for 60% ASIR (P = 0.004). The objective measures showed significant differences between FBP and 60% ASIR (P < 0.0001) for noise, with an estimated ratio of 0.82, and for CNR, with an estimated ratio of 1.26.

Conclusion

ASIR improved the subjective image quality of parameter sharpness and, objectively, reduced noise and increased CNR.

Vascular Disorders of the Cerebellum in Children

Key differences exist in the epidemiology, pathophysiology, and clinical presentation of vascular lesions of the cerebellum in children versus adults. An understanding of these differences and an appreciation of the distinct imaging features of these lesions aid in distinguishing normal vascular variations from pathology, in predicting lesion etiology, and in directing effective treatment strategies. This paper reviews the embryogenesis of the normal vascular system of the cerebellum and brainstem and then discusses the clinical and imaging features of the common vascular lesions affecting these structures in the pediatric population.

THE EFFECT OF ADAPTIVE STATISTICAL ITERATIVE RECONSTRUCTION ON THE ASSESSMENT OF DIAGNOSTIC IMAGE QUALITY AND VISUALISATION OF ANATOMICAL STRUCTURES IN PAEDIATRIC CEREBRAL CT EXAMINATIONS

The purpose of this study was to investigate the effect of adaptive statistical iterative reconstruction (ASiR) on the visualisation of anatomical structures and diagnostic image quality in paediatric cerebral computed tomography (CT) examinations. Forty paediatric patients undergoing routine cerebral CT were included in the study. The raw data from CT scans were reconstructed into stacks of 5 mm thick axial images at various levels of ASiR. Three paediatric radiologists rated six questions related to the visualisation of anatomical structures and one question on diagnostic image quality, in a blinded randomised visual grading study. The evaluated anatomical structures demonstrated enhanced visibility with increasing level of ASiR, apart from the cerebrospinal fluid space around the brain. In this study, 60 % ASiR was found to be the optimal level of ASiR for paediatric cerebral CT examinations. This shows that the commonly used 30 % ASiR may not always be the optimal level.

Radiation dose reduction in postoperative computed position control of cochlear implant electrodes in lambs - An experimental study

OBJECTIVE

Cochlear implants (CI) are standard treatment for prelingually deafened children and postlingually deafened adults. Computed tomography (CT) is the standard method for postoperative imaging of the electrode position. CT scans accurately reflect electrode depth and position, which is essential prior to use. However, routine CT examinations expose patients to radiation, which is especially problematic in children. We examined whether new CT protocols could reduce radiation doses while preserving diagnostic accuracy.

METHODS

To investigate whether electrode position can be assessed by low-dose CT protocols, a cadaveric lamb model was used because the inner ear morphology is similar to humans. The scans were performed at various volumetric CT dose-indexes CTDIvol)/kV combinations. For each constant CTDIvol the tube voltage was varied (i.e., 80, 100, 120 and 140kV). This procedure was repeated at different CTDIvol values (21mGy, 11mGy, 5.5mGy, 2.8mGy and 1.8mGy). To keep the CTDIvol constant at different tube voltages, the tube current values were adjusted. Independent evaluations of the images were performed by two experienced and blinded neuroradiologists. The criteria diagnostic usefulness, image quality and artifacts (scaled 1-4) were assessed in 14 cochlear-implanted cadaveric lamb heads with variable tube voltages.

RESULTS

Results showed that the standard CT dose could be substantially reduced without sacrificing diagnostic accuracy of electrode position. The assessment of the CI electrode position was feasible in almost all cases up to a CTDIvol of 2-3mGy. The number of artifacts did not increase for images within this dose range as compared to higher dosages. The extent of the artifacts caused by the implanted metal-containing CI electrode does not depend on the radiation dose and is not perceptibly influenced by changes in the tube voltage. Summarizing the evaluation of the CI electrode position is possible even at a very low radiation dose.

CONCLUSIONS

CT imaging of the temporal bone for postoperative electrode position control of the CI is possible with a very low and significantly radiation dose. The tube current-time product and voltage can be reduced by 50% without increasing artifacts. Low-dose postoperative CT scans are sufficient for localizing the CI electrode.

A multi-phased study of optimisation methodologies and radiation dose savings for head CT examinations

The impact of optimisation methods on dose reductions for head computerised tomography was undertaken in three phases for two manufacturer models. Phase 1: a Catphan(®)600 was employed to evaluate protocols where the impact of parameter manipulation on dose and image quality was gauged by psychophysical measurements of contrast and spatial resolution in terms of contrast discs and line pairs. mA, kV and pitch were systematically altered until the optimisation threshold was identified. Phantom studies provide dose comparisons during optimisation but lack anatomical detail. Phase 2: optimised protocols were tested on a porcine model permitting further dose reductions over phantom findings providing anatomical structures for image quality evaluation using relative visual grading analysis of anatomical criteria. Phase 3: patient images using pre- and post-optimised protocols were clinically audited using visual grading characteristic analysis and ordinal regression analysis providing a robust analysis of image quality data prior to clinical implementation.

Evaluation of image-enhanced paediatric computed tomography brain examinations

The aim of this study was to evaluate the possibility of reducing the radiation dose to paediatric patients undergoing computed tomography (CT) brain examination by using image-enhancing software. Artificial noise was added to the raw data collected from 20 patients aged between 1 and 10 y to simulate tube current reductions of 20, 40 and 60 mA. All images were created in duplicate; one set of images remained unprocessed whereas the other was processed with image-enhancing software. Three paediatric radiologists assessed the image quality based on their ability to visualise the high- and low-contrast structures and their overall impression of the diagnostic value of the image. For patients aged 6-10 y, it was found that dose reductions from 27 mGy (CTDI(vol)) to 23 mGy (15 %) in the upper brain and from 32 to 28 mGy (13 %) in the lower brain were possible for standard diagnostic CT examinations when using the image-enhancing filter. For patients 1-5 y, the results for standard diagnostics in the upper brain were inconclusive, for the lower brain no dose reductions were found possible.

VIEWDEX: an efficient and easy-to-use software for observer performance studies

The development of investigation techniques, image processing, workstation monitors, analysing tools etc. within the field of radiology is vast, and the need for efficient tools in the evaluation and optimisation process of image and investigation quality is important. ViewDEX (Viewer for Digital Evaluation of X-ray images) is an image viewer and task manager suitable for research and optimisation tasks in medical imaging. ViewDEX is DICOM compatible and the features of the interface (tasks, image handling and functionality) are general and flexible. The configuration of a study and output (for example, answers given) can be edited in any text editor. ViewDEX is developed in Java and can run from any disc area connected to a computer. It is free to use for non-commercial purposes and can be downloaded from http://www.vgregion.se/sas/viewdex. In the present work, an evaluation of the efficiency of ViewDEX for receiver operating characteristic (ROC) studies, free-response ROC (FROC) studies and visual grading (VG) studies was conducted. For VG studies, the total scoring rate was dependent on the number of criteria per case. A scoring rate of approximately 150 cases h(-1) can be expected for a typical VG study using single images and five anatomical criteria. For ROC and FROC studies using clinical images, the scoring rate was approximately 100 cases h(-1) using single images and approximately 25 cases h(-1) using image stacks ( approximately 50 images case(-1)). In conclusion, ViewDEX is an efficient and easy-to-use software for observer performance studies.

A method to analyse observer disagreement in visual grading studies: example of assessed image quality in paediatric cerebral multidetector CT images

The purpose was to demonstrate a non-parametric statistical method that can identify and explain the components of observer disagreement in terms of systematic disagreement as well as additional individual variability, in visual grading studies. As an example, the method was applied to a study where the effect of reduced tube current on diagnostic image quality in paediatric cerebral multidetector CT (MDCT) images was investigated. Quantum noise, representing dose reductions equivalent to steps of 20 mA, was artificially added to the raw data of 25 retrospectively selected paediatric cerebral MDCT examinations. Three radiologists, blindly and randomly, assessed the resulting images from two different levels of the brain with regard to the reproduction of high- and low-contrast structures and overall image quality. Images from three patients were assessed twice for the analysis of intra-observer disagreement. The intra-observer disagreement in test-retest assessments could mainly be explained by a systematic change towards lower image quality the second time the image was reviewed. The inter-observer comparisons showed that the paediatric radiologist was more critical of the overall image quality, while the neuroradiologists were more critical of the reproduction of the basal ganglia. Differences between the radiologists regarding the extent to which they used the whole classification scale were also found. The statistical method used was able to identify and separately measure a presence of bias apart from additional individual variability within and between the radiologists which is, at the time of writing, not attainable by any other statistical approach suitable for paired, ordinal data.