| increases the need to optimize the image quality and to examine the potential reduction of radiation doses to the patient. Low-contrast detail detectability is a method that has proven to be an appropriate evaluation method for this purpose. However, it is essential to recognize factors that affect detectability performance and understand how these factors influence image quality and radiation dose. It is argued that deep understanding of the influences of these factors is the key to image quality optimization in terms of contrast-detail detectability and radiation dose reduction. The purpose of this article is, therefore, to specify these factors and to explain their influence on detectability performance and hence on CT image quality. Further low-contrast detail studies are required to optimize imaging performance of different CT systems and scanners. Show
RésuméCet article porte sur les résultats de recherches récentes sur les facteurs qui influencent le rendement de détection des scanners de différents systèmes de tomodensitométrie (TDM). Ces systèmes comprennent les systèmes de TDM à détecteurs multiples avec des nombre de tranches différents, la TDM à double source et la TDM à faisceaux coniques. L'introduction d'un plus grand nombre de tranches pour la TDM à détecteurs multiples, la TDM à double source et la TDM à faisceaux coniques augmentent la nécessité d'optimiser la qualité de l'image et d'examiner la possibilité de diminuer la dose de radiation pour le patient. La détectabilité des détails à faible contraste est une méthode d'évaluation qui s'est avérée appropriée à cette fin. Cependant, il est essentiel de reconnaître les facteurs qui influent sur le rendement de détectabilité et de comprendre comment ces facteurs influencent la qualité de l'image et le dosage de radiation. On croit qu'une compréhension approfondie de l'influence de ces facteurs serait la clé de l'optimisation de la qualité de l'image en termes de détectabilité des détails à faible contraste et de réduction de la dose de radiation. Le but de cet article est donc de déterminer ces facteurs et d'expliquer leur influence sur le rendement de détectabilité, et donc sur la qualité des images de TDM. Il faudra d'autres études sur les détails à faible contraste pour optimiser le rendement d'imagerie de différents systèmes et scanners de TDM. IntroductionComputed tomography (CT) imaging technology is rapidly changing the conditions of image quality optimization and radiation dose reduction. Each CT system has its own specific image quality [1]. The introduction of multidetector CT (MDCT), using an increasing number of slices, dual-source CT (DSCT), and cone-beam CT (CBCT) has enormously increased the range of examinations, which has in turn increased the number of CT examinations [2], [3]. To further add to this technological complexity, different technical applications and software are utilized in systems from different manufacturers, and various models of CT scanners utilize different algorithmic software [1]. Several studies have shown that there is still misdiagnosis or loss of information in CT images, as some pathologic lesions and details are not detected by interpreters [4], [5], [6]. Although contrast and temporal resolutions have been significantly improved by the current advanced technology of MDCT, the spatial resolution or in-plane spatial resolution has not improved. Therefore, there are still some limitations in the rate of detection and accurate assessment [7], [8], [9]. Furthermore, the highest radiation dose from medical imaging modalities is received from CT scans [10]. Thus, dose reduction has become a very important goal in CT applications [11]. However, there are tradeoffs between image quality and dose; the higher the dose contributing to the image, the lower image noise, and hence, the better visualization of low-contrast structures. Detection of low-contrast details and lesions is primarily limited by noise, which can be reduced by increasing radiation dose [12], [13]. Consequently, there is an imperative need for image quality optimization and radiation dose reduction for CT images. Several methods are used to evaluate imaging performance and image quality. Detection quantum efficiency, receiver-operating characteristics, visual grading characteristics, and low-contrast detail (LCD) detectability are all commonly used methods [14], [15]. However, several authors state that LCD is the most appropriate method to optimize image quality and to examine the potential of radiation dose reduction [16], [17]. Since the common task of diagnostic CT scan images is the visual detection of lesions, detectability performance is an important measure of image quality [18]. The theory behind LCD implies that the detectability of details increases with the increasing size of objects or contrast between objects and their background [14], [19]. LCD is usually measured by using low-contrast detail phantoms that contain cylindrical objects of a range of different sizes and low-contrast levels [20], [21]. LCD phantom images are assessed subjectively by interpreter observation or objectively by measuring the contrast-to-noise ratio (CNR) [22]. LCD can also be used to compare and contrast the performance of different imaging systems [23]. LCD studies are also useful to examine image optimization and to assess the potential of dose reduction of imaging systems [17], [24]. However, recognizing and understanding the factors that influence the detectability performance of different CT scan systems are fundamental concerns in effectively implementing this method. The purpose of this review is to determine the factors influencing LCD performance of different CT systems and to explain their influences on image quality optimization. Section snippetsFactors Affecting Low-Contrast Detail Performance in CTDetectability performance of CT imaging systems is influenced by CT system specification, milliampere-second, peak kilovoltage, slice thickness, pitch, and beam collimation, as well as image processing and visualization. These factors should be adjusted to optimize image quality in terms of LCD performance by lowering image noise and maintaining lower radiation dose to the patient (Figure 1). Scanner SystemsEach CT system and model has its own performance ability according to its properties and specifications (Figure 2). The design criteria employed in CT systems fundamentally characterize the type of noise, which in turn affects the detectability performance of the produced images [25]. Image blur is largely determined by scanner specifications. The size of the sampling aperture is regulated by the focal spot size and the detector size; the size of the voxels is considered a blurring source [26]. ConclusionThe effects of low-contrast detail performance of different CT scanner systems have been discussed in this article. The impact level of the factors of contrast detail detectability on image quality is complex and does not exactly match from one type of scanner to another or from one unit to another. These factors are the ultimate key to optimizing image quality in terms of detail detectability, while utilizing lower doses. Although the performance detectability within CT is inherent to the AcknowledgmentWe acknowledge the cooperation of Julia Barrett, Radiographics, and Exxim Computing Corp., who gave us permission to use their figures. References (64)
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The extra radiation dose received by organs from multiple conae beam computed tomography (CBCT) scans can increase the probability of the secondary cancer risk. In this study, an effort has been made to assess CBCT dose and image quality for standard pre-sets defined for different organs namely, the chest, pelvis, brain, head and neck, and abdomen. The second goal was to investigate whether the radiation dose could be reduced while still achieving high image quality. Image quality was evaluated on the CatPhan Model 503 (Phantom Lab, NY), while organ kV- CBCT doses were evaluated using an Unfors device (Fluke Biomedical) to provide representative measurements for clinical settings. Nominal CBCT projections with reduced exposure times were reconstructed in 3D using the Unfiltered and Filtered-back Projection algorithms. Patient organ dose (mGy) per procedure for brain, chest, pelvis, abdomen, and head and neck were 7.9, 35.3, 28.1, 58.3, and 0.77, respectively. The experimental analysis suggests that adequate image quality could be obtained while decreasing the number of radiographic projections. Reducing the number of the radiographic projections will reduce the scan time and therefore the imaging dose. The proposed method provides an opportunity to reduce the organ doses comparatively lower than the standard CT doses for head and body protocols. The study provides a framework for delivering low radiation doses to critical organs with no risk of long-term exposure. 2021, European Journal of Radiology Show abstractNavigate Down To assess the diagnostic performance and reader confidence in determining the resectability of pancreatic cancer at computed tomography (CT) using a new deep learning image reconstruction (DLIR) algorithm. A retrospective review was conduct of on forty-seven patients with pathologically confirmed pancreatic cancers who underwent baseline multiphasic contrast-enhanced CT scan. Image data sets were reconstructed using filtered back projection (FBP), hybrid model-based adaptive statistical iterative reconstruction (ASiR-V) 60 %, and DLIR "TrueFidelity" at low(L), medium(M), and high strength levels(H). Four board-certified abdominal radiologists reviewed the CT images and classified cancers as resectable, borderline resectable, or unresectable. Diagnostic performance and reader confidence for categorizing the resectability of pancreatic cancer were evaluated based on the reference standards, and the interreader agreement was assessed using Fleiss k statistics. For prediction of margin-negative resections(ie, R0), the average area under the receiver operating characteristic curve was significantly higher with DLIR-H (0.91; 95 % confidence interval [CI]: 0.79, 0.98) than FBP (0.75; 95 % CI:0.60, 0.86) and ASiR-V (0.81; 95 % CI:0.67, 0.91) (p = 0.030 and 0.023 respectively). Reader confidence scores were significantly better using DLIR compared to FBP and ASiR-V 60 % and increased linearly with the increase of DLIR strength level (all p < 0.001). Among the image reconstructions, DLIR-H showed the highest interreader agreement in the resectability classification and lowest subject variability in the reader confidence. The DLIR-H algorithm may improve the diagnostic performance and reader confidence in the CT assignment of the local resectability of pancreatic cancer while reducing the interreader variability. 2016, Radiography Show abstractNavigate Down To develop a new method of evaluating image quality in computed tomography (CT) using an objective measure of low contrast-detail (LCD). To achieve this aim a new LCD-CT (CDCT) phantom needed to be designed and developed. A CT inverse image quality figure (CT-IQFinv) value, based on the planar radiography LCD method, was also devised. Validation of the CDCT phantom design and CT-IQFinv calculations were undertaken using 67 observers and software methods. The CDCT phantom was scanned on three multi-detector CT systems using variable factors of kVp, mAs and slice thickness. The results were compared to an a priori knowledge that image quality improves with increased photons reaching the detectors. Observer CT-IQFinv scores for the phantom's peripheral region were consistent with the a priori knowledge and generally consistent in the inner region, with one exception. The software CT-IQFinv scores for the phantom's peripheral region were also consistent with the a priori knowledge, however there were some inconsistencies. Software and observer CT-IQFinv score differed significantly (p < 0.05) however both were consistent with the a priori knowledge. The work reported is designed as proof of concept of development of LCD measure in CT. CT-IQFinv can be used as a measure of LCD image quality in CT when evaluating CT parameter of mAs, kVp and slice thickness. The results demonstrate potential for use of CT IQFinv, however at present further work is needed to overcome design and technical issue encountered in this project. A method for zinger artifact reduction in high-energy x-ray computed tomography2015, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Show abstractNavigate Down In x-ray imaging, the interaction of stray x-rays with an imaging sensor may produce speckle-type noise (i.e. zingers) which produces artifacts in tomography reconstructions. Zinger reduction can be accomplished through detector design and image filtering. A standard method for zinger filtering exists but produces many false positives and high discrepancy with the true signal. An approach is proposed through selective temporal frame averaging in which zinger noise is removed with improvements over the standard method. The accuracy of the proposed approach is compared with a standard approach using simulated projections of a phantom containing known artificial zinger and locations density. Comparing Radiation Dose between Contrast-Enhanced and Non-Contrast-Enhanced CTAC Acquisition in <sup>18</sup>F-FDG-PET/CT Examination2022, Malaysian Journal of Medicine and Health Sciences Physics and Principles of Computed Tomography2022, Computed Tomography: A Primer for Radiographers Research article Engineering Failure Analysis, Volume 27, 2013, pp. 262-271 Show abstractNavigate Down The article deals with the comprehensive research of temperature influence upon fracture energy of operational 12Cr1MoV steel of steam superheater collector of TP-100 type boiler. The authors found out that heating from 20 °С to 200 °С results in an increase of Charpy toughness and eventual reaching of plateau. There were also spotted the main dependencies of changes of steel microhardness along the thickness of collector considering on the distance from the hole. Research article Journal of Computational and Applied Mathematics, Volume 349, 2019, pp. 548-562 Show abstractNavigate Down In this paper, we construct wavelet tight frames with nvanishing moments for Dubuc–Deslauriers 2n-point semi-regular interpolatory subdivision schemes. Our motivation for this construction is its practical use for further regularity analysis of wide classes of semi-regular subdivision. Our constructive tools are local eigenvalue convergence analysis for semi-regular Dubuc–Deslauriers subdivision, the Unitary Extension Principle and the generalization of the Oblique Extension Principle to the irregular setting by Chui, He and Stöckler. This group of authors derives suitable approximation of the inverse Gramian for irregular B-spline subdivision. Our main contribution is the derivation of the appropriate approximation of the inverse Gramian for the semi-regular Dubuc–Deslauriers scaling functions ensuring nvanishing moments of the corresponding framelets. Research article Utility of dual phase liver CT for metastatic melanoma staging and surveillanceEuropean Journal of Radiology, Volume 82, Issue 12, 2013, pp. 2189-2193 Show abstractNavigate Down To evaluate the clinical utility of dual phase computed tomography (CT) for assessment of hepatic metastases in patients with metastatic melanoma. A retrospective case–control study of dual phase CT examinations consisting of late hepatic arterial and portal venous phases performed on patients with melanoma was undertaken. In 2010, 420 dual phase CT examinations were performed on 188 patients. Of these, 46 CT examinations on 24 patients with hepatic metastases were combined with 52 control studies for evaluation. Two blinded reviewers independently evaluated single portal venous phase alone and dual phase imaging on separate occasions. The presence of hepatic lesions, the conspicuity of the lesions, and the likelihood that the detected lesions were metastases was recorded. Agreement between readers, sensitivity and specificity was calculated. In no case was hepatic metastatic disease only apparent on arterial phase imaging. Arterially enhancing hepatic lesions only visible on the arterial phase or much more conspicuous on the arterial phase were present in 10 studies (10%), all of which were benign. Liver metastases were rated as being more accurately assessed on the portal venous phase in up to 100%. In a per scan analysis dual phase and venous phase imaging had similar sensitivities of 96% (95%, CI: 86–100) and 98% (95%, CI: 89–100), respectively. Single portal venous phase imaging is adequate for staging and surveillance in patients with metastatic melanoma. Research article Improvement of the radiographic method for measurement of effective energy of pulsed X-ray emission from a PF device for different anode's insert materialsApplied Radiation and Isotopes, Volume 136, 2018, pp. 21-26 Show abstractNavigate Down In this paper, effective energy of pulsed X-Ray emitted from a Mather-type plasma focus device in stored energy of 2.5 kJ with six different anode's insert materials was measured using radiographic method with attenuation filters. Since intensity and energy of X-ray beam were considerably changed with changing the insert material, the method was improved by using different filters simultaneously in all the experiments and selection of the best filter in each experiment according to the appropriate criteria. Effective energy of pulsed X-ray beam was measured 16, 28, 50, 51, 34 and 44 keV when aluminum, copper, zinc, tin, tungsten and lead were used as insert materials, and aluminum, copper, silver, silver, copper and lead were used as filters, respectively. Research article Preliminary performance of image quality for a low-dose C-arm CT system with a flat-panel detectorNuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Volume 784, 2015, pp. 565-569 Show abstractNavigate Down Digital flat panel imager (FPI)-based cone-beam computed tomography (CBCT) has been widely used in C-arm imaging for spine surgery and interventional procedures. The system provides real-time fluoroscopy with high spatial resolution and three-dimensional (3D) visualization of anatomical structure without the need for patient transportation in interventional suite. In this work, a prototype CBCT imaging platform with continuous single rotation about the gantry was developed by using a large-area flat-panel detector with amorphous Si-based thin film transistor matrix. The different 2D projection images were acquired during constant gantry velocity for reconstructed images at a tube voltage of 80–120 kVp, and different current (10–50 mA) conditions. Various scan protocols were applied to a chest phantom human by changing the number of projection images and scanning angles. The projections were then reconstructed into a volumetric data of sections by using a 3D reconstruction algorithm (e.g., filtered back projection). The preliminary quantitative X-ray performance of our CBCT system was investigated by using the American Association of Physicists in Medicine CT phantom in terms of spatial resolution, contrast resolution, and CT number linearity for mobile or fixed C-arm based CBCT application with limited rotational geometry. The novel results of the projection data with different scanning angles and angular increments in the orbital gantry platform were acquired and evaluated experimentally. Research article Radiation doses and size-specific dose estimate from CT brain examinations according to head sizes in a tertiary hospital in MalaysiaRadiation Physics and Chemistry, Volume 189, 2021, Article 109694 Show abstractNavigate Down The aim of the study is to evaluate radiation dose and its relationship with the effective head diameter obtained during CT brain examination performed via a 640 multi-slice CT scanner. Data from a total of 146 patients, who underwent CT brain examinations in our institutions, was collected retrospectively from January 2019 to June 2019. Data, such as volume Computed Tomography Dose Index (CTDIvol) value, scanning range, dose-length product (DLP) value, and diameter of the patient's head based on Antero-posterior (AP) and Lateral (LAT) were recorded in a standardized form for analyzation. Effective dose (E) and Size-Specific Dose Estimate (SSDE) were determined and compared within plain brain CT and contrast-enhanced CT (CECT). The mean Es of the plain brain CT and CECT were 2.02 ± 0.41 mSv and 4.23 ± 0.75 mSv, respectively, and differed significantly with a p-value of less than 0.05. There are no significant differences of E and SSDE in contrast enhancement when compared among genders (p-value > 0.05) and within race for plain brain CT. The radiation doses differed significantly between male (2.08 ± 0.47 mSv) and female (1.94 ± 0.31 mSv) patients. It was found that skin organs received the highest risk overall, followed by thyroid and then esophagus. This study shows that radiation doses from CT brain mostly depend upon the type of examination. Thus, extra safety measures should be considered for type of examination to reduce the potential risk associated with CT scans. What is the main factor that affects the contrast of a dental radiograph?Density difference: this is also known as the mass per unit volume. It is the most critical factor contributing to subject contrast. A higher density material will attenuate more x-rays than a lower density material.
What factors affect contrast resolution?Intuitively, an imaging system,s ability to detect objects of low contrast against the background is determined by the following three factors : contrast (i.e., mean brightness difference between the object and its surrounding background), size of the object and noise level.
What is the primary factor in controlling contrast?The factor that controls contrast is said to be KV and the factor that controls density is termed as mAs i.e. the product of milliampere and the duration of exposure.
What affects the contrast of the radiographic image?Radiographic contrast is dependent on the technical factors of the radiographs taken. The kilovoltage (kV) during the radiographic examination will determine the primary beams' energy; higher energy effects increased penetrating power.
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