Dual-source spiral CT with pitch up to 3.2 and 75 ms temporal resolution: image reconstruction and assessment of image quality

Standardizing technical parameters and terms for abdominopelvic photon-counting CT: laying the groundwork for innovation and evidence sharing

Photon-counting detector CT (PCD-CT) is a new technology that has multiple diagnostic benefits including increased spatial resolution, iodine signal, and radiation dose efficiency, as well as multi-energy imaging capability, but which also has unique challenges in abdominal imaging. The purpose of this work is to summarize key features, technical parameters, and terms, which are common amongst current abdominopelvic PCD-CT systems and to propose standardized terminology (where none exists). In addition, user-selectable protocol parameters are highlighted to facilitate both scientific evaluation and early clinical adoption. Unique features of PCD-CT systems include photon-counting detectors themselves, energy thresholds and bins, and tube potential considerations for preserved spectral separation. Key parameters for describing different PCD-CT systems are reviewed and explained. While PCD-CT can generate multi-energy images like dual-energy CT, there are new types of images such as threshold images, energy bin images, and special spectral images. The standardized terms and concepts herein build upon prior interdisciplinary consensus and have been endorsed by the newly created Society of Abdominal Radiology Photon-counting CT Emerging Technology Commission.

Assessment of temporal resolution and detectability of moving objects in CT: A task-based image quality study

The metrics used for assessing image quality in computed tomography (CT) do not integrate the influence of temporal resolution. A shortcoming in the assessment of image quality for imaging protocols where motion blur can therefore occur. We developed a method to calculate the temporal resolution of standard CT protocols and introduced a specific spatiotemporal formulation of the non-prewhitening with eye filter (NPWE) model observer to assess the detectability of moving objects as a function of their speed. We scanned a cubic water phantom with a plexiglass cylindrical insert (120 HU) using a large panel of acquisition parameters (rotation times, pitch factors and collimation widths) on two systems (GE Revolution Apex and Siemens SOMATOM Force) to determine the in-plane task-based transfer functions (TTF) and noise power spectra (NPS). The phantom set in a uniform rectilinear motion in the transverse plane allowed the temporal modulation transfer function (MTF) calculation. The temporal MTF appropriately compared the temporal resolution of the various acquisition protocols. The longitudinal TTF was measured using a thin tungsten wire. The detectability index showed the advantage of applying high rotation speed, wide collimations and high pitch for object detection in the presence of motion. No counterpart to the increase in these three parameters was found in the in-plane and longitudinal image quality.

Photon-counting CT in Thoracic Imaging: Early Clinical Evidence and Incorporation Into Clinical Practice

Photon-counting CT (PCCT) is an emerging advanced CT technology that differs from conventional CT in its ability to directly convert incident x-ray photon energies into electrical signals. The detector design also permits substantial improvements in spatial resolution and radiation dose efficiency and allows for concurrent high-pitch and high-temporal-resolution multienergy imaging. This review summarizes (a) key differences in PCCT image acquisition and image reconstruction compared with conventional CT; (b) early evidence for the clinical benefit of PCCT for high-spatial-resolution diagnostic tasks in thoracic imaging, such as assessment of airway and parenchymal diseases, as well as benefits of high-pitch and multienergy scanning; (c) anticipated radiation dose reduction, depending on the diagnostic task, and increased utility for routine low-dose thoracic CT imaging; (d) adaptations for thoracic imaging in children; (e) potential for further quantitation of thoracic diseases; and (f) limitations and trade-offs. Moreover, important points for conducting and interpreting clinical studies examining the benefit of PCCT relative to conventional CT and integration of PCCT systems into multivendor, multispecialty radiology practices are discussed.

Dual-source photon-counting CT: impact of residual cross-scatter on quantitative spectral results

Dual-source photon-counting CT combines the high temporal resolution and high pitch of dual-source CT with the material quantification capabilities of photon-counting CT. It, however, results in cross-scatter that increases in severity with increased patient size and collimation. This cross-scatter must be corrected to ensure the removal of scatter artifacts and improve quantitative accuracy. To evaluate residual cross-scatter of a first-generation dual-source photon-counting CT and the effect of phantom size, collimation, and radiation dose, a phantom was scanned in single- and dual-source modes with and without its extension ring at three collimations and three radiation doses. Virtual monoenergetic images (VMI) at 50 keV, VMI 150 keV, and iodine density maps were reconstructed to determine variation between acquisition parameters in single- and dual-source modes. Additionally, differences relative to single-source acquisitions and to single-source and small collimation acquisitions were calculated to reflect residual cross-scatter with and without matched collimation. At VMI 50 keV, inserts exhibited accuracy and similar variation between single- and dual-source modes, averaging 5.4 ± 2.6 and 6.2 ± 2.5 HU, respectively, across phantom size, collimation, and radiation dose. Differences relative to single-source measured 5.1 ± 8.5 and 0.4 ± 4.2 HU while differences relative to single-source and small collimation acquisitions were 6.4 ± 10.8 HU and -0.5 ± 3.9 HU for VMI 50 and 150 keV, respectively. This minimal residual cross-scatter increases confidence in the quantitative accuracy of spectral results necessary for clinical applications of dual-source photon-counting CT with motion, such as cardiac imaging.

CT Coronary Angiography: Technical Approach and Atherosclerotic Plaque Characterization

Coronary computed tomography angiography (CCTA) currently represents a robust imaging technique for the detection, quantification and characterization of coronary atherosclerosis. However, CCTA remains a challenging task requiring both high spatial and temporal resolution to provide motion-free images of the coronary arteries. Several CCTA features, such as low attenuation, positive remodeling, spotty calcification, napkin-ring and high pericoronary fat attenuation index have been proved as associated to high-risk plaques. This review aims to explore the role of CCTA in the characterization of high-risk atherosclerotic plaque and the recent advancements in CCTA technologies with a focus on radiomics plaque analysis.

Potential benefits of photon counting detector computed tomography in pediatric imaging

Photon counting detector (PCD) CT represents the newest advance in CT technology, with improved radiation dose efficiency, increased spatial resolution, inherent spectral imaging capabilities, and the ability to eliminate electronic noise. Its design fundamentally differs from conventional energy integrating detector CT because photons are directly converted to electrical signal in a single step. Rather than converting X-rays to visible light and having an output signal that is a summation of energies, PCD directly counts each photon and records its individual energy information. The current commercially available PCD-CT utilizes a dual-source CT geometry, which allows 66 ms cardiac temporal resolution and high-pitch (up to 3.2) scanning. This can greatly benefit pediatric patients by facilitating high quality fast scanning to allow sedation-free imaging. The energy-resolving nature of the utilized PCDs allows "always-on" dual-energy imaging capabilities, such as the creation of virtual monoenergetic, virtual non-contrast, virtual non-calcium, and other material-specific images. These features may be combined with high-resolution imaging, made possible by the decreased size of individual detector elements and the absence of interelement septa. This work reviews the foundational concepts associated with PCD-CT and presents examples to highlight the benefits of PCD-CT in the pediatric population.

Milestones in CT: Past, Present, and Future

In 1971, the first patient CT examination by Ambrose and Hounsfield paved the way for not only volumetric imaging of the brain but of the entire body. From the initial 5-minute scan for a 180° rotation to today's 0.24-second scan for a 360° rotation, CT technology continues to reinvent itself. This article describes key historical milestones in CT technology from the earliest days of CT to the present, with a look toward the future of this essential imaging modality. After a review of the beginnings of CT and its early adoption, the technical steps taken to decrease scan times-both per image and per examination-are reviewed. Novel geometries such as electron-beam CT and dual-source CT have also been developed in the quest for ever-faster scans and better in-plane temporal resolution. The focus of the past 2 decades on radiation dose optimization and management led to changes in how exposure parameters such as tube current and tube potential are prescribed such that today, examinations are more customized to the specific patient and diagnostic task than ever before. In the mid-2000s, CT expanded its reach from gray-scale to color with the clinical introduction of dual-energy CT. Today's most recent technical innovation-photon-counting CT-offers greater capabilities in multienergy CT as well as spatial resolution as good as 125 μm. Finally, artificial intelligence is poised to impact both the creation and processing of CT images, as well as automating many tasks to provide greater accuracy and reproducibility in quantitative applications.

Consistency of spectral results in cardiac dual-source photon-counting CT

We evaluate stability of spectral results at different heart rates, acquisition modes, and cardiac phases in first-generation clinical dual-source photon-counting CT (PCCT). A cardiac motion simulator with a coronary stenosis mimicking a 50% eccentric calcium plaque was scanned at five different heart rates (0, 60-100 bpm) with the three available cardiac scan modes (high pitch prospectively ECG-triggered spiral, prospectively ECG-triggered axial, retrospectively ECG-gated spiral). Subsequently, full width half max (FWHM) of the stenosis, Dice score (DSC) for the stenosed region, and eccentricity of the non-stenosed region were calculated for virtual monoenergetic images (VMI) at 50, 70, and 150 keV and iodine density maps at both diastole and systole. FWHM averaged differences of - 0.20, - 0.28, and - 0.15 mm relative to static FWHM at VMI 150 keV across acquisition parameters for high pitch prospectively ECG-triggered spiral, prospectively ECG-triggered axial, and retrospectively ECG-gated spiral scans, respectively. Additionally, there was no effect of heart rate and acquisition mode on FWHM at diastole (p-values < 0.001). DSC demonstrated similarity among parameters with standard deviations of 0.08, 0.09, 0.11, and 0.08 for VMI 50, 70, and 150 keV, and iodine density maps, respectively, with insignificant differences at diastole (p-values < 0.01). Similarly, eccentricity illustrated small differences across heart rate and acquisition mode for each spectral result. Consistency of spectral results at different heart rates and acquisition modes for different cardiac phase demonstrates the added benefit of spectral results from PCCT to dual-source CT to further increase confidence in quantification and advance cardiovascular diagnostics.

High-pitch, high temporal resolution, multi-energy cardiac imaging on a dual-source photon-counting-detector CT

OBJECTIVE

To measure the accuracy of material decomposition using a dual-source photon-counting-detector (DS-PCD) CT operated in the high-pitch helical scanning mode and compare the results against dual-source energy-integrating-detector (DS-EID) CT, which requires use of a low-pitch value in dual-energy mode.

METHODS

A DS-PCD CT and a DS-EID CT were used to scan a cardiac motion phantom consisting of a 3-mm diameter iodine cylinder. Iodine maps were reconstructed using DS-PCD in high-pitch mode and DS-EID in low-pitch mode. Image-based circularity, diameter, and iodine concentration of the iodine cylinder were calculated and compared between the two scanners. With institutional review board approval, in vivo exams were performed with the DS-PCD CT in high-pitch mode. Images were qualitatively compared against patients with similar heart rates that were scanned with DS-EID CT in low-pitch dual-energy mode.

RESULTS

On iodine maps, the mean circularity was 0.97 ± 0.02 with DS-PCD in high-pitch mode and 0.95 ± 0.06 with DS-EID in low-pitch mode. The mean diameter was 2.9 ± 0.2 mm with DS-PCD and 3.1 ± 0.2 mm with DS-EID, both of which are close to the 3 mm ground truth. For DS-PCD, the mean iodine concentration was 9.6 ± 0.8 mg/ml and this was consistent with the 9.4 ± 0.6 mg/ml value obtained with the cardiac motion disabled. For DS-EID, the concentration was 12.7 ± 1.2 mg/ml with motion enabled and 11.7 ± 0.5 mg/ml disabled. The background noise in the iodine maps was 15.1 HU with DS-PCD and 14.4 HU with DS-EID, whereas the volume CT dose index (CTDIvol ) was 3 mGy with DS-PCD and 11 mGy with DS-EID. On comparison of six patients (three on PCD, three on EID) with similar heart rates, DS-PCD provided iodine maps with well-defined coronaries even at a high heart rate of 86 beats per minute. Meanwhile, there were substantial motion artifacts in iodine maps obtained with DS-EID for patients with similar heart rates.

CONCLUSION

In a cardiac motion phantom, DS-PCD CT can perform accurate material decomposition in high-pitch mode, providing iodine maps with excellent geometric accuracy and robustness to motion at approximately 38% of the dose for similar noise as DS-EID CT.

Photon-counting detector CT: early clinical experience review

Since its development in the 1970s, X-ray CT has emerged as a landmark diagnostic imaging modality of modern medicine. Technological advances have been crucial to the success of CT imaging, as they have increasingly enabled improvements in image quality and diagnostic value at increasing radiation dose efficiency. With recent advances in engineering and physics, a novel technology has emerged with the potential to surpass several shortcomings and limitations of current CT systems. Photon-counting detector (PCD)-CT might substantially improve and expand the applicability of CT imaging by offering intrinsic spectral capabilities, increased spatial resolution, reduced electronic noise and improved image contrast. In this review we sought to summarize the first clinical experience of PCD-CT. We focused on most recent prototype and first clinically approved PCD-CT systems thereby reviewing initial publications and presenting corresponding clinical cases.

Gadolinium Enhances Dual-energy Computed Tomography Scan of Pulmonary Artery

OBJECTIVE

To evaluate the feasibility of using gadopentetate dimeglumine (Gd-DTPA) for dual-energy computed tomography pulmonary angiography (CTPA).

METHODS

Sixty-six patients were randomly divided into three groups and underwent CTPA. Group A had a turbo flash scan using an iohexol injection, Group B had a turbo flash scan using Gd-DTPA, and Group C had a dual-energy scan using Gd-DTPA. The original images of Group C were linearly blended with a blending factor of 0.5 or reconstructed at 40, 50, 60, 70, 80, 90, 100, and 110 keV, respectively. The groups were compared in terms of pulmonary artery CT value, image quality, and radiation dose.

RESULTS

The pulmonary artery CT values were significantly higher in Group C_40keV than in Groups B and C, but lower than in Group A. There was no significant difference in the image noise of Groups C_40keV, B, and C. Moreover, Group A had the largest beam hardening artifacts of the superior vena cava (SVC), followed by Groups B and C. Group C_40keV showed better vascular branching than the other three groups, among which Group B was superior to Group A. The subjective score of the image quality of Groups A, B, and C showed no significant difference, but the score was significantly higher in Group C_40keV than in Groups A and B. The radiation dose was significantly lower in Group B than in Groups A and C.

CONCLUSION

Gd-CTPA is recommended to patients who are unsuitable for receiving an iodine-based CTPA. Furthermore, a turbo flash scan could surpass a dual-energy scan without consideration for virtual monoenergetic imaging.

Progress of CT aortic angiography combined with coronary artery in the evaluation of acute aortic syndrome

Acute aortic syndrome (AAS) is a group of cardiovascular diseases that seriously threaten human life and health. AAS patients are often complicated with coronary artery disease and other related diseases, which require rapid and clear clinical diagnosis to avoid serious adverse events. In recent years, with the progress of science and technology, a variety of computer tomography (CT) angiography techniques have been applied in the clinic, and the diagnosis rate of AAS with coronary heart disease (CAD) has greatly increased. At the same time, the development of surgical technology and endovascular repair technology has significantly reduced the mortality and complication rate of AAS surgery. In the clinical diagnosis of AAS and related diseases, CT aortic angiography (CTA) combined with coronary CTA is increasingly applied to identify related diseases. Here, the current research progress on the technique of aortic CTA combined with coronary CTA is reviewed.

First Clinical Photon-counting Detector CT System: Technical Evaluation

Background The first clinical CT system to use photon-counting-detector (PCD) technology has become available for patient care. Purpose To assess the technical performance of the PCD-CT system using phantoms and representative participant exams. Materials and Methods Institutional review board approval and written informed consent from four participants were obtained. Technical performance of a dual-source PCD-CT system was measured for standard and high resolution (HR) collimations. Noise power spectrum (NPS), modulation transfer function (MTF), section sensitivity profile (SSP), iodine CT number accuracy in virtual monoenergetic images (VMI), and iodine concentration accuracy were measured. Four participants were enrolled (between May 2021 and August 2021) in this prospective study and scanned using similar or lower radiation doses compared to same-day exams performed using energy-integrating-detector (EID) CT. Results All standard technical performance measures met accreditation requirements. Relative to filtered-back-projection reconstructions, images from iterative reconstruction had lower noise magnitude but preserved NPS shape and peak-frequency. Maximum in-plane spatial resolutions of 125 and 208 microns were measured for PCD-HR and PCD-standard scans, respectively. Minimum values for SSP full-width-half-maximum measurements were 0.34-mm (0.2 mm nominal section thickness) and 0.64 mm (0.4-mm nominal section thickness) for PCD-HR and PCD-standard scans, respectively. In a PCD-CT 120-kV standard scan of a 40-cm phantom, VMI iodine CT numbers had a mean percent error of 5.7% and iodine concentration had root-mean-squared-error of 0.5 mg/cc, comparable to previously reported values for EID-CT. VMI, iodine map, and virtual non-contrast images were created for a coronary CT angiogram acquired with 66-ms temporal resolution. Participant PCD-CT images showed up to 47% lower noise and/or improved spatial resolution compared to EID-CT. Conclusions Technical performance of a new clinical photon-counting-detector CT is improved relative to current state-of-the-art CT system. The dual-source photon-counting-detector geometry facilitated 66-ms-temporal-resolution multi-energy cardiac imaging. Study-participant images illustrated the impact of the improved technical performance.

The ultrafast, high-pitch turbo FLASH mode of third-generation dual-source CT: Effect of different pitch and corresponding SFOV on image quality in a phantom study

PURPOSE

To investigate the effect of different pitches and corresponding scan fields of view (SFOVs) on the image quality in the ultrafast, high-pitch turbo FLASH mode of the third-generation dual-source CT using an anthropomorphic phantom.

METHODS

The phantom was scanned using the ultrafast, high-pitch turbo FLASH protocols of the third-generation dual-source CT with the different pitches and corresponding SFOVs (pitches: 1.55 to 3.2 with increments of 0.1, SFOVs: 50 cm to 35.4 cm). The objective parameters such as the CT number, image noises, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and artifacts index (AI), and image features from the head, chest, and abdomen were compared between the CT images with a pitch of 1.55 and SFOV of Ø 50 cm and a pitch of 3.2 and SFOV of Ø 35.4 cm. Then, the 18 series of CT images of the head, chest, and abdomen were evaluated by three radiologists independently.

RESULTS

The differences in the CT numbers were not statically significant between the CT images with a pitch of 1.55 and SFOV of Ø 50 cm and a pitch of 3.2 and SFOV of Ø 35.4 cm from most body parts and potential combinations (p > 0.05), Most of the image noises and the AI from the images with the pitch of 1.55 were significantly lower than those with the pitch of 3.2 (p < 0.05), and the SNR and CNR from the images with the pitch of 1.55 were higher than those with the pitch of 3.2. There were significant differences in the first-order features and texture features of the head (59.3%, 28.3%), chest (66%, 35.7%), and abdomen (71.6%, 64.7%) (p < 0.05). The subjective image quality was excellent when the pitch was less than 2.0 and gradually decreased with the increasing pitch. In addition, the image quality decreased significantly when the pitch was higher than 3.0 (all k≥0.69), especially in the head and chest.

CONCLUSIONS

In the ultrafast, high-pitch turbo FLASH mode of the third-generation DSCT, increasing the pitch and lowering the corresponding SFOV will change the image features and cause more artifacts degrading the image quality. Specific to the clinical needs, decreasing the pitch not only can expand the SFOV but also can improve the image quality.

High Pitch Helical CT Reconstruction

To avoid severe limited-view artifacts in reconstructed CT images, current multi-row detector CT (MDCT) scanners with a single x-ray source-detector assembly need to limit table translation speeds such that the pitch p (viz., normalized table translation distance per gantry rotation) is lower than 1.5. When , it remains an open question whether one can reconstruct clinically useful helical CT images without severe artifacts. In this work, we show that a synergistic use of advanced techniques in conventional helical filtered backprojection, compressed sensing, and more recent deep learning methods can be properly integrated to enable accurate reconstruction up to p=4 without significant artifacts for single source MDCT scans.

Noninvasive prediction of pulmonary hemodynamics in chronic thromboembolic pulmonary hypertension by electrocardiogram-gated computed tomography

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Easily measurable parameters from chest CT examinations enable prediction of pulmonary hemodynamics.

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ECG-gated CTPA is superior to non-gated CT.

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Non-invasive pH therapy monitoring or follow-up might be implemented in the future.

Purpose

The aim of the study was to investigate the potential of electrocardiogram (ECG)-gated computed tomography pulmonary angiography (CTPA) as a predictor of disease severity in patients with chronic thromboembolic pulmonary hypertension (CTEPH).

Method

Forty-five CTEPH patients with a mean age of 63.8 years±12.7 y (±standard deviation) who had undergone ECG-gated CTPA and right heart catheterization (RHC) were included in the study. Right ventricular to left ventricular volume ratio (RVV/LVV), diameter ratio on 4-chamber view (RVD4CH/LVD4CH), pulmonary trunk (PT) diameter, PT to aortic diameter ratio (PT/A), and septal angle were correlated to mean pulmonary artery pressure (mPAP). Moreover, RVV/LVV and RVD4CH/LVD4CH were adjusted to pulmonary diameter index (PADi) and PT/A index. Areas under the curve (AUC) for predicting mPAP above 40 mmHg, 35 mmHg, and 30 mmHg were calculated.

Results

RVD4CH/LVD4CH revealed the strongest correlation to mPAP before (r = 0.6507) and after (r = 0.7650; p < 0.0001) PT/A adjustment. The AUCs for predicting pH with mPAP over 40 mmHg and 30 mmHg were 0.9229 and 0.864, respectively. A cutoff value of 1.298 enabled prediction of pH with mPAP over 40 mmHg with a sensitivity, specificity, positive predictive, and negative predictive value of 80.00 %, 95.83 %, 88.46 %, and 94.12 %, respectively. Intra- and interobserver variability were excellent for all parameters.

Conclusion

Combining different and easily evaluable ECG-gated CTPA parameters enables excellent prediction of pulmonary hemodynamics in CTEPH patients. Ventricular diameter ratio on 4-chamber view adjusted by the PT/A ratio yielded the best correlation to mPAP.

Computed tomography recent history and future perspectives

Purpose: We provide a review of the key computed tomography (CT) technologies developed since the late 1980s and offer an overview of one of the future technologies under development. The focus of this review is mainly on the hardware and system development. The topics on the historical event linked to the early days of CT development and other innovations that contributed to the CT development, such as advanced image reconstruction techniques, are covered by companion papers in this special issue. Approach: The review is divided into five major sections, each linked to a key innovation in CT: helical spiral data acquisition, multi-slice CT, wide-cone CT, dual-source CT, and spectral CT. Given the limited scope of this review, only one of the future technologies, photon-counting CT, is discussed in detail. Whenever possible, both theory of operation and clinical examples are provided. Results: Theoretical analyses, phantom results, and clinical examples clearly demonstrate the efficacy and clinical relevancy of five historical technology developments and one future technology in CT. These technologies have improved and will continue to improve CT performance in terms of isotropic volume coverage, improved temporal resolution, and material differentiation and characterization capabilities. Conclusions: Over the past 30 years, technological developments of CT have contributed to the success of CT in many clinical applications such as trauma, oncology, cardiac imaging, and stroke. Advanced clinical applications have and will continue to demand more advanced technology development.

Accurate and robust sparse-view angle CT image reconstruction using deep learning and prior image constrained compressed sensing (DL-PICCS)

BACKGROUND

Sparse-view CT image reconstruction problems encountered in dynamic CT acquisitions are technically challenging. Recently, many deep learning strategies have been proposed to reconstruct CT images from sparse-view angle acquisitions showing promising results. However, two fundamental problems with these deep learning reconstruction methods remain to be addressed: (1) limited reconstruction accuracy for individual patients and (2) limited generalizability for patient statistical cohorts.

PURPOSE

The purpose of this work is to address the previously mentioned challenges in current deep learning methods.

METHODS

A method that combines a deep learning strategy with prior image constrained compressed sensing (PICCS) was developed to address these two problems. In this method, the sparse-view CT data were reconstructed by the conventional filtered backprojection (FBP) method first, and then processed by the trained deep neural network to eliminate streaking artifacts. The outputs of the deep learning architecture were then used as the needed prior image in PICCS to reconstruct the image. If the noise level from the PICCS reconstruction is not satisfactory, another light duty deep neural network can then be used to reduce noise level. Both extensive numerical simulation data and human subject data have been used to quantitatively and qualitatively assess the performance of the proposed DL-PICCS method in terms of reconstruction accuracy and generalizability.

RESULTS

Extensive evaluation studies have demonstrated that: (1) quantitative reconstruction accuracy of DL-PICCS for individual patient is improved when it is compared with the deep learning methods and CS-based methods; (2) the false-positive lesion-like structures and false negative missing anatomical structures in the deep learning approaches can be effectively eliminated in the DL-PICCS reconstructed images; and (3) DL-PICCS enables a deep learning scheme to relax its working conditions to enhance its generalizability.

CONCLUSIONS

DL-PICCS offers a promising opportunity to achieve personalized reconstruction with improved reconstruction accuracy and enhanced generalizability.

Deep learning enabled ultra-fast-pitch acquisition in clinical X-ray computed tomography

OBJECTIVE

In X-raycomputed tomography (CT), many important clinical applications may benefit from a fast acquisition speed. The helical scan is the most widely used acquisition mode in clinical CT, where a fast helical pitch can improve the acquisition speed. However, on a typical single-source helical CT (SSCT) system, the helical pitch p typically cannot exceed 1.5; otherwise, reconstruction artifacts will result from data insufficiency. The purpose of this work is to develop a deep convolutional neural network (CNN) to correct for artifacts caused by an ultra-fast pitch, which can enable faster acquisition speed than what is currently achievable.

METHODS

A customized CNN (denoted as ultra-fast-pitch network (UFP-net)) was developed to restore the underlying anatomical structure from the artifact-corrupted post-reconstruction data acquired from SSCT with ultra-fast pitch (i.e., p ≥ 2). UFP-net employed residual learning to capture the features of image artifacts. UFP-net further deployed in-house-customized functional blocks with spatial-domain local operators and frequency-domain non-local operators, to explore multi-scale feature representation. Images of contrast-enhanced patient exams (n = 83) with routine pitch setting (i.e., p < 1) were retrospectively collected, which were used as training and testing datasets. This patient cohort involved CT exams over different scan ranges of anatomy (chest, abdomen, and pelvis) and CT systems (Siemens Definition, Definition Flash, Definition AS+, Siemens Healthcare, Inc.), and the corresponding base CT scanning protocols used consistent settings of major scan parameters (e.g., collimation and pitch). Forward projection of the original images was calculated to synthesize helical CT scans with one regular pitch setting (p = 1) and two ultra-fast-pitch setting (p = 2 and 3). All patient images were reconstructed using the standard filtered-back-projection (FBP) algorithm. A customized multi-stage training scheme was developed to incrementally optimize the parameters of UFP-net, using ultra-fast-pitch images as network inputs and regular pitch images as labels. Visual inspection was conducted to evaluate image quality. Structural similarity index (SSIM) and relative root-mean-square error (rRMSE) were used as quantitative quality metrics.

RESULTS

The UFP-net dramatically improved image quality over standard FBP at both ultra-fast-pitch settings. At p = 2, UFP-net yielded higher mean SSIM (> 0.98) with lower mean rRMSE (< 2.9%), compared to FBP (mean SSIM < 0.93; mean rRMSE > 9.1%). Quantitative metrics at p = 3: UFP-net-mean SSIM [0.86, 0.94] and mean rRMSE [5.0%, 8.2%]; FBP-mean SSIM [0.36, 0.61] and mean rRMSE [36.0%, 58.6%].

CONCLUSION

The proposed UFP-net has the potential to enable ultra-fast data acquisition in clinical CT without sacrificing image quality. This method has demonstrated reasonable generalizability over different body parts when the corresponding CT exams involved consistent base scan parameters.

Deep learning-based forward and cross-scatter correction in dual-source CT

PURPOSE

Dual-source computed tomography (DSCT) uses two source-detector pairs offset by about 90°. In addition to the well-known forward scatter, a special issue in DSCT is cross-scattered radiation from X-ray tube A detected in the detector of system B and vice versa. This effect can lead to artifacts and reduction of the contrast-to-noise ratio of the images. The purpose of this work is to present and evaluate different deep learning-based methods for scatter correction in DSCT.

METHODS

We present different neural network-based methods for forward and cross-scatter correction in DSCT. These deep scatter estimation (DSE) methods mainly differ in the input and output information that is provided for training and inference and in whether they operate on two-dimensional (2D) or on three-dimensional (3D) data. The networks are trained and validated with scatter distributions obtained by our in-house Monte Carlo simulation. The simulated geometry is adapted to a realistic clinical setup.

RESULTS

All DSE approaches reduce scatter-induced artifacts and lead to superior results than the measurement-based scatter correction. Forward scatter, under the presence of cross-scatter, is best estimated either by our network that uses the current projection and a couple of neighboring views (fDSE 2D few views) or by our 3D network that processes all projections simultaneously (fDSE 3D). Cross-scatter, under the presence of forward scatter, is best estimated using xSSE XDSE 2D, with xSSE referring to a quick single scatter estimate of cross scatter, or by xDSE 3D that uses all projections simultaneously. By using our proposed networks, the total scatter error in dual could be reduced from about 18 HU to approximately 3 HU.

CONCLUSIONS

Deep learning-based scatter correction can reduce scatter artifacts in DSCT. To achieve more accurate cross-scatter estimations, the use of a cross-scatter approximation improves the results. Also, the ability to leverage across different projection angles improves the precision of the algorithm.

Physics-based iterative reconstruction for dual-source and flying focal spot computed tomography

PURPOSE

For single-source helical Computed Tomography (CT), both Filtered-Back Projection (FBP) and statistical iterative reconstruction have been investigated. However, for dual-source CT with flying focal spot (DS-FFS CT), a statistical iterative reconstruction that accurately models the scanner geometry and acquisition physics remains unknown to researchers. Therefore, our purpose is to present a novel physics-based iterative reconstruction method for DS-FFS CT and assess its image quality.

METHODS

Our algorithm uses precise physics models to reconstruct from the native cone-beam geometry and interleaved dual-source helical trajectory of a DS-FFS CT. To do so, we construct a noise physics model to represent data acquisition noise and a prior image model to represent image noise and texture. In addition, we design forward system models to compute the locations of deflected focal spots, the dimension, and sensitivity of voxels and detector units, as well as the length of intersection between x-rays and voxels. The forward system models further represent the coordinated movement between the dual sources by computing their x-ray coverage gaps and overlaps at an arbitrary helical pitch. With the above models, we reconstruct images by an advanced Consensus Equilibrium (CE) numerical method to compute the maximum a posteriori estimate to a joint optimization problem that simultaneously fits all models.

RESULTS

We compared our reconstruction with Siemens ADMIRE, which is the clinical standard hybrid iterative reconstruction (IR) method for DS-FFS CT, in terms of spatial resolution, noise profile, and image artifacts through both phantoms and clinical scan datasets. Experiments show that our reconstruction has a higher spatial resolution, with a Task-Based Modulation Transfer Function (MTF_task ) consistently higher than the clinical standard hybrid IR. In addition, our reconstruction shows a reduced magnitude of image undersampling artifacts than the clinical standard.

CONCLUSIONS

By modeling a precise geometry and avoiding data rebinning or interpolation, our physics-based reconstruction achieves a higher spatial resolution and fewer image artifacts with smaller magnitude than the clinical standard hybrid IR.

Chest CT in patients with shortness of breath: Comparing high pitch CT and conventional CT on respiratory artefacts and dose

INTRODUCTION

To investigate chest respiratory artefact reduction using High Pitch Dual Source Computed Tomography (HPCT) compared to conventional CT (CCT) in symptomatic patients with shortness of breath.

METHODS

Forty patients were prospectively examined on a second-generation Dual Source scanner. They were randomly divided into two groups: twenty patients underwent an experimental HPCT protocol and twenty control cases CCT protocol. Respiratory artefacts were evaluated using an ordinal score (0, 1 and 2) assigned by two readers with five and thirty years of experience. A qualitative assessment was performed using two categorical groups, group 1 = acceptable and group 2 = unacceptable. Dose Length Product (DLP) was compared.

RESULTS

The two groups showed a statistical difference in artefacts reduction (p < 0.0001). HPCT demonstrated no artefacts in 82% of cases, while CCT showed no artefacts in 39% of cases. DLP showed no statistical differences (p = 0.6) with mean = 266.9 for HPCT and mean = 282.65 for CCT. HPCT provides high table speed in the z-direction allowing a high temporal resolution, which reduces respiratory artefacts during free-breathing acquisition. Despite the use of two x-ray tubes, the HPCT did not increase the dose to the patient but provided the highest images quality.

CONCLUSIONS

In the emergency setting, HPCTs have been critical for achieving good image quality in uncooperative patients.

IMPLICATIONS FOR PRACTICE

Acute respiratory failure is a common emergency department presentation, and the choice of high-speed acquisition CT may increase image quality.

Principles and applications of dual source CT

This article describes the technical principles and clinical applications of dual source CT. A dual source CT (DSCT) is a CT system with two x-ray tubes and two detectors at an angle of approximately 90°. Both measurement systems acquire CT scan data simultaneously at the same anatomical level of the patient (same z-position). DSCT provides temporal resolution of approximately a quarter of the gantry rotation time for cardiac, cardio-thoracic and pediatric imaging. Successful imaging of the heart and the coronary arteries at high and variable heart rates has been demonstrated. DSCT systems can be operated at twice the spiral pitch of single source CT systems (up to pitch 3.2). The resulting high table speed is beneficial for pediatric applications and fast CT angiographic scans, e. g. of the aorta or the extremities. Operating both X-ray tubes at different tube potential (kV) enables the acquisition of dual energy data and the corresponding applications such as monoenergetic imaging and computation of material maps. Spectral separation can be improved by different filtration of the X-ray beams of both X-ray tubes. As a downside, DSCT systems have to cope with some challenges, among them the limited size of the second measurement system, and cross-scattered radiation.

Technological developments of X-ray computed tomography over half a century: User's influence on protocol optimization

Since the introduction of Computed Tomography (CT), technological improvements have been impressive. At the same time, the number of adjustable acquisition and reconstruction parameters has increased substantially. Overall, these developments led to improved image quality at a reduced radiation dose. However, many parameters are interrelated and part of automated algorithms. This makes it more complicated to adjust them individually and more difficult to comprehend their influence on CT protocol adjustments. Moreover, the user's influence in adapting protocol parameters is sometimes limited by the manufacturer's policy or the user's knowledge. As a consequence, optimization can be a challenge. A literature search in Embase, Medline, Cochrane, and Web of Science was performed. The literature was reviewed with the objective to collect information regarding technological developments in CT over the past five decades and the role of the associated acquisition and reconstruction parameters in the optimization process.

Principal Component Analysis in Projection and Image Domains-Another Form of Spectral Imaging in Photon-Counting CT

OBJECTIVE

We explore the feasibility of principal component analysis (PCA) as a form of spectral imaging in photon-counting CT.

METHODS

Using the data acquired by a prototype system and simulated by computer, we investigate the feasibility of spectral imaging in photon-counting CT via PCA for feature extraction and study the impacts made by data standardization and de-noising on its performance.

RESULTS

The PCA in the projection domain maintains the data consistence that is essential for tomographic image reconstruction and performs virtually the same as that in the image domain. The first three primary components account for more than 99.99% covariance of the data. Within anticipation, the contrast-to-noise ratio (CNR) between the target and background in the first principal component image can be larger than that in the image generated from the data acquired in each energy bin. More importantly, the CNR in the first principal component image may be larger than that in the image formed by the summed data acquired in all energy bins (i.e., the conventional polychromatic CT image). In addition, de-noising can not only reduce the noise in images but also improve the effectiveness/efficiency of PCA in feature extraction.

CONCLUSION

The PCA in either projection or image domain provides another form of spectral imaging in photon-counting CT that fits the essential requirements on spectral imaging in true color.

SIGNIFICANCE

The verification of PCA's feasibility in CT as a form spectral imaging and observation of its potential superiority in CNR over conventional polychromatic CT are meaningful in theory and practice.

Virtual clinical trial for quantifying the effects of beam collimation and pitch on image quality in computed tomography

Purpose: To utilize a virtual clinical trial (VCT) construct to investigate the effects of beam collimation and pitch on image quality (IQ) in computed tomography (CT) under different respiratory and cardiac motion rates. Approach: A computational human model [extended cardiac-torso (XCAT) phantom] with added lung lesions was used to simulate seven different rates of cardiac and respiratory motions. A validated CT simulator (DukeSim) was used in this study. A supplemental validation was done to ensure the accuracy of DukeSim across different pitches and beam collimations. Each XCAT phantom was imaged using the CT simulator at multiple pitches (0.5 to 1.5) and beam collimations (19.2 to 57.6 mm) at a constant dose level. The images were compared against the ground truth using three task-generic IQ metrics in the lungs. Additionally, the bias and variability in radiomics (morphological) feature measurements were quantified for task-specific lung lesion quantification across the studied imaging conditions. Results: All task-generic metrics degraded by 1.6% to 13.3% with increasing pitch. When imaged with motion, increasing pitch reduced motion artifacts. The IQ slightly degraded (1.3%) with changes in the studied beam collimations. Patient motion exhibited negative effects (within 7%) on the IQ. Among all features across all imaging conditions studies, compactness2 and elongation showed the largest ( - 26.5 % , 7.8%) and smallest ( - 0.8 % , 2.7%) relative bias and variability. The radiomics results were robust across the motion profiles studied. Conclusions: While high pitch and large beam collimations can negatively affect the quality of CT images, they are desirable for fast imaging. Further, our results showed no major adverse effects in morphology quantification of lung lesions with the increase in pitch or beam collimation. VCTs, such as the one demonstrated in this study, represent a viable methodology for experiments in CT.

Updates in Vascular Computed Tomography

Computed tomography angiography (CTA) has become a mainstay for the imaging of vascular diseases, because of high accuracy, availability, and rapid turnaround time. High-quality CTA images can now be routinely obtained with high isotropic spatial resolution and temporal resolution. Advances in CTA have focused on improving the image quality, increasing the acquisition speed, eliminating artifacts, and reducing the doses of radiation and iodinated contrast media. Dual-energy computed tomography provides material composition capabilities that can be used for characterizing lesions, optimizing contrast, decreasing artifact, and reducing radiation dose. Deep learning techniques can be used for classification, segmentation, quantification, and image enhancement.

User-Friendly Vendor-Specific Guideline for Pediatric Cardiothoracic Computed Tomography Provided by the Asian Society of Cardiovascular Imaging Congenital Heart Disease Study Group: Part 1. Imaging Techniques

Optimal performance of pediatric cardiothoracic computed tomography (CT) is technically challenging and may need different approaches for different types of CT scanners. To meet the technical demands and improve clinical standards, a practical, user-friendly, and vendor-specific guideline for pediatric cardiothoracic CT needs to be developed for children with congenital heart disease (CHD). In this article, we have attempted to describe such guideline based on the consensus of experts in the Asian Society of Cardiovascular Imaging CHD Study Group. This first part describes the imaging techniques of pediatric cardiothoracic CT, and it includes recommendations for patient preparation, scan techniques, radiation dose, intravenous injection protocol, post-processing, and vendor-specific protocols.

Initial clinical experience with high-pitch dual-source CT as a rapid technique for thoraco-abdominal evaluation in awake infants and young children

AIM

To evaluate dual-source high-pitch computed tomography (HPCT) imaging of the chest and abdomen as a rapid scanning technique to obtain diagnostic-quality imaging evaluation of infants and young children without sedation.

MATERIALS AND METHODS

Fifty-three paediatric patients (age 24.1±2 months) who underwent chest or abdomen HPCT (≥1.5) and standard pitch CT (SPCT, <1.5) on a dual-source 128-row multidetector CT system were included in the study. Image quality assessment was performed by two paediatric radiologists for diagnostic confidence, image artefacts, and image noise. Objective image noise was measured.

RESULTS

Most of the CT examinations were performed in children who were >1 year old (n=15 and n=20) followed by ≤1 year old (n=8 and n=10) in SPCT and HPCT, respectively. The mean radiation dose (SSDE) from HPCT was 1.96±1 mGy compared to 2.2±1 mGy for SPCT (p=0.3). No major artefacts were reported and overall image quality of all HPCT examinations was acceptable diagnostically. In addition, objective image noise values were not significantly different between HPCT compared with SPCT (11±3 versus 11±5, p=0.7).

CONCLUSION

Ultra-fast, HPCT can be performed without the need for sedation as a potential alternative to anaesthetised magnetic resonance imaging in infants and young children.

Technical Note: The use of DirectDensityTM and dual-energy CT in the radiation oncology clinic

PURPOSE

Two new tools available in Radiation Oncology clinics are Dual-energy CT (DECT) and Siemens' DirectDensity™ (DD) reconstruction algorithm, which allows scans of any kV setting to use the same calibration. This study demonstrates why DD scans should not be used in combination with DECT and quantifies the magnitude of potential errors in image quality and dose.

METHODS

A CatPhan 504 phantom was scanned with a dual-pass DECT and reconstructed with many different kernels, including several DD kernels. The HU values of various inserts were measured. The RANDO^® man phantom was also scanned. Bone was contoured and then histograms of the bone HU values were analyzed for Filtered-Backprojection (FBP) and DD reconstructions of the 80 and 140 kV scans, as well as several virtual, monoenergetic reconstructions generated from FBP and DD reconstructions. "Standard" dose distributions were calculated on several reconstructions of both phantoms for comparison.

RESULTS

The DD kernel overcorrected the high-Z material inserts relative to bone, giving an excessively low relative electron density (RED). A unique artifact was observed in the high density inserts of the CatPhan in the monoenergetic scans when utilizing a DD kernel, due to the overcorrection in the DD scan of the material, especially at lower kV.

CONCLUSIONS

While DD and DECT perform as expected when used independently, errors from their combined use were demonstrated. Dose errors from misuse of the DD kernel with DECT post-processing were as large as 2.5%. The DECT post-processing was without value because the HU differences between low and high energy were removed by the DD kernel. When using DD and DECT, we recommend the use of a DD reconstruction of the high energy scan for the dose calculation, and use of a FBP filter for the low and high energy scans for the DECT post-processing.

Computed Tomography Technology-and Dose-in the 21st Century

In the last decade or so, a number of disruptive technological advances have taken place in x-ray computed tomography, making possible new clinical applications. Changes in scanner design have included the use of two x-ray sources and two detectors or the use of large detector arrays that provide 16 cm of longitudinal coverage in one gantry rotation. These advances have allowed images of the entire heart to be acquired in just one heartbeat, lowering the effective dose from cardiac computed tomography from ~15 mSv to <1 mSv. Dual-energy computed tomography is now in widespread clinical use, enabling the assessment of material composition and concentration, as well as a range of new clinical applications. An emerging technology known as photon-counting detector computed tomography directly measures the energies of detected photons and is capable of simultaneously acquiring more than two energy data sets. Photon-counting detector computed tomography also provides advantages such as the ability to reject electronic noise, better iodine contrast-to-noise for a given dose, and spatial resolution as fine as 150 μm. Optimized x-ray tube potential selection has allowed reduction in radiation and contrast doses. Finally, wide adoption of iterative reconstruction and noise-reduction techniques has occurred. In all, body computed tomography doses have fallen dramatically, for example, by over a factor of 3 from the early 1980s. All of these advances increase the medical benefit and decrease the potential radiation risk associated with computed tomography. However, care must be taken to ensure that doses are not lowered to the level at which the clinical task is compromised.

High-pitch, 120 kVp/30 mAs, low-dose dual-source chest CT with iterative reconstruction: Prospective evaluation of radiation dose reduction and image quality compared with those of standard-pitch low-dose chest CT in healthy adult volunteers

PURPOSE

Objective of this study was to evaluate the effectiveness of the iterative reconstruction of high-pitch dual-source chest CT (IR-HP-CT) scanned with low radiation exposure compared with low dose chest CT (LDCT).

MATERIALS AND METHODS

This study was approved by the institutional review board. Thirty healthy adult volunteers (mean age 44 years) were enrolled in this study. All volunteers underwent both IR-HP-CT and LDCT. IR-HP-CT was scanned with 120 kVp tube voltage, 30 mAs tube current and pitch 3.2 and reconstructed with sinogram affirmed iterative reconstruction. LDCT was scanned with 120 kVp tube voltage, 40 mAs tube current and pitch 0.8 and reconstructed with B50 filtered back projection. Image noise, and signal to noise ratio (SNR) of the infraspinatus muscle, subcutaneous fat and lung parenchyma were calculated. Cardiac motion artifact, overall image quality and artifacts was rated by two blinded readers using 4-point scale. The dose-length product (DLP) (mGy∙cm) were obtained from each CT dosimetry table. Scan length was calculated from the DLP results. The DLP parameter was a metric of radiation output, not of patient dose. Size-specific dose estimation (SSDE, mGy) was calculated using the sum of the anteroposterior and lateral dimensions and effective radiation dose (ED, mSv) were calculated using CT dosimetry index.

RESULTS

Approximately, mean 40% of SSDE (2.1 ± 0.2 mGy vs. 3.5 ± 0.3 mGy) and 34% of ED (1.0 ± 0.1 mSv vs. 1.5 ± 0.1 mSv) was reduced in IR-HP-CT compared to LDCT (P < 0.0001). Image noise was reduced in the IR-HP-CT (16.8 ± 2.8 vs. 19.8 ± 3.4, P = 0.0001). SNR of lung and aorta of IR-HP-CT showed better results compared with that of LDCT (22.2 ± 5.9 vs. 33.0 ± 7.8, 1.9 ± 0.4 vs 1.1 ± 0.3, P < 0.0001). The score of cardiac pulsation artifacts were significantly reduced on IR-HP-CT (3.8 ± 0.4, 95% confidence interval, 3.7‒4.0) compared with LDCT (1.6 ± 0.6, 95% confidence interval, 1.3‒1.8) (P < 0.0001). SNR of muscle and fat, beam hardening artifact and overall subjective image quality of the mediastinum, lung and chest wall were comparable on both scans (P ≥ 0.05).

CONCLUSION

IR-HP-CT with 120 kVp and 30 mAs tube setting in addition to an iterative reconstruction reduced cardiac motion artifact and radiation exposure while representing similar image quality compared with LDCT.

Image Quality and Radiation Dose of High-Pitch Dual-Source Spiral Cardiothoracic Computed Tomography in Young Children with Congenital Heart Disease: Comparison of Non-Electrocardiography Synchronization and Prospective Electrocardiography Triggering

Objective

To compare image quality and radiation dose of high-pitch dual-source spiral cardiothoracic computed tomography (CT) between non-electrocardiography (ECG)-synchronized and prospectively ECG-triggered data acquisitions in young children with congenital heart disease.

Materials and Methods

Eighty-six children (≤ 3 years) with congenital heart disease who underwent high-pitch dual-source spiral cardiothoracic CT were included in this retrospective study. They were divided into two groups (n = 43 for each; group 1 with non-ECG-synchronization and group 2 with prospective ECG triggering). Patient-related parameters, radiation dose, and image quality were compared between the two groups.

Results

There were no significant differences in patient-related parameters including age, cross-sectional area, body density, and water-equivalent area between the two groups (p > 0.05). Regarding radiation dose parameters, only volume CT dose index values were significantly different between group 1 (1.13 ± 0.09 mGy) and group 2 (1.07 ± 0.12 mGy, p < 0.02). Among image quality parameters, significantly higher image noise (3.8 ± 0.7 Hounsfield units [HU] vs. 3.3 ± 0.6 HU, p < 0.001), significantly lower signal-to-noise ratio (105.0 ± 28.9 vs. 134.1 ± 44.4, p = 0.001) and contrast-to-noise ratio (84.5 ± 27.2 vs. 110.1 ± 43.2, p = 0.002), and significantly less diaphragm motion artifacts (3.8 ± 0.5 vs. 3.7 ± 0.4, p < 0.04) were found in group 1 compared with group 2. Image quality grades of cardiac structures, coronary arteries, ascending aorta, pulmonary trunk, lung markings, and chest wall showed no significant difference between groups (p > 0.05).

Conclusion

In high-pitch dual-source spiral pediatric cardiothoracic CT, additional ECG triggering does not substantially reduce motion artifacts in young children with congenital heart disease.

High-pitch dual-source paranasal sinus CT in agitated patients with maxillofacial trauma: analysis of image quality, motion artifacts, and dose aspects

Background Image quality benefits from high-pitch scanning in agitated patients by reducing acquisition time. Purpose To compare image quality and exposure parameters in patients with maxillofacial trauma on second- and third-generation dual-source computed tomography (DSCT). Material and Methods Four groups were compared. Group 1 was examined on second-generation DSCT (120 kV/50 mAs, pitch 3.0). The other three groups were examined on third-generation DSCT. Group 2 was scanned with 120 kV/50 mAs, pitch 2.2. Automated exposure control (AEC) was used in group 3 and group 4 with pitch factors of 2.2 and 3.0, respectively. Images of third-generation DSCT were reconstructed with iterative reconstruction (IR), of second-generation DSCT with filtered back-projection. CTDIvol, acquisition time, and image quality were compared. Results Thirty patients were included in each group. Average CTDIvol (2.76 ± 0.00 mGy, 2.66 ± 0.00 mGy, 0.74 ± 0.23 mGy, and 0.75 ± 0.17 mGy) was significantly lower on third-generation DSCT with AEC ( P < 0.001). Subjective image quality was rated worst in group 4 due to strong high-pitch artifacts, while in the remaining three groups it was rated good or very good with good inter-observer agreement (k > 0.64). Average acquisition time was significantly shorter with third-generation DSCT (0.47 s, 0.36 s, 0.38 s, 0.30 s; P < 0.001). Conclusion Third-generation DSCT yields faster acquisition times and substantial dose reduction with AEC. A pitch of 2.2 should be preferred, as it results in fewer artifacts. If AEC is used, latest IR ensures that diagnostic image quality is guaranteed.

On the data acquisition, image reconstruction, cone beam artifacts, and their suppression in axial MDCT and CBCT - A review

PURPOSE

In the clinic, computed tomography (CT) has evolved into an essential modality for diagnostic imaging by multidetector row CT (MDCT) and image guided intervention by cone beam CT (CBCT). Recognizing the increasing importance of axial MDCT/CBCT in clinical and preclinical applications, and the existence of CB artifacts in MDCT/CBCT images, we provide a review of CB artifacts' root causes, rendering mechanisms and morphology, and possible solutions for elimination and/or reduction of the artifacts.

METHODS

By examining the null space in Radon and Fourier domain, the root cause of CB artifacts (i.e., data insufficiency) in axial MDCT/CBCT is analytically investigated, followed by a review of the data sufficiency conditions and the "circle +" source trajectories. The rendering mechanisms and morphology of CB artifacts in axial MDCT/CBCT and their special cases (e.g., half/short scan and full scan with latitudinally displaced detector) are then analyzed, followed by a survey of the potential solutions to suppress the artifacts. The phenomenon of imaged zone indention and its variation over FBP, BPF/DBPF, two-pass and iterative CB reconstruction algorithms and/or schemes are discussed in detail.

RESULTS

An interdomain examination of the null space provides an insightful understanding of the root cause of CB artifacts in axial MDCT/CBCT. The decomposition of CB artifacts rendering mechanisms facilitates understanding of the artifacts' behavior under different conditions and the potential solutions to suppress them. An inspection of the imaged zone intention phenomenon provides guidance on the design and implementation of CB image reconstruction algorithms and schemes for CB artifacts suppression in axial MDCT/CBCT.

CONCLUSIONS

With increasing importance of axial MDCT/CBCT in clinical and preclinical applications, this review article can update the community with in-depth information and clarification on the latest progress in dealing with CB artifacts and thus increase clinical/preclinical confidence.

Combined prospectively electrocardiography- and respiratory-triggered sequential cardiac computed tomography in free-breathing children: success rate and image quality

BACKGROUND

Combined prospectively electrocardiography (ECG)- and respiratory-triggered sequential cardiac computed tomography (CT) has not been evaluated in free-breathing children.

OBJECTIVE

To evaluate the success rate and image quality of combined prospectively ECG- and respiratory-triggered sequential cardiac CT in free-breathing children.

MATERIALS AND METHODS

Image quality of combined prospectively ECG- and respiratory-triggered sequential cardiac CT in 870 children (≤5 years of age) was evaluated in terms of severe motion (maximal distance ≥2 mm) and band artifacts (maximal attenuation difference ≥100 Hounsfield units). The success rate of the scan mode was calculated. The causes of failed cases were assessed. Patient-related, radiation and image quality parameters were compared between success and failure groups.

RESULTS

Severe motion artifacts were observed in 10.6% (92/870) of patients due to cardiac phase error in 17 (18.5%), patient motion in 12 (13.0%), and unknown causes in 63 (68.5%). Severe band artifacts were seen in 13.2% (115/870) of patients. Combined prospectively ECG- and respiratory-triggered sequential cardiac CT was successfully performed in 78.5% (683/870) of patients, while it failed in 21.5% (187/870). All the evaluated patient-related, radiation and image quality parameters were significantly different (P≤0.001) between success and failure groups except effective dose (P>0.05).

CONCLUSION

Additional prospective respiratory triggering can reduce motion artifacts in prospectively ECG-triggered sequential cardiac CT in free-breathing children.

Cancer Patient-Derived Circulating Microparticles Enhance Lung Metastasis in a Rat Model: Dual-Source CT, Cellular, and Molecular Studies

PURPOSE

This study aimed to test the hypothesis that lung cancer patient-derived circulating microparticles (LCC-MPs) enhance metastatic lung tumors in a rat model.

PROCEDURES

The controls (n = 6) and LCC-MP-treated rats (n = 6) with N1S1-induced pulmonary metastatic hepatocellular carcinoma (HCC) underwent dual-source CT (DSCT) on days 10, 15, and 20. Cellular and molecular studies were performed subsequently.

RESULTS

DSCT revealed slow progression of metastatic lung tumors in the controls. Compared with the controls, the LCC-MP-treated rats exhibited significantly more and larger metastatic tumors on days 15 and 20 on DSCT, enhanced angiogenesis with higher microvessel count (CD34+), more CXCR4+ and VEGF+ cells in immunohistofluorescence studies, and higher protein expression levels of eNOS, angiopoietin, vascular endothelial growth factor, and CD31 on western blotting (Mann-Whitney test, all P < 0.05).

CONCLUSIONS

LCC-MPs can elicit oncogenic stimulation and accelerate metastatic HCC growth in rat lung as demonstrated on DSCT and enhanced tumoral angiogenesis as confirmed in cellular and molecular studies.

Changing the paradigm for diagnostic MRI in pediatrics: Don't hold your breath

Increasingly complex pediatric patients and improvements in technology warrant reevaluation of the risk associated with anesthesia for diagnostic imaging. Although magnetic resonance imaging is the imaging modality of choice for children given the potentially harmful effects of computerized tomography-associated ionizing radiation, we dare to suggest that certain patients would benefit from the liberalization of our current standard. Incorporating the use of newer computerized tomography technology may improve safety for those that are already at higher risk for adverse events. Furthermore, magnetic resonance imaging is not risk-free-what is often overlooked is the need for controlled ventilation and breath-holding to minimize motion artifact. As physicians at the forefront of the development and sustainability of the perioperative surgical home, anesthesiologists must work to not only optimize patients preoperatively but should also act as gatekeepers for procedural safety.

Application of low-dose dual-source computed tomography angiography in children with complex congenital heart disease

The objective of the present study was to evaluate image quality and radiation dosage using a low-dose prospectively electrocardiogram (ECG)-gated computed tomography (CT) protocol for dual-source angiography in children with complex congenital heart disease. A total of 206 patients with complex congenital heart disease were equally assigned into two groups at random. The children in group A underwent low-dose retrospective ECG-gated CT scanning with an ECG-pulsing technique, and group B underwent prospective ECG-gated scanning with an ECG-pulsing technique. Radiation dose volume computed tomography dose index (CTDI vol), dose length product (DLP) and effective dose (ED) were recorded after scanning. Raw data were transferred to workstations for post-processing, diagnosis, grading, comparison with intra-operation findings or cardiac catheterisation, and the coincidence, false negative rate and misdiagnosis rates of groups A and B, respectively, were subsequently recorded. The results of the present study indicated that the height, age and weight of the children in the two groups exhibited no significant differences. The image quality of group A was graded as 3.94±0.08, whereas the grade for the image quality in group B was 4.05±0.08; no significant difference was detected. The coincidence rates of groups A and B were 89.37 and 88.48%, respectively; the false negative rates of groups A and B were 9.66 and 10.60%, respectively; the misdiagnosis rates of groups A and B were 0.97 and 0.92%. No significant differences between the two groups were detected. The CTDI value of group A was 3.24±1.62 mGy, the DLP value was 47.53±33.28 mGy·cm², the ED value was 0.93±0.42 mSv. By contrast, the CTDI value of group B was 2.27±0.94 mGy, the DLP value was (27.03±17.64) mGy·cm², and the ED value was 0.53±0.23 mSv. Significant differences were detected between the two groups (CTDI t=5.287, P<0.05; DLP t=5.523, P<0.05; ED t=8.497, P<0.05), and the radiation dose of group B was markedly decreased, compared with group A. In conclusion, the present study demonstrated that prospectively ECG-gated scanning of dual-source CT is an effective method of examination for dose reduction in children with congenital heart disease without impairment of image quality, which suggests that this protocol may be suitable for future application and dissemination.

High-pitch dual-source CT angiography without ECG-gating for imaging the whole aorta: intraindividual comparison with standard pitch single-source technique without ECG gating

PURPOSE

We aimed to perform intraindividual comparison of computed tomography (CT) parameters, image quality, and radiation exposure between standard CT angiography (CTA) and high-pitch dual source (DS)-CTA, in subjects undergoing serial CTA of thoracoabdominal aorta.

METHODS

Eighteen subjects with thoracoabdominal CTA by standard technique and high-pitch DS-CTA technique within 6 months of each other were retrieved for intraindividual comparison of image quality in thoracic and abdominal aorta. Quantitative analysis was performed by comparison of mean aortic attenuation, noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Qualitative analysis was performed by visual assessment of motion artifacts and diagnostic confidence. Radiation exposure was quantified by effective dose. Image quality was apportioned to radiation exposure by means of figure of merit.

RESULTS

Mean aortic attenuation and noise were higher in high-pitch DS-CTA of thoracoabdominal aorta, whereas SNR and CNR were similar in thoracic aorta and significantly lower in high-pitch DS-CTA of abdominal aorta (P = 0.024 and P = 0.016). High-pitch DS-CTA was significantly better in the first segment of thoracic aorta. Effective dose was reduced by 72% in high-pitch DS-CTA.

CONCLUSION

High-pitch DS-CTA without electrocardiography-gating is an effective technique for imaging aorta with very low radiation exposure and with significant reduction of motion artifacts in ascending aorta; however, the overall quality of high-pitch DS-CTA in abdominal aorta is lower than standard CTA.

Evaluation of High-Pitch Ungated Pediatric Cardiovascular Computed Tomography for the Assessment of Cardiac Structures in Neonates

PURPOSE

We evaluated a high-pitch, non-electrocardiogram-gated cardiac computed tomographic protocol, designed to image both cardiac and extracardiac structures, including coronary arteries, in a neonatal population (less than 1 year old) that was referred for congenital heart disease assessment and compared it with an optimized standard-pitch protocol in an equivalent cohort.

MATERIALS AND METHODS

Twenty-nine high-pitch scans were compared with 31 age-matched, sex-matched, and weight-matched standard-pitch, dosimetrically equivalent scans. The visualization and subjective quality of both cardiac and extracardiac structures were scored by consensus between 2 trained blinded observers. Image noise, signal-to-noise and contrast-to-noise ratios, and radiation doses were also compared.

RESULTS

The high-pitch protocol better demonstrated the pulmonary veins (P=0.03) and all coronary segments (all P<0.05), except the distal right coronary artery (P=0.10), with no significant difference in the visualization of the remaining cardiac or extracardiac structures. Both contrast-to-noise and signal-to-noise ratios improved due to greater vessel opacity, with significantly fewer streak (P<0.01) and motion (P<0.01) artifacts. Image noise and computed tomographic dose index were comparable across the 2 techniques; however, the high-pitch acquisition resulted in a small, but statistically significant, increase in dose-length product [13.0 mGy.cm (9.0 to 17.3) vs. 11.0 mGy.cm (9.0 to 13.0), P=0.05] due to greater z-overscanning.

CONCLUSIONS

In neonates, a high-pitch protocol improves coronary artery and pulmonary vein delineation compared with the standard-pitch protocol, allowing a more comprehensive assessment of cardiovascular anatomy while obviating the need for either patient sedation or heart rate control.