Advanced image-based virtual monoenergetic dual-energy CT angiography of the abdomen: optimization of kiloelectron volt settings to improve image contrast

Low-iodine-dose computed tomography coupled with an artificial intelligence-based contrast-boosting technique in children: a retrospective study on comparison with conventional-iodine-dose computed tomography

BACKGROUND

Low-iodine-dose computed tomography (CT) protocols have emerged to mitigate the risks associated with contrast injection, often resulting in decreased image quality.

OBJECTIVE

To evaluate the image quality of low-iodine-dose CT combined with an artificial intelligence (AI)-based contrast-boosting technique in abdominal CT, compared to a standard-iodine-dose protocol in children.

MATERIALS AND METHODS

This single-center retrospective study included 35 pediatric patients (mean age 9.2 years, range 1-17 years) who underwent sequential abdominal CT scans-one with a standard-iodine-dose protocol (standard-dose group, Iobitridol 350 mgI/mL) and another with a low-iodine-dose protocol (low-dose group, Iohexol 240 mgI/mL)-within a 4-month interval from January 2022 to July 2022. The low-iodine CT protocol was reconstructed using an AI-based contrast-boosting technique (contrast-boosted group). Quantitative and qualitative parameters were measured in the three groups. For qualitative parameters, interobserver agreement was assessed using the intraclass correlation coefficient, and mean values were employed for subsequent analyses. For quantitative analysis of the three groups, repeated measures one-way analysis of variance with post hoc pairwise analysis was used. For qualitative analysis, the Friedman test followed by post hoc pairwise analysis was used. Paired t-tests were employed to compare radiation dose and iodine uptake between the standard- and low-dose groups.

RESULTS

The standard-dose group exhibited higher attenuation, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) of organs and vessels compared to the low-dose group (all P-values < 0.05 except for liver SNR, P = 0.12). However, noise levels did not differ between the standard- and low-dose groups (P = 0.86). The contrast-boosted group had increased attenuation, CNR, and SNR of organs and vessels, and reduced noise compared with the low-dose group (all P < 0.05). The contrast-boosted group showed no differences in attenuation, CNR, and SNR of organs and vessels (all P > 0.05), and lower noise (P = 0.002), than the standard-dose group. In qualitative analysis, the contrast-boosted group did not differ regarding vessel enhancement and lesion conspicuity (P > 0.05) but had lower noise (P < 0.05) and higher organ enhancement and artifacts (all P < 0.05) than the standard-dose group. While iodine uptake was significantly reduced in low-iodine-dose CT (P < 0.001), there was no difference in radiation dose between standard- and low-iodine-dose CT (all P > 0.05).

CONCLUSION

Low-iodine-dose abdominal CT, combined with an AI-based contrast-boosting technique exhibited comparable organ and vessel enhancement, as well as lesion conspicuity compared to standard-iodine-dose CT in children. Moreover, image noise decreased in the contrast-boosted group, albeit with an increase in artifacts.

Virtual Monoenergetic Images Facilitate Better Identification of the Arc of Riolan During Splenic Flexure Takedown

OBJECTIVE

This study aimed to investigate whether virtual monoenergetic images (VMIs) can aid radiologists and surgeons in better identifying the arc of Riolan (AOR) and to determine the optimal kilo electron volt (keV) level.

METHODS

Thirty-three patients were included. Conventional images (CIs) and VMI (40-100 keV) were reconstructed using arterial phase spectral-based images. The computed tomography (CT) attenuation and noise of the AOR, the CT attenuation of the erector spinal muscle, and the background noise on VMI and CI were measured, respectively. The signal-to-noise ratio, contrast-to-noise ratio (CNR), and signal intensity ratio were calculated. The image quality of the AOR was evaluated according to a 4-point Likert grade.

RESULTS

The CT attenuation, noise, CNR, and signal intensity ratio of the AOR were significantly higher in VMI at 40 and 50 keV compared with CI ( P < 0.001); VMI at 40 keV was significantly higher than 50 keV ( P < 0.05). No significant difference in signal-to-noise ratio, background noise, and CT attenuation of the spinal erector muscle was observed between VMI and CI ( P > 0.05). virtual monoenergetic image at 40 keV produced the best subjective scores.

CONCLUSIONS

Virtual monoenergetic image at 40 keV makes it easier to observe the AOR with optimized subjective and objective image quality. This may prompt radiologists and surgeons to actively search for it and encourage surgeons to preserve it during splenic flexure takedown.

Utility of Dual-Energy Computed Tomography in Clinical Conundra

Advancing medical technology revolutionizes our ability to diagnose various disease processes. Conventional Single-Energy Computed Tomography (SECT) has multiple inherent limitations for providing definite diagnoses in certain clinical contexts. Dual-Energy Computed Tomography (DECT) has been in use since 2006 and has constantly evolved providing various applications to assist radiologists in reaching certain diagnoses SECT is rather unable to identify. DECT may also complement the role of SECT by supporting radiologists to confidently make diagnoses in certain clinically challenging scenarios. In this review article, we briefly describe the principles of X-ray attenuation. We detail principles for DECT and describe multiple systems associated with this technology. We describe various DECT techniques and algorithms including virtual monoenergetic imaging (VMI), virtual non-contrast (VNC) imaging, Iodine quantification techniques including Iodine overlay map (IOM), and two- and three-material decomposition algorithms that can be utilized to demonstrate a multitude of pathologies. Lastly, we provide our readers commentary on examples pertaining to the practical implementation of DECT's diverse techniques in the Gastrointestinal, Genitourinary, Biliary, Musculoskeletal, and Neuroradiology systems.

Improved Detection of Endoleaks in Virtual Monoenergetic Images in Dual-Energy CT Angiography Following EVAR

OBJECTIVES

The objective of this prospective study was to evaluate the virtual monoenergetic images (VMI) and virtual noncontrast (VNC) phase in the detection of endoleaks after endovascular abdominal aortic repair (EVAR). The potential dose reduction of abbreviated examination protocols was calculated.

MATERIALS AND METHODS

Ninety-seven patients after the EVAR procedure were enrolled in this study. An initial single-source noncontrast acquisition was followed by two dual-energy acquisitions (arterial and 60 s delayed). Fast-kVp switching scanner was used. VNC images were reconstructed from the delayed phase. First examination session (reference) included a full triphasic study protocol consisting of true noncontrast (TNC) images and two postcontrast phases, the latter ones presented as classical polyenergetic reconstructions. Reading sessions II and III were performed by two independent and blinded readers evaluating VMIs in abbreviated protocols-biphasic (VNC + arterial, delayed phase), monophasic (VNC + delayed phase). The diagnostic accuracy of sessions II and III was calculated.

RESULTS

The calculated sensitivity of the biphasic protocol with the use of VMIs in endoleak detection was 100%, with a statistically significant increase in the number of endoleaks detected in comparison with the reference study. The monophasic protocol showed 83.33% sensitivity. The use of abbreviated examination protocols led to a decrease in the mean effective dose (ED) of 23.28% (biphasic protocol) and 61.37% (monophasic protocol).

CONCLUSION

The use of VMIs increases the number of endoleaks diagnosed with a possible radiation reduction by up to ¼ (biphasic protocol). Further reduction to a monophasic protocol leads to over 60% dose reduction but with a decrease in diagnostic accuracy.

Optimal combination periprosthetic vasculature visualization and metal artifact reduction by spectral computed tomography using virtual monoenergetic images in total hip arthroplasty

OBJECTIVES

To investigate the optimal parameters of spectral CT for preferably visualizing the periprosthetic vasculature and metal artifact reduction (MAR) in total hip arthroplasty (THA).

METHODS

A total of 34 THA of 30 patients were retrospectively included. Image reconstructions included conventional image (CI), CI combined with MAR (CIMAR), and virtual monoenergetic images (VMI) combined with MAR (VMIMAR) at 50-120 keV. The attenuation and standard deviation of the vessel and artifact, and the width of artifact were measured. Qualitative scoring was evaluated including the vascular contour, the extent of artifact, and overall diagnostic evaluation.

RESULTS

The attenuation, noise of the vessel and artifact, and the width of artifact decreased as the energy level increased (p < 0.001). The downtrend was relatively flat at 80-120 keV, and the vascular attenuation dropped to 200 HU at 90 keV. The qualitative rating of vascular contour was significantly higher at CIMAR (3.47) and VMIMAR 60-80 keV (2.82-3.65) compared with CI (2.03) (p ≤ 0.029), and the highest score occurred at 70 and 80 keV (3.65 and 3.56). The score of the extent of artifact was higher at VMIMAR 80 keV than CIMAR (3.53 VS 3.12, p = 0.003). The score of the overall diagnostic evaluation was higher at VMIMAR 70 and 80 keV (3.32 and 3.53, respectively) than CIMAR (3.12) (p ≤ 0.035).

CONCLUSION

Eighty kiloelectron volts on VMIMAR, providing satisfactorily reduced metal artifacts and improved vascular visualization, can be an optimal recommended parameter of spectrum CT for the assessment of periprosthetic vasculature in THA patients.

CRITICAL RELEVANCE STATEMENT

The metal artifact is gradually reducing with increasing energy level; however, the vascular visualization is worsening. The vascular visualization is terrible above 100 keV, while the vessel is disturbed by artifacts below 70 keV. The best performance is found at 80 keV.

KEY POINTS

• VMIMAR can provide both reduced metal artifacts and improved vascular visualization. • Eighty kiloelectron volts on VMIMAR performs best in vascular visualization of total hip arthroplasty patients. • Energy spectrum CT is recommended for routine use in patients with total hip arthroplasty.

Dual-Energy CT in Cardiothoracic Imaging: Current Developments

This article describes the technical principles and clinical applications of dual-energy computed tomography (DECT) in the context of cardiothoracic imaging with a focus on current developments and techniques. Since the introduction of DECT, different vendors developed distinct hard and software approaches for generating multi-energy datasets and multiple DECT applications that were developed and clinically investigated for different fields of interest. Benefits for various clinical settings, such as oncology, trauma and emergency radiology, as well as musculoskeletal and cardiovascular imaging, were recently reported in the literature. State-of-the-art applications, such as virtual monoenergetic imaging (VMI), material decomposition, perfused blood volume imaging, virtual non-contrast imaging (VNC), plaque removal, and virtual non-calcium (VNCa) imaging, can significantly improve cardiothoracic CT image workflows and have a high potential for improvement of diagnostic accuracy and patient safety.

Impact of CT Photon-Counting Virtual Monoenergetic Imaging on Visualization of Abdominal Arterial Vessels

PURPOSE

The novel photon-counting detector (PCD) technique acquires spectral data for virtual monoenergetic imaging (VMI) in every examination. The aim of this study was the evaluation of the impact of VMI of abdominal arterial vessels on quantitative and qualitative subjective image parameters.

METHODS

A total of 20 patients that underwent an arterial phase computed tomography (CT) scan of the abdomen with a novel PCD CT (Siemens NAEOTOM alpha) were analyzed regarding attenuation at different energy levels in virtual monoenergetic imaging. Contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were calculated and compared between the different virtual monoenergetic (VME) levels with correlation to vessel diameter. In addition, subjective image parameters (overall subjective image quality, subjective image noise and vessel contrast) were evaluated.

RESULTS

Our research showed decreasing attenuation levels with increasing energy levels in virtual monoenergetic imaging regardless of vessel diameter. CNR showed best overall results at 60 keV, and SNR at 70 keV with no significant difference to 60 keV (p = 0.294). Subjective image quality was rated best at 70 keV for overall image quality, vessel contrast and noise.

CONCLUSIONS

Our data suggest that VMI at 60-70 keV provides the best objective and subjective image quality concerning vessel contrast irrespective of vessel size.

Improving the Visualization of the Adrenal Veins Using Virtual Monoenergetic Images from Dual-Energy Computed Tomography before Adrenal Venous Sampling

(1) Background: This study explored the optimal energy level in advanced virtual monoenergetic images (VMI+) from dual-energy computed tomography angiography (DE-CTA) for adrenal veins visualization before adrenal venous sampling (AVS). (2) Methods: Thirty-nine patients were included in this prospective single-center study. The CT value, noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured in both adrenal veins and abdominal solid organs and were then compared between VMI+ within the range of 40-80 kiloelectron volt (keV). The visualization rate of the adrenal veins and the overall image quality of solid organs were subjectively compared among different keV VMI+. The AVS success rate was recorded for 20 patients. (3) Results: For the adrenal veins, 40 keV VMI+ had the peak CT value, noise and CNR (p < 0.05). Subjectively, the visualization rate was the highest at 40 keV (100% for the right adrenal vein, and 97.4% for the left adrenal vein) (p < 0.05). For solid organs, the CT value, noise and CNR at 50 keV were lower than those at 40 keV (p < 0.05), but the SNR was similar between 40 keV and 50 keV. The overall subjective image quality of solid organs at 50 keV was the best (p < 0.05). The AVS success rate was 95%. (4) Conclusions: For VMI+, 40 keV was the preferential energy level to obtain a high visualization rate of the adrenal veins and a high success rate of AVS, while 50 keV was the favorable energy level for the depiction of abdominal organs.

Pre-interventional assessment of right renal to right adrenal vein distance: Impact on procedure time and radiation dose in adrenal vein sampling

PURPOSE

Adrenal vein sampling (AVS) is the reference standard for evaluation of lateralized hormone production in primary aldosteronism. We aimed to investigate the impact of pre-interventional right renal vein (RRV) to right adrenal vein (RAV) distance measurement on fluoroscopy time, contrast agent exposure and radiation dose during AVS.

MATERIALS AND METHODS

Forty-five patients with primary aldosteronism undergoing AVS were enrolled in our retrospective study and divided into three groups. In the group "ruler" (n = 14), RRV-RAV-distances were determined pre-interventionally by cross-sectional imaging (CT/MRI) and AVS was performed by one interventional radiologist with limited experience in AVS. CT/MRI-derived and fluoroscopy-derived RRV-RAV-distances were correlated for aimed cannulation of the RAV. Patients in group "no ruler" (n = 24, three interventional radiologists with limited experience in AVS) and in group "expert", (n = 7, one expert interventional radiologist) underwent AVS without pre-interventional estimation of RRV-RAV-distances. Procedure parameters (fluoroscopy time, contrast agent volume, radiation dose) of group "ruler" were compared to both other groups by Kruskal-Wallis rank-sum test.

RESULTS

Correlation of CT/MRI-derived and fluoroscopy-derived RRV-RAV-distances was good (r = 0.74;p = 0.003). The median RRV-RAV-distance was 4.5cm at CT/MRI (95%-CI:4.2-5.0cm) and 4.0cm at fluoroscopy (95%-CI:3.8-4.5cm). Fluoroscopy time (p<0.0001), contrast agent exposure (p = 0.0003) and radiation dose (air kerma and dose area product both p = 0.038) were significantly lower in group "ruler" compared to group "no ruler" (all p<0.05), and similar to group "expert" (all p>0.05).

CONCLUSIONS

CT/MRI-derived pre-interventional renal-adrenal vein distance measurements correlate well with angiographic distance measurements. Pre-interventional estimation of the RRV-RAV-distance allows for aimed cannulation of the RAV with potential reduction of fluoroscopy time, contrast agent exposure and radiation-dose during AVS.

Multimodality imaging in cardiac amyloidosis: State-of-the-art review

Amyloidosis is a systemic disease, characterized by deposition of amyloid fibrils in various organs, including the heart. For the diagnosis of cardiac amyloidosis (CA) it is required a high level of clinical suspicion and in the presence of clinical, laboratorial, and electrocardiographic red flags, a comprehensive multimodality imaging evaluation is warranted, including echocardiography, magnetic resonance, scintigraphy, and computed tomography, that will confirm diagnosis and define the CA subtype, which is of the utmost importance to plan a treatment strategy. We will review the use of multimodality imaging in the evaluation of CA, including the latest applications, and a practical flow-chart will sum-up this evidence.

Quantitative dual-energy CT techniques in the abdomen

Advances in dual-energy CT (DECT) technology and spectral techniques are catalyzing the widespread implementation of this technology across multiple radiology subspecialties. The inclusion of energy- and material-specific datasets has ushered overall improvements in CT image contrast and noise as well as artifacts reduction, leading to considerable progress in radiologists' ability to detect and characterize pathologies in the abdomen. The scope of this article is to provide an overview of various quantitative clinical DECT applications in the abdomen and pelvis. Several of the reviewed applications have not reached mainstream clinical use and are considered investigational. Nonetheless awareness of such applications is critical to having a fully comprehensive knowledge base to DECT and fostering future clinical implementation.

Dual-Energy CT of the Heart: A Review

Dual-energy computed tomography (DECT) represents an emerging imaging technique which consists of the acquisition of two separate datasets utilizing two different X-ray spectra energies. Several cardiac DECT applications have been assessed, such as virtual monoenergetic images, virtual non-contrast reconstructions, and iodine myocardial perfusion maps, which are demonstrated to improve diagnostic accuracy and image quality while reducing both radiation and contrast media administration. This review will summarize the technical basis of DECT and review the principal cardiac applications currently adopted in clinical practice, exploring possible future applications.

Dual-Energy CT for the Detection of Portal Vein Thrombosis: Improved Diagnostic Performance Using Virtual Monoenergetic Reconstructions

Purpose: To investigate the diagnostic performance of noise-optimized virtual monoenergetic images (VMI+) in dual-energy CT (DECT) of portal vein thrombosis (PVT) compared to standard reconstructions. Method: This retrospective, single-center study included 107 patients (68 men; mean age, 60.1 ± 10.7 years) with malignant or cirrhotic liver disease and suspected PVT who had undergone contrast-enhanced portal-phase DECT of the abdomen. Linearly blended (M_0.6) and virtual monoenergetic images were calculated using both standard VMI and noise-optimized VMI+ algorithms in 20 keV increments from 40 to 100 keV. Quantitative measurements were performed in the portal vein for objective contrast-to-noise ratio (CNR) calculation. The image series showing the greatest CNR were further assessed for subjective image quality and diagnostic accuracy of PVT detection by two blinded radiologists. Results: PVT was present in 38 subjects. VMI+ reconstructions at 40 keV revealed the best objective image quality (CNR, 9.6 ± 4.3) compared to all other image reconstructions (p < 0.01). In the standard VMI series, CNR peaked at 60 keV (CNR, 4.7 ± 2.1). Qualitative image parameters showed the highest image quality rating scores for the 60 keV VMI+ series (median, 4) (p ≤ 0.03). The greatest diagnostic accuracy for the diagnosis of PVT was found for the 40 keV VMI+ series (sensitivity, 96%; specificity, 96%) compared to M_0.6 images (sensitivity, 87%; specificity, 92%), 60 keV VMI (sensitivity, 87%; specificity, 97%), and 60 keV VMI+ reconstructions (sensitivity, 92%; specificity, 97%) (p ≤ 0.01). Conclusions: Low-keV VMI+ reconstructions resulted in significantly improved diagnostic performance for the detection of PVT compared to other DECT reconstruction algorithms.

Deep learning-based reconstruction of virtual monoenergetic images of kVp-switching dual energy CT for evaluation of hypervascular liver lesions: Comparison with standard reconstruction technique

OBJECTIVE

To investigate clinical applicability of deep learning(DL)-based reconstruction of virtual monoenergetic images(VMIs) of arterial phase liver CT obtained by rapid kVp-switching dual-energy CT for evaluation of hypervascular liver lesions.

MATERIALS AND METHODS

We retrospectively included 109 patients who had available late arterial phase liver CT images of the liver obtained with a rapid switching kVp DECT scanner for suspicious intra-abdominal malignancies. Two VMIs of 70 keV and 40 keV were reconstructed using adaptive statistical iterative reconstruction (ASiR-V) for arterial phase scans. VMIs at 40 keV were additionally reconstructed with a vendor-agnostic DL-based reconstruction technique (ClariCT.AI, ClariPi, DL 40 keV). Qualitative, quantitative image quality and subjective diagnostic acceptability were compared according to reconstruction techniques.

RESULTS

In qualitative analysis, DL 40 keV images showed less image noise (4.55 vs 3.11 vs 3.95, p < 0.001), better image sharpness (4.75 vs 4.16 vs 4.3, p < 0.001), better image contrast (4.98 vs 4.72 vs 4.19, p < 0.017), better lesion conspicuity (4.61 vs 4.23 vs 3.4, p < 0.001) and diagnostic acceptability (4.59 vs 3.88 vs 4.09, p < 0.001) compared with ASiR-V 40 keV or 70 keV image sets. In quantitative analysis, DL 40 keV significantly reduced image noise relative to ASiR-V 40 keV images (49.9%, p < 0.001) and ASiR-V 70 keV images (85.2%, p = 0.012). DL 40 keV images showed significantly higher CNR_{lesion to the liver} and SNR_liver than ASiR-V 40 keV image and 70 keV images (p < 0.001).

CONCLUSION

DL-based reconstruction of 40 keV images using vendor-agnostic software showed greater noise reduction, better lesion conspicuity, image contrast, image sharpness, and higher overall image diagnostic acceptability than ASiR for 40 keV or 70 keV images in patients with hypervascular liver lesions.

Photon Counting CT Angiography of the Head and Neck: Image Quality Assessment of Polyenergetic and Virtual Monoenergetic Reconstructions

Background: The purpose of the present study was the evaluation of the image quality of polyenergetic and monoenergetic reconstructions (PERs and MERs) of CT angiographies (CTAs) of the head and neck acquired with the novel photon counting CT (PCCT) method in clinical routine. Methods: Thirty-seven patients were enrolled in this retrospective study. Quantitative image parameters of the extracranial, intracranial and cerebral arteries were evaluated for the PER and MER (40–120 keV). Additionally, two radiologists rated the perceived image quality. Results: The mean CTDI_vol used in the PCCT was 8.31 ± 1.19 mGy. The highest signal within the vessels was detected in the 40 keV MER, whereas the lowest noise was detected in the 115 keV MER. The most favorable contrast-to-noise-ratio (CNR) and signal-to-noise-ratio (SNR) were detected in the PER and low keV MER. In the qualitative image analysis, the PER was superior to the MER in all rated criteria. For MER, 60–65 keV was rated as best image quality. Conclusion: Overall, PCCT offers excellent image quality for CTAs of the head and neck. At the current state, the PER of the PCCT seems to be the most favorable reconstruction for diagnostic reporting.

Pancreatic adenocarcinoma: imaging techniques for diagnosis and management

Pancreatic cancer is a leading cause of death from cancer but only a minority of patients with pancreatic ductal adenocarcinomas are eligible for curative resection. The increasing role of neoadjuvant therapy provides hope of improving outcomes. However, progress is also reliant on advances in imaging that can identify disease earlier and accurately assess treatment response. Computed tomography remains the cornerstone in evaluation of resectability, offering excellent spatial resolution. However, in high-risk patients, additional magnetic resonance imaging and positron emission tomography-computed tomography may further guide treatment decisions. Conventional computed tomography can be limited in its ability to determine disease response after neoadjuvant therapy. Dual-energy computed tomography and computed tomography or magnetic resonance imaging perfusion studies emerging as potentially better alternatives. Combined with pioneering advances in radiomic analysis, these modalities also show promise in analysing tumour heterogeneity and thereby more accurately predicting outcomes. This article reviews these imaging techniques.

Dual-energy CT of acute bowel ischemia

Acute bowel ischemia is a condition with high mortality and requires rapid intervention to avoid catastrophic outcomes. Swift and accurate imaging diagnosis is essential because clinical findings are commonly nonspecific. Conventional contrast enhanced CT of the abdomen has been the imaging modality of choice to evaluate suspected acute bowel ischemia. However, subtlety of image findings and lack of non-contrast or arterial phase images can make correct diagnosis challenging. Dual-energy CT provides valuable information toward assessing bowel ischemia. Dual-energy CT exploits the differential X-ray attenuation at two different photon energy levels to characterize the composition of tissues and reveal the presence or absence of faint intravenous iodinated contrast to improve reader confidence in detecting subtle bowel wall enhancement. With the same underlying technique, virtual non-contrast images can help to show non-enhancing hyperdense hemorrhage of the bowel wall in intravenous contrast-enhanced scans without the need to acquire actual non-contrast scans. Dual-energy CT derived low photon energy (keV) virtual monoenergetic images emphasize iodine contrast and provide CT angiography-like images from portal venous phase scans to better evaluate abdominal arterial patency. In Summary, dual-energy CT aids diagnosing acute bowel ischemia in multiple ways, including improving visualization of the bowel wall and mesenteric vasculature, revealing intramural hemorrhage in contrast enhanced scans, or possibly reducing intravenous contrast dose.

Initial Investigation of Clinical Value of Noise-Optimized Virtual Monoenergetic Images Derived From Dual-Energy Computed Tomography Angiography in Preoperative Perforator Planning of Anterolateral Thigh Flap Transplantation

OBJECTIVE

To objectively and subjectively assess the image characteristics of noise-optimized virtual monoenergetic images [MEI (+)] and polyenergetic images (PEIs) from dual-energy computed tomography angiography and then to explore the clinical value of the optimal MEI (+) in preoperative perforator planning of anterolateral thigh (ALT) flap transplantation.

METHODS

Sixteen patients (32 thighs) who underwent lower extremity run-off dual-energy computed tomography angiography for planning ALT flap transplantation were enrolled. One standard PEI and 5 MEI (+) in 10-keV intervals (range, 40-80 keV) were reconstructed. First, we compared the image quality subjectively (branch order, image quality, and vascular network continuity) and objectively (vascular attenuation, image noise, signal-to-noise ratio, and the contrast-to-noise ratio). Then, we compared the clinical value (number, type, source artery, pedicle length, caliber, and location of all sizable perforators) between the optimal MEI (+) and PEI groups.

RESULTS

The 40-keV MEI (+) was rated superior subjective and objective image quality metrics to PEI (all P < 0.001). Compared with PEI, 40 keV MEI (+) increased the number of visible perforators, the percentage of perforators with identifiable types, and the measurable length of perforator pedicle (all P < 0.001).

CONCLUSIONS

We recommend 40 keV MEI (+) for the visualization of perforators and their contribution to the selection and location of suitable perforators in preoperative planning for ALT flaps.

A study on spinal level, length, and branch type of the inferior mesenteric artery and the position relationship between the inferior mesenteric artery, left colic artery, and inferior mesenteric vein

Background

This study was aimed to explore the clinical application of dual-energy computed tomography (DECT) monoenergetic plus (mono+) imaging to evaluate anatomical variations in the inferior mesenteric artery (IMA).

Methods

The clinical and imaging data of 212 patients who had undergone total abdominal DECT were retrospectively analyzed. The post-processing mono+ technique was used to obtain 40-keV single-level images in the arterial phase. Three-dimensional reconstruction was performed to evaluate the relationship between the IMA root position and the spinal level, IMA length, and IMA branch type, as well as the position of the left colic artery (LCA) and inferior mesenteric vein (IMV) at the IMA root level.

Results

The IMA root was located at the L3 level in 78.3% of cases and at the L2/L3 level in 3.3%. The highest vertebral level of IMA origin was L2 (4.2%), and the lowest was L4 (7.1%). The distance from the IMA root to the level of the sacral promontory was 99.58 ± 13.07 mm, which increased with the elevation of the IMA root at the spinal level. Of the patients, 53.8% demonstrated Type I IMA, 23.1% Type II, 20.7% Type III, and 2.4% Type IV. The length of the IMA varied from 13.6 to 66.0 mm. 77.3% of the IMAs belonged to Type A, the adjacent type, and 22.7% to Type B, the distant type.

Conclusion

DECT mono+ can preoperatively evaluate the anatomical characteristics of the IMA and the positional relationship between the LCA and IMV at the IMA root level, which would help clinicians plan individualized surgery for patients.

DECT mono+ optimal energy level can preoperatively determine the position of the IMA root.

DECT mono+ can preoperatively evaluate the anatomical characteristics of the IMA.

DECT mono+ can preoperatively determine the positional relationship between the LCA and IMV at the IMA root level.

Comparison of lung image quality between CT Ark and Brilliance 64 CT during COVID-19

AIM

This study is to compare the lung image quality between shelter hospital CT (CT Ark) and ordinary CT scans (Brilliance 64) scans.

METHODS

The patients who received scans with CT Ark or Brilliance 64 CT were enrolled. Their lung images were divided into two groups according to the scanner. The objective evaluation methods of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were used. The subjective evaluation methods including the evaluation of the fine structure under the lung window and the evaluation of the general structure under the mediastinum window were compared. Kappa method was used to assess the reliability of the subjective evaluation. The subjective evaluation results were analyzed using the Wilcoxon rank sum test. SNR and CNR were tested using independent sample t tests.

RESULTS

There was no statistical difference in somatotype of enrolled subjects. The Kappa value between the two observers was between 0.68 and 0.81, indicating good consistency. For subjective evaluation results, the rank sum test P value of fine structure evaluation and general structure evaluation by the two observers was ≥ 0.05. For objective evaluation results, SNR and CNR between the two CT scanners were significantly different (P<0.05). Notably, the absolute values ​​of SNR and CNR of the CT Ark were larger than Brilliance 64 CT scanner.

CONCLUSION

CT Ark is fully capable of scanning the lungs of the COVID-19 patients during the epidemic in the shelter hospital.

Evaluation of Modified Calcium Removal Algorithm in dual energy CT of Internal Carotid Artery

PURPOSE

To evaluate the performance of a dual-energy (DE) calcium removal software based on a modified three-material decomposition algorithm in assessing the stenosis of the internal carotid artery (ICA) in comparison with mixed images using digital subtraction angiography (DSA) as the reference standard.

METHODS

Forty-six patients (38 men; 67±8 years old), including 154 calcified ICA segments C1-C2 (59), C3-C5 (63), C6 (24), and C7 (8), were recruited in this retrospective study. Mixed images and virtual non-calcium (VNCa) images using the modified dual-energy computed tomography (DECT) algorithm were reconstructed. The differences between VNCa and DSA images vs. mixed and DSA images of degree of stenosis were compared. The intraclass correlation coefficient (ICC) was used for assessing the agreement between VNCa, mixed images, and DSA.

RESULTS

The degree of stenosis differed significantly between mixed and DSA images in the C3-C5 (30%±17.9% vs. 23.0%±16.9%, p = 0.026) and C6 (38.3%±15.4% vs. 28.5%±13.3%, p = 0.023) segments. The stenosis of VNCa images showed no significant difference with DSA images in all segments (all p > 0.05). The ICCs between VNCa and DSA images (0.86-0.97) were higher than those between the mixed and DSA images (0.68-0.96) in all segments.

CONCLUSION

The performance of a modified three-material decomposition DECT algorithm for calcium removal in ICA stenosis evaluation, particularly for the C3-C5 and C6 ICA segments, was promising.

Noise-optimized virtual monoenergetic imaging technology of the third-generation dual-source computed tomography and its clinical applications

The third-generation dual-source computed tomography (DSCT) is among the most advanced imaging methods. It employs noise-optimized virtual monoenergetic imaging (VMI+) technology. It uses the frequency-split method to extract high-contrast image information from low-energy images and low-noise information from images reconstructed at an optimal energy level, combining them to obtain the final image with improved quality. This review is the first to summarize the results of clinical studies that primarily and recently evaluated the VMI+ technique based on tumor, blood vessel, and other lesion classification. We aim to assist radiologists in quickly selecting the appropriate energy level when performing image reconstruction for superior image quality in clinical work and providing several ideas for future scientific research of the VMI+ technique. Presently, VMI+ reconstruction is mostly used for images of various tumors or blood vessels, including coronary plaques, coronary stents, deep vein thromboses, pulmonary embolisms (PEs), active arterial hemorrhages, and endoleaks after endovascular aneurysm repair. In addition, VMI+ has been used for imaging children's heads, liver lesions, pancreatic lacerations, and reducing metal artifacts. Regarding the reconstruction at the optimal energy level, the VMI+ technique yielded a higher image quality than the pre-optimized virtual monoenergetic imaging (VMI) technique and single-energy CT. Moreover, either low concentrations of contrast medium or low iodine injection rates can be applied before VMI+ reconstruction at a low-energy level to reduce contrast agent-related kidney injury risk. After reconstructing an image at the optimal energy level, both the image's window width and level can also be adjusted to improve the image effect's reach and diagnosis suitability. To improve image quality and lesion-imaging clarity and reduce the use of contrast agents, VMI+ reconstruction technology has been applied clinically, in which the selection of energy level is the key to the whole reconstruction process. Our review summarizes these optimal levels for radiologists' reference and suggests new ideas for the direction of future VMI+ research.

Impact of dual-energy 50-keV virtual monoenergetic images on radiologist confidence in detection of key imaging findings of small hepatocellular carcinomas using multiphase liver CT

BACKGROUND

Dual-energy virtual monoenergetic images can increase iodine signal, potentially increasing the conspicuity of hepatic masses.

PURPOSE

To determine if dual-energy 50-keV virtual monoenergetic images improve visualization of key imaging findings or diagnostic confidence for small (≤2 cm) hepatocellular carcinomas (HCC) at multiphase, contrast-enhanced liver computed tomography (CT).

MATERIAL AND METHODS

Patients with chronic liver disease underwent multiphase dual-energy CT imaging for HCC, with late arterial and delayed phase dual-energy 50-keV images reconstructed. Two non-reader subspecialized gastrointestinal (GI) radiologists established the reference standard, determining the location and diagnosis of all hepatic lesions using predetermined criteria. Three GI radiologists interpreted mixed kV CT images without or with dual-energy 50-keV images. Radiologists identified potential HCCs and rated their confidence (0-100 scales) in imaging findings of arterial enhancement, enhancing capsule, tumor washout, and LI-RADS 5 (2018) category.

RESULTS

In total, 45 patients (14 women; mean age = 59.5 ± 10.9 years) with chronic liver disease were included. Of them, 19 patients had 25 HCCs ≤2 cm (mean size = 1.5 ± 0.4 cm). There were 17 LI-RADS 3 and 4 lesions and 19 benign lesions. Reader confidence in imaging findings of arterial enhancement, enhancing capsule, and non-peripheral washout significantly increased with dual-energy images (P ≤ 0.022). Overall confidence in HCC diagnosis increased significantly with dual-energy 50-keV images (52.4 vs. 68.8; P = 0.001). Dual-energy images demonstrated a slight but significant decrease in overall image quality.

CONCLUSION

Radiologist confidence in key imaging features of small HCCs and confidence in imaging diagnosis increases with use of dual-energy 50-keV images at multiphase, contrast-enhanced liver CT.

CT Noise-Reduction Methods for Lower-Dose Scanning: Strengths and Weaknesses of Iterative Reconstruction Algorithms and New Techniques

Iterative reconstruction (IR) algorithms are the most widely used CT noise-reduction method to improve image quality and have greatly facilitated radiation dose reduction within the radiology community. Various IR methods have different strengths and limitations. Because IR algorithms are typically nonlinear, they can modify spatial resolution and image noise texture in different regions of the CT image; hence traditional image-quality metrics are not appropriate to assess the ability of IR to preserve diagnostic accuracy, especially for low-contrast diagnostic tasks. In this review, the authors highlight emerging IR algorithms and CT noise-reduction techniques and summarize how these techniques can be evaluated to help determine the appropriate radiation dose levels for different diagnostic tasks in CT. In addition to advanced IR techniques, we describe novel CT noise-reduction methods based on convolutional neural networks (CNNs). CNN-based noise-reduction techniques may offer the ability to reduce image noise while maintaining high levels of image detail but may have unique drawbacks. Other novel CT noise-reduction methods are being developed to leverage spatial and/or spectral redundancy in multiphase or multienergy CT. Radiologists and medical physicists should be familiar with these different alternatives to adapt available CT technology for different diagnostic tasks. The scope of this article is (a) to review the clinical applications of IR algorithms as well as their strengths, weaknesses, and methods of assessment and (b) to explore new CT image reconstruction and noise-reduction techniques that promise to facilitate radiation dose reduction. ^©RSNA, 2021.

Comparison of noise-optimized linearly blended images and noise-optimized virtual monoenergetic images evaluated by dual-source, dual-energy CT in cardiac vein assessment

BACKGROUND

The coronary venous system is frequently used as an entry route to the heart and treatment modalities for many cardiac diseases and many procedures. Consequently, evaluation of the coronary venous system and understanding cardiac vein anatomy is crucial.

PURPOSE

To determine the optimal image set in a comparison of noise-optimized linearly blended images (F_0.6) and noise-optimized virtual monoenergetic images (VMI+) evaluated by dual-energy computed tomography (DECT) for cardiac vein assessment.

MATERIAL AND METHODS

Thirty-four patients (mean age 58.2 ± 14.2 years) who underwent DECT due to chest pain were enrolled. Images were post-processed with the F_0.6, and VMI+ algorithms at energy levels in the range of 40-100 keV in 10-keV increments. Enhancement (HU), noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were objectively measured at two points in the great cardiac vein by consensus of two radiologists. Two blinded observers evaluated the subjective image quality of the great cardiac vein on a 4-point scale.

RESULTS

HU, noise, and SNR peaked at 40 keV VMI+ (P < 0.05) among 50-100 keV VMI+. CNR peaked at 100 keV VMI+; however, there were no significant differences compared to CNR images processed at 40-90 keV VMI+. HU and noise were significantly higher in 40 keV VMI+ than F_0.6 images; however, both SNR and CNR were significantly higher in F_0.6 images. An assessment of subjective vein delineation revealed that F_0.6 images had the highest scores.

CONCLUSION

F_0.6 images were superior to VMI+ and provided the optimal image set for cardiac vein assessment.

Reduction of microwave ablation needle related metallic artifacts using virtual monoenergetic images from dual-layer detector spectral CT in a rabbit model with VX2 tumor

The purpose of the study was to investigate the application of virtual monoenergetic images (VMIs) in reducing metal artifacts in rabbit VX2 liver cancer models treated with microwave ablation (MWA) therapy. A total of 31 VX2 liver cancer models that accepted CT-guided percutaneous microwave ablation were analyzed. Conventional images (CIs) with the most severe metallic artifacts and their corresponding energy levels from 40 to 200 keV with 10 keV increment of VMIs were reconstructed for further analysis. Objective image analysis was assessed by recording the attenuation (HU) and standard deviation of the most severe hyper/hypodense artifacts as well as artifact-impaired liver parenchyma tissue. Two radiologists visually evaluated the extent of artifact reduction, assessed data obtained by a diagnostic evaluation of liver tissues, and appraised the appearance of new artifacts according to the grade score. Statistical analysis was performed to compare the difference between CIs and each energy level of VMIs. For subjective assessment, reductions in hyperdense and hypodense artifacts were observed at 170–200 keV and 160–200 keV, respectively. The outcomes of the diagnostic evaluation of adjacent liver tissue were statistically higher at 140–200 keV for VMIs than for CIs. In terms of objective evaluation results, VMIs at 90–200 keV reduced the corrected attenuation of hyperdense and of artifact-impaired liver parenchyma compared with CIs (P < 0.001). When VMIs at 80–200 keV decreased the hypodense artifacts (P < 0.001). Therefore, we concluded that VMIs at 170–200 keV can obviously decrease the microwave ablation needle-related metal artifacts objectively and subjectively in rabbit VX2 liver cancer models.

Clinical Applications of Dual-Energy CT

Dual-energy CT (DECT) provides insights into the material properties of tissues and can differentiate between tissues with similar attenuation on conventional single-energy imaging. In the conventional CT scanner, differences in the X-ray attenuation between adjacent structures are dependent on the atomic number of the materials involved, whereas in DECT, the difference in the attenuation is dependent on both the atomic number and electron density. The basic principle of DECT is to obtain two datasets with different X-ray energy levels from the same anatomic region and material decomposition based on attenuation differences at different energy levels. In this article, we discuss the clinical applications of DECT and its potential robust improvements in performance and postprocessing capabilities.

Improved detectability of hypoattenuating focal pancreatic lesions by dual-layer computed tomography using virtual monoenergetic images

Background

Multidetector CT is the mainstay for radiologic evaluation of pancreatic pathology. Still, imaging of focal pancreatic lesions using MDCT is faced by a number of challenges that are related to the limited contrast between the lesion and surrounding parenchyma, such as detecting early-stage pancreatic cancer and subtle features of cystic lesions that point to malignancy. Dual-layer CT is the first dual-energy CT machine based on separation of high- and low-energy photons at the detector level. If improved contrast between the lesions and normal pancreatic parenchyma could be achieved on CT images, we may expect enhanced CT detection of pancreatic lesions. The purpose of this study was to evaluate whether virtual monoenergetic reconstructions generated using contrast-enhanced dual-layer CT could improve detectability of hypoattenuating focal pancreatic lesions compared to conventional polyenergetic reconstructions.

Results

Fifty-four lesions were identified and verified by histopathology or follow-up CT, MRCP, and/or EUS along with clinical data. Across the virtual monoenergetic spectrum, 40 KeV images had the highest contrast-to-noise and signal-to-noise ratios (p < 0.001, p < 0.001) and were significantly higher than conventional images (p < 0.001). Subjective scores for lesion visibility at low kiloelectron volt monoenergetic (40 and 50 KeV) images greatly exceeded conventional images (p < 0.001).

Conclusion

Low kiloelectron volt monoenergetic reconstructions of contrast-enhanced dual-layer CT significantly improve detectability of hypoattenuating focal pancreatic lesions compared to conventional polyenergetic reconstructions.

Noise reduction approach in pediatric abdominal CT combining deep learning and dual-energy technique

OBJECTIVES

To evaluate the image quality of low iodine concentration, dual-energy CT (DECT) combined with a deep learning-based noise reduction technique for pediatric abdominal CT, compared with standard iodine concentration single-energy polychromatic CT (SECT).

METHODS

From December 2016 to May 2017, DECT with 300 mg•I/mL contrast medium was performed in 29 pediatric patients (17 boys, 12 girls; age, 2-19 years). The DECT images were reconstructed using a noise-optimized virtual monoenergetic reconstruction image (VMI) with and without a deep learning method. SECT images with 350 mg•I/mL contrast medium, performed within the last 3 months before the DECT, served as reference images. The quantitative and qualitative parameters were compared using paired t tests and Wilcoxon signed-rank tests, and the differences in radiation dose and total iodine administration were assessed.

RESULTS

The linearly blended DECT showed lower attenuation and higher noise than SECT. The 60-keV VMI showed an increase in attenuation and higher noise than SECT. The combined 60-keV VMI plus deep learning images showed low noise, no difference in contrast-to-noise ratios, and overall image quality or diagnostic image quality, but showed a higher signal-to-noise ratio in the liver and lower enhancement of lesions than SECT. The overall image and diagnostic quality of lesions were maintained on the combined noise reduction approach. The CT dose index volume and total iodine administration in DECT were respectively 19.6% and 14.3% lower than those in SECT.

CONCLUSION

Low iodine concentration DECT, combined with deep learning in pediatric abdominal CT, can maintain image quality while reducing the radiation dose and iodine load, compared with standard SECT.

KEY POINTS

• An image noise reduction approach combining deep learning and noise-optimized virtual monoenergetic image reconstruction can maintain image quality while reducing radiation dose and iodine load. • The 60-keV virtual monoenergetic image reconstruction plus deep learning images showed low noise, no difference in contrast-to-noise ratio, and overall image quality, but showed a higher signal-to-noise ratio in the liver and a lower enhancement of lesion than single-energy polychromatic CT. • This combination could offer a 19.6% reduction in radiation dose and a 14.3% reduction in iodine load, in comparison with a control group that underwent single-energy polychromatic CT with the standard protocol.

Accuracy of Pulmonary Nodule Volumetry Using Noise-Optimized Virtual Monoenergetic Image and Nonlinear Blending Image Algorithms in Dual-Energy Computed Tomography: A Phantom Study

OBJECTIVE

The aim of the study was to assess accuracy of pulmonary nodule volumetry using noise-optimized virtual monoenergetic image (VMI+) and nonlinear blending image (NBI) algorithms in dual-energy computed tomography (DECT).

METHODS

An anthropomorphic chest phantom with 10 simulated nodules (5 solid nodules and 5 ground-glass opacities) was scanned using DECT80/Sn140kV, DECT100/Sn140kV, and single-energy CT (SECT120kV/200mAs), respectively. The dual-energy images were reconstructed using VMI+ (70 keV) and NBI algorithms. The contrast-to-noise ratio and absolute percentage error (APE) of nodule volume were measured to assess image quality and accuracy of nodule volumetry. The radiation dose was also estimated.

RESULTS

The contrast-to-noise ratio of SECT120kV/200mAs was significantly higher than that of NBI80/Sn140kV and VMI+80/Sn140kV (both corrected P < 0.05), whereas there were no significant differences between NBI100/sn140kV and SECT120kV/200mAs and between VMI+100/sn140kV and SECT120kV/200mAs (both corrected P > 0.05). The APE of SECT120kV/200mAs was significantly lower than that of NBI80/Sn140kV and VMI+80/Sn140kV in both types of nodules (all corrected P < 0.05), whereas there were no significant differences between VMI+100/sn140kV and SECT120kV/200mAs in solid nodules and between NBI100/Sn140kV and SECT120kV/200mAs in ground-glass opacities (both corrected P > 0.05). The radiation dose of DECT100/Sn140kV and DECT80/Sn140kV were significantly lower than that of SECT120kV/200mAs (both corrected P < 0.05).

CONCLUSIONS

The DECT100/sn140kV can ensure image quality and nodule volumetry accuracy with lower radiation dose compared with SECT120kV/200mAs. Specifically, the VMI+ algorithm could be used in solid nodules and NBI algorithm in ground-glass opacities.

Identification of pulmonary embolism: diagnostic accuracy of venous-phase dual-energy CT in comparison to pulmonary arteries CT angiography

OBJECTIVES

To evaluate the diagnostic accuracy of venous-phase dual-energy computed tomography (VP-DECT) in the identification of PE compared with standard CT pulmonary angiography (CTPA).

METHODS

This prospective IRB-approved study included 61 consecutive oncology patients (35 females, 26 males, mean age 66.91 years) examined by CTPA and VP-DECT. DECT data were post-processed on a SyngoVia workstation to obtain monoenergetic images (MEI+). The diagnosis of PE was based on the presence of any vascular perfusion defects. DECT images were evaluated independently by two radiologists (8 and 16 years of experience). A consensus reading of CTPA images (two senior radiologists, 18 and 24 years of experience) represented the reference for diagnosis. The diagnostic accuracy values of VP-DECT on a per-patient and per-lobe basis were assessed. Interobserver agreement was calculated using k-statistics. A value of p < 0.05 was considered statistically significant.

RESULTS

Thirty of 61 patients (49.18%) were diagnosed with PE by CTPA, with 57/366 lobes being involved (15.57%). The sensitivity and specificity of the per-patient analysis of VP-DECT images were 90.0% (27/30) and 100% (31/31) respectively, for both readers. As concerns the per-lobe analysis, the sensitivity ranged from 100% for the right lower lobe to 50% for the left upper lobe for reader 1, and from 100% for the left upper lobe to 69.23% for the lingula for reader 2. The interobserver agreement ranged from 0.8671 (patients' analysis) to 0.6419 (lobes' analysis).

CONCLUSION

VP-DECT could be considered an accurate imaging tool for diagnosing PE in a selected, high-prevalence population, compared with CTPA.

KEY POINTS

• With regard to the patients' analysis, venous-phase DECT sensitivity and specificity in diagnosing pulmonary embolism were 90% and 100%, respectively, for both readers. • With regard to the lobes' analysis, the sensitivity ranged from 100 to 50%, for reader 1, and from 100 to 69.23%, for reader 2, respectively. • The sensitivity and specificity of lung perfusion maps obtained from venous DECT were 73.33% and 67.74% as concerns the patients' analysis and 71.92% and 75.72% as regards the lobes' analysis, respectively.

Advanced monoenergetic reconstruction technique for dual-energy computed tomography to evaluate endoleaks after endovascular stent-graft placement

PURPOSE

To evaluate the usefulness of the advanced monoenergetic imaging (AMI) reconstruction technique for dual-energy computed tomography to evaluate endoleaks after endovascular stent-graft placement.

MATERIALS AND METHODS

Ninety-five dual-phase (early and delayed phases) enhanced CT examinations were performed for 60 patients who underwent endovascular stent-graft placement. AM images were reconstructed at 40 keV and compared with the standard 120-kVp images (SI). The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the aorta and endoleak were measured. Two radiologists subjectively assessed endoleak delineation and contrast enhancement conditions using a 5-point Likert scale (1: poor-5: excellent).

RESULTS

Mean SNRs of the aorta were higher by AMI (early; 34.7 ± 10.2 [SD], delay; 11.4 ± 3.2) than by SI (early; 23.1 ± 6.3, delay; 8.6 ± 2.2) (P < 0.001). SNRs of the endoleak were higher by AMI (early; 26.3 ± 7.5, delay; 10.5 ± 3.1) than by SI (early; 18.2 ± 4.7, delay; 8.3 ± 2.1) (P < 0.001). CNRs by AMI (early; 32.9 ± 9.8, delay; 8.9 ± 2.8) were higher than those by SI (early; 19.5 ± 6.0, delay; 4.7 ± 1.6) in both phases (P < 0.001). Endoleak delineation and contrast enhancement conditions by AMI (4.4 ± 1.0 and 4.5 ± 0.6) were higher than those by SI (3.4 ± 1.0 and 3.3 ± 0.8) in the delayed phase (P < 0.001). There was no difference in the early phase.

CONCLUSION

AMI may be useful for evaluating endoleaks after endovascular stent-graft placement.

Carotid and cerebrovascular dual-energy computed tomography angiography: Optimization of window settings for virtual monoenergetic imaging reconstruction

PURPOSE

Dedicated post-processing of dual-energy computed tomography angiography (DE-CTA) datasets has been shown to allow for increased vascular contrast. The goal of our study was to define optimal window settings for displaying virtual monoenergetic images (VMI) reconstructed from dual-energy carotid and cerebrovascular DE-CTA.

METHODS

Fifty-seven patients who underwent clinically-indicated carotid and cerebrovascular third-generation dual-source DE-CTA were retrospectively evaluated. Standard linearly-blended (M_0.6), 70-keV traditional VMI (M70), and 40-keV noise-optimized VMI (M40+) reconstructions were analyzed. For M70 and M40+ datasets, the subjectively best window setting (width and level, B-W/L) was independently determined by two observers and subsequently related with aortic arch attenuation to calculate optimized values (O-W/L) using linear regression. Subjective evaluation of image quality (IQ) between W/L settings were assessed by two additional readers. Repeated measures analysis of variance were performed to compare W/L settings and IQ indices between M_0.6, M70, and M40 + .

RESULTS

B-W/L and O-W/L for M70 were 580/210 and 560/200, and for M40+ were 1630/570 and 1560/550, respectively, higher than standard DE-CTA W/L settings (450/100). Highest subjective scores were observed for M40+ regarding overall IQ (all p < 0.001).

CONCLUSION

Application of O-W/L settings is mandatory to optimize subjective IQ of VMI reconstructions of DE-CTA.

Computed tomography for myocardial characterization in ischemic heart disease: a state-of-the-art review

This review provides an overview of the currently available computed tomography (CT) techniques for myocardial tissue characterization in ischemic heart disease, including CT perfusion and late iodine enhancement. CT myocardial perfusion imaging can be performed with static and dynamic protocols for the detection of ischemia and infarction using either single- or dual-energy CT modes. Late iodine enhancement may be used for the analysis of myocardial infarction. The accuracy of these CT techniques is highly dependent on the imaging protocol, including acquisition timing and contrast administration. Additionally, the options for qualitative and quantitative analysis and the accuracy of each technique are discussed.

Prospective Comparison of 70-kVp Single-Energy CT versus Dual-Energy CT: Which is More Suitable for CT Angiography with Low Contrast Media Dosage?

RATIONALE AND OBJECTIVES

To compare the objective and subjective image qualities between single-energy computed tomography (CT) at 70 kVp and virtual monoenergetic imaging (VMI) of dual-source dual-energy CT for CT angiography with 180 mgI/kg.

MATERIALS AND METHODS

Total 63 patients scanned with 180 mgI/kg were randomly divided into two groups: Group A (32 patients) underwent CT angiography at 70-kVp, and Group B (31 patients) underwent dual-energy CT. VMI sets were generated at 10-keV increments between 40 and 100 keV. We calculated aortic attenuation, contrast-to-noise-ratio (CNR), signal-to-noise-ratio, figure of merit of CNR, and effective dose for each protocol. Three radiologists scored overall image quality and various arteries' visibility using a four-point scale. Quantitative and qualitative comparisons between 70 kVp and VMI with the highest CNR were performed with the two-tailed t test or Kruskal-Wallis test.

RESULTS

The 40-keV images offered the highest CNR among VMIs. Aortic attenuation at 70 kVp was significantly lower than that at 40 keV (p < 0.001). However, the signal-to-noise-ratio, CNR, and figure of merit of CNR were significantly higher at 70 kVp than those at 40-keV (p < 0.001, p < 0.05, and p < 0.05, respectively). The effective dose of each group was almost equal. The qualitative visibility scores for various arteries, except the ascending and upper-abdominal aorta, were also better at 70 kVp than those at 40 keV.

CONCLUSION

Aortic attenuation at 70 kVp with 180 mg I/kg was lower than that of VMI at 40 keV, and the objective and subjective image qualities were higher at 70 kVp than those at 40 keV.

Advanced imaging techniques for chronic pancreatitis

MRI and MRCP play an important role in the diagnosis of chronic pancreatitis (CP) by imaging pancreatic parenchyma and ducts. MRI/MRCP is more widely used than computed tomography (CT) for mild to moderate CP due to its increased sensitivity for pancreatic ductal and gland changes; however, it does not detect the calcifications seen in advanced CP. Quantitative MR imaging offers potential advantages over conventional qualitative imaging, including simplicity of analysis, quantitative and population-based comparisons, and more direct interpretation of detected changes. These techniques may provide quantitative metrics for determining the presence and severity of acinar cell loss and aid in the diagnosis of chronic pancreatitis. Given the fact that the parenchymal changes of CP precede the ductal involvement, there would be a significant benefit from developing MRI/MRCP-based, more robust diagnostic criteria combining ductal and parenchymal findings. Among cross-sectional imaging modalities, multi-detector CT (MDCT) has been a cornerstone for evaluating chronic pancreatitis (CP) since it is ubiquitous, assesses primary disease process, identifies complications like pseudocyst or vascular thrombosis with high sensitivity and specificity, guides therapeutic management decisions, and provides images with isotropic resolution within seconds. Conventional MDCT has certain limitations and is reserved to provide predominantly morphological (e.g., calcifications, organ size) rather than functional information. The emerging applications of radiomics and artificial intelligence are poised to extend the current capabilities of MDCT. In this review article, we will review advanced imaging techniques by MRI, MRCP, CT, and ultrasound.

Advanced monoenergetic reconstruction technique in dual-energy computed tomography for evaluation of vascular anatomy before adrenal vein sampling

Background

In adrenal vein sampling, selecting the right adrenal vein is technically difficult and it is important to evaluate the right adrenal vein anatomy before adrenal vein sampling. The advanced monoenergetic reconstruction technique has recently become available and we hypothesized that this technique may be useful.

Purpose

To evaluate the usefulness of the advanced monoenergetic reconstruction technique in dual-energy computed tomography (CT; advanced monoenergetic images) for evaluation of vascular anatomy before adrenal vein sampling.

Material and Methods

Twenty-one patients underwent three-phase (20, 30, and 70 s) contrast-enhanced CT before adrenal vein sampling. Advanced monoenergetic images were reconstructed at 40 keV and analyzed objectively and subjectively in comparison with the standard 120-kVp images. As objective evaluation, the signal-to-noise ratio and contrast-to-noise ratio of the right adrenal vein were assessed. As subjective evaluation, two radiologists assessed the delineation of the right adrenal vein using a 5-point Likert scale (1 = poor, 5 = excellent). Furthermore, the technical success rate of adrenal vein sampling and procedure time were also evaluated.

Results

There was no difference in the signal-to-noise ratio between the two groups. The contrast-to-noise ratios of the right adrenal vein of advanced monoenergetic images were higher than those of the standard images ( P < 0.05). The Likert scores of advanced monoenergetic images were higher than those of the standard images ( P < 0.05). The technical success rate of adrenal vein sampling was 95% (20/21) and the median of procedure time was 103 min (range = 59–197 min).

Conclusion

Advanced monoenergetic imaging appears to be useful in the delineation of the right adrenal vein before adrenal vein sampling.

CT artifacts from port systems: Virtual monoenergetic reconstructions from spectral-detector CT reduce artifacts and improve depiction of surrounding tissue

PURPOSE

CT artifacts from port-systems are a common problem in staging- and restaging-examinations and reduce image quality and diagnostic assessment. The purpose of this study was to investigate the reduction of these artifacts using virtual monoenergetic images (VMI) from dual-energy spectral-detector CT (SDCT) in comparison to conventional CT-images (CI).

METHOD

50 SDCT-datasets of patients with artifacts from port-chamber and port-catheters were included in this IRB-approved, retrospective study. CI and VMI (range, 40-200 keV, 10 keV increment) were reconstructed from the same acquisition. The quantitative image analysis was performed ROI-based assessing mean and standard deviation of attenuation (HU) in most pronounced hypo- and hyperdense artifacts surrounding to the port-chamber and the distal end of the port-catheter in the superior vena cava. Subjectively, artifact reduction and diagnostic assessment of surrounding soft tissue were rated on 5-point Likert-scales.

RESULTS

In comparison to CI, VMI of higher keV-values showed strong reduction of hypo- and hyperattenuating artifacts around the port-chamber and port-catheter (CI/VMI_200keV: hypodense -104.7 ± 124.7HU/10.8 ± 58.1HU and -101.6 ± 101.5HU/-36.7 ± 32.9HU; hyperdense 240.8 ± 151.6HU/79.6 ± 81.3HU and 108.6 ± 129.3HU/25.9 ± 31.9HU; all p < 0.001). Image noise could also be reduced significantly. The subjective analysis showed significantly reduced artifacts around the port-chamber and port-catheter (CI/VMI_200keV: hypodense 3(1-4)/5(4-5) and 3(2-4)/5(4-5); hyperdense 3(1-4)/5(4-5) and 3(2-3)/5(3-5); all p < 0.001) and improved diagnostic assessment of pectoral/subclavian soft tissue for VMI of ≥100keV. Ratings for diagnostic assessment were best between 140-200 keV. Overall interrater agreement was high (ICC = 0.79).

CONCLUSIONS

Higher keV VMI enabled a significant reduction of artifacts from port-systems around the chamber and the catheter leading to improved assessment of surrounding soft tissue.

Advanced Virtual Monoenergetic Imaging: Improvement of Visualization and Differentiation of Intramuscular Lesions in Portal-Venous-phase Contrast-enhanced Dual-energy CT

PURPOSE

To evaluate the effect of advanced monoenergetic imaging (MEI+) postprocessing algorithm on the visualization of various intramuscular lesions on portal-venous-phase contrast-enhanced dual-energy computed tomography (DECT).

MATERIAL AND METHODS

Thirty-nine patients (64.3 ± 11.1 years; 26 males) with various intramuscular lesions ranging from malignancy, bleeding, inflammation, edematous changes, and benign neoplasms were included and underwent DECT (100/Sn150kV). Postprocessing with MEI+ technique was used to reconstruct images at four different keV levels (40, 60, 80, 100) and compared to the standard portal-venous-phase CT (CT_pv) images. Image quality was assessed qualitatively (conspicuity, delineation, sharpness, noise, and confidence) by two independent readers using 5-point Likert scales, 5 = excellent; as well as quantitatively by calculating signal-to-noise ratios (SNR), contrast-to-noise ratios (CNR), and area under the receiver operating characteristic (ROC) curve (AUC) for lesion characterization.

RESULTS

Highest lesion enhancement and diagnostic confidence were observed in MEI+ 40 keV, with significant differences to CT_pv (p < 0.001), as well as for malignant lesions (highest conspicuity, noise, and sharpness in MEI+ 40 keV; p < 0.001). CNR calculations revealed highest values for MEI+ 40 keV followed by 60 keV with significant differences to CT_pv, and increasing energy levels. ROC analysis showed highest diagnostic accuracy for 40-keV MEI+ datasets regarding the detection of malignant/benign lesions with AUC values of 98.9% (95%-confidence interval: 96.5, 100) and a standard error of 1.2, further AUC values decreased to 83.6% for MEI+100.

CONCLUSION

MEI+ at low keV levels can significantly improve lesion detection of benign versus malignant intramuscular entities in patients undergoing portal-venous-phase DECT scans due to increased CNR.

Optimal Kiloelectron Volt for Noise-Optimized Virtual Monoenergetic Images of Dual-Energy Pediatric Abdominopelvic Computed Tomography: Preliminary Results

Objective

To compare quantitative and qualitative image quality parameters in pediatric abdominopelvic dual-energy CT (DECT) using noise-optimized virtual monoenergetic image (VMI) and conventional VMI at different kiloelectron volt (keV) levels.

Materials and Methods

Thirty-six consecutive abdominopelvic DECT scans were retrospectively included. Noise-optimized VMI and conventional VMI were reconstructed at seven energy levels, from 40 keV to 100 keV at 10 keV intervals. The contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) of the liver, pancreas, and aorta were objectively measured and compared. Image quality was evaluated subjectively regarding image noise, image blurring of solid organ, bowel image quality and severity of beam-hardening artifacts. Optimal monoenergetic levels in keV for both algorithms were determined based on overall image quality score.

Results

The maximal CNR and SNR values for all investigated organs were observed at 40 keV in noise-optimized VMI (CNR and SNR of liver, pancreas, aorta in order [CNR; 20.93, 17.34, 46.75: SNR; 37.39, 33.80, 63.21]), at 60–70 keV and at 70 keV in conventional VMI (CNR; 8.12, 5.67, 15.97: SNR; 19.57, 16.66, 26.65). In qualitative image analysis, noise-optimized VMI and conventional VMI showed the best overall image quality scores at 60 keV and at 70 keV, respectively. Noise-optimized VMI at 60 keV showed superior CNRs, SNRs, and overall image quality scores compared to conventional VMI at 70 keV (p < 0.001).

Conclusion

Optimal energy levels for noise-optimized VMI and conventional VMI were 60 keV and at 70 keV, respectively. Noise-optimized VMI shows superior CNRs, SNRs and subjective image quality over conventional VMI, at the optimal energy level.

Establishment of a novel system for the preoperative prediction of adherent perinephric fat (APF) occurrence based on a multi-mode and multi-parameter analysis of dual-energy CT

Background

Adherent perinephric fat (APF) is evaluated preoperatively with the Mayo adhesive probability (MAP) scoring system using conventional single-form computed tomography (CT) images. An objective or quantitative indicator for predicting APF is urgently needed for clinical application.

Methods

A total of 150 patients with renal tumours who underwent laparoscopic partial nephrectomy (LPN) were retrospectively enrolled and divided into the APF group (n=100) and the non-APF group (n=50) according to surgical results. All patients underwent a renal contrast-enhanced dual-energy CT (DECT) scan. The obtained CT DICOM data were transmitted to the DECT post-processing workstation and adopted virtual non-contrast (VNC), Rho/Z Maps, and Monoenergetic Plus (mono+) modes separately to undergo a multi-parameter analysis. A logistic stepwise investigation was utilized to analyse the related risk factors. The cutoff value was determined by the Youden index. Fifty patients were prospectively enrolled to validate the constructed model. The area under the curve (AUC), sensitivity, specificity and accuracy of the model were calculated.

Results

The study demonstrated that age, sex, body mass index (BMI), smoking status, tumour diameter, exophytic status, degree of malignancy and posterior perinephric fat thickness were related to the occurrence of APF (P<0.05). Model 1 was selected with the contrast material (CM) parameter (cutoff point 0.5), model 2 was selected with the effective atomic number (Z_eff) parameter (cutoff point 6.5), and model 3 was selected with the slope K (K) parameter (cutoff point -0.95). The AUC, sensitivity, specificity and accuracy of model 1 were 0.94, 0.94, 0.93 and 0.94, respectively; for model 2, they were 0.94, 0.93, 0.93 and 0.96, respectively; and for model 3, they were 0.92, 0.92, 0.93 and 0.92, respectively.

Conclusions

Multi-mode and multi-parameter models of DECT can effectively be used to predict the occurrence of APF.

Value of virtual monochromatic spectral image of dual-layer spectral detector CT with noise reduction algorithm for image quality improvement in obese simulated body phantom

BACKGROUND

Dual-layer spectral detector CT (SDCT) may provide several theoretical advantages over pre-existing DECT approaches in terms of adjustment-free sampling number and dose modulation, beam hardening correction, and production spectral images by post-processing. In addition, by adopting noise reduction algorithm, high contrast resolution was expected even in low keV level. We surmised that this improvement would be beneficial to obese people. Therefore, our aim of study is to compare image quality of virtual monochromatic spectral images (VMI) and polychromatic images reconstructed from SDCT with different body size and radiation dose using anthropomorphic liver phantom.

METHODS

One small and one large size of body phantoms, each containing eight (four high- and four low-contrast) simulated focal liver lesions (FLLs) were scanned by SDCT (at 120 kVp) using different Dose Right Indexes (DRIs). VMI were reconstructed from spectral base images from 40 keV to 200 keV. Hybrid iterative reconstruction (iDose4) was used for polychromatic image reconstruction. Image noise and contrast to noise ratio (CNR) were compared. Five radiologists independently rated lesion conspicuity, diagnostic acceptability and subjective noise level in every image sets, and determined optimal keV level in VMI.

RESULTS

Compare with conventional polychromatic images, VMI showed superior CNR at low keV level regardless of phantom size at every examined DRIs (Ps < 0.05). As body size increased, VMI had more gradual CNR decrease and noise increase than conventional polychromatic images. For low contrast FLLs in large phantom, lesion conspicuities at low radiation dose levels (DRI 16 and 19) were significantly increased in VMI (Ps < 0.05). Subjective image noise and diagnostic acceptabilities were significantly improved at VMI in both phantom size.

CONCLUSIONS

VMI of dual-layer spectral detector CT with noise reduction algorithm provides improved CNR, noise reduction, and better subjective image quality in imaging of obese simulated liver phantom compared with polychromatic images. This may hold promise for improving detection of liver lesions and improved imaging of obese patients.

Postablation assessment of hepatocellular carcinoma using dual-energy CT: Comparison of half versus standard iodine contrast medium

This retrospective study was aimed to evaluate the reduced iodine load on image quality and diagnostic performance in multiphasic hepatic CT using a novel monoenergetic reconstruction algorithm (nMERA) in assessment of local tumor progression after radiofrequency ablation (RFA) of hepatocellular carcinoma (HCC). Ninety patients who underwent CT 1 month after RFA of HCC. Forty-five patients had multiphasic hepatic dual-energy CT with a half-reduced contrast medium (HRCM) of 277.5 mg I/kg. The nMERA (40-70-keV) images were reconstructed in each phase. Another 45 patients received a standard contrast medium (SCM) of 555 mg I/kg, and the images were reconstructed as a simulated 120-kVp images. Primary outcome was accuracy, sensitivity, specificity, and area under the receiver operating characteristic curve (AUC) in assessment of local tumor progression. Additional advanced assessments included the image noise, attenuation value, contrast-to-noise ratio (CNR), and subjective image quality between the groups. The accuracy, sensitivity and specificity of nMERA HRCM images were 95.7%, 100% and 93.9% for 40 keV, 95.7%, 85.7% and 100% for 50 keV, 83.0%, 42.8% and 100% for 60 keV, and 83.0%, 42.9% and 100% for 70 keV. The AUROC was 0.99, 0.99, 0.94, and 0.93 for 40-70 keV nMERA HRCM images, respectively. Compared with simulated 120-kVp SCM images, nMERA HRCM images demonstrated comparable noise at 70-keV (P < 0.05), and comparable CNR at 40- and 50-keV (P < 0.05). nMERA DECT enables the contrast medium to be reduced to up to 50% in multiphasic hepatic CT while preserving diagnostic accuracy.

Improving iodine contrast to noise ratio using virtual monoenergetic imaging and prior-knowledge-aware iterative denoising (mono-PKAID)

Multi-energy CT acquires simultaneous multiple x-ray attenuation measurements from different energy spectra which facilitates the computation of virtual monoenergetic images (VMI) at a specific photon energy (keV). Since the contrast between iodine attenuation and the attenuation of surrounding soft tissues increases at lower x-ray energies, VMIs in the range of 40-70 keV can be used to improve iodine visualization. However, at lower energy levels, image noise in VMIs is substantially increased, which counteracts the benefits from the increased iodine contrast, resulting in a decreased iodine contrast-to-noise ratio (CNR). There exists considerable data redundancy between multi-energy CT images created from the same acquisition. Similarly, a substantial spatio-spectral data redundancy exists between multi-energy CT images and the corresponding VMIs. In this work, we develop a denoising framework that exploits this data redundancy to improve iodine CNR in the VMIs. We accomplish this by applying prior-knowledge-aware iterative denoising to low-energy VMIs; we refer to the denoised images as mono-PKAID images. The proposed framework was evaluated using phantom and in vivo data acquired on a research whole-body photon-counting-detector CT, as well as using data from a commercial dual-source dual-energy CT system. The results of phantom experiments show that the proposed framework can preserve image resolution and noise texture compared to the original VMIs, while reducing noise to improve iodine CNR. Quantitative measurements show that the iodine CNR of 50 keV VMI is improved by 1.8-fold using the proposed method, relative to the VMI produced using commercial software (Mono+). With mono-PKAID, VMIs at lower keV take full advantage of higher iodine contrast without substantially increasing image noise. These observations were confirmed using patient data sets, which demonstrated that mono-PKAID reduced image noise, improved CNR in anatomical regions with iodine perfusion by 1.8-fold, and potentially enhanced the visibility of focal liver lesions.

Low-keV virtual monoenergetic imaging reconstructions of excretory phase spectral dual-energy CT in patients with urothelial carcinoma: A feasibility study

OBJECTIVES

To compare objective and subjective image quality between low keV virtual monoenergetic images (VMI) of the excretory phase and conventional venous phase images derived from spectral dual-energy CT (DECT) in the assessment of urothelial carcinoma.

METHODS

26 consecutive patients with histologically confirmed urothelial carcinoma who received clinically indicated venous- and excretory phase abdominal CT scans were included retrospectively. Attenuation, image noise as well as signal- and contrast-to-noise-ratio (SNR, CNR) in venous and excretory phase CT and excretory phase VMI from 40 to 70 keV were obtained from ROI-based measurements in the following regions: urothelial carcinoma, liver, pancreas, renal cortex, subcutaneous fat, renal vein/artery, portal vein, urinary bladder wall, lymph nodes, prostate/uterus. Subjective vessel contrast and delineation of primary tumor manifestations and distant metastases were rated on 5-point Likert scales.

RESULTS

In comparison to venous phase CT, attenuation and SNR in excretory phase VMI40keV were higher (p < 0.001), except for liver parenchyma, where they were comparable (p = 0.07 and p = 0.17, respectively). Regarding image noise, no significant difference was found between venous phase CT and excretory phase VMI40keV (p-range: 0.08-1.00), except for liver, portal vein and renal artery, where it was lower in VMI40keV (p < 0.05). CNR of urothelial carcinoma to circumjacent bladder wall was significantly higher in excretory phase VMI40keV compared to venous phase CT. Subjective vessel contrast and delineation of primary tumor and distant metastases received equivalent or higher Likert scores in excretory phase VMI40keV than in venous phase CT.

CONCLUSION

This feasibility study indicates that in the assessment of urothelial carcinoma, virtual monoenergetic excretory phase images at 40 keV acquired with spectral DECT could be feasible to maintain subjective and objective image quality as provided by conventional venous phase images. Still, equivalence with regards to metastatic lesion detection requires further investigation before employing this technique in a potential signal-scan, single-bolus approach.