Dual Energy Computed Tomography Scans of the Bowel: Benefits, Pitfalls, and Future Directions

Application of multi-spectral CT imaging in Crohn's disease: a systematic review

BACKGROUND

No quantitative computed tomography (CT) biomarker is actually sufficiently accurate to assess Crohn's disease (CD) lesion activity, with adequate precision to guide clinical decisions.

PURPOSE

To assess the available literature on the use of iodine concentration (IC), from multi-spectral CT acquisition, as a quantitative parameter able to distinguish healthy from affected bowel and assess CD bowel activity and heterogeneity of activity along the involved segments.

MATERIAL AND METHODS

A literature search was conducted to identify original research studies published up to February 2022. The inclusion criteria were original research papers (>10 human participants), English language publications, focus on dual-energy CT (DECT) of CD with iodine quantification (IQ) as an outcome measure. The exclusion criteria were animal-only studies, languages other than English, review articles, case reports, correspondence, and study populations <10 patients.

RESULTS

Nine studies were included in this review; all of which showed a strong correlation between IC measurements and CD activity markers, such as CD activity index (CDAI), endoscopy findings and simple endoscopic score for Crohn's disease (SES-CD), and routine CT enterography (CTE) signs and histopathologic score. Statistically significant differences in IC were reported between affected bowel segments and healthy ones (higher P value was P < 0.001), normal segments and those with active inflammation (P < 0.0001) as well as between patients with active disease and those in remission (P < 0.001).

CONCLUSION

The mean normalized IC at DECTE could be a reliable tool in assisting radiologists in the diagnosis, classification and grading of CD activity.

Dual-Energy CT Evaluation of Gastrointestinal Bleeding

Gastrointestinal (GI) bleeding is a potentially life-threatening condition accounting for more than 300 000 annual hospitalizations. Multidetector abdominopelvic CT angiography is commonly used in the evaluation of patients with GI bleeding. Given that many patients with severe overt GI bleeding are unlikely to tolerate bowel preparation, and inpatient colonoscopy is frequently limited by suboptimal preparation obscuring mucosal visibility, CT angiography is recommended as a first-line diagnostic test in patients with severe hematochezia to localize a source of bleeding. Assessment of these patients with conventional single-energy CT systems typically requires the performance of a noncontrast series followed by imaging during multiple postcontrast phases. Dual-energy CT (DECT) offers several potential advantages for performing these examinations. DECT may eliminate the need for a noncontrast acquisition by allowing the creation of virtual noncontrast (VNC) images from contrast-enhanced data, affording significant radiation dose reduction while maintaining diagnostic accuracy. VNC images can help radiologists to differentiate active bleeding, hyperattenuating enteric contents, hematomas, and enhancing masses. Additional postprocessing techniques such as low-kiloelectron voltage virtual monoenergetic images, iodine maps, and iodine overlay images can increase the conspicuity of contrast material extravasation and improve the visibility of subtle causes of GI bleeding, thereby increasing diagnostic confidence and assisting with problem solving. GI bleeding can also be diagnosed with routine single-phase DECT scans by constructing VNC images and iodine maps. Radiologists should also be aware of the potential pitfalls and limitations of DECT. ^©RSNA, 2023 Quiz questions for this article are available through the Online Learning Center.

Inflammatory bowel disease cross-sectional imaging: What's new?

Cross-sectional imaging-ultrasonography, computed tomography enterography, and magnetic resonance enterography-is a routine and indispensable tool for patients with Crohn's disease (CD) that helps to detect or monitor disease characteristics before, during, and after CD treatment. New emerging radiological technologies may have further clinical applications in the management of CD. In this review article, we focus on the latest developments in cross-sectional imaging in CD research, including its role in intra- and extra-luminal lesion detection, intestinal inflammation and fibrosis grading, therapeutic response assessment and outcome prediction, postoperative recurrence detection and prediction, and the gut-brain axis.

Comparison of the performance of conventional and spectral-based tagged stool cleansing algorithms at CT colonography

OBJECTIVES

To compare the performance of conventional versus spectral-based electronic stool cleansing for iodine-tagged CT colonography (CTC) using a dual-layer spectral detector scanner.

METHODS

We retrospectively evaluated iodine contrast stool-tagged CTC scans of 30 consecutive patients (mean age: 69 ± 8 years) undergoing colorectal cancer screening obtained on a dual-layer spectral detector CT scanner. One reader identified locations of electronic cleansing artifacts (n = 229) on conventional and spectral cleansed images. Three additional independent readers evaluated these locations using a conventional cleansing algorithm (Intellispace Portal) and two experimental spectral cleansing algorithms (i.e., fully transparent and translucent tagged stool). For each cleansed image set, readers recorded the severity of over- and under-cleansing artifacts on a 5-point Likert scale (0 = none to 4 = severe) and readability compared to uncleansed images. Wilcoxon's signed-rank tests were used to assess artifact severity, type, and readability (worse, unchanged, or better).

RESULTS

Compared with conventional cleansing (66% score ≥ 2), the severity of overall cleansing artifacts was lower in transparent (60% score ≥ 2, p = 0.011) and translucent (50% score ≥ 2, p < 0.001) spectral cleansing. Under-cleansing artifact severity was lower in transparent (49% score ≥ 2, p < 0.001) and translucent (39% score ≥ 2, p < 0.001) spectral cleansing compared with conventional cleansing (60% score ≥ 2). Over-cleansing artifact severity was worse in transparent (17% score ≥ 2, p < 0.001) and translucent (14% score ≥ 2, p = 0.023) spectral cleansing compared with conventional cleansing (9% score ≥ 2). Overall readability was significantly improved in transparent (p < 0.001) and translucent (p < 0.001) spectral cleansing compared with conventional cleansing.

CONCLUSIONS

Spectral cleansing provided more robust electronic stool cleansing of iodine-tagged stool at CTC than conventional cleansing.

KEY POINTS

• Spectral-based electronic cleansing of tagged stool at CT colonography provides higher quality images with less perception of artifacts than does conventional cleansing. • Spectral-based electronic cleansing could potentially advance minimally cathartic approach for CT colonography. Further clinical trials are warranted.

Reducing Visceral-Motion-Related Artifacts on the Liver with Dual-Energy CT: A Comparison of Four Different CT Scanner Techniques

Purpose: To assess the influence of different dual-energy CT (DECT) scanner techniques on the severity of visceral-motion-related artifacts on the liver. Methods: Two independent readers retrospectively evaluated visceral-motion-related artifacts on the liver on 120-kVp(-like), monoenergetic low- and high-keV, virtual non-contrast (VNC), and iodine images acquired on a dual-source, twin-beam, fast kV-switching, and dual-layer spectral detector scanner. Quantitative assessment: Depth of artifact extension into the liver, measurements of Hounsfield Units (HU) and iodine concentrations. Qualitative assessment: Five-point Likert scale (1 = none to 5 = severe). Artifact severity between image reconstructions were compared by Wilcoxon signed-rank and paired t-tests. Results: 615 contrast-enhanced routine clinical DECT scans of the abdomen were evaluated in 458 consecutive patients (mean age: 61 ± 14 years, 331 men). For dual-source and twin-beam scanners, depth of extension of artifacts into the liver was significantly shorter and artifact severity scores significantly lower for 120-kVp-like images compared with the other image reconstructions (p < 0.001, each). For fast kV-switching and spectral detector scanner images, depth of extension of artifacts was significantly shorter and artifact severity scores significantly lower for iodine images (p < 0.001, each). Dual-source 120-kVp-like and spectral detector iodine images reduced artifacts to an extent that no significant difference in HU or iodine concentrations between artifacts (dual-source: 97 HU, spectral detector: 1.9 mg/mL) and unaffected liver parenchyma (dual-source: 108 HU, spectral detector: 2.1 mg/mL) was measurable (dual-source: p = 0.32, spectral detector: p = 0.15). Conclusion: Visceral-motion-related artifacts on the liver can be markedly reduced by viewing 120-kVp-like images for dual-source and twin-beam DECT scanners and iodine images for fast kV-switching and dual-layer spectral detector DECT scanners.

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.

Reduction of Peristalsis-Related Streak Artifacts on the Liver with Dual-Layer Spectral CT

Background: Peristalsis-related streak artifacts on the liver compromise image quality and diagnostic accuracy. Purpose: To assess dual-layer spectral-detector computed tomography (CT) image reconstructions for reducing intestinal peristalsis-related streak artifacts on the liver. Methods: We retrospectively evaluated 220 contrast-enhanced abdominal dual-energy CT scans in 131 consecutive patients (mean age: 68 ± 10 years, 120 men) who underwent routine clinical dual-layer spectral-detector CT imaging (120 kVp, 40 keV, 200 keV, virtual non-contrast (VNC), iodine images). Two independent readers evaluated bowel peristalsis streak artifacts on the liver qualitatively on a five-point Likert scale (1 = none to 5 = severe) and quantitatively by depth of streak artifact extension into the liver and measurements of Hounsfield Unit and iodine concentration differences from normal liver. Artifact severity between image reconstructions were compared by Wilcoxon signed-rank and paired t-tests. Results: 12 scans were excluded due to missing spectral data, artifacts on the liver originating from metallic foreign materials, or oral contrast material. Streak artifacts on the liver were seen in 51/208 (25%) scans and involved the left lobe only in 49/51 (96%), the right lobe only in 0/51 (0%), and both lobes in 2/51 (4%) scans. Artifact frequency was lower in iodine than in 120 kVp images (scans 18/208 vs. 51/208, p < 0.001). Artifact severity was less in iodine than in 120 kVp images (median score 1 vs. 3, p < 0.001). Streak artifact extension into the liver was shorter in iodine than 120 kVp images (mean length 2 ± 4 vs. 12 ± 5 mm, p < 0.001). Hounsfield Unit and iodine concentration differed significantly between bright streak artifacts and normal liver in 120 kVp, 40 keV, 200 keV, and VNC images (p < 0.001, each), but not in iodine images (p = 0.23). Conclusion: Intestinal peristalsis-related streak artifacts commonly affect the left liver lobe at CT and can be substantially reduced by viewing iodine dual-energy CT image reconstructions.

Efficiency of dual-energy computed tomography enterography in the diagnosis of Crohn's disease

Background

This retrospective study aimed to investigate the usefulness of the optimized kiloelectron volt (keV) for virtual monoenergetic imaging (VMI) combined with iodine map in dual-energy computed tomography enterography (DECTE) in the diagnosis of Crohn’s disease (CD).

Methods

Seventy-two patients (mean age: 41.89 ± 17.28 years) with negative computed tomography enterography (CTE) were enrolled for investigating the optimized VMI keV in DECTE by comparing subjective and objective parameters of VMIs that were reconstructed from 40 to 90 keV. Moreover, 68 patients (38.27 ± 15.10 years; 35 normal and 33 CD) were included for evaluating the diagnostic efficacy of DECTE iodine map at the optimized VMI energy level and routine CTE for CD and active CD. Statistical analysis for all data was conducted.

Results

Objective and subjective imaging evaluations showed the best results at 60 keV for VMIs. The CT values of the normal group, active subgroup, and CD group during the small intestinal phase at routine 120 kVp or 60 keV VMI had significant differences. The diagnostic efficacy of an iodine map was the best when NIC = 4% or fat value = 45.8% for CD, whereas NIC < 0.35 or the fat value < 0.38 for active CD. The combined routine CTE and optimized VMI improved the diagnostic efficacy (P < 0.001).

Conclusions

VMI at 60 keV provided the best imaging quality on DECTE. NIC and fat value provided important basis for active CD evaluation. Routine CTE combined with VMI at 60 keV improved the diagnostic efficiency for CD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12880-021-00716-y.

Spectral CT of the abdomen: Where are we now?

Spectral CT adds a new dimension to radiological evaluation, beyond assessment of anatomical abnormalities. Spectral data allows for detection of specific materials, improves image quality while at the same time reducing radiation doses and contrast media doses, and decreases the need for follow up evaluation of indeterminate lesions. We review the different acquisition techniques of spectral images, mainly dual-source, rapid kV switching and dual-layer detector, and discuss the main spectral results available. We also discuss the use of spectral imaging in abdominal pathologies, emphasizing the strengths and pitfalls of the technique and its main applications in general and in specific organs.

Bowel Peristalsis Artifact on Dual-Energy CT: In Vitro Study on the Influence of Different Dual-Energy CT Platforms and Enteric Contrast Agents

BACKGROUND. The value of dual-energy CT (DECT) for bowel wall assessment is increasingly recognized. Although technical improvements reduce peristalsis artifact in conventional CT, the effects of peristalsis on DECT image reconstructions remain poorly studied. OBJECTIVE. The purpose of this study was to evaluate the influence of different DECT scanners and enteric contrast agents on the severity of bowel peristalsis artifact in vitro. METHODS. To simulate bowel peristalsis, a 3-cm-diameter corrugated hollow tube representing the bowel was oscillated constantly in the z-axis within a larger water-filled cylinder. The bowel was serially filled with air, water, and iodinated or experimental dark contrast material and scanned on four different DECT platforms (spectral detector, rapid peak kilovoltage switching, split filter, and dual source) to reconstruct 120-kVp-like and iodine images. Two readers rated each image reconstruction for artifact severity from 0 (none) to 3 (severe) and recorded the degree to which iodine images depicted bowel wall hyperattenuation on 120-kVp-like images as artifactual. Artifact severity scores were compared by ANOVA with Bonferroni correction. RESULTS. Interrater agreement on artifact scores was excellent (intraclass correlation coefficient, 0.82 [95% CI, 0.79-0.84]). For 120-kVp-like images, mean peristalsis artifact scores were lower (all p < .001) for split-filter (1.47) and dual-source (1.86) scanners than for spectral-detector (2.58) and rapid-kilovoltage-switching (2.74) scanners. Compared with those on 120-kVp images, peristalsis artifacts on iodine images were less severe for spectral-detector (score, 1.03; p < .001) and rapid-kilovoltage-switching (2.09; p < .001) systems but more severe for dual-source (2.77; p < .001) and split-filter (2.62; p < .001) systems. Peristalsis artifact was rated less severe with experimental dark bowel contrast medium (score, 1.79) than with other bowel contrast agents (all p < .001). Iodine images helped identify bowel wall hyperattenuation as artifactual in 94.7% of reviewed cases for spectral-detector and 40.7% of cases for rapid-kilovoltage-switching scanners. CONCLUSION. For spectral-detector and rapid-kilovoltage-switching DECT, iodine images minimize peristalsis artifact, but for dual-source and split-filter DECT, mixed 120-kVp-like images are preferred. Compared with iodinated contrast material and water, experimental dark bowel contrast material reduces peristalsis artifact. CLINICAL IMPACT. Knowledge of the preferred images for reducing peristalsis artifact can lessen the effect of peristalsis on clinical DECT interpretation. Dark enteric contrast agents, when they become clinically available, may further reduce the effects of peristalsis.

Small bowel radiology

PURPOSE OF REVIEW

Recent advances in computed tomography (CT), ultrasound (US), magnetic resonance imaging (MRI), and nuclear radiology have improved the diagnosis and characterization of small bowel pathology. Our purpose is to highlight the current status and recent advances in multimodality noninvasive imaging of the small bowel.

RECENT FINDINGS

CT and MR enterography are established techniques for small bowel evaluation. Dual-energy CT is a novel technique that has shown promise for the mesenteric ischemia and small bowel bleeding. Advanced US techniques and MRI sequences are being investigated to improve assessment of bowel inflammation, treatment response assessment, motility, and mural fibrosis. Novel radiotracers and scanner technologies have made molecular imaging the new reference standard for small bowel neuroendocrine tumors. Computational image analysis and artificial intelligence (AI) have the potential to augment physician expertise, reduce errors and variability in assessment of the small bowel on imaging.

SUMMARY

Advances in translational imaging research coupled with progress in imaging technology have led to a wider adoption of cross-sectional imaging for the evaluation and management of small bowel entities. Ongoing developments in image acquisition and postprocessing techniques, molecular imaging and AI have the strongest potential to transform the care and outcomes of patients with small bowel diseases.

Recognizing and Minimizing Artifacts at Dual-Energy CT

Dual-energy CT (DECT) is an exciting innovation in CT technology with profound capabilities to improve diagnosis and add value to patient care. Significant advances in this technology over the past decade have improved our ability to successfully adopt DECT into the clinical routine. To enable effective use of DECT, one must be aware of the pitfalls and artifacts related to this technology. Understanding the underlying technical basis of artifacts and the strategies to mitigate them requires optimization of scan protocols and parameters. The ability of radiologists and technologists to anticipate their occurrence and provide recommendations for proper selection of patients, intravenous and oral contrast media, and scan acquisition parameters is key to obtaining good-quality DECT images. In addition, choosing appropriate reconstruction algorithms such as image kernel, postprocessing parameters, and appropriate display settings is critical for preventing quantitative and qualitative interpretive errors. Therefore, knowledge of the appearances of these artifacts is essential to prevent errors and allows maximization of the potential of DECT. In this review article, the authors aim to provide a comprehensive and practical overview of possible artifacts that may be encountered at DECT across all currently available commercial clinical platforms. They also provide a pictorial overview of the diagnostic pitfalls and outline strategies for mitigating or preventing the occurrence of artifacts, when possible. The broadening scope of DECT applications necessitates up-to-date familiarity with these technologies to realize their full diagnostic potential.

Dual-energy CT enterography in evaluation of Crohn's disease: the role of virtual monochromatic images

PURPOSE

To assess the use of virtual monochromatic images (VMI) for discrimination of affected and non-affected bowel walls in patients with Crohn's disease (CD) as well as to compare mural enhancement between patients with and without CD.

MATERIALS AND METHODS

This retrospective study included 61 patients (47 with CD, 14 without CD). Attenuation value (AV), signal-to noise ratio (SNR), and contrast-to-noise ratio (CNR) were obtained at VMI energy levels from 40 to 110 keV in 10 keV increment. Analyses were performed among affected and non-affected bowel walls in CD patients, as well as from bowel walls in patients without CD. Image quality and mural enhancement were evaluated at VMI energy levels at 40, 70, and 110 keV.

RESULTS

At all energy levels of VMI, each quantitative data for AV, SNR, and CNR showed statistically significant difference between diseased and non-diseased bowel walls in CD patients. In the quantitative assessment of patients with and without CD, the optimal AV and SNR were obtained at 40 keV, and the optimal CNR was obtained at 70 keV. For the qualitative assessment, the best image quality and mural enhancement were obtained at 70 keV and 40 keV, respectively.

CONCLUSION

VMI are helpful for the differentiation of affected bowel walls in CD patients, providing high diagnostic accuracy.

Improved Sensitivity and Reader Confidence in CT Colonography Using Dual-Layer Spectral CT: A Phantom Study

Background Limited cathartic preparations for CT colonography with fecal tagging can improve patient comfort but may result in nondiagnostic examinations from poorly tagged stool. Dual-energy CT may overcome this limitation by improving the conspicuity of the contrast agent, but more data are needed. Purpose To investigate whether dual-energy CT improves polyp detection in CT colonography compared with conventional CT at different fecal tagging levels in vitro. Materials and Methods In this HIPAA-compliant study, between December 2017 and August 2019, a colon phantom 30 cm in diameter containing 60 polyps of different shapes (spherical, ellipsoid, flat) and size groups (5-9 mm, 11-15 mm) was constructed and serially filled with simulated feces tagged with four different iodine concentrations (1.26, 2.45, 4.88, and 21.00 mg of iodine per milliliter), then it was scanned with dual-energy CT with and without an outer fat ring to simulate large body size (total diameter, 42 cm). Two readers independently reviewed conventional 120-kVp CT and 40-keV monoenergetic dual-energy CT images to record the presence of polyps and confidence (three-point scale.) Generalized estimating equations were used for sensitivity comparisons between conventional CT and dual-energy CT, and a Wilcoxon signed-rank test was used for reader confidence. Results Dual-energy CT had higher overall sensitivity for polyp detection than conventional CT (58.8%; 95% confidence interval [CI]: 49.7%, 67.3%; 564 of 960 polyps vs 42.1%; 95% CI: 32.1%, 52.8%; 404 of 960 polyps; P < .001), including with the fat ring (48% and 31%, P < .001). Reader confidence improved with dual-energy CT compared with conventional images on all tagging levels (P < .001). Interrater agreement was substantial (κ = 0.74; 95% CI: 0.70, 0.77). Conclusion Compared with conventional 120-kVp CT, dual-energy CT improved polyp detection and reader confidence in a dedicated dual-energy CT colonography phantom, especially with suboptimal fecal tagging. © RSNA, 2020.

Dual-energy CT evaluation of gastrointestinal bleeding

Gastrointestinal bleeding is a common cause for hospital admissions and is an important cause of morbidity and mortality. Although endoscopy is accepted as the standard initial diagnostic modality for the evaluation of gastrointestinal bleeding, multiphasic computed tomography (CT) imaging has become an alternative diagnostic tool. Dual-energy CT with post-processing techniques may have additional advantages over single-energy computed tomography in evaluation of gastrointestinal bleeding. In this article, we discuss the role of dual-energy CT in the evaluation of gastrointestinal bleeding with potential advantages over conventional CT and limitations.