Reduced iodine load at CT pulmonary angiography with dual-energy monochromatic imaging: comparison with standard CT pulmonary angiography--a prospective randomized trial

Iterative image-domain decomposition for dual-energy CT

PURPOSE

Dual energy CT (DECT) imaging plays an important role in advanced imaging applications due to its capability of material decomposition. Direct decomposition via matrix inversion suffers from significant degradation of image signal-to-noise ratios, which reduces clinical values of DECT. Existing denoising algorithms achieve suboptimal performance since they suppress image noise either before or after the decomposition and do not fully explore the noise statistical properties of the decomposition process. In this work, the authors propose an iterative image-domain decomposition method for noise suppression in DECT, using the full variance-covariance matrix of the decomposed images.

METHODS

The proposed algorithm is formulated in the form of least-square estimation with smoothness regularization. Based on the design principles of a best linear unbiased estimator, the authors include the inverse of the estimated variance-covariance matrix of the decomposed images as the penalty weight in the least-square term. The regularization term enforces the image smoothness by calculating the square sum of neighboring pixel value differences. To retain the boundary sharpness of the decomposed images, the authors detect the edges in the CT images before decomposition. These edge pixels have small weights in the calculation of the regularization term. Distinct from the existing denoising algorithms applied on the images before or after decomposition, the method has an iterative process for noise suppression, with decomposition performed in each iteration. The authors implement the proposed algorithm using a standard conjugate gradient algorithm. The method performance is evaluated using an evaluation phantom (Catphan©600) and an anthropomorphic head phantom. The results are compared with those generated using direct matrix inversion with no noise suppression, a denoising method applied on the decomposed images, and an existing algorithm with similar formulation as the proposed method but with an edge-preserving regularization term.

RESULTS

On the Catphan phantom, the method maintains the same spatial resolution on the decomposed images as that of the CT images before decomposition (8 pairs/cm) while significantly reducing their noise standard deviation. Compared to that obtained by the direct matrix inversion, the noise standard deviation in the images decomposed by the proposed algorithm is reduced by over 98%. Without considering the noise correlation properties in the formulation, the denoising scheme degrades the spatial resolution to 6 pairs/cm for the same level of noise suppression. Compared to the edge-preserving algorithm, the method achieves better low-contrast detectability. A quantitative study is performed on the contrast-rod slice of Catphan phantom. The proposed method achieves lower electron density measurement error as compared to that by the direct matrix inversion, and significantly reduces the error variation by over 97%. On the head phantom, the method reduces the noise standard deviation of decomposed images by over 97% without blurring the sinus structures.

CONCLUSIONS

The authors propose an iterative image-domain decomposition method for DECT. The method combines noise suppression and material decomposition into an iterative process and achieves both goals simultaneously. By exploring the full variance-covariance properties of the decomposed images and utilizing the edge predetection, the proposed algorithm shows superior performance on noise suppression with high image spatial resolution and low-contrast detectability.

Nonlinear image blending for dual-energy MDCT of the abdomen: can image quality be preserved if the contrast medium dose is reduced?

OBJECTIVE

The objective of this study was to compare the image quality of a dual-energy nonlinear image blending technique at reduced load of contrast medium with a simulated 120-kVp linear blending technique at a full dose during portal venous phase MDCT of the abdomen.

SUBJECTS AND METHODS

Forty-five patients (25 men, 20 women; mean age, 65.6 ± 9.7 [SD] years; mean body weight, 74.9 ± 12.4 kg) underwent contrast-enhanced single-phase dual-energy CT of the abdomen by a random assignment to one of three different contrast medium (iomeprol 400) dose injection protocols: 1.3, 1.0, or 0.65 mL/kg of body weight. The contrast-to-noise ratio (CNR) and noise at the portal vein, liver, aorta, and kidney were compared among the different datasets using the ANOVA. Three readers qualitatively assessed all datasets in a blinded and independent fashion.

RESULTS

Nonlinear blended images at a 25% reduced dose allowed a significant improvement in CNR (p < 0.05 for all comparisons), compared with simulated 120-kVp linear blended images at a full dose. No statistically significant difference existed in CNR and noise between the nonlinear blended images at a 50% reduced dose and the simulated 120-kVp linear blended images at a full dose. Nonlinear blended images at a 50% reduced dose were considered in all cases to have acceptable image quality.

CONCLUSION

The dual-energy nonlinear image blending technique allows reducing the dose of contrast medium up to 50% during portal venous phase imaging of the abdomen while preserving image quality.

Substantial iodine volume load reduction in CT angiography with dual-energy imaging: insights from a pilot randomized study

We explored whether dual-energy computed tomography (DECT) can allow a significant reduction in iodinated contrast volume during computed tomography angiography (CTA) without hampering image quality or assessibility. We prospectively randomized patients clinically referred to CTA to single energy computed tomography (SECT) with full iodine volume load (group A), DECT with 50 % iodine volume load (group B), DECT with 40 % iodine volume load (group C), and DECT with 30 % iodine volume load (group D); and compared image quality and assessibility. Eighty patients were enrolled and prospectively randomized. The mean age was 61.7 ± 15.0 years and 56 (71 %) patients were male. The demographical characteristics, body mass index, or mean radiation dose did not differ between groups. Significant reductions in total contrast volume were achieved in groups B, C, and D; with mean administrated contrast volumes of 90.3 ± 10.1, 39.5 ± 4.6, 28.3 ± 6.5, and 23.9 ± 6.0 mL, respectively, in groups A to D (p < 0.0001). With regard to image quality, no significant decrease in the Likert scale was observed with reductions of up to 60 % of the contrast volume (groups B and C). DECT at 50-60 keV in association with up to 60 % iodine load reduction, allowed similar signal density, image noise, and signal to noise ratio that SECT imaging with full iodine load. In this pilot, prospective, randomized study, dual energy CTA with up to 60 % iodine volume load reduction provided similar image quality and assessibility than full iodine load with conventional SECT imaging.

Imaging techniques for tumour delineation and heterogeneity quantification of lung cancer: overview of current possibilities

Imaging techniques for the characterization and delineation of primary lung tumours and lymph nodes are a prerequisite for adequate radiotherapy. Numerous imaging modalities have been proposed for this purpose, but only computed tomography (CT) and FDG-PET have been implemented in clinical routine. Hypoxia PET, dynamic contrast-enhanced CT (DCE-CT), dual energy CT (DECT) and (functional) magnetic resonance imaging (MRI) hold promise for the future. Besides information on the primary tumour, these techniques can be used for quantification of tissue heterogeneity and response. In the future, treatment strategies may be designed which are based on imaging techniques to optimize individual treatment.

Reduced iodine load with CT coronary angiography using dual-energy imaging: a prospective randomized trial compared with standard coronary CT angiography

BACKGROUND

There is concern regarding the administration of iodinated contrast to patients with impaired renal function because of the increased risk of contrast-induced nephropathy.

OBJECTIVE

Evaluate image quality and feasibility of a protocol with a reduced volume of iodinated contrast and utilization of dual-energy coronary CT angiography (DECT) vs a standard iodinated contrast volume coronary CT angiography protocol (SCCTA).

METHODS

A total of 102 consecutive patients were randomized to SCCTA (n = 53) or DECT with rapid kVp switching (n = 49). Eighty milliliters and 35 mL of iodinated contrast were administered in the SCCTA and DECT cohorts, respectively. Two readers measured signal and noise in the coronary arteries; signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. A 5-point signal/noise Likert scale was used to evaluate image quality; scores of <3 were nondiagnostic. Agreement was assessed through kappa analyses.

RESULTS

Demographics and radiation dose were not significantly different; there was no difference in CNR between both cohorts (P = .95). A significant difference in SNR between the groups (P = .02) lost significance (P = .13) when adjusted for body mass index. The median Likert score was inferior for DECT for reader 1 (3.6 ± 0.6 vs 4.3 ± 0.6; P < .001) but not reader 2 (4.1 ± 0.6 vs 4.3 ± 0.5; P = .06). Agreement in diagnostic interpretability in the DECT and SCCTA groups was 91% (95% confidence interval, 86%-100%) and 96% (95% confidence interval, 90%-100%), respectively.

CONCLUSION

DECT resulted in inferior image quality scores but demonstrated comparable SNR, CNR, and rate of diagnostic interpretability without a radiation dose penalty while allowing for >50% reduction in contrast volume compared with SCCTA.

Dyspnea due to pulmonary vessel arteritis

Pulmonary arteritis is a rare cause of pulmonary hypertension. Causes of pulmonary arteritis can be divided into primary and secondary, as well as classified according to vessel size. Only large vessel vasculitis is associated with pulmonary hypertension; primary forms include Takayasu arteritis and giant cell arteritis. The diagnosis of pulmonary arteritis can be challenging and the associated morbidity is serious without prompt, directed treatment. The authors present a case involving a 48-year-old First Nations man presenting with a six-month history of exertional dyspnea and severe stenosis of the left pulmonary artery, who was ultimately diagnosed with pulmonary arteritis related to large vessel vasculitis.

Thoracic dual energy CT: acquisition protocols, current applications and future developments

Thanks to a simultaneous acquisition at high and low kilovoltage, dual energy computed tomography (DECT) can achieve material-based decomposition (iodine, water, calcium, etc.) and reconstruct images at different energy levels (40 to 140keV). Post-processing uses this potential to maximise iodine detection, which elicits demonstrated added value for chest imaging in acute and chronic embolic diseases (increases the quality of the examination and identifies perfusion defects), follow-up of aortic endografts and detection of contrast uptake in oncology. In CT angiography, these unique features are taken advantage of to reduce the iodine load by more than half. This review article aims to set out the physical basis for the technology, the acquisition and post-processing protocols used, its proven advantages in chest pathologies, and to present future developments.

Optimization of kiloelectron volt settings in cerebral and cervical dual-energy CT angiography determined with virtual monoenergetic imaging

RATIONALE AND OBJECTIVES

Dual-energy computed tomography (DECT) offers various fields of application, especially in angiography using virtual monoenergetic imaging. The aim of this study was to evaluate objective image quality indices of calculated low-kiloelectron volt monoenergetic DECT angiographic cervical and cerebral data sets compared to virtual 120-kV polyenergetic images.

MATERIALS AND METHODS

Forty-one patients (21 men, mean age 58 ± 14) who underwent DECT angiography of the cervical (n = 7) or cerebral vessels (n = 34) were retrospectively included in this study. Data acquired with the 80 and 140 kVp tube using dual-source CT technology were subsequently used to calculate low-kiloelectron volt monoenergetic image data sets ranging from 120 to 40 keV (at 10-keV intervals per patient). Vessel and soft tissue attenuation and image noise were measured in various regions of interest, and contrast-to-noise ratio (CNR) was subsequently calculated. Differences in image attenuation and CNR were compared between the different monoenergetic data sets and virtual 120-kV polyenergetic images.

RESULTS

For cervical angiography, 60-keV monoenergetic data sets resulted in the greatest improvements in vessel attenuation and CNR compared to virtual 120-kV polyenergetic data sets (+40%, +16%; all P < .01). Also for cerebral vessel assessment, 60-keV monoenergetic data sets provided the greatest improvement in vessel attenuation and CNR (+40%, +9%; all P < .01) compared to virtual 120-kV polyenergetic data sets.

CONCLUSIONS

60-keV monoenergetic image data significantly improve vessel attenuation and CNR of cervical and cerebral DECT angiographic studies. Future studies have to evaluate whether the technique can lead to an increased diagnostic accuracy or should be used for dose reduction of iodinated contrast material.

Objective and subjective image quality of liver parenchyma and hepatic metastases with virtual monoenergetic dual-source dual-energy CT reconstructions: an analysis in patients with gastrointestinal stromal tumor

RATIONALE AND OBJECTIVES

To compare in dual-energy CT (DECT) conventionally reconstructed polyenergetic images (PEI) at 120 kVp to virtual monoenergetic images (MEI) at different kiloelectron volt (keV) levels for evaluation of liver and gastrointestinal stromal tumor (GIST) hepatic metastases with regard to objective (IQob) and subjective image quality (IQsub) assessed by two readers of varying experience. Image quality was correlated to patient size and compared between PEI and MEI.

MATERIALS AND METHODS

From 50 examinations of 17 GIST patients (12 with hepatic metastases) undergoing abdominal dual-source DECT for staging, therapy monitoring or follow-up, PEI and nine MEI in 10-keV intervals from 40 to 120 keV were reconstructed. Liver contrast-to-noise ratios (CNR) and metastasis-to-liver ratios were calculated. MEI reconstructions with the highest IQob were compared to PEI for IQsub by one experienced reader (ER) and one inexperienced reader (IR). Patients' diameters were correlated to IQob and IQsub ratings.

RESULTS

MEI at 70 keV had the highest IQob with equal liver CNR and metastasis-to-liver ratio compared to PEI. The ER rated 70-keV MEI and PEI equally high (median 4), whereas the IR rated IQsub best in 70-keV MEI (median 5). Unlike in PEI, IQsub ratings in 70-keV MEI were not correlated to patient size.

CONCLUSIONS

MEI at 70 keV provided an IQob equivalent to PEI. Regarding the IR, IQsub was improved in 70-keV MEI compared to PEI and less dependent on patient size. Therefore, IRs might improve their diagnostic confidence in the assessment of hepatic GIST metastases by evaluating MEI reconstructions at 70 keV.

Imaging in Transcatheter Aortic Valve Replacement (TAVR): role of the radiologist

BACKGROUND

Transcatheter aortic valve replacement (TAVR) is a novel technique developed in the last decade to treat severe aortic stenosis in patients who are non-surgical candidates because of multiple comorbidities.

METHODS

Since the technique is performed using a transvascular approach, pre-procedural assessment of the aortic valve apparatus, ascending aorta and vascular access is of paramount importance for both appropriate patient selection and correct device selection. This assessment is performed by a multi-disciplinary team with radiology being an integral and important part.

RESULTS

Among imaging modalities, there is growing scientific evidence supporting the crucial role of MDCT in the assessment of the aortic valve apparatus, suitability of the iliofemoral or alternative pathway, and determination of appropriate coaxial angles. MDCT also plays an important role in post-procedure imaging in the assessment of valve integrity and position.

CONCLUSION

This review outlines the principal aspects of TAVR, the multidisciplinary approach and utilisation of different imaging modalities, as well as a step-by-step approach to MDCT acquisition protocols, reconstruction techniques, pre-procedure measurements and post-procedure assessment.

TEACHING POINTS

• TAVR is a new technique to treat severe aortic stenosis in high-risk and nonsurgical candidates. • MDCT assessment of the aortic annulus is important for appropriate patient and device selection. • Multidisciplinary approach is required for patient selection, procedure planning and performance. • MDCT is required for assessment of the aortic root, iliofemoral or alternative vascular pathway.

Low-contrast agent dose dual-energy CT monochromatic imaging in pulmonary angiography versus routine CT

OBJECTIVE

This study aimed to retrospectively evaluate the feasibility and reliability of low-contrast agent dose dual-energy computed tomography (DECT) monochromatic imaging in pulmonary angiography.

METHODS

Computed tomography pulmonary angiography was performed in 86 patients, 41 in 120-kVp computed tomography (CT) and 45 in DECT with low-contrast agent dose. The images in DECT were reconstructed at optimal kiloelectron-voltage (keV), demonstrating the best contrast-to-noise ratio between pulmonary artery and soft tissue, and at 70 keV. Image quality was compared by quantitative and subjective indexes. The radiation doses were recorded.

RESULTS

Compared with 120-kVp CT, optimal keV showed superior quantitative indexes with inferior subjective image quality, whereas 70 keV demonstrated no statistical difference in quantitative indexes with superior subjective image quality. All suspicious pulmonary embolisms in DECT were diagnosed confidently by combination of 2 kinds of monochromatic imaging. The radiation dose in DECT is almost twice as 120-kVp CT.

CONCLUSIONS

Low-contrast agent dose DECT monochromatic imaging in pulmonary angiography accommodates superior intravascular enhancement and contrast in pulmonary arteries, and improves diagnostic confidence with compatible radiation dose.

Clinical evaluation of automatic tube voltage selection in chest CT angiography

OBJECTIVE

To evaluate the clinical impact of automatic tube voltage selection on chest CT angiography (CTA).

METHODS

Ninety-three patients were prospectively evaluated with a CT protocol aimed at comparing two successive CTAs acquired under similar technical conditions except for the kV selection: (1) the initial CTA was systematically obtained at 120 kVp and 90 ref mAs; (2) the follow-up CTA was obtained with an automatic selection of the kilovoltage (Care KV; Siemens Healthcare) for optimised CTA.

RESULTS

At follow-up, 90 patients (97 %) underwent CTA with reduced tube voltage, 100 kV (n = 26; 28 %) and 80 kV (n = 64; 69 %), resulting in a significant dose-length-product reduction (follow-up: 87.27; initial: 141.88 mGy.cm; P < 0.0001; mean dose reduction: 38.5 %) and a significant increase in the CNR at follow-up (follow-up: 11.5 ± 3.5 HU; initial: 10.9 ± 3.7 HU; P = 0.03). The increase in objective image noise at follow-up (follow-up: 23.2 ± 6.7 HU vs. 17.8 ± 5.1 HU; P < 0.0001) did not alter the diagnostic value of images.

CONCLUSION

Automatic tube voltage selection reduced the radiation dose delivered during chest CT angiograms by 38.5 % while improving the contrast-to-noise ratio of the examinations.

KEY POINTS

• As low a dose as possible must be used for CT angiography. • Automatic tube voltage selection permits reduced patient exposure. • Lowering the kVp enables increased intravascular attenuation. • Automatic tube voltage selection does not compromise the overall image quality.

Optimization of keV-settings in abdominal and lower extremity dual-source dual-energy CT angiography determined with virtual monoenergetic imaging

OBJECTIVES

To compare objective image quality indices in dual-energy CT angiography (DE-CTA) studies of the abdomen and lower extremity using conventional polyenergetic images (PEIs) and virtual monoenergetic images (MEIs) at different kiloelectron volt (keV) levels.

METHODS

We retrospectively evaluated 68 dual-source DE-CTA studies. 50 patients (42 men, 71 ± 10 years) underwent abdominal DE-CTA. 18 patients (13 men, 67 ± 10 years) underwent lower extremity DE-CTA. MEIs from 40 to 120 keV were reconstructed. Signal intensity, noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed in infrarenal aorta, superior mesenteric, external iliac, femoral, popliteal, and lower leg arteries. Comparisons between MEIs and PEIs were performed with Dunnett's test.

RESULTS

222 arteries were evaluated. In abdominal arteries 70 keV MEIs showed statistically equal signal intensity, noise and CNR levels (+13%; +31%, -14% on average; all p>0.05) compared to PEIs; SNR was equal or slightly impaired (-7% on average; p<0.001-1.00). In lower extremity arteries 60 keV MEIs resulted in significantly higher signal intensity and CNR (+54%; +54% on average; all p<0.05) compared to PEIs at equal noise levels (+18% on average; all p>0.05) and equal or higher SNR (+49% on average; p<0.01-0.35).

CONCLUSIONS

Low-keV MEIs lead to equal or higher signal intensity and CNR compared to PEIs. In lower extremity DE-CTA, additional reconstruction of low-keV MEIs at 60 keV might increase diagnostic confidence.

Reduction of contrast medium volume in abdominal aorta CTA: multiphasic injection technique versus a test bolus volume

OBJECTIVE

The purpose of this study is to reduce the administered contrast medium volume in abdominal CTA by using a test bolus injection, with the preservation of adequate quantitative and qualitative vessel enhancement.

STUDY DESIGN

For this technical efficacy study 30 patients, who were referred for a CTA examination of the abdominal aorta, were included. Randomly 15 patients were assigned to undergo a multiphasic injection protocol and received 89 mL of contrast medium (Optiray 350) (protocol I). Fifteen patients were assigned to the test bolus injection protocol (protocol II), which implies injection of a 10 mL test bolus of Optiray 350 prior to performing CTA with a 40 mL of contrast medium. Quantitative assessment of vascular enhancement was performed by measuring the amount of Hounsfield Units in the aorta at 30 positions from the celiac trunk to the iliac arteries in both groups. Qualitative assessment was performed by three radiologists who scored the images at a 5-point scale.

RESULTS

Quantitative assessment showed that there was no significant difference in vascular enhancement for patients between the two protocols, with mean attenuation values of 280.9 ± 50.84 HU and 258.60 ± 39.28 HU, respectively. The image quality of protocol I was rated 4.31 (range: 3.67/5.00) and of protocol II 4.11 (range: 2.67/5.00). These differences were not statistically significant.

CONCLUSION

This study showed that by using a test bolus injection and the administration of 50 mL of contrast medium overall, CTA of the abdominal aorta can reliably be performed, with regard to quantitative and qualitative adequate vessel enhancement.

Optimal monochromatic energy levels in spectral CT pulmonary angiography for the evaluation of pulmonary embolism

Background

The aim of this study was to determine the optimal monochromatic spectral CT pulmonary angiography (sCTPA) levels to obtain the highest image quality and diagnostic confidence for pulmonary embolism detection.

Methods

The Institutional Review Board of the Shanghai Jiao Tong University School of Medicine approved this study, and written informed consent was obtained from all participating patients. Seventy-two patients with pulmonary embolism were scanned with spectral CT mode in the arterial phase. One hundred and one sets of virtual monochromatic spectral (VMS) images were generated ranging from 40 keV to 140 keV. Image noise, clot diameter and clot to artery contrast-to-noise ratio (CNR) from seven sets of VMS images at selected monochromatic levels in sCTPA were measured and compared. Subjective image quality and diagnostic confidence for these images were also assessed and compared. Data were analyzed by paired t test and Wilcoxon rank sum test.

Results

The lowest noise and the highest image quality score for the VMS images were obtained at 65 keV. The VMS images at 65 keV also had the second highest CNR value behind that of 50 keV VMS images. There was no difference in the mean noise and CNR between the 65 keV and 70 keV VMS images. The apparent clot diameter correlated with the keV levels.

Conclusions

The optimal energy level for detecting pulmonary embolism using dual-energy spectral CT pulmonary angiography was 65–70 keV. Virtual monochromatic spectral images at approximately 65–70 keV yielded the lowest image noise, high CNR and highest diagnostic confidence for the detection of pulmonary embolism.

Dual-energy CT: radiation dose aspects

OBJECTIVE

Various applications for dual-energy CT (DECT) have been investigated and have shown substantial clinical benefits. However, only limited data are available regarding the radiation dose associated with DECT imaging. The purpose of this article is to review the available literature regarding the radiation dose associated with DECT imaging applications in comparison with conventional single-energy CT techniques.

CONCLUSION

The rediscovery of DECT and the increasing availability of this technique on clinical CT systems have opened new dimensions for CT. The advanced spectral differentiation of materials within the human body as well as the selective visualization or subtraction of iodinated contrast material or xenon provides both advanced visualization of disease-specific molecular substrates as well as additional functional information within a single scan.

Pulmonary perfused blood volume with dual-energy CT as surrogate for pulmonary perfusion assessed with dynamic multidetector CT

PURPOSE

To compare measurements of regional pulmonary perfused blood volume (PBV) and pulmonary blood flow (PBF) obtained with computed tomography (CT) in two pig models.

MATERIALS AND METHODS

The institutional animal care and use committee approved all animal studies. CT-derived PBF and PBV were determined in four anesthetized, mechanically ventilated, supine swine by using two methods for creating pulmonary parenchymal perfusion heterogeneity. Two animals were examined after sequentially moving a pulmonary arterial balloon catheter from a distal to a central location, and two others were examined over a range of static airway pressures, which varied the extents of regional PBF. Lung sections were divided into blocks and Pearson correlation coefficients calculated to compare matching regions between the two methods.

RESULTS

CT-derived PBF, CT-derived PBV, and their associated coefficients of variation (CV) were closely correlated on a region-by-region basis in both the balloon occlusion (Pearson R = 0.91 and 0.73 for animals 1 and 2, respectively; Pearson R = 0.98 and 0.87 for comparison of normalized mean and CV for animals 1 and 2, respectively) and lung inflation studies (Pearson R = 0.94 and 0.74 for animals 3 and 4, respectively; Pearson R = 0.94 and 0.69 for normalized mean and CV for animals 3 and 4, respectively). When accounting for region-based effects, correlations remained highly significant at the P < .001 level.

CONCLUSION

CT-derived PBV heterogeneity is a suitable surrogate for CT-derived PBF heterogeneity.

SCCT expert consensus document on computed tomography imaging before transcatheter aortic valve implantation (TAVI)/transcatheter aortic valve replacement (TAVR)

Computed tomography (CT) plays an important role in the workup of patients who are candidates for implantation of a catheter-based aortic valve, a procedure referred to as transcatheter aortic valve implantation (TAVI) or transcatheter aortic valve replacement (TAVR). Contrast-enhanced CT imaging provides information on the suitability of the peripheral access vessels to accommodate the relatively large sheaths necessary to introduce the prosthesis. CT imaging also provides accurate dimensions of the ascending aorta, aortic root, and aortic annulus which are of importance for prosthesis sizing, and initial data indicate that compared with echocardiographic sizing, CT-based sizing of the prosthesis may lead to better results for postprocedural aortic valve regurgitation. Finally, CT permits one to predict appropriate fluoroscopic projections which are oriented orthogonal to the aortic valve plane. This consensus document provides recommendations about the use of CT imaging in patients scheduled for TAVR/TAVI, including data acquisition, interpretation, and reporting.

Imaging of acute pulmonary embolism

Acute pulmonary thromboembolism (PE) is a cardiovascular emergency associated with significant morbidity and a 5-35 % mortality for untreated pulmonary embolism. If promptly diagnosed and treated, the mortality rate can be significantly reduced. Diagnosis of acute PE continues to be a clinical challenge, with diagnostic imaging playing an important role. This review discusses the clinical challenges of diagnosing acute PE, presents an evidence-based review of the current tests and ever-evolving imaging technology, and highlights special considerations related to radiation dose, contrast media use, and pregnant patients.

Applications of dual-energy CT in urologic imaging: an update

This article discusses modern dual-energy computed tomography (DECT) and the unique material-specific information these scanners can provide. A description of the technical aspects of the various DECT techniques is provided. Specific clinical applications in urologic imaging, including chemical composition of urolithiasis, evaluation of renal masses, detection of urothelial neoplasms, and adrenal adenoma imaging, are discussed. The unique postprocessed image sets, including virtual noncontrast, iodine overlay, and stone composition, are described.