Changes in measured size of atherosclerotic plaque calcifications in dual-energy CT of ex vivo carotid endarterectomy specimens: effect of monochromatic keV image reconstructions

The transluminal attenuation gradient does not add diagnostic accuracy to coronary computed tomography

BACKGROUND

A method for improving the accuracy of coronary computed tomography angiography (CCTA) is highly sought after as it would help to avoid unnecessary invasive coronary angiographies. Measurement of the transluminal attenuation gradient (TAG) has been proposed as an alternative to other existing methods, i.e. CT perfusion and CT fractional flow reserve (FFR).

PURPOSE

To evaluate the incremental value of three types of TAG in high-pitch spiral CCTA with invasive FFR measurements as reference.

MATERIAL AND METHODS

TAG was measured using two semi-automatic methods and one manual method. A receiver operating characteristic (ROC) analysis was made to determine the usefulness of TAG alone as well as TAG combined with CCTA for detection of significant coronary artery stenoses defined by an invasive FFR value ≤0.80.

RESULTS

A total of 51 coronary vessels in 37 patients were included in this retrospective study. Hemodynamically significant stenoses were found in 13 vessels according to FFR. The ROC analysis TAG alone resulted in areas under the curve (AUCs) of 0.530 and 0.520 for the semi-automatic TAG and 0.557 for the manual TAG. TAG and CCTA combined resulted in AUCs of 0.567, 0.562 for semi-automatic TAG, and 0.569 for the manual TAG.

CONCLUSION

The results from our study showed no incremental value of TAG measured in single heartbeat CCTA in determining the severity of coronary artery stenosis degrees.

CT imaging features of carotid artery plaque vulnerability

Despite steady advances in medical care, cardiovascular disease remains one of the main causes of death and long-term morbidity worldwide. Up to 30% of strokes are associated with the presence of carotid atherosclerotic plaques. While the degree of stenosis has long been recognized as the main guiding factor in risk stratification and therapeutical decisions, recent evidence suggests that features of unstable, or ‘vulnerable’, plaques offer better prognostication capabilities. This paradigmatic shift has motivated researchers to explore the potentialities of non-invasive diagnostic tools to image not only the lumen, but also the vascular wall and the structural characteristics of the plaque. The present review will offer a panoramic on the imaging modalities currently available to characterize carotid atherosclerotic plaques and, in particular, it will focus on the increasingly important role covered by multidetector computed tomographic angiography.

Evaluating body composition by combining quantitative spectral detector computed tomography and deep learning-based image segmentation

PURPOSE

Aim of this study was to develop and evaluate a software toolkit, which allows for a fully automated body composition analysis in contrast enhanced abdominal computed tomography leveraging the strengths of both, quantitative information from dual energy computed tomography and simple detection and segmentation tasks performed by deep convolutional neuronal networks (DCNN).

METHODS AND MATERIALS

Both, public and private datasets were used to train and validate DCNN. A combination of two DCNN and quantitative thresholding was used to classify axial CT slices to the abdominal region, classify voxels as fat and muscle and to differentiate between subcutaneous and visceral fat. For validation, patients undergoing repetitive examination (±21 days) and patients who underwent concurrent bioelectrical impedance analysis (BIA) were analyzed. Concordance correlation coefficient (CCC), linear regression and Bland-Altman-Analysis were used as statistical tests.

RESULTS

Results provided from the algorithm toolkit were visually validated. The automated classifier was able to extract slices of interest from the full body scans with an accuracy of 98.7 %. DCNN-based segmentation for subcutaneous fat reached a mean dice similarity coefficient of 0.95. CCCs were 0.99 for both muscle and subcutaneous fat and 0.98 for visceral fat in patients undergoing repetitive examinations (n = 48). Further linear regression and Bland-Altman-Analyses suggested good agreement (r²:0.67-0.88) between the software toolkit and patients who underwent concurrent BIA (n = 39).

CONCLUSION

We describe a software toolkit allowing for an accurate analysis of body composition utilizing a combination of DCNN- and threshold-based segmentations from spectral detector computed tomography.

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.

Variation of degree of stenosis quantification using different energy level with dual energy CT scanner

PURPOSE

To investigate the variation in the quantification of the carotid degree of stenosis (DoS) with a dual energy computed tomography (CT), using different energy levels during the image reconstruction.

METHODS

In this retrospective study, 53 subjects (37 males; mean age 67 ± 11 years; age range 47-83 years) studied with a multi-energy CT scanner were included. Datasets were reconstructed on a dedicated workstation and from the CT raw data multiple datasets were generated at the following monochromatic energy levels: 66, 70, 77, and 86 kilo-electronvolt (keV). Two radiologists independently performed all measurements for quantification of the degree of stenosis. Wilcoxon test was used to test the differences between the Hounsifield unit (HU) values in the plaques at different keV.

RESULTS

The Wilcoxon analysis showed a statistically significant difference (p = 0.001) in the DoS assessment among the different keVs selected. The Bland-Altman analysis showed that the DoS difference had a linear relation with the keV difference (the bigger is the difference in keV, the bigger is the variation in DoS) and that for different keVs, the difference in DoS is reduced with its increase.

CONCLUSION

A standardization in the use of the energy level during the image reconstruction should be considered.

Automatic spectral imaging protocol and iterative reconstruction for radiation dose reduction in typical hepatic hemangioma computed tomography with reduced iodine load: a preliminary study

OBJECTIVE

To evaluate the effect of automatic spectral imaging protocol selection (ASIS) and adaptive statistical iterative reconstruction (ASiR) technique in the reduction of radiation and contrast medium dose in typical hepatic hemangioma (HH) dual energy spectral CT (DEsCT).

METHODS

62 patients with suspected HH were randomly divided into two groups equally: Group A, conventional 120-kVp CT with standard iodine load; Group B, DEsCT with ASIS technique and reduced iodine load, two sets of monochromatic spectral images were reconstructed: 69 keV level with 30% ASiR (Group B₁) and 52 keV level with 50% ASiR (Group B₂). The radiation and total iodine dose, quantitative analysis (standard deviation value, contrast-to-noise and contrast enhancement ratio) and qualitative analysis were evaluated.

RESULTS

No difference was observed in the standard deviation values, subjective image noise, and the diagnostic acceptability score among the three groups (p > 0.05). Contrast to noise [Group B₂  vs A, B₁ in arterial phase (AP): 19.51 ± 6.29 vs 15.77 ± 5.93, 11.46 ± 2.84; Group B₂  vs A, B₁ in portal venous phase (PVP): 9.96 ± 2.18 vs 8.19 ± 3.04, 6.01 ± 1.82], contrast enhancement ratio (Group B₂  vs A, B₁ in AP: 6.88 ± 2.01 vs 5.47 ± 2.01, 4.15 ± 1.28; Group B₂  vs A, B₁ in PVP: 5.58 ± 1.02 vs 4.54 ± 1.13, 3.49 ± 0.83), and the lesion conspicuity score (Group B₂  vs A, B₁ in AP: 3.93 ± 0.26 vs 3.45 ± 0.51, 3.10 ± 0.49; Group B₂  vs A, B₁ in PVP: 3.90 ± 0.31 vs 3.48 ± 0.57, 3.14 ± 0.44) for Group B₂ were higher than those in Group A and B₁ (p < 0.05). Compared to Group A, the radiation dose and total iodine dose in Group B were reduced by 30 and 41%, respectively (radiation dose in Group B vs A: 5.53 ± 1.59 vs 7.91± 2.71 mSv; iodine dose in Group B vs A: 18.85 ± 2.88 vs 31.78±3.89 ml; p < 0.05).

CONCLUSION

DEsCT with ASIS and ASiR technique can reduce the radiation dose without image quality degradation as compared to the conventional 120-kVp CT. The monochromatic spectral images at 52 keV level with 50% ASiR allows the reduction in total iodine dose without deteriorating diagnostic performance. Advances in knowledge: ASIS combined with ASiR technique, by using monochromatic spectral images at 52 keV level, represents a feasible imaging protocol to reduce the radiation and total iodine dose in assessment of typical HH.

Evaluation of image quality of coronary artery plaque with rapid kVp-switching dual-energy CT

We evaluated the virtual monochromatic imaging (VMI) energy levels that maximize image quality of each coronary plaque component in dual-energy computed tomography angiography in 495 coronary segments (45 for each energy level). Maximal signal-to-noise ratios were different for plaque, lumen, fat, and surrounding tissue (p<0.05). Maximal contrast-to-noise ratios were observed at 70keV for calcified plaque (CP), non-calcified plaque (NCP), and fat in comparison with the lumen (p<0.05), and 70keV and 120keV for NCP in comparison with fat (p=0.144). VMI demonstrated maximal image quality at different energy levels for each component of coronary artery plaque.

Dual energy computed tomography quantification of carotid plaques calcification: comparison between monochromatic and polychromatic energies with pathology correlation

PURPOSE

We compared carotid plaque calcification detection sensitivity and apparent cross-sectional area on CT as a function of CT beam energy using conventional CT techniques and virtual mono-energetic CT images generated from dual-energy acquisitions.

METHODS & MATERIALS

Five ex-vivo carotid endarterectomy (CEA) specimens were imaged with dual-energy computed tomography. Virtual monochromatic spectrum (VMS) CT images were reconstructed at energies between 40-140 keV. The same specimens were imaged using conventional polyenergetic spectrum (PS) CT with peak beam energies 80, 100, 120, and 140 kVp. The histological calcium areas on each corresponding CEA specimen were traced manually on digitized images of Toluidine-Blue/Basic-Fuchsin stained plastic sections.

RESULTS

40 keV VMS CT images provided high detection sensitivity (97 %) similar to conventional PS CT images (~96 %). The calcification size measured on CT decreased systematically with increasing CT beam energy; the rate of change was larger for the VMS images than for PS images.

CONCLUSION

From a single dual-energy CT, multiple VMS-CT images can be generated, yielding equivalent detection sensitivity and size correlations as conventional PS-CT in CEA calcification imaging. VMS-CT at 80-100 keV provided the most accurate estimates of calcification size, as compared to histology, but detection sensitivity was reduced for smaller calcifications on these images.

KEY POINTS

• Calcifications depicted at 80-100 keV were most similar to the histology standard. • Conventional polychromatic images demonstrated excellent correlation with plaque size at pathology. • Conventional polychromatic images systematically overestimate plaque size. • Plaque calcifications can be missed on high energy monochromatic images.

Clinical applications of spectral molecular imaging: potential and challenges

Spectral molecular imaging is a new X-ray-based imaging technology providing highly specific 3D imaging at high spatial resolution that has the potential to measure disease activity and response to treatment noninvasively. The ability to identify and quantify components of tissue and biomarkers of disease activity derive from the properties of the photon-processing detector. Multiple narrow sections of the energy spectrum are sampled simultaneously, providing a range of energy dependent Hounsfield units. As each material has a specific measurable X-ray spectrum, spectroscopic imaging allows for multiple materials to be quantified and differentiated from each other simultaneously. The technology, currently in its infancy, is set to grow rapidly, much as magnetic resonance did. The critical clinical applications have not yet been established, but it is likely to play a major role in identifying and directing treatment for unstable atherosclerotic plaque, assessing activity and response to treatment of a range of inflammatory diseases, and monitoring biomarkers of cancer and its treatment. If combined with Positron-emission tomography (PET), spectral molecular imaging could have a far greater effective role in cancer diagnosis and treatment monitoring than PET-CT does at present. It is currently used for small animal and specimen imaging. There are many challenges to be overcome before spectral imaging can be introduced into clinical medicine - these include technological improvements to detector design, bonding to the semiconductor layer, image reconstruction and display software, identifying which biomarkers are of most relevance to the disease in question, and accelerating drug discovery enabled by the new capabilities provided by spectral imaging.

Nuclear medicine and the emergency department patient: an illustrative case-based approach

Radiologists are familiar with the use of radiographs, computed tomography, magnetic resonance imaging and ultrasound in the acute clinical setting. However, there are some specific clinical scenarios which may be found in nuclear medicine imaging problem-solving tools. These clinical scenarios and imaging techniques are less frequent, and the referring clinician from the emergency department may not consider these alternatives. It is important for the radiologist to be aware of these techniques to be able to guide the clinician to use those tools, which may result in optimal patient care. In this article, we will discuss those nuclear medicine studies which have application in the setting of an emergency radiology practice.

Multi-modal CT scanning in the evaluation of cerebrovascular disease patients

Ischemic stroke currently represents one of the leading causes of severe disability and mortality in the Western World. Until now, angiography was the most used imaging technique for the detection of the extra-cranial and intracranial vessel pathology. Currently, however, non-invasive imaging tool like ultrasound (US), magnetic resonance (MR) and computed tomography (CT) have proven capable of offering a detailed analysis of the vascular system. CT in particular represents an advanced system to explore the pathology of carotid arteries and intracranial vessels and also offers tools like CT perfusion (CTP) that provides valuable information of the brain's vascular physiology by increasing the stroke diagnostic. In this review, our purpose is to discuss stroke risk prediction and detection using CT.

Microcomputed tomography with diffraction-enhanced imaging for morphologic characterization and quantitative evaluation of microvessel of hepatic fibrosis in rats

Backgroud

Hepatic fibrosis can lead to deformation of vessel morphology and structure. In the present feasibility study, high-resolution computed tomography (CT) using diffraction-enhanced imaging (DEI) was used to represent three-dimensional (3D) vessel microstructures of hepatic fibrosis in rats and to differentiate different stages of hepatic fibrosis using qualitative descriptions and quantitative measurement of microvessels.

Material and Methods

Three typical specimens at different stages, i.e., mild, moderate and severe hepatic fibrosis, were imaged using DEI at 15 keV without contrast agents. The correspondence between DEI-CT images and histopathological findings was determined. The 3D visualizations from different stages of hepatic fibrosis were presented using DEI-CT. Additionally, Qualitative descriptions and quantitative evaluation of vessel features, such as vessel trend, vascular distortion deformation, thrombus formation and texture features on the inner wall of the vessel, were performed.

Results

DEI-CT produced high-resolution images of the vessel microstructures in hepatic fibrosis that corresponded to information on actual structures observed from the histological sections. Combined with the 3D visualization technique, DEI-CT enabled the acquisition of an accurate description of the 3D vessel morphology from different stages of hepatic fibrosis. Qualitative descriptions and quantitative assessment of microvessels demonstrated clear differences between the different stages of hepatic fibrosis. The thrombus inside the vessel of severe liver fibrosis was accurately displayed, and corresponding analysis can provide an exact measurement of vessel stenosis rate.

Conclusions

DEI-CT may allow morphologic descriptions and quantitative evaluation of vessel microstructures from different stages of hepatic fibrosis and can better characterize the various stages of fibrosis progression using high-resolution 3D vessel morphology.

Dual-energy CT spectral and energy weighted data sets: carotid stenosis and plaque detection

RATIONALE AND OBJECTIVES

To evaluate dual-energy computed tomography spectral and energy weighted (W) image data sets concerning carotid stenosis and calcified plaque detection.

MATERIALS AND METHODS

Ninety patients were evaluated using contrast media injection. Energy used for dual-energy computed tomography was tin filter with 140/80 kiloVoltage and effective milli Ampere second was 147.4/270.6. Image reconstruction was performed using D30f kernel and 0.0, 0.3, 0.6, 0.8, 1.0 weightings. Data sets were analyzed using both qualitative and quantitative methods.

RESULTS

The signal-to-noise ratio, contrast-to-noise ratio, and figure-of-merit were significantly higher in 0.6-W compared to 140-kV or 80-kV data (all P < .05). Plaque thickness, span, and longitudinal diameters were different for 140-kV, 0.6-W, and 80-kV data (all P < .05). Stenotic intra-luminal diameter was significantly different among 140 kV, 0.6 W, and 80 kV data (all P < .05). A comparison between 0.6 W and digital subtraction angiography was nonsignificant (P > .05) in normal lumen measurement.

CONCLUSIONS

The dimension of calcified plaque and carotid artery with contrast media decreased with increased energy. The percentage of carotid artery stenosis does not vary with different energy. Care must be taken for procedural planning like sizing of stents. Measured diameters of the 0.6 W were close to digital subtraction angiography; we suggest that planning should be based on the images acquired using 0.6 weighting.

Imaging of the carotid artery vulnerable plaque

Atherosclerosis involving the carotid arteries has a high prevalence in the population worldwide. This condition is significant because accidents of the carotid artery plaque are associated with the development of cerebrovascular events. For this reason, carotid atherosclerotic disease needs to be diagnosed and those determinants that are associated to an increased risk of stroke need to be identified. The degree of stenosis typically has been considered the parameter of choice to determine the therapeutical approach, but several recently published investigations have demonstrated that the degree of luminal stenosis is only an indirect indicator of the atherosclerotic process and that direct assessment of the plaque structure and composition may be key to predict the development of future cerebrovascular ischemic events. The concept of "vulnerable plaque" was born, referring to those plaque's parameters that concur to the instability of the plaque making it more prone to the rupture and distal embolization. The purpose of this review is to describe the imaging characteristics of "vulnerable carotid plaques."