Current techniques for MR imaging of atherosclerosis

Diagnostic Methods of Atherosclerotic Plaque and the Assessment of Its Prognostic Significance-A Narrative Review

Cardiovascular diseases (CVD) are a leading cause of death. The most notable cause of CVD is an atherosclerotic plaque. The aim of this review is to provide an overview of different diagnostic methods for atherosclerotic plaque relevant to the assessment of cardiovascular risk. The methods can be divided into invasive and non-invasive. This review focuses on non-invasive with attention paid to ultrasonography, contrast-enhanced ultrasonography, intravascular ultrasonography, and assessment of intima-media complex, coronary computed tomography angiography, and magnetic resonance. In the review, we discuss a number of Artificial Intelligence technologies that support plaque imaging.

Clinical physiology: the crucial role of MRI in evaluation of peripheral artery disease

Peripheral artery disease (PAD) is a common vascular disease that primarily affects the lower limbs and is defined by the constriction or blockage of peripheral arteries and may involve microvascular dysfunction and tissue injury. Patients with diabetes have more prominent disease of microcirculation and develop peripheral neuropathy, autonomic dysfunction, and medial vascular calcification. Early and accurate diagnosis of PAD and disease characterization are essential for personalized management and therapy planning. Magnetic resonance imaging (MRI) provides excellent soft tissue contrast and multiplanar imaging capabilities and is useful as a noninvasive imaging tool in the comprehensive physiological assessment of PAD. This review provides an overview of the current state of the art of MRI in the evaluation and characterization of PAD, including an analysis of the many applicable MR imaging techniques, describing the advantages and disadvantages of each approach. We also present recent developments, future clinical applications, and future MRI directions in assessing PAD. The development of new MR imaging technologies and applications in preclinical models with translation to clinical research holds considerable potential for improving the understanding of the pathophysiology of PAD and clinical applications for improving diagnostic precision, risk stratification, and treatment outcomes in patients with PAD.

The Role of Imaging in Peripheral Interventions

Patient evaluation is critical to identify and quantitate patient's disease. Aside from the patient's history and physical examination, imaging can help confirm and determine the extent of disease. Imaging can aid in treatment planning once the decision to proceed to intervention has been made. This chapter will discuss the role of imaging before and after peripheral arterial interventions and how it may improve intervention outcomes. It will discuss the value of the arterial noninvasive examinations (ankle-brachial index, toe-brachial index, pulse volume recordings, and arterial duplex ultrasound), computed tomographic angiograms, magnetic resonance angiogram, and intravascular ultrasound.

Detection and Prediction of Peripheral Arterial Plaque Using Vessel Wall MR in Patients with Diabetes

Objectives

To evaluate the predictive performance of a newly developed delay alternating with nutation for tailored excitation (DANTE) pulse sequence for detecting lower extremity artery wall morphology and distribution in patients with peripheral artery disease (PAD) with diabetes.

Methods

Seventy-four PAD patients diagnosed according to 2011 WHO criteria were enrolled, who has diabetic diagnosis by 1999 WHO diabetes criteria. All patients received sequential DANTE, T2WI, DANTE-enhance, and CE-MRA scans. The images consisted of three parts: the iliac artery (segment 1), femoral artery (segment 2), and popliteal artery (segment 3). Regions of interest (ROIs) were drawn on vessels, muscle, and background, and multiple imaging metrics compared between modalities, including image quality score, image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). In the images with a score greater than 2, the lumen area (LA), total vessel area (TVA), and vessel thickness (VT) can be identified using semiautomatic image analysis vessel morphology parameters.

Results

All 222 arterial segments were successfully analyzed from 71 patients, after exclusion of three subjects with poor image quality (IQ < 2) in segment 3. There were 54 diabetic and 17 nondiabetic patients. Quantitative analysis shows that the CNR difference between diabetic patients and nondiabetic patients was statistically significant for the same segment, while there was no significant difference among the three segments of SNR and CNR. There were a total of 54 diabetics with plaque distribution data, which showed that LA of segments 1 and 2 was higher than that of segment 3. The VWI of segments 1 and 2 was lower than segment 3. Diabetic was associated with vascular WT 3 and WA3, which increased by 0.23 and 0.83 units on average compared without diabetic foot, respectively. Diabetic foot was associated with vascular WT 3, which increased by 0.37 units on average compared without diabetic foot. The incidence of segment 3 plaques was higher than that of segment 1. The incidence of the left and right plaques was different.

Conclusions

MR imaging using the DANTE and multicontrast sequence could evaluate plaque morphology, and distribution of lower extremities and the occurrence of diabetic foot development are closely related; it may predict occurrence of PAD with diabetic foot.

Loan sharking: changing patterns in, and challenging perceptions of, an abuse of deprivation

BACKGROUND

Illegal high interest lending or 'loan sharking' exploits the vulnerable and has profound negative impacts on individuals and communities. The 2008 UK financial crash and subsequent austerity programme coupled with changes in the consumer credit market have fuelled an increase in predatory lending.

METHODS

The study is a descriptive analysis of demographic, financial, health and behavioural data on 753 victims (2011-2017). A review of the causative factors and potential political, economic and public health responses is analysed.

RESULTS

Most victims were female but males were considerably more indebted. Illegal loans are largely taken out for routine living expenses and over 70% of victims reported other serious debts. Victims are disproportionately poor, unemployed and on benefits but fewer than half have had financial or benefits advice. Despite 90% reporting they would not borrow illegally again, 30% had previously done so from the same shark and over half considered them a friend.

CONCLUSIONS

The increase in loan sharking has coincided with the withdrawal of traditional sub-prime lenders and local welfare assistance schemes, and the low penetration of Credit Unions in many areas. Conventional perceptions of loan sharks and their relationships with victims are largely incorrect. A range of coordinated financial, political and social interventions is required.

Guiding peripheral arterial disease management with magnetic resonance imaging

Peripheral arterial disease (PAD) management is exceptionally challenging. Despite advances in diagnostic and therapeutic technologies, long-term vessel patency and limb salvage rates are limited. Patients with PAD frequently require extensive workup with noninvasive tests and imaging to delineate their disease and help guide appropriate management. Ultrasound and computed tomography are commonly ordered in the workup of PAD. Magnetic resonance imaging (MRI), on the other hand, is less often acknowledged as a useful tool in this disease. Nevertheless, MRI is an important test that can effectively characterize atherosclerotic plaque, assess vessel patency in highly calcified disease, and measure lower extremity perfusion.

MRI for peripheral artery disease: Introductory physics for vascular physicians

Magnetic resonance imaging (MRI) has advanced significantly in the past decade and provides a safe and non-invasive method of evaluating peripheral artery disease (PAD), with and without using exogenous contrast agents. MRI offers a promising alternative for imaging patients but the complexity of MRI can make it less accessible for physicians to understand or use. This article provides a brief introduction to the technical principles of MRI for physicians who manage PAD patients. We discuss the basic principles of how MRI works and tailor the discussion to how MRI can evaluate anatomic characteristics of peripheral arterial lesions.

Manual versus Automated Carotid Artery Plaque Component Segmentation in High and Lower Quality 3.0 Tesla MRI Scans

PURPOSE

To study the interscan reproducibility of manual versus automated segmentation of carotid artery plaque components, and the agreement between both methods, in high and lower quality MRI scans.

METHODS

24 patients with 30-70% carotid artery stenosis were planned for 3T carotid MRI, followed by a rescan within 1 month. A multicontrast protocol (T1w,T2w, PDw and TOF sequences) was used. After co-registration and delineation of the lumen and outer wall, segmentation of plaque components (lipid-rich necrotic cores (LRNC) and calcifications) was performed both manually and automated. Scan quality was assessed using a visual quality scale.

RESULTS

Agreement for the detection of LRNC (Cohen's kappa (k) is 0.04) and calcification (k = 0.41) between both manual and automated segmentation methods was poor. In the high-quality scans (visual quality score ≥ 3), the agreement between manual and automated segmentation increased to k = 0.55 and k = 0.58 for, respectively, the detection of LRNC and calcification larger than 1 mm2. Both manual and automated analysis showed good interscan reproducibility for the quantification of LRNC (intraclass correlation coefficient (ICC) of 0.94 and 0.80 respectively) and calcified plaque area (ICC of 0.95 and 0.77, respectively).

CONCLUSION

Agreement between manual and automated segmentation of LRNC and calcifications was poor, despite a good interscan reproducibility of both methods. The agreement between both methods increased to moderate in high quality scans. These findings indicate that image quality is a critical determinant of the performance of both manual and automated segmentation of carotid artery plaque components.

Intravascular MRI for Plaque Characterization: Are We Close to Reality?

Non-invasive external magnetic resonance imaging (MRI) of large vessel atherosclerosis is a robust and promising imaging modality that can be applied for the evaluation of the atherosclerotic process in large vessels. However, it requires expertise for setup and time for data acquisition and analysis. Intravascular MRI is a promising tool, but its use remains at the pre-clinical stage within selected research groups. In this review, the current status and future role of intravascular MRI for atherosclerotic plaque characterization are summarized, along with important challenges which will be necessary to overcome prior to the wide adoption of this technique.

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.

MRI in Lower Extremity Peripheral Arterial Disease: Recent Advancements

Evaluation of peripheral arterial disease by cardiovascular magnetic resonance imaging continues to develop. Of the clinical diagnostics tests currently available, magnetic resonance angiography is well established as one of the preferred techniques for determining areas of arterial occlusive disease affecting the lower extremities. Despite this, there have been new developments in non-gadolinium based contrast-enhanced studies as well as testing done at higher field strength scanners. In the research arena, magnetic resonance spectroscopy, calf muscle perfusion imaging and atherosclerotic plaque evaluation all have made significant advancements over the last year. These techniques are gaining traction as surrogate endpoints in clinical trials of novel therapeutics aimed at alleviating symptoms in patients with peripheral arterial disease.

[Clinical indications for the use of cardiac MRI. By the SIRM Study Group on Cardiac Imaging]

Cardiac magnetic resonance (CMR) is considered an useful method in the evaluation of many cardiac disorders. Based on our experience and available literature, we wrote a document as a guiding tool in the clinical use of CMR. Synthetically we describe different cardiac disorders and express for each one a classification, I to IV, depending on the significance of diagnostic information expected.

Usefulness of cardiovascular magnetic resonance imaging of the superficial femoral artery for screening patients with diabetes mellitus for atherosclerosis

Cardiovascular magnetic resonance (CMR) of the superficial femoral artery (SFA) allows direct and noninvasive visualization of atherosclerotic plaque burden. We examined atherosclerosis in 3 groups of patients without history or symptoms of peripheral arterial disease with varying expected burdens: those with diabetes mellitus (DM) and known coronary artery disease (CAD) (n = 24), those with DM and a high prevalence of CAD risk factors (n = 20), and controls of similar age without DM or CAD and few CAD risk factors (n = 15). We also assessed the diagnostic accuracy of this technique to differentiate among these 3 groups. T1-weighted spin-echocardiographic images were used to measure mean wall thickness (WT) and total wall volume indexed to total vessel volume. Diagnostic accuracy was assessed by area under receiver operating characteristics curve analysis. Patients with DM plus risk factors and DM plus CAD had higher mean WT (1.28 and 1.37 mm) and mean indexed wall volume (0.53 and 0.56) compared to controls (mean WT 1.16 mm and mean indexed wall volume 0.45; p <0.010 for all comparisons). Mean WT and indexed wall volume showed good diagnostic accuracy in discriminating controls from those with DM plus CAD (areas under curve 0.85 and 0.87, respectively, p <0.001), whereas only indexed wall volume discriminated DM plus risk factors from controls (area under curve 0.82, p <0.001). Neither could discriminate between DM plus risk factors and DM plus CAD. In conclusion, patients with DM plus risk factors and DM plus CAD had significantly greater atherosclerotic burden in the SFA on CMR imaging than controls of similar age, with good diagnostic accuracy in differentiating these groups. The high reproducibility and reliability of CMR of the SFA may facilitate improved assessment of atherosclerosis prevalence and progression/regression in studies of novel therapies.

Molecular imaging of matrix metalloproteinases in atherosclerotic plaques

Ischaemic stroke and myocardial infarction often result from the sudden rupture of an atherosclerotic plaque. The subsequent arterial thrombosis occluding the vessel lumen has been widely indicated as the crucial acute event causing peripheral tissue ischaemia. A complex cross-talk between systemic and intraplaque inflammatory mediators has been shown to regulate maturation, remodeling and final rupture of an atherosclerotic plaque. Matrix metalloproteinases (MMPs) are proteolytic enzymes (released by several cell subsets within atherosclerotic plaques), which favour atherogenesis and increase plaque vulnerability. Thus, the assessment of intraplaque levels and activity of MMP might be of pivotal relevance in the evaluation of the risk of rupture. New imaging approaches, focused on the visualisation of inflammation in the vessel wall and plaque, may emerge as tools for individualised risk assessment and prevention of events. In this review, we summarize experimental findings of the currently available invasive and noninvasive imaging techniques, used to detect the presence and activity of MMPs in atherosclerotic plaques.

Carotid MRI: a tool for monitoring individual response to cardiovascular therapy?

Stroke remains a leading cause of morbidity and mortality. While stroke-related mortality has declined over the past four decades, data indicate that the mortality rate has begun to plateau. This change in trend may be attributable to variation in individual response to therapies that were derived from population-based studies. Further reductions in stroke mortality may require individualized care governed by directly monitoring the effects of cardiovascular therapy. In this article, carotid MRI is considered as a tool for monitoring in vivo carotid atherosclerotic disease, a principal etiology of stroke. Carotid MRI has been previously utilized to identify specific plaque features beyond luminal stenosis that are predictive of transient ischemic attack and stroke. To gain perspective on the possibility of monitoring plaque change within the individual, clinical trials and natural history studies that have used serial carotid MRI are considered. Data from these studies indicate that patients with a lipid-rich necrotic core with or without intraplaque hemorrhage may represent the desired phenotype for monitoring treatment effects in the individual. Advances in tissue-specific sequences, acquisition resolution, scan time, and techniques for monitoring inflammation and mechanical forces are expected to enable earlier detection of response to therapy. In so doing, cost-effective multicenter studies can be conducted to confirm the anticipated positive effects on outcomes of using carotid MRI for individualized care in patients with carotid atherosclerosis. In accordance, carotid MRI is poised to emerge as a powerful clinical tool for individualized management of carotid atherosclerotic disease to prevent stroke.

Molecular MRI of Thrombosis

This review focuses on recent approaches in using targeted MRI probes for noninvasive molecular imaging of thrombosis. Probe design strategies are discussed: choice of molecular target; nanoparticle versus small-molecule probe; and gadolinium versus iron oxide imaging reporter. Examples of these different design strategies are chosen from the recent literature. Novel contrast agents used to image direct and indirect binding to fibrin have been described as well as direct binding to activated platelets. Emphasis is placed on probes where utility has been demonstrated in animal models or in human clinical trials.