Role of magnetic resonance imaging in aortic disease

MRI is a non-invasive imaging technique that permits the most comprehensive study of aortic diseases. It offers morphological, functional and biochemical information. Conventional ECG-gated spin-echo imaging, cine gradient-echo and contrast-enhanced 3D MR angiography have earned MRI the reputation of being the ideal tool for evaluating the aorta. The phase-contrast imaging technique enables the assessment of flow in the great vessels. MRI can be used to define the location and extent of aneurysms, dissections and aortic wall ulceration. This is the best technique to demonstrate areas of wall thickening related to aortitis or intramural haematoma. MRI may also be used as a tool to study aortic physiology by assessment of elastic aortic properties, stiffness and aortic wall shear stress. MRI is particularly useful in patients with either contraindications to iodinated contrast material or in those with known aneurysms who require sequential follow-up.

The roles of CMR and MSCT in adult congenital heart disease

Both CMR and MSCT give almost unrestricted access to intra-thoracic structures, whereas ultrasonic access may be limited in ACHD patients. MSCT, generally using intravascular contrast, gives superior spatial resolution more rapidly than CMR, although the radiation dose is a concern in younger patients who may require repeated studies. MSCT gives better visualisation of epicardial coronary arteries and small collateral vessels, and can show conduit calcification or stent location clearly. It provides an alternative to CMR in patients with a pacemaker or ICD. CMR offers unrivalled versatility of acquisition methods without ionizing radiation, enabling measurements of biventricular function, flow, myocardial viability, angiography and more. A dedicated CMR service should be available in a centre specializing in ACHD care. Appropriate understanding is needed for the evaluation of congenitally and surgically altered circulatory function, for example after Fontan operations, surgery for transposition of the great arteries or tetralogy of Fallot.

Cardiac resynchronization therapy: optimization and follow-up

Cardiac imaging techniques have an important role in the follow-up of patients undergoing cardiac resynchronization therapy (CRT) as they provide objective evidence of changes in cardiac dimensions and function. The role of echocardiography is well established in the assessment of left ventricular reverse remodelling and the evaluation of secondary (functional) mitral regurgitation. Additionally, echocardiography might be used for optimizing the programming of atrio-ventricular (AV) and inter-ventricular (VV) delays of current CRT devices. Acute benefits from this optimization have been demonstrated, but longer follow-up studies have failed to show a clear benefit of optimized CRT on top of simultaneous biventricular pacing on the outcome of patients with CRT. This chapter reviews the role of imaging in assessing follow-up and outcome of patients undergoing CRT, as well as the rationale, the methods used, and the clinical impact of optimization of the programming of CRT devices.

Evaluation of diastolic LV function

The evaluation of diastolic function in patients with reduced (HFREF) or preserved (HFPEF) left ventricular (LV) ejection fraction is important as it carries both diagnostic and prognostic information. In daily practice, this is most frequently done by standard echocardiographic techniques, including the evaluation of LV mass and LA volumes, as well as transmitral and pulmonary venous PW Doppler, CW Doppler for evaluation of the IVRT, and tissue Doppler imaging of the septal and lateral annular velocities. This permits grading the severity of diastolic dysfunction, which is related to outcome and may be used to estimate LV filling pressures. The latter needs further validation, especially in patients with HFPEF. Newer echocardiographic and cardiac magnetic resonance techniques, including myocardial deformation measurements during diastole, LV twist and untwisting, and parameters of left atrial function, are promising and will hopefully in the future help clinicians to make a more precise evaluation of diastolic function and filling pressures in heart failure patients.

Endocarditis

Imaging plays a key role in the assessment of infective endocarditis. Echocardiography, particularly transoesophageal echocardiography, gives useful information concerning the diagnosis of infective endocarditis, the assessment of the severity of the disease, the prediction of short-term and long-term prognosis, and the follow-up of patients under specific antibiotic therapy. Other imaging techniques, including magnetic resonance imaging, Computed tomography (CT) scan, and invasive angiography, are of limited value for the diagnosis of infective endocarditis, but are useful for the diagnosis and management of its complications. FDG PET/CT imaging seems the most promising new imaging technique, particularly for the diagnosis of prosthetic valve endocarditis

Aortic regurgitation

The workup of patients with aortic regurgitation is routinely based on echocardiography and includes a detailed morphologic assessment of the aortic valve with the determination of disease aetiology. The quantification of aortic regurgitation is based on an integration of qualitative and quantitative parameters. Haemodynamic consequences of aortic valve disease on left ventricular size, hypertrophy, and function, as well as potentially coexisting valve lesions, are assessed. Predictors of outcome and indications for surgery are substantially defined by echocardiographic parameters. Cardiac magnetic resonance has become an important complementary technique, both for the quantification of regurgitant severity and for the assessment of ventricular function. While the proximal parts of the ascending aorta are routinely visualized by transthoracic echocardiography, transoesophageal echocardiography (TOE) and in particular cardiac magnetic resonance (CMR) and cardiac computed tomography (CT) allow a more comprehensive assessment of the thoracic aorta.

Aortic valve stenosis

Echocardiography is the method of choice for the diagnosis, assessment of morphology, and aetiology, as well as quantification of aortic valve stenosis. It permits the additional evaluation of the consequences on left ventricular size and, function, wall thickness, mitral valve (functional regurgitation).Haemodynamic assessment can be performed by Doppler echocardiography providing transvalvular gradients and valve areas can be determined by the continuity equation. Recently, MR and CT imaging have gained importance for assessment of valve morphology, ventricular function, and associated aortic disease. In current practice their role in quantifying severity of valve stenosis, however, remains limited. It is important to be aware of the specific limitations and pitfalls of the various measurements. Final judgement should be based on an integrated approach involving all available information. Finally, imaging techniques provide important prognostic information in aortic valve stenosis and have a fundamental impact on the decision making process in clinical practice.

Hybrid imaging: combination of PET, SPECT, CT, and MRI

Hybrid scanners combining PET or SPECT with high resolution multi-detector CT are becoming the standard for almost all commercially available nuclear imaging systems. In addition, the newest generation of scanners offers combination of PET with MRI. Hybrid scanners offer the ability to assess the anatomy of the heart and coronary arteries, and the functional evaluation either at stress (for assessment of induced ischaemia), or at rest (for viability) in association with the left ventricular systolic function. Therefore, combining functional information with anatomy by using hybrid systems is appealing.

New developments in echocardiography/advanced echocardiography

The first part of this chapter illustrates how real-time three-dimensional echocardiography (3DE) has significantly improved and expanded the diagnostic efficacy of echocardiography providing anatomical and functional visualization of cardiac structures. The reader is introduced to the different applications of 3DE, to the different acquisition and display techniques of a 3D datasets and to the main artefacts which can possibly occur. The second part covers two-dimensional echocardiographic (2DE) and 3DE techniques for the assessment of global and regional myocardial function, its different parameters with typical findings and normal values. Clinical applications of the different techniques are explained focusing on the assessment of diastolic function, global systolic function, regional systolic function and dyssynchrony. Speckle tracking and Tissue Doppler are illustrated and their advantages and disadvantages discussed. Concise and practical information are provided to the reader to better understand and improve data acquisition, post-processing and data interpretation.

Cardiac masses and tumours

Cardiac tumours represent a rare but important cause of morbidity and mortality in clinical cardiology and are often challenging in diagnostic cardiac imaging. There is a broad spectrum of differential diagnosis for cardiac masses. This chapter is mainly focused on the diagnosis of primary and secondary cardiac tumours and intra-cardiac thrombi. Diagnostic imaging of cardiac tumours provides important clinical decision-making information, such as origin, size, extension, morphology, and mobility of the tumour, involvement of cardiac chambers, valves, myocardium and pericardium, invasiveness, vascularization, and tissue characterization. Echocardiography is usually the first imaging modality providing high sensitivity in detecting cardiac masses, particularly by transoesophageal approach, and detailed analysis of mass characteristics by the use of different imaging modalities, including 3D imaging, tissue Doppler imaging, and contrast imaging.