General Conclusions 539
18 General Conclusions
Jan Bogaert, Steven Dymarkowski, and Andrew M. Taylor
J. Bogaert, MD, P hD; S. Dymarkowski, MD, PhD
Department of Radiology, Gasthuisberg University Hospital, Catholic University of Leuven, Herestraat 49, 3000 Leuven, Belgium
A.M. Taylor, MD , MRCP, FRCR
Cardiothoracic Unit, Institute of Child Health and Great Ormond Street Hospital for Children, London, WC1N 3JH, UK
Imaging has become an essential part of medical decision-making. An arsenal of imaging modalities is currently available, as an extension to the patient‘s clinical examination. Although for cardiac diseases ultrasound is still the first-line imaging modality, the value of magnetic resonance imaging (MRI) is now widely recognized. As we have shown in the textbook, MRI has evolved over the last two decades to become an important and well-validated clinical imaging technique for the heart and great vessels.
In the early years of MRI in medicine, the heart was unquestionably the most difficult organ to in- vestigate. However improvements in MR hardware (e.g., fast gradients, coil design), MR software (e.g., MR sequence design, navigator echoes), and post- processing techniques have made of cardiac MRI not just an imaging technique, but one that com- bines many facets to investigate the cardiovascu- lar system and comes close to the goal of a com- plete examination with a single technical modality.
This property of MRI is not matched by any other technique. Relevant information on all aspects of the heart, including structure, global and regional ventricular function, valve function, flow patterns, myocardial perfusion, myocardial viability, and myocardial metabolism can be obtained in a totally noninvasive manner. The progress in other domains such as coronary artery luminal and wall imaging has been substantial.
In the current climate of rising health care costs, assessment of the cost-effectiveness of cardiac im- aging techniques and their effect on diagnosis, di- agnostic certainty, and patient management and outcome will be of utmost importance in the com- ing years. A description of the actual cost of each
cardiac imaging session is beyond the scope of this book due to the great differences in cost and reim- bursement between countries. The cost-effective- ness of MRI as a cardiac imaging technique is under active evaluation and will determine whether MRI results in significant economic benefits in diagnos- ing cardiac disease.
In Table 18.1 is shown the current clinical position of MRI in comparison to the other cardiac imaging techniques. This table is based on recent literature and, although potentially controversial, it should serve as a guideline for the clinician in choosing the most appropriate diagnostic imaging modality for a particular cardiovascular problem. In our opinion, MRI is the only imaging technique that achieves a satisfactory score for nearly all diagnostic aspects of the heart and great vessels; and, in many respects, MRI can be considered as the gold standard.
General Key Points:
• The key to a successful cardiac MRI examination is a thorough knowledge of cardiac MRI tech- niques, and of cardiac anatomy and physiology in normal and pathological conditions.
• Patient positioning and adequate ECG triggering are crucial to obtain optimal image quality.
• MRI competes well with other cardiac imaging techniques, and should be included in an integra- tive approach to the investigation of patients with cardiovascular disease.
• “Black-blood” and “bright-blood” sequences are used in different imaging planes to study cardiac anatomy and function.
• The heart should not be considered as a purely morphological structure, and the impact of a heart disease on cardiac pump activity must always be determined.
• Cardiac pump activity is a repetitive process of ejection and filling. Both processes can be accu- rately assessed with MRI techniques and should
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Table 18.1. Current clinical position of MR among the cardiac imaging modalities
MRI Echocardiography MDCT Nuclear
cardiology
X-ray angiography
TTE TEE
Cardiac anatomy Pericardium
Thickness +++ + ++ ++ 0 −
Effusion +++ ++ +++ +++ 0 ±
Calcifications + + − +++ 0 +
Inflammation +++ + − ++ + 0
Myocardium
Thickness +++ + ++ +++ − +
Mass +++ + + +++ 0 0
Tissue characterization ++(+) + + + + −
Cardiac cavities
Endoluminal masses +++ ++ +++ ++(+) 0 ++
Volume quantification +++ ++ ++ ++(+) ++ ++
Cardiac valves
Number of leaflets ++ ++ +++ ++ 0 ++
Valve integrity +(+) ++ +++ + 0 +
Perivalvular space (e.g., abscess ) ++ ++ +++ ++ 0 +
Intra- and extracardiac communications
Patent foramen ovale + + +++ − 0 0
Patent ductus arteriosus +(+) ++ ++ ++ 0 ++
Atrial septal defect ++ ++ +++ + 0 ++
Ventricular septal defect ++ ++ +++ ++ 0 +++
Extracardiac spaces +++ +(+) +(+) +++ 0 0
Cardiac function Systolic function
Global +++ ++ ++ ++ ++(+) ++
Regional +++ ++ ++ +(+) ++ +(+)
Stress imaging +++ +++ +++ + ++ ++
Diastolic function ++(+) +++ +++ 0 + +
Strain analysis +++ ++
a− 0 0 0
Valvular function
Valve stenosis ++ +++ ++(+) + 0 ++(+)
Valve regurgitation ++(+) ++ +++ 0 + ++
Myocardial perfusion ++(+) +(+) +(+) + ++(+) −
Myocardial viability
Myocardial edema +++ - - - - -
Myocardial ischemia ++(+) ++ ++ 0 ++(+) +
Myocardial stunning ++ ++ ++ 0 ++ +
Myocardial hibernation ++(+) ++ ++ 0 ++(+) +
Myocardial infarction +++ + + + ++ +
Myocardial metabolism + 0 0 0 +(+) 0
Coronary arteries
Anatomy ++ + − ++ 0 ++(+)
Patency + − − +(+) 0 +++
Calcifications − − − +++ 0 +
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General Conclusions 541
be part of a comprehensive functional evalua- tion.
• Cine-MRI, using the balanced steady-state free- precession (b-SSFP) technique, is currently the gold standard for global and regional functional cardiac analysis, at least if performed and inter- preted adequately.
• MRI tagging techniques enable noninvasive tracking of myocardial deformation during the cardiac cycle.
• Real-time cine-MRI techniques have potential to assess the constant hemodynamic variations of the heart.
• Velocity-encoded cine-MRI techniques enable noninvasive quantification of flow velocities and volumes in vessels and through cardiac valves.
• First-pass myocardial stress perfusion imaging and dobutamine stress MRI are able to detect hemodynamically significant stenoses. Their clinical value in assessing coronary artery disease (CAD) patients is currently underestimated.
• T2-weighted, short-tau inversion-recovery (STIR) fast spin-echo MRI is unique in detecting myo- cardial edema.
• Contrast-enhanced inversion-recovery (CE-IR) MRI with late or delayed imaging is currently the best approach to image myocardial infarction and scarring.
• The same approach can be used to evaluate a variety of nonischemic myocardial diseases (e.g., myocarditis, myocardial fibrosis, infiltrative dis- eases) and pericardial diseases (e.g., pericardial inflammation).
• Coronary MR angiography is indicated to explore the origin and proximal course of the epicardial coronary arteries. Detection and quantification of coronary artery stenoses, as well as wall imag- ing and plaque characterization, are possible but as yet unrefined for clinical use.
• Cardiac MRI is a highly valuable technique to study cardiac masses. Cardiac thrombi can be best assessed using a combination of cine-MRI and CE-IR MRI techniques.
• The contribution of MRI in valvular heart disease is three-fold: morphological evaluation, func- tional evaluation of the severity, and assessment of the impact of a valvular lesion on ventricular function.
• The role of MRI in congenital heart disease is mainly in the postoperative assessment and follow-up of patients.
• MRI and computed tomography (CT) are cur- rently the preferred techniques with which to assess the thoracic great vessels.
• Interventional MR (combined X-radiation and MRI, XMR) is a new and highly promising tool that will soon find its way to clinical use.
Table 18.1. Current clinical position of MR among the cardiac imaging modalities
MRI Echocardiography MDCT Nuclear
cardiology
X-ray angiography
TTE TEE
Wall imaging and characterization + − −(+++)
b+(+) 0 0
Flow and flow reserve + − −(+++)
b− + +
Great vessels
Anatomy +++ +(+) ++(+) +++ 0 +++
Vessel wall
Thickness +++ + ++ +++ 0 +
Integrity ++(+) + ++ ++ + −
Vessel lumen +++ + ++(+) +++ 0 +++
Flow pattern +++ + ++(+) + 0 ++
+++, Excellent; ++, good; +, average; −, poor; 0, not possible
a
Tissue Doppler imaging
b
Intracoronary echo-Doppler
Abbreviations: MDCT, multi-detector computed tomography; MRI, magnetic resonance imaging; TEE, transesophageal echocardiogra- phy; TTE, transthoracic echocardiography
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