Clinical utilities of cardiac MRI

Cardiac magnetic resonance imaging (MRI) has emerged as a useful research and a clinical tool in cardiology. Following the technical improvements of cardiac MRI in the late 1990s enthusiasm arose for the future of cardiac MRI. Slogans such as “One stop shop” appeared suggesting that cardiac MRI might be a single solution to the complex diagnostic problems in cardiology. The early phase of excitement has been replaced today by a more balanced view on the usefulness of MRI in the diagnostic armamentarium of cardiology.

Cardiac MRI is a non-invasive, non-ionising imaging technique, with high spatial resolution, that is considered to be the gold standard for morphological assessment of the heart, as well as the assessment of right and left ventricular systolic and diastolic function and mass.

1- Current indications for cardiac MRI

Cardiac MRI is never the first diagnostic approach in patients with heart related problems. Initially, these patients should be assessed by

• A careful review of clinical history,
• Rest ECG and clinical examination,
• Frequently followed by transthoracic echocardiography,
• Stress test and,
• A cardiac catherisation (if indicated).
• Cardiac MRI may be indicated in a subgroup of patients, for which these examinations do not provide adequate diagnostic information.

Due to its ability to characterise tissue and provide morphological definition of scar, inflammation and necrosis (late enhancement technique), cardiac MRI is well established for the diagnosis and follow-up of cardiomyopathies.

• Cardiac MRI can separate ischemic from non-ischemic cardiomyopathy, and is the most important imaging modality for the diagnosis and follow-up of patients with myocarditis.
• Cardiac MRI is increasingly important in the diagnosis and follow-up of patients with congenital heart disease, usually as a complement to echocardiography.
• In valvular disease, echocardiography remains the imaging modality of choice, but cardiac MRI is increasingly used as an aid to determine the timing for surgery.
• Cardiac MRI is the most accurate modality for the description of myocardial infarction, both in the acute and chronic phase. Cardiac MRI is important for the assessment of myocardial hibernation/viability. Infarct detection can be used to predict functional recovery, as well as overall risk and prognosis. The performance of cardiac MRI in the assessment of myocardial perfusion and ischemia is more detailed to that of SPECT.
• In addition, cardiac MRI is useful for the assessment of pericardial disease and cardiac tumors.

2- Common conditions for which cardiac MRI is indicated

• Assessment of myocardial function following myocardial infarction
• Assessment of myocardial viability/hibernation 
• Myocarditis 
• Cardiomyopathies 
• Congenital heart disease 
• Valvular disease 
• Pericardial disease 
• Myocardial tumor 
• Clinical research

3- Coronary MRI would be an alternative to ionising radiation from CT scans, but needs to be improved. Cardiac MRI is the modality of choice for the assessment of myocardial perfusion

At the moment, multislice CT is a better modality than cardiac MRI for the non invasive assessment of coronary arteries. However, CT scans are fast and yield high-quality diagnostic information but at the cost of exposure to ionising radiation with a subsequent increase in risk of cancer. Future developments in CT scanners are likely to reduce radiation burden. Nevertheless considering the progressive nature of coronary artery disease, there is a need for accurate non-ionising alternatives that can be used for repeated assessments. MRI is a non-ionising alternative for the visualizing of coronary anatomy but coronary MRI still needs to be improved for it to become part of the diagnostic routine.

Cardiac MRI provides a competitive alternative to SPECT for the assessment of myocardial perfusion. Therefore, to reduce exposure to ionising radiation, cardiac MRI is the modality of choice for the assessment of myocardial perfusion in patients without contraindications to cardiac MRI.

4- Disadvantages of cardiac MRI

Although cardiac MRI is a versatile and highly accurate imaging modality, there are several pratical limitations to the use of the technique.

Compared with CT scans and cardiac ultrasound, cardiac MRI examinations are time-consuming. Although routine examinations including perfusion and late enhancement can be completed within 25 min, time is needed for the preparation of patients and getting them in and out of the scanner. In patients with more complex diagnostic problems, or when there is a problem with image acquisition due to irregular heart rate or limited patient cooperation during breath holds, prolonged examination durations can be expected.

Most routine cardiac MRI techniques are dependent upon image acquisition during breathhold to eliminate movement artefacts. Both image quality and the duration of the examination are highly dependent upon the patient’s ability to do repeated breathhold of 5-10 sec. In patients unable to perform breatholds correctly, a poor image quality must be anticipated. 

Patients frequently have implanted pacemakers and cardiac devices. The major problem with devices in an MRI scanner, is heating of the tip of the lead(s). There is an increasing focus on these problems among the producers, and efforts are made to encounter these problems in the development of new gear. In contrast to devices, neither coronary stents, nor mechanical valves are considered contraindications against cardiac MRI examinations.

Arrhythmia was previously a problem for the quality of the images. Newer and fast imaging sequences, and improved arrhythmia rejection programming have reduced this problem, however, highly irregular rhythms may be a challenge to image quality.

Gadolinium based contrast agents are the main stay in the “late enhancement” and first pass techniques that allow assessment of myocardial perfusion and damage. In the past few years, there have been reports on nephrogenic systemic fibrosis related to the use of gadolinium-based contrast media in patients with renal failure. These contrast media should therefore are not to be used in patients with estimated GFR less than 30ml/min.

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.