Written by Petros G. Danias, Cardiologist Head of Heart MRI Research and Development Department Ioannis Andreou, Radiologist Director of Imaging Departments HYGEIA – MOTHER
Cardiac Magnetic Tomography was developed in the 1990s and 2000s and today it has reached a level of maturity so that it is now an established diagnostic technique in cardiology with applications in a multitude of diseases.
Cardiac MRI can be performed on 0.5 – 3Tesla scanners, although the majority of clinical examinations are performed on 1.5 and 3Tesla scanners. To obtain the images, special sequences of radio waves are used that stimulate the tissues, transferring energy to them and causing coordination of the rotation of the nucleus of hydrogen atoms.
For cardiac MRI most sequences are synchronized with the subject’s electrocardiographic signal and many of the images require breath holding to minimize respiratory motion. Voluntary or involuntary movement and arrhythmia can introduce artifacts and degrade the diagnostic value of the test.
As a modality, MRI inherently has a very high spatial resolution. This property makes it particularly useful in the study of the anatomy of the heart and the great vessels. High definition requires longer imaging times, which is not conducive to functional imaging. So in cardiac MRI there is usually a balance between speed in imaging and clarity, with a different weight each time in the way the data is obtained, depending on the requested question that we are asked to answer.
Cardiac MRI can acquire images in any axis, plane and direction and thus be applied to assess all aspects of the cardiovascular system (anatomy, tissue composition, functionality, flows, perfusion and viability of the myocardium), finding application in a wide range cardiac patients from neonates and childhood up to the elderly. The test is safe, bloodless and there is no exposure to ionizing radiation. The contrast agents used are not nephrotoxic and the newer generation contrast agents have no clinically significant side effects.
A cardiac MRI scan combines white and black blood sequences, where the blood pool is imaged with high signal (white) or no signal (black). Black blood sequences are used primarily for anatomical imaging, both of the great vessels and of the myocardium and other cardiac structures. Therefore, black blood sequences have application in patients with congenital heart disease, heart tumors, myocarditis and pericarditis, diseases of the great vessels and other extracardiac pathology. With white blood sequences, the functionality of the ventricles and heart valves is studied. Such sequences have applications in the assessment of left and right ventricular function to determine the ejection fraction in patients with coronary artery disease, myocarditis and cardiomyopathy, pericardial disease, valvular disease, congenital heart disease and heart tumors.
More specific applications include the study of phase contrast, where the phase change in the rotation of hydrogen atoms depends on the speed with which they move in a graded magnetic field, and thus the measured change is decoded into a flow rate. The method is applicable to valvular diseases and congenital heart diseases. The characteristic magnetic properties of the myocardium can be quantified and characterize the tissue composition of the myocardium, a technique with particular application in patients with myocarditis and cardiomyopathies.
The distribution of paramagnetic contrast substances during their entry into the myocardium is studied in first-pass imaging and is used to assess myocardial perfusion, both at rest and after intravenous administration of vasodilator drugs, to assess coronary reserve blood flow (ischemia). Retention of the contrast agent in the intercellular substance of the myocardium is demonstrated by taking images late after the administration of the contrast agent. This method is the best way to assess the viability of the myocardium and is applicable to patients with coronary heart disease and myocarditis / cardiomyopathies.
Finally, angiographic techniques, with or without intravenous contrast, selectively image the inner lumen of the vessels and are used to image the large vessels as well as the coronary arteries, with application to patients with congenital heart diseases, aortic diseases (aneurysm, dissection, vasculitis, etc.).
Due to the length of the examination, the availability of time and expertise to perform and interpret the examination, cardiac MRI is usually not the initial imaging examination in cardiac patients, but it is often the final one and the one that will determine the optimal therapeutic approach.
Cardiac MRI is internationally regarded as the reference method (gold standard) for measuring ventricular volumes and ejection fraction, tissue characterization of the myocardium and related diseases, quantitative measurement of transvalvular flows and myocardial viability. Assessment of perfusion and flow reserve has similar if not better efficacy than other imaging techniques and its use is increasing rapidly. In the assessment of coronary arteries, magnetic resonance imaging can reliably depict their origin and course, but lags behind CT angiography in terms of discrimination and clinical information for the presence of atherosclerotic coronary disease.
At HYGEIA in 2002, the Cardiac Magnetic Tomography Research and Development Department was established and since then approximately 10,000 examinations have been completed. The analysis of the first 1,000 cases was published in the Hellenic Cardiology Review and cases from our center have been included in a foreign language cardiac MRI journal.
I have worked in the news industry for over 10 years. I have a vast amount of experience in covering health news. I am also an author at News Bulletin 247. I am highly experienced and knowledgeable in this field. I am a hard worker and always deliver quality work. I am a reliable source of information and always provide accurate information.