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Cardiovascular magnetic resonance is an advanced noninvasive cardiovascular imaging technique that has become well established but continues to evolve. It has some advantages over SPECT myocardial perfusion imaging (MPI) in the evaluation of ischemic heart disease but also has limitations that restrict the potential patient population. Technical advances in hardware and software protocols are unlocking new diagnostic and prognostic possibilities. In many areas of cardiovascular disease, it is the reference standard. The versatility of CMR allows one scan to provide information on cardiovascular structure, function, fibrosis, perfusion, and tissue characterization. CMR is a robust technique for evaluating ischemic heart disease and cardiomyopathies and has a role to play in evaluating other conditions, such as valvular and pericardial disease. We will provide a brief overview of the methods of CMR imaging, discuss its advantages and limitations, and outline its use in specific disease states.
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CMR METHODS AND ADVANTAGES
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Magnetic resonance imaging is performed by having a patient lie in the bore of a large hollow magnet in which a magnetic field is generated, typically at 1.5 Tesla. The hydrogen atoms in the body, predominately in water and fat, behave like magnets and possess "spin." When the hydrogen protons are exposed to the magnetic field they align their spins.1,2 Radiofrequency pulses are generated by the magnet and excite the protons in specific planes of predetermined size and location so that their spins are aligned in a higher-energy state. Relaxation of the hydrogen nuclei to the lower-energy state gives off an electromagnetic signal that is detected by the scanner and processed into an image through a technique known as Fourier transformation.
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There are many substantive advantages of CMR compared with other imaging modalities, including its high spatial resolution and high signal-to-noise ratio. CMR can also provide a 3D assessment of the heart, allowing the selection of any imaging plane, and is not susceptible to attenuation artifacts. Using different CMR sequences can also aid in tissue characterization, allowing multiple aspects of the myocardium to be assessed in one study (Table 29-1).
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LIMITATIONS/CONTRAINDICATIONS
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There are several limitations to the routine use of CMR. Despite recent improvements, there continues to be limited hardware availability, and cardiac-specific software is necessary. CMR remains an expensive imaging modality; this is ...