In the last decade, cardiovascular magnetic resonance imaging (CMR) has changed dramatically. Technical and clinical advances have expanded CMR from primarily a tomographic imaging modality, providing static images of morphology, to one that is dynamic, allowing the rapid, high-resolution imaging of ventricular function, valvular motion, and myocardial perfusion. Moreover, CMR is now considered the gold standard for the assessment of regional and global systolic function, myocardial infarction (MI) and viability, and the assessment of congenital heart disease. The aims of this chapter are to provide an introduction to the technical aspects of CMR and to provide an overview of the clinical applications that are available to clinicians today.
Similar to other medical imaging techniques, magnetic resonance imaging (MRI) acquires images through the transmission and receiving of energy. However, unlike other modalities, MRI offers the capability to modulate both the emitted and received signals so that a multitude of tissue characteristics can be examined and differentiated without the need to change scanner hardware. As a result, from a single imaging session, one could obtain a wealth of information regarding cardiac function and morphology, myocardial perfusion and viability, hemodynamics, large vessel anatomy, and so forth. This information, however, is gathered not from a single long acquisition but rather from multiple short acquisitions, each requiring different pulse sequences (software programs that drive the scanner) with specific operational parameters and optimal settings. Unfortunately, magnetic resonance (MR) vendors may use proprietary names for the same imaging methods and settings.1,2 Thus the goal of this section is to clarify these issues and to provide a simple framework of the technical aspects of MRI. Where appropriate, we will discuss issues specific to CMR.
Magnetic Resonance Physics
It is important to recognize that an MRI scanner is not a single device, but rather consists of multiple separate components. A schematic of these components is shown in Fig. 23–1. A detailed explanation of each of these components is beyond the scope of this chapter; however, a basic understanding is useful. For instance, poor image quality may arise from a variety of problems, and the ability to quickly distinguish those that are complex (eg, hardware malfunction that requires servicing) from those that are simple (eg, motion artifact that can be immediately resolved by better communication with the patient) will be highly valuable.
Components of the MRI scanner. For a CMR study, the operator defines the type of examination and manipulates the imaging parameters from a control computer console using a graphical user interface (1). Software, known as a pulse sequence, is selected from a menu to acquire images that are appropriate for the diagnostic question. The precisely timed radiofrequency (RF) pulses, used to stimulate tissues, are generated by the pulse sequence controller (2), RF transmitter (3), and RF ...
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