Cardiac physiology investigated by new methods of imaging.

cardiology. Current methods include chest X-ray, echocardiography, nuclear scintigraphy, and catheterisation-based invasive techniques. The proliferation of imaging has undoubtedly led to major advances in the specialty. If William Harvey were alive today, however, he might be the first to tell us that the current imaging methods have severe limitations and drawbacks, related to issues such as insufficient resolution and information, the use of radiation, and of invasive procedures associated with risk and discomfort. This article explores the concept that the solution to many of these shortcomings may be the application of cardiac magnetic resonance imaging (MRI). Compared to the physics of X-rays or of ultrasound, the physics of magnetic resonance (MR) are substantially more complex.1 In short, atomic nuclei with an uneven number of protons, neutrons or both have the property of a nuclear spin. When these nuclei are exposed to an external magnetic field and are excited by radiofrequency waves they send out a signal in return, termed the free induction decay. These weak radiofrequency signals can be detected by MR coils and used to construct an image. Application of a magnetic field strength gradient allows imaging of the spatial distribution of the nuclear spins. The contrast of an MR image depends on spin density (the number of nuclei susceptible to MR imaging in the tissue), the relaxation parameters T1 and T2, the effects of flow and the type of pulse sequence used. A pulse sequence is a pattern of radiofrequency waves used to excite the nuclear spins.