Cardiovascular magnetic resonance.

ardiovascular magnetic resonance (CMR) is a new field in cardiology. CMR has enormous potential because of its major attributes of high image quality and resolution combined with non-ionising radiation and versatility. With recent major technological advances there has been a quantum leap in acquisition speed and image quality that makes its use in ischaemic heart disease robust and clinically valuable. This review will focus on the current clinical indications for CMR, starting with those that are well established, and moving on to the developing indications that are expected to reach clinical maturity soon; finally, the less advanced uses of CMR will be briefly summarised. Fundamentals of cardiovascular magnetic resonance What is magnetic resonance? Magnetic resonance (MR) is a fundamental property of some elements which contain an uneven number of nucleons (protons plus neutrons in the nucleus), and was first described in 1946. These atoms have a property known as net spin, and they absorb radio waves at a resonant frequency which is linearly related to the ambient magnetic field. Nearly all CMR is currently performed at the resonant frequency of hydrogen (63 MHz at 1.5 Tesla) because it is abundant and yields high signal. However, other nuclei can also be interrogated: phosphorus-31, carbon-13, sodium-23, potassium-39, and fluorine-19. These nuclei give lower signal and usually are only examined using MR spectroscopy, a technique which shows the spectrum of the radio signal. Important results in cardiology have been shown using P-31 MR spectroscopy. 1 For clinical MR, a process of image acquisition occurs which has some parallel with echo-cardiography. Energy is transmitted into the heart (radio waves), and after a delay an echo (radio waves) is received. In the intervening period, the hydrogen nucleus becomes excited, and subsequently relaxes. The rate of relaxation is defined by two parameters known as T1 and T2, and these can be manipulated to give varying contrast allowing tissue characterisa-tion. Many other parameters also aVect the signal , such as temperature and oxygen concentration and flow, and these therefore can also be measured using MR. Transmission and reception of the radio waves is achieved using special aerials known as coils. Conversion of the raw data into images requires fast computers and Fourier transformation. What is cardiovascular magnetic resonance? There are essentially three types of imaging sequence which are used in the cardiovascular system: x spin echo imaging—the blood is black and good quality anatomical imaging can be …