Basics of MRI (original) (raw)

Understanding MRI: basic MR physics for physicians

Postgraduate Medical Journal, 2013

More frequently hospital clinicians are reviewing images from MR studies of their patients before seeking formal radiological opinion. This practice is driven by a multitude of factors, including an increased demand placed on hospital services, the wide availability of the picture archiving and communication system, time pressures for patient treatment (eg, in the management of acute stroke) and an inherent desire for the clinician to learn. Knowledge of the basic physical principles behind MRI is essential for correct image interpretation. This article, written for the general hospital physician, describes the basic physics of MRI taking into account the machinery, contrast weighting, spin-and gradientecho techniques and pertinent safety issues. Examples provided are primarily referenced to neuroradiology reflecting the subspecialty for which MR currently has the greatest clinical application.

Magnetic Resonance Imaging MRI - An Overview

2007

Magnetic Resonance Imaging or MRI is a modern diagnostic tool for acquiring information from the interior of a human body. MRI can create three-dimensional images of a human organ without hurting t ...

Magnetic resonance imaging in medicine

Physics Education, 2001

Over the past twenty years, magnetic resonance imaging (MRI) has become one of the most important imaging modalities available to clinical medicine. It offers great technical flexibility, and is free of the hazards associated with ionizing radiation. In addition to its role as a routine imaging technique with a growing range of clinical applications, the pace of development in MRI methodology remains high, and new ideas with significant potential emerge on a regular basis. MRI is a prime example of the spin-off benefits of basic science, and is an area of medicine in which physical science continues to play a major role, both in supporting clinical applications and in developing new techniques. This article presents a brief history of MRI and an overview of the underlying physics, followed by a short survey of current and emerging clinical applications.

Principles of magnetic resonance imaging

2004

The concepts of magnetic resonance imaging are reviewed and its application to medical and biological systems is described. The magnetic resonance phenomenon can be described by both classical and quantum mechanical approaches. Magnetic resonance imaging is based on the techniques of nuclear magnetic resonance. The scanner first aligns the nuclear spins of hydrogen atoms in the patient and starts rotating them in a perfect concert. The nuclei emit maximum-strength electromagnetic waves at the start, but over time the rotating spins get out of synch, simply due to small differences in local magnetic fields. The unsynchronized spins cause the combined electromagnetic signal to decay with time, a phenomenon called relaxation. A slice is selected applying a gradient in a particular direction (X, Y or Z). Magnetic resonance signals are then formed by means of the application of magnetic field gradients along three different directions. Finally, the signals are acquired and Fourier transformed to form a two-dimensional or three-dimensional image. Important parameters determining the image quality such as signal-to-noise ratio, contrast and resolution are discussed too. A review of the most widely utilised imaging techniques is given including ultra-fast sequences.

Magnetic resonance imaging--1: Basic principles of image production.

British Medical Journal, 1991

Nuclear magnetic resonance has been a chemist's tool for determining the chemical composition of samples ever since the phenomenon was first described by Bloch et al and Purcell et al, work that gained them both the Nobel prize in 1952.' 2 Such nuclear magnetic resonance data were, and usually still are, presented as a spectrum which, crudely speaking, indicates the relative quantities of the atomic nucleus of interest in various molecular configurations. An important impetus for using nuclear magnetic resonance to create images grew out of Damadian's observation that nuclear relaxation times recorded from neoplastic tissues were different from those found in normal tissues.' Damadian's early work, however, provided numerical data without spatial information, but unless there is spatial information there can be no image. The vital breakthrough for creating images is credited to Paul Lauterbur. He suggested a method of localising the source of signals,4 which led to a technological explosion, pioneered-largely by British research groups in Nottingham,' Aberdeen6 and the Hammersmith Hospital in London.78 It switched the emphasis of magnetic resonance from numerical information to anatomical images. Relaxation times, even when spatially localised, were soon recognised to be of limited significance because many different pathological processes alter them similarly, and considerable overlap often exists between the values obtained from normal and pathological tissues. But it became abundantly clear that magnetic resonance imaging could provide exquisite anatomical information that rivalled, and in many cases exceeded, the capability of x ray computed tomography. Magnetic resonance imaging could also produce images without the risks of ionising radiation and with a minimum of discomfort to the patient.