MAGNETIC RESONANCE IMAGING (MRI) : AN INTRODUCTION

Nuclear magnetic resonance imaging(NMRI) gained popularity among other imaging systems due its high resolution capacity and chemical specific imaging .NMRI is a non- invasive imaging technique which uses magnetic fields and radio frequency waves for imaging the body .NMR images are maps that show the distribution density of hydrogen nuclei as well as parameters that reflect their motion in cellular water and lipids .The fact that NMR is less hazardous and images can be obtained in any cross section makes it more attractive.


PRINCIPLE OF MRI

MRI works based on the spin and magnetic moment possessed by protons or neutrons of our body .The response of protons(magnetic moment) when placed in an external magnetic field involving excitation of protons in presence of field and relaxation when removed produces two relaxation times T1 and T2. T1 is the spin lattice relaxation of perturbered nucleus(also called longitudinal relaxation) while T2 is the spin -spin relaxation of nucleus(also called transverse relaxation).T2 is smaller than T1 .Variations in relaxation time help in biological discrimination of tissues.


COMPONENTS OF MRI SYSYTEM

The basic components of an MRI system include The Magnet(superconducting magnet),RF transmitter system( RF transmitter, RF amplifier, RF transmitting coils),Detection system, Gradient system for spatial coding ,Patient couch.

ADVANTAGES OF MRI

This type of imaging system provides better contrast between tissues and provides different cross sectional images .Since there is no exposure to ionizing radiations it is least hazardous .With developing technology 3-D imaging using MRI becomes possible that can replace the slice by slice imaging techniques.

DISADVANTAGES OF MRI

The MRI signal strength is very low since it is based on very weak ionizing radiations .The superconducting coils present require cryogenic systems and hence larger cost .It takes longer time to construct images .These are the few disadvantages of MRI imaging. NMRI imaging technique is widely used and is one of the best reliable techniques of imaging.

APPLICATIONS OF MRI

MRI helps in soft tissue discrimination, identify regions of excessive fat deposition, measurement of blood flow ,observe functions myocardium to asses irregularities ,heart diseases etc. Besides these, imaging elements other than hydrogen is very useful .A localized phosphorous chemical shift imaging helps in analyzing metabolic activities while Sodium NMR helps in finding effective fraction of working hearts.