Few discoveries have truly transformed the modern medical science as much as imaging modalities , beginning from the discovery of “X - rays “in 1895  by Conrad Röntgen  ,  followed by computer processed combination of ‘ X - rays , the Computed Tomography Scan(C T Scan ) , which produced cross sectional images as virtual “slices “of body , allowing us to visualise the internal structures without cut - opening  it  ie non-  invasively , almost like imagining a fantasy !

CT Scan has been a remarkable discovery leading to the award of prestigious Nobel Prize in Physiology or Medicine, in the year 1979 to South Africa born American Physicist Dr Allan Cormack and British electrical engineer, Dr Godfrey Hounsefield .

MRI (Magnetic Resonance Imaging) went further and completely transformed the imaging process as this is extremely safe and equally versatile in acquiring images because it uses  safe - magnetic field gradients and radio waves instead of ionising radiation in CT scanner, to gather the pre requisite informations which is effectively converted into 2D and 3D images in any desired plane.

HISTORY OF MAGNETIC RESONANCE IMAGING  is very fascinating involving thirteen Nobel laureates which includes nine from physics , two each from chemistry and medicine with fair share of controversies ! This was one such discovery where the scientist holding the patent for MRI , Dr Raymond Damidian , was not found good enough for the award of coveted Nobel Prize ,  and who in protest ,brought out a full page advertisement justifying his claim in world famous newspaper ‘New York Times ‘ just before the Nobel prize award ceremony.

Dr Paul C Lauterbur and Sir Peter Mansfield, were awarded the Nobel prize in physiology or Medicine in 2003, for their seminal discovery in giving the ultimate concept and approximate design of modern MRI .

Dr Lauterbur , a chemist by training , postulated that Nuclear Magnetic Resonance ( NMR) property , first elucidated by Nobel laureate Dr Bloch and Dr Purcell , could be used for imaging by introduction of gradients in the magnetic field . He could for the first time take images of a cross section of tubes with ordinary water  ( H2O ) surrounded by heavy water ( D2O) containing isotope of Hydrogen ,Deuterium, which has an additional neutron in its nucleus , making it heavier and distinct in its magnetic resonance property . This ushered in all together a new era of transformation in imaging.

Sir Peter Mansfield ,son of a poor gas fitter , was a renowned physicist from United Kingdom , who could give a remarkable mathematical formula to help  rapidly detect and analyse the humungous data obtained by different gradients making MRI  , a much versatile and faster imaging tool , that it is today !

INDIA CONNECTION

Peter Mansfield, who was professor of physics at Nottingham, went to India to attend a conference on NMR where he heard Paul Lauterbur for the first time and got the much needed insight into the problem which eventually got him to share the Nobel prize by solving the mathematical puzzle brought forward by Dr Lauterbur .

PRINCIPLE BEHIND MAGNETIC RESONANCE IMAGING

Water is the most abundant molecule in all creatures including human beings. This is made up of Hydrogen and oxygen atoms. The nuclei of hydrogen atoms act like microscopic compass needles. Under very strong magnetic field such as 0.5 to 20 Tesla (one Tesla is twenty thousand times of Earth’s magnetic field) , hydrogen atoms present in tissue-  water get oriented to the magnetic field . These hydrogen atoms are subjected to radio waves which take them to a different high energy level and produce resonance. When these atoms return to their relaxation states they emit energy which is captured by the system. These are different for different tissues in health and disease states. Such emitted oscillations  due to relaxation of resonant Hydrogen atoms,  are turned into two or three dimensional image forms with the help of complex mathematical computation known as “Fourier Transform”.

Often it uses injectable contrast of paramagnetic molecule such as ‘Gadolinium’ to alter the local magnetic field in the tissue which further differentiates the normal from diseased.

MRI imaging besides helping the diagnosis also helps in following the progress of the disease through the treatment course without any radiation or possible damage to the body cells. This is a very useful imaging modality especially in pregnant females and in fast growing infants and children, where radiation is especially harmful. Unlike CT scan which doesn’t provide good soft tissue (Tissues other than Bone) details, MRI is very accurate in detailing soft tissues where CT scan gives poor results such as in crowded locations of hind brain and head - neck junctions.

 It is a very useful tool in differentiating white matter from grey matter within the Brain and spinal cord, making it an overwhelming choice of imaging for neuroscientists. Besides Head, neck, spine and CNS (Central Nervous System) parts, it has become a very useful tool for viewing abdominal structures such as Pancreas, Liver, kidney, etc both in health and disease states. Now it has almost replaced many routine surgical procedures such as Diagnostic laparotomy for looking into the diseased abdomen and Arthroscopy (looking into joints by producing a hole ) for injured or diseased  joints .

Many MRI offshoots such as mammography (Breast cancer imaging) Elastography (fatty Liver and cirrhosis) MRCP (pancreas and biliary system obstruction) etc. are very useful technique carried out by using magnetic resonance protocol.

Diffusion MRI  and Functional MRI (f - MRI ) are upcoming additional investigational tools which capture neuronal tracts and blood flow respectively in real time , unearthing many more hidden features of the ‘Mysteriously functioning dynamic Brain and nervous system operations .

Of late MRI is increasingly being used in Forensic and veterinary science studies and occasionally in palaeontological studies (fossil) in certain complex situations.

LIMITATIONS OF MRI

Unlike modern CT Scan, MRI remains quite costly because of heavy maintenance cost due to the necessity of keeping the superconducting magnet functioning in artificially created extreme cold environment effected by liquid Helium and a layer of liquid nitrogen around the magnet.

MRI takes a lot of time to complete the study and is prone to movement related artefacts easily.  These remain cause of worry.  Restless people and children find it difficult to take the test. Also for people who are claustrophobic (fear for narrow space) and dislike loud noises, produced by radio pulse generators or those who have metallic implants in their body, are not advised to take this test . Recently a lot of welcome changes have taken place in their design to address the above problems but it has only enhanced the cost substantially and has restricted its use in resource poor countries.

The Author is former Professor and Head, Department of Medicine, RIMS, Ranchi, Jharkhand.