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Magnetic Resonance Imaging is by far the most important diagnostic imaging discovery in medicine since the discovery of X-ray by Roentgen in 1895. The first clinical use of MRI took place in Nottingham University Hospital in England in 1967. Since then, its importance in radiology has been established beyond doubt.
In the early 1980s, MRI began attracting the attention of clinicians by its ability to visualize abnormalities in the posterior fossa of the brain and in the upper cervical spine. Computed Tomography by this time had established itself as an important diagnostic tool in head and body imaging. However, demonstrating lesions in the posterior fossa and the spine has always been a problem with CT because of the bony structures in these regions. This is because CT uses X-rays, unlike MRI which uses magnetism and radio waves.
Over the next few years, MRI gradually became a supplementary modality in diagnostic imaging, complementing CT in CNS investigations. MRI in those days took as long as two hours in one examination, and except for the head and spine which can be fixed and prevented from movement. MRI at that time only contributed minimally to other parts of the body, pictures from the chest and abdomen from MRI were not of diagnostic qualities as they were blurred from respiratory and heart movement. These are problems encountered with the use of low field strength magnets and the then prevailing know-how in technology.
With the introduction of higher field magnets in the mid-1980s, the clinical MRI scanners also equipped with options for faster scan time and much improved pulse sequence techniques. Soon the superiority of MRI over CT was fast realized. In the last 3 to 4 years, improved computer hardware and software gave MRI the means of obtaining good quality images in most other parts of the body.
MRI today is considered the imaging modality of choice for most parts of the body, outstripping CT in the CNS, especially in the spine, musculoskeletal system, neck and mediastinal structures, and the diagnostic usefulness in the cardiovascular diseases and abnormalities become unchallenged.
MRI has great potentials and its developmental progress will be exciting over the next few years. Recent progress resulted in ultrafast scanning time, down to milliseconds range, greatly facilitates the application of MRI fluoroscopy and functional MR imaging. Such advances excite further interest, resulting in further expanding the MRI's utilities and potentials as a clinically relevant diagnostic tools.
WHY IS MRI SUPERIOR?
Today, MRI has become the most effective scanning method in diagnosis because of its ability to display anatomy and any pathological changes with a definition incomparable by any other imaging techniques. MRI has set a new standard in diagnosis and enhances the level of health care in modern medicine.
MRI is superior to other imaging techniques because of the following advantages:
(1) Soft tissue differentiation is excellent giving display and boundary contrast between anatomical structures with unprecedented clarity.
(2) Its high sensitivity to early pathological changes makes early detection possible.
(3) Multi-planar display in any prescribed plane, i.e. axial, sagittal, coronal, and oblique.
(4) Multi-echo techniques giving any desirable number of parameters are carried out with no radiation harmful effects as it uses the magnetic principle.
In MRI studies, the excellent anatomical display and the sensitivity to early pathological changes are obtained in multiple parameters, making MRI the referred choice in the:
display of normal anatomy and developmental or congenital abnormalities,
early detection of diseases with unequaled clarity, and
studies of blood vessels and flow phenomena without the use of contrast.
Furthermore, of late, the importance of MRI in diagnosis is also greatly enhanced by its ability to do functional mapping of the brain.
Clinical usage of MRI
MRI is currently an indispensable diagnostic imaging technique for the early detection of any abnormal changes in tissues and organs, and is effective in every region of the human body.
CENTRAL NERVOUS SYSTEM
In the CNS, MRI by far is the most important and most accurate scanning method available. It allows for the precise demonstration of any space occupying lesion and disease process developing in the brain or spinal cord. These areas are not visualized in the same clarity in the other imaging modalities.
MRI's ability to see changes in the spinal cord, in areas that are insensitive to CT such as in the posterior fossa and in compartments that are only "accessible" with surgery, is of great advantage.
MRA or Arteriogram can be performed in the same sitting as the examination itself. This is done without any harmful effect from radiation or injection of IV contrast, and it can be repeated for follow-up studies for the purpose of post-operation assessment.
MRI is excellent for the study of brain matters, especially white matter disease. Research allowing MRI to do functional studies of the brain are in progress. These capabilities of the MRI help considerably in the treatment and management of patients with convulsions and other conditions like congenital abnormalities.
In the future, the MRI pictures and findings can be used for the purpose of planning and even surgical treatment of tumors and diseases of the brain.
MRI is also very useful in the studies of diseases in the extracranial, neck and postnasal space, with the advantage of its high sensitivity and excellent soft tissue differentiation and the ability to visualize pathology in as many planes and parameters as required by the radiologists.
SPINAL CORD
It is the modality of choice and replaces myelogram. Disc prolapses and intraspinal tumors can be imaged with such vividness and accuracy that it becomes the modality of choice.
ABDOMEN / PELVIS
MRI is a justifiable supplementary examination for liver abnormality. It may be used for further studies and to confirm diagnosis made on Ultrasound and CT of the liver. In dynamic contrast enhanced studies of the liver, this is the gold standard for haemangioma.
MEDIASTINAL AND RETROPERITONEAL SPACE
High quality imaging of masses in the retroperitoneal and mediastinal compartments makes the MRI a useful and non-hazardous imaging modality in oncology, and it is excellent for staging of diseases.
CARDIOVASCULAR SYSTEM
Without the use of invasive method, congenital heart diseases have been evaluated with MRI for many years. Aortic aneurysm is diagnosed with ease, and preferred to the aggressive Angiogram which is difficult in the study of dissecting aneurysms.
With the advent of cine-angiogram and the very ultra-fast millisecond imaging technique, studies of the cardiovascular system will be a very important aspect in cardiology.
Demonstration of the intracranial blood vessels, CSF studies and peripheral blood vessels are now available with details down to 1- 2 millimeters.
MUSCULOSKELETAL SYSTEM
MRI has now become the imaging modality of choice in musculoskeletal disease as it is able to differentiate and define soft tissue changes with clarity. Its ability to image the changes in the bony structures makes MRI essential for the purpose of staging bone tumors for surgery and management.
Joint diseases and periarticular soft tissue abnormalities are now best studied by MRI and this replaces Arthrography to a large extent. In the knees, for example, the MRI is able to demonstrate tear in the meniscus easily and precisely in areas not visible even to the Arthroscope.
Conclusion
MRI has a bright future as it has great potential. Improvements in the techniques, new programs and it other capabilities are emerging rapidly at regular intervals. New advances are recorded almost every few month. MRI has now established beyond doubt its important role in the diagnosis and management of patients.
In conclusion: MRI is an excellent tool for the diagnosis of most diseases in most parts of
the body as having already mentioned above. It is useful in resolving clinical problems. However, it is an expensive investigation and should not be ordered without proper knowledge of it benefits. Justification should be based along the lines set up in the policy and procedure for the use of MRI, so as not to abuse the system as this can easily come about especially when MRI has wide application benefits.
