Q. Magnetic Resonance Imaging (MRI) is useful to doctors for medical treatment. Explain in what way this facility has been provided to the public. [45 BPSC/2002]
Ans:
Magnetic Resonance Imagingis a non-invasive imaging technology that produces three dimensional detailed anatomical images. It is often used for disease detection, diagnosis, and treatment monitoring.
MRIs employ powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field. When a radiofrequency current is then pulsed through the patient, the protons are stimulated, and spin out of equilibrium, straining against the pull of the magnetic field. When the radiofrequency field is turned off, the MRI sensors are able to detect the energy released as the protons realign with the magnetic field.
The time it takes for the protons to realign with the magnetic field, as well as the amount of energy released, changes depending on the environment and the chemical nature of the molecules. Physicians are able to tell the difference between various types of tissues based on these magnetic properties.
MRI is useful to doctors for medical treatment:
- MRI scanners are particularly well suited to image the non-bony parts or soft tissues of the body. The brain, spinal cord and nerves, as well as muscles, ligaments, and tendons are seen much more clearly with MRI than with regular x-rays and CT; for this reason MRI is often used to image knee and shoulder injuries.
- In the brain, MRI can differentiate between white matter and grey matter and can also be used to diagnose aneurysms and tumors.
- MRI affects diagnosis and treatment in many specialties although the effect on improved health outcomes is disputed in certain cases.
- MRI is the investigative tool of choice for neurological cancers over CT, as it offers better visualization of the posterior cranial fossa, containing the brainstem and the cerebellum.
- The contrast provided between grey and white matter makes MRI the best choice for many conditions of the central nervous system, dementia, cerebrovascular disease, infectious diseases, Alzheimer’s disease and epilepsy.
- Cardiac MRI is complementary to other imaging techniques such as cardiac CT.
- It can be used to assess the structure and the function of the heart.
- MRI techniques can be used for diagnostic imaging of systemic muscle diseases.
- Real-time MRI refers to the continuous imaging of moving objects (such as the heart) in real time. Real-time MRI is likely to add important information on diseases of the heart and the joints, and in many cases may make MRI examinations easier and more comfortable for patients.
- The lack of harmful effects on the patient and the operator make MRI well-suited for interventional radiology, where the images produced by an MRI scanner guide minimally invasive procedures. Such procedures use no ferromagnetic instruments.
- In guided therapy, high-intensity focused ultrasound (HIFU) beams are focused on a tissue, that are controlled using MR thermal imaging. Due to the high energy at the focus, the temperature rises to above 65 °C (150 °F) which completely destroys the tissue.
This facility has been provided to the public in following way.
- MRI imaging facilities are available at the diagnostic centre or multispeciality hospitals which has the MRI scanner
- To obtain an MRI image, a patient taken to the scanner table to lie down and is placed inside a large magnet and must remain very still during the imaging process in order not to blur the image.
- A person will probably be unable to have an MRI if they have any metal inside their body e.g. pacemakers, shrapnel, and metallic foreign bodies in the eyes.
- The radiologist and the MRI technician are involved in the process of MRI imaging.
Because MRI does not use x-rays or other radiation, so it is extremely rare that a patient will experience side effects. It is the imaging modality of choice when frequent imaging is required for diagnosis or therapy, especially in the brain. However, MRI is more expensive than x-ray imaging or CT scanning. Further, injuries may occur as a result of failed safety procedures or human error. Strong magnetic field exerts very powerful forces on objects of iron, some steels, and other magnetizable objects. So, patients should notify their physicians of any form of medical or implant prior to an MR scan.
Medical societies recommend against overuse. They recommend that MRI not be the first procedure for creating a plan to diagnose or manage a patient’s complaint.
