Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging:

MRI is an important technique for the diagnosis of soft tissues of the human body. It is based on the principle of Nuclear Magnetic Resonance. By chemists, this is often referred to as NMR imaging, but in medicine, the adverb ‘nuclear’ is omitted, and the term used is magnetic resonance imaging (MRI). MRI can be used to distinguish between healthy and diseased tissues. It makes use of the fact that protons present in water, fats, lipids, etc. come to resonance at a given frequency. The images of the various parts of the body can be easily generated because the human body contains 75% water and each water molecule has two hydrogen nuclei. The distribution of water fats and lipids etc. changes due to various diseases in the body. So MRI can detect the body parts affected by the disease.

Technique: In order to get an image in MRI, a varying magnetic field is applied across the body part. The protons in different regions will come to resonance at different frequencies and the intensity of the signal will be proportional to the number of protons at each magnetic field. If the body part is rotated in a different direction, another projection can be determined. Then the data is combined to get a three-dimensional image of the body part.

The concept of MRI can be understood as for example if any container supposes a flask containing water (or, any other solution containing hydrogen nuclei) is placed in a spectrometer and exposed to a uniform magnetic field. In this case, only a single resonance signal is detected. Now the same flask is exposed to a strong uniform magnetic field and the field is developed by the tinted shape.

In this case, the protons in the different regions will resonate at different frequencies. The intensity of the signal will be proportional to the number of protons in each magnetic field. Therefore, the intensity of the signal will be a map of the distribution of protons in a sample. It will be a projection of the number of protons on a line parallel to the field strength.

MRI is also known as tomography (tomos means slice), and MRI is also known as Zeugmatography (Zeugma means to join). In clinical practice, MRI is used to distinguish pathologic tissue (such as brain tumors) from normal tissue. One advantage of an MRI scan is that it is harmless to the patient. It uses strong magnetic fields and non-ionizing radiation in the radio frequency range. MRI provides comparable resolution with far better contrast resolution (the ability to distinguish the differences between two arbitrarily similar but not identical tissues).

Applications of MRI:

(1) Diagnostic Imaging: MRI is extensively used in medical diagnostics to visualize and evaluate a wide range of anatomical structures. It provides detailed images of the brain, spine, joints, organs (such as the heart, liver, and kidneys), and soft tissues. MRI is particularly useful for detecting tumors, lesions, inflammation, and abnormalities in these areas.

(2) Neuroimaging: MRI is widely used in neurology to study the brain and its functioning. It helps in the diagnosis and assessment of conditions such as stroke, brain tumors, multiple sclerosis, Alzheimer’s disease, epilepsy, and other neurological disorders. Functional MRI (fMRI) is a specialized technique that measures brain activity by detecting changes in blood flow, providing insights into brain functions like language processing, memory, and sensory perception.

(3) Orthopedics: MRI is commonly used in orthopedics to examine musculoskeletal structures such as bones, joints, ligaments, tendons, and cartilage. It helps in diagnosing conditions like fractures, joint abnormalities, torn ligaments, cartilage damage, and degenerative diseases like arthritis. MRI can provide valuable information for surgical planning and monitoring treatment effectiveness.

(4) Cardiac Imaging: Cardiac MRI allows for a detailed assessment of the structure and function of the heart. It provides information about the heart’s chambers, valves, blood flow patterns, and the presence of any abnormalities or diseases. Cardiac MRI is particularly useful in diagnosing and monitoring conditions like heart failure, congenital heart defects, myocardial infarction (heart attack), and cardiomyopathies.

(5) Abdominal and Pelvic Imaging: MRI is used to evaluate organs in the abdomen and pelvis, including the liver, kidneys, pancreas, reproductive organs, and gastrointestinal tract. It helps in diagnosing and characterizing tumors, cysts, abscesses, inflammatory bowel diseases, and other conditions affecting these organs.

(6) Breast Imaging: MRI is an important tool for breast cancer diagnosis and staging. It can provide detailed images of breast tissue and help differentiate between benign and malignant lesions. Breast MRI is often used in conjunction with mammography and ultrasound for high-risk individuals and to assess the extent of disease in breast cancer patients.

(7) Vascular Imaging: MRI can provide detailed images of blood vessels and help in the diagnosis of vascular diseases, such as aneurysms, stenosis, and vascular malformations. Magnetic resonance angiography (MRA) is a specialized technique that focuses on visualizing blood vessels and is often used to evaluate the arteries supplying the brain, heart, and other organs.

These are just some of the many applications of MRI. The technology continues to advance, and new techniques are constantly being developed to enhance its capabilities and broaden its range of applications.