Magnetic resonance imaging (MRI) for medical students

All about MRI for medical students

1. MRI ( MAGNETIC RESONANCE IMAGING) BY- aarushika maurya ; bams – Ii (2020-21)

2. INTRODUCTION Magnetic resonance imaging (MRI) is a medical imaging technique that uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in your body. MRI does not involve X-rays or the use of ionizing radiation, which distinguishes it from CT and PET scans. MRI is a medical application of nuclear magnetic resonance (NMR) which can also be used for imaging in other NMR applications, such as NMR spectroscopy.

3. INTRODUCTION (Contd.) Most MRI machines are large, tube-shaped magnets. When you lie inside an MRI machine, the magnetic field temporarily realigns water molecules in your body. Radio waves cause these aligned atoms to produce faint signals, which are used to create cross-sectional MRI images — like slices in a loaf of bread.

4. PARTS OF MRI MACHINE

5. EARLY HISTORY OF MRI In 1946 Edward Purcell and Felix Bloch  independently discovered Nuclear Magnetic Resonance (NMR) which is the basis for Magnetic Resonance Imaging (MRI) technology. In 1952 Edward Purcell and Felix Bloch shared  The Nobel Prize in Physics for their discovery.

6. MRI is the most frequently used imaging test of the brain and spinal cord. It’s often performed to help diagnose:
Aneurysms of cerebral vessels
Disorders of the eye and inner ear
Multiple sclerosis
Spinal cord disorders
Stroke Tumors Brain injury from trauma MRI of the brain and spinal cord

7. MRI OF BRAIN

8. MRI of the heart and blood vessels MRI that focuses on the heart or blood vessels can assess: Size and function of the heart’s chambers
Thickness and movement of the walls of the heart
Extent of damage caused by heart attacks or heart disease
Structural problems in the aorta, such as aneurysms or dissections
Inflammation or blockages in the blood vessels

9. MRI OF HEART

10. MRI of other internal organs MRI can check for tumors or other abnormalities of many organs in the body, including the following:
Liver and bile ducts
Kidneys
Spleen
Pancreas
Uterus
Ovaries
Prostate

11. MRI OF LIVER Cirrhotic liver shows an enlarged hilar periportal space (defined as a distance between the right portal vein and the posterior edge of segment IV greater than 10 mm)

12. MRI of bones and joints MRI can help evaluate:
Joint abnormalities caused by traumatic or repetitive injuries, such as torn cartilage or ligaments
Disk abnormalities in the spine
Bone infections Tumors of the bones and soft tissues

13. MRI OF BONE

14. MRI of the breasts MRI can be used with mammography to detect breast cancer, particularly in women who have dense breast tissue or who might be at high risk of the disease.

15. INDICATIONS Medical emergencies. A confirmed or suspected medical emergency, such as spinal cord compression, which requires immediate surgical intervention. Developing infections or tumors . Back or neck pain is accompanied by constitutional symptoms (such as loss of appetite, weight loss, fever, chills, shakes, or night pain) that may indicate the presence of a tumor or infection. Radiculopathies . Back or neck pain is caused by suspected spinal nerve compression (radiculopathy) due to conditions such as spinal stenosis or herniated disc(s).

16. INDICATIONS (Contd.) Recurrent or chronic symptoms. There is an incomplete resolution of pain after a series of first-line treatments, such as pain-relieving medications and physical therapy, have been tried for several weeks —and the cause of pain needs further investigation. Progressively worsening symptoms . The pain and related symptoms such as numbness and weakness have progressively worsened despite nonsurgical treatment. Chronicity of fractures. An MRI is not the best diagnostic tool to examine problems in the bones, such as vertebral fractures. However, an MRI scan can detect swelling in the soft bone marrow tissue inside the bone, providing insight into whether a fracture is acute, chronic, benign, or malignant. 1

17. CONTRAINDICATIONS The MRI contrast agent, gadolinium, may cause potential complications in some patients with kidney and/or heart problems and may be contraindicated in such cases.
Patients on dialysis
Patients with a history of kidney disease (renal transplant, single kidney, renal cancer)
Patients with impaired kidney function may develop nephrogenic systemic fibrosis (NSF), a serious illness caused by the improper breakdown of the contrast agent in the kidney
Patients with diabetes mellitus or hypertension who are receiving treatment with medications

18. PREPARATIONS BEFORE MRI Before an MRI exam, eat normally and continue to take your usual medications, unless otherwise instructed. You will typically be asked to change into a gown and to remove things that might affect the magnetic imaging, such as:
Jewellery
Hairpins
Eyeglasses
Watches
Wigs
Dentures
Hearing aids
Underwire bras
Cosmetics that contain metal particles

19. DURING THE TEST The MRI machine looks like a long narrow tube that has both ends open. You lie down on a movable table that slides into the opening of the tube. A technologist monitors you from another room. You can talk with the person by microphone. The MRI machine creates a strong magnetic field around you, and radio waves are directed at your body. The procedure is painless. An MRI can last anywhere from 15 minutes to more than an hour. You must hold still because movement can blur the resulting images. During a functional MRI, you might be asked to perform a number of small tasks — such as tapping your thumb against your fingers, rubbing a block of sandpaper or answering simple questions. This helps pinpoint the portions of your brain that control these actions.

20. MRI PROCEDURE

21. AFTER THE TEST If you haven’t been sedated, you can resume your usual activities immediately after the scan. A radiologist will analyze the images from your scan and report the findings to your doctor. Your doctor will discuss important findings and next steps with you.

22. MRI INTERPRETATION

23. MRI INTERPRETATION (Contd.)

24. ABNORMAL MRI SIGNAL

25. DISADVANTAGES OF MRI The time needed for MRI is longer than that needed for CT. Also, MRI is usually less likely to be immediately available than CT. Thus, CT may be better in emergencies, such as serious injuries and stroke. MRI is also more expensive than CT. Other disadvantages include:
Claustrophobia and sometimes difficulty fitting within the MRI scanner because it is a small, enclosed space
The effects of the magnetic field on metal devices implanted in the body
Reactions to the contrast agent

26. LIMITATIONS OF MRI The MRI machine makes a tremendous amount of noise. The noise sounds like a continual, rapid hammering. Patients can be given earplugs or stereo headphones in an attempt to muffle the noise. The noise is from the rising electrical current in the gradient magnets’ wires as it is being opposed by the main magnetic field.
Patients must remain very still for extended periods of time when getting an MRI scan. The exams can range from 20 minutes to 90 minutes, sometimes more. Even very slight movement can cause distorted images that will have to be repeated.
If the area of the scan has orthopedic hardware (such as screws, plates or artificial joints) the image can have severe distortions. This hardware causes a significant alteration in the magnetic field and a uniform field is critical to good imaging.
MRI machines are very expensive; therefore the exams are also very expensive.

27. NON-MEDICAL USES OF MRI Being non-invasive and non-damaging, MRI can be used to study the anatomy of plants, their water transportation processes and water balance. It is also applied to veterinary radiology for diagnostic purposes. Outside this, its use in zoology is limited due to the high cost; but it can be used on many species.
In palaeontology it is used to examine the structure of fossils.

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