Magnetic Resonance Imaging (MRI)

What Is Magnetic Resonance Imaging (MRI)? Understand Its Principles and Unique Advantages

How MRI Works: High-Precision Imaging Without Ionizing Radiation

Magnetic Resonance Imaging (MRI) is a safe, non-invasive and accurate diagnostic imaging tool that involves without ionizing radiation and causes no pain. It uses strong magnetic field, radio-frequency, and advanced computer technology to provide excellent images of the human body. When the hydrogen protons (nuclei) inside the water molecules all over the body are being excited by the powerful magnetic field and radio-frequency, relax and subsequently returning to their balanced state, these hydrogen protons emit signals. The powerful computer systems receive, process, and reconstruct these signals into high-resolution, multi-slice images of the body.

Differences Between MRI and Other Tests (e.g., CT)

• Radiation risk
  Comparing with imaging tools that require the use x-ray, such as CT, MRI does NOT involve ionizing radiation, making the MRI scan more suitable for patients who may require repeated scan for monitoring, or patients who are more sensitive to radiation such as children.
• Image differentiation
  CT has the advantage in providing fast and high-resolution images in bone structures, respiratory system (lungs), and acute bleeding. MRI has the advantage in soft tissue differentiation, particularly in stroke, tumors, tendon and ligament tear.
• Examination time
  MRI takes longer scan time from 30 to 120 minutes, subject to body region. Patients are required remain completely still throughout the examination. CT scan usually takes 5 to 10 minutes to complete.
  
  

Clinical Uses of MRI: Covers Major Disease Diagnosis

Cancer Screening and Diagnosis (e.g., Prostate Cancer, Breast Cancer)

MRI serves as a vital tool in oncology, primarily utilized to diagnose tumors, determine precise clinical staging, and monitor structural changes before and after chemotherapy or radiotherapy treatments. Also, it plays a crucial role in systemic evaluations by checking whether cancer has spread, or metastasized, to the bones. Furthermore, MRI provides exceptional clarity when observing soft-tissue conditions, allowing clinicians to detect abnormalities that might otherwise be obscured on conventional scans.

Cardiovascular Examinations (Stroke Risk Assessment, Heart Disease)

With its exceptionally high sensitivity, MRI can comprehensively assess heart structure, evaluate cardiac function, and detect the presence of myocardial clots within a single, streamlined scan. These capabilities make it invaluable for stroke risk assessment and heart disease evaluation. By facilitating the early detection of brain strokes, MRI empowers radiology teams to initiate prompt, highly targeted interventions, ultimately leading to more effective treatment outcomes and improved patient recovery.

Musculoskeletal System and Spine (Back Pain, Arthritis, Nerve Compression)

MRI is currently the most precise method for examining the entire spine, as well as muscles and joints throughout the body.

Nervous System Examination

MRI provides very clear visualization of the brain and spinal cord anatomy. It is commonly used to diagnose brain tumors, multiple sclerosis, seizure (epilepsy) lesions, and to evaluate the degree of brain atrophy associated with cognitive impairment (such as Alzheimer's disease).

MRI Scan Process

Patient Preparation: Clothing Requirements, Fasting Tips, and Metal Declaration

1. Remove all metal items: Patients must remove any metallic objects on their body, place them into the storage locker provided, and change into the hospital's examination gown.
2. Fasting is usually not required: Most MRI scans (such as of the head, spine, and joints) do not require fasting. However, if the scan involves a specific procedure, patients are usually requested to stop eating two hours before the exam, but drinking of water is allowed.
   
   

Will You Feel Uncomfortable? How Long Will It Take?

During the scan, the patient lies flat on the examination table, and the body will be moved into the tube-shaped MRI machine.

1. Patient Safety and Implants: Prior to the procedure, it is critical to inform the Radiology Department staff if the patient has any implanted medical devices, worn equipment, or metal objects in the body, such as a cardiac pacemaker. Because the MRI machine utilizes a powerful magnetic field, the presence of metal can pose significant safety hazards to the patient and severely distort the clarity of the resulting images.
   
   
2. Procedure duration: The imaging process typically requires between 30 minutes to 2 hours to complete. For a successful scan, patients must remain completely still and relax as much as possible, as even minor movements can blur the images. Because maintaining this stillness can be challenging for younger patients, children and infants may be prescribed sedatives by their attending physician, administered either orally or via injection, to ensure their comfort and cooperation.
   
   
3. Acoustic Noise during the exam: During the operation of the scanner, the machine will generate loud, intermittent tapping and knocking noises. To protect the patient's hearing and minimize acoustic discomfort, the radiology team will provide specialized earplugs or earmuffs to wear throughout the duration of the examination.
   
   
4. Contrast agent injection (if needed): Depending on the specific diagnostic requirements, some patients may need an injection of an MRI contrast agent to enhance image detail. While these agents are highly effective, they carry a minimal risk of adverse effects. As with many medical interventions, severe reactions can occur in exceptionally rare cases; however, the risk of a fatal complication is extraordinarily low, occurring in approximately 1 out of every 400,000 administrations.

Possible Contrast Agent Reactions and Nursing Aftercare Guidance

If the scan involves injecting a gadolinium-based contrast agent, the patient should drink more water after the scan to help the kidneys remove the contrast agent. In general, patients can return to normal eating and daily activities immediately.

Side Effects of Contrast Agent and Recommended Management

Safety Notes and Limitations of Magnetic Resonance Imaging (MRI) Scan

Use of Contrast Agents — Risk Assessment and Side-Effect

Magnetic resonance imaging (MRI) may use gadolinium-based contrast agents, which are different from the iodine-based contrast agents used in CT scans. The risk of allergic reactions is extremely low. Common mild reactions include feeling cold or hot at the injection site, nausea, or headaches. Severe allergies (such as difficulty breathing) are very rare.

General Risks and Special Complications (Including Clarification of Rare Risks)

For patients with severely impaired kidney function (e.g., those with kidney failure), the use of gadolinium-based contrast agents carries a very low risk of causing “Nephrogenic Systemic Fibrosis” (NSF). Therefore, for high-risk patients, blood tests should be performed before injection of contrast agents to assess kidney function.

Who Should Not Have an MRI Scan? (Notes for Implants and Heart Pacemakers)

• Pacemaker (Heart Pacemaker): Although some newer pacemakers have “MRI-compatible” features, the mode must still be adjusted by a cardiologist before the examination, and the procedure must be carried out under close monitoring.
• Cochlear implants and brain aneurysm clips: It is necessary to confirm whether the device model meets MRI safety standards.
• Metal fragments inside the body: For example, for patients who work in metal grinding industry or if metal fragments have previously been shot into the eyes or body, it must be verified the location and nature by means of an X-ray exam before proceeding the MRI.
• Pregnant woman should avoid taking MRI examination during the first 3 months of her gestation.

Common Questions About MRI Scans

Does MRI Have Side Effects?

Since MRI does not utilize ionizing radiation, it is widely recognized as an exceptionally safe diagnostic procedure. However, approximately 1% of patients may experience a mild allergic reaction to the contrast agent. These minor reactions typically present as temporary localized discomfort, such as a sensation of coldness, abnormal warmth, or mild pain at the injection site, as well as general itching or nausea.

While an exceedingly small number of individuals may experience more severe systemic reactions—including bronchospasm or a significant drop in blood pressure—fatalities resulting from contrast allergies are extraordinarily rare in clinical practice.

Is a Contrast Agent always necessary for an MRI?

Not necessarily. The requirement for a contrast agent depends entirely on the purpose of the examination. For instance, routine imaging of the knee or spine typically does not require contrast to achieve a clear diagnosis. However, if the primary goal of the scan is to evaluate a tumor's blood supply, measure the severity of tissue inflammation, or investigate vascular disease, injecting a contrast agent becomes essential, as it significantly enhances image detail and improves overall diagnostic accuracy.

Can I Wear Makeup or Jewelry on the Day of the Exam?

No. For safety and image quality, you must remove makeup and all jewelry before entering the scanning room.

How MRI assists in Dementia Diagnosis

MRI is a critical tool in the diagnostic process for dementia. While an MRI alone cannot definitively diagnose dementia on its own, it plays a vital role in identifying the underlying cause of cognitive decline. Medical professionals utilize MRI scans in ruling out treatable conditions and identifying patterns of structural brain changes.

Different types of dementia affect different parts of the brain. High-resolution MRI scans allow neurologists to visualize and evaluate specific patterns of brain tissue loss (atrophy). MRI can detect significant shrinkage in the hippocampus, the region of the brain responsible for learning and memory. This is often one of the earliest structural signs of the Alzheimer's disease. Currently, there is AI tool based on the Asian metadata, to analysis the brain tissue atrophy and estimate the chance of having the Alzheimer's disease.  Our department provides MRI Brain with AI analysis of Alzheimer's disease services. Please feel free to contact the Department of Radiology to learn more.