MRI

By: Karim Sedky

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MRI by Mind Map: MRI

1. Defeniton

1.1. MRI is a technique that is used to create sectional pictures of the soft tissues of the human body as if it was cut in slices (tomography ) It is based on the application of strong magnetic fields followed by pulses of radio waves (Radiofrequency RF), and observing its effect on the tissues at a nuclear level (Nuclear Magnetic Resonance Imaging –NMRI)

1.2. MRI totally replaces conventional X-ray- generating equipment and film. Essentially it involves the behavior of protons in a magnetic field.

2. T1/T2

2.1. T1 Decay Longitudinal Relaxation NORMAL ANATOMY

2.1.1. Fluids have a long T l (i.e. they take a long time to re-establish their longitudinal magnetic moment), produce a weak signal and appear DARK

2.1.2. fat behaves in the opposite manner and has a short Tl, produces a strong signal and appears WHITE T1 is defined as the time it takes for the longitudinal magnetization 

2.2. T2 Decay Transverse Relaxation Show DISEASE

2.2.1. Fluids such as CSF have a long T2 (i.e. they dephase slowly) and give a strong signal and appear WHITE

2.2.2. Fat has a short T2, produces a weak signal and appears DARK 

3. Advantages

3.1. Ionizing radiation is not used

3.2. ➢ No adverse effects

3.3. ➢ Image manipulation

3.4. ➢ High resolution images in all planes

3.5. Excellent differentiation between different soft tissues

3.6. ➢ Excellent differentiation between normal and abnormal tissues.

4. Disadvantages

4.1. ➢ Bone does not give an MR signal, a signal is only obtainable from bone marrow

4.2. ➢ Scanning time can be long

4.2.1. ● motion artifacts

4.2.2. ● demanding on the patient

4.3. ➢ It is contraindicated in patients with

4.3.1. ● surgical clips

4.3.2. ● cardiac pacemakers

4.3.3. ● cochlear implants

4.3.4. ● first trimester of pregnancy

4.4. Equipment tends to be claustrophobic and noisy

4.5. ➢ Equipment is very expensive

4.6. ➢ Facilities are not widely available

5. Indications

5.1. Assessment of intracranial lesions particularly those involving ● posterior cranial fossa ● pituitary gland ● spinal cord

5.2. TMJ Investigations to show the soft tissue components of the joint including the disc position. MRI may be indicated: • When doubting internal derangement • Preoperatively before disc surgery.

5.3. Anterior Disc Displacement

5.4. Rheumatoid Arthritis

5.5. Tumour staging ● site ● size ● extent

5.6. Fracture + Haemosinus