MRI
by Karim Soliman
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