Magnetic Resonance Imaging

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Magnetic Resonance Imaging(MRI) is a non invasive medical imaging method widely used in hospitals and in research. In year 1946 Felix Bloch of Standard /university and Edward Purcell of Harvard University made the first succesful nuclear magnetic resonance experiment to study chemical compounds, they were awarded the Nobel Prize for physics in 1952. In early 1980's the first human magnetic resonance imaging( MRI) scanners became available, producing images of the inside of the body. while x-rays remain useful for looking at bones, MRI scans are the diagnostic tool of choice for soft-tissue organs,ligaments, the circulatory system and the spinal column and cord. They help physicians identify multiple scoliosis, tumors, tendonitis, strokes and many other condition. Also MRI is similar to a CT- Scan in that it produces cross sectional images of the body. But unlike CT-Scan MRI does not use x-rays, instead it uses a strong magnetic field and radiowaves to produce very clear and detailed computerized images of the inside of the body. MRI is commonly used to examine the brain, spine, joints, abdomen and pelvis. A special kind of MRI called Magnetic Resonance Angiography (MRA) examines the blood vessels.

The upshot is that MRI, for most applications,is far superior to other imaging tools in providing non-invasive images at high resolution.That's why hospitals pay millions of dollars for the multi-ton-benemoths and spend hundreds and thousands more a year operating them. Since 1997, when the first MRI exam was conducted on a person, the procedure has become quite common.In 2003, more than million scans were performedusing about 10 00 MRI scanners worldwide.



all MRI machines work on hydrogen atom as it is considered the most common atom in the body,90% of body is water (H20). The movement of the hydrogen protons in the magnetic field is the basis of MRI imaging. The protons are stimulated by a Radiofrequency(RF) coil and then left to relax in the direction of the magnetic field creating energy that is used for development of the image.

* Radio frequency
Resonance- radio frequency pulses in resonance push the aliugned protons(H+) to a higher energy level. Same as radiowaves it has a high wavelength,low energy electromagnetic waves. Radio frequency coils (the higher energy gained by the protons is re-transmitted-WMR signal-,the original magnetization begins to recover-t1-, the excessive spin begins to dephase-t2-.)acts as transmitter and receiver. the emitted energy is too small( despite 2500 times the magneticx field with resonance RF pulse) to convert them into images. the emitted energy is absorbed(k-space) analyzed and converted into images.

2 types of images
t1 Image
- all fliuids as C.S.F are black
- fats are white
- brain and spinal cord are dark grey

t2 image
- all fluids as C.S.F are white
- fats are black
- brain and spinal cord are light grey

Common Appearance in T1 and T2 W/S
1. low signal in T1 and low signal in T2 W/s (non mobile protons) a. cortical bone e.g ligament and tendons
b. mature fibroustissues e.g ligaments and tendons
c. calcifications either normal or pathological
2. high signal in T1 and low signal in T2 W/s
subacute hematoma
3. High signal in T1 and low signal in T2 W/S
fat and fat like structures e.g lipoma
4. Low signal in T1 and high signal in T2
the most common signal behavior
Ex. C.S.F , infarction, most tumors

3 MRI views
1. sagittal: as lateral image in x-ray
2. axial: as in CT
3. Coronal:used to detect scoliosis,intraspinal tumor, para spinal soft tissue...
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