Download Magnetic Resonance Imaging for the F1

Magnetic Resonance Imaging for the F1
What is MRI?
MR imaging is based on the naturally occurring magnetic moment that exists within the nuclei of
a hydrogen atom. When an external magnetic field is applied the protons within hydrogen nuclei
align themselves parallel to the field and begin to resonate. When a radiofrequency pulse is
applied to these protons it provides enough energy to dislodge them from this orientation. This is
a temporary phenomenon and the nuclei relax back into realignment with the external magnetic
field. Upon relaxation, energy is released in the form of RF waves. This echo is detected and a
signal of variable intensity for a given location is produced.
The signal is picked up by special aerials called coils and sent to a computer for processing. The
computer converts the radio signals into pictures which are displayed on the computer screen.
The imaging produced forms ‘slices’ of the area being examined.
Strengths and weaknesses of MRI
Strengths
Weaknesses
Multi-planar capabilities
Superior soft-tissue contrast
No known side-effects
Can be used in pregnancy
Limited use for bony imaging
Not ideal for patients with claustrophobia
Expensive
Time consuming.
Patient must lie very still for a good image.
Different types of MRI
T1 is when they programme the machine to only look at the longitudinal movement of protons. T1 images
are usually used to look at normal anatomical details. T2 is the transverse movement of protons and is
usually used to look at pathology because most tissues involved in disease tend to have a higher water
content than normal.
Key points:
- Anatomical MRI is T1 weighted.
T1 is best for looking at brain structure because fat
appears very bright and bone marrow contains a great
deal of fat.
- Functional MRI is T2 weighted.
Water and fluid are brighter on T2- ideal for tissue
oedema.
- White matter appears a light grey in T1 and a dark grey
in T2.
- Grey matter appears grey in both.
- Cerebrospinal fluid (CSF) appears black in T1 and white
in T2.
Indications for use (not an exhaustive list)
Examples
Brain
Brain tumors
Stroke
Dementia
Multiple sclerosis
Motor neurone disease
Brain infections
Brain injury
Alzheimer’s disease
Parkinson’s disease
Musculoskeletal
Athritis
Osteomyelitis
Cartilage damage
Tendon, muscle, ligaments (sports injuries)
Repetitive strain injuries.
Spinal injuries.
Acute cord compression.
Malignancies
Breast cancer
Prostate cancer
Gynecological malignancies
Rectal cancer
Lymph nodes
Metastases
Orbits
Exophthalmos
Eye injuries
Orbital tumour
Liver
Cirrhosis
Abscesses
Liver cancer
Vascular
Aneurysms
Atherosclerosis
Contraindications
(any metallic foreign bodies)
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Internal (implanted) defibrillator or pacemaker.
Cochlear (ear) implant.
Surgical clips such as those used on brain aneurysms.
Artificial heart valves.
Implanted drug infusion ports.
Implanted electronic device, including a cardiac pacemaker.
Artificial limbs or metallic joints.
Implanted nerve stimulators.
Pins, screws, plates, stents or surgical staples.