Background
•
MRI provides anatomic and physiological information noninvasively
•
No ionizing radiation used, in contrast to most other forms of diagnostic
imaging
•
First used in 1973, becoming increasingly popular
•
Very expensive machines
Principles
•
in depth physics required...
•
Based on the principle that certain nuclei in the human body, when
in a strong magnetic field and stimulated with radiofrequency waves,
will emit characteristic radiofrequency energy when that stimulus
is removed
The
process
•
Patient is put into the magnetic field
•
Radiofrequency pulse is applied
•
Hydrogen protons become excited and when they relax, a signal is
emitted
•
Signal is converted to an image by computers
•
Computer converts signal strength to a shade of grey
•
Strong signals are white, weak are black on the image
•
T1 and T2 are measurements of the rate of relaxation of the nuclei
after relaxation, this alters the signal of the nuclei
T1
weighted image - anatomic detail in multiple planes, identifies
areas of abnormal signal in bone marrow
T2
weighted image - soft tissue and marrow abnormalities
Uses
•
Musculoskeletal system
•
Good contrast in soft tissue - bone tumors
•
Diagnosing osteomyelitis in diabetic foot infections
•
Tendon pathology
•
Ligament damage
•
Tarsal coalition
•
Tarsal tunnel syndrome
•
Stress #'s
•
Plantar fasciitis
Comparisons
to other imaging techniques
•
Better soft tissue contrast than CT
•
Cross-sectional images prevent superimposing of images, as with
X-rays
•
Tissue types can be distinguished better than on X-ray
•
Can be used in any plane
Disadvantages
•
Magnetic tube - claustraphobia
•
Metallic objects on person (eg. pacemaker) exclude from imaging
•
Expensive
Reading
the image
•
White - high signal intensity
•
Black - low signal intensity
•
Grey - intermediate signal intensity
•
Fat and medullary bone - white
•
Cortical bone, calcification - black
•
Blood vessels - black (if normal)
