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Transforming Radio Frequenciesinto Images?
Let’s step back, and look at a device that is familiar to all of us…the Radio
The emitted energy of the protonsonce the RF is stopped is affected by in which tissue (the “lattice”) it resides: fat, muscle, ligament, bone, brain, etc.
RF Pulse sequence parameterswhich the technician adjusts
• The three pulse sequence parameters are
• Repetition time (TR) measured in msec• Echo time (TE) measured in msec• Flip angle measured in degrees
T1 and T2 relaxation times
Occur simultaneously andindependently of each other and formthe basis of tissue contrast in MR-reconstructed images
T1 •Low TR (400-700 msec)•Low TE (20-40 msec)
T2•High TR (2,000-3,000 msec)•High TE (40-70 msec)
Proton density•High TE (2,000-3,000msec)•Low TE (20-40 msec)
Basic Sequences
• T1 to view anatomy
• T2 to detect a pathologic process (edema, swelling)
• Proton Density (PD) great for ligamentous anatomy
Basic Pulse Sequences for MRI Imaging
Image type Fat Water Advantage
T1 Bright Dark Anatomical detail
T2 Intermediate Bright ++ edema
Fat Suppressed T2
Very Dark Very Bright ++++ edema
Fat Suppression
A very valuable tool to define whether a structure is composed of water (bright)
such as blood or fat (bone marrow)