General MRI Acronym Definitions

Spectroscopy Acronym Directory  General MRI Acronym Directory

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Acronym	PC
Expansion	Phase Contrast
Explanation	MRA technique utilizing phase shift properties of flowing blood. Spins that move along a gradient experience a phase shift in proportion to their velocity (maximum near +/- 180 degrees). A reference, flow-compensated image is acquired and then phase images are acquired, sensitized to flow in a particular direction (along a specific gradient). The reference mask is subtracted from the resulting images. Post-processing, e.g. MIP, can then be performed. Choosing the proper aliasing velocity (VENC) is important.
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Acronym	PE
Expansion	Phase Encoding
Explanation	In order to spatially localize a signal, phase-encoding supplies the orthogonal coordinate from the frequency encoding direction. During phase encoding of a slice, a brief gradient is applied causing the excited spins to rotate a known angle, and a signal is acquired. Successive views utilize larger gradients to produce larger phase shifts, but the amount of phase shift betweem successive views is a constant. In 3D imaging, phase-encoding is also performed in a secondary direction to localize a signal in 3D space.
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Acronym	PEG
Expansion	Phase Encode Grouping
Explanation (Diagram)	Phase encode grouping is used in cardiac gated cine imaging to acquiring multiple phase encode views per heartbeat, decreasing scan time to the point where breath hold thoracic imaging is possible. PEG™ is a trademark of Picker
Synonyms	Segmented k-space cine imaging, VPS, FastCard (GE)
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Reference	AYRNTKAMP, 9-14
Contributor	MN
Date Entered	5/7/98

Acronym	PET
Expansion	Positron Emission Tomography
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Acronym	PPG
Expansion	Peripheral Pulse Gating
Explanation (Diagram)	Method of triggering a gated acquisition by means of a fingertip optical detector that measures flow. Not as accurate as ECG-gating.
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Related Terms	ECG-gating, cardiac gated
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Acronym	PPM
Expansion	Parts per Millions
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Acronym	PSR
Expansion	Phase Sampling Ratio
Explanation	Ratio of the FOV in the phase encoding direction to the FOV in the frequency encode direction. The PSR can be altered to adjust the phase-encoding FOV to tailor to the anatomy imaged (abdomen, head).
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