Introduction to PET Physics



Abbreviations used

2D

Two-dimensional.  
In the context of PET, this means operating using interplane septa to divide the camera into a series of adjacent ring systems. See section 3.

2.5D

Two-and-a-half dimensional.  
In the context of PET, this means operating using coarse interplane septa to divide the camera into a series of adjacent mini-3D systems. Usually only applied to DHCI cameras. See section 3.

3D

Three-dimensional. 
In the context of PET, this means operating without the use of interplane septa. Also known as "positron volume imaging". See section 3.

3D-RP

Reprojection and Filtered Back-projection. 
A three-dimensional analogue of FBP which can be used to reconstruct data obtained from a PET camera operating in 3D mode. See section 4 and Kinahan and Rogers, 1990.

CFD

Constant-fraction Discriminator. 
A device for processing analogue electrical pulses. It generates a digital pulse when the signal reaches a constant fraction of the peak pulse height.See section 5.

CT

Computed Tomography.  
Generally refers to X-ray computed tomography, where an X-ray source is rotated around the subject to generate a set of projections which may be reconstructed to form an image.

DHCI

Dual-headed Coincidence Imaging.  
A PET tomograph employing two diametrically opposed rotating Anger cameras. Usually used as a dual purpose PET / SPECT machine. See section 3 and section 5, also Jarrit and Acton 1996.

FBP

Filtered Back-projection. 
An analytic reconstruction technique for data acquired as sets of one-dimensional projections. Used in 2D PET, also in SPECT and other tomographic techniques. See section 4 and Brooks and Di Chiro, 1976.

FORE

Fourier Rebinning.  
A reconstruction technique for 3D PET in which the three-dimensional dataset is reduced to a two-dimensional dataset without the introduction of significant image artefacts on reconstruction. Defrise et al 1997.

FOV

Field of View

FWHM

Full-width at half-maximum. 
If a function contains a peak, the FWHM is defined as the width of that peak at a function value of half the maximum peak height.

LLD

Lower  Level Discriminator. 
A device for processing analogue electrical pulses generated from a photon detector. Pulses are transmitted only if they correspond to events of energy greater than a certain threshold (the LLD setting or lower energy threshold). See section 5.

LOR

Line of Response. 
A line joining two detectors which are operating in coincidence mode in a PET camera. See section 2

NC

Normalisation Coefficient. 
In a PET camera, each line of response has a particular sensitivity relative to the mean. The NC is the reciprocal of this sensitivity. See section 6.

OS-EM

Ordered Subsets - Expectation Maximization. 
An iterative reconstruction technique. Hudson and Larkin, 1994

PET

Positron Emission Tomography . 
An in vivo radiotracer imaging technique in which compounds labelled with positron-emitting radionuclides are injected into the subject. The resulting positrons annihilate with electrons to form two anti-parallel gamma rays which are detected by the PET camera. See section 2.

PMT

Photo-multiplier Tube.  
A device for turning a pulse of light into an amplified electrical pulse.

PVI

Positron Volume Imaging.  
See 3D PET.

PSRF

Point source response function. 
A plot of response vs. position when a point source is placed within the field of view of an imaging system.

SPECT

Single Photon Computed Emission Tomography. 
An in vivo radiotracer imaging technique in which compounds labelled with photon-emitting radionuclides are injected into the subject. The resulting individual photons are then detected by the SPECT camera. See section 2.

ULD

Upper  Level Discriminator.  
A device for processing analogue electrical pulses generated from a photon detector. Pulses are transmitted only if they correspond to events of energy less than a certain threshold (the ULD setting or upper energy threshold). See section 5.

 
 

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Last revised by:

Ramsey Badawi

Revision date:

12 Jan 1999