Collimator (Gamma camera)

Last revised by Raymond Chieng on 15 Aug 2023

Citation, DOI, disclosures and article data

Citation:

Vajuhudeen Z, Chieng R, Morgan M, et al. Collimator (Gamma camera). Reference article, Radiopaedia.org (Accessed on 20 Apr 2024) https://doi.org/10.53347/rID-79719

DOI:

https://doi.org/10.53347/rID-79719

Permalink:

https://radiopaedia.org/articles/79719

rID:

79719

Article created:

3 Jul 2020, Zemar Vajuhudeen

Disclosures:

At the time the article was created Zemar Vajuhudeen had no recorded disclosures.

View Zemar Vajuhudeen's current disclosures

Last revised:

15 Aug 2023, Raymond Chieng ◉

Disclosures:

At the time the article was last revised Raymond Chieng had no financial relationships to ineligible companies to disclose.

View Raymond Chieng's current disclosures

Revisions:

6 times, by 5 contributors - see full revision history and disclosures

Sections:

Imaging Technology

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The collimator of a Gamma camera used in nuclear medicine differs in structure and function to the beam collimators used in general radiography.

They typically consist of a lead disc drilled with tens of thousands of closely packed holes, separated from each other by septa.

Each hole only accepts Gamma rays to travel through a narrow channel. The path of these rays, and therefore their origin of location, can be accurately mapped. All other rays travelling in various other directions are absorbed by the septa, and do not contribute to the image.

Hence, the primary function of the collimator in Gamma cameras is for accurate spatial localisation, and not scatter reduction (as is the case in general radiography).

The collimator is placed over the scintillator crystal of the Gamma camera, and positioned as close as possible to the patient, to maximise spatial resolution.

Types

Collimator types vary based on the specific photopeaks of the radionuclides being used.

low energy - used for nuclides emitting photons up to 160 keV
medium energy - used for nuclides emitting photons up to 250 keV
high energy - used for nuclides emitting photons > 250 keV

Note that the septal thickness will primarily determine the amount of photon energies being accepted.

Hole shape and diameter will primarily determine the sensitivity and spatial resolution of the Gamma camera.

Design

Collimators can also vary based on their design:

parallel hole - multiple holes which run parallel to each other (most common design)
pinhole - single hole with a single aperture, providing a magnified and inverted image with superior spatial resolution but lower sensitivity when compared with a parallel hole collimator. Used in imaging small structures.
converging - multiple holes which converge onto a central point, providing a magnified image with improved spatial resolution. Used in imaging small structures.
diverging - multiple holes which fan away from the centre, providing a minified image. Used in whole body imaging where a larger field of view is required.