Gamma camera Flashcards
What are gamma rays
photons (high energy light). emitted from the NUCLEUS
What is gamma radiation?
electromagnetic radiation that has high enough energy to knock an electron out of orbit or more. Originates from the nucleus of an atom usually from radioactive decay
Are gamma rays the same as Xrays?
No. They appear like xrays at the same energy but xrays are produced by interactions with electron shells of atoms
What is the scintillator made of?
thallium doped Na I that produces light when stimulated by gamma or photons
What are the components of a gamma camera?
collimator crystal (scintillator) photomultiplier tubes
What is septal penetration
photon/gamma ray pass through the septum of the collimator and reaches the scintillation crystal at the wrong location
What factors influence septal penetration
energy of the incident gamma ray thickness of the septum
How do you increase gamma camera resolution?
Reduce the diameter of the hole in the septa or increase the length of the septa
increasing the length of the septa of a gamma camera collimator
increases the resolution
If the septa in a gamma camera are not thick enough, what artifact can happen?
star artifact aka, lots of septal penetration
How does star artifact happen?
septa are not thick enough and there is a lot of septal penetration
How do you reduce star artifact?
increase septal thickness
In a gamma camera, is thicker or thinner crystal more sensitive?
thicker
Does a thicker or thinner crystal in a gamma camera result in higher resolution?
Thinner
Why are collimators used in gamma cameras
to decrease scatter
When do you use a parallel collimator?
object size = image size
When is a diverging collimator used?
Object size > image size
When are converging collimators used?
Object size < image size
When are pinhole collimators used?
to magnify very small areas such as the thyroid
What daily test has to be performed on gamma cameras?
daily flood Uniformly flood camera with radioactive source to look for nonuniformities
What is a daily flood test
Uniformly flood a gamma camera with radioactive source to look for nonuniformities
What is an intrinsic flood?
collimators are removed, point source is set at a distance away from the camera head
What is extrinsic flood?
parallel collimators on, flat uniform source
What weekly gamma camera test has to be performed?
weekly bar test Bar phantom is placed on camera head and imaged
What is a weekly bar test for gamma cameras?
Bar phantom is placed on camera head and imaged (intrinsic bar test)
(spatial resolution)
What does the weekly bar test?
detail resolution
Low energy radionuclides used with thin crystal gamma camera
Tc-99m or TI-201
full width half maximum (FWHM)
Defines the range of energies the camera will detect centered around the peak energy
Tc-99m is detected with what window?
20% = 140keV with 20% window (+/- 10%)
What range is acquired for Tc-99m imaging?
between 126keV (-10%) and 154 keV (+10%) peak is 140keV with a window of 20%
