Lecture 2 Flashcards
the energy must be converted into a form that is detectable for radiation to be detect..how
electrical current generated
what are examples of radiation detectors
ionization chambers, proportional counters, geiger mueller counters
what are examples of scintillation detectors
inorganic scintillators and organic liquid scintillators
what are examples of semiconductor detectors
Ge(Li) and Si(Li) detectors and CZT detectors
what are the basic components of a scintillation detector
scintillating material, light detector, voltage discriminator, and display/recording device
what scintillator would you pick for a gamma camera
sodium iodide iwth thallium, bismuth germanium oxide, barium or cesium fluoride, luthetium orthoscilicate, plastic
what is sodium iodide iwth thallium used in
nuclear medicine
what is bismuth germanium oxide used in
PET
what is barium or cesium fluoride used in
used in PET
what is luthetium orthoscilicate used in
PET and SPECT systems
what is the flow chart of gamma ray detection
gamma rays-scintillation crystal-light pulse-PM tube- voltage pulse
what is proportional along the gamma ray detection
magnitude of voltage pulse is proportional to intensity of the light signal proportional to the energy deposited in the crystal
what is positioning (pulse) arthmetic
positioning arithmetic refers to the electronic scheme used to determine the location fo the light pulse emitted when a gamma ray is absorbed in the NaI crystal. It does not tell you where the origin of the gamma ray was, but only where it got stuck in the crystal
how do you determine where the radiation came from?
collimate the detector
what is gamma camera collimation
it is designed to limit the detection of gamma rays whose rays are travelling in certain directions. Collimator material must be composed of dense material with high atomic number.
what material is often used for collimation of gamma camera
lead
what is the tradeoff in collimation
it is design is a trade off between resolution and sensitivity.
what does high resolution mean for the sensitivity
it means there is low sensitivity
what does high sensitivity mean for resolution
low resolution
what does high sensitivity mean for resolution
low resolution
what are things to consider when designing a collimator
it should have a hole length, hole diameter, and septal thickness
what is the collimator resolution proportional to
diameter times source distance
what is collimator sensitivity proportional to
hole diameter squared
what is the proportionality between resolution and sensitivity
the resoultion is sqared in proportion to the sensitivity
draw a semiconductor
gamma ray, Na/Csl crystal then hits a silicon photodiode and it generates an electrical signal
what is a silicon photodiode
it converts light into a digital plse. Quantum detection efficiency of 50-80%. It is used in multi-crystal gamma camera and PET
what are the benefits of silicon photodiodes
small, low noise, high speed, adn good spectral response
what is the best semiconductor materials
CdTE and CZT becuase they havve a high Z, density, and bandgap with the best energy resolutioon
CZT detector is
dense material with higher band gap so can be operated near room temperature and good energy resolution. 5-6 mm thickness overall
what are the spectrum dysnamics of these scans
each detector only scans the region of the mycocardium, and the system emplys high sensitivity collimators nad proprietary reconstruction algorithms. Scan around 2 times per minute
what technology does SPECT of the heart use
it is CZt
what else is CZT used for
breast, heart, rnadom whole body
what is the best parts of semiconductor technology
it has lightweight detectors that can be curved or shaped to meet clinical application. They have detectors with better energy and spatial resolution. Detectors can be used for both xray and gamma ray detection
what is the best parts of semiconductor technology
it has lightweight detectors that can be curved or shaped to meet clinical application. They have detectors with better energy and spatial resolution. Detectors can be used for both xray and gamma ray detection
what is intrinsic resolution a function of
crystal thickness, number of phtomultiplier tubes, design of light pipe, amount of light generated by gamma ray
what effect does crystal thickness have on instrinsic resolution
the resolution degrades with increasing crystal thickness
what effect does number of photomultiplier tubeshave on instrinsic resolution
it inproves with increased PMT
what effect does number of design of light pipe on instrinsic resolution
it can be imporved by elimination of light pipe or by improved design
what effect does number of amount of light generated by gamma rays have on instrinsic resolution
the resolution improves iwth increased energy
what effect does number of amount of light generated by gamma rays have on intrinsic resolution
the resolution improves with increased energy
what is the formula for energy resolution
energy resolution depends on gamma ray energy. R is proportional to 1/sqrt(E)
what is system resolution dependent on
collimator resolution and intrinsic resolution
what is the important part of collimator resolution
for all types of collimation, resolution degrades as the object is moved away from the collimator face
what does it mean if low bandgap
same photon has higher sensitivity because more electrons
what does high bandgap mean
it means they can be used at more room temperature
if the band gap is too low
it needs to be cooled down too much
what is important about energy resolution
reduced scatter in the image can be achieved by narrow image contrast large reduction in sensitivity. REduced scatter for accurate attenuation
better energy resolution
better window
what is better about CZT
it decreases dead speace
