Part IV Flashcards
generic term for device that transforms energy from one form to another
Transducer
2 classifications of radiation detector
non paralysable
paralysable
detector classification used for imaging PET or SPECT
non paralysable
detector classification that measures continuously, there is a need to reset device for it to detect other event
paralysable
properties of detectors
detector efficiency
energy resolution
temporal resolution
spatial resolution
ratio of gamma detector detected received over the no. of gamma rays emitted
detector efficiency
2 types of detector efficiency
geometric efficiency
intrinsic efficiency
configuration and the distance of the source
geometric efficiency
ability to absorb thickness and attenuation coefficient of the detecting material
intrinsic efficiency
energy resolution formula
100% x Full Wave at Half Maximum/ gamma energy
[..] keV good images detected by detector
50-300 keV
refers to the amount of blurring that is produced by an imaging system
spatial resolution
expresses how accurately a radiation detector system is able to determine the time of interaction
temporal resolution
the conversion of gamma ray energy into an electronic pulse and processing
dead time
two main types of detectors
scintillators
gas detectors
the basic of most diagnostic and imaging instruments
convert gamma in light -used in imaging
scintillators
typically used in non-imaging instrument,
use gases and once streak by gamma rays, there is ionization used
gas detectors
three main types of gas filled detectors
ionization chamber
proportional counters
geiger mueller counters
applied V for ionization chamber
100-400 V
[ionization chamber] used to assay activity levels in syringes. vials..etc.
dose calibrators
[ionization chamber] used for radiation protection purposes
survey meter
[ionization chamber] personnel monitoring
pocket dosimeters
T/F ionization chamber cannot detect a single radiation event
True
proportional counter gases
90% argon/xenon and 10% methane gas
applied voltage of proportional counters
400-800 V
adv. of proportional counters
greater electron amplification
pulse size is a factor 100-10000 times greater than ionization chamber
capable of detecting single radiation event
T/F Proportional Counters have little use in NM and is used mainly for measuring alpha and beta in research
T
applied V of geiger mueller counters
above 800 V
commonly used quenching gas in geiger mueller counters
heavy organic vapour (alcohol) and halogen gas (Cl)
T/F G-M counters is used in NM as survey meter to locate even a small amount of radioactivity
T
2 types of scintillation detectors
inorganic substances - solid
organic substances - liquid
Examples of inorganic substances
NaI (Tl), ZnS (Ag), CsI (Tl), CdS(Ag)
Example of organic substances
2,5 diphenyloxazole
basic components of scintillation counter
- Detector System -Scintillator and PMT
- Processing Unit - Gamma Spectrometer
- Display Unit
[detector system part] filter gamma, prevent misinterpretation, allows only parallel gamma rays to pass thru,
limits area of gamma camera
collimator
[detector system part] used to enhance and reshape photoactivity of the emitted light photons
pre-amplifier
[detector system part] refer to the dynodes of the PMT, amplify no. of electrons
amplifier
[processing unit part] to evaluate incoming electric signals coming from PMT
accept/reject signals not equivalent to predicted energy of radionuclide
PHA- Pulse Height Analyzer
counts on a scaler, needle deflection on a rate meter, a dot on a special type of paper, display data in monitor system
display unit
properties of ideal scintillator
- good absorber of incident photon
- conversion to light must be efficient and light intensity must be proportional to energy
- transparent to visible light
- wavelength of light emitted should correspond to PMT sensitivity
explain scintillation detectors
gamma is emitted → interacts with scintillator → ionization and excitation of other atoms (come back to ground state) → scintillator will emit light photons prop. to gamma photon → cause photocathode to emit electrons → dynodes attract incoming electrons (electron multiplier) emit secondary electrons → when electrons reach elec connectors potential pulse is generated (potential pulse generated identifies amount of energy coming from radiation → after measured/counted energy of radiation is converted to measurable V pulses
reasons to use NaI (Tl)
- relatively dense
- efficient
- transparent to its scintillation emission
- provide an output signal that is prop to amplitude to the the amt of energy absorbed in crystal
disadvantages of NaI (Tl)
fragile
hygroscopic - collects moisture
large crystal
Parts of PMT
crystal
reflector
Al or stainless steel jacket
transparent window
photocathode
focus grid
dynodes
MU metal (iron, nickel, copper, chromium)
[PMT part] reflect light emitted toward PMT
reflector
reflectors are made up of:
magnesium oxide
aluminum trioxide
titanium dioxide
[PMT part] protect the crystal
aluminum or stainless steel jacket
[PMT part] boundary between scintillator and PMT, permit exit of light from crystals t PMT
transparent window
[PMT part] photoemissive material that affects electrons when strike by light photons
photocathode
photocathode composition
cesium and antimony
sodium and potassium
T/F at 7-10 light photons that is converted into 1 electron
T
[PMT part] direct e- towards dynodes
focus grid
[PMT part] amplify e-
dynodes
[PMT part] collect all e- creating electrical signals
anode
seals PMT
MU metal
overall electron gain from dynode amplification
10^6
applied V for liquid scintillators
below 40 keV
[PET Scintillators] single crystals in early years of PET
NaI (Tl)
[PET Scintillators] most detector designs convert to this material because of its greater efficiency to 5ll keV
Bismuth Germinate (BGO)
[PET Scintillators] used widely in future gen PET scanners
Cesium doped Lutetium oxyorthosilicate LSO(Ce)
[PET Scintillators] others
barium fluoride (BaF2)
Yttriumaluminate (YA103[Ce] or YAP)
Cesium doped - gadolinium oxyorthosilicate (GSO)
4 components of LSC
organic solvent (cocktail)
primary solute (primary fluor)
secondary solute (wave shifter)
*additives
[LS component] dissolves the scintillator and radioactive samples
organic solvent (cocktail)
traditional and more environmentally harsh solvents
toluene, dioxane, xylene
commonly used organic solvents
diisopropylnapthalene (DIN)
phenyl xylyl ethane (PXE)
[LS component] absorbs the energy from the solvent and coverts light
primary solute (primary fluor)
primary fluor composition
pterphenyl and 2,5 diphenyloxozole (PPO)/ bis-MSB [p-bis -(methylstyryl) benzene]
[LS component] absorbs emissions of the primary solute and remit photons of longer wavelengths which are better matched to the PMT response
secondary solute (wave shifter)
secondary solute (wave shifter) composition
1,4-di [2,5 phenyloxozole] benzene
[LS component] improve some aspect of their performance (efficiency of energy transfer from the solvent to the primary solute)
additives
sometimes added to improve the dissolution of added samples such as blood
solubilizers (hyamine or hydroxide)
LS drawbacks
- insufficient
- low light output 1/3 of Na(Tl)
undesirable reduction in light output from the scintillation cocktail
quenching
caused by substances that compete with the primary fluor for absorption of energy from the solvent but not are not themselves scintillators
chemical quenching
most troublesome chemical quenchers
dissolved oxygen
caused by substances that absorb emissions of primary and secondary solute
color quenching
examples of color quenching substances
blood and other colored materials
fogged and dirty containers
occurs when a relatively large volume of sample is added to the scintillator solution, reducing concentration of solutes and output efficiency
dilute quenching
** due to condensation presence of fingerprint or dirt on the vial
optical quenching
semi conductor detectors composition
solid state gas analogs
- silicon or germanium coupled with lithium
-cadmium telluride (Cd Te)
-cadmium zinc telluride (CZT)
disadvantages of SCD
- Si and Ge CONDUCT A SIGNIFICANT AMOUNT OF THERMALLY INDUCED CURRENT AT ROOM TEMP (NOISE CURRENT)
- presence of impurities in crystals (use HP Ge)
- time consuming and expensive prep
- small crystal size
use of SCD in NM
in vitro applications
-tracer studies
-assay of radionuclidic purity of RPs
-handheld probes for lymphatic mapping
- compact gamma camera for scintimammography
In vivo counting systems
- probe system
- whole body counters
system designed to monitor radioactivity in localized parts of the body
probe system
measure activity in specific organ aka thyroid
also known as Organ Uptake
single probe system
used for renal function studies , lung clearance studies
also known as dynamic.perfusion counting
multi-probe systems
system designed to measure the total amount of radioactivity distribution
whole body counters
in vitro counting systems
well counters
dose calibrators
constructed mainly for counting samples of urine, blood and feces
count samples in standard test tube
well counters
major tool in “in vitro” assay
Na(Tl) well counters
type of ionization chamber used for assaying relatively large quantities of gamma and x-ray
-used for measuring or verifying the activity eluates
dose calibrators
difference b/w whole body counting and dose calibrators..
DC knows specific part of the body that receives the rad’n
device used in NM to view and analyze images of the distribution injected, inhaled or ingested
gamma camera
anger camera principles
gamma emmited by pt → collimator (allow only II gamma to pass thru) → scintillator material → convert rad’n to light photons → absorbed by PMT → electrical signals (1. x and y -plot location of radiation, used for spatial coordinate, z - analyzed by pulse height analyzer)
types of gamma cameras
- stationary gc w/ scanning capabilities
- scanning systems (SPECT) based on single or multi-head gc
- mobile gc for irradiation scanning
- handheld gc
stationary gc w/ scanning capabilities [purpose]
for determining distrib of administered RP in pt’s body
-gc produced planar images in cross sectional slices
scanning systems (SPECT) based on single or multi-head gc [purpose]
used for cardiac, whole body imaging and brain perfusion
-some have multi camera heads
-tomo images
mobile gc for irradiation scanning [purpose]
bedside assessment
only planar images
used for dx of cardiac pts
wheeled units - detector, stand, data processing console
handheld gc [purpose]
portable for real-time visualization and localization of rad’n markers
used to locate sentinel lymph nodes
R.O.L.L (radioguided ocult lesion localization )
S.N.O.L (sentinel node and occult localization)
image sensors used in handheld gc
cadmium zinc telluride
[gc collimators] all holes II to each other
parallel hole collimators
most common designs for parallel hole collimators
low-energy all-purpose (LEAP)
low-energy high-resolution (LEHR)
medium and high energy collimators
holes with large diameter sensitivity is relatively high, resolution is moderate
LEAP collimators
[gc collimators] oblique view for better visualization
adv. can be positioned close to body for max. gain resolution
slanthole collimators
[gc collimators] create magnified images, for large POU
converging collimators
[gc collimators] upside down converging, minified view
diverging collimators
[gc collimators] applied for rectangular camera need to image small POI like brain, heart
1D parallel, other direction - converged
fanbeam collimators
purpose of fanbeam collimators
arrangement allows data from the pt to use max. surface of the crystal
fan beam when flipped over
used for whole body sweeps
single pass diverging collimator
[gc collimators] cone shaped collimator have a single hole with interchangeable inserts that come w/ a 3,4,6mm aperture
pinhole colimators
produce magnified images of small organ like the thyroid or a joint
designed for low energy isotopes
pinhole collimators
distance from one septa to next
d- diameter
dist. from source to collimator
D-distance of collimator
thickness of colimator
L- length of colimator
As d increases
As L increases
As D increases
Rg increases (res down)
Rg decreases (res up)
Rg increases (res down)
efficiency of collimator
ratio of no of photons that paa thru the collimator to the n emitted
sensitivity
sharpness or detail of NM image
Spatial resolution
difference in density or intensity in parts of image corresponding to different concentration of activity in the pt
contrast
factors that affect contrast
film contrast
presence background act
scattered rad’n
