RNI Equipment Flashcards
which RNI procedure would be best imaged using a low energy ultra-high resolution collimator?.
MDP Bone scan
what is responsible for converting gamma energy into light photons?.
the scintillation crystal
In Pet/CT radionuclides produce…
2 Gamma photons of 511 keV
physical properties of Technetium 99m that make it ideal for radionuclide imaging.
- relatively short half life
- relatively short biological half life
- relatively short effective half- life
- non-toxic
- can be administered to patient
- gives off gamma radiation - 140kV
- inert in patient’s body
- stable in situ-
Requirements for transporting radionuclide when injecting patient on the ward
- radiographer wears PPE
- needs to be transported via a syringe tube (surrounded in tungsten) or lead lined cradle
- syringe needs to be labelled - patient’s details, radionuclide being used, Activity of radionuclide
- Take something to store everything after you have used it
- trained member of staff
- never leave cradle unattended
safety requirements needed to perform injections
- ID justifications
- giving information about when the patient will be injected and what time the scan will occur
- ensuring they avoid contact with children and pregnant women.
- perhaps isolate patient - due to radioactivity
- bringing spill kit and yellow bags for radioactive disposal for storage and spill clean
- geiger counters to monitor any residual doses on our hands/ body
Why do we use RNI?
- to look at the area and whole functions of organs - can observe radiation uptake
- monitor treatment i.e cancer treatment
- can cater to those who cannot receive contrast. E.g. those who cannot have a CT IVU can have a MAG3 renogram
- can be combined with 3D imaging - PET/SPECT
- Selective uptake of radiopharmaceuticals by various bodily systems
how does SPECT work
- camera is set up to focus on a specific piece of anatomy
- individual pictures are taken at 3 degree rotations
- this is done until it reaches a 360 degree rotation
- radiographer will overlay the images- creating a 3D image
components of a gamma camera (bottom to top)
- collimators
- scintillation crystals
- photomultiplier tube
- the amplifier
collimators are made of….
- a Lead plate
- septa
why are lead plates used for collimators?
- they are inexpensive
- have a high density
- high attenuation coefficient
Septa in collimators
- a series of small holes perpendicular to the face of the collimator
- the smaller the holes and the more often they are, increases resolution - however, the scans take longer
function of the collimators
- to produce an accurate correlation between the emission of a gamma photon from the source and the position of the photon striking the crystal detector
collimators are dependent on the type of radionuclide used
- low energy collimators (<150 keV) use Tc99m, TI201, I1213 ) - most commonly used
- Medium energy (< 375 keV use In111,Ga67)
- high energy (<500 keV use I131)
types of low energy collimators
LEAP - low Energy All Purpose - used for MAG3 renogram
LEHR - Low Energy High Resolution
LEUHR - Low Energy Ultra High Resolution - used for bone imaging (metastes)
types of medium energy collimators
MEAP - Medium Energy all purpose
types of high energy collimators
HEAP - high energy all purpose collimators
if we increase the hole diameter in the collimator, what happens to the resolution and sensitivity?
resolution decreases
sensitivity increases - allowing more gamma rays through with a steeper angle
if we increase the number of holes in the collimator, what happens to the resolution and sensitivity?
- no change to resolution
- sensitivity improves
if we increase the length of the holes in the collimator, what happens to the resolution and sensitivity?
- resolution increases - rays are able to travel in straight lines
- sensitvity decreases
if we increase the septal thickness in the collimator, what happens to the resolution and sensitivity?
- no change to resolution
- sensitivity decreases
if we increase the object distance from the collimator, what happens to the resolution and sensitivity?
- resolution decreases
- no changes to sensitivity
collimators: spatial resolution
- the ability of the imaging system to distinguish between 2 small points of activity positioned close together
- the smaller the holes, the greater the spatial resolution
collimators: Sensitivity
- the proportion of photon icidents on the collimator, which passes theoght the detector
- the larger the holes in the collimator, the greater the sensitivity (needed for function/uptake)
scintillation crystal
- sodium iodide activated with thallium NaI(Tl)
- no self absorption
- coated with a thin layer of aluminium: crystal is air-tight and light proof
- transparent- so no self absorption
- sensitive to rapid temperature changes - no more than 3 degrees per hour, or crystal will crack
- 50cms in diameter
what does the scintillation crystal do?
- convert absorbed energy to light flashes
scintillation length
- short- to prevent overlap
- the intensity of light builds up quickly and then dies away in <1µs (decrease dead-time effect)
crystal thickness
modern crystals are usually 9.3mm thick
- thicker crystals may reduce resolution
-
crystal detection and absorption
- 50 - 300keV range
- if smaller than 50 keV, then the crystal wont have enough energy to scintillate
- if higher than 300keV, then the photons will pass through the crystal without being absorbed, thus no scintillation
function of a photomultiplier tube
- converts the light from the scintillation event into electrical energy
- they determine the location of each scintillation event as it occurs in the crystal electronic logic circuit
dynode
an electrode in an electron tube that functions to produce secondary emission of electrons.
Science behind PMT’s
- light from the scintillation spreads in many directions and the nearest PM tube receives the most light
- PMT’s all communicate in array
- together, these signals give x and Y co-ordinates of the scintillation event
- the x and y give the computer the plot to mark as an event on the image matrix
- this process takes about 1 minute, however during this time the PMT cannot process another event - (dead-time)
How does the Pulse Height Analyzer (PHA) work?
- analyze the frequency distribution of the spectrum of photon energies that are captured by a gamma camera.
- comes after PMT
- exclude scatter rays
PHA consists of…..
circuits which compare the relative pulse heights from individual tubes
- uses a window of 15-20% of the peak energy value
