nuclear medicine Flashcards
what type of camera is used in nuclear medicine
gamma camera
what are the 4 main components of radiation detection in nuclear medicine
collimator, NaI crystals, photomultiplier tubes, computer
the gamma camera is capable of multiple different imaging techniques- SPECT
(dynamic, static)
what position would the gamma camera be for a cardiac scan
L mode
what is the L mode of the gamma camera
- camera rotates through 180 degrees from right anterior oblique to left posterior oblique when imaging the heart
what is the first layer of the gamma camera and what material is it made of
- collimator
- lead or tungsten (high density)
what is the purpose of the collimator
- acts as a filter (composed of thousands of precisely ligned holes)
- only allows gamma photons parallel to collimator
- helps with spacial mapping
what happens to the stray photons that cannot pass through the collimator as they are not parallel to ti
they get absorbed by septa (the walls between the holes)
what is spacial mapping
implemented to magnify the image of the zero kinetic energy ions with different scale factors.
be aware that different types of collimators are used based on radionuclide used
what photon energy level in KeV is consider low, medium or high eenrgy + its associated septal thickness
low energy = 150 (0.3mm)
medium energy = 300 (1mm)
high energy = 400 (2mm)
the higher the photon energy, the thicker the septum
what is the 2nd layer of the gamma camera
scintillator
what material is the scintillator made of
sodium iodide with thallium doping
what is the role of the scintillator
converts gamma photons into visible light scintillation
how does a scintillator produce light
- incoming photo energy absorbed by crystal
- excites electron up from valence band into conduction band
- electron de-excites and gets trapped briefly in activation centres (impurities)
- when it de-excites from the activation centre, a photon of visible light is emitted
what is the 3rd layer of the gamma camera
photomultiplier tube
what are the 3 components of the photomultiplier tube
- photocathode
- focusing grid
- anodes and dynodes (in evacuated glass tube)
explain how to photocathode works to produce a signal
- photocathode (-ve) converts light into electron via photoelectric effect
- focussing grid focuses electrons onto the first dynode
- dynodes emit electrons when struck by an electron (process known as electron avalanche)
- anode receives signal (in form of electron avalanche)
define electron avalanche
amplified original signal reducing the effect of scatter photon
- as the dynode gets hit with an electron from the photocathode, it begins to emit electrons itself causing an ‘avalanche’
how does the computer form an image after the signal is received from the photomultiplier tube
- uses anger logic to determine the position of each detection and forms an image
how often is quality control carried out on all gamma cameras to confirm they are working within specification
every morning
peak and uniformity ( measure of how close to peak intensity the emission is over the entire area to be cured, ) are also checked,
if outside the limit, patients image would eb affected and corrective long QC can be performed to recalibrate the camera
what are the 3 types of radioactive decay
alpha, beta, gamma
most scans use gamma emitters, which molecule is most used
technetium-99m
most therapies use alpha or beta emitters, which molecules are most likely used
radium-223
iodine-131
nuclear medicine produces functional images which show the physiology of an organ or system, hence compared to an MRI scan of a freshly dead person, the nuclear medicine brain scan can show if they are alive or not
compare nuclear medicine to MRI
MRI
- great detail
Nuclear medicine
- less detail
- can see physiological state (if organs are working etc)
what are 3 forms of nuclear medicine therapy
- bone (secondary metastasis)
- thyroid ablation (carcinoma or benign)
- neuroendocrine tumour
what radioactive molecule is used for bone cancer therapy
radium-223
what radioactive molecule is used for thyroid ablation
iodine-131
what radioactive molecule is used for neuroendocrine tumour
lutetium-177
know that the radiation source in nuclear medicine cant be ‘switched off’ as it moves around in syringes and pateints
radioactive material can be spilled, or excreted by patients
w
what are the 2 forms of radiation protection in nuclear medicine
gloves
syringe shields
what material are the syringe shields made of
tungsten
be aware that there are machines for contamination monitoring
what properties are needed in a suitable isotope for diagnostic imaging
- half life of 6hrs
(long enough for imaging, short enough to reduce radiation dose) - energy level of gamma emittion around 140 KeV, ideally suitable for efficient detection by scintillation instrument (gamma camera)
- suitable chemical properties, chemically incorporated into small molecule ligands and proteins that concentrate in specific organs or tissues when injected
- non-toxic
- parent nuclide half life of 66hrs (long enough to be transported), short enough for Tc99m formation
practice aseptic technique when working in the radiopharmacy
how is technetium-99m generated from molybdenum-99 in the radiopharmacy
- 0.9% saline solution (eluant) passed thru molybdenum absorbed alumina column
- daughter of molybdenum 99 decay is eluted (removed) from the column due to almost total lack of affinity for alumina
why is there a safety concern with the breakthrough of the parent nuclide into the eluent
If the parent nuclide is introduced into the patient, it will decay and produce extra radiation dose and degrade image
what is an elute
fluid used to wash through another substance to remove something
- extracting one material from another by washing with a solvent
if there is breakdown of the column structure, what can happen to the generator eluate produced
significant levels of AL3+ ions
- this can interfere with pharmaceutical synthesis
allowable levels of parent radionuclides and alumina are set by regulations
what does an alumina assessment test use
semiquantitative colorimetrical test with standard solution of Al3+
- performed first elution, if generator is moved and required for some pharmaceuticals
how do you test for radionuclide purity
- Tc-99m placed inside special 7mm thick lead shield
- shielded solution placed in dose calibrator
- any presence of measure activity from shielded solution must be Mo-99m due to high energy emission
what is the maximum allowed breakthrough of molybdenum-99m for the Tc-99m sample to still be considered as pure
0.15 uCi per mCi of Tc-99m
