Radiopharmacy Flashcards
what is nuclear medicine?
scans that give poor anatomical detail but do show functionality of the organs
what are radiopharmaceuticals made out of?
a ‘useful molecule’ that allows us to target the desired organ + a radioactive isotope that allows us to be detected on the imaging
what are the two views of imaging from a gamma camera?
planar imaging or view organs from multiple angles
how is radiation detected?
- radiopharmaceuticals are injected into the pt
- collimator is placed on the patient
- the gamma photons emitted straight-up from the pt is detected by the detector
why do we use a collimator on the pt?
gamma photons are emitted multi-directionally from the pt
this is stopped with the collimator, allowing the physician to differentiate between the different organs and see your desired organ
what is a collimator?
a sheet of lead with holes in areas to allow the visualisation of the your desired organ by gamma photons only exiting through these gaps.
what is the measurements used for radiation?
sievert (Sv)
what factors affect Sv?
- Storing
- Shielding (lead thickness0
why is ALARP important?
as it means that the radiation given to a pt is AS LOW AS REASONABLY POSSIBLE
what are effects of long exposure of radiation?
- effects the bone marrow
- skin reddening / burning
- pelvis radiotherapy = diarrhoea
- neck radiotherapy = vocal chord damage
what is the inverse square rule?
he strength of the X-ray beam is inversely proportional to the square of distance from the source (X). Standing back by double the distance from a source of radiation (d to 2d) will quarter the dose to the radiologist or radiographer.
how can limit radiation exposure?
- time
- distance
- shielding
what are idealistic pharmacokinetics of radiopharmaceuticals?
- short physical half life
- short biological half life
- nature of radioactive decay
what’s the difference between physical and biological Half life?
physical half life - the period of time required to reduce the radioactivity level of a source to exactly one half its original value due solely to radioactive decay.
biological half life - The time required for a biological system, such as that of a human, to eliminate, by natural processes, half of the amount of a substance (such as a radioactive material) that has entered it.
what are becquerels?
rate of disintegration
what are the different type of radioactive decay?
alpha, beta, gamma
what are the properties of alpha particles?
He nucleus, charge +2
large and collides with tissue = very damaging in small areas
easily shielded
no diagnostic agents but potential for therapeutic use
what are the properties of beta particles?
can be positive or negative
smaller than alpha particles - interact less with tissues
valuable for therapy but not diagnosis
what are the properties of beta+ particles?
known as positrons - antimatter
interact with beta -‘ve particles immediately after emission from the nucleus
what happens when B +’ve and B -‘ve particles collide?
produce 2 gamma rays
which is important in diagnostic procedures
what are the properties of gamma rays?
less interaction with tissue
energy emitted gamma ray is constant for a given radionuclide
valuable in diagnostic
what are the ideal diagnostic properties?
- gamma ray emission only
- for imaging studies, 100-250 Kev
- physical half life of approx. 1.5x(test duration)
- simple cheap
- rapid production
- least exposure to everyone even handling
- versatile chemistry
- chemical quantity
- pure sample
- predictable biodistribution
why is it important to have a predicable biodistribution of radiopharmaceuticals?
to allow us to test the pt’s organ functions rather than unpredictable radiopharmaceuticals so we can evaluate the functionality
describe 99m Tc
43 protons in the nucleus, 43 electrons
20 different isotopes - all radioactive
how is 99 Tc produced?
what’s the significance of 99Mo and 99TcM having difference energy states?
that they can be separated due to having different chemical properties
what is the source of 99Mo?
fission from a nuclear reactor,
no reactors within the UK, therefore, we rely on import
how does a technetium generator work?
contains a shielded glass column packed with alumina,
99Mo is strongly absorbed onto the column,
column is sealed
99Mo decays into 99m-Tc
99m-Tc is separated by passing saline thru the column
how long does it take for a technetium generator to re-establish an equilibrium?
24 hours
how do we know if we have impurities after using a technetium generator?
assess every time we pollute a new generator using a calibrator.
block all 99Tc using a lead shield (4mm thick) and test for any radiation, any radiation observed is due to 99Mo
what are the practical points when using a technetium generator?
- swab collection vial’s rubber bung
- elute in a grade A environment
- make sure the collection vial has reached atmospheric pressure before removal
-require shielding to the operator
when is sodium (99Tc) pertechnetate used?
most commonly for thyroid imaging
why is sodium (99Tc) pertechnetate taken up by the thyroid?
due to its similar shape and size as iodine
iodine (used to make thyroid hormones), however, sodium (99Tc) pertechnetate will not formate these
what are the properties of TcO4?
chemically stable due to having a valency of +7
Tc surrounded by ‘big’ oxygen molecules stopping ligand formation
how can we get the oxygen molecules in TcO4 to leave the molecule?
using tin ions which are more attracted to the oxygen, allowing dissociation to Tc, leaving Tc highly reactive
what happens when we leave Tc highly reactive?
ligands can form if done quickly IF NOT then water may react to form Tc colloid
what is stannous chloride used for?
a reducing agent
what should you be careful of when using Tc vials? and why?
so you do not inject air into the vial as the air will oxidise the stannous ion
why is the choice of ligand used in Tc-ligand important?
as it makes 20 different Tc complexes which allow use in clinical use
which determines the biodistribution
what does 99m-Tc bone radiopharmaceuticals do?
detect osteoblastic activity (bone growth & break down) which occurs to most tumours. therefore, allows tumour detection
how do 99m-Tc bone radiopharmaceuticals detect tumours?
by binding to hydroxyapatite Ca10(PO4)6(OH)2 which is found within growing bone
the greater the bone turnover the greater the uptake
how can we control the quality of radiopharmaceuticals?
mainly thru chromotagraphy…
1. column chromatography - HPLC
2. planar chromatography
this is calculated by radiochemical purity determination RCP (%)
what is the RCP needed for Tc-ligands?
> 95% to pass
what’s the difference between column and planar chromatography in use clinically ?
what are the planar chromatography?
- paper
- instant thin layer chromatography (ITLC)
what are the features of using paper as a stationary phase?
good resolution slower to develop
poor mechanical strength - collapses and tears easily
what are the features of using ITLC as a stationary phase?
glass fibre web inpregnated with modified
silica
stationary phases, silica gel and silicic acid much faster to develop
resolution poor
what are the mobile phases used ?
Butanone or acetone may be used to separate 99mTcO4 from mixture
Saline used to separated 99mTcO4 and 99mTc- ligand from 99mTc-colloid
Exceptions include 99mTc MAG3 which is more difficult to separate
how does the chromatography process work?
is the sample volume important for radiopharmaceuticals?
yes as smaller samples allow a better resolution but a specific volume is not needed
should the spots of the sample applied to chromatography dry?
drying will allow the sample to react with the air, which is not ideal
how do we process chromatogram?
Scan using chromatogram scanner - scintillation detector connected to ratemeter. Signal passed to a chart recorder
Chromatogram counting - cut and count
Can be simply cut in half and counted in a dose calibrator or Cut into smaller sections (e.g. 10) and count each section
what are the problems we may see once undergoing quality control?
- Reaction with the support, especially by drying spots
- Splashing when spotting
- Interaction with dyes used to visualise solvent front
- Grease from fingers
- Strips touching wet walls of the
developing chamber - Contamination with other radiopharmaceuticals when spotting
- Incorrect mobile phase
- Correct, but contaminated mobile phase
- Insufficient mobile phase to allow full development to the requires solvent front
- Contaminated forceps or scissors
- Uneven sample spotting
- Poor mixing of mobile phase components
- Sample washed off by using too much mobile phase in the chamber
- Selective evaporation of the mobile phase component on storage
how will free TcO4- and reduced Tc affect the pt?
will be taken up by unintended organs - unnecessarily radiating
causing sub-diagnostic imaging which will require a doubling in the dose of radiation exposure to the pt
