Radiopharmacy Flashcards
What are radiopharmaceuticals (RPs) made up of?
*radioisotope- selected based on properties
*a non radioactive component- Na+ or Cl- ions- influences tissue distribution of radiopharm- minimal risk of toxicity
What factors should be considered when choosing the correct radiopharmaceuticals for diagnostics?
*minimum half life
*mode of decay
*cost, availability
*physical properties
*organ/tissue specificity ?
How long should half life be?
*long enough to synthesise radiopharmaceutical
*long enough to accumulate in target tissue
*BUT must minimise radiation dose to patient
*range from 2min (C15) to several days
What are the modes of decay of radiopharmaceuticals?
*Beta minus (B-) decay- radioactive atoms contain too many neutrons- decay= conversion to a proton arms and B- particle
*Positron (B+) decay- nuclei have too many protons - decay= conversion to neutron and B+ particle
*Gamma decay- nucleus changes energy status by emitting a gamma ray photon
*Electron capsure (EC)- nucleus captured inner orbital electrons converting proton to neutron
What is beta minus decay?
Too many neutrons- convert neutron to proton and B- particle
What is positron decay?( B+)
Too many protons, one converted to neutron and B+ particle
What is gamma decay?
Change in energy status higher to lower by emitting gamma ray photon
What instrument is most cost effective and ideal in radiopharmacy?
Radioisotope generators
-inexpensive
-long shelf lives
What are the most expensive ways to make isotopes?
Accelerator or cyclotron produced radioisotopes- only one isotope made at a time
What methods are used to detect radiopharmaceuticals?
*Gamma scintigraphy- radiopharmaceut emits gamma radiation- detected by gamma camera- need to match energy of decaying gamma photon is within energy window of camera (100-250keV)
Energies outside range- low quality images
*Positron emission tomography (PET)
Positron decay results in emission of 2 511keV gamma ray photons 180°C apart
What is [201TI]?
An analog of K+
Acts as marker for myocyte permeability (muscle cell)
Actively transported into cells by Na2+/K+ pump
What are the disadvantages of [201TI] thallous chloride?
Low emission energy range
Cyclotron produced
What is [99mTc]?
An isonitrile tracer - techetium sestamibi
- most widely used RP in nuclear med
-available by generator 24h a day
-T1/2= 6h
-optimal gamma ray emission for gamma imaging
What is the nuclear stress test used for?
Myocardial perfusion imaging
*RP such as 201TI or 99mTC injected IV
*lie 15-45mins
*scan when rested
*walk on treadmill- increase stress
*monitor blood pressure and rhythm whole time
*at peak exercise, inject RP again
*scan when stressed
*compare images
What Rp’s are used to look for myocardial necrosis?
[111In]- labelled anti myosin antibody- detect areas of irreversible damage
*[99mTC]- labelled glucarate- used in a&e
What RP is used to test for myocardial inflammation?
[111In]- labelled leukocytes
Heart cell death= acute inflammatory response= Leukos influx to site
*leukos isolated from blood, tagged with 111In
*injected back in
-long time- blood handling and prep
What is brain imaging used for?
*screen for primary tumours
*evaluate patients with cerebrovascular disease
*detect intracranial injury
*study patients with intracranial disease eg meningitis
What RP’s are used in brain imaging?
Non lipophilic RPs- only want passage through damaged brain barrier
- 99mTC- penetate and 99mTC-glucepate
What does bone imaging show?
*mineral content
*trauma
*inflammation
*neoplastic injury
What is the most requested diagnostic nuclear medicine procedure?
Bone seeking
Using 99mTC MDP
Why is iodine used in thyroid imaging?
Thyroid traps and concentrates iodine from blood plasma
Prolonged storage in thyroid = easy visualisation
What RP is used in thyroid imaging?
[123I] NaI orally 24 hours before test
Why are radiopharmacueticals used in therapeutics for conditions such as cancer?
Rapidly dividing cells more radiosensitive
Goal= destroy diseased tissue whilst sparing healthy
What RP is used in thyroid conditions such as thyroid carcinoma?
High dose 131I therapy
-can’t leave hospital until radiation below 1220MBq
-patients have probs had thyroid removed
-destroys thyroid carcinoma
What does therapeutic use of RP’s usually involve?
*destruction of tumour cells
*palliative care
What is a radio pharmacy?
Lab designed for prep and dispensing of solutions labelled with radioisotopes for therapeutic and diagnostic purposes
How should a radio pharmacy be designed ?
*must allow preparation of sterile pyrogen free pharmaceuticals
*smooth surfaces and non absorbent for easy cleaning
*2 way protective laminar flow hood
What are two potential health hazards to staff working in radio pharmacy?
External- gamma radiation exposure
Internal- ingestion inhalation etc- especially of long half life pharmaceuticals
What protection should be used in radio pharmacy?
*appropriate shielding from source- tungsten syringe shield , generators housed behind lead bricks, bins should be lead shielded
*strength restriction of source
*restricted period of exposure
What is the difference between wet and dry column generators ?
Wet- permanently installed reservoir of eluant (saline)
Dry- use of small vials of sterile eluant (saline)
How is RP added to cold kits?
*generator eluate measured and diluted if necessary with saline
*appropriate volume of elite and required 99mTC added ASEPTICALLY to cold kit
*via syringe and needle (using tungsten shield)
*vial inverted few times
*incubated at room temp
What is a rapid may to produce 99mTC in house?
Technetium generator
