Radiopharmaceutics Flashcards

Question

What happens on a molybdenum column

Answer 1

* Put in Mo⁹⁹- this adherse to the aluminium column * Mo⁹⁹- breaks down into Tc⁹⁹ * Saline is passed through the tube and flushes technecium out of the column * Leaving molybdenum behind

Answer 2

* Molybdenum= 67 hr half-life * Time to re-establish equilibrium is 22.89

Answer 3

* Based on: Ease of operation; Efficiency and safety profile; Cost * Practical points * Must swab collection vial's rubber bund * Should elute in a grade A environment * Make sure collection vial has reached atmospheric pressure before removal- try to prevent aerosol production * Require shielding to protect operator

Answer 4

* This is defined by the B.P. as * The radio, expressed as a percentage, of the radioactivity of the Radionuclide concerned to the total radioactivity of the source * E.g. with ⁹⁹Tc Sodium pertechnetate, what percentage is 99-mTcand how much is 99-Tc and 99Mo impurities are there

Answer 5

* 99-Tc/ 99-Mo generator * Not done routinely * Can identify unknown isotopes (e.g. if have a spill) * Can be useful with unlicensed material * Methods * Molybdenum breakthrough test- if there is significant exposure after placing in sheild= molybdenum * Gamma spectroscopy * Measurement of energies emitted * Measurement of decayed sample * Determination of half-life

Answer 6

* Can be administered directly in that form * Most common indication is thyroid imaging * Why is pertechnetate taken up by thyroid * TcO₄ has similar shape and size to iodine * TcO₄ -tetrahedral- 4 x 10^-23 cm³ * Iodide - spherical- 4.2x10^-23 cm³ * Thyroid uptake * ~2% of TcO₄ * ~20% of iodide

Answer 7

* More commonly manipulated to produce Tc in different chemical form * Different chemistry= different biodistribution * Get information from different parts of body * TcO₄- chemically stable, Tc has valency of +7 * In order to make TcO₄ react, need to alter valency state of Tc * Oxidation states of -1 to +7 are known

Answer 8

* ^99mTc can exist in valency states of +7 to -1 and form range of co-ordination complexes * It is eluted in most stable oxidation state (+7) * All 7 electrons are shared with 4 oxygens * Tc ion is surrounded by big O and ligand can't get near * Tin Ions in kit are more attractive to oxygens, which leave Tc leaving it highly reactive * In this state can attach to ligand or may react with water to give Tc colloid

Answer 9

* Might still have some of TcO4 and Tc-colloid there are impurities- they are not useful for scan they just irradiate the body so must be kept to a minimum * Most vials are N rich- Not Oxygen because more oxygen will attach to Tc

Answer 10

* Simple technique- usually single addition of TcO₄^- to a kit- a freeze dried vial containing all required components * Stannous chloride most frequently used reducing agent * Kits commercially available products with product licences * Generally multidose containers * All manipulation performed aseptically

Answer 11

* NEVER inject air into any technetium radiopharmaceutical vial * The oxygen in 0.1mL air can oxidise the stannou ion used in many commercial kits as a reducing agent

Answer 12

* Contain all the required ingredients for preparation of Tc radiopharmaceuticals * Ligand, Sn⁺⁺, buffers- pH affects oxidation state, stabilisers * Single, sterile freeze dried rubber capped vial * Vials contain nitrogen atmosphere * Prevent oxidation of Sn²⁺ * Addition of TcO₄dissolves freeze dried powder and chemical reaction occurs * Some kits need boiling

Answer 13

* Choice of ligand important- structure of Tc-ligand determines biodistribution * Compounds containing N,S,O and P atoms capable of sharing or donating electrons * Over 20 different Tc complexes in routine clinical use * Prepared daily as required in radiopharmacy department * Preparation kept as simpple as possible * Less handling- lower radiation exposure of staff * Less chance of microbial contamination

Answer 14

* Methylene diphosphonate (medronate, MDP) * P-C-P bonds resistant to phosphatase enzyme * Can be labelled with Tc-structure * Binds to hydroxyapatite Ca₁₀(PO₄)₆(OH)₂-imaging during bone growth- osteoblast * Greater the bone turnover, greater uptake * Can detect changes before change in bone density

Answer 15

* Radiochemical purity determination RCP is the % of the radionuclide that is present in the stated chemical form * Mostly assessed through chromatography * % of Tc-ligand should be \>95% to pass * % of free TcO₄^- and reduced Tc \<5%

Answer 16

* Most assays rely on separation methods * Column chromatography- HPLC * Good separation but all activity may not be recovered from column * Expensive equipment; requires expertise to un * Planar chromatography- Use of stationary phase e.g. ITLC SG or filter paper + mobile phase * Separation not always as good, but all activity may be measured

Answer 17

* Butanone or acetone may be used to separate 99m TcO4 from mixture * Saline used to separated 99mTcO₄ and 99mTc-ligand from 99mTc-colloid * Exceptions include 99mTc MAG3 which is more difficult to separate

Answer 18

* Free TcO₄^- will be taken up in salivary glands, thyroid and stomach * Reduced Tc goes to liver and spleen- i.e. irradiation of unintended organs * Sub-diagnostic images * Repeat scan required- doubling radiation dose to the patient