6 How do they do that? 99mTc eluted from generator Mix Kits Images Physiology Methods of localizationA radionuclide can be combined with various stable compounds that are localized by specific organs.
7 Methods of Localization Passive Diffusion Compound diffuses across a biologic membrane from a compartment of higher concentration to one of lower concentration.99mTc-DTPA (brain imaging)99mTc DTPA aerosol133Xe ventilation111In DTPA cisternographyMyocardial perfusion with 99mTc SestamibiFiltration of 99mTc DTPA by kidney
8 Methods of localization Ion Exchange (Chemisorption) The diophosphates are absorbed onto and form a complex with the Calcium Hydroxyapatite crystals. They bind exclusively to the mineral phase of the bone and not to organic matrix.Phosphate bone-scanning (MDP, HDP)Where bone modeling is most active is where the highest amount of Tc-MDP accumulates.
9 Methods of localization Capillary blockage Pulmonary capillaries and small arterioles trap larger particles99mTc MAA particles trapped in the lung capillaries
10 Methods of localization Phagocytosis Engulfment and ingestion by specialized cellsColloid scanning for Liver (middle range particles)Colloid scanning for the Spleen (largest particles)Colloid scanning for bone marrow (smallest particles)Colloid scanning for lymph nodesRemoval of 99mTc sulfur colloid particles by the reticuloendothelial cells in the liver, spleen and bone marrow
11 Methods of localization Active Transport Movement of a compound across a biologic membrane against a concentration gradient, uphill, from a lower to a higher concentration.Iodine or Tc for thyroidPertechnetate for Meckel’s diverticulumPertechnetate for stomachPertechnetate for choroid plexusPertechnetate for hepatobiliary imagingPertechnetate for salivary glandThallium in myocardium
12 Methods of localization Cell Sequestration To separate certain cells apart from the wholeLeukocytes for abscess scanning (WBC)Labeled plateletsSequestration of heat-damaged 99mTc labeled rbc’s by the spleen
13 Methods of localization Metabolism 18F-FDG uptake in myocardial, brain tissues and tumorsPET imaging ~ glucose metabolism
14 Methods of localization Receptor binding 11C-dopamine binding to the dopamine receptors in the brain ~ Neuroreceptor imaging
15 Methods of localization Compartmental localization Partitioning and Retention of the radiopharmaceutical into a biologic compartment.Cardiac scanning with labeled RBC’s (gated blood pool)Cisternogram with In111 DTPA (injected intrathecally and confined to CSFCompartmental Leakage : Labeled RBC’s for GI bleeding detection
16 Methods of localization Antigen-antibody Specific for a tumor associated antigen imagingLocalizes via an antibody-antigen reactionMonoclonal antibodies131 I , 111In and 99mTc labeled antibody to localize tumorsOctreotide,
17 Methods of localization Chemotaxis 111In labeled leukocytes to localize infections
18 BiodistributionConsists of absorption, distribution, metabolism, plasma clearance and excretion.Organ systems involved in 99mTc pertechnetate biodistribution:*Stomach* Salivary glands* Thyroid* Bowel* Choroid plexus* Brain* Sweat glands* Kidney
19 Reducing agentChemically, 99mTcO-4 is nonreactive and won’t label by direct addition of a pharmaceutical compound.The oxidation state needs to first be reduced to allow reaction (tagging)Reducing agents:Stannous chloride (most common)Stannous citrate, stannous tartrate, ferrous sulfate, sodium borohydride
20 Oxygen in the vial Oxygen can cause oxidation of the stannous ion Especially before the addition of 99mTcFree 99mTcSome kits (MDP,HDP) have an antioxidant to prevent oxidationAscorbic acid, gentisic acid
21 Kits Facilitated nuclear pharmacy Long shelf-life Some are as simple as just adding 99mTcO-4Sterile environment, laminar flow hood,New laws
22 Colloids Size falls between a solution and a suspension Particles range between 10 nm and 1µmGelatin : stabilizing agent used to prevent aggregationExamples : 99mTc Sulfur colloid & 99mTc MAAAggregation :
23 Physicochemical Tests Determine purity and integrity of a radiopharmaceuticalCheck for particulate matter, color, clarityParticle size /number of colloids checked under microscopepH : 2-9 (ideal is 7.4 ~ same as blood)Radionuclide Purity : Moly breakthroughRadiochemical Purity : free 99mTcO-4Chemical Purity: Aluminum
24 Biologic Tests Sterilization: membrane filtration is most common Radionuclides can be sensitive to heat sterilizationSterility testing takes longer than the half-life of radionuclides.Okay to used as long as the manufacturer has established sterility and apyrogenicity at the production level.
26 Dispensing Prescription Name ID number Technologist Type of radiopharmaceuticalDose givenCan Vary per licenseTalk about biodose / udm / paper records, etc..Some licensing (?called..Jeff Jones workind on) - info required on film
27 Pediatric doses Biodistribution is different in children Dose must be adjustedUsually calculated based on weight or body surface area
28 Disposal Decay in storage ~ most common Sewer Incineration Burial in landfill*RecordsMore in chapter 11
29 Decay in Storage Radionuclides with half-lives of 120days or less. Can be released to waste when:10 half-livesRadioactivity cannot be detected above backgroundRadioactive signs are removed
30 Sewerage system Radioactive material must be soluble Biologic matter Quantity of monthy allowancesBiologic matter
31 Transfer to an Authorized Recipient Long-lived radionuclidesUsually buried or incinerated
32 Good Practice Radiation signs Wear Lab coat and gloves Absorbent paper Lead containersFilm badgeIdentify radionuclide containersSurvey work areaDo not eat or drink in radiation labMonitor hands and feet
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