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37 Cards in this Set
- Front
- Back
Properties of an ideal diagnostic radiopharmaceutical:
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· Pure gamma emitter.
· Gamma energy of 100 - 250 keV. · Effective half-life of 1.5 X test duration. · High target:nontarget ratio. · Minimal radiation dose to patient and nuclear medicine personal. · Patient safety. · Low chemical reactivity. · Inexpensive · Readily available · Simple preparation and quality control if manufactured in house. |
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What is a good effective half life for a diagnostic radiopharmaceutical and why?
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· Aim for 1½x the duration of the procedure
· This is a compromise between a desire to minimize radiation dose to patient and to maximize the signal, counting statistics and image quality for the technician. |
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How do you calculate an effective half-life of a radiopharmaceutical?
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(1/t-effective) = (1/t-biological) + (1/t-physical)
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What do "extremes" look like in determining the effective half-life?
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1. Long biological half-life:
(1/t-effective) = (1/t-physical) In this case, the half life is the physical half-life of the radionuclide. i.e. Tc-99m sulfur colloid used to image the liver 2. Long physical half-life: (1/t-effective) = (1/t-biological) In this case, the half life is determined by how long the radionuclide stays in the body. |
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Radiopharmaceutical used to image bone. Effective half-life: 6 hours
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Tc-99m methylene diphosphate (MDP). This is an example of the ideal radiopharmaceutical because the procedure takes 4 hours.
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How do you make Technitium-99m (Tc⁴⁺) from Pertechnetate anion (TcO₄⁻)
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Use the Stannous reduction method
· Mix pertechnetate with tin (Sn²⁺) · Avoid atmospheric oxygen which will contaminate the reaction |
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What are the radioisotopes of iodine?
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I-123, I-125, and I-131
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What are the properties of the iodine radionuclides?
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I-123 : ideal radionuclide, but expensive (100-400 µCi)
I-125 : low photon energy (30 keV) I-131 : widely used, BUT: high energy gamma emitter (359 keV) AND beta emitter, long half-life |
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What radionuclide is used to treat hyperthyroidism (Graves disease) and thyroid cancer? What precautions should you take?
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I-131 (ca. 30 mCi). Should delay pregnancy for at least 3-6 months after treatment (long half-life, after all...)
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What FOUR radionuclides are used to image new bone growth and what ONE radionucleide is used to treat bone pain?
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Bone growth:
· Ca-45 · Sr-85 · F-18 ·Tc-99m methylene diphosphate (MDP) Bone Pain: · Sr-89 (a beta-emitter) |
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What radionuclide is used to image the gall bladder and detect bile stones?
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Tc-99m labeled iminodiacetic acid (IDA)
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What radionuclide is used to image liver damage?
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Tc-99m sulfur colloid and Tc-99m micro-aggregated albumin. Healthy Kupffer cells phagocytose the colloidal particles while damaged liver areas show up as dim, "cold" spots.
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What radionuclide is used to image the entire heart?
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Tc-99m labeled red blood cells
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What radionuclide is used to image damaged heart tissue?
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Tc-99m (Sn)-tetracycline binds necrotic cardiac tissue (binds to calcium released)
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What radionuclide is used to image healthy heart tissue?
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I-123-16-iodo-9-hexadecanoic acid (used as an energy source in high-energy tissues)
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What radionuclide is used in cardiac stress tests?
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Tl-201 (a potassium analog, it is blood-flow dependent, so it concentrates in healthy tissue and avoids ischemic tissue)
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What radionuclide is used to image tumors?
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Ga-67 (it acts like iron, binds transferrin and accumulates at tumors / sites of inflammation)
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What TWO radionuclides are used for lung perfusion studies and how do they work?
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· Tc-99m macro-aggregated albumin is injected and accumulates in the lungs.
· Embolisms block blood flow so the Tc-99m doesn't image affected areas. · Xe-133 gas is inhaled and images the entire lung. · Any mismatch represents an area of the lung affected by an embolism. |
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How is cerebral death diagnosed? What radionuclide is used?
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· Tc-99m pentetate (DTPA) follows blood flow and will normally distribute to the brain
· In cases of cerebral death, Tc-99m pentetate flows in the vessels outside the skull but is not detected in the brain. |
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How is doxorubicin cardiotoxicity monitored?
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· Tc-99m labeled red blood cells are injected
· The left ventricle radioactivity is monitored at the beginning and ending of contractions. · A healthy heart will have twice as much radioactive blood at end-diastole as at end-systole. Smaller differences indicate cardiotoxicity. |
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Name NINE mechanisms of radiopharmaceutical localization and give examples of each :
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· Active Transport
- I-131 NaI for thyroid imaging · Phagocytosis - Tc-99m sulfur colloid for liver/spleen imaging · Capillary blockade - Tc-99m MAA for pulmonary perfusion imaging · Cell Sequestration - heat-damaged Tc-99m RBCs for spleen imaging · Simple/Exchange Diffusion - F-18 NaF for bone imaging · Compartmental Localization - Xe-133 gas for pulmonary perfusion · Chemisorption - In-111 platelets bound to a thrombus · Antigen / Antibody Reaction - In-111 Oncoscint for localization of ovarian/colorectal carcinoma · Receptor Binding - In-111 octoreotide binding to tumor somatostatin receptor sites |
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Define : "Radiopharmaceutical"
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A chemical containing a radioactive isotope used for diagnosis, mitigation or treatment of disease.
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Define : "Isotope"
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Atoms with an equal number of protons but an unequal number of neutrons.
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What TWO tools are commonly used to visualize radioactivity?
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· a Gamma Camera - (2-D images)
· Single photon emission computerized tomography (SPECT) - (3-D images) |
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What equipment is used to make materials radioactive and how does it work?
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A Cyclotron bombards elements with neutrons making them radioactive.
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How many protons, neutrons and nucleons are in the following? Which number would normally be left out?
14 C 6 |
Nucleons (protons + neutrons) : 14
- this information should always be given Protons : 6 - this information is unique to the element (in this case "C") and is normally left blank Neutrons : 8 (i.e. top-number - bottom number) |
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What are the three basic forms of radioactive decay and what do they look like?
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Alpha - two protons and two neutrons
Beta - high energy "electron" (positron) Gamma - high energy, ionizing radiation |
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Which form of radioactive decay is the most damaging? Which is the most penetrating? Which is considered the most dangerous?
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Alpha - very damaging, awful penetration (blocked by paper)
Beta - moderately damaging, moderate penetration (blocked by aluminum foil) Gamma - moderate-to-low damage, high penetration (blocked by lead) Since gamma penetrates far and can disrupt chemical bonds, it's considered the most dangerous |
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What is the radioactive decay law? (Differential AND Functional form)
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Differential:
∂A/∂t = -λA (λ ≥ 0) Functional: A = Aₒe^(-λt) t₁/₂ = ln(2) / λ |
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What TWO units are used to measure radioactivity?
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The Becquerel [Bq]
- SI unit of one disintegration per second The Curie [Ci] - Historical unit of 1 gram pure Ra-226 |
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How do activity and specific activity differ?
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Activity is disintegrations per unit time
(i.e. suppose a 5mg isotope has 20 mCi activity) Specific activity is disintegractions per unit time per unit mass (i.e. the 5mg isotope has 4 mCi/mg activity) |
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What are the TWO units for absorbed radiation dose?
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The Gray [Gy]
- SI unit of 1 Joule per kg The Radiation Absorbed Dose [rad] - 100 ergs per g (equivalent to 0.01 Gy) |
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What are the the TWO biological dose-equivalent units?
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The Sievert [Sv]
- the SI unit of 1 Gy x "quality factor" - the quality factor varies among types of radiation (alpha, beta, etc) The Radiation Equivalent Man (rem) - 1 rem = QF x 1 rad - 1 rem = 0.01 Sv - Radiation sickness if > 100rem |
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What are the TWO greatest sources of radiation exposure? What are "normal" exposures per year?
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Radon gas - 200 mrem/yr
Smoking - ~150 mrem/yr Average person accumulates: 360 mrem/yr (non-smoker) med X-rays/CAT scans generate 55 mrem/tr |
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What are the values for the "Quality Factor" for different forms of radiation?
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β, ɣ, X-ray : 1
neutrons : 1 - 20 α-particles : 20 |
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What affects a radiation dose?
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· Type and energy of radiation
· Amount of radionuclide (total body dose) · Radionuclide distribution in the body · Relative size and sensitivity of tissues (rapidly differentiating cells – fetus, hematopoietic tissues, germ cells of the reproductive organs) · Physical half-life · Biological half-life - Effective half-life |
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By what direct and indirect actions can radiation cause damage?
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Indirect - ionizing radiation can create reactive ions, such as free radicals and peroxides and can alter sulfhydryl groups on proteins
Direct - DNA damage (mutagneic and carcinogenic) |