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Answers to Sample Certification Questions

I. Radiopharmacy and Nuclear Medicine Physics

II. Clinical Procedures

Radionuclide Generators

  1. Correct answer: a. Na pertechnetate is the most highly oxidized chemical form of Tc, in which the oxidation number is 7+. Choice b is incorrect. Hydrolyzed reduced Tc is an insoluble colloid localizing in the RES. Choice c is also incorrect and represents an insoluble form. Choice d is impossible since sulfate is not used to elute the generator.
  2. Correct answer: c. Transient equilibrium is reached when the parent's half-life is approximately 10 times that of the daughter. In this case, the half-life of Mo-99 (67 hr) is 11 times that of Tc-99m (6 hr), producing a ratio of 11:1. The Mo/Tc generator is considered an ideal example of transient equilibrium.

    3. Choices a and d are incorrect since they don't even represent types of equilibrium. Choice b is also incorrect since the requirement for secular equilibrium is that the half-life of the parent be >> half-life of the daughter, e.g., 100:1 or greater.
  3. Correct answer: d. The daughter can't decay until it is formed. Since the rate of formation of the daughter is slow, in the equilibrium mixture, the daughter will appear to decay with the parent's half-life. When separated from the mixture (e.g., when the generator is eluted), the daughter decays with its characteristic half-life.
  4. Correct answer: c. Soluble "aluminum ion breakthrough" can, under certain conditions, appear in the eluate. While not harmful to the patient, it interferes with preparation of Tc-bone agents, Tc-sulfur colloid, and Tc-RBC labeling. It is therefore mandatory to prove that the level of this chemical impurity does not exceed 10 ppm. It is also possible that the eluate will contain a small amount of Mo-99. This is called "Mo-breakthrough" and must not exceed 0.15 mCi Mo-99/mCi Tc-99m at time of administration. Testing for this radionuclide impurity is mandatory for all licensees. It is also possible that colloidal "hydrolyzed reduce Tc", a radiochemical impurity that is taken up in the RES, will be present in the eluate. While not mandatory to quantify its presence, this simple, rapid, inexpensive test is highly recommended.
  5. Correct answer: d. The actual time required to reach maximum activity level in the Mo/Tc generator is 23 hr. This is an ideal equilibrium time since the generator is typically eluted every 24 hr, right after equilibrium is reached. This maximizes the yield of pertechnetate removed from the generator.
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Physics of Nuclear Medicine

  1. Correct answer is "d". All other answers are incorrect since the other "iso" terms require one number to be constant and the other two numbers to be variable. Isomers can never be isotopes, isotones, or isobars.
  2. Correct answer is "a". In b- decay, an electron is emitted from the nucleus. Other than the source (nucleus rather than outer orbitals), it is indistinguishable from an ordinary electron.
  3. Correct answer is "a". Gamma rays and X-rays of the same energy have almost identical interactions in matter. The primary difference is their source: gammas are emitted from the nucleus; X-rays, from the outer orbitals.
  4. Correct answer is "a". In beta-minus decay, the Z number of the daughter always increases by one unit to counterbalance the -1 charge on the emitted electron. There is only negligible change in mass. The generic equation representing this decay is shown below:


  5. Correct answer is "d". 1 mCi = 10-3 Ci X 3.7 X 1010 dps/Ci = 3.7 X 107 dps
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Math Problems

  1. Correct answer is "b". Logically, 100 mCi to 50 mCi to 25 mCi requires two half-lives. If 24 hr = 2 half-lives, then the half-life = 12 hr. Mathematically,

    2.  

     

    At = A0 X 0.5 (elapsed time/half-life)

  2. Correct answer is "b". Any time one half-value layer is removed from between the source and the detector, the intensity reading doubles. Since I0 is 10 mR/hr, new reading will be 20 mR/hr.
  3. Correct answer is "b". Fraction remaining = 62.5/1000 = 0.0625 = 0.5 n where n = # of half-lives. Taking the log of both sides, log 0.0625 = n x log 0.5 and n = log 0.0625/log 0.5 therefore n = 4
  4. Correct answer is "d". Fraction remaining = 0.5 # of half-lives = 0.519/6
  5. Correct answer is "c". 40 hr/week x 50 weeks/yr = 2000 hr/yr. Dose rate received is therefore 5000 mR/2000 hr = 2.5 mR/hr. By inverse square law, 40 mR/hr x (1 ft)2 = 2.5 mR/hr x d2. d2 = 16 ft2 and therefore d = 4 ft
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Radiopharmacy

  1. Correct answer is "b". This mechanism is also referred to as capillary blockage.
  2. Correct answer is "b". Particulate blockade refers to capillary blockade; hydrolysis of colloid particles has nothing to do with liver/spleen uptake and may not even take place.
  3. Correct answers are "a, b, d". I125 can not be imaged due to the low energy of its gamma and X-rays (28 and 35 keV)
  4. Correct answer is "d". Tl1+ is a K1+ analog; its distribution is directly proportional to blood flow. Choice "b" is incorrect- Tl-201 is excluded from acutely infarcted myocardium.
  5. Correct answer is "a". It is the only reducing agent in the list.
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Quality Control

  1. Correct answer is "b". System "a" is reversed. Systems listed in "c" and "d" are suitable for hepatobiliary agents, but not for the simpler radiopharmaceuticals, e.g., MDP, DTPA, SC, GH, MIAA, pertechnetate.
  2. Correct answer is "d". Hydrolyzed reduced Tc, Tc-MAA, and all other insoluble compounds tend to stay where they are spotted on the chromatography strip. Since they don't migrate, they are inseparable and therefore this impurity is not quantifiable in the presence of insoluble compounds.
  3. Correct answer is "b". Determination of unshielded Tc-99m activity first leaves a charge on the ionization chamber that takes up to 4-5 minutes to bleed off. Artifactually high readings of Mo-99 are likely to be obtained even if no Mo-99 is present, causing a test failure.
  4. Correct answer is "a". Thyroid monitoring is required at 24 hours. None of the other choices represents a legal requirement.
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