Free Nuclear Medicine Practice Test

1. A radiation exposure of three millisieverts (mSv) is equivalent to which of the following?

a. The U.S. average per capita annual exposure from natural radiation sources
b. A flat-film chest x ray (lateral or posterior-anterior)
c. Dental x rays
d. Positron emission tomography (PET) scanning

2. Which of the following radiopharmaceutical names ALL refer to a compound that includes a radioactive isotope of iodine?

a. Ceretec, dimercaptosuccinic acid (DMSA), iobenguane sulfate
b. Neurolite, MAG3, medronate
c. Metaiodobenzylguanidine (MIBG), iobenguane sulfate
d. Pentetreotide, MIBG, OctreoScan

3. Which of the following nuclear medicine instruments forms images resulting from the annihilation of pairs of matter and antimatter particles?

a. Positron emission tomography (PET) scanner
b. Single-photon emission computed tomography (SPECT) scanner
c. Multigated acquisition (MUGA) scanner
d. Scintigraphy scanner

4. Radioimmunotherapy (RIT) for cancer is founded on which of the following ideas?

a. Antibodies can be designed to attach only to tumor cells
b. Radionuclides can be delivered to cancerous tissue
c. Malignant tissue can be destroyed with minimal effects on the surrounding healthy tissue
d. All of the above

5. At the end of the first stage of a Schilling test, less than 5% of the radionuclide-labeled micronutrient administered to a patient is found in her urine. The test then is repeated with the addition of intrinsic factor, given orally with the radiolabeled micronutrient. This time, more than 20% of the micronutrient is found in the patient's urine. Most likely, this patient will be diagnosed with which of the following?

a. Dietary folic acid deficiency
b. Dietary iron deficiency
c. Pernicious anemia
d. Dietary vitamin B12 deficiency

Answers and Explanations

1. A: Ionizing radiation comes from a variety of natural sources. Galactic cosmic radiation and solar particle events constitute sources from outer space. Earth's magnetic field and atmosphere prevent most space radiation from reaching the surface, but a small amount penetrates. From the ground, radioactivity from uranium in rocks, and especially from radon gas, constitutes a natural, terrestrial source of ionizing radiation, as do bananas and other foods. Overall, a typical individual in the United States receives an annual approximate dose of 3 millisieverts (mSv), and this can double in high-altitude cities, such as Denver and Salt Lake City. Dental x rays typically are in the area of 5 microsieverts (Sv), with some variation, but they should not provide exposures as high as 50 Sv. Flat-film chest x-ray radiography (lateral and posterior-anterior) imparts ionizing radiation doses typically in the range of 10-100 Sv, but a dose of 3 mSv would be way out of the normal range. Typically, positron emission tomography (PET) scanning imparts a dose in the range of 5-7 mSv, somewhat higher than the usual annual background radiation dose in the United States.

2. C: Iobenguane sulfate is used to reach adrenergic nervous tissue; thus, it locates in the adrenal gland and can be used to image or to treat neoplasias such as pheochromocytoma and neuroblastoma. It also is known as metaiodobenzylguanidine (MIBG). When the attached iodine is I-123, the compound is used for imaging. When I-131 is attached, the compound can be used to destroy tumor cells. In either case, the thyroid gland is in jeopardy, as free iodide resulting from metabolism of the compound concentrates in the thyroid with a high risk of thyroid carcinoma. For this reason, administration of nonradioactive potassium iodide is recommended prior to administration of the radiopharmaceutical. Ceretec, dimercaptosuccinic acid (DMSA), Neurolite, MAG3, and medronate all are forms of technetium-99 (Tc-99m). Pentetreotide, also known as OctreoScan, includes indium-111 as the radionuclide.

3. A: All of the nuclear medicine imaging modalities listed make use of a gamma camera, which detects gamma rays resulting from radiopharmaceuticals administered to patients as tracers. Scintigraphy, single-photon emission computed tomography (SPECT), and multigated acquisition (MUGA) all use gamma cameras to detect gamma rays emitted directly from the tracer. Scintigraphy refers to the generation of flat two-dimensional images from areas in which the gamma-emitting traces have concentrated. SPECT is a tomographic application of scintigraphy; thus, two-dimensional images are used to create three-dimensional information. MUGA is a radionuclide angiography technique used to evaluate ventricular function in the heart. PET is very similar to SPECT, except that the gamma radiation is not produced directly from the tracer. Instead of a gamma emitter, a positron emitter, such as 18-fluorodeoxyglucose (18F) is used. Resulting from a type of beta decay in which a proton is converted to a neutron, a positron is the antimatter counterpart of an electron, having the same mass but the opposite charge. When two identical but opposite particles meet, the mass of the particles is converted to energy. This is called pair annihilation. Thus, when a positron is released, it soon meets up with an electron, and energy is released as two gamma ray photons, which are then detected by the gamma camera.

4. D: Radioimmunotherapy (RIT) combines the destructive power of radionuclides on biological tissue with the specificity of immunoglobulins (antibodies). Using molecular features presented on the membranes of tumor cells, specific antibodies can be developed. The target tissue, the tumor in this case, is known as the antigen. The antigen contains various epitopes, areas with a specific shape that are recognized by specific antibodies. Antibodies are complexed with radionuclides at one end, while the other end is what links up with the epitope on the target antigen. Thus, antibodies carrying therapeutic radionuclides can be designed to attach only to tumor cells and delivered to the cancerous tissue by intravenous infusion or by injection directly into the tumor tissue. This maximizes the radiation dose that can be delivered to malignant tissue and minimizes exposure of the surrounding healthy tissue. It also keeps the radiation source within the malignant tissue for a fairly long time.

5. C: The Schilling test is given to patients with signs of vitamin B12 deficiency. Vitamin B12 contains the element cobalt, so it can be labeled with cobalt-57 or cobalt-58. In stage 1 of the test, patients are given an oral preparation of the labeled vitamin B12 plus an intramuscular injection of unlabeled vitamin B12. The intramuscular injection is to saturate binding sites for the vitamin in the liver so as to maximize the proportion of the orally administered dose that gets excreted by the kidneys-if absorption in the small intestine is adequate. If absorption is not adequate (suggested when less than 5% of the labeled B12 is found in the urine), this could be due to a lack of production of intrinsic factor by the parietal cells of the stomach. Thus, in stage 2 of the Schilling test, the patient is given intrinsic factor along with the labeled B12. If the amount of B12 in the urine then increases, this means that the patient is not producing his or her own intrinsic factor. The type of anemia resulting from vitamin B12 deficiency due to lack of intrinsic factor is known as pernicious anemia. Lack of vitamin B12 in the diet produces the same type of anemia as that caused by lack of dietary folic acid, but in such cases the stage 1 Schilling test result would be normal. Iron deficiency has nothing to do with the Schilling test.


Last Updated: 07/05/2018

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