Question

5. The localization mechanism of "F-sodium fluoride is by uptake A. via nucleophilic substitution B. within myocytes C. in hydroxyapatite crystals D. of long-chain fatty acid complexes 6. The primary source of energy for the heart is from A. glucose B. protein C. fatty acids D. amino acids 7. C-Choline is used for imaging all of the following EXCEPT A. prostate cancer B. brain cancer C. colon cancer D. breast cancer 1"F-FDOPA is used to evaluate A. melanoma B. Parkinson's disease C. Alzheimer's disease D. Pick's disease 8. Which PET radiopharmaceutical provides a noninvasive method to quantify tumor hypoxia in solid tumors of the brain, head and neck cancers, and lung cancers? A. 1F-FMISO B. "N-ammonia C. "F-FDOPA D. "C-sodium acetate 9. 10. The cyclotron production of O, is performed by deuteron irradiation of A."D В."N C. I"F D. "O

Answer 1

5. The localisation mechanism of 18F - NaF is by uptake in Hydroxyapatite crystals.

C. The mechanism of skeletal uptake of ¹⁸F-NaF is based on ion exchange. Bone hardness is due to a crystalline matrix of calcium and phosphate known as hydroxyapatite, which is composed of many different positive and negative ions. Bone. ¹⁸F ions exchange with hydroxyl ions (OH^–) on the surface of the hydroxyapatite to form fluoroapatite. This exchange occurs at a rapid rate. However, the actual incorporation of 18F ions into the crystalline matrix of bone may take days or weeks.

Uptake of ¹⁸F-NaF is a function of osseous blood flow and reflects bone remodeling, and the uptake indicates osteoblastic activity by identifying reactive changes in the underlying affected bone. Abnormal areas of increased ¹⁸F-NaF uptake depicted on PET/CT images indicate osteolytic and osteoblastic processes. The rate-limiting step in the passing of ¹⁸F ions from blood to bone is thought to be blood flow. Differences in regional blood flow will demonstrate a nonuniform pattern of uptake. Mechanisms leading to increased uptake are not limited to neoplastic processes and include any process of bone remodeling. Normal physiologic uptake in adults is generally uniform.

6. The primary source of energy for the heart is from Fatty Acids.

C. Unlike skeletal muscles, Heart functions almost exclusively aerobically and has virtually no glycogen reserves. The heart can use a variety of substrates to oxidatively regenerate ATP depending upon availability. However, main source of energy for cardiac muscles are fatty acids (60-70%). Lactate can also be used, and becomes a very important substrate during exercise. The heart can also utilize amino acids and ketones instead of fatty acids. Ketone bodies (like acetoacetate) are particularly important in diabetic acidosis. During ischemia and hypoxia, the coronary circulation is unable to deliver metabolic substrates to the heart to support aerobic metabolism. Under these conditions, the heart is able to utilize glycogen (a storage form of carbohydrate) temporarily as a substrate for anaerobic production of ATP and the formation of lactic acid. However, the amount of ATP that the heart is able to produce by this pathway is very small compared to the amount of ATP that can be produced via aerobic metabolism. Furthermore, the heart has a limited supply of glycogen, which is rapidly depleted under severely hypoxic conditions.

7.  ¹¹C-Choline is used for imaging all of the following except Breast.

D. ¹¹C-Choline is used in PET imaging studies. Radionuclide is ¹¹C with a Half-life 20.4 minutes. ¹¹C-choline distributes mainly to the pancreas, kidneys, liver, spleen, brain, prostate and colon. Following intravenous administration, ¹¹C-choline undergoes metabolism resulting in the detection of ¹¹C-betaine as the major metabolite in blood.

8. ¹⁸F-FDOPA is used to evaluate Parkinson's disease.

B. ¹⁸F-FDOPA is used to evaluate Dopamine receptors in the brain (Parkinson’s disease is characterized by loss of dopaminergic neurons in the brain). It is also used in the evaluation of Amino acid (AA) transporters as a diagnostic marker for many benign and malignant tumors and overexpression of DOPA decarboxylase which is a characteristic feature of neuroendocrine tumors. Here the radionuclide is ¹⁸F.

9. The answer is ¹⁸F-FMISO.

A. PET hypoxia imaging utilizes radiopharmaceuticals compounds that identify regions of tumor hypoxia. The most commonly used radiopharmaceutical to detect hypoxia is ¹⁸F-fluoromisonidazole (FMISO). When FMISO diffuses into cells, it is first reduced by nitroreductase to a radical form. Under hypoxic conditions, these radicals will bind to intracellular macromolecules and accumulate inside the cell. Positive accumulation of FMISO is proportional to the extent of hypoxia, with high FMISO uptake indicative of a low tissue O₂ concentration.

10. The correct answer is ¹⁴N.

B. ¹⁵O is commonly produced by deuteron bombardment of a nitrogen gas target via the ¹⁴N (d,n) ¹⁵O reaction. The short-lived isotope ¹⁵O is a clinically important radionuclide for positron emission tomography (PET). ¹⁵O is used for metabolic oxygen consumption measurements, ¹⁵O-CO is used for lung perfusion and blood distribution measurements, and ¹⁵OH2O is used for measuring regional cerebral blood flow.