Passage
The radiopharmaceutical 2-deoxy-2-(¹⁸F) fluoro-D-glucose (abbreviated as ¹⁸F-FDG) is a modified form of D-glucose in which the hydroxyl group on the 2-carbon of the molecule has been replaced with a positron-emitting ¹⁸F radionuclide. Synthesis of ¹⁸F-FDG is accomplished in several steps involving both nuclear and chemical reactions, as shown in Figure 1.
Figure 1 Synthetic scheme for 2-deoxy-2-(¹⁸F) fluoro-D-glucoseInitially, a target of ¹⁸O-enriched water (¹⁸OH₂) is bombarded by protons using a cyclotron to achieve a (p-n) nuclear reaction in which a proton hitting the ¹⁸O nucleus is absorbed by the nucleus, causing the ejection of a neutron and forming an ¹⁸F nucleus. Following separation of the resulting ¹⁸F⁻ anions from the residual ¹⁸OH₂ via an ion exchange column, ¹⁸F⁻ is used in a nucleophilic substitution reaction with an acetylated mannose triflate substrate. Subsequent hydrolysis to remove the acetyl protecting groups yields ¹⁸F-FDG.Because ¹⁸F-FDG is an analog of D-glucose, it is readily taken into cells by the same metabolic processes as D-glucose. Once inside the cells, the positron emissions of the ¹⁸F radionuclide can be detected by positron emission tomography (PET) scans to produce diagnostic medical images of objects such as tumors. Emissions from the ¹⁸F radionuclide subsequently diminish over time via radioactive decay (Figure 2) .
Figure 2 Nuclear decay of the ¹⁸F radionuclideBecause of limitations in the spatial resolution of PET scanners, when an object (such as a tumor) is smaller than 30 mm in diameter, the measured specific uptake value (SUV) of ¹⁸F-FDG accumulated within the object is lower than the actual SUV. The recovery coefficient (the ratio of the measured SUV to the actual SUV) shows that the measured SUV decreases as the size of the object decreases below the 30-mm threshold (Figure 3) .
Figure 3 Recovery coefficient as a function of object size in a PET scan with a spatial resolution of 7 mm using ordered subsets expectation maximization (OSEM) image processing
Adapted from: S. Yu. "Review of F-FDG Synthesis and Quality Control." Biomed Imaging Interv J. ©2006 Department of Biomedical Imaging, Faculty of Medicine, University of Malaysa; and P. E. Kinahan, et al., "Positron emission tomography-computed tomography standardized uptake values in clinical practice and assessing response to therapy." Semin Ultrasound CT MR. ©2010 Elsevier.
-Which of the following products is formed from ¹⁸F-FDG following a positron emission? (Note: Assume any anions produced acquire hydrogen ions from the aqueous physiological environment.)

Question

Passage
The radiopharmaceutical 2-deoxy-2-(¹⁸F) fluoro-D-glucose (abbreviated as ¹⁸F-FDG) is a modified form of D-glucose in which the hydroxyl group on the 2-carbon of the molecule has been replaced with a positron-emitting ¹⁸F radionuclide. Synthesis of ¹⁸F-FDG is accomplished in several steps involving both nuclear and chemical reactions, as shown in Figure 1.

Passage The radiopharmaceutical 2-deoxy-2-(<sup>18</sup>F) fluoro-D-glucose (abbreviated as <sup>18</sup>F-FDG) is a modified form of D-glucose in which the hydroxyl group on the 2-carbon of the molecule has been replaced with a positron-emitting <sup>18</sup>F radionuclide. Synthesis of <sup>18</sup>F-FDG is accomplished in several steps involving both nuclear and chemical reactions, as shown in Figure 1. <strong>Figure 1</strong> Synthetic scheme for 2-deoxy-2-(<sup>18</sup>F) fluoro-D-glucoseInitially, a target of <sup>18</sup>O-enriched water (<sup>18</sup>OH<sub>2</sub>) is bombarded by protons using a cyclotron to achieve a (p-n) nuclear reaction in which a proton hitting the <sup>18</sup>O nucleus is absorbed by the nucleus, causing the ejection of a neutron and forming an <sup>18</sup>F nucleus. Following separation of the resulting <sup>18</sup>F<sup>−</sup> anions from the residual <sup>18</sup>OH<sub>2</sub> via an ion exchange column, <sup>18</sup>F<sup>−</sup> is used in a nucleophilic substitution reaction with an acetylated mannose triflate substrate. Subsequent hydrolysis to remove the acetyl protecting groups yields <sup>18</sup>F-FDG.Because <sup>18</sup>F-FDG is an analog of D-glucose, it is readily taken into cells by the same metabolic processes as D-glucose. Once inside the cells, the positron emissions of the <sup>18</sup>F radionuclide can be detected by positron emission tomography (PET) scans to produce diagnostic medical images of objects such as tumors. Emissions from the <sup>18</sup>F radionuclide subsequently diminish over time via radioactive decay (Figure 2) . <strong>Figure 2</strong> Nuclear decay of the <sup>18</sup>F radionuclideBecause of limitations in the spatial resolution of PET scanners, when an object (such as a tumor) is smaller than 30 mm in diameter, the measured specific uptake value (SUV) of <sup>18</sup>F-FDG accumulated within the object is lower than the actual SUV. The recovery coefficient (the ratio of the measured SUV to the actual SUV) shows that the measured SUV decreases as the size of the object decreases below the 30-mm threshold (Figure 3) . <strong>Figure 3</strong> Recovery coefficient as a function of object size in a PET scan with a spatial resolution of 7 mm using ordered subsets expectation maximization (OSEM) image processing Adapted from: S. Yu. Review of F-FDG Synthesis and Quality Control. Biomed Imaging Interv J. ©2006 Department of Biomedical Imaging, Faculty of Medicine, University of Malaysa; and P. E. Kinahan, et al., Positron emission tomography-computed tomography standardized uptake values in clinical practice and assessing response to therapy. Semin Ultrasound CT MR. ©2010 Elsevier. -Which of the following products is formed from <sup>18</sup>F-FDG following a positron emission? (Note: Assume any anions produced acquire hydrogen ions from the aqueous physiological environment.) A) B) C) D)

Figure 1 Synthetic scheme for 2-deoxy-2-(¹⁸F) fluoro-D-glucoseInitially, a target of ¹⁸O-enriched water (¹⁸OH₂) is bombarded by protons using a cyclotron to achieve a (p-n) nuclear reaction in which a proton hitting the ¹⁸O nucleus is absorbed by the nucleus, causing the ejection of a neutron and forming an ¹⁸F nucleus. Following separation of the resulting ¹⁸F⁻ anions from the residual ¹⁸OH₂ via an ion exchange column, ¹⁸F⁻ is used in a nucleophilic substitution reaction with an acetylated mannose triflate substrate. Subsequent hydrolysis to remove the acetyl protecting groups yields ¹⁸F-FDG.Because ¹⁸F-FDG is an analog of D-glucose, it is readily taken into cells by the same metabolic processes as D-glucose. Once inside the cells, the positron emissions of the ¹⁸F radionuclide can be detected by positron emission tomography (PET) scans to produce diagnostic medical images of objects such as tumors. Emissions from the ¹⁸F radionuclide subsequently diminish over time via radioactive decay (Figure 2) .

Figure 2 Nuclear decay of the ¹⁸F radionuclideBecause of limitations in the spatial resolution of PET scanners, when an object (such as a tumor) is smaller than 30 mm in diameter, the measured specific uptake value (SUV) of ¹⁸F-FDG accumulated within the object is lower than the actual SUV. The recovery coefficient (the ratio of the measured SUV to the actual SUV) shows that the measured SUV decreases as the size of the object decreases below the 30-mm threshold (Figure 3) .

Figure 3 Recovery coefficient as a function of object size in a PET scan with a spatial resolution of 7 mm using ordered subsets expectation maximization (OSEM) image processing
Adapted from: S. Yu. "Review of F-FDG Synthesis and Quality Control." Biomed Imaging Interv J. ©2006 Department of Biomedical Imaging, Faculty of Medicine, University of Malaysa; and P. E. Kinahan, et al., "Positron emission tomography-computed tomography standardized uptake values in clinical practice and assessing response to therapy." Semin Ultrasound CT MR. ©2010 Elsevier.
-Which of the following products is formed from ¹⁸F-FDG following a positron emission? (Note: Assume any anions produced acquire hydrogen ions from the aqueous physiological environment.)

Quizplus · Accepted Answer

11ecba2d_1226_7e76_a3bf_19c9938c8978_MD0008_00 Radioactive beta decay can occur in three forms: β⁻-decay (electron emission), β⁺-decay (positron emission), and electron capture. In β⁻-decay, a neutron converts to a nuclear proton and emits an electron. In β⁺-decay, a nuclear proton converts to a neutron (the opposite of β⁻-decay) and ejects a positron (an electron with a positive charge). In electron capture, a proton captures an electron near the nucleus and converts to a neutron without a positron or electron emission. In all three forms of beta decay, the mass number remains unchanged whereas the atomic number either increases (β⁻-decay) or decreases (β⁺-decay and electron capture) by 1. As the atomic number changes, the identity of the element changes accordingly. As stated in the passage, ¹⁸F is a positron-emitter (undergoes β⁺-decay). When the ¹⁸F in ¹⁸F-FDG emits a positron (e⁺) by β⁺-decay, one of the protons in its nucleus is converted to a neutron, yielding a new nucleus with the same mass number (18) but an atomic number that is decreased by 1 (9 − 1 = 8). The result is an ¹⁸O nucleus. 11ecba2d_1226_7e77_a3bf_3573f8a24cd3_MD0008_00 Acquisition of a hydrogen ion by the oxygen anion yields a hydroxyl group appended to an inert glucose molecule. (Choice B) A ¹⁴N nucleus could form only if ¹⁸F were to eject an alpha particle by alpha decay, but ¹⁸F emits positrons by β⁺-decay. (Choice C) A ¹⁸Ne nucleus would not form unless ¹⁸F were to undergo β⁻-decay (electron emission) instead of β⁺-decay (positron emission), but ¹⁸F is a positron-emitter. (Choice D) The mass number and identity of the ¹⁸F nucleus would remain unchanged if it underwent a gamma decay, but ¹⁸F undergoes β⁺-decay. Educational objective: Positron emission occurs during β⁺-decay, in which a nuclear proton converts to a neutron. This causes the atomic number of the nucleus to decrease by 1 while the mass number of the nucleus remains unchanged.

Passage The Radiopharmaceutical 2-Deoxy-2-(18F)fluoro-D-Glucose (Abbreviated as 18F-FDG) Is a Modified Form

Passage The Radiopharmaceutical 2-Deoxy-2-(¹⁸F)fluoro-D-Glucose (Abbreviated as ¹⁸F-FDG) Is a Modified Form