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.
-Compared to the effective nuclear charge of ¹⁸O, the effective nuclear charge of ¹⁸F is:

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. -Compared to the effective nuclear charge of <sup>18</sup>O, the effective nuclear charge of <sup>18</sup>F is: A) higher, because <sup>18</sup>F and <sup>18</sup>O have the same number of core electrons but <sup>18</sup>F has fewer neutrons. B) lower, because <sup>18</sup>F has more valence electrons than <sup>18</sup>O. C) higher, because <sup>18</sup>F and <sup>18</sup>O have the same number of core electrons but <sup>18</sup>F has more protons. D) lower, because <sup>18</sup>F has an equal number of protons and electrons.

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.
-Compared to the effective nuclear charge of ¹⁸O, the effective nuclear charge of ¹⁸F is:

Quizplus · Accepted Answer

11ecba2d_1229_d9e1_a3bf_833e053f4161_MD0008_00 Each proton in the nucleus of an atom contributes one unit of positive charge that exerts an electrostatic attraction on the negatively charged electrons around the atom. However, in atoms with several electrons, the core electrons positioned between the valence electrons and the nucleus provide a shielding constant S that counteracts part of the full nuclear charge Z attracting the valence electrons. As a result, the valence electrons experience an effective nuclear charge Z_eff that is less than the full nuclear charge, such that 11ecba2d_1229_d9e2_a3bf_a300defcae27_MD0008_00 Precisely calculating S is complex and depends upon the electron density of a given electron orbital configuration, but a rough, first-order approximation can be made by setting S equal to the number of core electrons. When comparing atoms within the same period (row) of the periodic table, this approximation shows that Z_eff increases as the atomic number increases, but this approximation does not distinguish between different rows of the periodic table and only shows that Z_eff increases as the group (column) number increases. Although ¹⁸F and ¹⁸O both have two core electrons, ¹⁸F has more protons. Therefore, when comparing the effective nuclear charge of ¹⁸O to the effective nuclear charge of ¹⁸F, the ¹⁸F atom has the greater atomic number and higher Z_eff: 11ecba2d_122a_00f3_a3bf_7132afc2d85e_MD0008_00 11ecba2d_122a_00f4_a3bf_95fc7158db8d_MD0008_00 (Choice A) Neutrons have no charge and do not contribute to the nuclear charge of an atom. (Choice B) Although valence electrons can contribute slightly to the shielding constant S, nuclear protons and core electrons influence Z_eff to a much greater extent than valence electrons. (Choice D) All atoms in their elemental state have equal numbers of protons and electrons, but the difference in Z_eff between two atoms of different elements depends on the relative number of nuclear protons and core electrons. Educational objective: The nuclear charge Z (number of protons) influencing a valence electron is diminished by the shielding constant S, which results in an effective nuclear charge Z_eff that is less than the full nuclear charge. By setting S equal to the number of core electrons, Z_eff can be estimated as Z_eff = Z − S.

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