11 DESCRIPTION

11.1 Chemical Characteristics

Sodium Fluoride F-18 Injection, USP, is a positron emitting radiopharmaceutical, containing no-carrier-added, radioactive fluoride F-18 that is used for diagnostic purposes in conjunction with PET imaging. It is administered by intravenous injection. The active ingredient, sodium fluoride F-18, has the molecular formula Na[18F] with a molecular weight of 40.99, and has the following chemical structure:

Na+18F–

Sodium Fluoride F-18 Injection, USP, is provided as a ready-to-use, isotonic, sterile, pyrogen-free, preservative-free, clear and colorless solution. Each mL of the solution contains between 370 MBq to 7,400 MBq (10 mCi to 200 mCi) sodium fluoride F-18, at the EOS reference time, in 0.9% aqueous sodium chloride. The pH of the solution is between 4.5 and 8. The solution is presented in 30 mL multiple-dose glass vials with variable total volume and total radioactivity in each vial.

11.2 Physical Characteristics

Fluoride F-18 decays by positron (β+) emission and has a half-life of 109.7 minutes. Ninety-seven percent of the decay results in emission of a positron with a maximum energy of 633 keV and 3% of the decay results in electron capture with subsequent emission of characteristic X-rays of oxygen. The principal photons useful for diagnostic imaging are the 511 keV gamma photons, resulting from the interaction of the emitted positron with an electron (Table 2). Fluorine F-18 atom decays to stable 18O-oxygen.

Table 2. Principal Emission Data for Fluoride F-18

Produced by positron annihilation From: Kocher, D.C. Radioactive Decay Data Tables DOE/TIC-11026, 69, 1981
** Radiation/Emission**	** % Per Disintegration**	** Mean Energy**
Positron(β+)	96.73	249.8 keV
Gamma(±)*	193.46	511.0 keV

The specific gamma ray constant for fluoride F-18 is 5.7 R/hr/mCi (1.35 x 10-6 Gy/hr/kBq) at 1 cm. The half-value layer (HVL) for the 511 keV photons is 4.1 mm lead (Pb) or 2.9 mm tungsten (W) alloy. A range of values for the attenuation of radiation results from the interposition of various thickness of Pb or Tungsten alloy. The range of attenuation coefficients for this radionuclide is shown in Table 3. For example, the interposition of an 8.3 mm thickness of Pb or 5.8 mm thickness of W alloy with a coefficient of attenuation of 0.25 will decrease the external radiation by 75%.

Table 3. Radiation Attenuation of 511 keV Photons by lead (Pb) and Tungsten (W) alloy shielding

** Shield Thickness** (Pb) mm	** Shield Thickness** (W) Alloy mm	** Coefficient of** Attenuation
0	0	0.00
4	3	0.50
8	6	0.25
13	9	0.10
26	19	0.01
39	28	0.001
53	37	0.0001

Table 4 lists the fraction of radioactivity remaining at selected time intervals from the calibration time. This information may be used to correct for physical decay of the radionuclide.

Table 4. Physical Decay Chart for Fluoride F-18

calibration time
** Time Since Calibration**	** Fraction Remaining**
0*	1.00
15 minutes	0.909
30 minutes	0.826
60 minutes	0.683
110 minutes	0.500
220 minutes	0.250
440 minutes	0.060
12 hours	0.011
24 hours	0.0001