Use of radiopharmaceuticals in diagnostic nuclear medicine in the United States: 1960-2010.

To reconstruct reliable nuclear medicine-related occupational radiation doses or doses received as patients from radiopharmaceuticals over the last five decades, the authors assessed which radiopharmaceuticals were used in different time periods, their relative frequency of use, and typical values of the administered activity. This paper presents data on the changing patterns of clinical use of radiopharmaceuticals and documents the range of activity administered to adult patients undergoing diagnostic nuclear medicine procedures in the U.S. between 1960 and 2010. Data are presented for 15 diagnostic imaging procedures that include thyroid scan and thyroid uptake; brain scan; brain blood flow; lung perfusion and ventilation; bone, liver, hepatobiliary, bone marrow, pancreas, and kidney scans; cardiac imaging procedures; tumor localization studies; localization of gastrointestinal bleeding; and non-imaging studies of blood volume and iron metabolism. Data on the relative use of radiopharmaceuticals were collected using key informant interviews and comprehensive literature reviews of typical administered activities of these diagnostic nuclear medicine studies. Responses of key informants on relative use of radiopharmaceuticals are in agreement with published literature. Results of this study will be used for retrospective reconstruction of occupational and personal medical radiation doses from diagnostic radiopharmaceuticals to members of the U.S. radiologic technologists' cohort and in reconstructing radiation doses from occupational or patient radiation exposures to other U.S. workers or patient populations.

Microfluidic continuous-flow radiosynthesis of [18F]FPEB suitable for human PET imaging.

The synthesis of fluorine-18 labeled 3-fluoro-5-[(pyridin-3-yl)ethynyl] benzonitrile ([18F]FPEB) for imaging metabotropic glutamate receptor subtype type 5 (mGluR5) was achieved with a commercial continuous-flow microfluidics device. This work represents the first positron emission tomography (PET) radiopharmaceutical that is suitable for human use with this technology. We also describe a validated synthesis of [18F]FPEB with a commercial reactor-based system.

1H and 13C nuclear magnetic resonance studies of the hindered phencyclone adducts of some smaller branched N-alkyl maleimides: rigorous aryl proton assignments with high-resolution two-dimensional (COSY45) spectroscopy, and anisotropic shielding effects and ab initio geometry optimizations.

Phencyclone, 1, a potent Diels-Alder diene, reacts with a series of N-alkylmaleimides, 2, to form hindered adducts, 3. The 300 MHz 1H and 75 MHz 13C NMR studies of these adducts at ambient temperatures have demonstrated slow rotations on the nuclear magnetic resonance (NMR) timescales for the unsubstituted bridgehead phenyl groups, and have revealed substantial magnetic anisotropic shielding effects in the 1H spectra of the N-alkyl groups of the adducts. The selected N-alkyl groups for the target compounds emphasized smaller branched alkyls, including C3 (isopropyl, a); C4 (isobutyl, b; and t-butyl, c); C5 (n-pentyl, d; isopentyl [isoamyl], e; 1-ethylpropyl, f; t-amyl, g;) and a related C8 isomer (1,1,3,3-tetramethylbutyl ["t-octyl"], h). The straight-chain n-pentyl analog was included as a reference. This present work on the branched N-alkylmaleimide adducts appreciably extends our earlier compilation on the N-n-alkylmaleimide adducts. Key methods for proton assignments included "high-resolution" 1H-1H chemical shift correlation spectroscopy, COSY45. 13C NMR of the adducts, 3, verified the expected number of aryl carbons for slow exchange limit (SEL) spectra of the bridgehead phenyl groups. The synthetic routes involved reaction of the corresponding amines, 4, with maleic anhydride to give the N-alkylmaleamic acids, 5, which underwent cyclodehydration to form the maleimides, 2. Magnetic anisotropic shielding magnitudes for alkyl group protons in the adducts were calculated relative to corresponding proton chemical shifts in the maleimides. Geometry optimizations for the above adducts (and for the N-n-butylmaleimide adduct) were performed at the Hartree-Fock level with the 6-31G* basis set. The existence of different contributing conformers for the adducts is discussed with respect to their calculated energies and implications regarding experimentally observed anisotropic shielding magnitudes.

Self-organized patchiness in asthma as a prelude to catastrophic shifts.

Asthma is a common disease affecting an increasing number of children throughout the world. In asthma, pulmonary airways narrow in response to contraction of surrounding smooth muscle. The precise nature of functional changes during an acute asthma attack is unclear. The tree structure of the pulmonary airways has been linked to complex behaviour in sudden airway narrowing and avalanche-like reopening. Here we present experimental evidence that bronchoconstriction leads to patchiness in lung ventilation, as well as a computational model that provides interpretation of the experimental data. Using positron emission tomography, we observe that bronchoconstricted asthmatics develop regions of poorly ventilated lung. Using the computational model we show that, even for uniform smooth muscle activation of a symmetric bronchial tree, the presence of minimal heterogeneity breaks the symmetry and leads to large clusters of poorly ventilated lung units. These clusters are generated by interaction of short- and long-range feedback mechanisms, which lead to catastrophic shifts similar to those linked to self-organized patchiness in nature. This work might have implications for the treatment of asthma, and might provide a model for studying diseases of other distributed organs.

Topographical distribution of pulmonary perfusion and ventilation, assessed by PET in supine and prone humans.

Using positron emission tomography (PET) and intravenously injected (13)N(2), we assessed the topographical distribution of pulmonary perfusion (Q) and ventilation (V) in six healthy, spontaneously breathing subjects in the supine and prone position. In this technique, the intrapulmonary distribution of (13)N(2), measured during a short apnea, is proportional to regional Q. After resumption of breathing, regional specific alveolar V (sVA, ventilation per unit of alveolar gas volume) can be calculated from the tracer washout rate. The PET scanner imaged 15 contiguous, 6-mm-thick, slices of lung. Vertical gradients of Q and sVA were computed by linear regression, and spatial heterogeneity was assessed from the squared coefficient of variation (CV(2)). Both CV and CV were corrected for the estimated contribution of random imaging noise. We found that 1) both Q and V had vertical gradients favoring dependent lung regions, 2) vertical gradients were similar in the supine and prone position and explained, on average, 24% of Q heterogeneity and 8% of V heterogeneity, 3) CV was similar in the supine and prone position, and 4) CV was lower in the prone position. We conclude that, in recumbent, spontaneously breathing humans, 1) vertical gradients favoring dependent lung regions explain a significant fraction of heterogeneity, especially of Q, and 2) although Q does not seem to be systematically more homogeneous in the prone position, differences in individual behaviors may make the prone position advantageous, in terms of V-to-Q matching, in selected subjects.

The Role of the Practice of Nuclear Pharmacy in Positron Emission Tomography.

As nuclear medicine evolved from an obscure research tool to a mainstream clinical diagnostic and therapeutic modality, so has the role of the practice of pharmacy in nuclear medicine also evolved. A similar evolution is unfolding today in the practice of positron emission tomography (PET). The skills of many diverse professionals, including pharmacists, are essential for the safe and efficient operation of a modern PET facility. The importance of the role of pharmacists in PET has been increasing as the use of PET radiopharmaceuticals has matured from research to clinical to commercial arenas. While it is clear that pharmacists can contribute clinical and technical skills to the operation of a PET center, perhaps one of the most important factors influencing the increased role of pharmacists in PET is their expertise and experience in the drug regulatory process. The commercial distribution of PET radiopharmaceuticals, primarily [18F]2-fluorodeoxyglucose (FDG), is currently being performed by a variety of corporate and institutional facility partnerships, with the likelihood of several new players entering the marketplace in the near future. This factor has served to dramatically increase the role for nuclear pharmacy in PET. The practice of nuclear pharmacy is a well-established component of PET. The role of nuclear pharmacists in PET is complementary to the many other professionals currently practicing in this specialty. With the rapidly increasing clinical demand for FDG imaging, it is likely that the number of facilities and institutions entering into the commercial distribution of PET radiopharmaceuticals will also increase. Such growth will also serve to solidify and expand the role for the practice of nuclear pharmacy in PET.

Pharmacokinetics of 18F-labeled trovafloxacin in normal and Escherichia coli-infected rats and rabbits studied with positron emission tomography.

OBJECTIVE: To measure tissue pharmacokinetics of trovafloxacin (CP 99,219) in normal and infected animals by both direct tissue radioactivity measurements and positron emission tomography (PET). METHODS: Concentrations of [18F]trovafloxacin were measured in normal and infected rats (n=6/group), at 10, 30, 60, and 120 min after injection, by radioactivity measurements. In normal rabbits (n=4) and rabbits with Escherichia coli thigh infection (n=4), tissue concentrations of drug were measured over 2 h with PET. After acquiring the final images, the rabbits were killed and tissue concentrations measured with PET were compared to the results of direct tissue radioactivity measurements. RESULTS: In both species, there was rapid distribution of [18F] trovafloxacin in most peripheral organs. Peak concentrations of more than five times the MIC90 of most Enterobacteriaceae and anaerobes (>100-fold for most organisms) were achieved in all tissues and remained above this level for >2 h. Particularly high peak concentrations were achieved in the kidney (>75 micro g/g), liver (>100 micro g/g), blood (>40 micro g/g), and lung (>10 micro g/g). Even though the concentration of trovafloxacin in infected muscle was reduced (p<0.01), the peak concentration was still >4 micro g/g and tissue levels remained above 2 micro g/g for more than 2 h. Due to the lower concentrations that were achieved in the brain (peak approximately 5 micro g/g), it is expected that trovafloxacin will have limited central nervous system toxicity. CONCLUSION: PET with [18F]trovafloxacin is a useful technique for non-invasive measurements of tissue pharmacokinetics.