Ventricular synchrony is not significantly determined by absolute myocardial perfusion in patients with chronic heart failure: A 13N-ammonia PET study.

BACKGROUND: It is thought that heart failure (HF) patients may benefit from the evaluation of mechanical (dys)synchrony, and an independent inverse relationship between myocardial perfusion and ventricular synchrony has been suggested. We explore the relationship between quantitative myocardial perfusion and synchrony parameters when accounting for the presence and extent of fixed perfusion defects in patients with chronic HF. METHODS: We studied 98 patients with chronic HF who underwent rest and stress Nitrogen-13 ammonia PET. Multivariate analyses of covariance were performed to determine relevant predictors of synchrony (measured as bandwidth, standard deviation, and entropy). RESULTS: In our population, there were 43 (44%) women and 55 men with a mean age of 71 ± 9.6 years. The SRS was the strongest independent predictor of mechanical synchrony variables (p < .01), among other considered predictors including: age, sex, body mass index, smoking, diabetes mellitus, dyslipidemia, hypertension, rest myocardial blood flow (MBF), and myocardial perfusion reserve (MPR). Results were similar when considering stress MBF instead of MPR. CONCLUSIONS: The existence and extent of fixed perfusion defects, but not the quantitative PET myocardial perfusion parameters (sMBF and MPR), constitute a significant independent predictor of ventricular mechanical synchrony in patients with chronic HF.

A highly sensitive assay for xanthine oxidoreductase activity using a combination of [(13) C2 ,(15) N2 ]xanthine and liquid chromatography/triple quadrupole mass spectrometry.

In this study, we developed a highly sensitive assay for xanthine oxidoreductase (XOR) activity utilizing a combination of [(13) C2 ,(15) N2 ]xanthine and liquid chromatography (LC)/triple quadrupole mass spectrometry (TQMS). In this assay, the amount of [(13) C2 ,(15) N2 ]uric acid (UA) produced by XOR was determined by using LC/TQMS. For this assay, we synthesized [(13) C2 ,(15) N2 ]xanthine as a substrate, [(13) C2 ,(15) N2 ]UA as an analytical standard, and [(13) C3 ,(15) N3 ]UA as an internal standard. The [(13) C2 ,(15) N2 ]UA calibration curve obtained using LC/TQMS under the selected reaction monitoring mode was evaluated, and the results indicated good linearity (R(2) = 0.998, weighting of 1/x(2) ) in the range of 20 to 4000 nM. As a model reaction of less active samples, the XOR activity of serial-diluted mouse plasma was measured. Thereby, the XOR activity of the 1024-fold-diluted mouse plasma was 4.49 ± 0.44 pmol/100 µL/h (mean ± standard deviation, n = 3). This value is comparable to the predicted XOR activity value of healthy human plasma. Hence, this combination method may be used to obtain high-sensitivity measurements required for XOR activity analysis on various organs or human plasma.

Impact of time-of-flight on qualitative and quantitative analyses of myocardial perfusion PET studies using (13)N-ammonia.

BACKGROUND: The impact of time-of-flight (TOF) in myocardial perfusion (13)N-ammonia positron emission tomography (PET) is unclear. METHODS AND RESULTS: Twenty consecutive subjects underwent rest and adenosine stress (13)N-ammonia myocardial perfusion PET. Two sets of images were reconstructed using TOF-ordered subset expectation maximization (TOF-OSEM) and 3-dimensional row-action maximum likelihood algorithm (3D-RAMLA). Qualitative and quantitative analyses from the TOF-OSEM and 3D-RAMLA reconstructions were compared. Count profile curves revealed that TOF relatively increased the uptake of (13)N-ammonia at the lateral walls, and apical thinning was emphasized on the TOF images. Both segmental rest and stress myocardial blood flow (MBF) values were higher with TOF-OSEM use than with 3D-RAMLA use (rest MBF: 0.955 ± 0.201 vs 0.836 ± 0.185, P < .001; stress MBF: 2.149 ± 0.697 vs 2.058 ± 0.721, P < .001). The differentiation of MBF between reconstructions was more enhanced under rest conditions. Thus, segmental myocardial flow reserve (MFR) observed using TOF-OSEM reconstruction was lower than that observed using 3D-RAMLA (2.25 ± 0.57 vs 2.46 ± 0.75, P < .001). No remarkable differences were observed between segmental and territorial results. CONCLUSIONS: TOF increased lateral wall counts and emphasized apical thinning. Quantitatively, TOF reconstruction showed increased MBF, especially under relatively low perfusion conditions.

Membrane interactions of phylloseptin-1, -2, and -3 peptides by oriented solid-state NMR spectroscopy.

Phylloseptin-1, -2, and -3 are three members of the family of linear cationic antimicrobial peptides found in tree frogs. The highly homologous peptides encompass 19 amino acids, and only differ in the amino acid composition and charge at the six most carboxy-terminal residues. Here, we investigated how such subtle changes are reflected in their membrane interactions and how these can be correlated to their biological activities. To this end, the three peptides were labeled with stable isotopes, reconstituted into oriented phospholipid bilayers, and their detailed topology determined by a combined approach using (2)H and (15)N solid-state NMR spectroscopy. Although phylloseptin-2 and -3 adopt perfect in-plane alignments, the tilt angle of phylloseptin-1 deviates by 8° probably to assure a more water exposed localization of the lysine-17 side chain. Furthermore, different azimuthal angles are observed, positioning the amphipathic helices of all three peptides with the charged residues well exposed to the water phase. Interestingly, our studies also reveal that two orientation-dependent (2)H quadrupolar splittings from methyl-deuterated alanines and one (15)N amide chemical shift are sufficient to unambiguously determine the topology of phylloseptin-1, where quadrupolar splittings close to the maximum impose the most stringent angular restraints. As a result of these studies, a strategy is proposed where the topology of a peptide structure can be determined accurately from the labeling with (15)N and (2)H isotopes of only a few amino acid residues.

Robust and low cost uniform (15)N-labeling of proteins expressed in Drosophila S2 cells and Spodoptera frugiperda Sf9 cells for NMR applications.

Nuclear magnetic resonance spectroscopy is a powerful tool to study structural and functional properties of proteins, provided that they can be enriched in stable isotopes such as (15)N, (13)C and (2)H. This is usually easy and inexpensive when the proteins are expressed in Escherichiacoli, but many eukaryotic (human in particular) proteins cannot be produced this way. An alternative is to express them in insect cells. Labeled insect cell growth media are commercially available but at prohibitive prices, limiting the NMR studies to only a subset of biologically important proteins. Non-commercial solutions from academic institutions have been proposed, but none of them is really satisfying. We have developed a (15)N-labeling procedure based on the use of a commercial medium depleted of all amino acids and supplemented with a (15)N-labeled yeast autolysate for a total cost about five times lower than that of the currently available solutions. We have applied our procedure to the production of a non-polymerizable mutant of actin in Sf9 cells and of fragments of eukaryotic and viral membrane fusion proteins in S2 cells, which typically cannot be produced in E. coli, with production yields comparable to those obtained with standard commercial media. Our results support, in particular, the putative limits of a self-folding domain within a viral glycoprotein of unknown structure.

Toward hyperpolarized molecular imaging of HIV: synthesis and longitudinal relaxation properties of (15) N-Azidothymidine.

Previously unreported (15) N labeled Azidothymidine (AZT) was prepared as an equimolar mixture of two isotopomers: 1-(15) N-AZT and 3-(15) N-AZT. Polarization decay of (15) N NMR signal was studied in high (9.4 T) and low (~50 mT) magnetic fields. (15) N T1 values were 45 ± 5 s (1-(15) N-AZT) and 37 ± 2 s (3-(15) N-AZT) at 9.4 T, and 140 ± 16 s (3-(15) N-AZT) at 50 mT. (15) N-AZT can be potentially (15) N hyperpolarized by several methods. These sufficiently long (15) N-AZT T1 values potentially enable hyperpolarized in vivo imaging of (15) N-AZT, because of the known favorable efficient (i.e., of the time scale shorter than the longest reported here (15) N T1 ) kinetics of uptake of injected AZT. Therefore, 3-(15) N-AZT can be potentially used for HIV molecular imaging using hyperpolarized magnetic resonance imaging.

Synthesis of [(3) H], [(13) C3 , (15) N], and [(14) C]SCH 900567: an inhibitor of TNF-α (tumor necrosis factor alpha) converting enzyme (TACE).

SCH 900567 is a specific inhibitor of tumor necrosis factor-alpha converting enzyme and is a potential candidate for the treatment of rheumatoid arthritis. [(3) H]SCH 900567 was synthesized to support the initial drug metabolism and pharmacokinetics studies. Stable isotope-labeled [(13) C3 , (15) N]SCH 900567 was requested by the bioanalytical group as an internal standard for Liquid chromatography-tandem mass spectrometry (LC-MS/MS) method development as well as by the drug metabolism and pharmacokinetics group for a potential microdose study. [(13) C3 , (15) N]SCH 900567 is synthesized via a linear sequence of seven steps from commercially available materials in 2.6% overall yield. [(14) C]SCH 900567 was needed for a quantitative whole body autoradiography studies and was prepared from unlabeled Active Pharmaceutical Ingredient (API) via hydrolysis of the hydantoin moiety followed by rebuilding the hydantoin ring using potassium [(14) C]cyanate to give the desired product in 42.8% overall yield. Activation of the hydantoin moiety of SCH 900567 to achieve hydrolysis followed by derivatization of the resulting amino acid to avoid decarboxylation during cyclization is also discussed.

Synthesis of (13) C2 (15) N2 -labeled anti-inflammatory and cytoprotective tricyclic bis(cyanoenone) ([(13) C2 (15) N2 ]-TBE-31) as an internal standard for quantification by stable isotope dilution LC-MS method.

Tricyclic bis(cyanoenone), TBE-31, one of the most potent activators of the Keap1/Nrf2/antioxidant response element pathway, has been developed as a new anti-inflammatory and cytoprotective agent. (13) C2 (15) N2 -labeled TBE-31 ([(13) C2 (15) N2 ]-TBE-31), which has two (13) C and two (15) N atoms in two cyano groups, was designed to develop a method for quantification of cell, tissue, and plasma levels of TBE-31 that involves chromatography/mass spectrometry coupled with the use of a stable isotope-labeled internal standard. [(13) C2 (15) N2 ]-TBE-31 was successfully synthesized in four steps from a previously reported intermediate, which is prepared in 11 steps from cyclohexanone, by introduction of two (13) C atoms with ethyl [(13) C]formate and two (15) N atoms with hydroxyl[(15) N]amine. The stable isotope dilution liquid chromatography-mass spectrometry method for quantification of TBE-31 was successfully developed using [(13) C2 (15) N2 ]-TBE-31 to compensate for any variables encountered during sample processing and analysis.

A surrogate analyte method to determine D-serine in mouse brain using liquid chromatography-tandem mass spectrometry.

A bioanalytical method for determining endogenous d-serine levels in the mouse brain using a surrogate analyte and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. [2,3,3-(2)H]D-serine and [(15)N]D-serine were used as a surrogate analyte and an internal standard, respectively. The surrogate analyte was spiked into brain homogenate to yield calibration standards and quality control (QC) samples. Both endogenous and surrogate analytes were extracted using protein precipitation followed by solid phase extraction. Enantiomeric separation was achieved on a chiral crown ether column with an analysis time of only 6 min without any derivatization. The column eluent was introduced into an electrospray interface of a triple-quadrupole mass spectrometer. The calibration range was 1.00 to 300 nmol/g, and the method showed acceptable accuracy and precision at all QC concentration levels from a validation point of view. In addition, the brain d-serine levels of normal mice determined using this method were the same as those obtained by a standard addition method, which is time-consuming but is often used for the accurate measurement of endogenous substances. Thus, this surrogate analyte method should be applicable to the measurement of d-serine levels as a potential biomarker for monitoring certain effects of drug candidates on the central nervous system.

Characterizing the normal range of myocardial blood flow with 8²rubidium and ¹³N-ammonia PET imaging.

BACKGROUND: Diagnosis of coronary disease and microvascular dysfunction may be improved by comparing myocardial perfusion scans with a database defining the lower limit of normal myocardial blood flow and flow reserve (MFR). To maximize disease detection sensitivity, a small normal range is desirable. Both (13)N-ammonia and (82)Rb tracers are used to quantify blood flow and MFR using positron emission tomography (PET). The goal of this study was to investigate the trade-off between noise and accuracy in both (82)Rb and (13)N-ammonia normal databases formed using a net retention model. METHODS: Fourteen subjects with <5% risk of CAD underwent rest and stress (82)Rb and (13)N-ammonia dynamic PET imaging in a randomized order within 2 weeks. Myocardial blood flow was quantified using a one-compartment model for (82)Rb, and a two-compartment model for (13)N-ammonia. A simplified model was used to estimate tracer retention, with tracer-specific net extraction functions derived to obtain flow estimates. RESULTS: Normal variability of retention reserve was equivalent for both tracers (±15% globally, ±16% regionally) and was lower in comparison to compartment model results (P < .05). The two-compartment model for (13)N-ammonia had the smallest normal range of global blood flow resulting in a lower limit of normal MFR = 2.2 (mean - 2 SD). CONCLUSION: These results suggest that the retention model may have higher sensitivity for detection and localization of abnormal flow and MFR using (82)Rb and (13)N-ammonia, whereas the (13)N-ammonia two-compartment model has higher precision for absolute flow quantification.

Endogenous compounds labeled with radionuclides of short half-life-some perspectives.

In the article, the strategy and synthesis of some endogenous compounds labeled mainly with (11) C are presented. There are some examples illustrating how endogenous labeled compounds in connection with positron emission tomography have unique properties to describe various biological processes, and a few examples of the use of tracers labeled with (13) N and (15) O are also discussed. Labeled endogenous compounds may be an important asset to describe the conditions and the status of biological systems and might therefore be a key for the future search of individualized medicine.

Radiosynthesis of [13N]dantrolene, a positron emission tomography probe for breast cancer resistant protein, using no-carrier-added [13N]ammonia.

Dantrolene (1) is a substrate for breast cancer resistant protein, which is widely distributed in the blood-brain-barrier, intestine, gall bladder, and liver. PET study with 1 labeled with a positron emitter can be used to visualize BCRP and to elucidate the effect of BCRP on the pharmacokinetics of drugs. The objective of this study was to label 1 using nitrogen-13 ((13)N, a positron emitter; half-life: 9.9min). Using no-carrier-added [(13)N]NH(3) as the labeling agent, we synthesized [(13)N]dantrolene ([(13)N]1) for the first time. The reaction of carbomyl chloride 2b with [(13)N]NH(3) gave an unsymmetrical urea [(13)N]3, followed by cyclization of [(13)N]3 to afford [(13)N]1. Due to its instability, 2b was prepared in situ by treating amine 5 with triphosgene in a ratio of 4 to 1 and used for subsequent [(13)N]ammonolysis without purification.

Compensated second-order recoupling: application to third spin assisted recoupling.

We consider the effect of phase shifts in the context of second-order recoupling techniques in solid-state NMR. Notably we highlight conditions leading to significant improvements for the Third Spin Assisted Recoupling (TSAR) mechanism and demonstrate the benefits of resulting techniques for detecting long-distance transfer in biomolecular systems. The modified pulse sequences of PAR and PAIN-CP, Phase-Shifted Proton Assisted Recoupling (AH-PS-PAR) and Phase-Shifted Proton-Assisted Insensitive Nuclei Cross Polarization (ABH-PS-PAIN-CP), still rely on cross terms between heteronuclear dipolar couplings involving assisting protons that mediate zero-quantum polarization transfer between low-γ nuclei ((13)C-(13)C, (15)N-(15)N, (15)N-(13)C polarization transfer). Using Average Hamiltonian Theory we show that phase inversion compensates off-resonance contributions and yields improved polarization transfer as well as substantial broadening of the matching conditions. PS-TSAR greatly improves on the standard TSAR based methods because it alleviates their sensitivity to precise RF settings which significantly enhances robustness of the experiments. We demonstrate these new methods on a 19.6 kDa protein (U-[(15)N, (13)C]-YajG) at high magnetic fields (up to 900 MHz (1)H frequency) and fast sample spinning (up to 65 kHz MAS frequency).

Three-dimensional positron emission tomography/computed tomography analysis of 13NO3- uptake and 13N distribution in growing kohlrabi.

We report the application of three-dimensional positron emission tomography/computed tomography (PET/CT) for the analysis of (13)NO(3)(-) uptake and (13)N distribution in growing kohlrabi. The analytical procedures, equipment parameters, and image reconstruction mode for plant imaging were tested and selected. (13)N in growing kohlrabi plants was imaged versus time using both PET movies and PET/CT tomograms. The (13)NO(3)(-) transport velocity in kohlrabi from root to petiole was estimated to be 1.0 cm/min. The appearance of shell-shaped (13)NO(3)(-) transport pathways, corresponding to the kohlrabi corm, suggests the existence of special routes with higher efficiency for (13)NO(3)(-) transport, which tends to have the shortest distances to the leaves or buds. Standardized uptake values (SUVs), used as the representative figures for describing (13)N distribution, were quantified versus time at some putative sites of interest. For multiple analysis of the same-plant, (13)N distribution in kohlrabi under normal conditions, methionine sulfoximine (MSX) stress, and recovery from MSX stress was examined. The (13)N distribution variation studies were also done under the above three growth conditions. Our results suggest a significant downregulation of nitrate uptake in kohlrabi in the presence of MSX.

Coronary calcium score scans for attenuation correction of quantitative PET/CT 13N-ammonia myocardial perfusion imaging.

PURPOSE: The aim of this study was to evaluate whether ECG-triggered coronary calcium scoring (CCS) scans can be used for attenuation correction (AC) to quantify myocardial blood flow (MBF) and coronary flow reserve (CFR) assessed by PET/CT with (13)N-ammonia. METHODS: Thirty-five consecutive patients underwent a (13)N-ammonia PET/CT scan at rest and during standard adenosine stress. MBF values were calculated using AC maps obtained from the ECG-triggered CCS scan during inspiration and validated against MBF values calculated using standard non-gated transmission scans for AC. CFR was calculated as the ratio of hyperaemic over resting MBF. In all 35 consecutive patients intraobserver variability was assessed by blinded repeat analysis for both AC methods. RESULTS: There was an excellent correlation between CT AC and CCS for global MBF values at rest (n = 35, r = 0.94, p < 0.001) and during stress (n = 35, r = 0.97, p < 0.001) with narrow Bland-Altman (BA) limits of agreement (-0.21 to 0.10 ml/min per g and -0.41 to 0.30 ml/min per g) as well as for global CFR (n = 35, r = 0.96, p < 0.001, BA -0.27 to 0.34). The excellent correlation was preserved on the segmental MBF analysis for both rest and stress (n = 1190, r = 0.93, p < 0.001, BA -0.60 to 0.50) and for CFR (n = 595, r = 0.87, p < 0.001, BA -0.71 to 0.74). In addition, reproducibility proved excellent for global CFR by CT AC (n = 35, r = 0.91, p < 0.001, BA -0.42-0.58) and CCS scans (n = 35, r = 0.94, p < 0.001, BA -0.34-0.45). CONCLUSION: Use of attenuation maps from CCS scans allows accurate quantitative MBF and CFR assessment with (13)N-ammonia PET/CT.

Efficient system for the preparation of [13N]labeled nitrosamines.

In the present Letter, a fast and reproducible method for the synthesis of N-[(13)N]nitrosamines is reported. The labeling strategy is based on trapping [(13)N]NO2- in an anion exchange resin. The reaction with secondary amines in the presence of Ph(3)P and Br(2) led to the formation of the desired nitrosamines in short reaction times (2 min) with excellent radiochemical conversion (>45%). Final radiotracers were obtained after purification in good radiochemical yields (>30%, decay corrected). Radiochemical purity was above 99% in all cases.

Production of nitrogen-13-labeled ammonia by using 11MeV medical cyclotron: our experience.

A method has been developed for the production of (13)N-labeled ammonia in usable quantities with negligible contamination. A system was developed and a process for the production of nitrogen-13 ammonium ions from a target material in the form of a dilute solution of ethanol in natural water, i.e. the bombardment of oxygen-16 with protons within the target material. The system includes a device for producing a proton beam which travels along a pre selected path and strikes the target material in a target chamber. This target chamber is positioned in the path of the proton beam such that subjection of the target material to the beam produces nitrogen-13 atoms and alpha particles. These nitrogen-13 atoms are converted in the aqueous solution to ammonium ions and oxides and are conducted from the target holder to a purification cartridge for collecting a purified product containing the ammonium ions.

Production of [13N]ammonia from [13C]methanol on a 7.5 MeV cyclotron using 13C(p, n)13N reaction: Detection of myocardial infarction in a mouse model.

[13N]Ammonia is commonly produced using 16O(p, α)13N reaction but one of the limiting factor of this reaction is the relatively small nuclear cross-section at proton energies of <10 MeV. An alternative production method using 13C(p, n)13N reaction, which has a higher nuclear cross-section at low proton energies, is more suitable for a preclinical PET imaging facility equipped with a <10 MeV cyclotron. Here, we report a novel method to produce [13N]ammonia from [13C]methanol for preclinical use on a 7.5 MeV cyclotron. A tantalum solution target (80 µl) consisting of a havar window supplied by the cyclotron manufacturer for the production of [18F]fluoride was used without any modifications. The final bombardment parameters were optimized as follow: [13C]methanol concentration in target solution - 10%, bombardment time - 8 min, and beam current - 2.2 µA. These parameters provided doses of [13N]ammonia which were sufficient to conduct preclinical PET imaging studies in a mouse model of myocardial infarction. Under optimized conditions, the operational lifetime of the target was approximately 150 µAmin. Radionuclide identity of the product as 13N was confirmed by measuring the decay half-life and its radionuclide purity was confirmed by γ-ray spectroscopic analysis. Gas chromatography revealed that the final [13N]ammonia dose was not distinguishable from water, showing no traces of methanol. As expected, PET/CT imaging in healthy CD-1 mice indicated the accumulation of [13N]ammonia in myocardial tissue; mice with myocardial infarction created by left ascending coronary ligation showed clear perfusion deficit in affected tissue. This work demonstrates the proof-of-concept of using 13C(p, n)13N reaction to produce [13N]ammonia from [13C]methanol with a <10 MeV cyclotron, and its diagnostic application in imaging cardiac perfusion.

13N-NH3: a selective contrast-enhancing tracer for brain tumor.

PURPOSE: The purpose of this study is to determine whether there is a qualitative and quantitative relationship between the breakdown of the blood-brain barrier, defined radiologically by the contrast enhancement of MRI, and the uptake of N-NH3 in brain tumors. METHODS: The results of N-NH3 PET in 42 patients suspected of having brain tumors were compared with the findings of contrast-enhanced MRI. A histopathological diagnosis was carried out in 33 patients, and a clinical diagnosis was performed in the remaining patients. PET and MRI images were visually inspected, and the contrast index (CI) of MRI and the uptake index (UI) of N-NH3 were measured. RESULTS: Contrast enhancement of MRIs was seen in 20 of 29 brain tumors (69%). Increased uptake of N-NH3 was seen in 24 of 29 brain tumors (83%). Nineteen of 20 contrast-enhancing brain tumors exhibited the increased uptake of N-NH3 (95%). Areas of the increased N-NH3 uptake corresponded to areas enhanced on MR images in the majority of cases. Five out of nine nonenhancing tumors exhibited increased uptake of N-NH3 (56%). The contrast enhancement of MRIs was seen in nine of 13 nonneoplastic lesions (69%). None of the nonneoplastic lesions showed increased uptake of N-NH3, yielding a specificity of 100% for brain tumors (0 of 13). CI for tumor tissue was 1.46+/-0.64. UI of N-NH3 for tumor tissue was 1.64+/-0.71. CI and UI for tumor tissue were significantly correlated (r=0.86, P<0.01). A statistically significant difference in uptake levels of N-NH3 between contrast-enhancing tumors and nonenhancing tumors (1.88+/-0.66, n=20 vs. 1.11+/-0.52, n=9, P<0.01) was observed. UI was higher in brain tumors compared with the nonneoplastic lesions (1.64+/-0.71 vs. 0.71+/-0.19, P<0.01). CONCLUSION: N-NH3 is a potential selective contrast-enhanced tracer for brain tumor, and may prove especially useful for evaluating the contrast-enhancing lesions on MRI to distinguish brain tumors from nonneoplastic lesions.

Synthesis of 11C, 18F, 15O, and 13N radiolabels for positron emission tomography.

Positron emission tomography (PET) is a powerful and rapidly developing area of molecular imaging that is used to study and visualize human physiology by the detection of positron-emitting radiopharmaceuticals. Information about metabolism, receptor/enzyme function, and biochemical mechanisms in living tissue can be obtained directly from PET experiments. Unlike magnetic resonance imaging (MRI) or computerized tomography (CT), which mainly provide detailed anatomical images, PET can measure chemical changes that occur before macroscopic anatomical signs of a disease are observed. PET is emerging as a revolutionary method for measuring body function and tailoring disease treatment in living subjects. The development of synthetic strategies for the synthesis of new positron-emitting molecules is, however, not trivial. This Review highlights key aspects of the synthesis of PET radiotracers with the short-lived positron-emitting radionuclides (11)C, (18)F, (15)O, and (13)N, with emphasis on the most recent strategies.