Safety, pharmacokinetics, metabolism and radiation dosimetry of 18F-tetrafluoroborate (18F-TFB) in healthy human subjects

BACKGROUND

18F-Tetrafluoroborate (18F-TFB) is a promising iodide analog for PET imaging of thyroid cancer and sodium/iodide symporter (NIS) reporter activity in viral therapy applications. The aim of this study was to evaluate the safety, pharmacokinetics, biodistribution, and radiation dosimetry of high-specific activity 18F-TFB in healthy human subjects.

METHODS

18F-TFB was synthesized with specific activity of 3.2 ± 1.3 GBq/μmol (at the end of synthesis). Dynamic and whole-body static PET/CT scans over 4 h were performed after intravenous administration of 18F-TFB (333-407 MBq) in four female and four male healthy volunteers (35 ± 11 years old). Samples of venous blood and urine were collected over the imaging period and analyzed by ion-chromatography HPLC to determine tracer stability. Vital signs and clinical laboratory safety assays were measured to evaluate safety.

RESULTS

18F-TFB administration was well tolerated with no significant findings on vital signs and no clinically meaningful changes in clinical laboratory assays. Left-ventricular blood pool time-activity curves showed a multi-phasic blood clearance of 18F-radioactivity with the two rapid clearance phases over the first 20 min, followed by a slower clearance phase. HPLC analysis showed insignificant 18F-labeled metabolites in the blood and urine over the length of the study (4 h). High uptakes were seen in the thyroid, stomach, salivary glands, and bladder. Urinary clearance of 18F-TFB was prominent. Metabolic stability was evidenced by low accumulation of 18F-radioactivity in the bone. Effective doses were 0.036 mSv/MBq in males and 0.064 mSv/MBq in females (p = 0.08, not significant).

CONCLUSIONS

This initial study in healthy human subjects showed 18F-TFB was safe and distributed in the human body similar to other iodide analogs. These data support further translational studies with 18F-TFB as NIS gene reporter and imaging biomarker for thyroid cancer and other disease processes that import iodide.

Pulmonary function monitoring during adenosine myocardial perfusion scintigraphy in patients with chronic obstructive pulmonary disease

OBJECTIVE

To determine whether adenosine could be safely administered to patients with chronic obstructive pulmonary disease (COPD) for coronary vasodilatation during perfusion scintigraphy without causing bronchospasm.

MATERIAL AND METHODS

The study was divided into two phases. In the monitoring phase, patients with COPD were pretreated with an inhaled bronchodilator (albuterol) and had pulmonary function monitored during the infusion of a graduated dose of adenosine. Eligibility for entry into this phase of the study was determined on the basis of results of pulmonary function testing (PFT) during resting. Once we had shown that adenosine could be safely administered to patients with COPD, an implementation phase was begun. Entry did not require resting PFT, and patients were administered adenosine without monitoring of pulmonary function. Differences between patients with normal pulmonary function or mild COPD and those with more severe COPD were analyzed statistically.

RESULTS

Of 94 patients entered into the monitoring phase, none had obvious bronchospasm. The dosage of adenosine was reduced in four patients because of a decrease in forced expiratory volume in 1 second (FEV1) of 20% in comparison with baseline (FEV1 before administration of albuterol). The mean FEV1 decreased slightly from 1.83 L after administration of albuterol to 1.78 L during the maximal adenosine dose. Patients with a remote history of asthma, positive result of a methacholine challenge test, or mild COPD (FEV1 60 to 80% of the maximal predicted value for age) did not differ significantly in their response to infusion of adenosine from those with moderate or severe COPD (FEV1 30 to 59% of the maximum predicted for age). Of 117 patients in the implementation phase, 2 had bronchospasm during infusion of adenosine that was quickly terminated by stopping the administration in one patient and reducing the dose of adenosine in the other.

CONCLUSION

This study shows that adenosine can be safely administered intravenously to selected patients with known or suspected COPD to produce coronary vasodilatation for myocardial perfusion imaging. Patients who are within the guidelines established for this study should be considered for adenosine coronary vasodilatation with use of bronchodilator pretreatment, a graduated dose of adenosine, and regular chest auscultation during the infusion.

The influence of gating on measurements of myocardium at risk and infarct size during acute myocardial infarction by tomographic technetium 99m-labeled sestamibi imaging

BACKGROUND

Serial perfusion imaging with 99mTc-labeled sestamibi has been useful in the assessment of myocardial salvage from reperfusion therapy during acute myocardial infarction. Studies in animal models have shown that discernible perfusion defects can be created by left ventricular asynergy from partial volume effects in the setting of homogenous perfusion tracer distribution. The purpose of this study was to examine the influence of gating on serial perfusion images during acute myocardial infarction to determine the magnitude of potential partial volume effects.

METHODS AND RESULTS

99mTc-labeled sestamibi was injected into 18 patients during acute myocardial infarction and 29 patients 5 to 8 days after myocardial infarction. Tomographic imaging was acquired in gated format (16 frames per R-R cycle of the electrocardiogram) for each set of images. All frames were summed to produce ungated images. Tomographic images were quantified on three different thresholds to define the perfusion defect: 50%, 60%, and 70% of maximal counts. Severity of perfusion defects was calculated as the lowest ratio of minimum/maximum counts on five short-axis slices. Regional wall motion was assessed subjectively on the gated images by cine-loop display. Radionuclide ventriculography was performed at 6 weeks. There was a close correlation between perfusion defect size on ungated images and end-diastolic and end-systolic images independent of the quantitative threshold used (r = 0.90 to 0.93; p < 0.0001 for all correlations). Gated images provided consistently significantly greater estimates of perfusion defect size and severity by a small increment (3% to 9% of the left ventricle; p < 0.05 for all comparisons) independently of the quantitative threshold used or the time of imaging (acute or late). Ungated images provided slightly better correlations with left ventricular ejection fraction at 6 weeks independently of the quantitative threshold used and despite significant wall motion abnormalities present on both the acute and final studies.

CONCLUSIONS

The differences between perfusion defect size for gated and ungated images were highly significant as a group, but the magnitude of difference was small and not clinically relevant. The larger estimates provided by end-diastolic gated images are opposite the difference expected if partial volume effects were significantly influencing perfusion defect size. Partial volume effects appear to have minimal impact on clinical tomographic imaging during acute myocardial infarction for the quantification of myocardium at risk and infarct size.