Effects of administration route on uptake kinetics of 18F-sodium fluoride positron emission tomography in mice

Abstract18F-sodium fluoride (18F-NaF) is a positron emission tomography (PET) radiotracer widely used in skeletal imaging and has also been proposed as a biomarker of active calcification in atherosclerosis. Like most PET radiotracers, 18F-NaF is typically administered intravenously. However in small animal research intravenous administrations can be challenging, because partial paravenous injection is common due to the small calibre of the superficial tail veins and repeat administrations via tail veins can lead to tissue injury therefore limiting the total number of longitudinal scanning points. In this paper, the feasibility of using intra-peritoneal route of injection of 8F-NaF to study calcification in mice was studied by looking at the kinetic and uptake profiles of normal soft tissues and bones versus intra-vascular injections. Dynamic PET was performed for 60 min on nineteen isoflurane-anesthetized male Swiss mice after femoral artery (n = 7), femoral vein (n = 6) or intraperitoneal (n = 6) injection of 8F-NaF. PET data were reconstructed and the standardised uptake value (SUV) and standardised uptake value ratio (SUVr) were estimated from the last three frames between 45- and 60-min and 8F-NaF uptake constant (Ki) was derived by Patlak graphical analysis. In soft tissue, the 18F-NaF perfusion phase changes depending on the type on injection route, whereas the uptake phase is similar regardless of the administration route. In bone tissue SUV, SUVr and Ki measures were not significantly different between the three administration routes. Comparison between PET and CT measures showed that bones that had the highest CT density displayed the lowest PET activity and conversely, bones where CT units were low had high 8F-NaF uptake. Intraperitoneal injection is a valid and practical alternative to the intra-vascular injections in small-animal 18F-NaF PET imaging providing equivalent pharmacokinetic data. CT outcome measures report on sites of stablished calcification whereas PET measures sites of higher complexity and active calcification.

Non-invasive Standardised Uptake Value for Verification of the Use of Previously Validated Reference Region for [18F]Flortaucipir and [18F]Florbetapir Brain PET Studies

Purpose The simplified reference tissue model (SRTM) is commonly applied for the quantification of brain positron emission tomography (PET) studies, particularly because it avoids arterial cannulation. SRTM requires a validated reference region which is obtained by baseline-blocking or displacement studies. Once a reference region is validated, the use should be verified for each new subject. This verification normally requires volume of distribution (VT) of a reference region. However, performing dynamic scanning and arterial sampling is not always possible, specifically in elderly subjects and in advanced disease stages. The aim of this study was to investigate the use of non-invasive standardised uptake value (SUV) approaches, in comparison to VT, as a verification of the previously validated grey matter cerebellum reference region for [18F]flortaucipir and [18F]florbetapir PET imaging in Alzheimer’s disease (AD) patients and controls. Procedures Dynamic 130-min [18F]flortaucipir PET scans obtained from nineteen subjects (10 AD patients) and 90-min [18F]florbetapir dynamic scans obtained from fourteen subjects (8 AD patients) were included. Regional VT’s were estimated for both tracers and were considered the standard verification of the previously validated reference region. Non-invasive SUVs corrected for body weight (SUVBW), lean body mass (SUL), and body surface area (SUVBSA) were obtained by using later time intervals of the dynamic scans. Simulations were also performed to assess the effect of flow and specific binding (BPND) on the SUVs. Results A low SUV corresponded well with a low VT for both [18F]flortaucipir and [18F]florbetapir. Simulation confirmed that SUVs were only slightly affected by flow changes and that increases in SUV were predominantly determined by the presence of specific binding. Conclusions In situations where dynamic scanning and arterial sampling is not possible, a low SUV(80–100 min) for [18F]flortaucipir and a low SUV(50–70 min) for [18F]florbetapir may be used as indication for absence of specific binding in the grey matter cerebellum reference region.

Laryngeal gout mimicking chondrosarcoma with concurrent longus colli tendinitis

A 42-year-old man with multiple comorbidities, including gout, presented to the emergency department with severe odynophagia for 4 days with intermittent dysphagia for 1–2 months. A CT scan of the neck showed right longus colli tendinitis and partially calcified excrescences from the right thyroid cartilage which raised suspicion of a cartilaginous tumour. He underwent an MRI scan of the neck to better evaluate the thyroid cartilage findings, which showed a heterogeneous mass suspicious for a chondroid tumour. He then underwent a positron-emission tomography-CT scan which showed a fluorodeoxyglucose-avid mass containing foci of calcification involving the right thyroid cartilage and adjacent strap muscle, with high standardised uptake value of 7.7. He subsequently underwent a CT-guided biopsy and an open biopsy of the right thyroid cartilage, and the results revealed gouty tophi. To our knowledge, this is the first reported case of laryngeal gout with longus coli tendinitis, both of which are rare conditions.

Cyclo-oxygenase-2 expression is associated with mean standardised uptake value on 18F-Fluorodeoxyglucose positron emission tomography in oesophageal adenocarcinoma

Objectives: This pilot study investigated the association of four PET image features and cyclo-oxygenase-2 (COX-2) expression in patients with oesophageal adenocarcinoma. The prognostic significance of these biomarkers was also assessed. Methods: 50 consecutive patients [median age = 68 (range 47 – 84), males = 45) with oesophageal adenocarcinoma had PET/CT staging between January 2011 and July 2015. The maximum and mean standardised uptake values (SUVmax and SUVmean), metabolic tumour volume (MTV) and tumour lesion glycolysis (TLG) were calculated from the primary tumour. Their association with COX-2 status was assessed using Mann-Whitney U tests. Kaplan-Meier and Cox regression analysis tested their prognostic significance. A p-value < 0.05 was considered statistically significant. Results: 32 tumours (64.0%) were COX-2 positive. There was a significant association between SUVmean and COX-2 status (p = 0.019). TLG (hazard ratio (HR) 1.001, 95 % confidence intervals (CI) 1.000 – 1.002, p = 0.018) was significantly associated with overall survival on multivariable analysis. Conclusions: This study investigated the association between PET image features and COX-2 expression in oesophageal adenocarcinoma. The preliminary results signal that a combination of TLG (calculated as product of MTV and SUVmean) and COX-2 status may be a strong and clinically important prognostic biomarker. Our research group are planning a prospective, multi-centre study to validate these findings. Advances in knowledge: Mean standardised uptake value (SUVmean) on PET imaging is associated with COX-2 expression in oesophageal adenocarcinoma.

[18F]Florbetapir positron emission tomography: identification of muscle amyloid in inclusion body myositis and differentiation from polymyositis

ObjectivesWith the tools available currently, confirming the diagnosis of inclusion body myositis (IBM) can be difficult. Many patients are initially misdiagnosed with polymyositis (PM). In this observational study at a UK adult neuromuscular centre, we investigated whether amyloid positron emission tomography could differentiate between IBM and PM.MethodsTen patients with IBM and six with PM underwent clinical review, [18F]florbetapir positron emission tomography and MRI of skeletal musculature. Differences in [18F]florbetapir standardised uptake value ratios in skeletal muscle regions of interest were evaluated. Relationships between [18F]florbetapir standardised uptake value ratios and measures of disease severity (clinical and by MRI of skeletal muscle) were assessed.Results[18F]florbetapir standardised uptake value ratios were significantly higher in those with IBM compared with PM for all assessed regions (total-[18F]florbetapir standardised uptake value ratio 1.45 (1.28 to 2.05) vs 1.01 (0.80 to 1.22), p=0.005). For total-[18F]florbetapir standardised uptake value ratios≥1.28, sensitivity and specificity for IBM was 80% and 100%, respectively.Conclusions[18F]florbetapir amyloid positron emission tomography differentiates IBM from PM. Successful development could facilitate accurate diagnosis, inclusion in clinical trials and help avoid unnecessary exposure to potentially harmful treatments.