[18F]FB(ePEG12)12-exendin-4 noninvasive imaging of insulinoma negative for insulin immunostaining on specimen from endoscopic ultrasonography-guided fine needle aspiration: a case report with review of literature.

Insulinomas are the most common functional pancreatic neuroendocrine neoplasm; when treatment is delayed, they induce hyperinsulinemic hypoglycemia, which is life-threatening. As surgical resection is the only curative treatment for insulinoma, preoperative localization is crucial; however, localization based on conventional imaging modalities such as computed tomography (CT) and magnetic resonance imaging is often inconclusive. Somatostatin receptor-targeted imaging is another option for detecting pancreatic neuroendocrine neoplasms but has low sensitivity and is not specific for insulinoma. The clinical application of other localizing approaches such as selective arterial calcium stimulation and endoscopic ultrasonography-guided fine needle aspiration (EUS-FNA) is limited by their being invasive and/or technically complex. Moreover, an EUS-FNA specimen of an insulinoma may be negative on insulin immunostaining. Thus, a noninvasive and clinically practical insulinoma-specific diagnostic tool to discriminate insulinomas with high accuracy is anticipated. Glucagon-like peptide-1 receptor (GLP-1R)-targeted imaging has emerged in the effort to fulfill this need. We recently developed the novel fluorine-18-labeled exendin-4-based probe conjugated with polyethylene glycol, [18F]FB(ePEG12)12-exendin-4 (18F-exendin-4) for positron emission tomography (PET) imaging and reported its clinical benefit in a case of insulinoma in the pancreatic tail. We report here a case of insulinoma in the pancreatic head in which an EUS-FNA specimen was negative on insulin immunostaining while precise preoperative localization and conclusive evidence for curative enucleation was provided by 18F-exendin-4 PET/CT (Japan Registry of Clinical Trials; jRCTs051200156).

Application of a Flexible PET Scanner Combined with 3 T MRI Using Non-local Means Reconstruction: Qualitative and Quantitative Comparison with Whole-Body PET/CT.

PURPOSE: Flexible positron emission tomography (fxPET) employing a non-local means reconstruction algorithm was designed to fit existing magnetic resonance imaging (MRI) systems. We aimed to compare the qualitative and quantitative performance of fxPET among fxPET with MR-based attenuation correction (MRAC), fxPET with CT-based attenuation correction (CTAC) using CT as a part of WB PET/CT, and whole-body (WB) PET/CT. PROCEDURES: Sixteen patients with suspected head and neck cancer underwent 2-deoxy-2-[18F]fluoro-D-glucose WB PET/CT scans, followed by fxPET and 3 T MRI scans. Phantom data were compared among the three datasets. For registration accuracy, we measured the distance between the center of the tumor determined by fxPET and that in MRI. We compared image quality, detection rates, and quantitative values including maximal standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and tumor-to-muscle ratio (TMR) among the three datasets. RESULTS: The phantom data in fxPET, except the percent contrast recoveries of 17-mm and 22-mm hot spheres, were inferior to those in WB PET/CT. The mean registration accuracy was 4.4 mm between fxPET using MRAC and MRI. The image quality was comparable between two fxPET datasets, but significantly inferior to WB PET/CT (p < 0.0001). In contrast, detection rates were comparable among the three datasets. SUVmax was significantly higher, and MTV and TLG were significantly lower in the two fxPET datasets compared with the WB PET/CT dataset (p < 0.005). There were no significant differences in SUVmax, MTV, and TLG between the two fxPET datasets or in TMR among the three datasets. All quantitative values had significantly positive correlations. CONCLUSIONS: Compared with WB PET/CT, the phantom data and image quality were inferior in fxPET. However, the results of the detection rates and quantitative values suggested the clinical feasibility of fxPET.

Optimal Cutoff Value of Fractional Flow Reserve Derived From Coronary Computed Tomography Angiography for Predicting Hemodynamically Significant Coronary Artery Disease.

BACKGROUND: The optimal cutoff value of fractional flow reserve (FFR) derived from coronary computed tomography angiography (FFRCT) remains unclear. METHODS: The current study population consisted of 93 patients with 139 vessels, who had suspected coronary artery disease by computed tomography angiography and underwent invasive FFR. We evaluated diagnostic performance of FFRCT according to different FFRCT cutoff values and FFRCT ranges with invasive FFR ≤0.80 as the reference standard. RESULTS: In per-vessel analysis, median invasive FFR was 0.85 (interquartile range, 0.75-0.90), and 57 out of 139 vessels (41%) showed hemodynamically significant stenosis (≤0.80). Median FFRCT was 0.77 (interquartile range, 0.66-0.84; mean difference [invasive FFR-FFRCT], 0.06±0.11). Per-vessel accuracy, sensitivity, specificity, positive predictive value, and negative predictive value were 73%, 95%, 59%, 61%, and 94% for the cutoff value of FFRCT ≤0.80, 81%, 86%, 78%, 73%, and 89% for FFRCT ≤0.75, and 83%, 74%, 89%, 82%, and 83% for FFRCT ≤0.70, respectively. Per-vessel accuracy across the different ranges of FFRCT ≤0.60, 0.61 to 0.70, 0.71 to 0.80, 0.81 to 0.90, and >0.90 with the cutoff value of FFRCT ≤0.80 were 95%, 74%, 32%, 93%, and 100%, respectively. Setting a gray zone of FFRCT 0.71 to 0.80 provided high positive predictive value (82%; n=42/51) in the range of FFRCT ≤0.70 and high negative predictive value (94%; n=48/51) in FFRCT >0.80. CONCLUSIONS: This study suggested that referral to invasive coronary angiography should be considered individually in the range of FFRCT 0.71 to 0.80, whereas dichotomous decision could be made in FFRCT ≤0.70 and >0.80. Future prospective studies evaluating clinical outcomes are needed to establish optimal FFRCT-based diagnostic algorithm.