Systematic evaluation of 99mTc-tetrofosmin versus 99mTc-sestamibi to study murine myocardial perfusion in small animal SPECT/CT

Background: The “back-translation” of clinically available protocols to measure myocardial perfusion to preclinical imaging in mouse models of human disease is attractive for basic biomedical research. With respect to singlephoton emission computed tomography (SPECT) approaches, clinical myocardial perfusion imaging protocols are established with different 99mTc-labeled perfusion tracers; however, studies evaluating and optimizing protocols for these tracers in high-resolution pinhole SPECT in mice are lacking. This study aims at evaluating two clinically available 99mTc-labeled myocardial perfusion tracers (99mTc-sestamibi vs. 99mTc-Tetrofosmin) in mice using four different imaging protocols. Methods: Adult C57BL/6 male mice were injected with 99mTc-sestamibi (MIBI) or 99mTc-Tetrofosmin (TETRO) (4 MBq/g body weight) either intravenously through the tail vein (n = 5) or retroorbitally (n = 5) or intraperitoneally (i. p.) under anesthesia (n = 3) or i.p. in an awake state (n = 3) at rest. Immediately after injection, a multi-frame singlephoton emission computed tomography/computed tomography (SPECT/CT) acquisition was initiated with six subsequent time frames of 10 min each. Reconstructed images of the different protocols were assessed and compared by visual analysis by experts and by time-activity-curves generated from regions-of-interest for various organs (normalized uptake values). Results: Visually assessing overall image quality, the best image quality was found for MIBI for both intravenous injection protocols, whereas TETRO only had comparable image quality after retroorbital injections. These results were confirmed by quantitative analysis where left ventricular (LV) uptake of MIBI after tail vein injections was found significantly higher for all time points accompanied with a significantly slower washout of 16% for MIBI vs. 33% for TETRO (p = 0.009) from 10 to 60 min post injection (PI). Interestingly, LV washout from 10 to 60 min PI was significantly higher for TETRO when applied by tail vein injections when compared to retroorbital injections (22%, p = 0.008). However, liver uptake was significant and comparable for both tracers at all time points. Radioactivity concentration in the lungs was negligible for all time points and both tracers. Conclusion: Intravenous MIBI injection (both tail vein and retroorbital) results in the best image quality for assessing myocardial perfusion of the murine heart by SPECT/CT. TETRO has a comparable image quality only for the retroorbital injection route

Intraoperative 3-D mapping of parathyroid adenoma using freehand SPECT

Background: Freehand single photon emission computed tomography (fSPECT) is a three-dimensional (3-D) tomographic imaging modality based on data acquisition with a handheld detector that is moved freely, in contrast to conventional, gantry-mounted gamma camera systems. In this pilot study, we evaluated the feasibility of fSPECT for intraoperative 3-D mapping in patients with parathyroid adenomas. Methods: Three patients (range 30 to 45 years) diagnosed with hyperparathyroidism (one primary and two tertiary) underwent parathyroid scintigraphy with technetium-99m sestamibi (99mTc-MIBI) to localize parathyroid adenomas. Two patients were referred with persistent hyperparathyroidism after conventional parathyroidectomy. In all three patients, a planar scintigraphy of the neck was performed 10 min after injection (p.i.) followed by SPECT/CT (Symbia T2, Siemens Healthcare) and a correlative ultrasound 2 h p.i. 99mTc-MIBI scan was performed the day before surgery in two patients and at the same day in one patient. fSPECT images were acquired intraoperatively using declipse SPECT (SurgicEyeTM). Results: A total of five parathyroid adenomas were successfully located with SPECT/CT. fSPECT allowed intraoperative detection of all adenomas, and successful parathyroidectomy was accomplished. Parathyroid hormone level decreased intraoperatively in all three patients, on average, by 79% (range 72% to 91%). Conclusion: In this preliminary study, we could demonstrate that intraoperative localization of parathyroid adenomas is feasible using the freehand SPECT technology, thus allowing an image-guided parathyroidectomy

Hydroxyfasudil-Mediated Inhibition of ROCK1 and ROCK2 Improves Kidney Function in Rat Renal Acute Ischemia-Reperfusion Injury

Renal ischemia-reperfusion (IR) injury (IRI) is a common and important trigger of acute renal injury (AKI). It is inevitably linked to transplantation. Involving both, the innate and the adaptive immune response, IRI causes subsequent sterile inflammation. Attraction to and transmigration of immune cells into the interstitium is associated with increased vascular permeability and loss of endothelial and tubular epithelial cell integrity. Considering the important role of cytoskeletal reorganization, mainly regulated by RhoGTPases, in the development of IRI we hypothesized that a preventive, selective inhibition of the Rho effector Rho-associated coiled coil containing protein kinase (ROCK) by hydroxyfasudil may improve renal IRI outcome. Using an IRI-based animal model of AKI in male Sprague Dawley rats, animals treated with hydroxyfasudil showed reduced proteinuria and polyuria as well as increased urine osmolarity when compared with sham-treated animals. In addition, renal perfusion (as assessed by 18F-fluoride Positron Emission Tomography (PET)), creatinine- and urea-clearances improved significantly. Moreover, endothelial leakage and renal inflammation was significantly reduced as determined by histology, 18F-fluordesoxyglucose-microautoradiography, Evans Blue, and real-time PCR analysis. We conclude from our study that ROCK-inhibition by hydroxyfasudil significantly improves kidney function in a rat model of acute renal IRI and is therefore a potential new therapeutic option in humans

F-labeled glycoconjugate of PD156707 for imaging ET A receptor expression in thyroid carcinoma by positron emission tomography

Abstract: Disturbances of the endothelin axis have been described in tumor angiogenesis and in highly vascularized tumors, such as thyroid carcinoma. Consequently, the endothelin (ET) receptor offers a molecular target for the visualization of the endothelin system in vivo by positron emission tomography (PET). We therefore endeavoured to develop a subtype-selective ET A receptor (ET A R) radioligand by introduction of a glycosyl moiety as a hydrophilic building block into the lead compound PD156707. Employing click chemistry we synthesized the triazolyl conjugated fluoroglucosyl derivative 1 that had high selectivity for ET A R (4.5 nM) over ET B R (1.2 µM)

Non-Invasive Imaging of Acute Renal Allograft Rejection in Rats Using Small Animal 18F-FDG-PET

BACKGROUND: At present, renal grafts are the most common solid organ transplants world-wide. Given the importance of renal transplantation and the limitation of available donor kidneys, detailed analysis of factors that affect transplant survival are important. Despite the introduction of new and effective immunosuppressive drugs, acute cellular graft rejection (AR) is still a major risk for graft survival. Nowadays, AR can only be definitively by renal biopsy. However, biopsies carry a risk of renal transplant injury and loss. Most important, they can not be performed in patients taking anticoagulant drugs. METHODOLOGY/PRINCIPAL FINDINGS: We present a non-invasive, entirely image-based method to assess AR in an allogeneic rat renal transplantation model using small animal positron emission tomography (PET) and (18)F-fluorodeoxyglucose (FDG). 3 h after i.v. injection of 30 MBq FDG into adult uni-nephrectomized, allogeneically transplanted rats, tissue radioactivity of renal parenchyma was assessed in vivo by a small animal PET-scanner (post operative day (POD) 1,2,4, and 7) and post mortem dissection. The mean radioactivity (cps/mm(3) tissue) as well as the percent injected dose (%ID) was compared between graft and native reference kidney. Results were confirmed by histological and autoradiographic analysis. Healthy rats, rats with acute CSA nephrotoxicity, with acute tubular necrosis, and syngeneically transplanted rats served as controls. FDG-uptake was significantly elevated only in allogeneic grafts from POD 1 on when compared to the native kidney (%ID graft POD 1: 0.54+/-0.06; POD 2: 0.58+/-0.12; POD 4: 0.81+/-0.06; POD 7: 0.77+/-0.1; CTR: 0.22+/-0.01, n = 3-28). Renal FDG-uptake in vivo correlated with the results obtained by micro-autoradiography and the degree of inflammatory infiltrates observed in histology. CONCLUSIONS/SIGNIFICANCE: We propose that graft FDG-PET imaging is a new option to non-invasively, specifically, early detect, and follow-up acute renal rejection. This method is potentially useful to improve post-transplant rejection monitoring

A Closer Look at the Bromine–Lithium Exchange with <i>tert</i>-Butyllithium in an Aryl Sulfonamide Synthesis

A practical protocol for the one-pot synthesis of various aryl sulfonamides, notably of pyridine-core-substituted 7-azaindolyl sulfonamides, is described. A key step is the well-known bromine–lithium exchange reaction of an aryl bromide with <i>tert</i>-butyllithium (<i>t</i>-BuLi). Differing from the common practice to use 2 or more equiv of organolithium, the exact amount of <i>t</i>-BuLi needed for a sufficient exchange reaction is determined for each aryl bromide in a GC–MS-assisted experiment