Multi-tracer PET correlation analysis reveals disease-specific patterns in Parkinson's disease and asymptomatic LRRK2 pathogenic variant carriers compared to healthy controls.

Several genetic pathogenic variants increase the risk of Parkinson's disease (PD) with pathogenic variants in the leucine-rich repeat kinase 2 (LRRK2) gene being among the most common. A joint pattern analysis based on multi-set canonical correlation analysis (MCCA) was utilized to extract PD and LRRK2 pathogenic variant-specific spatial patterns in relation to healthy controls (HCs) from multi-tracer Positron Emission Tomography (PET) data. Spatial patterns were extracted for individual subject cohorts, as well as for pooled subject cohorts, to explore whether complementary spatial patterns of dopaminergic denervation are different in the asymptomatic and symptomatic stages of PD. The MCCA results are also compared to the traditional univariate analysis, which serves as a reference. We identified PD-induced spatial distribution alterations common to DAT and VMAT2 in both asymptomatic LRRK2 pathogenic variant carriers and PD subjects. The inclusion of HCs in the analysis demonstrated that the dominant common PD-induced pattern is related to an overall dopaminergic terminal density denervation, followed by asymmetry and rostro-caudal gradient with deficits in the less affected side still being the best marker of disease progression. The analysis was able to capture a trend towards PD-related patterns in the LRRK2 pathogenic variant carrier cohort with increasing age in line with the known increased risk of this patient cohort to develop PD as they age. The advantage of this method thus resides in its ability to identify not only regional differences in tracer binding between groups, but also common disease-related alterations in the spatial distribution patterns of tracer binding, thus potentially capturing more complex aspects of disease induced alterations.

Characterization of the partial volume effect along the axial field-of-view of the Biograph Vision Quadra total-body PET/CT system for multiple isotopes.

BACKGROUND: Total-body PET scanners with axial field of views (FOVs) longer than 1 m enable new applications to study multiple organs (e.g., the brain-gut-axis) simultaneously. As the spatial resolution and the associated partial volume effect (PVE) can vary significantly along the FOV, detailed knowledge of the contrast recovery coefficients (CRCs) is a prerequisite for image analysis and interpretation of quantitative results. The aim of this study was to determine the CRCs, as well as voxel noise, for multiple isotopes throughout the 1.06 m axial FOV of the Biograph Vision Quadra PET/CT system (Siemens Healthineers). MATERIALS AND METHODS: Cylindrical phantoms equipped with three different sphere sizes (inner diameters 7.86 mm, 28 and 37 mm) were utilized for the PVE evaluation. The 7.86 mm sphere was filled with F-18 (8:1 and 4:1), Ga-68 (8:1) and Zr-89 (8:1). The 28 mm and 37 mm spheres were filled with F-18 (8:1). Background concentration in the respective phantoms was of ~ 3 kBq/ml. The phantoms were measured at multiple positions in the FOV (axial: 0, 10, 20, 30, 40 and 50 cm, transaxial: 0, 10, 20 cm). The data were reconstructed with the standard clinical protocol, including PSF correction and TOF information with up to 10 iterations for maximum ring differences (MRDs) of 85 and 322; CRCs, as well as voxel noise levels, were determined for each position. RESULTS: F-18 CRCs (SBR 8:1 and 4:1) of the 7.86 mm sphere decreased up to 18% from the center FOV (cFOV) toward the transaxial edge and increased up to 17% toward the axial edge. Noise levels were below 15% for the default clinical reconstruction parameters. The larger spheres exhibited a similar pattern. Zr-89 revealed ~ 10% lower CRCs than F-18 but larger noise (9.1% (F-18), 19.1% (Zr-89); iteration 4, cFOV) for the default reconstruction. Zr-89 noise levels in the cFOV significantly decreased (~ 28%) when reconstructing the data with MRD322 compared with MRD85 along with a slight decrease in CRC values. Ga-68 exhibited the lowest CRCs for the three isotopes and noise characteristics comparable to those of F-18. CONCLUSIONS: Distinct differences in the PVE within the FOV were detected for clinically relevant isotopes F-18, Ga-68 and Zr-89, as well as for different sphere sizes. Depending on the positions inside the FOV, the sphere-to-background ratios, count statistics and isotope used, this can result in an up to 50% difference between CRCs. Hence, these changes in PVE can significantly affect the quantitative analysis of patient data. MRD322 resulted in slightly lower CRC values, especially in the center FOV, whereas the voxel noise significantly decreased compared with MRD85.

Image quality assessment along the one metre axial field-of-view of the total-body Biograph Vision Quadra PET/CT system for 18F-FDG.

AIM: Recently, total-body PET/CT systems with an extended axial field-of-view (aFOV) became commercially available which allow acquiring physiologic information of multiple organs simultaneously. However, the nominal aFOV may clinically not be used effectively due to the inherently reduced sensitivity at the distal ends of the aFOV. The aim of this study was to assess the extent of the useful aFOV of the Biograph Vision Quadra PET/CT system. METHODS: A NEMA image quality (IQ) phantom mimicking a standard [18F]FDG examination was used. Image contrast and noise were assessed across the 106 cm aFOV of the Biograph Vision Quadra PET/CT system (Siemens Healthineers). Phantom acquisitions were performed at different axial positions. PET data were rebinned to simulate different acquisition times for a standard injected activity and reconstructed using different filter settings to evaluate the noise and images along the axial direction. RESULTS: Image noise and contrast were stable within the central 80 cm of the aFOV. Outside this central area, image contrast variability as well as image noise increased. This degradation of IQ was in particular evident for short acquisition times of less than 30 s. At 10 min acquisition time and in the absence of post-reconstruction filtering, the useful aFOV was 100 cm. For a 2 min acquisition time, a useful aFOV with image noise below 15% was only achievable using Gaussian filtering with axial extents of between 83 and 103 cm when going from 2 to 6 mm full-width-half-maximum, respectively. CONCLUSION: Image noise increases substantially towards the ends of the aFOV. However, good IQ in compliance with generally accepted benchmarks is achievable for an aFOV of > 90 cm. When accepting higher image noise or using dedicated protocol settings such as stronger filtering a useful aFOV of around 1 m can be achieved for a 2 min acquisition time.

Spatiotemporal patterns of putaminal dopamine processing in Parkinson's disease: A multi-tracer positron emission tomography study.

Alterations in different aspects of dopamine processing may exhibit different progressive behaviours throughout the course of Parkinson's disease. We used a novel data-driven multivariate approach to quantify and compare spatiotemporal patterns related to different aspects of dopamine processing from cross-sectional Parkinson's subjects obtained with: 1) 69 [11C]±dihydrotetrabenazine (DTBZ) scans, most closely related to dopaminergic denervation; 2) 73 [11C]d-threo-methylphenidate (MP) scans, marker of dopamine transporter density; 3) 50 6-[18F]fluoro-l-DOPA (FD) scans, marker of dopamine synthesis and storage. The anterior-posterior gradient in the putamen was identified as the most salient feature associated with disease progression, however the temporal progression of the spatial gradient was different for the three tracers. The expression of the anterior-posterior gradient was the highest for FD at disease onset compared to that of DTBZ and MP (P = 0.018 and P = 0.047 respectively), but decreased faster (P = 0.006) compared to that of DTBZ. The gradient expression for MP was initially similar but decreased faster (P = 0.015) compared to that for DTBZ. These results reflected unique temporal behaviours of regulatory mechanisms related to dopamine synthesis (FD) and reuptake (MP). While the relative early disease upregulation of dopamine synthesis in the anterior putamen prevalent likely extends to approximately 10 years after symptom onset, the presumed downregulation of dopamine transporter density may play a compensatory role in the prodromal/earliest disease stages only.

Understanding the importance of quality control and quality assurance in preclinical PET/CT imaging.

The fundamental principle of experimental design is to ensure efficiency and efficacy of the performed experiments. Therefore, it behoves the researcher to gain knowledge of the technological equipment to be used. This should include an understanding of the instrument quality control and assurance requirements to avoid inadequate or spurious results due to instrumentation bias whilst improving reproducibility. Here, the important role of preclinical positron emission tomography/computed tomography and the scanner's required quality control and assurance is presented along with the suggested guidelines for quality control and assurance. There are a multitude of factors impeding the continuity and reproducibility of preclinical research data within a single laboratory as well as across laboratories. A more robust experimental design incorporating validation or accreditation of the scanner performance can reduce inconsistencies. Moreover, the well-being and welfare of the laboratory animals being imaged is prime justification for refining experimental designs to include verification of instrumentation quality control and assurance. Suboptimal scanner performance is not consistent with the 3R principle (Replacement, Reduction, and Refinement) and potentially subjects animals to unnecessary harm. Thus, quality assurance and control should be of paramount interest to any scientist conducting animal studies. For this reason, through this work, we intend to raise the awareness of researchers using PET/CT regarding quality control/quality assurance (QC/QA) guidelines and instil the importance of confirming that these are routinely followed. We introduce a basic understanding of the PET/CT scanner, present the purpose of QC/QA as well as provide evidence of imaging data biases caused by lack of QC/QA. This is shown through a review of the literature, QC/QA accepted standard protocols and our research. We also want to encourage researchers to have discussions with the PET/CT facilities manager and/or technicians to develop the optimal designed PET/CT experiment for obtaining their scientific objective. Additionally, this work provides an easy gateway to multiple resources not only for PET/CT knowledge but for guidelines and assistance in preclinical experimental design to enhance scientific integrity of the data and ensure animal welfare.

NEMA NU 4-2008 performance evaluation and MR compatibility tests of an APD-based small animal PET-insert for simultaneous PET/MR imaging.

An avalanche photodiode (APD)-based small animal positron emission tomography (PET)-insert was fully evaluated for its PET performance, as well as potential influences on magnetic resonance imaging (MRI) performance. This PET-insert has an extended axial field of view (FOV) compared with the previous design to increase system sensitivity, as well as an updated cooling and temperature regulation to enable stable and reproducible PET acquisitions. The PET performance was evaluated according to the National Electrical Manufacturers Association NU4-2008 protocol. The energy and timing resolution's full width at half maximum were 16.1% and 4.7 ns, respectively. The reconstructed radial spatial resolution of the PET-insert was 1.8 mm full width at half maximum at the center FOV using filtered back projection for reconstruction and sensitivity was 3.68%. The peak noise equivalent count rates were 70 kcps for a rat-like and 350 kcps for a mouse-like phantom, respectively. Image quality phantom values and contrast recovery were comparable to state-of-the art PET-inserts and standalone systems. Regarding MR compatibility, changes in the mean signal-to-noise ratio for turbo spin echo and echo-planar imaging sequences were below 8.6%, for gradient echo sequences below 1%. Degradation of the mean homogeneity was below 2.3% for all tested sequences. The influence of the PET-insert on theB0maps was negligible and no influence on functional MRI sequences was detected. A mouse and rat imaging study demonstrated the feasibility ofin vivosimultaneous PET/MRI.

Cross-validation study between the HRRT and the PET component of the SIGNA PET/MRI system with focus on neuroimaging.

BACKGROUND: The Siemens high-resolution research tomograph (HRRT - a dedicated brain PET scanner) is to this day one of the highest resolution PET scanners; thus, it can serve as useful benchmark when evaluating performance of newer scanners. Here, we report results from a cross-validation study between the HRRT and the whole-body GE SIGNA PET/MR focusing on brain imaging. Phantom data were acquired to determine recovery coefficients (RCs), % background variability (%BG), and image voxel noise (%). Cross-validation studies were performed with six healthy volunteers using [11C]DTBZ, [11C]raclopride, and [18F]FDG. Line profiles, regional time-activity curves, regional non-displaceable binding potentials (BPND) for [11C]DTBZ and [11C]raclopride scans, and radioactivity ratios for [18F]FDG scans were calculated and compared between the HRRT and the SIGNA PET/MR. RESULTS: Phantom data showed that the PET/MR images reconstructed with an ordered subset expectation maximization (OSEM) algorithm with time-of-flight (TOF) and TOF + point spread function (PSF) + filter revealed similar RCs for the hot spheres compared to those obtained on the HRRT reconstructed with an ordinary Poisson-OSEM algorithm with PSF and PSF + filter. The PET/MR TOF + PSF reconstruction revealed the highest RCs for all hot spheres. Image voxel noise of the PET/MR system was significantly lower. Line profiles revealed excellent spatial agreement between the two systems. BPND values revealed variability of less than 10% for the [11C]DTBZ scans and 19% for [11C]raclopride (based on one subject only). Mean [18F]FDG ratios to pons showed less than 12% differences. CONCLUSIONS: These results demonstrated comparable performances of the two systems in terms of RCs with lower voxel-level noise (%) present in the PET/MR system. Comparison of in vivo human data confirmed the comparability of the two systems. The whole-body GE SIGNA PET/MR system is well suited for high-resolution brain imaging as no significant performance degradation was found compared to that of the reference standard HRRT.

Quantitative Rodent Brain Receptor Imaging.

Positron emission tomography (PET) is a non-invasive imaging technology employed to describe metabolic, physiological, and biochemical processes in vivo. These include receptor availability, metabolic changes, neurotransmitter release, and alterations of gene expression in the brain. Since the introduction of dedicated small-animal PET systems along with the development of many novel PET imaging probes, the number of PET studies using rats and mice in basic biomedical research tremendously increased over the last decade. This article reviews challenges and advances of quantitative rodent brain imaging to make the readers aware of its physical limitations, as well as to inspire them for its potential applications in preclinical research. In the first section, we briefly discuss the limitations of small-animal PET systems in terms of spatial resolution and sensitivity and point to possible improvements in detector development. In addition, different acquisition and post-processing methods used in rodent PET studies are summarized. We further discuss factors influencing the test-retest variability in small-animal PET studies, e.g., different receptor quantification methodologies which have been mainly translated from human to rodent receptor studies to determine the binding potential and changes of receptor availability and radioligand affinity. We further review different kinetic modeling approaches to obtain quantitative binding data in rodents and PET studies focusing on the quantification of endogenous neurotransmitter release using pharmacological interventions. While several studies have focused on the dopamine system due to the availability of several PET tracers which are sensitive to dopamine release, other neurotransmitter systems have become more and more into focus and are described in this review, as well. We further provide an overview of latest genome engineering technologies, including the CRISPR/Cas9 and DREADD systems that may advance our understanding of brain disorders and function and how imaging has been successfully applied to animal models of human brain disorders. Finally, we review the strengths and opportunities of simultaneous PET/magnetic resonance imaging systems to study drug-receptor interactions and challenges for the translation of PET results from bench to bedside.

Data Curation for Preclinical and Clinical Multimodal Imaging Studies.

PURPOSE: In biomedical research, imaging modalities help discover pathological mechanisms to develop and evaluate novel diagnostic and theranostic approaches. However, while standards for data storage in the clinical medical imaging field exist, data curation standards for biomedical research are yet to be established. This work aimed at developing a free secure file format for multimodal imaging studies, supporting common in vivo imaging modalities up to five dimensions as a step towards establishing data curation standards for biomedical research. PROCEDURES: Images are compressed using lossless compression algorithm. Cryptographic hashes are computed on the compressed image slices. The hashes and compressions are computed in parallel, speeding up computations depending on the number of available cores. Then, the hashed images with digitally signed timestamps are cryptographically written to file. Fields in the structure, compressed slices, hashes, and timestamps are serialized for writing and reading from files. The C++ implementation is tested on multimodal data from six imaging sites, well-documented, and integrated into a preclinical image analysis software. RESULTS: The format has been tested with several imaging modalities including fluorescence molecular tomography/x-ray computed tomography (CT), positron emission tomography (PET)/CT, single-photon emission computed tomography/CT, and PET/magnetic resonance imaging. To assess performance, we measured the compression rate, ratio, and time spent in compression. Additionally, the time and rate of writing and reading on a network drive were measured. Our findings demonstrate that we achieve close to 50 % reduction in storage space for µCT data. The parallelization speeds up the hash computations by a factor of 4. We achieve a compression rate of 137 MB/s for file of size 354 MB. CONCLUSIONS: The development of this file format is a step to abstract and curate common processes involved in preclinical and clinical multimodal imaging studies in a standardized way. This work also defines better interface between multimodal imaging modalities and analysis software.

Reproducibility and Comparability of Preclinical PET Imaging Data: A Multicenter Small-Animal PET Study.

The standardization of preclinical imaging is a key factor to ensure the reliability, reproducibility, validity, and translatability of preclinical data. Preclinical standardization has been slowly progressing in recent years and has mainly been performed within a single institution, whereas little has been done in regards to multicenter standardization between facilities. This study aimed to investigate the comparability among preclinical imaging facilities in terms of PET data acquisition and analysis. In the first step, basic PET scans were obtained in 4 different preclinical imaging facilities to compare their standard imaging protocol for 18F-FDG. In the second step, the influence of the personnel performing the experiments and the experimental equipment used in the experiment were compared. In the third step, the influence of the image analysis on the reproducibility and comparability of the acquired data was determined. Distinct differences in the uptake behavior of the 4 standard imaging protocols were determined for the investigated organs (brain, left ventricle, liver, and muscle) due to different animal handling procedures before and during the scans (e.g., fasting vs. nonfasting, glucose levels, temperature regulation vs. constant temperature warming). Significant differences in the uptake behavior in the brain were detected when the same imaging protocol was used but executed by different personnel and using different experimental animal handling equipment. An influence of the person analyzing the data was detected for most of the organs, when the volumes of interest were manually drawn by the investigators. Coregistration of the PET to an MR image and drawing the volume of interest based on anatomic information yielded reproducible results among investigators. It has been demonstrated that there is a huge demand for standardization among multiple institutions.

PET/MRI Hybrid Systems.

Over the last decade, the combination of PET and MRI in one system has proven to be highly successful in basic preclinical research, as well as in clinical research. Nowadays, PET/MRI systems are well established in preclinical imaging and are progressing into clinical applications to provide further insights into specific diseases, therapeutic assessments, and biological pathways. Certain challenges in terms of hardware had to be resolved concurrently with the development of new techniques to be able to reach the full potential of both combined techniques. This review provides an overview of these challenges and describes the opportunities that simultaneous PET/MRI systems can exploit in comparison with stand-alone or other combined hybrid systems. New approaches were developed for simultaneous PET/MRI systems to correct for attenuation of 511 keV photons because MRI does not provide direct information on gamma photon attenuation properties. Furthermore, new algorithms to correct for motion were developed, because MRI can accurately detect motion with high temporal resolution. The additional information gained by the MRI can be employed to correct for partial volume effects as well. The development of new detector designs in combination with fast-decaying scintillator crystal materials enabled time-of-flight detection and incorporation in the reconstruction algorithms. Furthermore, this review lists the currently commercially available systems both for preclinical and clinical imaging and provides an overview of applications in both fields. In this regard, special emphasis has been placed on data analysis and the potential for both modalities to evolve with advanced image analysis tools, such as cluster analysis and machine learning.

Standardization of Small Animal Imaging-Current Status and Future Prospects.

The benefit of small animal imaging is directly linked to the validity and reliability of the collected data. If the data (regardless of the modality used) are not reproducible and/or reliable, then the outcome of the data is rather questionable. Therefore, standardization of the use of small animal imaging equipment, as well as of animal handling in general, is of paramount importance. In a recent paper, guidance for efficient small animal imaging quality control was offered and discussed, among others, the use of phantoms in setting up a quality control program (Osborne et al. 2016). The same phantoms can be used to standardize image quality parameters for multi-center studies or multi-scanners within center studies. In animal experiments, the additional complexity due to animal handling needs to be addressed to ensure standardized imaging procedures. In this review, we will address the current status of standardization in preclinical imaging, as well as potential benefits from increased levels of standardization.

Influence of Co-57 and CT Transmission Measurements on the Quantification Accuracy and Partial Volume Effect of a Small Animal PET Scanner.

PURPOSE: Non-invasive in vivo positron emission tomography (PET) provides high detection sensitivity in the nano- to picomolar range and in addition to other advantages, the possibility to absolutely quantify the acquired data. The present study focuses on the comparison of transmission data acquired with an X-ray computed tomography (CT) scanner or a Co-57 source for the Inveon small animal PET scanner (Siemens Healthcare, Knoxville, TN, USA), as well as determines their influences on the quantification accuracy and partial volume effect (PVE). A special focus included the impact of the performed calibration on the quantification accuracy. PROCEDURES: Phantom measurements were carried out to determine the quantification accuracy, the influence of the object size on the quantification, and the PVE for different sphere sizes, along the field of view and for different contrast ratios. RESULTS: An influence of the emission activity on the Co-57 transmission measurements was discovered (deviations up to 24.06 % measured to true activity), whereas no influence of the emission activity on the CT attenuation correction was identified (deviations <3 % for measured to true activity). The quantification accuracy was substantially influenced by the applied calibration factor and by the object size. The PVE demonstrated a dependency on the sphere size, the position within the field of view, the reconstruction and correction algorithms and the count statistics. Depending on the reconstruction algorithm, only ∼30-40 % of the true activity within a small sphere could be resolved. The iterative 3D reconstruction algorithms uncovered substantially increased recovery values compared to the analytical and 2D iterative reconstruction algorithms (up to 70.46 % and 80.82 % recovery for the smallest and largest sphere using iterative 3D reconstruction algorithms). The transmission measurement (CT or Co-57 source) to correct for attenuation did not severely influence the PVE. CONCLUSIONS: The analysis of the quantification accuracy and the PVE revealed an influence of the object size, the reconstruction algorithm and the applied corrections. Particularly, the influence of the emission activity during the transmission measurement performed with a Co-57 source must be considered. To receive comparable results, also among different scanner configurations, standardization of the acquisition (imaging parameters, as well as applied reconstruction and correction protocols) is necessary.

Comparison of small animal CT contrast agents.

Non-invasive in vivo small animal computed tomography (CT) imaging provides high resolution bone scans but cannot differentiate between soft tissues. For most applications injections of contrast agents (CAs) are necessary. Aim of this study was to uncover the advantages and disadvantages of commercially available CT CAs (ExiTron nano 12 000 and 6000, eXIA 160 and 160XL, Fenestra VC and LC) regarding their pharmacokinetics, toxicological side-effects and the influence of anesthesia on the biodistribution, based on an injection volume of 100 µL/25 g body weight. The pharmacokinetics of the CAs were determined for up to five days. The CA-induced toxicological/physiological side-effects were evaluated by determining blood counts, liver enzymes, thyroxine and total protein values, pro-inflammatory mediators (messenger ribonucleic acid (mRNA)), histology and immunohistochemistry. ExiTron nano 12 000 and 6000 yielded a long-term contrast enhancement (CE) in the liver and spleen for up to five days. Some of the evaluated CAs did not show any CE at all. Anesthesia did not impair the CAs' biodistribution. The CAs differentially affected the body weight, blood counts, liver enzymes, thyroxine and total protein values. ExiTron nano 12 000 and 6000 induced histiocytes in the liver and spleen. Moreover, ExiTron nano 12 000 and eXIA 160 enhanced tumor necrosis factor (TNF) mRNA expression levels in the kidneys. Thus, we recommend ExiTron nano 12 000 and 6000 when multiple injections should be avoided. We recommend careful selection of the employed CA in order to achieve an acceptable CE in the organs of interest and to avoid influences on the animal physiology. Copyright © 2016 John Wiley & Sons, Ltd.

Acetazolamide sensitive tissue calcification and aging of klotho-hypomorphic mice.

UNLABELLED: Klotho, a protein expressed mainly in the kidney, is required for the inhibitory effect of FGF23 on renal 1,25(OH)2D3 formation. Klotho counteracts vascular calcification and diverse age-related disorders. Klotho-hypomorphic mice (kl/kl) suffer from severe vascular calcification and rapid aging. The calcification is at least in part caused by excessive 1,25(OH)2D3, Ca(2+), and phosphate concentrations in blood, which trigger osteogenic signaling including upregulation of alkaline phosphatase (Alpl). As precipitation of calcium and phosphate is fostered by alkaline pH, extracellular acidosis could counteract tissue calcification. In order to induce acidosis, acetazolamide was added to drinking water (0.8 g/l) of kl/kl and wild-type mice. As a result, acetazolamide treatment of kl/kl mice partially reversed the growth deficit, tripled the life span, almost completely reversed the calcifications in trachea, lung, kidney, stomach, intestine, and vascular tissues, the excessive aortic alkaline phosphatase mRNA levels and the plasma concentrations of osteoprotegerin, osteopontin as well as fetuin-A, without significantly decreasing FGF23, 1,25(OH)2D3, Ca(2+), and phosphate plasma concentrations. In primary human aortic smooth muscle cells, acidotic environment prevented phosphate-induced alkaline phosphatase mRNA expression. The present study reveals a completely novel effect of acetazolamide, i.e., interference with osteoinductive signaling and tissue calcification in kl/kl mice. KEY MESSAGES: Klotho deficient (kl/kl) mice suffer from hyperphosphatemia with dramatic tissue calcification. Acetazolamide (ACM) treatment partially reversed the growth deficit of kl/kl mice. In kl/kl mice, ACM reversed tissue calcification despite continued hyperphosphatemia. ACM tripled the life span of kl/kl mice. In human aortic smooth muscle cells, low extracellular pH prevented osteogenic signaling.

Quantification of ß-Amyloidosis and rCBF with Dedicated PET, 7 T MR Imaging, and High-Resolution Microscopic MR Imaging at 16.4 T in APP23 Mice.

UNLABELLED: We present a combined PET/7 T MR imaging and 16.4 T microscopic MR imaging dual-modality imaging approach enabling quantification of the amyloid load at high sensitivity and high resolution, and of regional cerebral blood flow (rCBF) in the brain of transgenic APP23 mice. Moreover, we demonstrate a novel, voxel-based correlative data analysis method for in-depth evaluation of amyloid PET and rCBF data. METHODS: We injected 11C-Pittsburgh compound B (PIB) intravenously in transgenic and control APP23 mice and performed dynamic PET measurements. rCBF data were recorded with a flow-sensitive alternating inversion recovery approach at 7 T. Subsequently, the animals were sacrificed and their brains harvested for ex vivo microscopic MR imaging at 16.4 T with a T2*-weighted gradient-echo sequence at 30-µm spatial resolution. Additionally, correlative amyloid histology was performed. The 11C-PIB PET data were quantified to nondisplaceable binding potentials (BPND) using the Logan graphical analysis; flow-sensitive alternating inversion recovery data were quantified with a simplified version of the Bloch equation. RESULTS: Amyloid load assessed by both 11C-PIB PET and amyloid histology was highest in the frontal cortex of transgenic mice (11C-PIB BPND: 0.93±0.08; amyloid histology: 15.1%±1.5%), followed by the temporoparietal cortex (11C-PIB BPND: 0.75±0.08; amyloid histology: 13.9%±0.7%) and the hippocampus (11C-PIB BPND: 0.71±0.09; amyloid histology: 9.2%±0.9%), and was lowest in the thalamus (11C-PIB BPND: 0.40±0.07; amyloid histology: 6.6%±0.6%). However, 11C-PIB BPND and amyloid histology linearly correlated (R2=0.82, P<0.05) and were significantly higher in transgenic animals (P<0.01). Similarly, microscopic MR imaging allowed quantifying the amyloid load, in addition to the detection of substructures within single amyloid plaques correlating with amyloid deposition density and the measurement of hippocampal atrophy. Finally, we found an inverse relationship between 11C-PIB BPND and rCBF MR imaging in the voxel-based analysis that was absent in control mice (slopetg: -0.11±0.03; slopeco: 0.004±0.005; P=0.014). CONCLUSION: Our dual-modality imaging approach using 11C-PIB PET/7 T MR imaging and 16.4 T microscopic MR imaging allowed amyloid-load quantification with high sensitivity and high resolution, the identification of substructures within single amyloid plaques, and the quantification of rCBF.

Regeneration of degenerated urinary sphincter muscles: improved stem cell-based therapies and novel imaging technologies.

Stress urinary incontinence (SUI) is a largely ousted but significant medical, social, and economic problem. Surveys suggest that nowadays approximately 10% of the male and 15% of the female population suffer from urinary incontinence at some stage in their lifetime. In women, two major etiologies contribute to SUI: degeneration of the urethral sphincter muscle controlling the closing mechanism of the bladder outflow and changes in lower pelvic organ position associated with degeneration of connective tissue or with mechanical stress, including obesity and load and tissue injury during pregnancy and delivery. In males, the reduction of the sphincter muscle function is sometimes due to surgical interventions as a consequence of prostate cancer treatment, benign prostate hyperplasia, or of neuropathical origin. Accordingly, for women and men different therapies were developed. In some cases, SUI can be treated by physical exercise, electrophysiological stimulation, and pharmacological interventions. If this fails to improve the situation, surgical interventions are required. In standard procedures, endoprostheses for mechanical support of the weakened tissue or mechanical valves for a bladder outflow control are implanted. In 20% of cases treated, repeat procedures are required as implants yield all sorts of side effects in time. Based on preclinical studies, the application of an advanced therapy medicinal product (ATMP) such as implantation of autologous cells may be a curative and long-lasting therapy for SUI. Cellular therapy could also be an option for men suffering from incontinence caused by injury of the nerves controlling the muscular sphincter system. Here we briefly report on human progenitor cells, especially on mesenchymal stromal cells (MSCs), their expansion and differentiation to smooth muscle or striated muscle cells in vitro, labeling of cells for in vivo imaging, concepts of improved, precise, yet gentle application of cells in muscle tissue, and monitoring of injected cells in situ.

Checkpoint kinase Chk2 controls renal Cyp27b1 expression, calcitriol formation, and calcium-phosphate metabolism.

Checkpoint kinase 2 (Chk2) is the main effector kinase of ataxia telangiectasia mutated (ATM) and responsible for cell cycle regulation. ATM signaling has been shown to upregulate interferon-regulating factor-1 (IRF-1), a transcription factor also expressed in the kidney. Calcitriol (1,25 (OH)2D3), a major regulator of mineral metabolism, is generated by 25-hydroxyvitamin D 1α-hydroxylase in the kidney. Since 25-hydroxyvitamin D 1α-hydroxylase expression is enhanced by IRF-1, the present study explored the role of Chk2 for calcitriol formation and mineral metabolism. Chk2-deficient mice (chk2 (-/-)) were compared to wild-type mice (chk2 (+/+)). Transcript levels of renal 25-hydroxyvitamin D 1α-hydroxylase, Chk2, and IRF-1 were determined by RT-PCR; Klotho expression by Western blotting; bone density by µCT analysis; serum or plasma 1,25 (OH)2D3, PTH, and C-terminal FGF23 concentrations by immunoassays; and serum, fecal, and urinary calcium and phosphate concentrations by photometry. The renal expression of IRF-1 and 25-hydroxyvitamin D 1α-hydroxylase as well as serum 1,25 (OH)2D3 and FGF23 levels were significantly lower in chk2 (-/-) mice compared to chk2 (+/+) mice. Plasma PTH was not different between the genotypes. Renal calcium and phosphate excretion were significantly higher in chk2 (-/-) mice than in chk2 (+/+) mice despite hypophosphatemia and normocalcemia. Bone density was not different between the genotypes. We conclude that Chk2 regulates renal 25-hydroxyvitamin D 1α-hydroxylase expression thereby impacting on calcium and phosphate metabolism.

Assessment of murine brain tissue shrinkage caused by different histological fixatives using magnetic resonance and computed tomography imaging.

Especially for neuroscience and the development of new biomarkers, a direct correlation between in vivo imaging and histology is essential. However, this comparison is hampered by deformation and shrinkage of tissue samples caused by fixation, dehydration and paraffin embedding. We used magnetic resonance (MR) imaging and computed tomography (CT) imaging to analyze the degree of shrinkage on murine brains for various fixatives. After in vivo imaging using 7 T MRI, animals were sacrificed and the brains were dissected and immediately placed in different fixatives, respectively: zinc-based fixative, neutral buffered formalin (NBF), paraformaldehyde (PFA), Bouin-Holland fixative and paraformaldehyde-lysine-periodate (PLP). The degree of shrinkage based on mouse brain volumes, radiodensity in Hounsfield units (HU), as well as non-linear deformations were obtained. The highest degree of shrinkage was observed for PLP (68.1%, P < 0.001), followed by PFA (60.2%, P<0.001) and NBF (58.6%, P<0.001). The zinc-based fixative revealed a low shrinkage with only 33.5% (P<0.001). Compared to NBF, the zinc-based fixative shows a slightly higher degree of deformations, but is still more homogenous than PFA. Tissue shrinkage can be monitored non-invasively with CT and MR. Zinc-based fixative causes the smallest degree of brain shrinkage and only small deformations and is therefore recommended for in vivo ex vivo comparison studies.

Longitudinal PET-MRI reveals ß-amyloid deposition and rCBF dynamics and connects vascular amyloidosis to quantitative loss of perfusion.

The dynamics of ß-amyloid deposition and related second-order physiological effects, such as regional cerebral blood flow (rCBF), are key factors for a deeper understanding of Alzheimer's disease (AD). We present longitudinal in vivo data on the dynamics of ß-amyloid deposition and the decline of rCBF in two different amyloid precursor protein (APP) transgenic mouse models of AD. Using a multiparametric positron emission tomography and magnetic resonance imaging approach, we demonstrate that in the presence of cerebral ß-amyloid angiopathy (CAA), ß-amyloid deposition is accompanied by a decline of rCBF. Loss of perfusion correlates with the growth of ß-amyloid plaque burden but is not related to the number of CAA-induced microhemorrhages. However, in a mouse model of parenchymal ß-amyloidosis and negligible CAA, rCBF is unchanged. Because synaptically driven spontaneous network activity is similar in both transgenic mouse strains, we conclude that the disease-related decline of rCBF is caused by CAA.