Perinatal exposure to the immune-suppressant di-n-octyltin dichloride affects brain development in rats

Disruption of the immune system during embryonic brain development by environmental chemicals was proposed as a possible cause of neurodevelopmental disorders. We previously found adverse effects of di-n-octyltin dichloride (DOTC) on maternal and developing immune systems of rats in an extended one-generation reproductive toxicity study according to the OECD 443 test guideline. We hypothesize that the DOTC-induced changes in the immune system can affect neurodevelopment. Therefore, we used in-vivo MRI and PET imaging and genomics, in addition to behavioral testing and neuropathology as proposed in OECD test guideline 443, to investigate the effect of DOTC on structural and functional brain development. Male rats were exposed to DOTC (0, 3, 10, or 30 mg/kg of diet) from 2 weeks prior to mating of the F0-generation until sacrifice of F1-animals. The brains of rats, exposed to DOTC showed a transiently enlarged volume of specific brain regions (MRI), altered specific gravity, and transient hyper-metabolism ([18F]FDG PET). The alterations in brain development concurred with hyper-responsiveness in auditory startle response and slight hyperactivity in young adult animals. Genomics identified altered transcription of key regulators involved in neurodevelopment and neural function (e.g. Nrgrn, Shank3, Igf1r, Cck, Apba2, Foxp2); and regulators involved in cell size, cell proliferation, and organ development, especially immune system development and functioning (e.g. LOC679869, Itga11, Arhgap5, Cd47, Dlg1, Gas6, Cml5, Mef2c). The results suggest the involvement of immunotoxicity in the impairment of the nervous system by DOTC and support the hypothesis of a close connection between the immune and nervous systems in brain development.

Estimating foraging behavior in rodents using a modified paradigm measuring threat imminence dynamics

Animals need to respond to threats to avoid danger and approach rewards. In nature, these responses did not evolve alone but are always accompanied by motivational conflict. A semi-naturalistic threat imminence continuum model models the approach-avoidance conflict and is able to integrate multiple behaviors into a single paradigm. However, its comprehensive application is hampered by the lack of a detailed protocol and data about some fundamental factors including sex, age, and motivational level. Here, we modified a previously established paradigm measuring threat imminence continuum dynamics, involving modifications of training and testing protocols, and utilization of commercial materials combined with open science codes, making it easier to replicate. We demonstrate that foraging behavior is modulated by age, hunger level, and sex. This paradigm can be used to study foraging behaviors in animals in a more naturalistic manner with relevance to human approach-avoid conflicts and associated psychopathologies.

The Potential of Iron Oxide Nanoparticle-Enhanced MRI at 7 T Compared With 3 T for Detecting Small Suspicious Lymph Nodes in Patients With Prostate Cancer

BACKGROUND

Accurate detection of lymph node (LN) metastases in prostate cancer (PCa) is a challenging but crucial step for disease staging. Ultrasmall superparamagnetic iron oxide (USPIO)-enhanced magnetic resonance imaging (MRI) enables distinction between healthy LNs and nodes suspicious for harboring metastases. When combined with MRI at an ultra-high magnetic field, an unprecedented spatial resolution can be exploited to visualize these LNs.

PURPOSE

The aim of this study was to explore USPIO-enhanced MRI at 7 T in comparison to 3 T for the detection of small suspicious LNs in the same cohort of patients with PCa.

MATERIALS AND METHODS

Twenty PCa patients with high-risk primary or recurrent disease were referred to our hospital for an investigational USPIO-enhanced 3 T MRI examination with ferumoxtran-10. With consent, they underwent a 7 T MRI on the same day. Three-dimensional anatomical and T2*-weighted images of both examinations were evaluated blinded, with an interval, by 2 readers who annotated LNs suspicious for metastases. Number, size, and level of suspicion (LoS) of LNs were paired within patients and compared between field strengths.

RESULTS

At 7 T, both readers annotated significantly more LNs compared with 3 T (474 and 284 vs 344 and 162), with 116 suspicious LNs on 7 T (range, 1-34 per patient) and 79 suspicious LNs on 3 T (range, 1-14 per patient) in 17 patients. For suspicious LNs, the median short axis diameter was 2.6 mm on 7 T (1.3-9.5 mm) and 2.8 mm for 3 T (1.7-10.4 mm, P = 0.05), with large overlap in short axis of annotated LNs between LoS groups. At 7 T, significantly more suspicious LNs had a short axis <2.5 mm compared with 3 T (44% vs 27%). Magnetic resonance imaging at 7 T provided better image quality and structure delineation and a higher LoS score for suspicious nodes.

CONCLUSIONS

In the same cohort of patients with PCa, more and more small LNs were detected on 7 T USPIO-enhanced MRI compared with 3 T MRI. Suspicious LNs are generally very small, and increased nodal size was not a good indication of suspicion for the presence of metastases. The high spatial resolution of USPIO-enhanced MRI at 7 T improves structure delineation and the visibility of very small suspicious LNs, potentially expanding the in vivo detection limits of pelvic LN metastases in PCa patients.

Subnodal Correspondence of PSMA Expression and USPIO-MRI in Metastatic Pelvic Lymph Nodes in Prostate Cancer

OBJECTIVES

Two advanced imaging modalities used to detect lymph node (LN) metastases in prostate cancer patients are prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography and ultrasmall superparamagnetic iron oxide (USPIO)-enhanced magnetic resonance imaging (MRI). As these modalities use different targets, a subnodal comparison is needed to interpret both their correspondence and their differences. The aim of this explorative study was to compare ex vivo 111In-PSMA μSPECT images with high-resolution 7 T USPIO μMR images and histopathology of resected LN specimens from prostate cancer patients to assess the degree of correspondence at subnodal level.

MATERIALS AND METHODS

Twenty primary prostate cancer patients who underwent pelvic LN dissection were included and received USPIO contrast and 111In-PSMA. A total of 41 LNs of interest (LNOIs) were selected for ex vivo imaging based on γ-probe detection or palpation. μSPECT and μMRI acquisition were performed immediately after resection. Overlay of μSPECT images on MR images was performed, and the level of correspondence (LoC) between μSPECT and μMR findings was assessed according to a 4-point Likert classification scheme.

RESULTS

Forty-one LNOIs could be matched to an LN on ex vivo μMRI. Coregistration of μSPECT and USPIO-enhanced water-selective multigradient echo MR images was successful for all 41 LNOIs. Ninety percent of the lesions showed excellent correspondence regarding the presence of metastatic tissue and affected subnodal site (LoC 4; 37/41). In only 1 of 41 LNOIs, a small metastasis was misclassified by both techniques. Three LNOIs were classified as LoC 3 (7%) and 1 LNOI as LoC 2. All LoC 2 and LoC 3 lesions had PSMA-expressing metastases on final histopathology.

CONCLUSIONS

Coregistration of μSPECT and USPIO-μMRI showed excellent subnodal correspondence in the majority (90%) of LNs. Ex vivo imaging may thus help localize small cancer deposits within resected LNs and could contribute to improved interpretation of in vivo imaging of LNs.

Glucose versus fructose metabolism in the liver measured with deuterium metabolic imaging

Chronic intake of high amounts of fructose has been linked to the development of metabolic disorders, which has been attributed to the almost complete clearance of fructose by the liver. However, direct measurement of hepatic fructose uptake is complicated by the fact that the portal vein is difficult to access. Here we present a new, non-invasive method to measure hepatic fructose uptake and metabolism with the use of deuterium metabolic imaging (DMI) upon administration of [6,6'-²H₂]fructose. Using both [6,6'-²H₂]glucose and [6,6'-²H₂]fructose, we determined differences in the uptake and metabolism of glucose and fructose in the mouse liver with dynamic DMI. The deuterated compounds were administered either by fast intravenous (IV) bolus injection or by slow IV infusion. Directly after IV bolus injection of [6,6'-²H₂]fructose, a more than two-fold higher initial uptake and subsequent 2.5-fold faster decay of fructose was observed in the mouse liver as compared to that of glucose after bolus injection of [6,6'-²H₂]glucose. In contrast, after slow IV infusion of fructose, the ²H fructose/glucose signal maximum in liver spectra was lower compared to the ²H glucose signal maximum after slow infusion of glucose. With both bolus injection and slow infusion protocols, deuterium labeling of water was faster with fructose than with glucose. These observations are in line with a higher extraction and faster turnover of fructose in the liver, as compared with glucose. DMI with [6,6'-²H₂]glucose and [6,6'-²H₂]fructose could potentially contribute to a better understanding of healthy human liver metabolism and aberrations in metabolic diseases.

A consensus protocol for functional connectivity analysis in the rat brain

Task-free functional connectivity in animal models provides an experimental framework to examine connectivity phenomena under controlled conditions and allows for comparisons with data modalities collected under invasive or terminal procedures. Currently, animal acquisitions are performed with varying protocols and analyses that hamper result comparison and integration. Here we introduce StandardRat, a consensus rat functional magnetic resonance imaging acquisition protocol tested across 20 centers. To develop this protocol with optimized acquisition and processing parameters, we initially aggregated 65 functional imaging datasets acquired from rats across 46 centers. We developed a reproducible pipeline for analyzing rat data acquired with diverse protocols and determined experimental and processing parameters associated with the robust detection of functional connectivity across centers. We show that the standardized protocol enhances biologically plausible functional connectivity patterns relative to previous acquisitions. The protocol and processing pipeline described here is openly shared with the neuroimaging community to promote interoperability and cooperation toward tackling the most important challenges in neuroscience.

Imatinib attenuates reperfusion injury in a rat model of acute myocardial infarction

Following an acute myocardial infarction, reperfusion of an occluded coronary artery is often accompanied by microvascular injury, leading to worse long-term prognosis. Experimental studies have revealed the potential of tyrosine-kinase inhibitor imatinib to reduce vascular leakage in various organs. Here, we examined the potential of imatinib to attenuate microvascular injury in a rat model of myocardial reperfusion injury. Isolated male Wistar rat hearts (n = 20) in a Langendorff system and male Wistar rats (n = 37) in an in vivo model were randomly assigned to imatinib or placebo and subjected to ischaemia and reperfusion. Evans-blue/Thioflavin-S/TTC staining and Cardiac Magnetic Resonance Imaging were performed to assess the extent of reperfusion injury. Subsequently, in vivo hearts were perfused ex vivo with a vascular leakage tracer and fluorescence and electron microscopy were performed. In isolated rat hearts, imatinib reduced global infarct size, improved end-diastolic pressure, and improved rate pressure product recovery compared to placebo. In vivo, imatinib reduced no-reflow and infarct size with no difference between imatinib and placebo for global cardiac function. In addition, imatinib showed lower vascular resistance, higher coronary flow, and less microvascular leakage in the affected myocardium. At the ultrastructural level, imatinib showed higher preserved microvascular integrity compared to placebo. We provide evidence that low-dose imatinib can reduce microvascular injury and accompanying myocardial infarct size in a rat model of acute myocardial infarction. These data warrant future work to examine the potential of imatinib to reduce reperfusion injury in patients with acute myocardial infarction.

Mechanical high-intensity focused ultrasound creates unique tumor debris enhancing dendritic cell-induced T cell activation

Introduction

In situ tumor ablation releases a unique repertoire of antigens from a heterogeneous population of tumor cells. High-intensity focused ultrasound (HIFU) is a completely noninvasive ablation therapy that can be used to ablate tumors either by heating (thermal (T)-HIFU) or by mechanical disruption (mechanical (M)-HIFU). How different HIFU ablation techniques compare with respect to their antigen release profile, their activation of responder T cells, and their ability to synergize with immune stimuli remains to be elucidated.

Methods and results

Here, we compare the immunomodulatory effects of T-HIFU and M-HIFU ablation with or without the TLR9 agonist CpG in the ovalbumin-expressing lymphoma model EG7. M-HIFU ablation alone, but much less so T-HIFU, significantly increased dendritic cell (DC) activation in draining lymph nodes (LNs). Administration of CpG following T- or M-HIFU ablation increased DC activation in draining LNs to a similar extend. Interestingly, ex vivo co-cultures of draining LN suspensions from HIFU plus CpG treated mice with CD8⁺ OT-I T cells demonstrate that LN cells from M-HIFU treated mice most potently induced OT-I proliferation. To delineate the mechanism for the enhanced anti-tumor immune response induced by M-HIFU, we characterized the RNA, DNA and protein content of tumor debris generated by both HIFU methods. M-HIFU induced a uniquely altered RNA, DNA and protein profile, all showing clear signs of fragmentation, whereas T-HIFU did not. Moreover, western blot analysis showed decreased levels of the immunosuppressive cytokines IL-10 and TGF-β in M-HIFU generated tumor debris compared to untreated tumor tissue or T-HIFU.

Conclusion

Collectively, these results imply that M-HIFU induces a unique context of the ablated tumor material, enhancing DC-mediated T cell responses when combined with CpG.

Abstract P1047: Imatinib Attenuates Reperfusion Injury In A Rat Model Of Acute Myocardial Infarction

Background: Reperfusion of an occluded coronary artery is often accompanied by injury of the microvasculature (MVI), which portends a worse long term prognosis after an acute myocardial infarction (AMI). In previous experimental studies, the tyrosine-kinase inhibitor imatinib has shown to reduce vascular leakage and therefore could have a potential role to prevent MVI. This study aims to provide a potential therapeutic approach using imatinib to attenuate reperfusion injury.

Methods: First, 16 isolated male Wistar rat hearts were randomly assigned to 10 μM imatinib or placebo and subjected to 40 min of global ischemia followed by 120 min of reperfusion ex vivo in a Langendorff setup. Global infarct size and mechanical function were assessed. Second, 25 male Wistar rats were randomly assigned to 30 mg/kg imatinib or placebo intravenously and subjected to 45 min of left anterior descending coronary artery ligation followed by 180 min of reperfusion in vivo. Cardiovascular magnetic resonance imaging was performed to assess infarct size and cardiac function. Subsequently, hearts were perfused ex vivo with a fluorescent vascular leakage tracer and used for fluorescence- and electron microscopy.

Results: In isolated hearts, imatinib reduced global infarct size (imatinib 36.2±7.9 vs placebo 50.0±8.0% infarcted area/total area, p<0.01), improved end diastolic pressure (imatinib 44.2±8.0 vs placebo 59.5±13.5 mmHg, p<0.05) and rate pressure product recovery (imatinib 39.0±6.8 vs placebo 26.2±7.6% of baseline, p<0.05). In vivo, imatinib reduced infarct size (imatinib 12.6±8.8 vs placebo 25.6±9.3% infarcted area/left ventricle, p<0.01), but did not improve global cardiac function. At the end of reperfusion, imatinib showed lower vascular resistance, higher coronary flow and less microvascular leakage (all p<0.05). At the ultrastructural level, imatinib showed better preserved microvascular integrity compared to placebo.

Conclusion: This study provides evidence that imatinib attenuates reperfusion injury in an ex vivo and in vivo AMI rat model, mainly by protection of the coronary microcirculation. These data warrant future work to examine the potential of imatinib to reduce reperfusion injury in patients with AMI.

Novel Fluorinated Poly (Lactic-Co-Glycolic acid) (PLGA) and Polyethylene Glycol (PEG) Nanoparticles for Monitoring and Imaging in Osteoarthritis

Polymeric nanoparticles (NPs) find many uses in nanomedicine, from drug delivery to imaging. In this regard, poly (lactic-co-glycolic acid) (PLGA) and polyethylene glycol (PEG) particles are the most widely applied types of nano-systems due to their biocompatibility and biodegradability. Here we developed novel fluorinated polymeric NPs as vectors for multi-modal nanoprobes. This approach involved modifying polymeric NPs with trifluoroacetamide (TFA) and loading them with a near-infrared (NIR) dye for different imaging modalities, such as magnetic resonance imaging (MRI) and optical imaging. The PLGA-PEG-TFA NPs generated were characterized in vitro using the C28/I2 human chondrocyte cell line and in vivo in a mouse model of osteoarthritis (OA). The NPs were well absorbed, as confirmed by confocal microscopy, and were non-toxic to cells. To test the NPs as a drug delivery system for contrast agents of OA, the nanomaterial was administered via the intra-articular (IA) administration method. The dye-loaded NPs were injected in the knee joint and then visualized and tracked in vivo by fluorine-19 nuclear magnetic resonance and fluorescence imaging. Here, we describe the development of novel intrinsically fluorinated polymeric NPs modality that can be used in various molecular imaging techniques to visualize and track OA treatments and their potential use in clinical trials.

Pyruvate-lactate exchange and glucose uptake in human prostate cancer cell models. A study in xenografts and suspensions by hyperpolarized [1-13 C]pyruvate MRS and [18 F]FDG-PET

Reprogramming of energy metabolism in the development of prostate cancer can be exploited for a better diagnosis and treatment of the disease. The goal of this study was to determine whether differences in glucose and pyruvate metabolism of human prostate cancer cells with dissimilar aggressivenesses can be detected using hyperpolarized [1-¹³ C]pyruvate MRS and [¹⁸ F]FDG-PET imaging, and to evaluate whether these measures correlate. For this purpose, we compared murine xenografts of human prostate cancer LNCaP cells with those of more aggressive PC3 cells. [1-¹³ C]pyruvate was hyperpolarized by dissolution dynamic nuclear polarization (dDNP) and [1-¹³ C]pyruvate to lactate conversion was followed by ¹³ C MRS. Subsequently [¹⁸ F]FDG uptake was investigated by static and dynamic PET measurements. Standard uptake values (SUVs) for [¹⁸ F]FDG were significantly higher for xenografts of PC3 compared with those of LNCaP. However, we did not observe a difference in the average apparent rate constant k_pl of ¹³ C label exchange from pyruvate to lactate between the tumor variants. A significant negative correlation was found between SUVs from [¹⁸ F]FDG PET measurements and k_pl values for the xenografts of both tumor types. The k_pl rate constant may be influenced by various factors, and studies with a range of prostate cancer cells in suspension suggest that LDH inhibition by pyruvate may be one of these. Our results indicate that glucose and pyruvate metabolism in the prostate cancer cell models differs from that in other tumor models and that [¹⁸ F]FDG-PET can serve as a valuable complementary tool in dDNP studies of aggressive prostate cancer with [1-¹³ C]pyruvate.

Nanoparticles for "two color" 19F magnetic resonance imaging: Towards combined imaging of biodistribution and degradation

The use of polymeric nanoparticles (NPs) as therapeutics has been steadily increasing over past decades. In vivo imaging of NPs is necessary to advance the therapeutic performance. 19F Magnetic Resonance Imaging (19F MRI) offers multiple advantages for in vivo imaging. However, design of a probe for both biodistribution and degradation has not been realized yet. We developed polymeric NPs loaded with two fluorocarbons as promising imaging tools to monitor NP biodistribution and degradation by 19F MRI. These 200 nm NPs consist of poly(lactic-co-glycolic acid) (PLGA) loaded with perfluoro-15-crown-5 ether (PFCE) and PERFECTA. PERFECTA/PFCE-PLGA NPs have a fractal sphere structure, in which both fluorocarbons are distributed in the polymeric matrix of the fractal building blocks, which differs from PFCE-PLGA NPs and is unique for fluorocarbon-loaded colloids. This structure leads to changes of magnetic resonance properties of both fluorocarbons after hydrolysis of NPs. PERFECTA/PFCE-PLGA NPs are colloidally stable in serum and biocompatible. Both fluorocarbons show a single resonance in 19F MRI that can be imaged separately using different excitation pulses. In the future, these findings may be used for biodistribution and degradation studies of NPs by 19F MRI in vivo using "two color" labeling leading to improvement of drug delivery agents.

Repeatability and reproducibility of longitudinal relaxation rate in 12 small-animal MRI systems

BACKGROUND

Many translational MR biomarkers derive from measurements of the water proton longitudinal relaxation rate R1, but evidence for between-site reproducibility of R1 in small-animal MRI is lacking.

OBJECTIVE

To assess R1 repeatability and multi-site reproducibility in phantoms for preclinical MRI.

METHODS

R1 was measured by saturation recovery in 2% agarose phantoms with five nickel chloride concentrations in 12 magnets at 5 field strengths in 11 centres on two different occasions within 1-13 days. R1 was analysed in three different regions of interest, giving 360 measurements in total. Root-mean-square repeatability and reproducibility coefficients of variation (CoV) were calculated. Propagation of reproducibility errors into 21 translational MR measurements and biomarkers was estimated. Relaxivities were calculated. Dynamic signal stability was also measured.

RESULTS

CoV for day-to-day repeatability (N = 180 regions of interest) was 2.34% and for between-centre reproducibility (N = 9 centres) was 1.43%. Mostly, these do not propagate to biologically significant between-centre error, although a few R1-based MR biomarkers were found to be quite sensitive even to such small errors in R1, notably in myocardial fibrosis, in white matter, and in oxygen-enhanced MRI. The relaxivity of aqueous Ni2+ in 2% agarose varied between 0.66 s-1 mM-1 at 3 T and 0.94 s-1 mM-1 at 11.7T.

INTERPRETATION

While several factors affect the reproducibility of R1-based MR biomarkers measured preclinically, between-centre propagation of errors arising from intrinsic equipment irreproducibility should in most cases be small. However, in a few specific cases exceptional efforts might be required to ensure R1-reproducibility.

Imaging Hyperpolarized Pyruvate and Lactate after Blood-Brain Barrier Disruption with Focused Ultrasound

Imaging of hyperpolarized ¹³C-labeled substrates has emerged as an important magnetic resonance (MR) technique to study metabolic pathways in real time in vivo. Even though this technique has found its way to clinical trials, in vivo dynamic nuclear polarization is still mostly applied in preclinical models. Its tremendous increase in signal-to-noise ratio (SNR) overcomes the intrinsically low MR sensitivity of the ¹³C nucleus and allows real-time metabolic imaging in small structures like the mouse brain. However, applications in brain research are limited as delivery of hyperpolarized compounds is restrained by the blood–brain barrier (BBB). A local noninvasive disruption of the BBB could facilitate delivery of hyperpolarized substrates and create opportunities to study metabolic pathways in the brain that are generally not within reach. In this work, we designed a setup to apply BBB disruption in the mouse brain by MR-guided focused ultrasound (FUS) prior to MR imaging of ¹³C-enriched hyperpolarized [1-¹³C]-pyruvate and its conversion to [1-¹³C]-lactate. To overcome partial volume issues, we optimized a fast multigradient-echo imaging method (temporal resolution of 2.4 s) with an in-plane spatial resolution of 1.6 × 1.6 mm², without the need of processing large amounts of spectroscopic data. We demonstrated the feasibility to apply ¹³C imaging in less than 1 h after FUS treatment and showed a locally disrupted BBB during the time window of the whole experiment. From detected hyperpolarized pyruvate and lactate signals in both FUS-treated and untreated mice, we conclude that even at high spatial resolution, signals from the blood compartment dominate in the ¹³C images, leaving the interpretation of hyperpolarized signals in the mouse brain challenging.

MRI evaluation of vulvar squamous-cell carcinoma in fresh radical local excision specimens for cancer localization and prediction of surgical tumor-free margins

In the surgical treatment of vulvar squamous-cell carcinoma (VSCC), tumor-free margins of 8 mm or more are considered adequate. However, limited perioperative information on the tumor-free margins other than the surgeon's own estimation is available. The purpose of this study was therefore to investigate the feasibility of ex vivo MRI in localizing VSCC and to assess the surgical tumor-free margins in fresh radical local excision (RLE) specimens to guide the surgeon during resections. Nine patients with biopsy-proven VSCC scheduled for RLE were prospectively included. Intact fresh specimens were scanned using a 7 T preclinical MR-scanner. Whole mount H&E-stained slides were obtained every 3 mm and correlated with ex vivo MRI. A pathologist annotated VSCC and minimal tumor-free margins (3 o'clock, 9 o'clock, basal) on the digitalized histological slides. An observer with knowledge of histology (the non-blinded annotation) and a radiologist blinded to histology (the blinded annotation) separately performed annotation of the same features on ex vivo MRI. Linear correlation and agreement of the ex vivo MRI measurements with histology were assessed. Diagnostic performance for VSCC localization and identification of margins less than 8 mm was expressed as positive and negative predictive values (PPV, NPV). In 153 matched ex vivo MRI slices, the observer correctly identified 79/91 margins as less than 8 mm (PPV 87%) and 110/124 margins as 8 mm or greater (NPV 89%). The radiologist correctly annotated absence of VSCC in 73/81 (NPV 90%) and presence in 65/72 (PPV 90%) slices. Sixty-four of 90 margins were correctly identified as less than 8 mm (PPV 71%) and 83/102 margins as 8 mm or greater (NPV 81%). Both non-blinded and blinded annotations were linearly correlated and demonstrated good agreement with histology. Accurate localization of VSCC and measurements of the surgical tumor-free margins in fresh RLE specimens using ex vivo MRI seems feasible. High diagnostic performance in VSCC localization and identification of margins less than 8 mm suggest ex vivo MRI to be clinically applicable.

MRI as a tool to assess surgical margins and pseudocapsule features directly following partial nephrectomy for small renal masses

PURPOSE

To evaluate the feasibility of ex vivo 7T MRI to assess surgical margins (SMs) and pseudocapsule (PC) features after partial nephrectomy (PN).

MATERIALS AND METHODS

In this prospective, IRB-approved study, seven patients undergoing a PN for nine tumours between November 2014 and July 2015 were included for analysis after obtaining informed consent. MRI of the specimen was acquired using a 7T small bore scanner. The imaging protocol consisted of anatomical T1-, T2- and diffusion-weighted imaging. After formalin fixation, specimens were cut for pathology work-up in the same orientation as the MR images were obtained. The entire specimen was processed into H&E slides that were digitally scanned, annotated and correlated with radiological findings for negative SMs, PC presence, PC continuity and extra-PC-extension (EPCE). Sensitivity and specificity of MRI for assessment of these endpoints were calculated.

RESULTS

The sensitivity and specificity for assessment of the SM were 100% and 75%, respectively. Two false-positive outcomes were reported, both in case of EPCE and a SM ≤0.5 mm. For the presence of a PC, sensitivity and specificity were 100% and 33%, respectively. Two false-positive scans with anatomical structures mimicking the presence of a PC occurred. If a PC was present, continuity and EPCE were assessed with a sensitivity and specificity of 75% and 100% and 67% and 100%, respectively.

CONCLUSION

Ex vivo 7T MRI is a feasible tool for perioperative evaluation of SMs, and if present, PC features after PN. This may facilitate maximal sparing of renal parenchyma without compromising oncological outcomes.

KEY POINTS

• Ex vivo MRI may contribute to improvement of negative surgical margins during partial nephrectomy. • Due to the assessment of surgical margins within a limited time span from obtaining the partial nephrectomy specimen, surgery for more complex tumours is possible with maximum sparing of healthy renal parenchyma without compromising oncological outcomes. • The intra operative assessment of pseudocapsule continuity along the resection margin enables maximal sparing of healthy renal parenchyma without delayed diagnosis of incomplete resection.

Visualization of calcium phosphate cement in teeth by zero echo time 1 H MRI at high field

¹ H magnetic resonance imaging (MRI) by a zero echo time (ZTE) sequence is an excellent method to image teeth. Calcium phosphate cement (CPC) materials are applied in the restoration of tooth lesions, but it has not yet been investigated whether they can be detected by computed tomography (CT) or MRI. The aim of this study was to optimize high-field ZTE imaging to enable the visualization of a new CPC formulation implanted in teeth and to apply this in the assessment of its decomposition in vivo. CPC was implanted in three human and three goat teeth ex vivo and in three goat teeth in vivo. An ultrashort echo time (UTE) sequence with multiple flip angles and echo times was applied at 11.7 T to measure T₁ and T₂ * values of CPC, enamel and dentin. Teeth with CPC were imaged with an optimized ZTE sequence. Goat teeth implanted with CPC in vivo were imaged after 7 weeks ex vivo. T₂ * relaxation of implanted CPC, dentin and enamel was better fitted by a model assuming a Gaussian rather than a Lorentzian distribution. For CPC and human enamel and dentin, the average T₂ * values were 273 ± 19, 562 ± 221 and 476 ± 147 μs, respectively, the average T₂ values were 1234 ± 27, 963 ± 151 and 577 ± 41 μs, respectively, and the average T₁ values were 1065 ± 45, 972 ± 40 and 903 ± 7 ms, respectively. In ZTE images, CPC had a higher signal-to-noise-ratio than dentin and enamel because of the higher water content. Seven weeks after in vivo implantation, the CPC-filled lesions showed less homogeneous structures, a lower T₁ value and T₂ * separated into two components. MRI by ZTE provides excellent contrast for CPC in teeth and allows its decomposition to be followed.

Ex vivo MRI evaluation of prostate cancer: Localization and margin status prediction of prostate cancer in fresh radical prostatectomy specimens

PURPOSE

To investigate the ability of high field ex vivo magnetic resonance imaging (MRI) to localize prostate cancer (PCa) and to predict the margin status in fresh radical prostatectomy (RP) specimens using histology as the reference standard.

MATERIALS AND METHODS

This Institutional Review Board (IRB)-approved study had written informed consent. Patients with biopsy-proved PCa and a diagnostic multiparametric 3T MRI examination of the prostate prior to undergoing RP were prospectively included. A custom-made container provided reference between the 7T ex vivo MRI obtained from fresh RP specimens and histological slicing. On ex vivo MRI, PCa was localized and the presence of positive surgical margins was determined in a double-reading session. These findings were compared with histological findings obtained from completely cut, whole-mount embedded, prostate specimens.

RESULTS

In 12 RP specimens, histopathology revealed 36 PCa lesions, of which 17 (47%) and 20 (56%) were correlated with the ex vivo MRI in the first and second reading session, respectively. Nine of 12 (75%) index lesions were localized in the first session, in the second 10 of 12 (83%). Seven and 8 lesions of 11 lesions with Gleason score >6 and >0.5 cc were localized in the first and second session, respectively. In the first session none of the four histologically positive surgical margins (sensitivity 0%) and 9 of 13 negative margins (specificity 69%) were detected. In second session the sensitivity and specificity were 25% and 88%, respectively.

CONCLUSION

Ex vivo MRI enabled accurate localization of PCa in fresh RP specimens, and the technique provided information on the margin status with high specificity.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:439-448.

Hypertension, cerebrovascular impairment, and cognitive decline in aged AβPP/PS1 mice

Cardiovascular risk factors, especially hypertension, are also major risk factors for Alzheimer's disease (AD). To elucidate the underlying vascular origin of neurodegenerative processes in AD, we investigated the relation between systolic blood pressure (SBP) cerebral blood flow (CBF) and vasoreactivity with brain structure and function in a 16-18 months old double transgenic AβPP_swe/PS1_dE9 (AβPP/PS1) mouse model for AD. These aging AβPP/PS1 mice showed an increased SBP linked to a declined regional CBF. Furthermore, using advanced MRI techniques, decline of functional and structural connectivity was revealed in the AD-like mice coupled to impaired cognition, increased locomotor activity, and anxiety-related behavior. Post mortem analyses demonstrated also increased neuroinflammation, and both decreased synaptogenesis and neurogenesis in the AβPP/PS1 mice. Additionally, deviant levels of fatty acids and sterols were present in the brain tissue of the AβPP/PS1 mice indicating maladapted brain fatty acid metabolism. Our findings suggest a link between increased SBP, decreased cerebral hemodynamics and connectivity in an AD mouse model during aging, leading to behavioral and cognitive impairments. As these results mirror the complex clinical symptomatology in the prodromal phase of AD, we suggest that this AD-like murine model could be used to investigate prevention and treatment strategies for early AD patients. Moreover, this study helps to develop more efficient therapies and diagnostics for this very early stage of AD.

In vivo MR guided boiling histotripsy in a mouse tumor model evaluated by MRI and histopathology

Boiling histotripsy (BH) is a new high intensity focused ultrasound (HIFU) ablation technique to mechanically fragmentize soft tissue into submicrometer fragments. So far, ultrasound has been used for BH treatment guidance and evaluation. The in vivo histopathological effects of this treatment are largely unknown. Here, we report on an MR guided BH method to treat subcutaneous tumors in a mouse model. The treatment effects of BH were evaluated one hour and four days later with MRI and histopathology, and compared with the effects of thermal HIFU (T-HIFU). The lesions caused by BH were easily detected with T2 w imaging as a hyper-intense signal area with a hypo-intense rim. Histopathological evaluation showed that the targeted tissue was completely disintegrated and that a narrow transition zone (<200 µm) containing many apoptotic cells was present between disintegrated and vital tumor tissue. A high level of agreement was found between T2 w imaging and H&E stained sections, making T2 w imaging a suitable method for treatment evaluation during or directly after BH. After T-HIFU, contrast enhanced imaging was required for adequate detection of the ablation zone. On histopathology, an ablation zone with concentric layers was seen after T-HIFU. In line with histopathology, contrast enhanced MRI revealed that after BH or T-HIFU perfusion within the lesion was absent, while after BH in the transition zone some micro-hemorrhaging appeared. Four days after BH, the transition zone with apoptotic cells was histologically no longer detectable, corresponding to the absence of a hypo-intense rim around the lesion in T2 w images. This study demonstrates the first results of in vivo BH on mouse tumor using MRI for treatment guidance and evaluation and opens the way for more detailed investigation of the in vivo effects of BH. Copyright © 2016 John Wiley & Sons, Ltd.

Structural-functional connectivity deficits of neocortical circuits in the Fmr1 (-/y) mouse model of autism

Fragile X syndrome (FXS), the most common inherited form of intellectual disability disorder and a frequent cause of autism spectrum disorder (ASD), is characterized by a high prevalence of sensory symptoms. Perturbations in the anatomical connectivity of neocortical circuits resulting in their functional defects have been hypothesized to contribute to the underlying etiology of these disorders. We tested this idea by probing alterations in the functional and structural connectivity of both local and long-ranging neocortical circuits in the Fmr1 (-/y) mouse model of FXS. To achieve this, we combined in vivo ultrahigh-field diffusion tensor magnetic resonance imaging (MRI), functional MRI, and viral tracing approaches in adult mice. Our results show an anatomical hyperconnectivity phenotype for the primary visual cortex (V1), but a disproportional low connectivity of V1 with other neocortical regions. These structural data are supported by defects in the structural integrity of the subcortical white matter in the anterior and posterior forebrain. These anatomical alterations might contribute to the observed functional decoupling across neocortical regions. We therefore identify FXS as a "connectopathy," providing a translational model for understanding sensory processing defects and functional decoupling of neocortical areas in FXS and ASD.

In vivo ³¹P magnetic resonance spectroscopic imaging (MRSI) for metabolic profiling of human breast cancer xenografts

PURPOSE

To study cancer associated with abnormal metabolism of phospholipids, of which several have been proposed as biomarkers for malignancy or to monitor response to anticancer therapy. We explored 3D (31) P magnetic resonance spectroscopic imaging (MRSI) at high magnetic field for in vivo assessment of individual phospholipids in two patient-derived breast cancer xenografts representing good and poor prognosis (luminal- and basal-like tumors).

MATERIALS AND METHODS

Metabolic profiles from luminal-like and basal-like xenograft tumors were obtained in vivo using 3D (31) P MRSI at 11.7T and from tissue extracts in vitro at 14.1T. Gene expression analysis was performed in order to support metabolic differences between the two xenografts.

RESULTS

In vivo (31) P MR spectra were obtained in which the prominent resonances from phospholipid metabolites were detected at a high signal-to-noise ratio (SNR >7.5). Metabolic profiles obtained in vivo were in agreement with those obtained in vitro and could be used to discriminate between the two xenograft models, based on the levels of phosphocholine, phosphoethanolamine, glycerophosphocholine, and glycerophosphoethanolamine. The differences in phospholipid metabolite concentration could partly be explained by gene expression profiles.

CONCLUSION

Noninvasive metabolic profiling by 3D (31) P MRSI can discriminate between subtypes of breast cancer based on different concentrations of choline- and ethanolamine-containing phospholipids.

Dietary lipids do not contribute to the higher hepatic triglyceride levels of fructose- compared to glucose-fed mice

Fructose consumption has been associated with the surge in obesity and dyslipidemia. This may be mediated by the fructose effects on hepatic lipids and ATP levels. Fructose metabolism provides carbons for de novo lipogenesis (DNL) and stimulates enterocyte secretion of apoB48. Thus, fructose-induced hepatic triglyceride (HTG) accumulation can be attributed to both DNL stimulation and dietary lipid absorption. The aim of this study was to assess the effects of fructose diet on HTG and ATP content and the contributions of dietary lipids and DNL to HTG. Measurements were performed in vivo in mice by magnetic resonance imaging (MRI) and novel magnetic resonance spectroscopy (MRS) approaches. Abdominal adipose tissue volume and intramyocellular lipid levels were comparable between 8-wk fructose- and glucose-fed mice. HTG levels were ∼1.5-fold higher in fructose-fed than in glucose-fed mice (P<0.05). Metabolic flux analysis by (13)C and (2)H MRS showed that this was not due to dietary lipid absorption, but due to DNL stimulation. The contribution of oral lipids to HTG was, after 5 h, 1.60 ± 0.23% for fructose and 2.16 ± 0.35% for glucose diets (P=0.26), whereas that of DNL was higher in fructose than in glucose diets (2.55±0.51 vs.1.13±0.24%, P=0.01). Hepatic energy status, assessed by (31)P MRS, was similar for fructose- and glucose-fed mice. Fructose-induced HTG accumulation is better explained by DNL and not by dietary lipid uptake, while not compromising ATP homeostasis.

Multinutrient diets improve cerebral perfusion and neuroprotection in a murine model of Alzheimer's disease

Nutritional intervention may retard the development of Alzheimer's disease (AD). In this study we tested the effects of 2 multi-nutrient diets in an AD mouse model (APPswe/PS1dE9). One diet contained membrane precursors such as omega-3 fatty acids and uridine monophosphate (DEU), whereas another diet contained cofactors for membrane synthesis as well (Fortasyn); the diets were developed to enhance synaptic membranes synthesis, and contain components that may improve vascular health. We measured cerebral blood flow (CBF) and water diffusivity with ultra-high-field magnetic resonance imaging, as alterations in these parameters correlate with clinical symptoms of the disease. APPswe/PS1dE9 mice on control diet showed decreased CBF and changes in brain water diffusion, in accordance with findings of hypoperfusion, axonal disconnection and neuronal loss in patients with AD. Both multinutrient diets were able to increase cortical CBF in APPswe/PS1dE9 mice and Fortasyn reduced water diffusivity, particularly in the dentate gyrus and in cortical regions. We suggest that a specific diet intervention has the potential to slow AD progression, by simultaneously improving cerebrovascular health and enhancing neuroprotective mechanisms.

A longitudinal study of cognition, proton MR spectroscopy and synaptic and neuronal pathology in aging wild-type and AβPPswe-PS1dE9 mice

Proton magnetic resonance spectroscopy (¹H MRS) is a valuable tool in Alzheimer’s disease research, investigating the functional integrity of the brain. The present longitudinal study set out to characterize the neurochemical profile of the hippocampus, measured by single voxel ¹H MRS at 7 Tesla, in the brains of AβPPSswe-PS1dE9 and wild-type mice at 8 and 12 months of age. Furthermore, we wanted to determine whether alterations in hippocampal metabolite levels coincided with behavioral changes, cognitive decline and neuropathological features, to gain a better understanding of the underlying neurodegenerative processes. Moreover, correlation analyses were performed in the 12-month-old AβPP-PS1 animals with the hippocampal amyloid-β deposition, TBS-T soluble Aβ levels and high-molecular weight Aβ aggregate levels to gain a better understanding of the possible involvement of Aβ in neurochemical and behavioral changes, cognitive decline and neuropathological features in AβPP-PS1 transgenic mice. Our results show that at 8 months of age AβPPswe-PS1dE9 mice display behavioral and cognitive changes compared to age-matched wild-type mice, as determined in the open field and the (reverse) Morris water maze. However, there were no variations in hippocampal metabolite levels at this age. AβPP-PS1 mice at 12 months of age display more severe behavioral and cognitive impairment, which coincided with alterations in hippocampal metabolite levels that suggest reduced neuronal integrity. Furthermore, correlation analyses suggest a possible role of Aβ in inflammatory processes, synaptic dysfunction and impaired neurogenesis.

Disturbed energy metabolism and muscular dystrophy caused by pure creatine deficiency are reversible by creatine intake

Creatine (Cr) plays an important role in muscle energy homeostasis by its participation in the ATP-phosphocreatine phosphoryl exchange reaction mediated by creatine kinase. Given that the consequences of Cr depletion are incompletely understood, we assessed the morphological, metabolic and functional consequences of systemic depletion on skeletal muscle in a mouse model with deficiency of l-arginine:glycine amidinotransferase (AGAT(-/-)), which catalyses the first step of Cr biosynthesis. In vivo magnetic resonance spectroscopy showed a near-complete absence of Cr and phosphocreatine in resting hindlimb muscle of AGAT(-/-) mice. Compared with wild-type, the inorganic phosphate/β-ATP ratio was increased fourfold, while ATP levels were reduced by nearly half. Activities of proton-pumping respiratory chain enzymes were reduced, whereas F(1)F(0)-ATPase activity and overall mitochondrial content were increased. The Cr-deficient AGAT(-/-) mice had a reduced grip strength and suffered from severe muscle atrophy. Electron microscopy revealed increased amounts of intramyocellular lipid droplets and crystal formation within mitochondria of AGAT(-/-) muscle fibres. Ischaemia resulted in exacerbation of the decrease of pH and increased glycolytic ATP synthesis. Oral Cr administration led to rapid accumulation in skeletal muscle (faster than in brain) and reversed all the muscle abnormalities, revealing that the condition of the AGAT(-/-) mice can be switched between Cr deficient and normal simply by dietary manipulation. Systemic creatine depletion results in mitochondrial dysfunction and intracellular energy deficiency, as well as structural and physiological abnormalities. The consequences of AGAT deficiency are more pronounced than those of muscle-specific creatine kinase deficiency, which suggests a multifaceted involvement of creatine in muscle energy homeostasis in addition to its role in the phosphocreatine-creatine kinase system.

Increased intramyocellular lipids but unaltered in vivo mitochondrial oxidative phosphorylation in skeletal muscle of adipose triglyceride lipase-deficient mice

Adipose triglyceride lipase (ATGL) is a lipolytic enzyme that is highly specific for triglyceride hydrolysis. The ATGL-knockout mouse (ATGL(-/-)) accumulates lipid droplets in various tissues, including skeletal muscle, and has poor maximal running velocity and endurance capacity. In this study, we tested whether abnormal lipid accumulation in skeletal muscle impairs mitochondrial oxidative phosphorylation, and hence, explains the poor muscle performance of ATGL(-/-) mice. In vivo ¹H magnetic resonance spectroscopy of the tibialis anterior of ATGL(-/-) mice revealed that its intramyocellular lipid pool is approximately sixfold higher than in WT controls (P = 0.0007). In skeletal muscle of ATGL(-/-) mice, glycogen content was decreased by 30% (P < 0.05). In vivo ³¹P magnetic resonance spectra of resting muscles showed that WT and ATGL(-/-) mice have a similar energy status: [PCr], [P(i)], PCr/ATP ratio, PCr/P(i) ratio, and intracellular pH. Electrostimulated muscles from WT and ATGL(-/-) mice showed the same PCr depletion and pH reduction. Moreover, the monoexponential fitting of the PCr recovery curve yielded similar PCr recovery times (τPCr; 54.1 ± 6.1 s for the ATGL(-/-) and 58.1 ± 5.8 s for the WT), which means that overall muscular mitochondrial oxidative capacity was comparable between the genotypes. Despite similar in vivo mitochondrial oxidative capacities, the electrostimulated muscles from ATGL(-/-) mice displayed significantly lower force production and increased muscle relaxation time than the WT. These findings suggest that mechanisms other than mitochondrial dysfunction cause the impaired muscle performance of ATGL(-/-) mice.

Magnetic resonance imaging studies on gadonanotube-reinforced biodegradable polymer nanocomposites

We report about the in vitro cytotoxicity and MRI studies of Gd(3+)ions-doped ultra-short single-walled carbon nanotube (gadonanotubes), gadonanotubes- reinforced poly(lactic-co-glycolic acid) (PLGA) polymer nanocomposites and in vivo small animal MRI studies using the gadonanotubes. These studies were performed to explore the suitability of gadonanotubes-reinforced PLGA polymer nanocomposite as a model scaffold for noninvasive magnetic resonance imaging (MRI) to evaluate nanotube release during the degradation process of the scaffold and their biodistribution upon release from the polymer matrix in vivo. The gadonanotubes at 1-100 ppm and the gadonanotubes/PLGA nanocomposites (2 wt % gadonanotubes) did not show any cytotoxicity in vitro as demonstrated using the LIVE/DEAD viability assay. For the first time, r(2) relaxivity measurements were obtained for the superparamagnetic gadonanotubes. In vitro 7T MRI of the superparamagnetic gadonanotubes ([Gd] = 0.15 mM) suspended in a biocompatible 1% Pluronic F127 solution, gave a r(2) value of 578 mM(-1) s(-1). Upon subcutaneous injection of the gadonanotubes suspension into the dorsal region of rats, the high r(2) value translated into excellent and prolonged negative contrast enhancement of in vivo T(2)weighted proton MRI images. The in vitro characterization of the nanocomposite discs and their degradation process by MRI, showed strong influence of the gadonanotube on water proton relaxations. These results indicate that the gadonanotubes/PLGA nanocomposites are suitable for further in vivo studies to track by MRI the biodegradation release and biodistribution of gadonanotubes.

In vivo magnetic resonance imaging of the distribution pattern of gadonanotubes released from a degrading poly(lactic-co-glycolic Acid) scaffold

To improve the mechanical properties of polymers used in bone repair, it has been suggested to incorporate single-walled carbon nanotubes (CNTs). However, concern exists about the biosafety of the CNTs in vivo. Therefore, the aim of this study was to develop a magnetic resonance imaging technique to examine the distribution pattern of CNTs after release from a degrading poly(lactic-co-glycolic acid) (PLGA) scaffold in vivo. Five rats received a PLGA scaffold with incorporated gadolinium-labeled single-walled CNTs ("gadonanotubes") subcutaneously. The rats were analyzed up to 5 weeks, subsequently euthanized, followed by histological evaluation of the explanted scaffolds with their surrounding tissue. A significant increase in intensity of the scaffold surrounding tissue was shown in the time period around 3 weeks, as compared to internal control areas. The intensity declined soon thereafter. This is suggested to be caused by the release of gadonanotubes from the degrading scaffold into the surrounding tissue. Histological imaging showed encapsulation by connective fibrous tissue and some mild inflammation around the scaffolds. In conclusion, magnetic resonance imaging is an excellent technique to study the biological fate of gadonanotubes. However, to formulate solid conclusions on the distribution pattern of gadonanotubes in vivo the experimental setup requires further optimization.

Gated dynamic 31P MRS shows reduced contractile phosphocreatine breakdown in mice deficient in cytosolic creatine kinase and adenylate kinase

We developed a new dedicated measurement protocol for dynamic (31)P MRS analysis in contracting calf muscles of the mouse, using minimally invasive assessment of the contractile force combined with the acquisition of spectroscopic data gated to muscle contraction and determination of phosphocreatine (PCr) recovery rate and ATP contractile cost. This protocol was applied in a comparative study of six wild type (WT) mice and six mice deficient in cytosolic creatine kinase and adenylate kinase isoform 1 (MAK(-/-) mice) using 70 repeated tetanic contractions at two contractions per minute. Force levels during single contractions, and metabolite levels and tissue pH during resting conditions were similar in muscles of MAK(-/-) and WT mice. Strikingly, muscle relaxation after contraction was significantly delayed in MAK(-/-) mice, but during repeated contractions, the decrease in the force was similar in both mouse types. Gated data acquisition showed a negligible PCr breakdown in MAK(-/-) immediately after contraction, without a concomitant decrease in ATP or tissue pH. This protocol enabled the determination of rapid PCr changes that would otherwise go unnoticed due to intrinsic low signal-to-noise ratio (SNR) in mouse skeletal muscles combined with an assessment of the PCr recovery rate. Our results suggest that MAK(-/-) mice use alternative energy sources to maintain force during repeated contractions when PCr breakdown is reduced. Furthermore, the absence of large increases in adenosine diphosphate (ADP) or differences in force compared to WT mice in our low-intensity protocol indicate that creatine kinase (CK) and adenylate kinase (AK) are especially important in facilitating energy metabolism during very high energy demands.

Localized sensitivity enhanced in vivo 13C MRS to detect glucose metabolism in the mouse brain

The application of in vivo 13C MR spectroscopy to mouse brain models is potentially valuable for improving the understanding of cerebral carbohydrate metabolism and glutamatergic neurotransmission in various neuropathologies. However, the low sensitivity of 13C nuclei and contaminating signals of lipids in the relatively small mouse brain make this application rather challenging. To meet these technical challenges, localized semi-adiabatic distortionless enhanced polarization transfer (DEPT) MR spectroscopy in combination with a continuous intravenous [1,6-13C2] glucose infusion was implemented to detect glucose metabolism in isoflurane-anesthetized mice at 7T. The signal enhancement and high spectral resolution obtained in these experiments enabled the separate determination of 13C label incorporation into as much as 13 metabolites from a 175 microL volume. Signal increases of glucose (C6), glutamine (C3, C4), and glutamate (C3, C4) were determined with a time resolution of 8.6 min. This study demonstrates an optimized MR method for the application of in vivo 13C MRS in mouse brain.

Changes in cerebral blood volume and amyloid pathology in aged Alzheimer APP/PS1 mice on a docosahexaenoic acid (DHA) diet or cholesterol enriched Typical Western Diet (TWD)

High dietary cholesterol and low dietary docosahexaenoic acid (DHA) intake are risk factors for Alzheimer's disease (AD). However, it is unclear how these components influence the course of the disease. We investigated the effects of dietary lipids on beta-amyloid deposition and blood circulation in the brains of 18-month-old APP/PS1 mice. Starting at 6 months of age, mice were fed a regular rodent chow, a Typical Western Diet (TWD) containing 1% cholesterol, or a diet with a high (0.5%) level of DHA for 12 months. Relative cerebral blood volume (rCBV) and flow (CBF) were determined with (2)H MR spectroscopy and gradient echo contrast enhanced MRI. Deposition of beta-amyloid was visualized in fixed brain tissue with immunohistochemistry. The TWD diet increased plaque burden in the dentate gyrus of the hippocampus, but did not significantly reduce rCBV. In contrast, the DHA-enriched diet increased rCBV without changing blood flow indicating a larger circulation in the brain probably due to vasodilatation and decreased the amount of vascular beta-amyloid deposition. Together, our results indicate that the long-term intake of dietary lipids can impact both brain circulation and beta-amyloid deposition, and support the involvement of hemodynamic changes in the development of AD.

Creatine uptake in brain and skeletal muscle of mice lacking guanidinoacetate methyltransferase assessed by magnetic resonance spectroscopy

Creatine (Cr) levels in skeletal muscle and brain of a mouse model of Cr deficiency caused by guanidinoacetate methyltransferase absence (GAMT-/-) were studied after Cr supplementation with 2 g.kg body wt-1.day-1 Cr for 35 days. Localized 1H magnetic resonance spectroscopy (MRS) was performed in brain (cerebellum and thalamus/hippocampus) and in hind leg muscle of GAMT-/- mice before and after Cr supplementation and in control (Con) mice. As expected, a signal for Cr was hardly detectable in MR spectra of GAMT-/- mice before Cr supplementation. In the thalamus/hippocampus region of these mice, an increase in N-acetylasparate (NAA) was observed. During Cr administration, Cr levels increased faster in skeletal muscle compared with brain, but this occurred only during the first day of supplementation. Thereafter, Cr levels increased by 0.8 mM/day in all studied locations. After 35 days of Cr supplementation, Cr levels in all locations were higher compared with Con mice on a Cr-free diet and NAA levels normalized. Only because of the repeated MRS measurements performed in this longitudinal Cr supplementation study on GAMT-/- mice were we able to discover the initial faster uptake of Cr in skeletal muscle compared with brain, which may represent muscular Cr uptake independent of Cr transporter expression. Our results can provide the basis for additional experiments to optimize Cr supplementation in GAMT deficiency, as increases in brain Cr are slow in patients after Cr supplementation.

Magnetic resonance imaging and T2 relaxometry of human median nerve at 7 Tesla

Measurements of T2 relaxation times in tissues have provided a unique, noninvasive method to investigate the microenvironment of water molecules in vivo. As more clinical imaging is performed at higher field strengths, tissue relaxation times need to be reassessed in order to optimize tissue contrast. The purpose of this study was to investigate the water proton T2 relaxation time in human median nerve at 7 T. High-resolution images of the wrist were obtained using a home-built dedicated microstrip coil. Gradient echo images provided a good anatomical delineation of the wrist structure, with a clear definition of the median nerve, tendons, bone, and connective tissue within the wrist in an acquisition time of 2 min. Measurements of the T2 relaxation time were performed with a spin echo imaging sequence. The T2 relaxation time of the median nerve was 18.3 +/- 1.9 ms, which is significantly shorter than the T2 measured in previous studies performed at 1.5 T and 3 T. Further, the T2 relaxation time of the median nerve is shorter than the T2 relaxation time of other tissues, such as brain tissue, at the same field strength. Since the T2 relaxation time of water protons is sensitive to the water microenvironment, relaxation measurements and, in general, a more quantitative magnetic resonance imaging approach might help in detecting and investigating diseases of peripheral nervous system, such as compressive and inflammatory neuropathies, in humans.

Measurements of T1 and T2 relaxation times of colon cancer metastases in rat liver at 7 T

The purpose of this study was to investigate the magnetic resonance imaging (MRI) characteristics of colon cancer metastases in rat liver at 7 T. A dedicated RF microstrip coil of novel design was built in order to increase the signal-to-noise ratio and, in combination with respiratory triggering, to minimize motion artifacts. T1- and T2-weighted MR imaging was performed to follow tumor growth. T1-weighted images provided a good anatomical delineation of the liver structure, while the best contrast between metastases and normal liver tissue was achieved with T2-weighted images. Measurements of T1 and T2 relaxation times were performed with inversion recovery FLASH and Carr-Purcell-Meiboom-Gill and inversion recovery FLASH imaging sequences, respectively, for quantitative MR characterization of metastases. Both the T1 and T2 of the metastases were significantly higher than those of normal liver tissue. Further, an increase in the T1 relaxation time of the metastases was observed with tumor growth. These findings suggest that quantitative in vivo MR characterization provides information on tumor development and possibly response to therapy, though additional studies are needed to elucidate the correlation between the changes in relaxation times and tumor microenvironment.