Contrast-enhanced magnetic resonance microangiography reveals remodeling of the cerebral microvasculature in transgenic ArcAß mice.

Amyloid-ß (Aß) deposition in the cerebral vasculature is accompanied by remodeling which has a profound influence on vascular integrity and function. In the current study we have quantitatively assessed the age-dependent changes of the cortical vasculature in the arcAß model of cerebral amyloidosis. To estimate the density of the cortical microvasculature in vivo, we used contrast-enhanced magnetic resonance microangiography (CE-µMRA). Three-dimensional gradient echo datasets with 60 µm isotropic resolution were acquired in 4- and 24-month-old arcAß mice and compared with wild-type (wt) control mice of the same age before and after administration of superparamagnetic iron oxide nanoparticles. After segmentation of the cortical vasculature from difference images, an automated algorithm was applied for assessing the number and size distribution of intracortical vessels. With CE-µMRA, cerebral arteries and veins with a diameter of less than the nominal pixel resolution (60 µm) can be visualized. A significant age-dependent reduction in the number of functional intracortical microvessels (radii of 20-80 µm) has been observed in 24-month-old arcAß mice compared with age-matched wt mice, whereas there was no difference between transgenic and wt mice of 4 months of age. Immunohistochemistry demonstrated strong fibrinogen and Aß deposition in small- and medium-sized vessels, but not in large cerebral arteries, of 24-month-old arcAß mice. The reduced density of transcortical vessels may thus be attributed to impaired perfusion and vascular occlusion caused by deposition of Aß and fibrin. The study demonstrated that remodeling of the cerebrovasculature can be monitored noninvasively with CE-µMRA in mice.

Cooperation of Th1 and Th17 cells determines transition from autoimmune myocarditis to dilated cardiomyopathy.

Myocarditis is a potentially lethal inflammatory heart disease of children and young adults that frequently leads to dilated cardiomyopathy (DCM). Since diagnostic procedures and efficient therapies are lacking, it is important to characterize the critical immune effector pathways underlying the initial cardiac inflammation and the transition from myocarditis to DCM. We describe here a T-cell receptor (TCR) transgenic mouse model with spontaneously developing autoimmune myocarditis that progresses to lethal DCM. Cardiac magnetic resonance imaging revealed early inflammation-associated changes in the ventricle wall including transient thickening of the left ventricle wall. Furthermore, we found that IFN-γ was a major effector cytokine driving the initial inflammatory process and that the cooperation of IFN-γ and IL-17A was essential for the development of the progressive disease. This novel TCR transgenic mouse model permits the identification of the central pathophysiological and immunological processes involved in the transition from autoimmune myocarditis to DCM.

Increased blood oxygen level-dependent (BOLD) sensitivity in the mouse somatosensory cortex during electrical forepaw stimulation using a cryogenic radiofrequency probe.

Functional MRI (fMRI) based on the blood oxygen level-dependent (BOLD) contrast is widely used in preclinical neuroscience. The small dimensions of rodent brain place high demands on spatial resolution, and hence on the sensitivity of the fMRI experiment. This work investigates the performance of a 400-MHz cryogenic quadrature transceive radiofrequency probe (CryoProbe) with respect to the enhancement of the BOLD sensitivity. For this purpose, BOLD fMRI experiments were performed in mice during electrical forepaw stimulation using the CryoProbe and a conventional room temperature surface coil of comparable dimensions. Image signal-to-noise ratio (SNR) and temporal SNR were evaluated as quality measures for individual images and for fMRI time series of images, resulting in gains (mean ± standard deviation) with factors of 3.1 ± 0.7 and 1.8 ± 1.0 when comparing the CryoProbe and room temperature coil. The CryoProbe thermal shield temperature did not affect the noise characteristics, with temporal noise levels being 63 ± 16% of the corresponding room temperature value. However, a significant effect on BOLD amplitudes was found, which was attributed to temperature-dependent baseline cerebral blood volumes. Defined local thermal conditions were found to be a critical parameter for achieving an optimal and reproducible fMRI signal. In summary, the CryoProbe represents an attractive alternative for the enhancement of image SNR, temporal SNR and BOLD sensitivity in mouse fMRI experiments.

Accurate assessment of carotid artery stenosis in atherosclerotic mice using accelerated high-resolution 3D magnetic resonance angiography.

OBJECT: High-resolution magnetic resonance angiography (MRA) enables non-invasive detection and longitudinal monitoring of atherosclerosis in mouse models of human disease. However, MRA is hampered by long acquisition times putting high demands on the physiological stability of the animal. Therefore, we evaluated the feasibility of accelerated MRA using the parallel imaging technique SENSE with regard to both lesion detection and quantification. MATERIALS AND METHODS: MRA acquisitions of supra-aortic vessels were performed in ApoE (-/-) mice that have been shown to develop atherosclerotic plaques. Findings obtained from accelerated data sets were compared to fully sampled reference data sets and histology. RESULTS: Our results revealed only minor differences in detecting vascular lesions for data collections accelerated by factors of up to 3.3 using a four-element coil array. For vessels with a mean lumen diameter of 500 µm, morphometry of stenotic lesions revealed no substantial deviations from reference (fully sampled) data for all investigated acceleration factors. For the highest acceleration factor of 3.3, an average deviation of the degree of stenosis of 4.9 ± 3.6% was found. Common carotid stenoses assessed by in vivo MRA displayed a good correlation with histological analyses (slope of linear regression = 0.97, R (2) = 0.98). CONCLUSION: According to the results of this work, we have demonstrated the feasibility and accuracy of accelerated high-resolution 3D ToF MRA in mice suitable for detailed depiction of mouse supra-aortic vessels and amenable to non-invasive quantification of small atherosclerotic lesions.

Accelerated cardiovascular magnetic resonance of the mouse heart using self-gated parallel imaging strategies does not compromise accuracy of structural and functional measures.

BACKGROUND: Self-gated dynamic cardiovascular magnetic resonance (CMR) enables non-invasive visualization of the heart and accurate assessment of cardiac function in mouse models of human disease. However, self-gated CMR requires the acquisition of large datasets to ensure accurate and artifact-free reconstruction of cardiac cines and is therefore hampered by long acquisition times putting high demands on the physiological stability of the animal. For this reason, we evaluated the feasibility of accelerating the data collection using the parallel imaging technique SENSE with respect to both anatomical definition and cardiac function quantification. RESULTS: Findings obtained from accelerated data sets were compared to fully sampled reference data. Our results revealed only minor differences in image quality of short- and long-axis cardiac cines: small anatomical structures (papillary muscles and the aortic valve) and left-ventricular (LV) remodeling after myocardial infarction (MI) were accurately detected even for 3-fold accelerated data acquisition using a four-element phased array coil. Quantitative analysis of LV cardiac function (end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), ejection fraction (EF) and LV mass) in healthy and infarcted animals revealed no substantial deviations from reference (fully sampled) data for all investigated acceleration factors with deviations ranging from 2% to 6% in healthy animals and from 2% to 8% in infarcted mice for the highest acceleration factor of 3.0. CNR calculations performed between LV myocardial wall and LV cavity revealed a maximum CNR decrease of 50% for the 3-fold accelerated data acquisition when compared to the fully-sampled acquisition. CONCLUSIONS: We have demonstrated the feasibility of accelerated self-gated retrospective CMR in mice using the parallel imaging technique SENSE. The proposed method led to considerably reduced acquisition times, while preserving high spatial resolution at sufficiently high CNR. The accuracy of measurements of both structural and functional parameters of the mouse heart was not compromised by the application of the proposed accelerated data acquisition method.

Increasing temporal resolution of DSC perfusion MRI using the analytic image concept.

OBJECT: Dynamic susceptibility contrast MRI (DSC-MRI) is increasingly being used to evaluate cerebral microcirculation. In this study, the use of the analytic image reconstruction (AIR), with the aim to increase the temporal resolution, is evaluated for DSC-MRI in small animals. MATERIALS AND METHODS: Imaging was performed using a T (2)*- weighted sequence to acquire male Lewis rats raw data. Results show that AIR satisfactory reconstructs DSC-MRI while preserving a good reconstruction quality and the image characteristics compared to the full k-space and keyhole reconstructed images. The combination of the choice of the baseline image and the proposed asymmetric acquisition schema enables an increase in temporal resolution, by a factor of four, thus having more sample points for better estimating perfusion parameters. RESULTS: Computer simulations result in a mean cerebral blood volume of 1.22 that deviates from the full k-space value by -3% and a mean cerebral blood flow of 1.97 deviating from the full k-space value by -3% when the mean transit time did not change. Even if these deviations increase when achieving real acquisitions, AIR still better computes quantitative values than keyhole. CONCLUSION: AIR allows a good reconstruction of the dynamic stage of the image series thus leading to better dynamic effects analysis.

Performance of a 200-MHz cryogenic RF probe designed for MRI and MRS of the murine brain.

A cryogenic 200-MHz RF transmit/receive probe (CryoProbe) made of copper and designed for murine brain studies is described. The probe operates at 30K and its performance was compared to a home-made surface coil of equal dimensions and a mouse head volume resonator, both operating at room temperature (RT). Since for small volumes of tissue interrogated (<5 mL) sample noise and thermal noise of the receiver are of comparable magnitude, considerable noise reduction can be achieved by cooling of the receiver system, e.g., using cold helium gas. The effect of temperature lowering on the signal-to-noise ratio (SNR) was assessed in phantom and in vivo murine brain studies using conventional MRI sequences (spin and gradient echo) and single voxel MR spectroscopy. Consistent sensitivity increases were observed for the CryoProbe. SNR increases by a factor>or=2 for the phantom experiments and by factors of 1.8 to 1.9 for in vivo experiments when compared to the RT surface coil for both MRI and MRS experiments. These results are in good agreement with estimated SNR gains for a circular surface coil probe cooled to 30K. The use of a cryogenic probe represents an economically attractive option to enhance the sensitivity in small animal MRI/MRS.