Response of the primary auditory and non-auditory cortices to acoustic stimulation: A manganese-enhanced MRI study

Structural and functional features of various cerebral cortices have been extensively explored in neuroscience research. We used manganese-enhanced MRI, a non-invasive method for examining stimulus-dependent activity in the whole brain, to investigate the activity in the layers of primary cortices and sensory, such as auditory and olfactory, pathways under acoustic stimulation. Male Sprague-Dawley rats, either with or without exposure to auditory stimulation, were scanned before and 24-29 hour after systemic MnCl2 injection. Cortex linearization and layer-dependent signal extraction were subsequently performed for detecting layer-specific cortical activity. We found stimulus-dependent activity in the deep layers of the primary auditory cortex and the auditory pathways. The primary sensory and visual cortices also showed the enhanced activity, whereas the olfactory pathways did not. Further, we performed correlation analysis of the signal intensity ratios among different layers of each cortex, and compared the strength of correlations between with and without the auditory stimulation. In the primary auditory cortex, the correlation strength between left and right hemisphere showed a slight but not significant increase with the acoustic simulation, whereas, in the primary sensory and visual cortex, the correlation coefficients were significantly smaller. These results suggest the possibility that even though the primary auditory, sensory, and visual cortices showed enhanced activity to the auditory stimulation, these cortices had different associations for auditory processing in the brain network.open0

Multidisciplinary Functional MR Imaging for Prostate Cancer

Various functional magnetic resonance (MR) imaging techniques are used for evaluating prostate cancer including diffusion-weighted imaging, dynamic contrast-enhanced MR imaging, and MR spectroscopy. These techniques provide unique information that is helpful to differentiate prostate cancer from non-cancerous tissue and have been proven to improve the diagnostic performance of MRI not only for cancer detection, but also for staging, post-treatment monitoring, and guiding prostate biopsies. However, each functional MR imaging technique also has inherent challenges. Therefore, in order to make accurate diagnoses, it is important to comprehensively understand their advantages and limitations, histologic background related with image findings, and their clinical relevance for evaluating prostate cancer. This article will review the basic principles and clinical significance of functional MR imaging for evaluating prostate cancer

Quantitative in-vivo imaging of tumor microenvironments

Tumor hypoxia, which develops heterogeneously in locally advanced tumors is known to affect radiation sensitivity and development to metastases. In vivo knowledge of hypoxia distribution in solid tumors provides prognostic information and can be potentially used for input for dose escalation in radiation therapy. Tumor hypoxia results from a mismatch between supply and consumption of oxygen in a tumor. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is well known to provide permeability/perfusion information of solid tumors and may provide surrogate information regarding tumor hypoxia. In this study, (1) DCE-MRI data with the injection of Gd-DTPA was analyzed with Gaussian mixture model (GMM) based classification to verify regions of perfused, hypoxic, necrotic areas in a prostate rat tumor model. The results of pattern recognition on the DCE-MRI show the feasibility on delineation of tumor microenvironments. (2) To increase the spatial/temporal accuracy of such classification, a compressed sensing algorithm is used to enhance the quality of DCE-MRI uptake curves

Acceleration of multi-dimensional propagator measurements with compressed sensing

NMR can probe the microstructures of anisotropic materials such as liquid crystals, stretched polymers and biological tissues through measurement of the diffusion propagator, where internal structures are indicated by restricted diffusion. Multi-dimensional measurements can probe the microscopic anisotropy, but full sampling can then quickly become prohibitively time consuming. However, for incompletely sampled data, compressed sensing is an effective reconstruction technique to enable accelerated acquisition. We demonstrate that with a compressed sensing scheme, one can greatly reduce the sampling and the experimental time with minimal effect on the reconstruction of the diffusion propagator with an example of anisotropic diffusion. We compare full sampling down to 64x sub-sampling for the 2D propagator measurement and reduce the acquisition time for the 3D experiment by a factor of 32 from similar to 80 days to similar to 2.5 days.close6

Implementation of P22 Viral Capsids As Intravascular Magnetic Resonance T-1 Contrast Conjugates via Site-Selective Attachment of Gd(III)-Chelating Agents

P22 viral capsids and ferritin protein cages are utilized as templating macromolecules to conjugate Gd(III)-chelating agent complexes, and we systematically investigates the effects of the macromolecules' size and the conjugation positions of Gd(III)-chelating agents on the magnetic resonance (MR) relaxivities and the resulting image contrasts. The relaxivity values of the Gd(III)-chelating agent-conjugated P22 viral capsids (outer diameter: 64 nm) are dramatically increased as compared to both free Gd(III)-chelating agents and Gd(III)-chelating agent-conjugated ferritins (outer diameter: 12 nm), suggesting that the large sized P22 viral capsids exhibit a much slower tumbling rate, which results in a faster T1 relaxation rate. Gd(III)-chelating agents are attached to either the interior or exterior surface of P22 viral capsids and the conjugation positions of Gd(III)-chelating agents, however, do not have a significant effect on the relaxivity values of the macromolecular conjugates. The contrast enhancement of Gd(III)-chelating agent-conjugated P22 viral capsids is confirmed by in vitro phantom imaging at a short repetition times (TR) and the potential usage of Gd(III)-chelating agent-conjugated P22 viral capsids for in vivo MR imaging is validated by visualizing a mouse's intravascular system, including the carotid, mammary arteries, the jugular vein, and the superficial vessels of the head at an isotropic resolution of 250 ??m.close6

The robustness of T2 value as a trabecular structural index at multiple spatial resolutions of 7 Tesla MRI

Purpose: To evaluate the robustness of MR transverse relaxation times of trabecular bone from spin-echo and gradient-echo acquisitions at multiple spatial resolutions of 7 T. Methods: The effects of MRI resolutions to T-2 and T-2* trabecular bone were numerically evaluated by Monte Carlo simulations. T-2, T-2* and trabecular structural indices from multislice multi-echo and UTE acquisitions were measured in defatted human distal femoral condyles on a 7 T scanner. Reference structural indices were extracted from high-resolution microcomputed tomography images. For bovine knee trabecular samples with intact bone marrow, T-2 and T-2* were measured by degrading spatial resolutions on a 7 T system. Results: In the defatted trabecular experiment, both T-2 and T-2* values showed strong (vertical bar r vertical bar> 0.80) correlations with trabecular spacing and number, at a high spatial resolution of 125 mu m(3). The correlations for MR image-segmentation-olutions of 250 and 500 mu m(3). The correlations for T-2* rapidly dropped (vertical bar r vertical bar< 0.50) at a spatial resolution of 500 mu m(3), whereas those for T-2* remained consistently high (vertical bar r vertical bar> 0.85). In the bovine trabecular experiments with intact marrow, low- resolution (approximately 1 mm(3), 2 minutes) T-2 values did not shorten (vertical bar r vertical bar> 0.95 with respect to approximately 0.4mm(3), 11 minutes) and maintained consistent correlations (vertical bar r vertical bar > 0.70) with respect to trabecular spacing (turbo spin echo, 22.5 minutes). Conclusion: T-2 measurements of trabeculae at 7 T are robust with degrading spatial resolution and may be preferable in assessing trabecular spacing index with reduced scan time, when high-resolution 3D micro-MRI is difficult to obtain

Dual MRI T1 and T2 (*) contrast with size-controlled iron oxide nanoparticles

Contrast-enhancing magnetic resonance mechanism, employing either positive or negative signal changes, has contrast-specific signal characteristics. Although highly sensitive, negative contrast typically decreases the resolution and spatial specificity of MRI, whereas positive contrast lacks a high contrast-to-noise ratio but offers high spatial accuracy. To overcome these individual limitations, dual-contrast acquisitions were performed using iron oxide nanoparticles and a pair of MRI acquisitions. Specifically, vascular signals in MR angiography were positively enhanced using ultrashort echo (UTE) acquisition, which provided highly resolved vessel structures with increased vessel/tissue contrast. In addition, fast low angle shot (FLASH) acquisition yielded strong negative vessel contrast, resulting in the higher number of discernible vessel branches than those obtained from the UTE method. Taken together, the high sensitivity of the negative contrast delineated ambiguous vessel regions, whereas the positive contrast effectively eliminated the false negative contrast areas (e.g., airways and bones), demonstrating the benefits of the dual-contrast method.close0

A Quick Method to Measure Hydroxyl Ion Contents in Bone Mineral Crystals Using Solid State NMR

A 31P CP MAS technique with a pre-saturation pulse was developed to measure OH- contents of bone quickly. This technique could save experimental time at least 128 times compared with a 2D 1H-31P HetCor technique. It also yielded higher signal to noise ratio (SNR), which decreased measurement error. The OH- content in bovine bone was 66.1 mol%