-
Chunqi Qian,
Xin Yu,
Der-Yow Chen, Stephen Dodd,
Nadia Bouraoud,
Nikorn Pothayee,
Yun Chen,
Scott Beeman,
Kevin Bennett,
Joseph Murphy-Boesch,
Alan Koretsky
[show abstract]
[hide abstract]
ABSTRACT: Purpose:To assess the feasibility of imaging deep-lying internal organs at high spatial resolution by imaging kidney glomeruli in a rodent model with use of a newly developed, wireless amplified nuclear magnetic resonance (MR) detector.Materials and Methods:This study was approved by the Animal Care and Use Committee at the National Institutes of Health/National Institute of Neurologic Disorder and Stroke. As a preclinical demonstration of this new detection technology, five different millimeter-scale wireless amplified nuclear MR detectors configured as double frequency resonators were chronically implanted on the medial surface of the kidney in five Sprague-Dawley rats for MR imaging at 11.7 T. Among these rats, two were administered gadopentetate dimeglumine to visualize renal tubules on T1-weighted gradient-refocused echo (GRE) images, two were administered cationized ferritin to visualize glomeruli on T2*-weighted GRE images, and the remaining rat was administered both gadopentetate dimeglumine and cationized ferritin to visualize the interleaved pattern of renal tubules and glomeruli. The image intensity in each pixel was compared with the local tissue signal intensity average to identify regions of hyper- or hypointensity.Results:T1-weighted images with 70-μm in-plane resolution and 200-μm section thickness were obtained within 3.2 minutes to image renal tubules, and T2*-weighted images of the same resolution were obtained within 5.8 minutes to image the glomeruli. Hyperintensity from gadopentetate dimeglumine enabled visualization of renal tubules, and hypointensity from cationic ferritin enabled visualization of the glomeruli.Conclusion:High-spatial-resolution images have been obtained to observe kidney microstructures in vivo with a wireless amplified nuclear MR detector.© RSNA, 2013Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13121352/-/DC1.
Radiology 02/2013; · 5.73 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A completely wireless detection coil with an integrated parametric amplifier has been constructed to provide local amplification and transmission of MR signals. The sample coil is one element of a parametric amplifier using a zero-bias diode that mixes the weak MR signal with a strong pump signal that is obtained from an inductively coupled external loop. The NMR sample coil develops current gain via reduction in the effective coil resistance. Higher gain can be obtained by adjusting the level of the pumping power closer to the oscillation threshold, but the gain is ultimately constrained by the bandwidth requirement of MRI experiments. A feasibility study here shows that on a NaCl/D(2) O phantom, (23) Na signals with 20 dB of gain can be readily obtained with a concomitant bandwidth of 144 kHz. This gain is high enough that the integrated coil with parametric amplifier, which is coupled inductively to external loops, can provide sensitivity approaching that of direct wire connection.
Magnetic Resonance in Medicine 01/2012; 68(3):989-96. · 2.96 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The spatiotemporal characteristics of the hemodynamic response to increased neural activity were investigated at the level of individual intracortical vessels using BOLD-fMRI in a well-established rodent model of somatosensory stimulation at 11.7 T. Functional maps of the rat barrel cortex were obtained at 150 × 150 × 500 μm spatial resolution every 200 ms. The high spatial resolution allowed separation of active voxels into those containing intracortical macro vessels, mainly vein/venules (referred to as macrovasculature), and those enriched with arteries/capillaries and small venules (referred to as microvasculature) since the macro vessel can be readily mapped due to the fast T2 decay of blood at 11.7 T. The earliest BOLD response was observed within layers IV-V by 0.8s following stimulation and encompassed mainly the voxels containing the microvasculature and some confined macrovasculature voxels. By 1.2s, the BOLD signal propagated to the macrovasculature voxels where the peak BOLD signal was 2-3 times higher than that of the microvasculature voxels. The BOLD response propagated in individual venules/veins far from neuronal sources at later times. This was also observed in layers IV-V of the barrel cortex after specific stimulation of separated whisker rows. These results directly visualized that the earliest hemodynamic changes to increased neural activity occur mainly in the microvasculature and spread toward the macrovasculature. However, at peak response, the BOLD signal is dominated by penetrating venules even at layers IV-V of the cortex.
NeuroImage 08/2011; 59(2):1451-60. · 5.89 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Recent in vivo MRI studies at 7.0 T have demonstrated extensive heterogeneity of T(2)* relaxation in white matter of the human brain. In order to study the origin of this heterogeneity, we performed T(2)* measurements at 1.5, 3.0, and 7.0 T in normal volunteers. Formalin-fixed brain tissue specimens were also studied using T(2)*-weighted MRI, histologic staining, chemical analysis, and electron microscopy. We found that T(2)* relaxation rate (R(2)* = 1/T(2)*) in white matter in living human brain is linearly dependent on the main magnetic field strength, and the T(2)* heterogeneity in white matter observed at 7.0 T can also be detected, albeit more weakly, at 1.5 and 3.0 T. The T(2)* heterogeneity exists also in white matter of the formalin-fixed brain tissue specimens, with prominent differences between the major fiber bundles such as the cingulum (CG) and the superior corona radiata. The white matter specimen with substantial difference in T(2)* has no significant difference in the total iron content, as determined by chemical analysis. On the other hand, evidence from histologic staining and electron microscopy demonstrates these tissue specimens have apparent difference in myelin content and microstructure.
Magnetic Resonance in Medicine 10/2009; 62(6):1652-7. · 2.96 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: There are few in vivo noninvasive methods to study neuroplasticity in animal brains. Functional MRI (fMRI) has been developed for animal brain mapping, but few fMRI studies have analyzed functional alteration due to plasticity in animal models. One major limitation is that fMRI maps are characterized by statistical parametric mapping making the apparent boundary dependent on the statistical threshold used. Here, we developed a method to characterize the location of center-of-mass in fMRI maps that is shown not to be sensitive to statistical threshold. Utilizing centers-of-mass as anchor points to fit the spatial distribution of the BOLD response enabled quantitative group analysis of altered boundaries of functional somatosensory maps. This approach was used to study cortical reorganization in the rat primary somatosensory cortex (S1) after sensory deprivation to the barrel cortex by follicle ablation (F.A.). FMRI demonstrated an enlarged nose S1 representation in the 3D somatotopic functional maps. This result clearly demonstrates that fMRI enables the spatial mapping of functional changes that can characterize multiple regions of S1 cortex and still be sensitive to changes due to plasticity.
NeuroImage 09/2009; 49(2):1667-76. · 5.89 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In recent years, biotechnology and biomedical research have benefited from the introduction of a variety of specialized nanoparticles whose well-defined, optically distinguishable signatures enable simultaneous tracking of numerous biological indicators. Unfortunately, equivalent multiplexing capabilities are largely absent in the field of magnetic resonance imaging (MRI). Comparable magnetic-resonance labels have generally been limited to relatively simple chemically synthesized superparamagnetic microparticles that are, to a large extent, indistinguishable from one another. Here we show how it is instead possible to use a top-down microfabrication approach to effectively encode distinguishable spectral signatures into the geometry of magnetic microstructures. Although based on different physical principles from those of optically probed nanoparticles, these geometrically defined magnetic microstructures permit a multiplexing functionality in the magnetic resonance radio-frequency spectrum that is in many ways analogous to that permitted by quantum dots in the optical spectrum. Additionally, in situ modification of particle geometries may facilitate radio-frequency probing of various local physiological variables.
Nature 07/2008; 453(7198):1058-63. · 36.28 Impact Factor
