In vivo fiber tracking in the rat brain on a clinical 3T MRI system using a high strength insert gradient coil

Department of Radiology, Stanford University School of Medicine, Stanford, CA, USA.
NeuroImage (Impact Factor: 6.36). 05/2007; 35(3):1077-85. DOI: 10.1016/j.neuroimage.2007.01.006
Source: PubMed

ABSTRACT In vivo neuroimaging methods permit longitudinal quantitative examination of the dynamic course of neurodegenerative conditions in humans and animal models and enable assessment of therapeutic efforts in mitigating disease effects on brain systems. The study of conditions affecting white matter, such as multiple sclerosis, demyelinating conditions, and drug and alcohol dependence, can be accomplished with diffusion tensor imaging (DTI), a technique uniquely capable of probing the microstructural integrity of white matter fibers in the living brain. We used a 3T clinical MR scanner equipped with an insert gradient coil that yields an order of magnitude increase in performance over the whole-body hardware to acquire in vivo DTI images of rat brain. The resolution allowed for fiber tracking evaluation of fractional anisotropy (FA) and apparent diffusion coefficients in the genu and splenium of the corpus callosum. A comparison of short (46 min) and long (92 min) acquisition time DTI protocols indicated low but adequate signal-to-noise ratio (SNR=6.2) of the shorter protocol to conduct quantitative fiber tracking enhanced by multiple acquisitions. As observed in human studies, FA in the rat splenium was higher than in the genu. Advantages of this technology include the use of similar user interface, pulse sequences, and field strength for preclinical animal and clinical human research, enhancing translational capabilities. An additional benefit of scanning at lower field strength, such as 3 T, is the reduction of artifacts due to main field inhomogeneity relative to higher field animal systems.

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Available from: Edith V Sullivan, Apr 11, 2015
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    • "Using an IGC instead of a SGC for MRN is interesting, as it exhibits both submillisecond switching time and gradient strengths of hundreds of millitesla per meter. Fast high magnetic performance systems are in development and currently used in clinical research for imaging routines such as diffusion tensor imaging, which requires fast gradient switches and gradient amplitudes of 300 mT/m [14]–[17]. Such imaging sequences usually use low duty cycle gradient pulses, thereby allowing a long experiment time without any temperature increase. "
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    ABSTRACT: The purpose of this paper is to provide some practical insights regarding the use of a commercially available imaging coil as a magnetic resonance navigation (MRN) propulsion actuator. MRN relies on magnetic resonance imaging (MRI) technology to navigate magnetic therapeutic or imaging agents to a target location. When such a target is accessible only through complex vessel pathways, an imaging gradient coil (IGC) insert can be used to generate high slew rate gradient pulses. Although temperature rise might not be an issue for imaging routines, knowing precisely the temperature coil response is of primary importance for MRN-assisted interventions as it may limit propulsion performance and ultimately lead to system breakdown. This paper reports the impact of four parameters, namely, duty cycle, frequency, amplitude, and gradient direction on the temperature behavior of an IGC with external diameter suitable to fit inside the bore of a clinical MRI scanner and internal diameter appropriate for small animals. A minimum rise time of 300 µs was measured and magnetic gradients up to 325 mT · m −1 were generated. The insert can sustain burst-mode propulsion at maximum power for slightly less than 2 min before reaching its maximum admissible temperature. Temperature management is one of the future challenges in MRN research. Index Terms— Imaging gradient coil (IGC), magnetic resonance navigation (MRN), magnetic targeting, temperature response.
    IEEE Transactions on Magnetics 08/2014; 50(8). DOI:10.1109/TMAG.2014.2309944 · 1.39 Impact Factor
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    • "Thus, findings have the potential to directly translate from basic science to clinical science, within reason. Rodent imaging is commonly acquired with specialized coils and high-field scanners (up to 17.4 T), although commercial-grade clinical scanners can be used for studies with less stringent requirements on spatial resolution and SNR (Pfefferbaum et al., 2004; Lee et al., 2006; Mayer et al., 2007; Pillai et al., 2011). The higher field strength and the smaller bore size of such high-field magnet not only allow for sub-millimeter resolution at appropriate SNR, but also provide a more homogeneous static magnetic field (Nieman et al., 2005). "
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    ABSTRACT: The use of structural magnetic resonance imaging (sMRI) and diffusion tensor imaging (DTI) in animal models of neuropathology is of increasing interest to the neuroscience community. In this work, we present our approach to create optimal translational studies that include both animal and human neuroimaging data within the frameworks of a study of post-natal neuro-development in intra-uterine cocaine-exposure. We propose the use of non-invasive neuroimaging to study developmental brain structural and white matter pathway abnormalities via sMRI and DTI, as advanced MR imaging technology is readily available and automated image analysis methodology have recently been transferred from the human to animal imaging setting. For this purpose, we developed a synergistic, parallel approach to imaging and image analysis for the human and the rodent branch of our study. We propose an equivalent design in both the selection of the developmental assessment stage and the neuroimaging setup. This approach brings significant advantages to study neurobiological features of early brain development that are common to animals and humans but also preserve analysis capabilities only possible in animal research. This paper presents the main framework and individual methods for the proposed cross-species study design, as well as preliminary DTI cross-species comparative results in the intra-uterine cocaine-exposure study.
    Frontiers in Psychiatry 10/2011; 2:53. DOI:10.3389/fpsyt.2011.00053
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    • "Sensible improvements are offered by the use of high magnetic field, yet an accurate choice of the acquisition and processing parameters is needed, namely for in-vivo studies. Few studies reported DTI analysis in rodent brain in presence of stroke [9] and in developing stages [10]; tractography has been performed in mouse [11], [12] and in rat [13], [14]. To our knowledge, a single reference atlas reconstruction has been carried out, so far [15]; however, in mouse and by means of ex-vivo scans. "
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    ABSTRACT: The tractographic reconstruction of anatomical and microstructural features provided by Magnetic Resonance (MR) Diffusion Tensor Imaging (DTI) gives essential information of brain damage in several pathological animal models. The optimization of a tractographic protocol is undertaken in normal rats for the future construction of a reference atlas, as prerequisite for preclinical pathological in-vivo studies. High field, preclinical in-vivo DTI faces important difficulties relevant to Signal-to-Noise Ratio (SNR), distortion, high required resolution, movement sensitivity. Given a pixel-size of 0.17 mm and TE/TR = 29/6500 ms, b value and slice thickness were fixed at 700 s/mm(2) and 0.58 mm, respectively, on preventive ex-vivo studies. In-vivo studies led to the choice of 30 diffusion directions, averaged on 16 runs. The final protocol required 51 min scanning and permitted a reliable reconstruction of main rat brain bundles. Tract reconstruction stopping rules required proper setting. In conclusion, the viability of DTI tractography on in-vivo rat studies was shown, towards the construction of a normal reference atlas.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2011; 2011:8467-70. DOI:10.1109/IEMBS.2011.6092089
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