Article

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: 6.13). 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.

0 Bookmarks
 · 
93 Views
  • Source
    [Show abstract] [Hide abstract]
    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). · 1.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper reports the successful navigation of a 1-mm Chrome-Steel bead along three consecutive polymethyl methacrylate channels inside the bore of a 1.5-T magnetic resonance imaging (MRI) scanner. The bead traveled at a mean velocity of 14 cm·s$^{-1}$. This was accomplished using an imaging gradient coil (IGC) insert located inside the MRI tube. While targeting one side of a bifurcation has been previously demonstrated using unidirectional gradient coils, this is the first time that magnetic resonance navigation (MRN) of a bead along consecutive channels is reported. Experimental results confirm that a clinical regular MRI can be used to propel a 1-mm device. In addition, when used at maximum power, IGC temperature rise becomes a serious issue that can ultimately damage the insert and limit the overall performance. Consequently, this paper aims to give some insight into coil temperature management for IGC-assisted procedures. A 33-min thermal stress test was carried out using 100% of the IGC power. Steady-state oscillation can be reached by interleaving propulsion periods with cooling periods, thus enabling longer propulsion procedures. Experimental data showed that the cooling time can be used for imaging purposes with no performance loss, thus enabling MRN-assisted procedures with multiplexed particle distribution assessment.
    IEEE Transactions on Robotics 06/2014; 30(3):719-727. · 2.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This study investigates the peri-tumor signal abnormalities of a spontaneous brain tumor in a rat by using a 4 cm high-temperature superconducting (HTS) surface resonator. Fractional anisotropy (FA) values derived from diffusion tensor imaging reflect the interstitial characteristic of the peri-lesional tissues of brain tumors. Low FA indicates interstitial tumor infiltration and tissue injury, while high FA indicates better tissue integrity. Better delineation of tissue contents obtained by the HTS surface resonator at 77 K may facilitate therapeutic strategy and improve clinical outcomes.
    Applied Physics Letters 02/2013; 102(6). · 3.52 Impact Factor

Preview

Download
0 Downloads
Available from