Reduced field-of-view diffusion-weighted imaging of the brain at 7 T

Department of Radiology and Biomedical Imaging, University of California, San Francisco MC 2512, CA 94158-2512, USA.
Magnetic Resonance Imaging (Impact Factor: 2.09). 12/2010; 28(10):1541-5. DOI: 10.1016/j.mri.2010.06.025
Source: PubMed


Ventral and rostral regions of the brain are of emerging importance for the MRI characterization of early dementia, traumatic brain injury and epilepsy. Unfortunately, standard single-shot echo planar diffusion-weighted imaging of these regions at high fields is contaminated by severe imaging artifacts in the vicinity of air-tissue interfaces. To mitigate these artifacts and improve visualization of the temporal and frontal lobes at 7 T, we applied a reduced field-of-view strategy, enabled by outer volume suppression (OVS) with novel quadratic phase radiofrequency (RF) pulses, combined with partial Fourier and parallel imaging methods. The new acquisition greatly reduced the level of artifacts in six human subjects (including four patients with early symptoms of dementia).

Download full-text


Available from: Douglas Kelley
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The human medial temporal lobe performs an essential role in memory formation and retrieval. Diseases involving the hippocampus such as Alzheimer disease present a unique opportunity for advanced imaging techniques to detect abnormalities at an early stage. In particular, it is possible that diffusion imaging will measure abnormal microarchitecture beyond the realm of macroscopic imaging. However, this task is formidable because of the detailed anatomy of the medial temporal lobe, the difficulties in obtaining high-quality diffusion images of adequate resolution, and the challenges in diffusion data processing. Moreover, it is unclear if any differences will be significant for an individual patient or simply groups of patients. Successful endeavors will need to address each of these challenges in an integrated fashion. The rewards of such analysis may be detection of microscopic disease in vivo, which could represent a landmark accomplishment for the field of neuroradiology.
    Full-text · Article · Dec 2010 · Topics in magnetic resonance imaging: TMRI
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ultra-high field 7T MRI offers superior signal-to-noise and spatial resolution relative to any other noninvasive imaging technique. By revealing fine anatomical details of the living brain, 7T MRI allows neuroimaging researchers the opportunity to observe in patients disease-related structural changes previously apparent only on postmortem tissue analysis. Alzheimer's disease (AD) is a natural subject for this technology, and I review here two AD-related applications of 7T MRI: direct visualization of cortical plaques, and high resolution hippocampal imaging. I also discuss limitations of this technology as well as expected advances that are likely to establish 7T MRI as an increasingly important tool for the diagnosis and tracking of AD.
    No preview · Article · Jan 2011 · Journal of Alzheimer's disease: JAD
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Diffusion tensor imaging (DTI) and advanced related methods such as diffusion spectrum and kurtosis imaging are limited by low signal-to-noise ratio (SNR) at conventional field strengths. DTI at 7 T can provide increased SNR; however, B0 and B1 inhomogeneity and shorter T2⁎ still pose formidable challenges. The purpose of this study was to quantify and compare SNR at 7 and 3 T for different parallel imaging reduction factors, R, and TE, and to evaluate SNRs influences on fractional anisotropy (FA) and apparent diffusion coefficient (ADC). We found that R>4 at 7 T and R≥2 at 3 T were needed to reduce geometric distortions due to B0 inhomogeneity. For these R at 7 T, SNR was 70-90 for b=0 s/mm(2) and 22-28 for b=1000s/mm(2) in central brain regions. SNR was lower at 3 T (40 for b=0 s/mm(2) and 15 for b=1000 s/mm(2)) and in lateral brain regions at 7 T due to B1 inhomogeneity. FA and ADC did not change with MRI field strength, SENSE factor or TE in the tested range. However, the coefficient of variation for FA increased for SNR <15 and for SNR <10 in ADC, consistent with published theoretical studies. Our study demonstrates that 7 T is advantageous for DTI and lays the groundwork for further development. Foremost, future work should further address challenges with B0 and B1 inhomogeneity to take full advantage for the increased SNR at 7 T.
    Full-text · Article · Jul 2011 · Magnetic Resonance Imaging
Show more