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: 2.02). 12/2010; 28(10):1541-5. DOI: 10.1016/j.mri.2010.06.025
Source: PubMed

ABSTRACT 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).

  • [Show abstract] [Hide abstract]
    ABSTRACT: Localized high-resolution diffusion tensor images (DTI) from the midbrain were obtained using reduced field-of-view (rFOV) methods combined with SENSE parallel imaging and single-shot echo planar (EPI) acquisitions at 7T. This combination aimed to diminish sensitivities of DTI to motion, susceptibility variations, and EPI artifacts at ultra-high field. Outer-volume suppression (OVS) was applied in DTI acquisitions at 2- and 1-mm(2) resolutions, b=1000s/mm(2), and six diffusion directions, resulting in scans of 7- and 14-min durations. Mean apparent diffusion coefficient (ADC) and fractional anisotropy (FA) values were measured in various fiber tract locations at the two resolutions and compared. Geometric distortion and signal-to-noise ratio (SNR) were additionally measured and compared for reduced-FOV and full-FOV DTI scans. Up to an eight-fold data reduction was achieved using DTI-OVS with SENSE at 1mm(2), and geometric distortion was halved. The localization of fiber tracts was improved, enabling targeted FA and ADC measurements. Significant differences in diffusion properties were observed between resolutions for a number of regions suggesting that FA values are impacted by partial volume effects even at a 2-mm(2) resolution. The combined SENSE DTI-OVS approach allows large reductions in DTI data acquisition and provides improved quality for high-resolution diffusion studies of the human brain.
    Magnetic Resonance Imaging 03/2013; · 2.02 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Eight different reduced field-of-view (FOV) MRI techniques suitable for high field human imaging were implemented, optimized, and evaluated at 7T. These included selective Inner-Volume Imaging (IVI) based methods, and Outer-Volume Suppression (OVS) techniques, some of which were previously unexplored at ultra-high fields. Design considerations included use of selective composite excitation and adiabatic refocusing radio-frequency (RF) pulses to address B1 inhomogeneities, twice-refocused spin echo techniques, frequency-modulated pulses to sharply define suppressed regions, and pulse sequence designs to improve SNR in multi-slice scans. The different methods were quantitatively compared in phantoms and in vivo human brain images to provide measurements of relative signal to noise ratio (SNR), power deposition (specific absorption rate, SAR), suppression of signal, artifact strength and prevalence, and general image quality. Multi-slice signal losses in out-of-slice locations were simulated for IVI methods, and then measured experimentally across a range of slice numbers. Corrections for B1 nonuniformities demonstrated an improved SNR and a reduction in artifact power in the reduced-FOV, but produced an elevated SAR. Multi-slice sequences with reordering of pulses in traditional and twice-refocused IVI techniques demonstrated an improved SNR compared to conventional methods. The combined results provide a basis for use of reduced-FOV techniques for human imaging localized to a small FOV at 7T.
    Magnetic Resonance Imaging 07/2013; · 2.02 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Reduced field of view diffusion weighted imaging (rFOV DWI) was less used in MR breast imaging. We compared the imaging qualities, ADC values and application values between rFOV DWI and SS-EPI DWI in 87cases. rFOV DWI presented images with higher resolution, less distortion than SS-EPI DWI. Our findings may assist clinicians improve the diagnosis of the breast diseases. Backgroud This study aimed to compare the imaging quality, ADC values and application values between reduced field-of-view diffusion weighted imaging(rFOV DWI)and single-shot echo-planar-imaging diffusion weighted imaging(SS-EPI DWI)of breast. Patients and Methods 87 cases (75 with normal breast, 12 with mammary cancer) were scanned with SS-EPI DWI and rFOV DWI(b values=800 s/mm2). Image quality and ADC values of breast were compared between SS-EPI DWI and rFOV DWI. Results The average image quality score of 87 cases was 4.73 in rFOV DWI and 3.62 in SS-EPI DWI. The difference was statistically significant difference (P<0.01). The resolution of rFOV DWI was 2.25 mm×1.23mm which was higher than the resolution that(2.25 mm×2.25mm )of SS-EPI DWI. The mean ADC value of 75 cases with normal breast was 1.696×10-3mm2/s by rFOV DWI and 1.832×10-3mm2/s by SS-EPI DWI, and the difference was statistically significant (P<0.01).The mean ADC value of 12 cases with breast cancer was 1.065×10-3mm2/s by rFOV DWI and 1.192×10-3mm2/s by SS-EPI DWI with statistically significant difference(P<0.05). Conclusion rFOV DWI presented images with higher resolution, less distortion than SS-EPI DWI, which may be helpful in disease diagnosis.
    Clinical Breast Cancer 01/2013; · 2.63 Impact Factor

Full-text (2 Sources)

Available from
Jun 3, 2014