Structure of the water resonance in small voxels in rat brain detected with high spectral and spatial resolution MRI

Fan, Xiaobing; Du, Wei; MacEneaney, Peter; Zamora, Marta; Karczmar, Gregory S.

doi:10.1002/jmri.10193

Cited by 16 publications

(22 citation statements)

References 24 publications

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“…Each 4D complex array (k x × k y × k z × t) was Fourier transformed in all dimensions to produce three spatial dimensions and one spectral dimension (x × y × z × υ). For the complex spectrum, υ, spectral ghosting was corrected at each point (x, y,z), 43 an improved estimate of the frequency of the water peak was determined, 44 and real and imaginary components were phased to produce pure absorption and dispersion spectra. Spectra were phased using conventional techniques.…”

Section: C Data Processingmentioning

confidence: 99%

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3D high spectral and spatial resolution imaging of ex vivo mouse brain

et al. 2015

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Purpose: Widely used MRI methods show brain morphology both in vivo and ex vivo at very high resolution. Many of these methods (e.g., T 2 * -weighted imaging, phase-sensitive imaging, or susceptibility-weighted imaging) are sensitive to local magnetic susceptibility gradients produced by subtle variations in tissue composition. However, the spectral resolution of commonly used methods is limited to maintain reasonable run-time combined with very high spatial resolution. Here, the authors report on data acquisition at increased spectral resolution, with 3-dimensional high spectral and spatial resolution MRI, in order to analyze subtle variations in water proton resonance frequency and lineshape that reflect local anatomy. The resulting information compliments previous studies based on T 2 * and resonance frequency. Methods: The proton free induction decay was sampled at high resolution and Fourier transformed to produce a high-resolution water spectrum for each image voxel in a 3D volume. Data were acquired using a multigradient echo pulse sequence (i.e., echo-planar spectroscopic imaging) with a spatial resolution of 50 × 50 × 70 µm 3 and spectral resolution of 3.5 Hz. Data were analyzed in the spectral domain, and images were produced from the various Fourier components of the water resonance. This allowed precise measurement of local variations in water resonance frequency and lineshape, at the expense of significantly increased run time (16-24 h). Results: High contrast T 2 * -weighted images were produced from the peak of the water resonance (peak height image), revealing a high degree of anatomical detail, specifically in the hippocampus and cerebellum. In images produced from Fourier components of the water resonance at −7.0 Hz from the peak, the contrast between deep white matter tracts and the surrounding tissue is the reverse of the contrast in water peak height images. This indicates the presence of a shoulder in the water resonance that is not present at +7.0 Hz and may be specific to white matter anatomy. Moreover, a frequency shift of 6.76 ± 0.55 Hz was measured between the molecular and granular layers of the cerebellum. This shift is demonstrated in corresponding spectra; water peaks from voxels in the molecular and granular layers are consistently 2 bins apart (7.0 Hz, as dictated by the spectral resolution) from one another. Conclusions: High spectral and spatial resolution MR imaging has the potential to accurately measure the changes in the water resonance in small voxels. This information can guide optimization and interpretation of more commonly used, more rapid imaging methods that depend on image contrast produced by local susceptibility gradients. In addition, with improved sampling methods, high spectral and spatial resolution data could be acquired in reasonable run times, and used for in vivo scans to increase sensitivity to variations in local susceptibility. C 2015 American Association of Physicists in Medicine. [http://dx

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Section: C Data Processingmentioning

confidence: 99%

“…Because of the voxel-by-voxel improved estimation of the peak location 44 in the spectral processing described above, B 0 maps were produced with greater precision than the nominal spectral resolution of the raw data.…”

Section: C Data Processingmentioning

confidence: 99%

3D high spectral and spatial resolution imaging of ex vivo mouse brain

et al. 2015

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“…It is equivalent to a Lorentzian shape in the frequency domain. Experimental results on animal models at high magnetic field, [1][2][3][4] however, suggest that the water resonance from some of the voxels exhibits nonLorentzian behavior, such as split peaks. Such phenomena are related to the heterogeneity in water composition inside the voxels, owing to subvoxelar tissue/vascular compartmentation.…”

Section: Introductionmentioning

confidence: 99%

“…[5][6][7] It has been demonstrated that decomposition of different water spectral components using high-resolution echo-planar spectroscopic imaging (EPSI) can improve the contrast of structural imaging and enhance the sensitivity in delineating lesions after administrating contrast media. 3,4,8,9 It is a logical extension to explore the usefulness of the high-resolution EPSI technique in human brain at clinical field strength. A number of recent fMRI studies have reported the observation of non-Lorentzian MR signal changes in the brain during functional tasks.…”

Section: Introductionmentioning

confidence: 99%

Anatomical and functional brain imaging using high‐resolution echo‐planar spectroscopic imaging at 1.5 Tesla

Karczmar

Uftring

et al. 2005

NMR in Biomedicine

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High-resolution echo-planar spectroscopic imaging (EPSI) of water resonance (i.e. without water suppression) is proposed for anatomic and functional imaging of the human brain at 1.5 T. Water spectra with a resolution of 2.6 Hz and a bandwidth of 333 Hz were obtained in small voxels (1.7 x 1.7 x 3 mm3) across a single slice. Although water spectra appeared Lorentzian in most of the voxels in the brain, non-Lorentzian broadening of the water resonance was observed in voxels containing blood vessels. In functional experiments with a motor task, robust activation in motor cortices was observed in high-resolution T2* maps generated from the EPSI data. Shift of the water resonance frequency occurred during neuronal activation in motor cortices. The activation areas appeared to be more localized after excluding the voxels in which the lineshape of the water resonance had elevated T2* and became more non-Lorentzian during the motor task. These preliminary results suggest that high-resolution EPSI is a promising tool to study susceptibility-related effects, such as BOLD contrast, for improved anatomical and functional imaging of the brain.

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“…[25][26][27] For example, deoxyhemoglobin in small venules within an image voxel can produce resolved components of the water signal. [28][29][30] In such cases, destructive interference between the various components of the water resonance causes signal loss and distortion in conventional MRI where FID data are used (i.e. either single or multiple echoes).…”

Section: Discussionmentioning

confidence: 99%

Comparison of high‐resolution echo‐planar spectroscopic imaging with conventional MR imaging of prostate tumors in mice

Fan

Foxley

et al. 2005

NMR in Biomedicine

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High spectral and spatial resolution (HiSS) MRI of rodent tumors has previously been performed using conventional spectroscopic imaging to obtain images with improved contrast and anatomic detail. The work described here evaluates the use of much faster echo-planar spectroscopic imaging (EPSI) to acquire HiSS data from rodent tumor models of prostate cancer. A high-resolution EPSI pulse sequence was implemented on a 4.7 T Bruker scanner. Three-dimensional EPSI data were Fourier-transformed along the k-space and temporal (free-induction decay) axes to produce detailed water and fat spectra associated with each small image voxel. The data were used to generate images of spectral parameters, e.g. peak-height images for each small voxel. Two variants of EPSI were performed; gradient-echo or spin-echo excitation with EPSI readout. These imaging methods were tested in commonly used rodent prostate cancers, including seven mice implanted with non-metastatic AT2.1 (n ¼ 3) and metastatic AT3.1 (n ¼ 4) prostate tumors on the hind leg, and 10 mice implanted with LNCaP prostate cancers in situ. The peak-height images derived from EPSI datasets provide more detailed tumor anatomy, improved signal-to-noise and contrast-to-noise ratios compared with the gradient-echo or spin-echo images at all echo times. The results suggest that HiSS MRI data from small animal models of prostate cancer can be acquired using EPSI, and that this approach improves imaging of heterogeneous tissue and vascular environments inside the tumors compared with conventional MR techniques.

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Structure of the water resonance in small voxels in rat brain detected with high spectral and spatial resolution MRI

Cited by 16 publications

References 24 publications

3D high spectral and spatial resolution imaging of ex vivo mouse brain

3D high spectral and spatial resolution imaging of ex vivo mouse brain

Anatomical and functional brain imaging using high‐resolution echo‐planar spectroscopic imaging at 1.5 Tesla

Comparison of high‐resolution echo‐planar spectroscopic imaging with conventional MR imaging of prostate tumors in mice

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