Improved diffusion-weighting efficiency of pulsed gradient stimulated echo MR measurements with background gradient cross-term suppression

Finsterbusch, Jürgen

doi:10.1016/j.jmr.2008.01.002

Cited by 6 publications

(14 citation statements)

References 18 publications

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“…Some studies modified the pulse sequence of pulsegradient stimulated echo to suppress or to compensate for the cross-term (32)(33)(34)(35)(36)(37). In this study we used the extra b values from the cross-term interaction between the diffusion and imaging gradients instead of suppressing them.…”

Section: Discussionmentioning

confidence: 99%

Potential in reducing scan times of HARDI by accurate correction of the cross‐term in a hemispherical encoding scheme

Cho¹,

Yeh²,

Yi³

et al. 2009

Magnetic Resonance Imaging

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Purpose: To reduce the scan time of high angular resolution diffusion imaging (HARDI) by using the hemispherical encoding scheme with the cross-term correction. Materials and Methods:Unidirectional and 45°crossing phantoms were built to evaluate the accuracy of the fiber orientation estimation when using a hemispherical encoding scheme with and without the cross-term correction. The q-ball imaging using the spherical harmonic basis was adopted for estimation of fiber orientation. By recalculating the diffusion gradient strengths, we make the actual b value in all directions equal to the expected b value for the correction of the cross-term. Results:The separation angles measured on the crossing phantom are 42.67°Ϯ 1.50°, 42.75°Ϯ 2.10°, and 42.93°Ϯ 2.78°for cross-term-free results, for the results from the hemispherical encoding scheme with and without the crossterm correction. The angular errors in mapping the unidirectional phantom are 1.87°-2.29°and 4.01°-4.92°for the results using the hemispherical encoding scheme with and without correcting for the cross-term at different b values. Conclusion:Using the hemispherical encoding scheme with the cross-term correction can potentially halve the scan time of HARDI and obtain accurate fiber orientation estimation simultaneously. This will be helpful in the clinical application of HARDI. THE DEVELOPMENT OF diffusion nuclear magnetic resonance (NMR) enables us to noninvasively retrieve microstructural information that can hardly be detected using conventional NMR methods (1,2). Diffusion tensor imaging (DTI) was later proposed to measure the fiber orientation by estimating threedimensional probability distribution using a Gaussian approximation (3). This opened the door to advances in white matter (WM) connectivity (4 -8). Even though DTI can well assess the integrity of axonal fibers and accurately define the fiber orientation within a voxel containing fibers with a coherent orientation, its drawback is that the fiber orientation estimate is ambiguous in voxels containing multiple orientation structures. This drawback was highlighted in human cerebral studies with the millimeter width of a typical magnetic resonance imaging (MRI) voxel (9,10). In order to address the inability of DTI to resolve intravoxel fiber crossings, several reconstruction methods based on the high angular resolution diffusion imaging (HARDI) sampling scheme (11-17) were proposed and assessed to resolve intravoxel fiber crossings via numerical phantoms and in vivo studies. However, long acquisition times due to the need to obtain a great deal of diffusion-weighted images (DWIs) in HARDI (Ϸ60 -400 DWIs) limit the possibility of routine HARDI and its clinical applications.In previous studies, shortening of the acquisition times of HARDI was achieved using an improved reconstruction method with a lower number of DWIs. Khachaturian et al (18) boosted a sampling efficiency gain of 274%-377% for q-ball imaging (QBI) by nonlinearly fusing the diffusion signal from separate low and high wavevector acquis...

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Section: Discussionmentioning

confidence: 99%

Potential in reducing scan times of HARDI by accurate correction of the cross‐term in a hemispherical encoding scheme

Cho¹,

Yeh²,

Yi³

et al. 2009

Magnetic Resonance Imaging

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“…1), this case can be considered as the ''short-echo-train" regime because the echo train, and thus d 1 , is too short to achieve the optimum diffusion-weighting efficiency with g 0 ¼ 1. For d 1 ¼ d 3 , which will not be considered in detail here, the short-echo-train regime reduces to a previously described modification of the MAGSTE sequence [13]. If g 0 > 1, the first gradient pulse in the readout interval has the lower amplitude (Fig.…”

Section: Readmentioning

confidence: 91%

“…In the first, a third gradient pulse of inverted polarity is introduced which yields an increased diffusion-weighting efficiency [13]. Thereby, the assumption of identical delay times at the begin and end of each interval that is present in most non-imaging experiments, was retained.…”

Section: Introductionmentioning

confidence: 99%

“…In this work, the idea of using bipolar diffusion-weighting gradient pulses in MAGSTE sequences [13], so far considered and investigated only for identical delay times, is applied to generalized MAGSTE in order to achieve a further improvement of the diffusion-weighting efficiency for imaging experiments. The gradient pulse with the lower amplitude is replaced by a combination of two gradient pulses with full amplitude but opposite polarities.…”

Section: Introductionmentioning

confidence: 99%

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Generalized MAGSTE with bipolar diffusion-weighting gradient pulses

Finsterbusch

2009

Journal of Magnetic Resonance

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“…Furthermore, they are based on an extension of the stimulated-echo sequence where additional refocusing pulses are inserted in the DW period, which reduces the signal-to-noise ratio to some extent. Some of methods developed for cross-term compensation have already been used in vivo (25)(26)(27).…”

Section: Introductionmentioning

confidence: 99%

BOLD background gradient contributions in diffusion‐weighted fMRI—comparison of spin‐echo and twice‐refocused spin‐echo sequences

2010

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The interaction ('cross terms') between diffusion-weighting gradients and susceptibility-induced background gradient fields around vessels has an impact on apparent diffusion coefficient (ADC) measurements and diffusion-weighted functional magnetic resonance imaging (DFMRI) experiments. Monte-Carlo (MC) simulations numerically integrating the Bloch equations for a large number of random walks in a vascular model were used to investigate to what extent such interactions would influence the extravascular signal change as well as the ADC change observed in DFMRI experiments. The vascular model consists of a set of independent, randomly oriented, infinite cylinders whose internal magnetic susceptibility varies as the state changes between rest and activation. In such a network, the cross terms result in the observation of a functional increase in ADC accompanied by a descending percent signal change with increasing diffusion weighting. It is shown that the twice-refocused spin-echo sequence permits sufficient yet not total suppression of such effects compared to the standard Stejskal-Tanner spin-echo diffusion weighting under experimentally relevant conditions.

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Improved diffusion-weighting efficiency of pulsed gradient stimulated echo MR measurements with background gradient cross-term suppression

Cited by 6 publications

References 18 publications

Potential in reducing scan times of HARDI by accurate correction of the cross‐term in a hemispherical encoding scheme

Potential in reducing scan times of HARDI by accurate correction of the cross‐term in a hemispherical encoding scheme

Generalized MAGSTE with bipolar diffusion-weighting gradient pulses

BOLD background gradient contributions in diffusion‐weighted fMRI—comparison of spin‐echo and twice‐refocused spin‐echo sequences

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