Multiple‐modulation‐multiple‐echo magnetic resonance

Sigmund, Eric E.; Cho, HyungJoon; Song, Yi‐Qiao

doi:10.1002/cmr.a.20097

Cited by 10 publications

(15 citation statements)

References 69 publications

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“…the effects of spin relaxation ( T 1 , T 2 ), RF‐flip angles α i and flip‐angle inhomogeneities, can be normalized out:

\begin{matrix} \frac{M_{Q}}{M_{Q, 0}} = \frac{A_{Q} \cdot B_{Q} \cdot C_{Q}}{A_{Q} \cdot B_{Q} \cdot C_{Q, 0}} = \frac{C_{Q}}{C_{Q, 0}} \\ = \exp (- \sum_{mn} (b_{mn, Q} - b_{mn, Q, 0}) D_{italicmn}) \end{matrix}

The RF pulse flip angles α i are chosen to minimize variations of the product of the magnetization fraction A Q and the relaxation weighting B Q between the coherence pathways. That is, optimal RF‐flip angles maximally equalize the analytical expressions of A Q × B Q for all retained echoes, in contrast to earlier work, which did not consider the relaxation weighting B Q in the flip‐angle optimization . For the five RF pulse sequence (Fig.…”

Section: Theorymentioning

confidence: 95%

“…In this article, we will use the coherence pathway formalism , an alternative but formally equivalent notation to the echo pathway description , to calculate the echo times, relaxation and diffusion weighting of each echo in the sequence. In short, the amplitude of each echo in the sequence can be expressed as a product of the total magnetization M 0 with three factors:

M_{Q} = M_{0} \cdot A_{Q} \cdot B_{Q} \cdot C_{Q}

each a function of the coherence pathway Q leading to the echo.…”

Section: Theorymentioning

confidence: 99%

“…The magnetization fraction remaining after relaxation effects A Q × B Q (Equation ): T 1 = 1400ms, T 2 = 50ms of each echo of the previous version and the new variation (with five RF pulses, Figure a) of the MEDITATE sequence, using typical timing schemes. By utilizing longitudinal magnetization storage, more magnetization is retained in the latter echoes of the MEDITATE variation presented in this work.…”

Section: Theorymentioning

confidence: 99%

“…1a: human muscle T 1 = 1420 ms, T 2 = 32 ms at 3T (27)) the optimal angles are calculated to be 61°À73°À100°À45°À90°. In previous work on the MEDITATE diffusion sequence (16,25,26), it was shown that the full apparent diffusion tensor can be estimated in two shots in a spectroscopic approach (26). However, the lower gradient strengths available on clinical scanners require longer timing τ i to achieve the same diffusion weighting.…”

Section: Coherence Pathway Formalismmentioning

confidence: 99%

“…In this article, we will describe the adaptation of the original MEDITATE method (25,16,26) to the current method ( Fig. 1a).…”

Section: Introductionmentioning

confidence: 99%

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Multiple‐echo diffusion tensor acquisition technique (MEDITATE) on a 3T clinical scanner

2013

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This paper describes the concepts and implementation of an MRI method, Multiple Echo Diffusion Tensor Acquisition Technique (MEDITATE), which is capable of acquiring apparent diffusion tensor maps in two scans on a 3T clinical scanner. In each MEDITATE scan, a set of RF-pulses generates multiple echoes whose amplitudes are diffusion-weighted in both magnitude and direction by a pattern of diffusion gradients. As a result, two scans acquired with different diffusion weighting strengths suffice for accurate estimation of diffusion tensor imaging (DTI)-parameters. The MEDITATE variation presented here expands previous MEDITATE approaches to adapt to the clinical scanner platform, such as exploiting longitudinal magnetization storage to reduce T2-weighting. Fully segmented multi-shot Cartesian encoding is used for image encoding. MEDITATE was tested on isotropic (agar gel), anisotropic diffusion phantoms (asparagus), and in vivo skeletal muscle in healthy volunteers with cardiac-gating. Comparisons of accuracy were performed with standard twice-refocused spin echo (TRSE) DTI in each case and good quantitative agreement was found between diffusion eigenvalues, mean diffusivity, and fractional anisotropy derived from TRSE-DTI and from the MEDITATE sequence. Orientation patterns were correctly reproduced in both isotropic and anisotropic phantoms, and approximately so for in vivo imaging. This illustrates that the MEDITATE method of compressed diffusion encoding is feasible on the clinical scanner platform. With future development and employment of appropriate view-sharing image encoding this technique may be used in clinical applications requiring time-sensitive acquisition of DTI parameters such as dynamical DTI in muscle.

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“…the effects of spin relaxation ( T 1 , T 2 ), RF‐flip angles α i and flip‐angle inhomogeneities, can be normalized out:

\begin{matrix} \frac{M_{Q}}{M_{Q, 0}} = \frac{A_{Q} \cdot B_{Q} \cdot C_{Q}}{A_{Q} \cdot B_{Q} \cdot C_{Q, 0}} = \frac{C_{Q}}{C_{Q, 0}} \\ = \exp (- \sum_{mn} (b_{mn, Q} - b_{mn, Q, 0}) D_{italicmn}) \end{matrix}

Section: Theorymentioning

confidence: 95%

M_{Q} = M_{0} \cdot A_{Q} \cdot B_{Q} \cdot C_{Q}

each a function of the coherence pathway Q leading to the echo.…”

Section: Theorymentioning

confidence: 99%

Section: Theorymentioning

confidence: 99%

Section: Coherence Pathway Formalismmentioning

confidence: 99%

“…In this article, we will describe the adaptation of the original MEDITATE method (25,16,26) to the current method ( Fig. 1a).…”

Section: Introductionmentioning

confidence: 99%

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Multiple‐echo diffusion tensor acquisition technique (MEDITATE) on a 3T clinical scanner

2013

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Accelerated radial diffusion spectrum imaging using a multi‐echo stimulated echo diffusion sequence

Baete

Boada

2017

Magnetic Resonance in Med

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Purpose: Diffusion spectrum imaging (DSI) provides us noninvasively and robustly with anatomical details of brain microstructure. To achieve sufficient angular resolution, DSI requires a large number of q-space samples, leading to long acquisition times. This need is mitigated here by combining the beneficial properties of Radial q-space sampling for DSI with a Multi-Echo Stimulated Echo Sequence (MESTIM). Methods: Full 2D k-spaces for each of several q-space samples, along the same radially outward line in q-space, are acquired in one readout train with one spin and three stimulated echoes. RF flip angles are carefully chosen to distribute spin magnetization over the echoes and the DSI reconstruction is adapted to account for differences in diffusion time among echoes. Results: Individual datasets and bootstrapped reproducibility analysis demonstrate image quality and SNR of the morethan-twofold-accelerated RDSI MESTIM sequence. Orientation distribution functions (ODF) and tractography results benefit from the longer diffusion times of the latter echoes in the echo train. Conclusion: A MESTIM sequence can be used to shorten RDSI acquisition times significantly without loss of image or ODF quality. Further acceleration is possible by combination with simultaneous multi-slice techniques. Magn Reson Med 79:306-316,

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Dynamic diffusion-tensor measurements in muscle tissue using the single-line multiple-echo diffusion-tensor acquisition technique at 3T

2015

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When diffusion biomarkers display transient changes, i.e. in muscle following exercise, traditional diffusion tensor imaging (DTI) methods lack temporal resolution to resolve the dynamics. This paper presents an MRI method for dynamic diffusion tensor acquisitions on a clinical 3T scanner. This method, SL-MEDITATE (Single Line Multiple Echo Diffusion Tensor Acquisition Technique) achieves a high temporal resolution (4s) (1) by rapid diffusion encoding through the acquisition of multiple echoes with unique diffusion sensitization and (2) by limiting the readout to a single line volume. The method is demonstrated in a rotating anisotropic phantom, in a flow phantom with adjustable flow speed, and in in vivo skeletal calf muscle of healthy volunteers following a plantar flexion exercise. The rotating and flow-varying phantom experiments show that SL-MEDITATE correctly identifies the rotation of the first diffusion eigenvector and the changes in diffusion tensor parameter magnitudes, respectively. Immediately following exercise, the in vivo mean diffusivity (MD) time-courses show, before the well-known increase, an initial decrease which is not typically observed in traditional DTI. In conclusion, SL-MEDITATE can be used to capture transient changes in tissue anisotropy in a single line. Future progress might allow for dynamic DTI when combined with appropriate k-space trajectories and compressed sensing reconstruction.

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Multiple‐modulation‐multiple‐echo magnetic resonance

Cited by 10 publications

References 69 publications

Multiple‐echo diffusion tensor acquisition technique (MEDITATE) on a 3T clinical scanner

Multiple‐echo diffusion tensor acquisition technique (MEDITATE) on a 3T clinical scanner

Accelerated radial diffusion spectrum imaging using a multi‐echo stimulated echo diffusion sequence

Dynamic diffusion-tensor measurements in muscle tissue using the single-line multiple-echo diffusion-tensor acquisition technique at 3T

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