inhomogeneity mitigation in CEST using parallel transmission

Tse, Desmond H. Y.; Silva, Nuno da; Poser, Benedikt A.; Shah, N. Jon

doi:10.1002/mrm.26624

Cited by 20 publications

(22 citation statements)

References 58 publications

(92 reference statements)

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“…The proposed method reduces the

B_{1}^{+}

influence on the CEST effect through the application of 2 interleaved pTx modes during the saturation period. Unlike previous work by Tse et al, which applied pTx to CEST imaging, MIMOSA does not require additional optimization steps. In comparison to

B_{1}^{+}

correction methods that require 2 or more CEST acquisitions with different B 1 values, MIMOSA requires just a single measurement to obtain comparable homogeneity for rNOE measurements.…”

Section: Discussionmentioning

confidence: 99%

“…However, there are also challenges at UHF because the inhomogeneity of the main magnetic field (B 0 ) and the transmit field (

B_{1}^{+}

) increase . Thus, quantitative CEST measurements at UHF usually require correction or mitigation of B 0 and

B_{1}^{+}

inhomogeneity effects. For example, the local effective

B_{1}^{+}

value influences the magnitude of CEST contrast .…”

Section: Introductionmentioning

confidence: 99%

“…In addition to a modulation of the amplitudes and phases, different RF pulse profiles can be applied for each coil element (transmit SENSE) . The transmit SENSE approach recently has also been applied to optimize the saturation pulse train in CEST MRI and thus to mitigate

B_{1}^{+}

inhomogeneity effects. However, this approach usually requires optimization of the saturation pulses for each individual patient, which complicates translation into clinical studies.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Multiple interleaved mode saturation (MIMOSA) for B₁⁺ inhomogeneity mitigation in chemical exchange saturation transfer

Liebert

Zaiß

Gumbrecht

et al. 2019

Magnetic Resonance in Med

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Purpose To mitigate B1+ inhomogeneity in quantitative CEST MRI at ultra‐high magnetic field strengths (B0 ≥ 7 Tesla) using a parallel transmit system. Methods Multiple interleaved mode saturation employs interleaving of 2 complementary phase sets during the saturation pulse train. Phase differences of 45° (first mode) and 90° (second mode) between 2 adjacent transmitter coil channels are used. The influence of the new saturation scheme on the CEST contrast was analyzed using Bloch‐McConnell simulations. The presented method was verified in phantom and in vivo measurements of the healthy human brain. The relayed nuclear Overhauser effect was evaluated, and the inverse magnetic transfer ratio metric was calculated. Results were compared to a published B1+ correction method. All measurements were conducted on a whole‐body 7 Tesla MRI system using an 8 transmitter and 32 receiver channel head coil. Results Simulations showed that the inverse magnetic transfer ratio metric contrast of relayed nuclear Overhauser effect shows a smaller dependency on the relative amplitudes of the 2 different modes than the contrasts of Cr and amide proton transfer. Measurements of an egg white phantom showed markedly improved homogeneity compared to the uncorrected inverse magnetic transfer ratio metric (relayed nuclear Overhauser effect) images and slightly improved results compared to B1+ corrected images. In vivo multiple interleaved mode saturation images showed similar contrast compared to B1+ corrected images. Conclusion Multiple interleaved mode saturation can be used as a simple method to mitigate B1+ inhomogeneity effects in CEST MRI at ultra‐high magnetic field strengths. Compared to previous B1+ correction methods, acquisition time can be reduced because an additional scan, usually required for B1+ correction, can be omitted.

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“…The proposed method reduces the

B_{1}^{+}

B_{1}^{+}

correction methods that require 2 or more CEST acquisitions with different B 1 values, MIMOSA requires just a single measurement to obtain comparable homogeneity for rNOE measurements.…”

Section: Discussionmentioning

confidence: 99%

“…However, there are also challenges at UHF because the inhomogeneity of the main magnetic field (B 0 ) and the transmit field (

B_{1}^{+}

) increase . Thus, quantitative CEST measurements at UHF usually require correction or mitigation of B 0 and

B_{1}^{+}

inhomogeneity effects. For example, the local effective

B_{1}^{+}

value influences the magnitude of CEST contrast .…”

Section: Introductionmentioning

confidence: 99%

B_{1}^{+}

inhomogeneity effects. However, this approach usually requires optimization of the saturation pulses for each individual patient, which complicates translation into clinical studies.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Multiple interleaved mode saturation (MIMOSA) for B₁⁺ inhomogeneity mitigation in chemical exchange saturation transfer

Liebert

Zaiß

Gumbrecht

et al. 2019

Magnetic Resonance in Med

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show abstract

“…Moreover, parallel transmit excitation (pTx) or active

B_{1}

shimming may improve the accurate CEST quantification for whole‐brain acquisitions and reducing the number of

B_{1}

sampling points. Tse et al recently introduced a CEST approach applying pTx that significantly reduces the contrast variation related to

B_{1}

inhomogeneity. Alternatively, it may be possible to combine the snapshot‐EPI approach with the multiple interleaved mode saturation (MIMOSA) method of Liebert et al to mitigate the

B_{1}

dependency.…”

Section: Discussionmentioning

confidence: 99%

Whole‐brain snapshot CEST imaging at 7 T using 3D‐EPI

Akbey

Ehses

Stirnberg

et al. 2019

Magnetic Resonance in Med

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Purpose: The aim of this work is to develop a fast and robust CEST sequence in order to allow the acquisition of a whole-brain imaging volume after a single preparation block (snapshot acquisition). Methods: A 3D-CEST sequence with an optimized 3D-EPI readout module was developed, which acquires the complete k-space data following a single CEST preparation for 1 saturation offset. Whole-brain mapping of the Z-spectrum with 2 mm isotropic resolution is achieved at 68 saturation frequencies in 5 minutes (4.33 s per offset). We analyzed the B 1 distribution in order to optimize B 1 correction and to provide accurate CEST quantification across the whole brain. Results: We obtained maps for 3 different CEST contrasts from 4 healthy subjects.Based on our B 1 distribution analysis, we conclude that 3 B 1 sampling points allow for sufficient compensation of B 1 variations across most of the brain. Two brain regions, the cerebellum and the temporal lobes, are difficult to quantify at 7 T due to very low B 1 that was achieved in these regions. Conclusions:The proposed sequence enables robust acquisition of 2 mm isotropic whole-brain CEST maps at 7 Tesla within a total scan time of 16 minutes. K E Y W O R D SAPT, B 1 -correction, CEST, chemical exchange saturation transfer, 3D-EPI, rNOE, UHF, whole brain F I G U R E 1 Schematic sequence diagram of the 3D-CEST sequence. CEST saturation (shaded area, t sat = 3.6 s) is followed by a centricreordered 3D-EPI readout with binominal water excitation (t readout = 734 ms). The GRAPPA autocalibration scan and the external 3-readout phase correction scan (ePC) are acquired at the beginning of the measurement before the irradiation offset loop (δω)

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“…Both are potentially quantitative, but at high fields their implementation has been severely limited to date by high SAR and sensitivity to both and B0 inhomogeneities that make true quantification harder. Such methods will also strongly benefit from a better integration of pTX technology (Tse et al, 2017).…”

Section: Future Perspectivesmentioning

confidence: 99%

How to choose the right MR sequence for your research question at 7 T and above?

Marques

Norris

2018

NeuroImage

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inhomogeneity mitigation in CEST using parallel transmission

Abstract: A pTx-based pulsed CEST presaturation scheme is proposed and validated by simulations and 7T in vivo imaging. Magn Reson Med 78:2216-2225, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Cited by 20 publications

References 58 publications

Multiple interleaved mode saturation (MIMOSA) for B₁⁺ inhomogeneity mitigation in chemical exchange saturation transfer

Multiple interleaved mode saturation (MIMOSA) for B₁⁺ inhomogeneity mitigation in chemical exchange saturation transfer

Whole‐brain snapshot CEST imaging at 7 T using 3D‐EPI

How to choose the right MR sequence for your research question at 7 T and above?

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inhomogeneity mitigation in CEST using parallel transmission

Abstract: A pTx-based pulsed CEST presaturation scheme is proposed and validated by simulations and 7T in vivo imaging. Magn Reson Med 78:2216-2225, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Cited by 20 publications

References 58 publications

Multiple interleaved mode saturation (MIMOSA) for B1+ inhomogeneity mitigation in chemical exchange saturation transfer

Multiple interleaved mode saturation (MIMOSA) for B1+ inhomogeneity mitigation in chemical exchange saturation transfer

Whole‐brain snapshot CEST imaging at 7 T using 3D‐EPI

How to choose the right MR sequence for your research question at 7 T and above?

Contact Info

Product

Resources

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Multiple interleaved mode saturation (MIMOSA) for B₁⁺ inhomogeneity mitigation in chemical exchange saturation transfer

Multiple interleaved mode saturation (MIMOSA) for B₁⁺ inhomogeneity mitigation in chemical exchange saturation transfer