Dataset Information

Phase relaxed localized excitation pulses for inner volume fast spin echo imaging.

ABSTRACT:

Purpose

To design multidimensional spatially selective radiofrequency (RF) pulses for inner volume imaging (IVI) with three-dimensional (3D) fast spin echo (FSE) sequences. Enhanced background suppression is achieved by exploiting particular signal properties of FSE sequences.

Theory and methods

The CPMG condition dictates that echo amplitudes will rapidly decrease if a 90° phase difference between excitation and refocusing pulses is not present, and refocusing flip angles are not precisely 180°. This mechanism is proposed as a means for generating additional background suppression for spatially selective excitation, by biasing residual excitation errors toward violating the CPMG condition. 3D RF pulses were designed using this method with a 3D spherical spiral trajectory, under-sampled by factor 5.6 for an eight-channel PTx system, at 3 Tesla.

Results

3D-FSE IVI with pulse durations of approximately 12 ms was demonstrated in phantoms and for T2 -weighted brain imaging in vivo. Good image quality was obtained, with mean background suppression factors of 103 and 82 ± 6 in phantoms and in vivo, respectively.

Conclusion

Inner Volume Imaging with 3D-FSE has been demonstrated in vivo with tailored 3D-RF pulses. The proposed design methods are also applicable to 2D pulses. Magn Reson Med 76:848-861, 2016. © 2015 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

SUBMITTER: Malik SJ

PROVIDER: S-EPMC4988531 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Publications

Phase relaxed localized excitation pulses for inner volume fast spin echo imaging.

Malik Shaihan J SJ Hajnal Joseph V JV

Magnetic resonance in medicine 20151009 3

<h4>Purpose</h4>To design multidimensional spatially selective radiofrequency (RF) pulses for inner volume imaging (IVI) with three-dimensional (3D) fast spin echo (FSE) sequences. Enhanced background suppression is achieved by exploiting particular signal properties of FSE sequences.<h4>Theory and methods</h4>The CPMG condition dictates that echo amplitudes will rapidly decrease if a 90° phase difference between excitation and refocusing pulses is not present, and refocusing flip angles are not ...[more]

PMID: 26451691

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Project description:PurposeSpin-echo functional MRI (SE-fMRI) has the potential to improve spatial specificity when compared with gradient-echo fMRI. However, high spatiotemporal resolution SE-fMRI with large slice-coverage is challenging as SE-fMRI requires a long echo time to generate blood oxygenation level-dependent (BOLD) contrast, leading to long repetition times. The aim of this work is to develop an acquisition method that enhances the slice-coverage of SE-fMRI at high spatiotemporal resolution.Theory and methodsAn acquisition scheme was developed entitled multisection excitation by simultaneous spin-echo interleaving (MESSI) with complex-encoded generalized slice dithered enhanced resolution (cgSlider). MESSI uses the dead-time during the long echo time by interleaving the excitation and readout of 2 slices to enable 2× slice-acceleration, while cgSlider uses the stable temporal background phase in SE-fMRI to encode/decode 2 adjacent slices simultaneously with a "phase-constrained" reconstruction method. The proposed cgSlider-MESSI was also combined with simultaneous multislice (SMS) to achieve further slice-acceleration. This combined approach was used to achieve 1.5-mm isotropic whole-brain SE-fMRI with a temporal resolution of 1.5 s and was evaluated using sensory stimulation and breath-hold tasks at 3T.ResultsCompared with conventional SE-SMS, cgSlider-MESSI-SMS provides 4-fold increase in slice-coverage for the same repetition time, with comparable temporal signal-to-noise ratio. Corresponding fMRI activation from cgSlider-MESSI-SMS for both fMRI tasks were consistent with those from conventional SE-SMS. Overall, cgSlider-MESSI-SMS achieved a 32× encoding-acceleration by combining Rinplane × MB × cgSlider × MESSI = 4 × 2 × 2 × 2.ConclusionHigh-quality, high-resolution whole-brain SE-fMRI was acquired at a short repetition time using cgSlider-MESSI-SMS. This method should be beneficial for high spatiotemporal resolution SE-fMRI studies requiring whole-brain coverage.

Dataset Information

Phase relaxed localized excitation pulses for inner volume fast spin echo imaging.

Purpose

Theory and methods

Results

Conclusion

Publications

Phase relaxed localized excitation pulses for inner volume fast spin echo imaging.

Similar Datasets

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