Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 81, Issue 6, Pages 3745-3753Publisher
WILEY
DOI: 10.1002/mrm.27664
Keywords
7T MRI; breathing-induced field fluctuations; multi-shot EPI; spinal cord imaging; T2*mapping
Funding
- H2020 Marie Sklodowska-Curie Actions [659263]
- Wellcome Trust [102645/Z/13/Z, 202788/Z/16/Z]
- Wellcome Centre for Integrative Neuroimaging [203139/Z/16/Z]
- Wellcome Trust [202788/Z/16/Z] Funding Source: Wellcome Trust
- EPSRC [EP/J005444/1] Funding Source: UKRI
- Marie Curie Actions (MSCA) [659263] Funding Source: Marie Curie Actions (MSCA)
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Purpose: Spinal cord MRI at ultrahigh field is hampered by time-varying magnetic fields associated with the breathing cycle, giving rise to ghosting artifacts in multi-shot acquisitions. Here, we suggest a correction approach based on linking the signal from a respiratory bellows to field changes inside the spinal cord. The information is used to correct the data at the image reconstruction level. Methods: The correction was demonstrated in the context of multi-shot T2*-weighted imaging of the cervical spinal cord at 7T. A respiratory trace was acquired during a high-resolution multi-echo gradient-echo sequence, used for structural imaging and quantitative T2* mapping, and a multi-shot EPI time series, as would be suitable for fMRI. The coupling between the trace and the breathing-induced fields was determined by a short calibration scan in each individual. Images were reconstructed with and without trace-based correction. Results: In the multi-echo acquisition, breathing-induced fields caused severe ghosting in images with long TE, which led to a systematic underestimation of T2* in the spinal cord. The trace-based correction reduced the ghosting and increased the estimated T2* values. Breathing-related ghosting was also observed in the multi-shot EPI images. The correction largely removed the ghosting, thereby improving the temporal signal-to-noise ratio of the time series. Conclusions: Trace-based retrospective correction of breathing-induced field variations can reduce ghosting and improve quantitative metrics in multi-shot structural and functional T2*-weighted imaging of the spinal cord. The method is straightforward to implement and does not rely on sequence modifications or additional hardware beyond a respiratory bellows.
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