Direct comparison of respiration-correlated four-dimensional magnetic resonance imaging (4DMRI) reconstructed based on concurrent internal navigator and external bellows

Publication date: Available online 9 November 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Guang Li, Jie Wei, Devin Olek, Mo Kadbi, Neelam Tyagi, Kristen Zakian, James Mechalakos, Joseph O. Deasy, Margie Hunt
PurposeTo compare the image quality of amplitude-binned four-dimensional magnetic resonance imaging (4DMRI) reconstructed using two concurrent respiratory (navigator and bellows) waveforms.Methods and MaterialsA prospective, respiratory-correlated 4DMRI scanning program was employed to acquire T2-weighted single-breath 4DMRI image using an internal navigator and external bellows. After 10-second training of a surrogate signal, 2D MRI image acquisition was triggered at a level (bin) and anatomic location (slice) until the bin-slice table was filled for 4DMRI reconstruction. The bellows signal was always collected, even when the navigator trigger was used, to retrospectively reconstruct a bellows-rebinned 4DMRI. Ten volunteers participated in this IRB-approved 4DMRI study and four scans were acquired for each subject, including coronal and sagittal scans triggered by either navigator or bellows, and six 4DMRI images (navigator-triggered, bellows-rebinned, and bellows-triggered) were reconstructed. The simultaneously acquired waveforms and resulting 4DMRI image quality were compared using signal correlation, bin/phase shift, and binning motion artifacts. The consecutive bellows-triggered 4DMRI was used for indirect comparison.ResultsCorrelation coefficients between navigator and bellows signals were found to be patient-specific and inhalation-/exhalation-dependent, ranging from 0.1 to 0.9, due to breathing irregularities (>50% scans) and commonly-observed bin/phase shifts (-1.1±0.6 bin) in both 1D waveforms and diaphragm motion extracted from 4D images. The navigator-triggered 4DMRI contains much fewer binning motion artifacts at the diaphragm than bellows-rebinned and bellows-triggered 4DMRI. Coronal scans are faster than sagittal scans due to fewer slices and higher achievable acceleration factors.ConclusionNavigator-triggered 4DMRI contains substantially fewer binning motion artifacts than bellows-rebinned and bellows-triggered 4DMRI, primarily due to the deviation of the external from the internal surrogate. This study compares two concurrent surrogates during the same 4DMRI scan and their resulting 4DMRI quality. The navigator-triggered 4DMRI scanning protocol is preferred to the bellows-based, especially the coronal scans, for clinical respiratory motion simulation.

Teaser

Summary: This study presents direct comparison of two concurrent respiratory surrogates: internal navigator and external bellows, and their corresponding 4DMRI image quality. Sixty 4DMRI images in ten volunteers were reconstructed and compared. We found that phase shift is common in the concurrent 1D waveforms and motions extracted from 4DMRI images. Navigator-triggered 4DMRI image quality is far superior. This study provides better understanding of external-internal motion relationship, as well as potential use of 4DMRI in replacing 4DCT.


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