Abstract
ObjectTo develop a novel approach for highly accelerated Magnetic Resonance Fingerprinting (MRF) acquisition.Materials and methodsThe proposed method combines parallel imaging, soft-gating and key-hole approaches to highly accelerate MRF acquisition. Slowly varying flip angles (FA), commonly used during MRF acquisition, lead to a smooth change in the signal contrast of consecutive time-point images. This assumption enables sharing of high frequency data between different time-points, similar to what is done in some dynamic MR imaging methods such as key-hole. The proposed approach exploits this information using a SOft-weighted key-HOle (MRF-SOHO) reconstruction to achieve high acceleration factors and/or increased resolution without compromising image quality or increasing scan time. MRF-SOHO was validated on a standard T1/T2 phantom and in in-vivo brain acquisitions reconstructing T1, T2 and proton density parametric maps.ResultsAccelerated MRF-SOHO using less data per time-point and less time-point images enabled a considerable reduction in scan time (up to 4.6x), while obtaining similar T1 and T2 accuracy and precision when compared to zero-filled MRF reconstruction. For the same number of spokes and time-points, the proposed method yielded an enhanced performance in quantifying parameters than the zero-filled MRF reconstruction, which was verified with 2, 1 and 0.7 (sub-millimetre) resolutions.ConclusionThe proposed MRF-SOHO enabled a 4.6x scan time reduction for an in-plane spatial resolution of 2x2 mm2 when compared to zero-filled MRF and enabled sub-millimetric (0.7x0.7 mm2) resolution MRF.
Highlights
Quantitative Magnetic Resonance Imaging (MRI) techniques, such as T1, T2 and proton density (M0) parametric maps, have been developed to enable direct objective comparison and characterization of diseased and healthy tissue [1,2,3,4,5,6]
Magnetic Resonance Fingerprinting (MRF)-SOHO was validated on a standard T1/T2 phantom and in in-vivo brain acquisitions reconstructing T1, T2 and proton density parametric maps
Accelerated MRF-SOHO using less data per time-point and less time-point images enabled a considerable reduction in scan time, while obtaining similar T1 and T2 accuracy and precision when compared to zero-filled MRF reconstruction
Summary
Quantitative Magnetic Resonance Imaging (MRI) techniques, such as T1, T2 and proton density (M0) parametric maps, have been developed to enable direct objective comparison and characterization of diseased and healthy tissue [1,2,3,4,5,6]. Magnetic Resonance Fingerprinting (MRF) [7] has been recently introduced to retrieve multiple and simultaneous parametric maps from a single acquisition under the assumption that unique signal evolutions or “fingerprints” can be generated from different tissues. This is achieved using a variable encoding and acquisition scheme that typically varies flip angles (FA) and repetition times (TR) throughout the scan. Multiple parameters are reconstructed in MRF via pixel-wise template matching of a measured signal (series of time-point images) to a previously generated dictionary of signals. The low quality of the highly undersampled time-point images can introduce bias in the parametric values if the template matching based MRF reconstruction fails to distinguish between signal and noise or undersampling artefacts [9]
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