Abstract
To overcome long acquisition times of Chemical Shift Imaging (CSI), a new Magnetic Resonance Spectroscopic Imaging (MRSI) technique called Reduction of Acquisition time by Partition of the sIgnal Decay in Spectroscopic Imaging (RAPID-SI) using blipped phase encoding gradients inserted during signal acquisition was developed. To validate the results using RAPID-SI and to demonstrate its usefulness in terms of acquisition time and data quantification; simulations, phantom and in vivo studies were conducted, and the results were compared to standard CSI. The method was based upon the partition of a magnetic resonance spectroscopy (MRS) signal into sequential sub-signals encoded using blipped phase encoding gradients inserted during signal acquisition at a constant time interval. The RAPID-SI technique was implemented on a clinical 3 T Siemens scanner to demonstrate its clinical utility. Acceleration of data collection was performed by inserting R (R = acceleration factor) blipped gradients along a given spatial direction during data acquisition. Compared to CSI, RAPID-SI reduced acquisition time by the acceleration factor R. For example, a 2D 16x16 data set acquired in about 17 min with CSI, was reduced to approximately 2 min with the RAPID-SI (R = 8). While the SNR of the acquired RAPID-SI signal was lower compared to CSI by approximately the factor √R, it can be improved after data pre-processing and reconstruction. Compared to CSI, RAPID-SI reduces acquisition time, while preserving metabolites information. Furthermore, the method is flexible and could be combined with other acceleration methods such as Parallel Imaging.
Highlights
IntroductionChemical Shift Imaging (CSI) [1], a technique currently available as a clinical imaging tool, is used to provide tissue metabolite maps in vivo to help characterize neurological and metabolic disease, and improve tumour treatment [2,3]
Chemical Shift Imaging (CSI) [1], a technique currently available as a clinical imaging tool, is used to provide tissue metabolite maps in vivo to help characterize neurological and metabolic disease, and improve tumour treatment [2,3].CSI suffers from the time cost in obtaining these metabolite maps, and its impact on the spatial resolution and Signal to Noise Ratio (SNR) [2,3]
The effect of field inhomogeneity was insignificant on the accuracy of the data quantification when the level of field inhomogeneity (e.g: difference in full width at half maximum (FWHM) of the metabolite peaks from one voxel to another) is around 8 Hz (ΔB0 map B4)
Summary
Chemical Shift Imaging (CSI) [1], a technique currently available as a clinical imaging tool, is used to provide tissue metabolite maps in vivo to help characterize neurological and metabolic disease, and improve tumour treatment [2,3]. CSI suffers from the time cost in obtaining these metabolite maps, and its impact on the spatial resolution and Signal to Noise Ratio (SNR) [2,3]. To overcome this problem and expand its clinical use, significant effort has been made to promote high-resolution Magnetic.
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