Combined MR data acquisition of multicontrast images using variable acquisition parameters and K -space data sharing

Abstract

Abstract-A new technique to reduce clinical magnetic resonance imaging (MRI) scan time by varying acquisition parameters and sharing -space data between images, is proposed. To improve data utilization, acquisition of multiple images of different contrast is combined into a single scan, with variable acquisition parameters including repetition time (TR), echo time (TE), and echo train length (ETL). This approach is thus referred to as a "combo acquisition." As a proof of concept, simulations of MRI experiments using spin echo (SE) and fast SE (FSE) sequences were performed based on Bloch equations. Predicted scan time reductions of 25%-50% were achieved for 2-contrast and 3-contrast combo acquisitions. Artifacts caused by nonuniform -space data weighting were suppressed through semi-empirical optimization of parameter variation schemes and the phase encoding order. Optimization was assessed by minimizing three quantitative criteria: energy of the "residue point spread function (PSF)," energy of "residue profiles" across sharp tissue boundaries, and energy of "residue images." In addition, results were further evaluated by quantitatively analyzing the preservation of contrast, the PSF, and the signal-to-noise ratio. Finally, conspicuity of lesions was investigated for combo acquisitions in comparison with standard scans. Implications and challenges for the practical use of combo acquisitions are discussed.Index Terms-Combined/combo acquisition, -space data sharing, MRI, scan time reduction, variable acquisition parameter.

Combo acquisitions: Balancing scan time reduction and image quality

“…Each criterion essentially measures the energy of the difference of an image characteristic, such as the PSF, in images acquired with combo and standard acquisitions. For instance, the E(PSF res ) was defined as (assuming that the PE direction is along the y ‐axis) where N contrast is the number of different contrasts in a multicontrast acquisition, N tissues is the number of tissues used in phantom data, and w ij PSF are the weighting factors that depend on the respective diagnostic importance of a contrast and on the signal level from the corresponding standard acquisition of a tissue for each contrast (1). In general, optimization of a combo acquisition was achieved by minimizing all three quantitative criteria, since minimization of these criteria corresponded to a reduction of artifacts.…”

“…Spoiler gradients were inserted to dephase any unwanted or remnant transverse magnetization. As a starting point for the implementation of each protocol, its design from the simulation studies in Ref 1. was used.…”

“…Recently the “combo acquisition” approach was proposed to reduce MRI scan time and improve data utilization in a clinical setting (1). This technique combines the acquisition of images of different contrasts into a single acquisition, using variable acquisition parameters and k‐space data sharing.…”

“…In addition, the method can be implemented on most commercially available scanners, including those already in clinical use. For a more complete list of other approaches for reducing scan time, the reader is referred to Ref 1…”

“…The design and optimization of combo acquisition protocols was previously described in great detail (1). As a proof of concept, simulations of MRI experiments using SE (19) and TSE (FSE or RARE (20)) sequences were performed based on Bloch equations and the use of a realistic brain phantom model (21).…”