Estimating absolute‐phase maps using ESPIRiT and virtual conjugate coils. Issue 3 (11th March 2016)

• Record Type: Journal Article
• Authors: Uecker, Martin; Lustig, Michael
• Is Part Of: Magnetic resonance in medicine. Volume 77:Issue 3(2017)
• Page Start: 1201
• Page End: 1207
• Publication Date: 2016-03-11
• Subjects: parallel imaging -- partial Fourier -- ESPIRiT -- virtual coil; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.26191
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: To develop an ESPIRiT‐based method to estimate coil sensitivities with image phase as a building block for efficient and robust image reconstruction with phase constraints. Theory and Methods: ESPIRiT is a new framework for calibration of the coil sensitivities and reconstruction in parallel magnetic resonance imaging. Applying ESPIRiT to a combined set of physical and virtual conjugate coils (VCC‐ESPIRiT) implicitly exploits conjugate symmetry in k‐space similar to VCC‐GRAPPA. Based on this method, a new post‐processing step is proposed for the explicit computation of coil sensitivities that include the absolute phase of the image. The accuracy of the computed maps is directly validated using a test based on projection onto fully sampled coil images and also indirectly in phase‐constrained parallel‐imaging reconstructions. Results: The proposed method can estimate accurate sensitivities which include low‐resolution image phase. In case of high‐frequency phase variations VCC‐ESPIRiT yields an additional set of maps that indicates the existence of a high‐frequency phase component. Taking this additional set of maps into account can improve the robustness of phase‐constrained parallel imaging. Conclusion: The extended VCC‐ESPIRiT is a useful tool for phase‐constrained imaging. Magn Reson Med 77:1201–1207, 2017. © 2016 International Society for Magnetic Resonance in Medicine