O-space imaging: Highly efficient parallel imaging using second-order nonlinear fields as encoding gradients with no phase encoding

• Published in: Magnetic resonance in medicine Vol. 64; no. 2; pp. 447 - 456
• Main Authors: Stockmann, Jason P., Ciris, Pelin Aksit, Galiana, Gigi, Tam, Leo, Constable, R. Todd
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.08.2010; Wiley Subscription Services, Inc
• Subjects: Algorithms; Aliasing; Brain - anatomy & histology; dynamic shimming; Electromagnetic Fields; Humans; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Image processing; Image reconstruction; Imaging techniques; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Nonlinear Dynamics; nonlinear gradient encoding; O-space; parallel imaging; Phantoms, Imaging; projection imaging; Redesign; Sensitivity and Specificity; Signal Processing, Computer-Assisted; Spatial data; Spherical harmonics; parallel imaging; dynamic shimming; projection imaging; nonlinear gradient encoding; O-Space
• ISSN: 0740-3194; 1522-2594; 1522-2594
• DOI: 10.1002/mrm.22425

Recent improvements in parallel imaging have been driven by the use of greater numbers of independent surface coils placed so as to minimize aliasing along the phase‐encode direction(s). However, gains from increasing the number of coils diminish as coil coupling problems begin to dominate and the ratio of acceleration gain to expense for multiple receiver chains becomes prohibitive. In this work, we redesign the spatial‐encoding strategy in order to gain efficiency, achieving a gradient encoding scheme that is complementary to the spatial encoding provided by the receiver coils. This approach leads to “O‐space” imaging, wherein the gradient shapes are tailored to an existing surface coil array, making more efficient use of the spatial information contained in the coil profiles. In its simplest form, for each acquired echo the Z2 spherical harmonic is used to project the object onto sets of concentric rings, while the X and Y gradients are used to offset this projection within the imaging plane. The theory is presented, an algorithm is introduced for image reconstruction, and simulations reveal that O‐space encoding achieves high encoding efficiency compared to sensitivity encoding (SENSE) radial k‐space trajectories, and parallel imaging technique with localized gradients (PatLoc), suggesting that O‐space imaging holds great potential for accelerated scanning. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.