Development of a compact NMR system to measure pO in a tissue-engineered graft.

Cellular macroencapsulation devices, known as tissue engineered grafts (TEGs), enable the transplantation of allogeneic cells without the need for life-long systemic immunosuppression. Islet containing TEGs offer promise as a potential functional cure for type 1 diabetes. Previous research has indicated sustained functionality of implanted islets at high density in a TEG requires external supplementary oxygen delivery and an effective tool to monitor TEG oxygen levels.

Fast spin-echo approach for accelerated B gradient-based MRI.

Purpose: To expand on the previously developed -encoding technique, frequency-modulated Rabi-encoded echoes (FREE), to perform accelerated image acquisition by collecting multiple lines of k-space in an echo train.

Methods: FREE uses adiabatic full-passage pulses and a spatially varying RF field to encode unique spatial information without the use of traditional B gradients. The original implementation relied on acquiring single lines of k-space, leading to long acquisitions.

Correcting image distortions from a nonlinear -gradient field in frequency-modulated Rabi-encoded echoes.

Purpose: To correct image distortions that result from nonlinear spatial variation in the transmit RF field amplitude ( ) when performing spatial encoding with the method called frequency-modulated Rabi encoded echoes (FREE).

Theory And Methods: An algorithm developed to correct image distortion resulting from the use of nonlinear static field (B ) gradients in standard MRI is adapted herein to correct image distortion arising from a nonlinear -gradient field in FREE. From a -map, the algorithm performs linear interpolation and intensity scaling to correct the image.

B -gradient-based MRI using frequency-modulated Rabi-encoded echoes.

Purpose: Reduce expense and increase accessibility of MRI by eliminating pulsed field (B ) gradient hardware.

Methods: A radiofrequency imaging method is described that enables spatial encoding without B gradients. This method, herein referred to as frequency-modulated Rabi-encoded echoes (FREE), utilizes adiabatic full passage pulses and a gradient in the RF field (B ) to produce spatially dependent phase modulation, equivalent to conventional phase encoding.

Reducing the Complexity of Model-Based MRI Reconstructions via Sparsification.

Model-based reconstruction methods have emerged as a powerful alternative to classical Fourier-based MRI techniques, largely because of their ability to explicitly model (and therefore, potentially overcome) moderate field inhomogeneities, streamline reconstruction from non-Cartesian sampling, and even allow for the use of custom designed non-Fourier encoding methods. Their application in such scenarios, however, often comes with a substantial increase in computational cost, owing to the fact that the corresponding forward model in such settings no longer possesses a direct Fourier Transform based implementation. This paper introduces an algorithmic framework designed to reduce the computational burden associated with model-based MRI reconstruction tasks.

MRI exploiting frequency-modulated pulses and their nonlinear phase.

Frequency-modulated (FM) pulses can provide several advantages over conventional amplitude-modulated pulses in the field of MRI; however, the manner in which spins are manipulated imprints a quadratic phase on the resulting magnetization. Historically this was considered a hindrance and slowed the widespread adoption of FM pulses. This article seeks to provide a historical perspective of the different techniques that researchers have used to exploit the benefits of FM pulses and to compensate for the nonlinear phase created by this class of pulses in MRI.