Maksym Yushchenko¹, Mathieu Sarracanie¹, and Najat Salameh^1
1Center for Adaptable MRI Technology (AMT Center), Department of Biomedical Engineering, University of Basel, Allschwil, Switzerland

We describe a method to capture wave displacement in vivo in the human forearm for magnetic resonance elastography (MRE) at low magnetic field (0.1 T). Taking advantage of the inherently low spatial frequency nature of propagating waves, the proposed method samples a very low fraction (10%) of the 3D k-space, combined with efficient motion-encoding, processing schemes, and an optimized RF quadrature volume coil. For the first time, acquisitions are demonstrated in humans at a field below 1.5 T within only a few minutes (1-3 min).

Jacob M White^1,2, Monika Śliwiak², Sara V Bates^3,4, Jason P Stockmann^2,3, Lawrence L Wald^1,2,3, and Clarissa Z Cooley^2,3
1Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA, United States, ²A. A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, United States, ³Harvard Medical School, Boston, MA, United States, ⁴Division of Newborn Medicine, Department of Pediatrics, Massachusetts General Hospital, Boston, MA, United States

Point-of-care MRI scanners sited in the neonatal intensive care unit (NICU) can provide immense benefits for diagnosing and monitoring neonatal brain injury. While NICU sited systems can address some of the transport concerns, a truly portable “isolette-side” imager with a neonate-specific design could further improve imaging access. We present a neonate-specific lightweight MRI permanent magnet design for use at the bedside in the NICU. We examine two magnet designs demonstrating the feasibility of realizing a sufficiently homogeneous main magnet with mean B₀ of 125mT weighing under 15kg, both with and without a built-in gradient of 10mT/m.

Sai Abitha Srinivas^1,2, Christopher E Vaughn^1,2, Jonathan B Martin^1,2, and William A Grissom^1,2,3,4
1Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, ²Vanderbilt University Institute of imaging science, Nashville, TN, United States, ³Radiology, Vanderbilt University, Nashville, TN, United States, ⁴Electrical Engineering, Vanderbilt University, Nashville, TN, United States

Traditional B₀ gradients have several drawbacks including high acoustic noise, PNS, bulkiness, and high cost. To address this, we demonstrate the use of Bloch-Siegert (BS) RF encoding for phase encoding using an optimized square root solenoid with a Bucking coil for high efficiency encoding and a nested uniform saddle coil for the imaging Tx/Rx coil at 47.5mT, a field strength that is especially attractive due to its low SAR and accessibility. The coil performance was evaluated in simulation and experimentally, and 2D BS phase encoded imaging and reconstructions were performed using optimized ‘U’ shaped BS pulses.

Thomas O'Reilly¹, Wouter Teeuwisse¹, and Andrew Webb^1
1Radiology, Leiden University Medical Center, Leiden, Netherlands

Halbach arrays are an appealing magnet design for low field MRI due to their low weight and cost typically suffer from relatively high B0 inhomogeneity. In this work we show a new approach to shimming Halbach arrays using higher order Halbach inserts which can be designed to target specific spherical harmonic terms. We demonstrate the principle by correcting for the x2-y2 spherical harmonic, improving B₀ homogeneity of a 31cm diameter bore Halbach array by 50% and show that in simulations homogeneities of 280 ppm can be achieved over a 20 cm sphere by correcting up to 5th order spherical harmonics.

N Reid Bolding¹, Christopher Vaughn², Colin Blades-Thomas³, William A Grissom², and Mark A Griswold^3
1Physics, Case Western Reserve University, Cleveland, OH, United States, ²Biomedical Engineering, Vanderbilt University, Nashville, TN, United States, ³Radiology, Case Western Reserve University, Cleveland, OH, United States

This work presents a $75 phase modulated 2.07MHz radiofrequency power amplifier (RFPA) measuring 8.5x4.5cm for Selective Encoding through Nutation and Fingerprinting (SENF). By eliminating the need for a gradient system and imaging in a low B0, SENF shows great potential to reduce the cost, size, and accessibility of magnetic resonance imaging (MRI) equipment. Here we present the development of a transmit stage of a SENF coil unit. Special consideration has been given to simplifications that can be made in RFPA design in this specific application.