Matthew J. Riffe

On-coil multiple channel transmit system based on class-D amplification and pre-amplification with current amplitude feedback

A complete high‐efficiency transmit amplifier unit designed to be implemented in on‐coil transmit arrays is presented. High power capability, low power dissipation, scalability, and cost minimization were some of the requirements imposed to the design. The system is composed of a current mode class‐D amplifier output stage and a voltage mode class‐D preamplification stage. The amplitude information of the radio frequency pulse was added through a customized step‐down DC‐DC converter with current amplitude feedback that connects to the current mode class‐D stage. Benchtop measurements and imaging experiments were carried out to analyze system performance. Direct control of B1 was possible and its load sensitivity was reduced to less than 10% variation from unloaded to full loaded condition. When using the amplifiers in an array configuration, isolation above 20 dB was achieved between neighboring coils by the amplifier decoupling method. High output current operation of the transmitter was proved on the benchtop through output power measurements and in a 1.5T scanner through flip angle quantification. Finally, single and multiple channel excitations with the new hardware were demonstrated by receiving signal with the body coil of the scanner. Magn Reson Med, 2013.

Parallel excitation for B‐field insensitive fat‐saturation preparation

Multichannel transmission has the potential to improve many aspects of MRI through a new paradigm in excitation. In this study, multichannel transmission is used to address the effects that variations in B0 homogeneity have on fat‐saturation preparation through the use of the frequency, phase, and amplitude degrees of freedom afforded by independent transmission channels. B1 homogeneity is intrinsically included via use of coil sensitivities in calculations. A new method, parallel excitation for B‐field insensitive fat‐saturation preparation, can achieve fat saturation in 89% of voxels with Mz ≤ 0.1 in the presence of ±4 ppm B0 variation, where traditional CHESS methods achieve only 40% in the same conditions. While there has been much progress to apply multichannel transmission at high field strengths, particular focus is given here to application of these methods at 1.5 T. Magn Reson Med, 2012.

Identification and mitigation of interference sources present in SSB-based wireless MRI receiver arrays

Single sideband amplitude modulation (SSB) is an appealing platform for highly parallel wireless MRI detector arrays because the spacing between channels is ideally limited only by the MRI signal bandwidth. However this assumes that no other sources of interference are present outside that bandwidth. This work investigates the practical interference between multiple SSB‐encoded MRI signals.

Device localization and dynamic scan plane selection using a wireless magnetic resonance imaging detector array.

A prototype wireless guidance device using single sideband amplitude modulation (SSB) is presented for a 1.5T magnetic resonance imaging system.

Device localization and dynamic scan plane selection using a wireless MRI detector array

A prototype wireless guidance device using single sideband amplitude modulation (SSB) is presented for a 1.5T magnetic resonance imaging system.

Device localization and dynamic scan plane selection using a wireless magnetic resonance imaging detector array: Device Localization Using a Wireless MRI Array

A prototype wireless guidance device using single sideband amplitude modulation (SSB) is presented for a 1.5T magnetic resonance imaging system.