Fig 1.
Simplified schematic overview of the add-on system.
Arrows show the direction of communication. Black arrows indicate digital signals, red arrows indicate low-power RF signals, orange arrows indicate high-power RF signals, and blue arrows indicate low-power low-frequency analog signals. The dashed gray lines indicate that the enclosed components are part of the original system.
Fig 2.
Simplified representation of two modulation strategies using two channels.
Strategy 1 plays out a rectangular pulse on the exciter and performs the entire modulation with the IQ modulators. Strategy 2, which is used in the implemented system, uses a pre-modulated signal from the exciter to always use the full dynamic range of the modulators, as well as a 180° change in phase from sample to sample to minimize the effect of systematic errors in the modulators.
Fig 3.
Pictures of modulators and amplifiers.
A) Modulator unit containing two modulators. The position of the modulator ICs is indicated by the white arrows. B) High-power amplifier. The red arrow points to the final amplifier stage LDMOS IC. C) Power amplifier racks at the back of the magnet; each rack accommodates 16 amplifiers.
Fig 4.
Overview of the receive chain.
A) shows the original receive chain as provided by the vendor. B) shows the receive chain after including custom components. C) shows the custom second-stage amplifier with bias tee for the on-coil pre-amps. D) shows one of the 32-channel switches (SRS and SSS).
Fig 5.
A) shows the polycarbonate frame that defines the mechanical structure. B) shows an inside view of one half of the array. 16 micro strip-line elements with meanders are visible. C) shows the two halves of the array mounted on the bore liner, with the T/R switches on the bore liner to the right side of the image (service end).
Fig 6.
Schematic of the body array showing four elements including the decoupling network for diagonally placed and head-on elements. Ce is used to set the correct current distribution on the element, Cp and Cs are the parallel and series capacitors of the matching network, and Cc and Zd are part of the decoupling network. The 180°-lines are used for balancing the feed; the 90° delay lines are used as part of the decoupling network. These lines are semi-rigid cables from Huber+Suhner AG, Herisau, Switzerland.
Fig 7.
Phantom B1 maps and SAR distribution.
Comparison of simulated B1+ maps (A,B,E) and measured B1+ maps (C,D,F) in the body-sized phantom. Please note that only half of the channels are shown for better depiction. G shows an axial cut through the body model at the position of the highest SAR in the CP+ mode, with the SAR distribution normalized to 1 W total input power as an overlay.
Fig 8.
In-vivo flip angle maps with TIAMO image (A) for orientation. The maps show the CP+ (B, C) and CP2+ (D, E) modes in transverse (B, D) and coronal (C, E) orientation. The maps (C,E) have a field of view of 50 cm in z-direction.
Fig 9.
In-vivo images of a large volunteer using TIAMO.
Three overlapping stations of 50 cm were acquired. The left images show coronal views, the three images on the right show transverse views of the same volunteer. All images were acquired with the body coil in Tx/Rx mode.
Fig 10.
2D spatially selective excitation in a body-sized phantom using the 32-channel Tx/Rx body coil. The transmit sampling rate was 100 kHz.