A coil combination for magnetic resonance perfusion imaging of mice in vivo at 7 T

Abstract

A radio frequency (rf) coil combination of a birdcage resonator and a receive-only surface coil was developed for in vivo magnetic resonance imaging of mice at 7.0 T. Since this coil was designed for spin labeling perfusion measurements, the length of the birdcage resonator needed to be 110 mm at a diameter of 35 mm. This was challenging since this length extended 1/10 of the wavelength at the spectrometer Larmor frequency of 300.3 MHz. Symmetric drive with homogeneous B1 field was achieved by introduction of a new rf coupling scheme using an additional conductor path ring at zero potential. This design allowed a balanced drive of the coil without the use of an additional balun. The receive-only surface coil was realized as a single loop with a diameter of 24 mm. To avoid coupling between the coils, active decoupling using p-i-n diode switches was integrated. These switches showed good characteristics and the coil combination was not sensitive to effects such as contrast alterations, rf shielding of the transmit pulse by the receive coil, and possible receive coil destruction during transmission. The improved performance of the coil combination with respect to a stand-alone surface coil or a stand-alone birdcage resonator was demonstrated in phantoms and mice. In comparison with a stand-alone suface coil, the coil combination provided more uniform contrast behavior and an extended depth of view. In addition, the combination showed an improved signal-to-noise ratio with respect to a stand-alone birdcage resonator.

In vivo assessment of absolute perfusion and intracapillary blood volume in the murine myocardium by spin labeling magnetic resonance imaging

“…Further details are described in Ref. (23). Using this coil in combination with adiabatic hyperbolic secant inversion pulses (24) guaranteed exact spin inversion over the whole mouse and detection with high SNR.…”

A double-tuned1H/23Na dual resonator system for tissue sodium concentration measurements in the rat brain via Na-MRI

“…The optimal solution for accurate TSC quantification consists of a volume resonator for B 1 field transmission and a separate surface coil for detection [9]. The benefits of this set-up have been demonstrated previously as part of singletuned 1 H [8], 23 Na [9], and double-tuned 1 H/ 129 Xe [10] transmit-only receive-only (TORO) coil systems. However, such a TORO solution, while common in clinical MRI, has proved difficult to realise in rodent imaging due to the small sizes involved:…”

“…However these come at the expense of longer minimum time to echo (TE) values, which negatively affect the quantification accuracy due to the presence of a short T 2 -relaxation component of sodium nuclei in vivo (~ 1 ms). Although volume resonators may be used to produce very homogeneous B 1 fields, their limited signal sensitivity significantly reduces the achievable SNR [8]. The optimal solution for accurate TSC quantification consists of a volume resonator for B 1 field transmission and a separate surface coil for detection [9].…”

Reducing signal‐to‐noise ratio degradation due to coil coupling in a receiver array for 35Cl MRI at 9.4 T: A comparison of matching and decoupling strategies

“…Moreover, the capacitors were placed at alternating ends of the legs to distribute the current as evenly as possible. The coil was connected to the coaxial cable via a ground ring and split matching capacitors in order to balance the coil and to avoid the usage of cable traps.…”