Doppler ultrasound triggering for cardiac MRI at 7T

Abstract

Doppler ultrasound was applied as a new trigger method in CMR at 7T. The transmission line and transducer were locally approved as 7T MR conditional, and were successfully tested for image synchronization at 7T. In the future, this method needs to be evaluated in a larger patient population. Magn Reson Med 80:239-247, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Doppler ultrasound cardiac gating of intracranial flow at 7T

“…The Doppler ultrasound (DUS) device and signal processing algorithms used in this work consist of a custom-built DUS unit and a signal processing unit [15,25,26] (north medical GmbH, Hamburg, Germany). The DUS unit transmits 1 MHz pulses with a repetition frequency of 3.2 kHz to a single 1 × 1 cm-piezoelectric element transducer, made from non-magnetic lead zirconate titanate, placed on the subjects' chest.…”

“…In addition, a resonant circuit is placed at the end of the transmission line. A safety assessment was performed in [25] for the case where the transducer was placed within the transmitting volume of a 7T cardiac array coil. In the present work, the transducer is placed more than 25 cm from the end of the transmitting head coil, where the E-and H-fields are significantly reduced compared to the placement in [25].…”

“…A safety assessment was performed in [25] for the case where the transducer was placed within the transmitting volume of a 7T cardiac array coil. In the present work, the transducer is placed more than 25 cm from the end of the transmitting head coil, where the E-and H-fields are significantly reduced compared to the placement in [25]. In this study, B 1 mapping was performed in a phantom setup prior to any human examinations, and neither the transducer nor the cable affected the B 1 field [25].…”

“…In the present work, the transducer is placed more than 25 cm from the end of the transmitting head coil, where the E-and H-fields are significantly reduced compared to the placement in [25]. In this study, B 1 mapping was performed in a phantom setup prior to any human examinations, and neither the transducer nor the cable affected the B 1 field [25]. The DUS processing unit was placed inside the scanner room, keeping it at a distance corresponding to a field of 20 mT (200 Gauss) following local safely guidelines for investigational devices.…”

“…The feasibility of gating MRscans by DUS was first investigated by Rubin et al [24]. The safety and efficacy of DUS-gating at 7T has been investigated for cardiac imaging [25]. In more recent work, DUS-gating was shown to be as successful as ECG for cardiac cine imaging at 1.5 T [15], cine imaging and phase contrast imaging at 3 T [26,27], and fetal cardiac imaging [28][29][30].…”