Reduction of the radiofrequency heating of metallic devices using a dual‐drive birdcage coil

Abstract

In this work, it is demonstrated that a dual-drive birdcage coil can be used to reduce the radiofrequency heating of metallic devices during magnetic resonance imaging. By controlling the excitation currents of the two channels of a birdcage coil, the radiofrequency current that is induced near the lead tip could be set to zero. To monitor the current, the image artifacts near the lead tips were measured. The electric field distribution was controlled using a dual-drive birdcage coil. With this method, the lead currents and the lead tip temperatures were reduced substantially [<0.3°C for an applied 4.4 W/kg SAR compared to >4.9°C using quadrature excitation], as demonstrated by phantom and animal experiments. The homogeneity of the flip angle distribution was preserved, as shown by volunteer experiments. The normalized root-mean-square error of the flip angle distribution was less than 10% for all excitations. The average specific absorption rate increased as a trade-off for using different excitation patterns. Magn Reson Med 69:845-852, 2013. V C 2012 Wiley Periodicals, Inc.

Safety of Simultaneous Scalp or Intracranial EEG during MRI: A Review

“…There is an advantage of less heating using short cables at 4T magnetic fields [117] and showed agreement with water-gel phantom experiments. The summaries of the safety researches of EEG and implants in MRI using animal samples are included in Table 1.…”

“…Overall at 0.35T [103] and 1.5T it has been found that risks can be managed under specific configurations (low SAR sequences and often a head transmit-receive coil) and the production of heating is less when DBS equipment are fully implanted [34,59,[104][105][106][107][108][109][110][111][112][113]. In 3T MRI fields and higher [34,59,107,[109][110][111][114][115][116][117][118], similar results in terms of heating have been obtained but more caution is required when dealing with DBS implants and wires as well as pulse sequences in general require greater SAR. The summaries of the safety studies of DBS external electrodes and implants in MRI are listed in Table 2.…”

The Safety of Using Body-Transmit MRI in Patients with Implanted Deep Brain Stimulation Devices

“…Finally, while this work addressed minimising tissue-heating by limiting the overall sequence SAR, the growing availability of multi-channel RF excitation technology could in the future offer alternative efficient methods of obtaining high quality images whilst controlling local RF power deposition to safe levels [56]. …”

Construction and modeling of a reconfigurable MRI coil for lowering SAR in patients with deep brain stimulation implants

“…In 2011 Eryaman et al demonstrated the possibility of modifying the electric field of an RF coil to generate regions of low E-field magnitude in the body without significantly altering the transmit sensitivity [14]. In 2012 it was shown that the low tangential electric field region of a linearly-polarized birdcage transmitter can be steered to coincide with a wire implant to reduce the SAR [16]. Recently, we demonstrated that at 1.5 T, this low-field region is thick enough to encompass a generic DBS lead with wire segments that were up to 60° out of plane, reducing the SAR at the implant tip by up to 500 fold below that of commercially available coils [18].…”