MRI safety and MRI implant safety: 1st E-field measurement @ 7T



How to check MRI safety and MRI implant safety? This question is not straightforward unless use of full non-magnetic electric field probe. However this latter condition is necessary but not sufficient. Indeed, the effective permittivity of the non-magnetic electric field probe should also match the one of the gelled saline MRI phantom. Lastly, no artifact should be induced by the non-magnetic electric field probe on the MRI images. Kapteos non-magnetic electric field probes fulfill all these conditions, whatever the static magnetic field (0.55T to 7T) of the MRI machine.


The following results have been carried out on a 7T Bruker MRI machine at Creatis laboratory in France with a non-magnetic electric field probe eoProbe™ ET1-bio presenting a 1-mm spatial resolution.



Checking artifact-free behavior of the non-magnetic electric field probe


The artifact-free behavior of Kapteos bio-line probes on the MRI images have been already validated several years ago for MRI machines up to 4.7T. We present here first results on a 7T MRI machine. For that purpose, two MRI images (256 x 256 pixels) have been taken:

  • the first one concerning a golden kiwifruit,

  • the second one concerning an agar gelled saline phantom.

The probe appears as a black disk surrounded by a white crown, surrounded itself by a black crown. From the center to the probe edge, these three elements correspond to:

  • the 1.75-mm diameter electro-optic crystal acting as the non-magnetic electric field probe transducer,

  • the gel filling the gap between the transducer and the probe sheath,

  • the high permittivity probe sheath and some air cavity created by the probe insertion.

With agar gelled saline phantom, the probe insertion inside the phantom has led to cracks in the phantom that are clearly visible on the image. Apart these mechanical damages, no image artifact is caused by the non-magnetic electric field probe itself.









Permittivity matching of the non-magnetic electric field probe

From the international standard IEC 62209-2, a human-tissue simulating phantom should present a permittivity with a value of 45.3 for its real part at 300 MHz (7T MRI). Kapteos non-magnetic electric field probes for biological applications are composed of a high permittivity sheath (εr ≅ 23) and a high permittivity transducer (εr ≅ 48), thus leading to a very good permittivity matching with the phantom.

This constitutes a key point as the E-field distribution in a phantom can be strongly modified, both in magnitude and direction, when an element is insert