Novel Sensors Could Make MRI Scans Safer

Researchers at Georgia Tech have received a four-year $1.65 million grant from the National Institutes of Health (NIH) to develop novel sensors for safer MRI imaging. The research will be conducted by Professor Levent Degertekin, the George W. Woodruff Chair in Mechanical Systems in the George W. Woodruff School of Mechanical Engineering, as well as postdoctoral researcher Yusuf S. Yaras at Georgia Tech, and collaborators Associate Professor Ozgur Kocaturk (project Co-PI) at Bogazici University, Turkey, Associate Professor John Oshinski at Emory University in Atlanta, Georgia and Dr. Robert Lederman at the National Heart, Lung and Blood Institute (NHLBI) in Bethesda, Maryland. The research will build on work Degertekin previously conducted with funding from an NIH R21 grant, the Georgia Research Alliance, and NSF I-Corps.

Although adverse events related to MRI are rare, safety concerns due to radiofrequency (RF) induced heating have a significant impact in clinical use, especially for a growing number of patients with medical implants. Current regulations based on estimated specific absorption rate (SAR) impose unnecessary restrictions on RF power levels, sometimes reducing the diagnostic efficacy, while even these low levels can create safety issues for specific patients.

Degertekin and his collaborators are developing miniature sensors with local electromagnetic field and temperature measurement capability that could be placed on critical locations on the patient, for example, over an orthopedic implant, during the MRI scans, alleviating these limitations while improving safety and efficacy.

A rendering of the novel sensor

These sensors could also have an impact on interventional MRI applications, where minimally invasive procedures are performed with MRI guidance. Active markers, essentially miniature coils that locally measure the RF signal emitted from the tissue, are used to track devices such as catheters and biopsy needles inside the patient body during interventional MRI procedures. Current active markers use long conductive transmission lines which suffer from RF-induced heating, an issue exacerbated in higher field (3T, 7T) MR systems used for higher resolution imaging.

Degertekin’s team recently developed a miniature acousto-optical (AO) RF field sensor to address these problems.  The AO sensor detects the RF signal using a small antenna coupled to a piezoelectric transducer which modulates the light reflected from a Bragg grating on an optical fiber.

Schematic of sensor field

This enables the RF signal to be transmitted over the optical fiber instead of conductive transmission lines, and making the sensor totally free of RF induced heating and electromagnetic interference. The device can measure temperature as well as the local electromagnetic field with high sensitivity for both SAR evaluation and position tracking when coupled with a properly designed antenna.

The team also proposed a novel packaging strategy to embed their AO RF field sensors in sleeves that can conform to any commercially available MRI compatible catheter, significantly increasing the device options for interventional MRI. Successful demonstration of the AO sensor as an active MRI marker with a non-conducting transmission line could pave the way for more effective, more efficient and safer interventional procedures.

“We expect that our acousto-optical position tracking sensors will especially impact minimally invasive treatments of congenital heart diseases in children, who cannot be imaged under ionizing X-rays, and biopsies for cancer diagnosis,” says Degertekin, whose research program utilizes optics and ultrasound for a range of applications including intravascular ultrasound imaging of coronary arteries, guiding and monitoring therapies in the brain, and new types of transducers for remote powering of medical implants.