Atomic magnetometers used to make ultra-low field MRI

November 7, 2011—LANL researchers are developing a system to make ultra-low field magnetic resonance imaging (MRI) commercially viable for medical applications.

The researchers have been working on an ultra-low field MRI system using low temperature SQUIDS (supercomputing quantum interference devices). Ultra-low field MRI with low temperature SQUIDs in a shielded room has many potential advantages for medical imaging, such as convenience, enhanced contrast, and open design. However, the need for SQUIDs, associated cryogens (low temperature liquids used as refrigerants), and a shielded room made of a special metal alloy are significant drawbacks to a commercially viable system. A SQUID-based system is not cheap because SQUIDS require frequent attention, with cryogens having to be replenished.

The team investigated alternative non-cryogenic detection methods and focused on substituting an atomic magnetometer (a tiny but sensitive low-power magnetic sensor) for SQUIDs in ultra-low field MRI. The substitution of a magnetometer and a flux transformer required the researchers to change the nuclear magnetic resonance frequency and increase the pre-polarization field strength of the system to obtain the needed sensitivity for imaging.

Advantages of the new system

Using this alternative method, the researchers reduced the time needed to take an MRI image. They obtained quality images of a hand with in-plane resolution of 2.5 x 2.5 mm2 after it was in the machine for only five minutes. Conventional commercial MRIs require that the body part being scanned remain immobilized in the machine for substantial periods of time while data for an image is collected. In addition, the new system achieves high sensitivity and good-quality imaging without a shielded room or any large-size structure. This makes the system cost-effective, convenient, compact, and portable.

The researchers believe that it may be possible to implement a high-sensitivity, multi-channel, non-resonant MRI detection system employing atomic magnetometers. This would make the image quality of ultra-low field MRI scanners comparable to other scanners used for anatomical imaging. Moreover, the multi-channel system would enable large-size imaging of the head, spine, or even whole body by covering the imaging area with an array of flux transformers connected to atomic magnetometers that operate independently. The hand image is only the first step in showing the feasibility of the non-cryogenic ultra-low field method of anatomical imaging.

Researchers include Igor Savukov, Todor Karaulanov, Petr Volegov, Andrei Matlashov, Michelle Espy, Algis Urbaitis, John Gomez, A. Castro, and Shaun Newman of the Laboratory's Applied Modern Physics group. The Journal of Magnetic Resonance published the work and featured it on the journal cover. The National Institutes of Health funds the research, which supports the Lab’s Global Security mission area and the Science of Signatures science pillar.