Localized Oscillating Magnetic Fields: New Method for Accelerated MR Imaging

• Accelerating signal acquisition
• Simple field shaping
• Avoiding time limitations and disadvantages of conventional techniques
• Improving quality, i.e. increasing the signal-to-noise-ratio
• Reducing complexity of creating local gradient fields

• Accelerated MR imaging
• MR imaging of dynamic samples

For spatially resolved MR signal detection linear magnetic field gradients are used to locate the origin of a signal. To further increase spatial resolution and processing time, modern MR scanners are additionally using multiple RF coils at different positions, with each of them having its individual sensitivity profile within the sample. Furthermore, the principle of applying multiple spatially confined magnetic field components is known as a method for additional spatial resolution, but the PatLock principle is using static fields only. For many applications, e.g. using moving samples, typical imaging durations are still too long and further improvement of the spatial information is hence desired.

A novel imaging method based on the localized temporal variation of the magnetic field has been developed to overcome the aforementioned shortcomings and to further reduce acquisition durations for magnetic resonance imaging.
Common parallel imaging is based on the concept of using instead of a single RF receive coil a set of several small RF receive coils detecting only a small portion of the object. Therefore, spatial information of the origin of the magnetization is intrinsically provided thus reducing the imaging duration by a factor of 2 to 20.
As a possible implementation of the invention for further accelerated imaging, local magnetic fields can be generated by a set of current loops that are placed close to the object as shown in figure 1. A temporal current variation induces a local varying magnetic field that modifies the local Larmor frequency of the magnetization. One possibility of the proposed method applies different frequencies and phases to each coil separately during the acquisition of the MR signal. Based on these locally different modulations the spatial origin of the acquired signal can be localized by appropriate mathematical reconstruction procedures. With this additional local information, the conventional imaging process can be accelerated. Experimental results demonstrate an additionally reduced acquisition time by a factor of 2 to 4.

PCT (WO2020007794A1), EP, US, JP, CN

Scheffler, et al., "Spread‐spectrum magnetic resonance imaging" Magn Reson Med. 2019, 877–885 (2019)