Tracking head movement inside an MR scanner using electromagnetic coils

Abstract

Prospective motion corrections in brain imaging for MRI are fairly challenging. Monitoring involuntary head movement inside MR scanner is crucial for prospective motion correction. This initial study delves into utilizing simulations to track the head's movements within an MRI scanner, achieved by measuring induced voltage changes from time-varying magnetic field gradients in head-mounted coils. The ultimate aim is to create an inventive approach for prospective motion corrections. The voltage induced in a circular coil of wire that is exposed to time-varying x-, y- and z-magnetic field gradients, is calculated for varying positions and orientations (POSE) of the coils. Similar steps are taken for a system of five coils confined to faces of a cube and it is established whether the voltage changes due to gradient pulses applied along three directions can be used to calculate the change in POSE of the set of coils. This induced voltage led to form a system of linear equations and then find a calibration matrix. Inverting the calibration matrix enables the estimation of movement parameters from the calculated voltage in the coils. Our software gives robust measurement of the six degrees of freedoms to monitor head movement accurately so far ≈0.3 mm and ≈0.05∘. By using this standard method one can identify the POSE of the coils as well head within an MR scanner. Even after, addition of noise voltage (up to 20 μV) estimated parameters does not blow up. This electromagnetic field based real-time tracking is highly accurate, non-invasive and compatible with standard MRI hardware.

Keywords

• Real-time motion tracking
• EMF tracking
• Head motion
• Prospective motoring
• Coils array