Non-contact MRI in-bore motion sensing method using CW Doppler radar with band-pass filtering

A method using Doppler radar for noncontact sensing of subject motion within a magnetic resonance imaging (MRI) apparatus during an MRI scan, the method comprising:

• (a) transmitting by a quadrature radio configured for single channel transmission with a first directional antenna a band-pass filtered continuous wave radio signal at a microwave frequency, wherein the transmitted band-pass filtered continuous wave radio signal is a monotone radio signal, spectrally separated from an MRI Larmor frequency, wherein the first directional antenna is positioned above a target motion-sensing region;
• (b) receiving by the quadrature radio configured for dual channel reception with the first directional antenna and with a second directional antenna a band-pass filtered reflected radio signal, wherein the first directional antenna is positioned above the target motion-sensing region, wherein there is a frequency offset between the single channel transmission and the dual channel reception;
• and
• (c) detecting the subject motion from the received band-pass filtered reflected radio signal using the quadrature radio implementing Doppler radar;
• wherein detecting comprises:
• (i) digitally down-converting radar raw data by direct IQ demodulation,
• (ii) correcting for DC offset, and
• (iii) performing phase or linear demodulation to produce a movement signal;
• wherein the first directional antenna is connected to the quadrature radio using a hardware front-end chain comprising first band-pass filter, a second band-pass filter, and an RF coupler;
• wherein the second directional antenna is connected directly to the quadrature radio using a third band-pass filter,
• wherein the first band-pass filter, the second band-pass filter, and the third band-pass filter are configured to block MRI RF interference outside the radar operating frequency and mitigate kW-level RF peak power leakage from the MRI apparatus;
• wherein the first directional antenna is connected to the RF coupler, wherein the first band-pass filter is positioned between a transmission output of the quadrature radio and an input of the RF coupler, wherein the second band-pass filter is positioned between an output of the RF coupler and a reception input of the quadrature radio;
• wherein the second directional antenna is connected to a reception input of the quadrature radio, wherein the third band-pass filter is positioned between the reception input of the quadrature radio and the second directional antenna;
• wherein the first directional antenna and the second directional antenna are positioned in a bore of the MRI apparatus and the quadrature radio operates at a transmit power level below 1 mW.