Non-contact MRI in-bore motion sensing method using CW Doppler radar with band-pass filtering
Noncontact sensing of subject motion using Doppler radar within a magnetic resonance imaging (MRI) apparatus transmits a band-pass filtered continuous wave radio signal at a microwave frequency and receives a band-pass filtered reflected radio signal. The subject motion is detected from the received band-pass filtered reflected radio signal using a quadrature radio receiver with a software defined radio implementing Doppler radar. A first antenna, used for transmission and reception, is connected to the quadrature radio using band-pass filters and an RF coupler. A second antenna, used for reception, is connected directly to the quadrature radio using band-pass filters. The antennas are positioned in a bore of the MRI apparatus.
1 . 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.
2 . The method of claim 1 wherein the RF coupler is a circulator, directional coupler, or hybrid coupler.
3 . The method of claim 1 wherein the received band-pass filtered reflected radio signal is a Doppler phase modulated monotone radio signal.
4 . The method of claim 1 wherein the quadrature radio uses a receiver local oscillator frequency that is offset from a transmit oscillator frequency.
5 . The method of claim 1 wherein the receiver local oscillator frequency offset is within a demodulation bandwidth of the quadrature radio.
6 . The method of claim 1 wherein the first directional antenna and the second directional antenna are positioned symmetric with iso-center of a bore of the MRI apparatus, above a subject landmark (LM) position.
7 . The method of claim 1 wherein the first directional antenna and the second directional antenna are attached to a ceiling of a bore of the MRI apparatus.
8 . The method of claim 1 wherein the first directional antenna and the second directional antenna are embedded within a body coil of the MRI apparatus.