System, method and apparatus for measuring blood flow and blood volume
A method of calculating blood flow in an organ of a subject using output radiofrequency signals transmitted to the organ and input radiofrequency signals received from the organ, the method comprises determining a phase shift of the input radiofrequency signals relative to the output radiofrequency signals and using the phase shift to calculate the blood flow in the organ.
1. A method of determining a blood flow quantity in an organ of a subject, the method comprising:
placing a plurality of electrodes on the organ;
transmitting by a portion of said electrodes output radiofrequency signals to the organ;
receiving by another portion of said electrodes input radiofrequency signals from the organ;
by a dedicated electronic circuitry, reducing or eliminate amplitude modulation of said input radiofrequency signals by amplifying said input radiofrequency signals and limiting their amplitude; and
by a signal processing circuit, determining a phase shift of said input radiofrequency signals relative to said output radiofrequency signals, following said reduction or elimination of said amplitude modulation, and determining at least one quantity selected from the group consisting of a stroke volume and a cardiac output, using said phase shift.
2. The method of claim 1 , wherein said reducing or eliminating amplitude modulation comprises maintaining a phase modulation of said input radiofrequency signals.
3. The method of claim 1 , further comprising mixing the output radiofrequency signals and said input radiofrequency signals following said reduction or elimination of said amplitude modulation thereby to provide a mixed radiofrequency signal.
4. The method of claim 3 , wherein said electronic circuitry is designed and configured to filter out a portion of said mixed radiofrequency signal so as to substantially increase a signal-to-noise ratio of a remaining portion of said mixed radiofrequency signal.
5. The method of claim 3 , wherein said mixing comprises providing a radiofrequency sum and a radiofrequency difference.
6. The method of claim 5 , further comprising filtering out said radiofrequency sum.
7. The apparatus of claim 6 , wherein said filtering is by low pass filter characterized by a cutoff frequency of about 35 Hz.
8. The method of claim 4 , wherein said signal-to-noise ratio is increased by at least 10 dB.
9. The apparatus of claim 1 , wherein said input radiofrequency signals correspond to impedance value from about 25Ω to about 35Ω.