Blood-vessel recognition blood-flow measurement method
A blood-vessel recognition blood-flow measurement method including: obtaining a real-time Doppler spectrum by performing a Fourier transform on a temporal waveform of the intensity of scattered light of laser light in a living body; calculating a normalized real-time Doppler spectrum and a normalized zero spectrum; calculating a region spectrum from a subtracted spectrum that is calculated through subtraction of these calculated spectra; calculating a PS reference spectrum by subtracting, from the region spectrum, the maximum value of the region spectrum in a predetermined PS reference region; calculating an average frequency on the basis of a computational spectrum that is obtained by replacing an element of which the PS reference spectrum is negative with zero; and determining a blood flow velocity by comparing the calculated average frequency with a predetermined threshold.
1. A blood-vessel recognition blood-flow measurement method comprising:
obtaining a real-time Doppler spectrum by performing a Fourier transform on a temporal waveform of an intensity of scattered light produced when laser light is radiated onto a living body;
setting, as a first frequency region, a frequency range higher than a frequency at which an intensity of the real-time Doppler spectrum becomes a same level as a noise floor intensity;
calculating a normalized real-time Doppler spectrum by normalizing the real-time Doppler spectrum with an average value of the real-time Doppler spectrum in the first frequency region;
calculating a normalized zero spectrum by normalizing a zero spectrum measured when laser light is radiated in a state in which a blood flow does not exist, with the average value of the zero spectrum in the first frequency region;
calculating a subtracted spectrum by subtracting the normalized zero spectrum from the normalized real-time Doppler spectrum;
setting, as a second frequency region, a frequency range in which a low-frequency noise can be removed;
calculating a region spectrum by removing, from the subtracted spectrum, a spectrum in a frequency region lower than the second frequency region;
setting, as a third frequency region, a frequency range including a spike noise in the region spectrum;
calculating a PS reference spectrum by subtracting, from the region spectrum, the maximum value of the region spectrum in the third frequency region;
obtaining a computational spectrum by replacing an element of which the PS reference spectrum is negative with zero;
calculating an average frequency based on the computational spectrum; and
determining a blood flow velocity according to the calculated average frequency.
2. A blood-vessel recognition blood-flow measurement method according to claim 1 , wherein, the determining of the blood flow velocity comprises determining that a blood vessel exists, in response to the average frequency being larger than a predetermined first threshold.
3. A blood-vessel recognition blood-flow measurement method according to claim 2 , wherein the determining of the blood flow velocity comprises determining that a blood vessel exists, in response to the average frequency being smaller than a predetermined second threshold that is larger than the first threshold.
4. A blood-vessel recognition blood-flow measurement method according to claim 1 , wherein the calculating of the average frequency comprises:
obtaining, in the second frequency region, frequency integral values of the computational spectrum and of a spectrum that is obtained by multiplying the computational spectrum by a frequency;
comparing a predetermined integral cut-off value with the frequency integral value of the computational spectrum; and
setting, as a result of the comparison, the average frequency based on the following expressions:
if I f >I fCUT ,ω ave =I ωf /I f ; and
if I f ≤I fCUT ,ω ave =0.