Optics: measuring and testing – By light interference – Having light beams of different frequencies
Reexamination Certificate
2000-02-01
2003-04-01
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By light interference
Having light beams of different frequencies
C600S310000
Reexamination Certificate
active
06542246
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a blood vessel imaging system for imaging blood vessels, and more particularly to a blood vessel imaging system which can image blood vessels with arteries and veins distinguished from each other. This invention also relates to a method and system for determining a spatial distribution of a pulsation wave signal representing a pulsation wave of an artery of an organism.
2. Description of the Related Art
In the clinical field, there has been a wide demand for imaging arteries and veins clearly distinguished from each other. For example, since arteriosclerosis generally starts at the periphery of the arteries, it will be useful in diagnosing arteriosclerosis if the inner walls of the peripheral arteries can be imaged distinguished from those of the veins.
There has been wide known angiography as a system for imaging blood vessels. However angiography is disadvantageous in that load on the testee is heavy and the testee generally must stay in the hospital.
Further there has been proposed technique for imaging a part of an organism on the basis of penetration of light through the part as disclosed in “Japanese ME Academy Magazine BME”, vol.8, No.5, 1994, pp. 41~50. However it is very difficult to image arteries and veins clearly distinguished from each other by the technique.
Also, as a technique for extracting information representing a pulsation wave of an artery, a technique has heretofore been known, in which measuring light beams having two different wavelengths are irradiated to an organism, a logarithm of pulsation wave amplitude is calculated from each of detection signals obtained by detecting the measuring light beams having passed through the organism, and thereafter pulsation wave components are calculated in accordance with the ratio of the two logarithms to each other. However, with this technique for directly detecting the measuring light beams, it is impossible to determine a spatial distribution of a pulsation wave signal representing pulsation wave information.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a blood vessel imaging system which can image blood vessels with arteries and veins clearly distinguished from each other without exposing the testee to heavy load.
Another object of the present invention is to provide a method of determining a spatial distribution of a pulsation wave signal, wherein a spatial distribution of a pulsation wave signal representing a pulsation wave of an artery of an organism is capable of being determined.
The specific object of the present invention is to provide a system for carrying out the method of determining a spatial distribution of a pulsation wave signal.
In blood vessel imaging systems in accordance with one aspect of the present invention, an optical heterodyne detection system is employed in order to ensure high spatial resolution to an organism as a scattering medium, and arteries and veins are distinguished from each other on the basis of the fact that the output signal of the heterodyne detection system is modulated by the pulsation wave unique to arteries when the measuring light beam is projected onto an artery.
That is, in accordance with a first aspect of the present invention, there is provided a blood vessel imaging system comprising
a measuring light source which emits a measuring light beam,
a scanning means which causes the measuring light beam to scan an organism,
an optical heterodyne detection system consisting of an optical system which splits the measuring light beam upstream of the organism into a first light beam traveling to impinge upon the organism and a second light beam traveling not to impinge upon the organism and combines the second light beam with the first beam emanating from the organism into a combined light beam, a frequency shifter which causes the first and second light beams to have frequencies different from each other, and a beat component detecting means which detects beat components of the combined light beam, and
an image signal generating means which generates an image signal on the basis of the ratio of the intensity of a pulsation wave band signal to the intensity of a beat signal included in an output signal of the optical heterodyne detection system.
It is preferred that the blood vessel imaging system be further provided with a frequency analysis means which analyzes the output signal of the optical heterodyne detection system, and the image signal generating means obtains the intensity ratio on the basis of the pulsation wave band signal and the beat signal separated from each other by the frequency analysis means on a frequency axis.
It is preferred that the image signal generating means generates an image signal representing artery parts of the organism when the intensity ratio is higher than a predetermined threshold level.
A blood vessel imaging system in accordance with a second embodiment of the present invention comprises a measuring light source, a scanning means and an optical heterodyne detection system similar to those in the blood vessel imaging system of the first aspect and is further provided with an image signal generating means which generates an image signal on the basis of the degree of modulation at a pulsation wave band frequency of a beat signal included in an output signal of the optical heterodyne detection system.
In the blood vessel imaging system in accordance with the second aspect, it is preferred that a pulsation wave detecting means which detects a pulsation wave of the organism be provided, and the image signal generating means samples the signal value when the beat signal is in a predetermined phase on the basis of an output signal of the pulsation wave detecting means.
Further it is preferred that the image signal generating means generates an image signal representing artery parts of the organism when the degree of modulation is higher than a predetermined threshold level.
Further it is preferred in the blood vessel imaging systems in accordance with both the first and second aspects of the present invention that the measuring light source comprises a linear or two-dimensional array of a plurality of light emitting portions, and the optical heterodyne detection system is arranged to be able to detect in parallel beat components of the combined light beams based on the measuring light beams from the respective light emitting portions, and the measuring light source and the optical heterodyne detection system also function as at least a part of said scanning means.
The beat component detection signal (beat signal) output from the heterodyne detection system described above represents intensity of only straight light components traveling straight through the organism or scattered light components close to the straight light components except influence of scattering by the organism which is a scattering medium.
The artery part and the vein part are distinguished from each other in the following manner. While the first light beam split from the measuring light beam as emitted from the light source is being projected onto an artery part, the output signal of the optical heterodyne detection system consists of a pulsation wave signal a at a frequency of about 1 Hz generated by pulsation of the artery and a beat signal b superimposed one on the other as shown in FIG.
5
. While the first light beam is being projected onto a vein part, there is generated no pulsation wave signal.
When the output signal which varies with time as shown in
FIG. 5
is sampled at a certain timing and subjected to frequency analysis, a spectrum such as shown in
FIG. 2
is obtained. In
FIG. 2
, the pulsation wave signal component is indicated at A and the beat signal component is indicated at B. The intensities of the pulsation wave signal and the beat signal vary in response to the pulsation as shown by the solid line and the broken line in FIG.
2
and with attenuation of the first light beam d
Font Frank G.
Natividad Phil
Sughrue & Mion, PLLC
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