Blood vessel imaging system

Details Blood vessel imaging system Blood vessel imaging system

1999-11-22

2002-04-16

Lateef, Marvin M. (Department: 3737)

Surgery

Diagnostic testing

Measuring or detecting nonradioactive constituent of body...

C600S476000, C600S500000, C600S502000, C600S504000, C600S505000, C356S319000, C356S450000, C356S484000, C356S485000

Reexamination Certificate

active

06374128

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 further relates to a system which can clearly distinguish arteries and veins from each other.
This invention further relates to a system for measuring the flow rate of light scattering fluid such as arterial blood and venous blood.
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 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.
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 blood vessel distinguishing system which cyan clearly distinguish arteries and veins from each other without
9
sing the testee to heavy load.
Still another object of the present invention is to provide a flow rate measuring system for measuring the flow rate of light scattering fluid such as arterial blood and venous blood. In the blood vessel imaging system in accordance with 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 spectral broadening (Doppler broadening) of beat component detection signal output from the heterodyne detection system changes with the flow rate of blood in the blood vessel.
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
0
and a beat component detecting means which detects beat components of the combined light beam,
a filtering means which detects, out of the beat component detection signal output from the beat component detecting means, off-centered components in a frequency band deviated from the center frequency of the beat component detection signal by a predetermined width, and
an image signal generating means which generates an image signal according to whether the off-centered beat signal detected by the filtering means is higher or lower than a predetermined threshold level.
For example, the image signal generating means generates an image signal representing artery parts of the organism on the basis of components of the off-centered beat signal which are higher than the predetermined threshold level, and generates an image signal representing vein parts of the organism on the basis of components of the off-centered beat signal which are lower than the predetermined threshold level.
It is preferred that the blood vessel imaging system be provided with an in-phase time detecting means which detects in-phase times at which broadening of the spectrum of the beat component detection signal becomes of a predetermined phase, and a synchronization detecting means which samples the off-centered beat signal at the in-phase times and inputs the off-centered beat signal thus obtained into the image signal generating means.
The in-phase time detecting means may be, for instance, a means for detecting the pulse wave of the organism, or for detecting the times at which the center frequency component of the beat component detection signal takes a predetermined peak value.
Further it is preferred 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.
When a fluid which causes multiple scattering of the measuring light flows in a direction perpendicular to the direction of travel of the measuring light, the peak value of the beat signal is lowered and the spectrum of the beat signal is broadened. For example,
FIG. 4A
shows a spectrum of the beat signal when the flow rate of the fluid is 0, and
FIGS. 4B
to
4
D show those for different flow rates of the fluid which increase in this order. As can be seen from
FIGS. 4A
to
4
D, the peak value of the intensity of the beat signal becomes lower and the spectrum of the beat signal is broadened (Doppler broadening) as the flow rate of the fluid increases.
Since blood is also a fluid which causes multiple scattering of light, the same phenomenon occurs when the measuring light beam passes through a blood vessel. Since arterial blood is generally higher than venous blood in flow rate, the reduction in the peak value of the intensity of beat signal and broadening of the spectrum are larger when the measuring light beam travels through an artery than when the measuring light beam travels through a vein.
In
FIG. 5
, line a shows a spectrum of the beat signal when the measuring light beam travels through an artery and line b shows a spectrum of the beat signal when the measuring light beam travels through a vein. When components of the beat signal in a frequency band deviated from the center frequency &ohgr; of the beat signal by a predetermined width &Dgr;f are detected by use of a band-pass filter having transmission characteristics shown by line c, and an image signal is generated on the basis of components of the off-centered beat signal (made up of components of the beat signal in said frequency band) which are higher or lower than a predetermined threshold level, an image signal representing only artery parts or vein parts of the organism can be generated.
That is, when the predetermined threshold value is set, for instance, at d in
FIG. 5
, and an image signal is generated on the basis of components of the off-centered beat signal which are higher than the predetermined threshold level d, a signal representing only artery parts of the organism can be generated. On the other hand, when an image signal is generated on

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