Apparatus for measuring concentration of hemoglobin

Abstract: An apparatus for measuring a concentration of hemoglobin includes a light application device (58) for applying light to a detection region (V) containing a blood vessel (12) present in a living body; an imaging device (40,46) for capturing an image of the detection region (V) to which the light is applied; and an analyzer (70) for analyzing the concentration of hemoglobin in blood flowing through the blood vessel (12) by processing the captured image, the analyzer (70) comprising a light intensity detector (73) for detecting a light intensity of a body tissue and a light intensity of blood using the captured image and a calculator (75) for calculating the concentration of hemoglobin from a ratio of the light intensity of the body tissue relative to the light intensity of blood thus detected.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for analyzing blood in a non-invasive manner. More particularly, it relates to an apparatus for measuring a concentration of hemoglobin in blood without collecting or isolating it. 2. Description of Related Art A conventional apparatus for measuring in vivo a concentration of hemoglobin is utilized in applying a plurality of light beams each having a different wavelength to a living body, substituting the values thus obtained with respect to each wavelength, in the equation of modified Lambert-Beer's law as below to determine a concentration C of hemoglobin or an amount ΔC of change of the concentration of hemoglobin as solutions of simultaneous equations (see, for example, WO-A-93/11701 or Japanese Unexamined Patent Publication No. HEI 2(1990)-95262). The equation is: log (Io/I) = ε CD + S where lo represents an intensity of incident light, I an intensity of transmitted light (intensity of reflection light), S a living body scattering term, ε an absorption coefficient and D a thickness of a blood layer. The above conventional apparatus, however, has suffered from such problems that a light source is required which applies a plurality of light beams each having different wavelength individually upon a living body and that the values obtained upon measurement need to be calibrated depending on an intensity of the incident light. SUMMARY OF THE INVENTION The present invention has been conceived in view of the above circumstances. Thus, an object of the present invention is to provide an apparatus for measuring a concentration of hemoglobin using a light source having one wavelength (or one wavelength band) and eliminating the need of calibrating the concentration depending on an intensity of incident light. The present invention provides an apparatus for measuring a concentration of hemoglobin according to claim 1. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing the structure of an embodiment of the present invention. FIG. 2 is a flowchart showing the operation of the embodiment. FIG. 3 is a view explaining an example of a light intensity image obtained in the embodiment. FIG. 4 is a view explaining a cut region of the image shown in FIG. 3. FIG. 5 is a histogram showing an example of a light intensity distribution of the image captured in the embodiment. FIG. 6 is a graph showing the characteristics exhibited on measurement in the embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be detailed in conjunction with a preferred embodiment, which is not intended to limit the scope of the present invention. The apparatus is characterized by measuring a concentration of hemoglobin in blood present in a living body in non-invasive manner. The living body is that of mammals including human bodies. By the detection region referred to as in the light application means for applying light to the detection region containing the blood vessel present in the living body is meant a predetermined region containing the blood vessel that is present as it is in the living body, and is not meant part of the living body surgically removed in vitro. The thickness of the blood vessel contained in a subject region is not limited, but capillary or small arteries and veins located as near as a skin are preferable to produce a good result in reproduction. Incidentally, blood information obtained in capillary or small arteries and veins can be translated into information on thick vessels (medium-size or large arteries and veins). By the light intensity of the body tissue is meant a light intensity emitted from a portion of the body tissue which thus is a light intensity transmitted through or reflected from the body tissue, and by the light of intensity of blood is meant likewise. In the light application means of the present invention, either a continuous or an intermittent light source may be used; the continuous light source that continuously applies light to the detection region includes a laser, a halogen lamp or a tungsten lamp while the intermittent light source that applies light intermittently to the detection region includes a pulse laser (for example, 7000 series manufactured by Spectra-Physics Co., Ltd.) and a flush lamp (for example, DSX series manufactured by Sugawara Laboratories, Inc., Japan). In addition to the above light source, preferably the light application means may comprise (1) an optical fiber, (2) a reflector, (3) a lens, (4) a slit or the like, all of which allow light from the light source to be properly directed to the detection region. Alternatively, appropriate combinations such as those of (1) and (2); (1) and (3); (1), (2) and (3); (1), (2), (3) and (4); (2) and (3); and (2), (3) and (4) may be incorporated in the light application means. In this case, the reflector may be replaced with a prism. In particular, the light application means may include a polarizing means for applying polarizing light to the detection region. An example of the imaging means of the present invention is a general CCD image sensor. In an optical system for allowing the reflection light from the detection region to be directed to the CCD image sensor, the imaging means may comprise an optical fiber, various kinds of reflectors, a polarizing element, a lens of each kind, a prism, a slit or a filter, and preferably comprises, if the reflection light from the detection region is faint, an image intensifier. The imaging means may further comprise polarizing means for removing unnecessary scattered light emitted from the detection region. Desirably, the imaging means may comprise, in its signal processing system, a video signal processing circuit for processing, as video signals, output signals from each pixel of the CCD image sensor while supplying scanning signals to the CCD image sensor, and a VTR or a laser disc recorder for recording the video signals. The light application means and imaging means may be a commercially available video microscope system. The analysis means may be a commercially available personal computer (for example, Power Mac manufactured by Apple Computer Inc.). The analysis means further comprises blood vessel diameter detecting means for detecting a diameter of the blood vessel obtained in the captured image and calculating means for calculating the concentration of hemoglobin based on the detected diameter of the blood vessel. Preferably the calculating means comprises means for calculating the concentration C of hemoglobin from the following equation: C = K•log(I T /I B ) where C represents a concentration of hemoglobin, I T a light intensity of a body tissue, I B a light intensity of blood and K a constant. Preferably the light intensity detecting means may comprise means for examining a frequency distribution on intensity of pixels in the captured image and means for detecting, when the frequency distribution shows peak values at intensity A and B (A < B), the luminance A as the light intensity of blood and the intensity B as the light intensity of the body tissue. The light intensity detecting means of the present invention detects the light intensity I T of the blood tissue and the light intensity I B of body from the image obtained with the imaging means. By the way, C=0 is obtained with respect to a portion of the body tissue. Then the equation (1) produces the following equation: log (Io/I T ) = S With respect to blood, the equation is given: log (Io/I B ) = ε CD + S Subtracting the equation (2) from the equation (3) produces the following equation: log (I T /I B ) = ε CD Here D represents a thickness of a blood layer which is a constant determined by the diameter of the blood vessel. This value is determined depending on the diameter obtained in the image. In addition, ε is a constant determined depending on wavelength of light incident upon the detection region. Accordingly, the calculating means can calculate the concentration C of hemoglobin from the equation (4). These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. FIG. 1 is a view showing an essential part of the embodiment of the present invention. Light emitted from a light source 22 of a halogen lamp is applied to a diffuser 26 via an optical fiber 24 and a filter 23. The light is scattered by the diffuser 26 and uniformly applied to a plate 28. Thus, the plate 28 substantially serves as a light-emitting face such that a real image is formed thereon via an optical system comprising lenses 30 and 32 and a dichroic mirror 34, a real image 36, the real image traversing blood vessels 12 that exist inside of a skin surface 16 of a living body. The filter 23 needs to have a center wavelength of 550nm and a half width of 40nm. The plate 28 may be a light diffusing board, for example that of a frost type manufactured by Sigma Optical Materials Co., Ltd. The region of the real image 36 on the plate 28 including the blood vessels 12 is referred to as a region V. The reflection light from the region V is received in a CCD 40 via the beam splitter 34 and a lens 38. The filter 23, the diffuser 26, the plate 28, the lenses 30, 32 and 38, the beam splitter 34 and the CCD 40 are all accommodated in a probe 58. The probe 58 has a tip 59 allowed to closely contact the skin surface 16 via a transparent plate 66 made of plastic or glass to give a stable image free from being shifted. Image signals output from each pixel of the CCD 40 are processed by a video signal processing circuit 46. The video signal processing circuit 46 successively forms one frame image per one thirtieth second, and the frame images thus formed are sequentially recorded in a video recorder (for example, a laser disk recorder) 50. Reference numeral 70 denotes analysis means for analyzing blood flowing through the blood vessels 12 contained in the detection region V by processing the captured image. The analysis means 70 can be, for example, a commercially available personal computer. The analysis means 70 comprises cutting means 71 for cutting (trimming) a predetermined region of the image output from a video recorder 50, frequency distribution forming means 72 for forming a frequency distribution curve (histogram) on intensity of each pixel of the cut predetermined region, light intensity detecting means 73 for detecting, when a frequency distribution curve shows maximum values at A and B (A < B), the intensity A as a light intensity I B of blood and the intensity B as a light intensity I T of a body tissue, blood vessel diameter detecting means 74 for detecting, with the light intensities, the diameter D of the blood vessel contained in the predetermined region of the cut image, hemoglobin concentration calculating means 75 for calculating the concentration of hemoglobin based on the light intensities I B and I T and the diameter D of the blood vessel, and correction means 76 for correcting, if necessary, the concentration of hemoglobin thus calculated. Each image or histogram formed in the analysis means 70 is monitored by a monitoring television 80. The flowchart of FIG.2 shows the procedure of calculation of the concentration of hemoglobin using the analysis means 70 which will be explained hereinafter The analysis means 70 processes a plurality of frames or fields of images recorded in time series in the video recorder 50, by reading them sequentially. A frame of an image IM containing a blood vessel BL is cut as shown in FIG. 3 (step S1), followed by cutting a predetermined region AR (having, for example, 10 X 100 pixels) as shown in FIG. 4 (step S2). A distribution (histogram) of frequency on intensity of pixels of the predetermined region AR is prepared as shown in FIG. 5 (step S3), followed by detecting the lower intensity value as the light intensity I B of blood and the higher intensity value as the light intensity I T of the body tissue on the two maximum values of intensity (step S4). The calculation of r=log (I T /I B ) is performed (step S5), followed by determining the diameter D of the blood vessel BL from the image (step S6), performing the calculation of C=r/εD (step S7), and adding the value to Ct which is already calculated (step S8). The above operation of S1 to S8 is repeated by the number of a plurality of frames, i.e., by the number F of frames (step S9), followed by calculating the mean value C av by dividing Ct by the number F of frames (step S10), and correcting the mean value C av obtained in capillary and small arteries and veins such that it is translated into the value corresponding to medium-size and large arteries and veins, thereby calculating the concentration of hemoglobin HGB (step S11). In practice, this operation is conducted based on a correction function experimentally obtained. Measurement Embodiment Blood vessels of the lips of a human being were imaged using the apparatus shown in FIG. 1, followed by measuring an intensity of scattered light I T of a body tissue and an intensity of scattered light I B of blood. The imaging was performed such that incident light was applied on the blood vessels contained in the lips of the same human being, with the amount of the incident light varied at six stages. FIG. 6 shows the characteristics of the light intensity I T of blood and the light intensity I B of the body tissue when the amount of incident light applied on the blood was varied. From FIG. 6, it is understood that the light intensity I B of blood over the light intensity I T of the body tissue is constant regardless of change on the amount of incident light, thus eliminating the need of calibrating the measured concentration of hemoglobin with respect to the intensity of the incident light. An examination was made on the correlation between a concentration of hemoglobin HGB value X measured by a blood analyzer and a concentration of hemoglobin HGB value Y calculated in accordance with the present invention with respect to nine subjects having a hemoglobin value of 14 to 18 [g/dI]. The correlation coefficient was 0.861, thus proving that the apparatus of the present invention is sufficiently practical. In accordance with the present invention, the concentration of hemoglobin can be measured using a light source having one wavelength (or one wavelength band), and eliminating the need of calibrating a concentration of hemoglobin depending on a light intensity.

Claims: An apparatus for measuring a concentration of hemoglobin comprising: light application means (22, 23, 24, 26, 28, 30, 32, 34) for applying light to a detection region (V) containing a blood vessel (12) present in a living body, said light application means comprising a filter (23) having a determined wavelength or wavelength band, imaging means (38, 40) for capturing an image of the detection region (V) to which the light is applied, and analysis means for analyzing the concentration of hemoglobin in blood flowing through the blood vessel by processing the captured image, the analysis means (70) comprising: light intensity detection means (73) for detecting a light intensity of a body tissue and a light intensity of blood using the captured image, blood vessel diameter detecting means (74) for detecting the diameter of the blood vessel (12) obtained in the captured image, calculating means (75) for calculating the concentration of hemoglobin from a ratio of the light intensity of the body tissue relative to the light intensity of blood thus detected, the detected blood vessel diameter and the wavelength of light incident upon the detection region. The apparatus for measuring the concentration of hemoglobin of claim 1, wherein the calculating means (70) comprises means (75) for calculating a concentration C of hemoglobin from the following equation: C = K.Log (IT / IB) where C represents a concentration of hemoglobin, IT a light intensity of a body tissue, IB a light intensity of blood and K a constant determined by the diameters of the blood vessel and the wavelength or wavelength band of the filter (23). The apparatus for measuring the concentration of hemoglobin of claim 1, wherein the light intensity detecting means (73) comprises means (72) for examining a frequency distribution on intensity of pixels in the captured image and means for detecting an intensity A as the light intensity of blood and an intensity B as the light intensity of the body tissue when the frequency distribution shows peak values at the intensities A and B, where A < B.

Inventors: ASANO KAORU, ISHIHARA KEN, MAEKAWA YASUNORI, ASANO, KAORU, ISHIHARA, KEN, MAEKAWA, YASUNORI
Applicants: ISHIHARA KEN, SYSMEX CORP, ISHIHARA, KEN, SYSMEX CORPORATION
Application year: 1995
Main classification: A61B5
IPC codes: A61B5, G01B11, G01N33, G01N21