Where, h_a , h_s , and h are correction terms of μ_a , μ_s , and g , respectively. The iterative calculations continue until h_a , h_s , and h_g have dropped below predefined maximum values .

More equations that optical parameters

For a number of equations larger than the number of optical parameters to be determined, e.g. in case of repetitions of measurements with the same number of detectors in a given configuration, the method of principal components may be used to select the number of parameters to be determined, said parameters explaining most of the variability of the measurements. The unexplained the variability is then ascribed to a residual component accounting for the uncertainty of the determination.

This system including repeated measurements may be solved by various methods known in the art including weighted multiple regression analysis.

Determination of Calibration Matrix A

In a preferred embodiment, the optical properties are calculated using multiple polynomial regression in combination with a Newton-Raphson algorithm MRP/N-R.

The method is based on a calibration model wherein calibration matrix containing R , T , and^α values for a range of optical properties "° , "^s , and of interest is obtained. The calibration matrix can be obtained in two ways, either using a) Monto Carlo simulation or b) a measurement setup using a set of phantoms with well- defined optical properties.

(a) Using Monto Carlo simulation (MC)

With a range of optical properties of interest MC is initiated, in each single MC simulation the spatially resolved diffuse reflectance R as a function of the radial distance^rR , the spatially resolved diffuse transmittance T as a function of the radial distance^?τ , and the angularly resolved total transmittance^α as a function of the deflection angle ^ and the acceptance angle ^ is recorded. A with i.e. sample thickness

= 1 mm, and beam diameter^b = 1 mm. The refractive indices of the sample n * , the wall n^w , and the surrounding media n„ has to be specified.

In preferred embodiment, the predetermined calibration matrix is derived from known values of optical parameters of the turbid medium.

Using measurement setup

In a setup R , T ._and^a measurements are done using phantoms with optical properties in a range of interest. The phantoms can be made of well-defined aqueous solutions of Intralipid and black ink. The scattering and absorption spectra of the Intralipid and the black ink are determined using an integrating sphere setup and traditional transmission spectroscopy measurements. On the basis of these spectra, a matrix of phantoms with a range of ^^a , ^^s , and can be made. The applied range of Intralipid concentrations is 0.6, 0.8, ...1.6 %, and the range of the ink concentrations is 0.0, 0.2, ...1.2 % for typical skin tissue optical parameters.

With the generated calibration matrix a triple-polynomial fits is found:

[x_flt X_xfit X,,,R μ_β μ_a² /-/¹ A ?

Where,^l~i-^flt are functions of ^^a , ^ , and % , and A, B and_are 4_X3 matrices of fitting coefficients X . determined by least-squares regression. Thus,^l~3'^βt constitute the calibration model.

Since the method implies exactly three variables in order to predict "ⁿ , "^s , and , a dimension reduction must be performed. For this the Principal Component Analysis

(PCA) is used, that is, we perform PCA on the calibration matrix and then use the resulting three main principal components as input i.e. X^1~3 to the calibration.

In another preferred embodiment, the predetermined calibration matrix is obtained from measurements on samples of the turbid medium having known optical parameters .

Further preferred embodiments are defined in the subclaims .

"Apparatus for of Determining Optical Parameters"

In another aspect, according to the present invention, these objects are fulfilled by providing an apparatus for determining optical parameters of a turbid medium, the apparatus comprising

a sample holder for holding a sample of the turbid medium;

illuminating light for illuminating light onto said sample when said sample is placed in said sample holder, said illuminating light illuminating the sample along an axis of incidence; at least one spatial detector for detecting spatially resolved diffused light from at least one input/output port (ni≥l) of said sample in at least one spatial position; and

at least one angular detector for detecting angularly resolved scattered light from at least two input/output ports (n 2) of said sample in at least two different angular positions with respect to said axis of incidence; said at least one spatial detector and said at least one angular detector optionally being a^' single detector.

Preferred embodiments are defined in the subclaims.

"Computer Program for Carrying out the Method of Determining Optical Parameters"

In still another aspect, according to the present invention, these objects are fulfilled by providing a computer program for use in running a computer for carrying out the method according to the invention, in particular such a computer program stored on a computer usable medium.

"Use of Optical Parameters Determined by the Method of Determining Optical Parameters"

A typical application of the present invention is to use of one or more optical parameters of the turbid medium determined according to the method for the determination of one or more material parameters of the turbid medium. In a preferred embodiment, the one or more determined material parameters is the concentration of one or more components of the turbid medium, said components being either dissolved or dispersed in the turbid medium.

Defini tion of Terms and Expressions

In the present context it is intended that the term "spatially resolved diffused light" designates diffused light which is sampled along an axis of distance from the point of illuminating light.

In the present context it is intended that the term "angularly resolved scattered light" designates scattered light which is sample along a set of angles from the point of illuminating light.

3. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, by way of examples only, the invention is further disclosed with detailed description of preferred embodiments. Reference is made to the drawings in which

FIG. 1 shows an illustration of the concepts of spatial resolved and angular resolved diffused light;

FIGS. 2A-2C illustrate a turbid medium that can take any form, gas, liquid or solid;

FIG. 3A shows an embodiment of an apparatus for determining optical properties of a turbid medium according to the invention;

FIG. 3B shows another embodiment with a compact sample/detection system;

FIGS. 4A and 4B show sectional views of specific embodiments of the compact sample/detection system in FIG. 3B;

FIG. 5 shows another embodiment of a sample/detection system;

, FIG. 6 illustrates an embodiment of an illuminating light beam with two wavelengths;

FIG. 7 shows an embodiment comprising four light sources;

FIG. 8 shows another embodiment wherein the direction of the light through the sample is inverted compared to the system shown in FIG. 5; and FIG. 9 shows a flow chart of the electronics for an embodiment of the apparatus.

DETAILED DESCRIPTION

"Spatial resolved and angular resolved diffused light"

FIG. 1 shows an illustration of the concepts of spatial resolved and angular resolved diffused light.

Illuminating light enters a turbid medium 1 along an axis of incidence 2; here the turbid medium is illustrated in an ellipsoidal shape. The light interacts with the components of the turbid medium, including chromophores and scattering components. Spatial resolved diffused light is measured in spatial detectors 3 and 4. Angular resolved diffused light is measured in angular detectors

5 and 6 positioned at different angles with respect to the axis of incidence of the illuminating light.

"Shape of turbid medium"

FIGS. 2A-2C illustrate a turbid medium 1 that can take any form, gas, liquid or solid. In case of a fluid the turbid medium is confined by suitable container means e.g. behind container walls 7, see FIG. 2A. As illustrated in FIGS. 2A and 2B the spatial resolved diffused light of both transmitted type and reflected type can be measured.

FIG. 2C shows a sectional view of cuvette containing a turbid medium. The cuvette has walls of thickness d_w and a cavity of diameter d_s. The illuminating beam has a beam width of d . The spatial detector R is placed at a radial distance from the axis of incidence of r.

"Preferred Optical Configurations"

FIG. 3A shows an embodiment of an apparatus for determining optical properties of a turbid medium according to the invention.

The apparatus comprises an illuminating light source, here a light beam 10 from a collimated laser embodied in form of a laser diode 8. The light from the laser diode is broken by a beam splitter 9 to obtain a reference beam for measuring the power of the laser diode in reference detector 17e.

A sample of a turbid medium is placed in a sample holder 11; here the sample holder is adapted to receive a cuvette 12 containing a sample of a turbid fluid, or a solid sample.

The sample holder is made of a suitable material, e.g. aluminum, molded polymer e.g. plastic, etc.

The cuvette is made of a suitable material, e.g. a polymer to provide a cheap disposable-type cuvette, or a high quality-type cuvette made of glass such as silica, BK7, etc.

The sample holder is equipped with openings for allowing light to communicate with input/output light ports of the sample; here the openings of the sample holder are illustrated by pinholes 13, 14, and 15 in opposite faces thereof, respectively. Pinhole 13 has a diameter of 0.2 mm. It is placed in the illuminated face of the sample holder at a radial distance of 2.5 mm from the axis of incidence of the illuminating light. It allows communication of light in a spatial output port of the sample, here a spatial resolved diffused reflection output port. A spatial detector 17a for detecting said reflected diffused light

(R) from the sample, here the spatial detector 17a, is mounted directly on the sample holder. The spatial detector could be mounted as an integral part of the sample holder.

Pinhole 14 has a diameter of 0.2 mm. It is placed in the opposite face of the illuminating face of the sample holder at a radial distance of 2.0 mm from the axis of incidence of the illuminating light. It allows communication of light in a spatial output port of the sample, here a spatial resolved diffused transmission output port for transmitted diffused light (T) . A spatial detector 17b for detecting said transmitted diffused light from the sample is mounted directly on the sample holder. In this case, the detector 17b is similar to detector 17a.

Pinhole 15 has a diameter of 0.2 mm. It is placed in the opposite face of the illuminating face of the sample holder at the axis of incidence of the illuminating light. It allows communication of light in an angular output port of the sample, here an angular resolved scattered output port for angular resolved scattered light. A Fourier lens 16 separates the angles for two angles, the smaller angle at zero degrees (α₀) and the larger angle at 5 degrees (oci) , respectively, thereby directing the angular resolved scattered light to two angular detectors 17c and 17d, respectively. Here, the angular detectors 17c and 17d are of the same type as the spatial detectors 17a and 17b. The acceptance angles of the angular detectors could be optimized by providing a plate with further pinholes after the Fourier lens 16. The input port of the sample facing the illuminated face of the holder is not shown in this figure.

The diameter of the pinholes 13, 14, and 15, and the light propagation distances from the point of illumination on the sample, or equivalent the radial distances from the detectors to the axis of incidence of the illuminating light, are set according to the geometrical configuration.

The geometrical configuration is found using a set of simulated data with random combination of the optical properties of interest. The data is generated using Monte Carlo simulation, given the sample thickness, the phase function, etc. In each case, using the calibration matrix the prediction errors of the optical properties is minimized by finding an optimal combination of angles (α) and distances (r) reflectance and transmittance, respectively.

The selection of the detectors depends on the wavelength used. In the range 400-1000nm, standard silicon photo diodes can be used (e.g. a standard BPW34) . Above lOOOn , InGaAs photo diodes could be used.

The detectors 17a, 17b, 17c, and 17d could be arranged in form ring detectors having their respective radial distances from the axis of incidence of the illuminating light. This could increase the sensitivity of the setup. The detector signals are recorded in respective recording means, and processed in a computer (not shown) .

FIG. 3B shows another embodiment with a compact detection system 18.

FIGS. 4A and 4B show in sectional views of specific embodiments of the compact detection system 18 in FIG. 3B along line A-A.

Lights from the sample are guided by means of a light guide block 14.

The detection system 18 guides two spatially resolved diffused lights (Ti) and (T₂) , and angular resolved scattered lights (α₀) and (o-i) to a detector array 19. The detector array consists of multiple detectors, placed in a row (array) . In this embodiment, measurement is not made for spatial resolved diffuse reflection (R) .

In FIG. 4A, the detection system is made of two plates 20 and 21 in which the input/output light ports are made for light communication with the sample. The plates are assembled and spaced with e.g. screws 22, 23. In the space between the plates, a light guiding material is placed. On top of the plate 20, a detector array 19 is mounted. Spatial resolved diffused light is transmitted to the detector array through optical wave-guides, here optical fibers 23, 24. The type of optical fibers is selected depending of the wavelength and the number of wavelengths of the illuminating light. If a single wavelength is used, single mode optical fibers are preferred. Otherwise, multi mode optical fibers are used. In FIG. 4A the optical fibers are shown at two different radial distances. However, the number of radial distances can be increased, just by increasing the number of detectors (e.g. pixels) in the detector array and the number of optical fibers at increasing radial distances.

To resolve the angular resolved scattered lights (α₀) and (c-i) , a lens can be used, here a small plano-convex lens 25 is used. The lens is placed between the two plates 20 and 21. The focal length of the lens depends on the distance to the sample and the resolved angles, here a focal length of 15 mm has been used together with resolved angles of zero degree and 5 degrees, respectively. The lens focuses angular resolved light to the detector array through pinhole 26 (α₀) and 27 (oci) , respectively.

Again the number of detectors of the detector array and the number of angels can be increased. The selection of the detector array depends on the wavelength and the number of detectors. In an embodiment, the light guide block was connected to a four-element silicon array detector (e.g. of the type LD4C-5T from Centronic) .

Another embodiment of the detection system is shown in FIG. 4B. The detection system is a molded unit 28 in which four light channels 29, 30, 31 and 32 are made. The molded unit is made of non-transparency material to avoid optic crosstalk between the channels. Each channel guides light from the sample to the detector array 19, which are placed on the molded unit.

To further optimize the system, the channels could be embodied with optical fibers to increase the sensitivity of the system. Also, the channels could be in form of cylindrical rings to further increase the sensitivity of the system. No lens for the angular transmittance is used in this embodiment. A light channel 31 is used to guide the light at a given angle. If necessary a lens could be inserted in the molded unit to optimize the performance.

FIG. 5 shows another apparatus for determining optical properties of a turbid medium according to the invention. Pinhole plates 33, 34 and 35 define the geometrical configuration of the system. Exchange of the pinhole plates with modified pinholes provides easily for a new setup whereby a large range of optical properties suitable for several applications can be determined.

Plate 33 defines the radial distance of the pinhole 13 from the axis of incidence of the illuminating light. The pinhole allows measurement of spatially resolved diffused reflection. From the pinhole light is guided to a detector 17a via light guide 36a. The light guide can comprise any suitable transparent materiel, e.g. glass. Preferably the light guide is coated with a reflective layer to increase the amount of guided light.

Similarly, the plate 34 the pinhole 14 for measuring spatially resolved diffuse transmittance. From the pinhole light is guided to a detector 17b via light guide 36b. The detectors 17a, 17b can be of a common type. The selection depends on the applied wavelength.

The pinhole plate 35 defines the conditions for measuring angular resolved total transmittance. The pinhole plate can easily be exchanged with another pinhole plate defining a different pinhole configuration whereby angular resolved total transmittance can be measured at different angels. A wide area of angles can be covered, and thereby a large range of optical properties is possible. The angular resolved scattered light is deflected in a lens 37 and detected in a suitable detector, here a detector array 38 which can cover all angles selected by the pinholes.

In a particular embodiment several wavelength are used, either simultaneously or sequentially.

FIG. 6 illustrates an embodiment of an illuminating light beam with two wavelengths. A beam splitter 39 combines beams 40, 41 from two illuminating light source, here laser diodes 42 and 43. A reference detector 17e measures the power from both light sources. The output from the beam splitter is a beam 44 consisting of two different wavelengths. The laser diodes are switched on/off thereby allowing one diode to be turned on at a time, or modulated with two different frequencies.

In another embodiment, multiple light sources are applied.

FIG. 7 shows an embodiment comprising four light sources, here four laser diodes 45a, 45b, 45c and 45d, coupled to four optical fibers 46a, 46b, 46c, 46d and a multi port optical fiber coupler array 48; the latter further being coupled to an output optical fiber 47. The output optical fiber carries the wavelengths of the four light sources the selection of which is obtained by switching the diodes on/off, respectively. A collimator 50 collimates the light from the output optical fiber into a collimated light beam 49. This collimated light beam is split by a beam splitter 9 to obtain a reference beam 51. A reference detector 17e measures the power of each light source. The output light beam of the beam splitter comprises the wavelengths of the four light sources. The light sources can be selected individually, or selected in combinations of each or more thereof.

In still another embodiment, a monochromator is used instead of the multiple light sources whereby a specific wavelength can be selected. An optical fiber couples the monochromator to the collimator. A power reference of the collimated light beam is obtained by using a beam splitter as described previously for the multiple light source .

FIG. 8 shows another embodiment wherein the direction of the light through the sample is inverted compared to the system shown in FIG. 5,

The sample 12 is placed between two plates 52 and 53 with input/output ports 13, 14 and 15. Multiple light beams 54a, 54b, 54c and 54d are coupled to the input/output ports, e.g. directed at the ports as individual beams or guided to the ports in multiple beams. Here, beams 54a and 54b define the inverted direction of light for the spatial resolved diffused light reflection and transmittance, respectively, and beam 54c and 54d define those for the angular resolved scattered transmittance. The detector 55 detects the output light from the light output port 56.

An advantage of one detector and several light sources is that a more specific detector can be applied, e.g. a photo multiplier, or a spectrograph which will enhance the system to cover a large range of wavelengths and allow use of a white light source, e.g. a halogen light source. FIG.9 shows a flow chart of the electronics for an embodiment of the apparatus. Each detector 57 generates a current, which is proportional to the light absorbed by the detector. All the detectors are connected to a converter block 58, in which the current is transformed to a voltage and amplified to obtain a suitable voltage. This voltage is sampled/converted into a digital word. In a preferred embodiment, each detector has its own preamplifier and ADC whereby all the channels are sampled at the same time eliminating time delays between the channels. In another embodiment, several detectors share a common analog-to-digital conversion. The output of the converter block is coupled to a digital signal bus 59, on which each ADC can be addressed and the digital word can be obtained. A driver block 60 is also coupled to the digital signal bus. The driver block controls and powers the light sources 61. A computer e.g. a digital signal processor (DSP) 62 handles the communication and instructions to both the converter block and the driver block. The control algorithm in the DSP turns the light sources on/off and receives digital words from the result of the conversion. The digital words are processed, using the PCA and MRP/N-R method, by the DSP and represents the optical properties of the sample in a measurement. The DSP has an output interface 63 for communicating with an external device, here a PC. The PC is used to display the information in a graphical form and to record the information from the measurement.

"Test Simulations'

The optical parameters μ_a , μ_s , and g are extracted from

MC simulated recordings of various combinations of angularly and spatially resolved reflected and transmitted intensities from a thin turbid sample using multivariate calibration.

The basic geometrical configuration of the set-up we used for the simulations in our analyses is shown in FIG. 2C.

The set-up imitates a cuvette with sample thickness d_s = 1 mm, wall thickness_w = 1 mm, and beam diameter d_b = 1 mm. The refractive indices of the sample n_s , the wall ιι_w , and the surrounding media n_m were 1.33, 1.49, and 1.00, respectively.

During each single MC simulation, we thus recorded: (a) the spatially resolved diffuse reflectance R as a function of the radial distance r_R , (b) the spatially resolved diffuse transmittance T as a function of the radial distance r_τ , and (c) the angularly resolved transmittance a as a function of the deflection angle θ and the acceptance angle φ .

As a first step to solve the inverse problem of extracting μ_a , μ_s , and g using multivariate calibration, we generated a database of MC simulations using the geometrical configuration in FIG. 2C and a set of optical properties within typical biological ranges:

0 < μ < 2 cm^"1

( 1 ) 10 < ._J < 200 cm^"1

0.85 < < 0.99

The simulated reflectance and transmittance recordings were tabulated and stored in a 21x19x11 calibration matrix, i.e. a data base containing all combinations of

21 values of μ_a , 19 values of μ_s , and 11 values of g . The single simulations of the calibration model was generated using on 140^s photons .

Next, we applied multiple polynomial regression (MPR) in conjunction with a Newton-Raphson (N-R) algorithm to calculate μ_a , μ_s , and g from R , T , and a recordings of

MC simulated prediction data with random distributions of optical properties. Based on preliminary investigations, we chose to use third-order polynomials for our further analyses .

Thus, the principle of the applied three-dimensional MPR/N-R method is as follows:

First, we select the relevant R , T , and/or a data from the simulated 21x19x11 calibration matrix and denote them

:

[^γ\.flt^X2,flt^XXflt]= Ma a"^' Hz J (2! x A - [l μ_s μ_s² μ, & g g² g³]c

Where, X]-_{3r flt}^are functions of μ_a , μ_s , and g , and A, B and C are 4x3 matrices of fitting coefficients determined by least-squares regression. Thus, -^_.-._3,?, constitute the calibration model. The next step is to solve the inverse problem of determining μ_a and μ from recordings of the simulated prediction data sets I_H_

Then, we use the Newton-Raphson algorithm to perform converging iterative calculations of μ_a , μ_s , and g :

k = 0.1.2.3,...,

Where, h_a , h_s , and h_g are correction terms of μ_a , μ_s , and g , respectively. The calculations continue until h_a , h_s , and h have dropped below predefined maximum values .

Since the MPR/N-R method implies exactly three variables in order to predict μ_a , μ_s , and g , we have to apply some sort of dimension reduction. For this we use Principal Component Analysis (PCA) , that is, we perform PCA on the 21x19x11 calibration matrix and then use the resulting three main principal components as input i.e. X_:_₃ to the calibration and prediction algorithms. In order to test the prediction performances of the configuration in FIG. 2C, we first generated a set of prediction data with 20 random combinations of optical properties within the ranges:

0 < μ_a < 2 cm^"1 50</_i<100cm-^{1 (5)} 0.85 <g<0.95

The prediction data were generated using 1-10⁷ photons, and Table 1 shows the results from the prediction tests using these data in conjunction with the configuration in FIG. 2C. In each case the prediction errors were minimized by finding the optimal combinations of angles a and distances r .

Table 1 shows mean prediction errors for the set-up in FIG . 2C .

Mean Prediction Errors ( % )_a s⁸ μ

0.17 0.45 0.43

Table 2 shows the optimal angles and the distances corresponding to errors listed in Table 1 for the set-up in FIG. 2C. Angles θ (°) Distances r

(mm)

2.0 2.5

Claims

METHOD AND APPARATUS FOR DETERMINATION OF OPTICAL PARAMETERS OF TURBID MEDIA AND USE THEREOFCLAIMS

1. A method of determining optical parameters of a turbid medium, the method comprising

providing n measurements Y of said produced light from said sample, said n measurements being composed of ni measurements of said produced spatially resolved diffused light at different spatial positions and n₂ measurements of said produced angularly resolved scattered light at different angular positions, wherein n=nι+n₂≥m, and nχ>l and n₂>2, said spatial positions and angular positions being equal or different; and

deriving said at least m optical parameters X from said n measurements .

2. The method according to claim 1 wherein said at least m optical parameters X are determined by solving n equations Y=AX with respect to said at least optical parameters X, wherein A is a predetermined calibration matrix relating each of said n measurements Y to the optical parameters X of said sample.

3. The method according to claim 1 or 2 wherein said at least m optical parameters are the absorption coefficient μ_a, the scattering coefficient μ_s, and the anisotropy factor g (m=3), and said n measurements are at least one measurements of spatially resolved diffused light (ni≥l) and at least two measurements of angularly resolved scattered light (n₂>2) .

4. The method according to claim 1 or 2 wherein said at least m optical parameters are the absorption coefficient μ_a, the scattering coefficient μ_s, and the anisotropy factor g and the refractive index n (m=4), and said n measurements are two measurements of spatially resolved diffused light (nι>2) and two measurements of angularly resolved scattered light (n₂>2) .

5. The method according to claims 1-4 wherein said n equations are solved by Newton-Raphson iteration.

6. The method according to claims 1-5 wherein said measurements at said different spatial positions of said produced spatially resolved diffused light comprise measurement of transmitted spatially resolved diffused light and measurement of reflected spatially resolved diffused light with respect to said illuminating light illuminated onto said sample.

7. The method according to claim 6 wherein said measurement of reflected spatially resolved diffused light is substituted by a second measurement of transmitted spatially resolved diffused light in another spatial position.

8. The method according to claims 6 or 7 wherein said transmitted, reflected, or both, spatially resolved diffused lights are measured in a detector close to the sample.

9. The method according to claims 1-8 wherein one of said angularly resolved scattered lights is measured in an angle between 1 and 180 degrees, preferably 1 and 60 degrees, in particular 1 and 30 degrees, most preferred 1 and 10 degrees with respect to said axis of incidence of the illuminating light, and a second of said angularly resolved scattered lights is measured in an angle about 0 degrees .

10. The method according to claim 1 wherein said transmitted and reflected spatially resolved diffused lights and said angularly resolved scattered light are measured in one detector.

11. The method according to claims 2-10 wherein the predetermined calibration matrix is obtained from measurements on samples of the turbid medium having known optical parameters.

12. The method according to claims 2-10 wherein the predetermined calibration matrix is derived from known values of optical parameters of the turbid medium.

13. An apparatus for determining optical parameters of a turbid medium, the apparatus comprising

a compartment containing a sample of the turbid medium; illuminating light for illuminating light onto said sample when said sample is placed in said sample holder, said illuminating light illuminating the sample along an axis of incidence;

at least one spatial detector for detecting spatially resolved diffused light from at least one input/output port (ni≥l) of said sample in at least one spatial position; and

at least one angular detector for detecting angularly resolved scattered light from at least two input/output ports (n>2) of said sample in at least two different angular positions with respect to said axis of incidence; said at least one spatial detector and said at least one angular detector optionally being a single detector.

14. The apparatus according to claim 13 wherein said at least one spatial detector is positioned to measure transmitted spatially resolved diffused light and at least one other spatial detector is positioned to measure said reflected spatially resolved diffused light with respect to said illuminating light when illuminated onto said sample.

15. The apparatus according to claim 13 wherein at least two spatial detectors are positioned to measure said reflected spatially resolved diffused light and said transmitted spatially resolved diffused light; said spatial detectors being positioned in different spatial positions distal to the point of incidence of said illuminating light when illuminated onto said sample.

16. The apparatus according to claims 13-15 wherein said transmitted, reflected, or both, spatially resolved diffused lights are measured in one or more spatial detectors close to the sample.

17. The apparatus according to claims 13-16 wherein said at least one angular detector for detecting angularly one of said angularly resolved scattered lights is positioned in an angular position having an angle between 1 and 180 degrees, preferably 1 and 60 degrees, in particular 1 and 30 degrees, most preferred 1 and 10 degrees with respect to said axis of incidence of the illuminating light, and at least one other angular detector for detecting said angularly resolved scattered lights is positioned in an angle about 0 degrees.

18. The apparatus according to claim 13-17 wherein said transmitted and reflected spatially resolved diffused lights and said angularly resolved scattered light are guided in optical waveguides to said at least one spatial and said at least one angular detector.

19. The apparatus according to claims 13-18 wherein said at least one spatial detector for detecting spatially resolved diffused light from at least one input/output port (ni≥l) of said sample in at least one spatial position; and

said at least one angular detector for detecting angularly resolved scattered light from at least two input/output ports (n₂>2) of said sample in at least two different angular positions with respect to said axis of incidence is a single detector.

20. The^"apparatus according to claims 13-19 further comprising recording means for recording n simultaneous measurements Y of said at least one spatial detector and said at least one angular detectors wherein n=nι+n₂>m.

21. The apparatus according to claims 13-20 further comprising storing means for storing a predetermined calibration matrix A, said matrix comprising n measurements of said at least one spatial detector and said at least one angular detector for known at least m optical parameters X of the medium.

22. The apparatus according to claims 13-21 further computing means for providing and solving n simultaneous equations Y=AX of said n simultaneous measurements Y from said measuring means and said calibration matrix A from said storing means with respect to said m optical parameters X.

23. A computer program for use in running a computer for carrying out the method as claimed in claims 1-12.

24. A computer program as claimed in claim 23 said program being stored on a computer usable medium.

25. Use of one or more optical parameters of the turbid medium determined according to the method as claimed in claims 1-12 for the determination of one or more material parameters of the turbid medium.

26. Use according to claim 25 wherein the one or more material parameter is the concentration of one or more components of the turbid medium, said components being either dissolved or dispersed in the turbid medium.