WO1994015181A1

WO1994015181A1 - A method and device for determining the level of gaseous or liqu id media in tubes

Info

Publication number: WO1994015181A1
Application number: PCT/SE1993/001087
Authority: WO
Inventors: Janne Lundberg; Thord Nilson; Tjorsten Silander
Original assignee: Ab Tesi
Priority date: 1992-12-18
Filing date: 1993-12-17
Publication date: 1994-07-07
Also published as: SE9203834L; SE9203834D0

Abstract

The present invention relates to a method for determining the level of gaseous or liquid media that have different optical reflec tion properties and are contained in a tube. According to the invention, a generally horizontal laser beam is caused to impinge on the tube at an angle such that no directly reflected light will impinge on the laser. The intensity of the light reflected from the tube is measured by at least one detector and the laser beam and the detector or detectors are moved vertically along the height of the tube. The measurement values obtained from the detector or detectors are recorded during movement of the laser, and the levels of the media contained in the tube are calculated on the basis of the recorded measurement values, these values being different for different media due to the different reflective properties thereof. The method can be applied with particular advantage to determine the sedimentation rate of blood. The invention also relates to a device for carrying out the method.

Description

A Method and Device for Determining the Level of Gaseous or Liquid Media in Tubes

The present invention relates to a method for deter- mining the level of gaseous or liquid media that have different optical reflection properties and are con¬ tained in a tube. The method relates particularly, but not exclusively, to measuring the level of red blood cells in relation to blood plasma in the so-called sedimentation reaction in blood (" blood sedimentation rate". The invention also relates to a device for carrying out the method.

One of the most common blood tests is the so-called blood sedimentation test. In different cases of sick¬ ness and disease, the blood cells tend to agglomerate into a rouleau formation and therewith will settle more quickly at the bottom of an upright tube, to which an anticoagulant has been added. The supernatant liquid layer is comprised of plasma and the height of this clear layer in millimeters denotes the value of the settling reaction, which is measured precisely one hour after having placed the test tube and sample in a measuring stand. A large number of sedimentation tests are performed every day in doctors' surgeries, medical consultation rooms, hospitals, blood donation centres and laboratories. It is necessary to activate for each sample concerned a timing clock which rings after a time period of sixty minutes has lapsed from the time of starting the clock, whereupon it is necessary to interrupt all other activities in order to read the value of the sedimentation reaction. This greatly disturbs other activities and it has long been consid¬ ered highly beneficial to automatize reading of the sedimentation reaction.

Swedish Patent Specification No. 8009126-7 describes a method of obtaining automatically an indication of the boundary surface between plasma and sedimented blood cells after one hour. According to this patent speci¬ fication, there is used in the sedimentation tube a body which swells when absorbing blood and plasma. The body has a density which causes it to float in the boundary layer between blood vessels and plasma. After one hour, the body will have swollen to an extent such as to fasten to the wall of the tube.

One drawback with this known method resides in the necessity of placing the body in the tube, and conse¬ quently present-day standardized routines for measur¬ ing the blood sedimentation rate have been changed, among other things.

Swedish Patent Specification No. 8904207-1 describes a method of measuring the difference in impedence be¬ tween plasma and sedimented blood cells. It has been found, however, that this signal is so weak as to make reading of the sedimentation value difficult in prac- tice.

There has long been a desire to fully automatize reading of the sedimentation reaction while retaining present test routines, with the aid of methods with which no device except the test tube will come into contact with the blood.

There is also a need in industry to read positively the level of different gaseous or liquid media in riser pipes or overflow pipes, for instance.

An object of the present invention is to satisfy these desiderata, and in particular to provide a method and a device which will enable reading of the sedimenta- tion reaction in a test tube or in a plurality of mutually sequential test tubes to be automated.

According to the invention, this object is achieved with a method of determining the level of gaseous or liquid media having different optical reflection properties and contained in a tube, wherein the method is characterized by causing a generally horizontal laser beam to impinge on the tube at an angle such that no directly reflected light will fall on the laser, measuring the intensity of light reflected from the tube with the aid of at least one detector, moving the laser beam and the detector or detectors along the length of the tube, recording the measurement values obtained from the detector or detectors during said movement along the tube, and calculating the level of the media contained in the tube on the basis of the recorded measurement values, said measurement values being different for different media due to the different reflective properties thereof.

In one preferred embodiment of the invention for determining the blood sedimentation reaction, the tube is comprised of a sedimentation tube, i.e. a test tube which has been pre-treated with an anticoagulant and which is filled with whole blood and placed on a reading stand, whereafter the blood cells are allowed to settle over a period of one hour and the height of the plasma column above the sedimented blood cells and/or the height of the column of blood cells is then determined by causing a generally horizontal laser beam to impinge on the sedimentation tube at an angle such that no directly reflected light will fall on the laser, measuring the intensity of the light reflected from the sedimentation tube with the aid of at least one detector, moving the laser beam and the detector or detectors along the length of the tube, and record¬ ing the measurement values obtained from the detector or detectors during said movement along the tube, and calculating the sedimentation rate of the blood on the basis of the recorded measurement values.

According to one advantageous variant of this embodi¬ ment of the inventive method, the detector or detec- tors is/are positioned so that they will only be impinged upon by reflected diffuse light. The inven¬ tion is preferably applied such that a horizontal row of vertical sedimentation tubes are measured with the aid of one and the same laser beam which is moved horizontally along the row of tubes until directly reflected light from the outer surface of the tube in the row to be measured impinges on a detector which is located on the same level as the laser beam. After the laser beam has been positioned in front of the sedi¬ mentation tube whose contents are to be measured, said tube being indicated by light that is reflected di¬ rectly from the outer surface of the tube and impinges on the detector on the same level as the laser beam, the beam is moved horizontally forwards and backwards around this position so as to determine the horizontal position in which reflected diffuse light gives the strongest possible output signal from the aforesaid detector. The measurement values can be obtained conveniently from one or more detectors placed on a vertical level that is different to the vertical level of the laser beam.

The invention also relates to a device for carrying out the aforesaid method. This device is characterized in that it comprises a unit which includes a laser and at least one detector for reflected light, wherein the laser is so positioned in relation to the tube con¬ taining said media whose levels are to be measured, that light reflected directly from the tube will not impinge upon the laser, means for moving the unit vertically, means for recording the signals of said detector or detectors, and means for determining the boundaries or interfaces between the media contained in the tube on the basis of said signals.

According to one advantageous embodiment of the inven¬ tive device, the device includes a stand for support¬ ing a sedimentation tube or a horizontal row of sedi- mentation tubes and means for moving the unit horizon¬ tally together with the means for moving said unit vertically. A glass plate is arranged between the unit containing the laser and the detector and the sedimen- tation tube, and the laser beam impinges on the glass plate at an angle other than 90°. The laser beam forms with the normal to the plane of the glass plate an angle of up to 45° and an advantage is gained when at least one detector is placed on a vertical level different to the vertical level of the laser.

An exemplifying embodiment of the invention will now be described in more detail with reference to the accompanying drawings, in which

Figure 1 is a schematic perspective view of one part of a preferred embodiment of an inventive device;

Figure 2 illustrates the device of Figure 1 schemati- cally from above;

Figure 3 illustrates schematically the beam path in one variant of an inventive device; and

Figures 4A-4C illustrate schematically different detector patterns for a device constructed in accor¬ dance with the invention.

The inventive device includes a laser 1 which is carried by a carrier 3 together with a detector 2, preferably a photodiode. The carrier 3 is carried in turn by a slide rod 4 and a spindle 5, which rotates in a nut (not shown) mounted within the carrier 3. The spindle 5 is journalled for rotation in respective upper and lower blocks 6 and 7 and is rotated by means of a motor M attached to the lower block 7. The carri¬ er 3 can thus be moved up and down between respective blocks 6, 7, by activating the motor M. The blocks 6, 7 are mounted on a frame 8 which is carried for horizontal movement by a spindle 9 and a slide rod 10, similar to the carrier 3. Although not shown, the spindle 9 and the slide rod 10 are mounted in a fixed frame on which a motor for rotating the spindle 9 is mounted.

The device illustrated in Figure 1 is also provided with a position indicator which indicates the position of the laser 1 in a vertical direction and also possi¬ bly in a horizontal direction. The position indicators may be of an inductive type, particularly when DC motors are used to rotate the spindles 5 and 9, or may be stepping motors with which the stepping movements of the motors are measured and used as a basis for determining the position of the laser.

Figure 2 illustrates the part of the inventive device illustrated in Figure 1 from above and shows said part placed behind a row of sedimentation tubes 11. As shown in Figure 2, a glass plate 12 is placed between the row of tubes 11 and the unit comprised of the laser 1 and the detector 2. The Figure also shows that the laser and the detector are inclined to the plane of the carrier 3 at an angle α.

When the device illustrated in Figures 1 and 2 is in operation, the laser beam is moved up and down a sedimentation tube 11, for example the tube furthest to the right in Figure 2, and the reflective light detected by the detector 2 is recorded continuously by some appropriate recording unit, preferably a micro¬ processor. Because the strength of the reflected light will vary according to whether the laser beam impinges on a part of the tube which contains sedimented blood cells, blood plasma or air, it can be determined from the measurement values read-off where the boundary lines between blood cells and blood plasma or between blood plasma and air are located. Because the position of the laser is also given by the aforesaid position indicators, the heights of these boundary lines is also known, therewith enabling the height of the plasma column to be calculated readily in an appropri- ate calculating or computing device, for instance by the aforesaid microprocessor.

As will be seen from Figure 2, the laser beam L falls obliquely on the glass plate 12 and forms an angle a to the normal to the plane of the glass plate. This avoids light L reflected directly from the glass plate from entering the laser 1 or the detector 2, which would render meaningful measuring impossible, since the strength or intensity of light reflected directly from the glass plate is greater than the strength or intensity of the reflected diffuse light that the detector 2 is intended to detect. The angle α may reach 45°. Light L and L reflected directly from the outer surface and inner surface of the sedimenta- tion tube is also prevented from entering the detector 2. The detector 2 is reached solely by reflected diffuse light L during vertical movement of the laser 1 along the tube located furthest to the right in Figure 2.

Naturally, the direction in which light L , L is reflected directly from the sedimentation tube will also depend on the lateral position of the laser 1 relative to the tube. An example of this is shown in Figure 3, in which direct reflection from the outer surface of the tube passes into the detector 2. The relatively strong signal then delivered by the detec¬ tor can be used to indicate that the laser beam has impinged on a tube or to determine the correct lateral position of the laser in relation to the tube whose contents are to be measured when moving the laser sideways between different tubes. In order to carry out the actual measuring process, the laser is moved slightly sideways so that only diffuse light will impinge on the detector 2. Preferably, movement of the laser to a measuring position is effected after having moved the laser forwards and backwards around the position of direct reflection from the outer surface of the tube in order to choose a position in which the strongest possible output signal is obtained from diffuse light. When moving the laser, however, it shall be ensured that the laser beam will not pass through a diametrical plane in the sedimentation tube, so as to avoid direct reflections into the laser.

According to a variant of the embodiment illustrated in Figures 1 and 2, several detectors can be arranged in different patterns around the laser. This is illuε- trated schematically in Figures 4A-4C, which illus¬ trate three examples of detector patterns.

In the Figure 4A variant, a detector 22 is arranged vertically beneath the laser 21. This ensures that directly reflected light will not reach the detector, since the direct reflections lie in the same horizon¬ tal plane as the laser beam. In the Figure 4B variant, two detectors 32, 33 are arranged beneath the laser 31, while in the Figure 4C variant, two detectors 42, 43 are arranged above the laser 41 and two detec¬ tors 44, 45 are arranged beneath the laser. In addi¬ tion, a detector 46 is arranged on one side of the laser 41 and on the same vertical level as said laser, this detector being used to determine the lateral position of the laser. In the case of this variant, measuring can be effected in the point at which the laser beam reflected directly from the outer surface of the tube impinges on the detector 46, since the detectors 42-45 can be used to effect the actual measuring process. One advantage obtained with the use of several detectors is that a stronger measuring signal is obtained by addition, therewith enabling a laser of weaker power to be used, which is beneficial from a safety aspect since the requirement for the tubes to be visible and accessible from in front of the tubes makes it difficult to screen outgoing laser radiation.

If the blood plasma is so permeable to light that no measurable diffuse light is reflected as the laser beam passes through the tube, it is conceivable to utilize the light rays (L in Figures 1 and 3) that are reflected directly from the inside of the tube to determine where the partition line between air and blood plasma lies. Because the refractive index of air and blood plasma differ from one another, the lateral position of this light beam will vary according to whether the laser beam passes through plasma or air. The boundary line between plasma and air will thus be indicated by lateral movement of the light beam L reflected from the inside of the tube.

According to one variant of the invention, it is also possible to utilize this difference in refractive index to fully determine the vertical height of the plasma column, by moving the laser beam vertically up and down after having determined the position of the beam L reflected from the inside of the tube and said 3 beam having impinged on a given detector. As the laser beam reaches the air layer above the plasma column during upward movement of the laser beam, the light reflected from the inside of the tube will have a different direction due to the differing refractive index of the air, which enables the boundary line between air and plasma to be indicated because the detector no longer records directly reflected light. When the laser beam impinges on sedimented blood cells as the beam is moved downwards, the laser light is absorbed and no light is reflected from the inside of the tube. The boundary line between plasma and blood cells is also detected in this case by the fact that no directly reflected light impinges on the detector. The direction of the light L reflected from the outer surface of the tube is independent of the content of the tube and direct reflection from the outer tube surface can thus be distinguished from the direct reflection from the inside of the tube, because this reflection does not change direction and passes beyond the detector on one occasion during vertical movement of the laser along the tube.

The laser used in the described device is preferably of the same type as the lasers used in CD players and may be comprised of a 5 mW semiconductor laser desig¬ nated LT022PD, while the detectors may comprise the pin diode BPW34.

The laser is preferably spaced at a distance of 20-60 mm from the sedimentation tube, which normally has a diameter of about 10 mm. By using a laser as the light source, there is obtained a beam which has a small focus point and high light intensity, which provides good measuring precision. The liquid present in the transilluminated part of the tube will under such conditions have a diameter of 0.1-0.3 mm. The accuracy of the optical measurement becomes 1 mm ±0.1 mm and the accuracy to which the position of the laser is determined can be also maintained at the same level.

The described measuring device is intended to deter¬ mine the sedimentation rate of blood after one hour of sedimentation in the sedimentation tube and the afore¬ said microprocessor will give automatically a signal when the measuring process shall commence. In order to make this possible, it is necessary to inform the microprocessor when a sedimentation tube is placed in the stand in front of the actual measuring device. This can be achieved in many different ways, for instance by placing pressure-sensitive sensors in the bottom of the stand, so that the sensors will be activated by the weight of the tubes. Alternatively, the person taking the blood sample may indicate where the tube has been placed with the aid of a keyboard, wherein the time at which this position is indicated is taken as a starting point for the countdown from the microprocessor. In this latter case, the person who has taken the sample may also enter the identity of the person from which the sample was taken together with other information that may be considered valuable together with the measurement value on a later print- out from the microprocessor.

The result of the measuring process is either printed out by a printer or shown on a display. The result may also be transmitted directly to a central computer system in which patient information is stored. A computer unit may also be arranged to store the sedi¬ mentation value for a short or longer period of time, for instance for one or more weeks, wherein a series of blood sedimentation values for one and the same patient can be printed out in response to a command entered through a keyboard. Naturally, it is also possible to program the computer so as to print out temporal variations in the blood sedimentation values in a graphic form. Identification of patient and corresponding blood tests can be effected with bar codes and personal identity numbers.

The described exemplifying embodiment can be modified so as to read-off the relevant state of the blood sedimentation sequence after the lapse of a selected period of time shorter than one hour, if so desired.

As will be understood, the microprocessor automatical¬ ly controls the activation of respective spindle drive motors for horizontal and vertical movement of the laser on the basis of the aforesaid information relat¬ ing to where and when a sedimentation tube is placed in the tube stand. It will also be understood that the aforedescribed device can be modified in many ways within the scope of the present invention. For instance, a single vertically movable laser may be provided for each tube and the measuring process can be controlled by a time clock which is activated by the person placing the tube in the tube stand. Evaluation of the signals delivered by the detector or detectors, however, shall still be effected by means of a microprocessor or equivalent means. Furthermore, the lateral positions of the laser may be calibrated and programmed before¬ hand, so as to obviate the necessity of determining the lateral position of the laser prior to each mea¬ suring operation. Furthermore, other types of drive systems, for instance belt drives, rack and pinion drives, hydraulic or pneumatic motors, etc., may be used to move the laser horizontally and vertically. Neither shall the invention be considered restricted to the aforedescribed method and device for determin- ing blood sedimentation rate, since the method and device can also be used in laboratories and within industry, for instance the medical and chemical indus¬ try, for measuring the levels of gaseous or liquid media in tubes, and in particular in pipes, for in- stance riser pipes, where solely one side of the pipe is available for measurement, since reflected light is utilized in the measuring process. The invention is therefore limited solely by the content of the follow¬ ing Claims.

Claims

1. A method for determining the level of gaseous or liquid media that have different optical reflection properties and are contained in a tube, characterized by causing a generally horizontal laser beam to im¬ pinge on the tube at an angle such that no directly reflected light will fall on the laser; measuring the intensity of light reflected from the tube by means of at least one detector; moving the laser beam and the detector or detectors vertically along the length of the tube; recording the measurement values obtained from the detector or detectors during said movement; and calculating the level of the media contained in the tube on the basis of the recorded measurement values, these values being different for different media owing to the different reflective properties of said media.

2. A method according to Claim l for determining the sedimentation reaction of blood, characterized in that the tube is a sedimentation tube (11) , i.e. a test tube which has been pre-treated with an anticoagulant and which is filled with whole blood and placed on a reading stand, wherein the blood is then allowed to sediment for one hour and the height of a plasma column above sedimented blood vessels and/or the height of the column of blood vessels is then read-off by causing a generally horizontal laser beam (L) to impinge on the sedimentation tube at an angle such that no directly reflected light will impinge on the laser; in that the intensity of the light (L ) re¬ flected from the tube is measured by at least one detector (2) ; in that the laser beam and the detector or detectors are moved vertically along the length of the tube; in that the measurement values obtained from the detector or detectors are recorded during said movement; and in that the sedimentation rate of the blood is calculated on the basis of the measurement values recorded.

3. A method according to Claim 1 or 2, characterized in that the detector (2) is positioned so that only reflected diffuse light (L ) will impinge thereon.

4. A method according to any one of Claims 1-3, in which the contents of a horizontal row of vertical sedimentation tubes are measured with the aid of a laser beam (L) , characterized in that the laser beam (L) is moved horizontally along the row of tubes (11) until light (L ) which is reflected directly from the outer surface of the tube to be measured impinges on a detector (2; 46) arranged on the same vertical level as the laser beam (L) .

5. A method according to Claim 4, characterized in that the laser beam (L) is placed in front of the sedimentation tube (11) to be measured, this position being indicated in that directly reflected light (L ) from the outer surface of the tube impinges on the detector (2; 46) on the same vertical level as the laser beam; in that the laser beam is then moved horizontally forwards and backwards around this posi¬ tion so as to determine the horizontal position in which reflected diffuse light will produce the stron¬ gest possible output signal from said detector.

6. A method according to any one of Claims 1-5, characterized in that the measurement values are obtained from one or more detectors (22; 32, 33; 42- 45) located on a vertical level that is different to the vertical level of the laser beam.

7. A method according to Claim 1, characterized in that light reflected directly from the inside of the tube is caused to impinge on one detector; and in that the level of the medium through which the directly reflected light passes is determined by recording the point at which the signal from the detector of directly reflected light ceases as the laser moves vertically.

8. A device for determining the level of gaseous or liquid media that have different optical reflection properties and are contained in a tube, characterized in that the device comprises a unit which includes a laser (1) and at least one detector (2) for reflected light, wherein the laser is so placed in relation to the tube containing said media, whose levels are to be determined, that light (L -L ) reflected directly from the tube will not impinge on the laser; means (5, M) for moving the unit vertically; means for recording the signals produced by the detector; and means for determining the boundaries between different media on the basis of these signals, said signals being differ¬ ent for different media due to the different reflec- tive properties of said media.

9. A device according to Claim 8 for determining the sedimentation rate of blood, characterized in that the tube is a vertically positioned sedimentation tube (11) filled with whole blood, and in that the device includes a timing device.

10. A device according to Claim 9, comprising a stand for accommodating a horizontal row of sedimentation tubes (11) , characterized in that the device includes means (9) for moving the unit horizontally together with its vertical movement means (5, M) .

11. A device according to any one of Claims 8-10, characterized in that a glass plate (12) is placed between the tube (11) and the unit comprising the laser (1) and the detector (2) ; and in that the laser beam (L) impinges on the glass plate (12) at an angle other than 90°.

12. A device according to Claim 12, characterized in that the laser beam (L) defines an angle (or) of up to 45° with the normal to the plane of the glass plate (12).

13. A device according to any one of Claims 8-12, characterized in that at least one detector (22; 32, 33; 42-45) is placed on a vertical level that is different to the vertical level of the laser (1) .