Method and device for determining density of substance in bone tissue

FIELD: medicine.

SUBSTANCE: invention relates to medicine, namely to radiodiagnostics of bone tissue state, and can be used in determination of such diseases as osteoporosis and osteopathy. Method includes irradiation of bone tissue by collimated beam of gamma-radiation, movement of gamma-radiation source and detector with movement of irradiation zone into bone tissue depth, registration of reversely dispersed irradiation with respect to falling beam and determination of substance density. Energy of gamma-irradiation photons is selected within the range from 50 keV to 1 MeV. Movement of gamma-irradiation source and detector is carried out by layer-by-layer displacement of zone of reversely dispersed irradiation. In addition, distribution of substance density along axis of probing is obtained by calculation of density in second measurement for second layer of substance and all following dimensions of layers to n-th one, by value of density, obtained in first measurement for first layer and all measurements for (n-1) layers. Device consists of patient's extremity fixer, gamma-irradiation source, collimator and detector of dispersed gamma-irradiation, combined into rigid assembly, moved by movement device along symmetry axis with displacement of irradiation zone into bone tissue depth. Movement device includes electric drive, connected by means of mechanic transmission links with rigid assembly.

EFFECT: application of invention will make it possible to probe bone tissue to essential depth and ensures more accurate determination of substance density distribution alone axis of probing.

4 cl, 2 dwg, 1 tbl, 1 ex

The invention relates to medicine, namely to radiation diagnostics of the bone tissue, and may be used to determine, for example, diseases such as osteoporosis and osteopathy.

Bone inorganic mineral matter consists mainly of calcium phosphate and carbonate - about 65%) [France, Grunge. "Osteoporosis" /translated from German/. M: "Medicine", 1995, p.27]. Osteoporosis is a systemic disease of the skeleton from a group of metabolic osteopathy is characterized by decrease in bone mass and impaired microarchitecture bone tissue, which leads to a decrease in mineral bone density (BMD) and, consequently, to increased risk of fractures. Common after-effects of fractures associated with osteoporosis is high mortality, high levels of disability and severe economic burden borne by the patients, the healthcare system and the state as a whole. In this regard, of particular importance are methods for the quantification of osteoporosis. Measurement of BMD method is called is the main quantitative indicator in determining the severity of osteoporosis and risk of fractures. Known methods and devices, based on:

- radiography certain areas of the skeleton, along with a series of wedge-shaped x-ray manual this is it [the patent of the Russian Federation 2159577];

- quantitative measurement of calcium, bone mass and BMD using x-ray radiography, which uses a phantom with a known composition that mimics the bone. Through the area under miss x-rays, register it with the other hand and get a picture of the limbs and phantom and by comparing determine the calcium content, bone mass and BMD [U.S. patent 5335260];

- dual energy gamma absorptiometry, which quantify the mineral density of bone tissue, regardless of the presence of fat or other soft tissues. In this method, the study area is irradiated by a beam of penetrating radiation, containing gamma-radiation of the two energies, and measured the attenuation of the radiation intensity for each of these set of two energies and the results of the measurements is determined by the mass density of the bone tissue [US 3996471];

- automatic x-ray densitometry of bone tissue, which provides multiple exposures of the study area x-rays with different energy levels [U.S. patent 6320931];

- x-ray densitometry, which receive the x-ray image of the object in the different energy fields of radiation using a fluorescent screen that is sensitive to different the m areas energy x-ray radiation, made in the form of a multilayer screen, each layer which absorbs x-ray radiation in its energy range. With each layer of the screen, closer to the object, serves as a filter for subsequent layers, with each layer emits light in different layers of the wavelength range, and the resulting optical image obtained using tsvetochuvstvitelnyh sotapanna [international application WO2008033051];

- low-dose rate measurement of the mineral content in bone by measuring the backscattering of gamma radiation from the bones and comparing the intensities of two spectral regions of the back-scattered radiation. This is one area of the spectrum of A₁due to coherent or Thomson-Rayleigh scattering, and the other As₂- a combination of Rayleigh and Compton radiation. Setting W=A₁/A₂approximately linearly dependent on the content of minerals in the bone, since the coherent scattering is mainly determined by the content of calcium in bone tissue [U.S. patent 5351689].

Most of the known methods for their implementation require a very expensive, large and heavy equipment, and in some cases are accompanied by high dose irradiation. Systems such as, for example, devices for dual energy gamma absorptiometry, require the exchange is consistent placement and can be serviced only by qualified personnel. As a result, their use is limited to only a small number of large, well-funded medical clinics.

Meanwhile, for mass screening studies and initial detection and prevention of osteoporosis patients require portable devices, with which you could quickly carry out non-invasive, inexpensive, low doses of the study of the mineral content in bone that does not require complicated techniques for the analysis of measurement results.

The closest selected for the prototype are the method and apparatus of determining the content of mineral substances in the calcaneus [U.S. patent 6252928]. In the known method prototype produce radiation calcaneus collimated beam of gamma radiation and register the radiation scattered in the backward direction with respect to the incident beam. The calcium content is determined by the intensity of gamma radiation scattered in the opposite direction from the heel bone. The device includes a support frame for fixing the legs of the patient and installed it axially symmetric collimator, which houses the radioactive source, and coaxially with him cylindrical symmetric scintillation detector. As a source of gamma radiation using¹⁰⁹Cd (T_1/2=1,29 year), which emits caracteristicile x-ray K-series silver with energy 22-25 Kev. The gamma-ray source, collimator, radiation and a detector of back-scattered gamma radiation are located on the same axis of symmetry and United into a rigid Assembly that is configured to move along the guide rails along its symmetry axis, and spring-loaded to ensure tight contact with the leg of the patient, which is fixed on the base frame so that the rear part of the heel was in front of the source of gamma radiation. The method is based on measuring the intensity of back-scattered from the calcaneus gamma radiation source. The choice of the energy of the gamma radiation produced so as to provide a strong dependence of the absorption intensities of the primary and scattered radiation from the calcium content. Gamma radiation is scattered in the tissues of the heel and recorded by a scintillation detector, the signal from the detector of the scattered gamma radiation is supplied to the recording unit and compared with the signals received from earlier standards mineral density. This is compared with the standards to judge the content of calcium in the studied object. Periodic measurement of the calcium content in the heel bone of the patient using this method allows you to monitor changes in bone density during the development of osteoporosis.

The known method and apparatus have a number of disadvantages. Among them is the choice of the bottom of the second energy used gamma radiation. As a consequence, the study can only be conducted for those bones that are hidden by a small thickness of soft tissues, such as the calcaneus. The intensity of the scattered radiation depends not only on the content of calcium in the bone tissue, but also on the thickness of the soft tissues, which is usually unknown, and the measurement result will be distorted. In addition, this method allows you to get only an average value of the density of the investigated bone. In this way it is impossible to obtain the density distribution of the material inside the bone.

The basis of the present invention the goal is to create accurate and reliable method of determining the density of a substance in the bone tissue and the device, allowing to probe the bone tissue to a considerable depth and to measure not only the average but also the density distribution of matter along the axis sensing.

The problem is solved in that in the method of determining the density of a substance in bone tissue, comprising, as a prototype, the irradiation of bone collimated beam from a source of gamma radiation, the movement of the gamma-ray source and detector with the displacement of the irradiation zone deep into the bone, registered by the detector back-scattered radiation with respect to the incident beam and the determination of the density prophetic the STV on the results of measurement of back-scattered radiation, according to the invention the energy of the photons of gamma radiation is chosen in the range from 50 Kev to 1 MeV, the movement of the gamma radiation source and detector is carried out with the possibility of layer-by-layer displacement zone of the back-scattered radiation, and obtaining the density distribution of matter along the axis of the sensing performed by calculating the density in the second dimension for the second substance layer and all subsequent measurements of the layers up to the n-th value of the density obtained in the first measurement for the first layer and all the measurements for (n-1) layers.

The problem is solved also by the fact that the device for determining the density of a substance in the bone tissue, containing, as a prototype, the latch limb of the patient, the gamma-ray source, collimator, radiation and a detector of scattered gamma radiation, arranged on the same axis of symmetry and United into a rigid Assembly that is configured to move through the device move along the symmetry axis with the displacement of the irradiation zone deep into the bone block the signal from the detector of the scattered gamma radiation associated with the computer, unlike the prototype, the moving device includes an actuator associated gear reduction units with hard Assembly and connected to the control unit moves associated with the computer the leader.

It is advisable to perform a drive in the form of an electric motor and sensor positioning a rigid Assembly that is associated with the control unit moving.

It is also advisable to perform a drive in the form of a stepper motor.

The essence of the proposed method of measuring the mineral content of bone tissue lies in the fact that the movable detector of gamma radiation back-scattered radiation from a small area (about 2 cm²section of a thin layer (about 3 mm) of the subject bone. In this case, the detector can be moved along the direction sensing synchronously with the said site of exposure, always being at the same distance from him. This is because the detector and the radiation source are rigidly connected and placed in the collimator. The collimator is made of metal of high density forms a cylindrical or conically converging (in the direction of the sensing ring beam of gamma radiation. In addition, the collimator passes into the detector back-scattered gamma radiation only mentioned a small area of bone tissue. Thus, there is the possibility of layer-by-layer density measurement, and the small volume of substance, i.e. it is possible to obtain the density distribution of matter along the axis sensing. ), The public honors from the prototype is the use of hard gamma radiation, up to 1 MeV, and the moving Assembly source/collimator/detector radiation in the measurement process. The use of hard gamma radiation allows to probe the bone tissue to a considerable depth. At these energies the dominant process is Compton scattering, which directs photons in the opposite direction in the detector. The higher the density, the greater is the dispersion and the more radiation detector registers.

Figure 1 shows a diagram of the inventive device with electric drive on the basis of the stepping motor and for determining the content and distribution of the material density in trabecular bone type calcaneus (heel bone).

The device contains latch 1 with restrictive straps 2 for stationary limb of the patient 3, and axially symmetric collimator 4 made of metal of high density, the gamma radiation source 5, the radiation detector 6, are combined in a rigid Assembly 7. The movement Assembly 7 provides a moving device including the actuator on the basis of the stepping motor 8 and the gear reduction system of units 9, 10, 11, connecting the stepping motor 8 with a rigid Assembly 7 and the control unit moves 12 rigid Assembly 7 connected to the stepper motor 8. The radioactive source is made in the form of a ring, the axis of which coincides with the axis 13 cylindrically symmetric detector 6 radiation, such as NaI (TI) scintillator. Unit 14 the signal from the detector is connected to the detector 6. In turn, both units 14 and 12 through the interface unit 15 is connected to the computer 16.

The device operates as follows.

The limb of the patient 3 is fixed by the belt 2 in the latch 1. Assembly 7 consisting of a source 5 of gamma radiation, the collimator 4 of the radiation detector 6 back-scattered gamma radiation, taken to the extreme from the limb of the patient position. When the Assembly 7 is in this position, the area from which the detector 6 detects back-scattered radiation, is located on the surface of the limb of the patient 3. Make the first measurement and the obtained value is save in a special file of the computer 16. This value is the calculated density of the first substance layer. Then at the command of the control unit moving 12 associated with the computer 16, the moving Assembly 7 in the direction of the limb of the patient 3 a distance equal to the width of the layer area measurements (approximately 3 mm). Moving, Assembly 7 stops. Now the area from which the detector 6 detects back-scattered radiation, is located at a depth of one layer measurements inside the limb of the patient 3. Make the second measurement and the received value is also maintained in the same file. From this value and the value obtained in the first measurement will be calculated density of the second layer of the substance. Next, all the described process is repeated, and thus the measurement zone, layer by layer, moving deep into the limb of the patient. The density of the substance in the n-th layer in the measurement is calculated using the values obtained from all previous measurements for (n-1) layers. So, as the check-in area back-scattered radiation into is the determination of the density distribution of matter in the study of bone tissue.

The movement Assembly 7 is as follows. When the Assembly 7 rests, its position is known, it is either the initial position or the position in which you were n-th dimension. Therefore, if the drive is made on the basis of the stepper motor 8, the control unit moving 12 supplies the stepping motor 8 required number of pulses corresponding to the movement of the width of the layer measurements, and moves the Assembly 7 to the next measurement. If the drive is made on the basis of the conventional motor, the control unit moving 12 associated with the computer 16, starts it, and produces a position monitoring Assembly according to the information received from the positioning sensor (not shown in figure 1), the implementation of the tion, for example, on the basis of LEDs and photodiodes. As soon as the Assembly is moved in the width of the layer measurements, the control unit moving 12 off the motor 8.

As an example of the method and implementation, the devices consider the following option. Was specified function of density of a substance to the distance into the object. Figure 2 shows the graph of this function. Was carried out numerical simulations for four different photon energy: 50 Kev, 250 Kev, 500 Kev, 1 MeV.

The following instrument parameters were taken for all four examples.

Full source activity 5 2.6×10⁷photon/sec.

After the collimator 4 in the incident beam particle count was 4.1×10⁵.

The diameter of the ring source 5 was 3.2, see

The diameter of the detector 6 was 3.0, see

The diameter of the zone in which the measured density of the substance, 2,0, see

The width of the layer in which the measured density of the substance, 0,3, see

The distance from the source 5 to the measurement zone to 8,0 see

The distance from the detector 6 to zone measurement 10,0 see

For each substance layer had 10 seconds of measurement time.

The calculation of the density layers of matter gives the same result for any of these 4 photon energy (what should be), so the calculated density is given in a single table column. However, the accuracy with to the Torah, the result for the density of the substance, different for different energies and layers. The most uniform results on the accuracy gives the energy of 1 MeV (~8% for the outer layers and ~20% for a depth of 10 cm). The highest precision (~5%) is obtained for the energy of 50 Kev and outer layers. To increase the measurement accuracy is sufficient to increase the measurement time or the intensity of the source, or both together. The results are shown in the table.

The range of photon energy from 50 Kev to 1 MeV is chosen from the condition of matching two contradictory requirements, namely allowable radial load on the patient and obtain the necessary accuracy of measurement of density of substance of bone tissue. Within this range, the penetrating power of radiation and the proportion of back-scattered photons sufficient to solve the technical problem set out in this invention. Beyond the boundaries of this range, for energies less than 50 Kev, the penetrating ability of the radiation becomes insufficient to solve the problem, and for energies above 1 MeV begins the photoproduction of electron-positron pairs, which leads to a relative decrease in the fraction of Compton scattering and, as consequence, to decrease to an unacceptable level the number of photons entering the detector.

Using the proposed method and device allow to probe the bone tissue to a considerable depth (~10 cm) and calc is th the density distribution of matter along the axis sensing with the required precision.

In addition, layer-by-layer measurement allows to determine the density of a substance located in the depth of the object of study (i.e. bone), with the required accuracy as possible, by calculation, to eliminate the effect of the outer layers (i.e. soft tissue), distorting the measurement results. This fact gives the opportunity to conduct research not only for bone substance, under a thin layer of soft tissue, but also in other parts of the body of the patient.

1. The method of determining the density of a substance in bone tissue, comprising the irradiation of bone collimated beam from a source of gamma radiation, the movement of the gamma-ray source and detector with the displacement of the irradiation zone deep into the bone, registered by the detector back-scattered radiation with respect to the incident beam and determining the density of a substance on the results of measurement of back-scattered radiation, characterized in that the energy of photons of gamma radiation is chosen in the range from 50 Kev to 1 MeV, the movement of the gamma radiation source and detector is carried out with the possibility of layer-by-layer displacement zone of the back-scattered radiation, and obtaining the density distribution of matter along the axis of the sensing performed by calculating the density in the second dimension for the second substance layer and all subsequent measurements of the layers up to the n-th, the density value obtained in the first measurement for the first layer and all the measurements for (n-1) layers.

2. Device for determining the density of a substance in bone tissue containing the latch limb of the patient, the gamma-ray source, collimator, radiation and a detector of scattered gamma radiation, located on the Noi to the axis of symmetry and United into a rigid Assembly, made with the possibility of moving through the device move along the symmetry axis with the displacement of the irradiation zone deep into the bone block the signal from the detector of the scattered gamma radiation associated with the computer, wherein the moving device includes an actuator associated gear reduction units with rigid Assembly and connected to the control unit moves associated with the computer.

3. The device according to claim 2, characterized in that the actuator includes a motor and sensor positioning a rigid Assembly that is connected to the control unit moving.

4. The device according to claim 2, characterized in that the actuator includes a stepper motor.