RU2750976C1 - Method for determining density of bone tissue based on standing wave emission from peripheral skeleton microseisms - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to the field of medical methods for determining density of bone tissue, particularly, diagnostics of osteoporosis in the peripheral parts of the skeleton. The method for determining density of bone tissue is based on isolation of standing waves from microseisms of the peripheral skeleton. Noise records are therein recorded on the surface of the body at observation points for at least 5 seconds at a sampling frequency of 1000 kHz. The records are divided into fragments with a duration of 8192 counts and the amplitude spectra thereof are calculated. For each observation point, the amplitude spectra of all fragments are averaged. The presence of standing waves is determined by the appearance of quasi-regular peaks in the averaged spectrum of fragments of noise records. The quality factor is calculated, and the density of bone tissue is estimated by the value thereof.

EFFECT: reduced harmful effects on humans are ensured due to the absence of X-ray emission in obtaining diagnostic characteristics of osteoporosis by using elastic standing waves for estimation of mineral density of bone tissue.

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Description

The invention relates to the field of medical methods for determining the density of bone tissue, in particular, the diagnosis of osteoporosis in the peripheral parts of the skeleton.

Osteoporosis is an asymptomatic condition that is often only diagnosed when a fracture occurs. About 200 million people worldwide suffer from osteoporosis, and 8.9 million fractures occur annually. The prevalence of fracture of the proximal femur is 18-23% [Kanis JA, Cooper C, Rizzoli R et al (2017) Identification and management of patients at increased risk of osteoporotic fracture: outcomes of an ESCEO expert consensus meeting. Osteoporoslnt 28: 2023-2034; WD Leslie, SR Majumdar et al (2018) Performance of FRAX in clinical practice according to sex and osteoporosis definitions: the Manitoba BMD registry..Osteoporosislnternational 29: 759-767.] Spine - 75.6% of all fractures [Marshall D, Johnell O, Wedel H (1996) Metaanalysis of how well measures of bone mineral density predict occurrence of osteoporotic fractures. BMJ 312: 1254-1259; Stone KL, Seeley DG, Lui LY, Cauley JA, Ensrud K, Browner WS, Nevitt MC, Cummings SR, Osteoporotic Fractures Research Group (2003) BMD at multiple sites and risk of fracture of multiple types: long-term results from the Study of Osteoporotic Fractures. J BoneMiner Res 18 (11): 1947-1954. https://doi.org/10.1359/jbmr.2003. 11/18/1947]. Fractures of the proximal femur are one of the main causes of reduced quality of life and mortality [Leslie WD, Lix LM, Johansson H, Oden A, McCloskey E, Kanis JA, Manitoba Bone Density Program (2010) Independent clinical validation of a Canadian FRAX tool: fracture prediction and model calibration. J BoneMinerRes 25 (11): 2350-2358. https://doi.org/ 10.1002 / jbmr.l23; Kanis JA, McCloskey EV, Johansson H, Oden A, Melton LJ III, Khaltaev N (2008) A reference standard for the description of osteoporosis. Bone 42 (3): 467-475. https://doi.org/10.1016/j.bone. 2007.11.001].

In the Russian Federation, 34 million people are at risk of osteoporotic fractures (14 million people suffer from osteoporosis, 24 million have osteopenia). It is estimated that every minute in the country, people over 50 have 7 vertebral fractures, every 5 minutes - a hip fracture. Mortality after a hip fracture in a number of Russian cities reaches 45-52% [Goh, Maylyn; Nguyen, Harm H. Identifying and addressing osteoporosis knowledge gaps in women with premature ovarian insufficiency and early menopause: A mixed-methods study / CLINICAL ENDOCRINOLOGY): 1-10 / DOI:10.1111/cen.14049]. Thus, early diagnosis of a decrease in bone mineral density is of great importance, allowing for timely treatment and prevention of fractures.

The main diagnostic methods for osteoporosis are quantitative computed tomography, quantitative ultrasound densitometry and the "gold standard" diagnosis - dual energy X-ray densitometry (DEXA), [Kim T-H, Lee Y-S, Byun DW, Jang S, Jeon D-S, Lee H-H. (2013) Evaluation of the Osteoporosis health belief scale in Korean women. J BoneMetab. 20 (l): 25-30; Horan ML, Kim KK, Gendler P, Froman RD, Patel MD. (1998) Development and evaluation of the osteoporosis self-efficacy scale. ResNursHealth. 21 (5): 395-403].

The DEXA method has good reproducibility, accuracy, and allows using quantitative indicators to assess the state of bone tissue in dynamics. DEXA uses two different X-rays to assess bone density in the spine and hip. The denser the bone tissue, the greater the absorption of X-ray radiation passing through it. The procedure takes little time and the radiation doses are very low.

In modern densitometers, it is also possible with the help of special software to study the microarchitectonics of the bone. The disadvantages include the X-ray principle, lack of mobility, high cost of equipment. Dual-energy X-ray absorptiometry is not advisable for patients with hip prostheses and signs of degenerative changes in the spine, and this method is contraindicated in pregnant women.

At the present stage, it became necessary to create a fundamentally new method, characterized by good reproducibility, the ability to obtain quantitative characteristics to be assessed in dynamics, which has no contraindications, and has a low research cost.

The objective of the invention is to create a new method of using elastic standing waves for assessing bone mineral density, which has no contraindications.

A new nonradiative approach for quantifying bone structure based on the isolation of standing waves from microseisms is described below. In this study, we tried to compare the results of the new proposed method with the DEXA method in assessing bone mineral density (hereinafter BMD), as well as to show the positive aspects of the new method.

The technical result of the invention is to reduce the harmful effects on humans, namely in the absence of exposure to X-ray radiation, to obtain the diagnostic characteristics of osteoporosis.

The technical result is achieved in a method for determining the density of bone tissue based on the separation of standing waves from microseisms of the peripheral skeleton, in which noise records with a high sampling rate are recorded on the body surface at observation points, the records are divided into fragments, their amplitude spectra are calculated, then for each observation point the amplitude spectra of all fragments are averaged, and, according to the appearance of short fragments of noise recordings of quasi-regular peaks in the averaged spectrum, the presence of standing waves is established, the figure of merit is calculated, and the density of bone tissue is estimated from its value.

In the method, continuous noise records at observation points are made for at least 5 seconds at a sampling rate of 1000 kHz, after which the noise records are divided into fragments of 8192 samples each, fragments with a duration of ~ 0.0082 s.

In the method, the figure of merit is calculated by the formula Q = W / kA, where W is the value of the frequency of the coherent peak, kA is the width of the peak.

The proposed method is based on an approach to isolating standing waves in the peripheral skeleton (bones of the thoracic and pelvic limbs), based on the fact that the object under study can vibrate at natural frequencies when exposed to elastic vibrations from noise sources of artificial or natural origin. It is known that a standing wave is formed as a result of the superposition of two traveling waves with the same amplitude, frequency and phase (when the waves move towards each other). Any closed and limited object (in our case it is a bone) has an infinite number of standing wave modes.

As shown in the results (on physical modeling and field experiments) [Kolesnikov Y.I., Fedin K.V., Luckymore N. (2019) Direct determination of resonant properties of near-surface sediments using microtremor // Soil Dynamics and Earthquake Engineering. 2019. T. 125. - C. 105739-105739 (8 pages)], the accumulation of a large number of amplitude spectra of relatively short fragments of noise records leads to the appearance of regular peaks in the averaged spectrum corresponding to standing waves. The criterion that these are standing waves is the regular nature of these peaks.

To assess the capabilities of such a resonance densitometry method based on the separation of standing waves, a series of laboratory measurements was carried out.

The registration of the microseismic field is carried out using an ultrasonic receiver made on the basis of TsST-19 piezoceramic disks with a diameter of 2 mm and a thickness of 1 mm. A long copper wire from 50 cm is attached to one of the sides of the piezoceramic, due to which the wobble of the natural frequencies of the piezoceramics itself is leveled. If such a receiver is used to measure the elastic velocity in the material, then the signal will be short, that is, the “tail” part of the signal will be absent. The other side of the piezoceramic (sensor) is fixed motionlessly on one of the points indicated in figure 1 (clavicle, wrist joint, hip joint, knee joints, ankle joints and lumbar spine L1-L4). The locations for installing the sensors were selected according to the recommendations of doctors from the NIIKEL Clinic, a branch of the ICG SB RAS.

It is known that bone density can vary greatly, as will be shown below. The axis of maximum sensitivity of the sensor should be directed perpendicular to the surface on which it is installed. To register noise signals, a Bordo-423 digital oscilloscope is used, as well as a preamplifier. As a result of this experimental setup, coherent oscillations associated with standing waves were identified against the background of incoherent noise.

The measurement technique itself and the equipment have been used more than once in the course of other studies, the description of the equipment and the measurement technique can be found in the work [Kolesnikov Yu.I., Fedin K.V., Ngomayezve L. Diagnostics of solid road surface by elastic standing waves // Engineering survey ... - 2018. - T. 12. - No. 7-8. - S. 84-91].

The recorded noise in the peripheral part of the skeleton is formed due to micro-oscillations, the sources of which are both the internal organs of the person himself and external noise effects on the body. This noise was sufficient for the accumulation of coherent amplitude peaks during measurements.

The instrument must be calibrated before taking measurements. For this, a second piston-type piezoceramic sensor is used. One of the sensors works as a signal emitter, connecting to a pulse generator, in this case, a G5-54 pulse generator is used, and the second sensor is used as a receiver. The registration of the velocities of longitudinal waves in the reference samples is carried out. If the speed in the test sample coincides with the reference, then the device is working properly. It is also worth paying attention to the signal, it must match the supplied form from the pulse generator.

The range of measured frequencies in the measuring device should be from 1 to 20 kHz, since standing waves are formed in bones in this frequency range. The recording time for each sensor position is approximately 5 seconds at a sampling rate of 1 MHz. For averaging over time, the original noise records were divided into fragments of 8192 counts, amplitude spectra were calculated for them, which were then averaged. Further averaging over the entire record of observations made it possible to neutralize the effect of the disappearance of peaks of individual standing wave modes in the spectra of records recorded at points near the nodes of these modes. The number of fragments ranged from 8 to 32, that is, until regular coherent peaks appeared. Fragment duration ~ 0.0082 s.

Using the method, diagnostic criteria for determining the parameter of bone density (quality factor) were obtained using the method of isolating standing waves from the accumulated amplitude spectra obtained during observations on a group of 15 male volunteers aged 50 to 70 years. In subjects, the parameter of bone density in the lumbar spine, generated by the resonance method, was compared with the "gold standard" of diagnosis, which is now dual-energy X-ray absorptiometry (DEXA). In the case of the DEXA method itself, the accuracy makes it possible to measure from 2% of bone loss per year. As our results have shown, the accuracy of the resonance method is not worse.

Figure 1 shows the installation points of the sensors (in addition to the indicated points, the sensors are installed on the spine sections from L1 to L4), where: 1.1 and 1.2 - the clavicle, 2.1 and 2.2 - the wrist joint, 3.1 and 3.2 - the hip joint, 4.1 and 4.2 - the knee joint , 5.1 and 5.2 - ankle joint.

Figure 2 shows fragments of noise recordings obtained with recordings of natural acoustic noise (tracks 1 -3).

Figure 3 shows an example of an accumulated recording amplitude spectrum. The level of natural acoustic noise (up to 1000 kHz) is sufficient to distinguish coherent peaks.

To test the applicability of the new method for assessing bone density, the method was tested on a group of 15 male volunteers aged 50 to 70 years. In these subjects, the parameter of bone density (quality factor) in the lumbar spine obtained by the resonance method was compared with the BMD values estimated using DEXA (densitometer "Lunar Prodigy", GE, USA).

In technology, in order to understand that the resonator is weakened, a dimensionless value of the quality factor of the material is used. It is the product of the maximum energy in the resonator during oscillation by the energy lost in the radian cycle [Harlow, James H. (2004) Electric power transformer engineering. CRC Press, pp. 2-216. ISBN 978-0-8493-1704-0. Archived from the original on 2016-12-02]. In our case, when measuring the amplitude-frequency distribution, this is the ratio of the frequency of the coherent peak to its width, which is defined as 0.707 of its maximum amplitude [Tooley, Michael H. Electronic circuits: fundamentals and applications. Newnes. pp. 77-78. ISBN 978-0-7506-6923-8. Archived from the original on 2016-12-01]. The quality factor of the resonator is called Q-factor. If the material (in our case, it is bone) has a higher density, then the visually coherent peak will be narrow.

Figure 4 shows the magnitude of a resonant filter with a voltage gain of 0.707 (half power width) [Dennis Bohn. (2008) "Bandwidth in Octaves Versus Q in Bandpass Filters", www.rane.com. Retrieved 2019-11-20].

Figure 5 shows an example of a fragment of the accumulated amplitude spectrum obtained on the L4 spine in a 34-year-old man. The frequency of the coherent peak is 2.34, its amplitude is 0.283. The peak width is defined as 0.283 * 0.707 = 0.2. The figure of merit Q was calculated as follows:

where W is the frequency of the coherent peak, and kA is the width of the peak.

If the object (bone) in question is a material with a good (high) quality factor (i.e., dense, with Q greater than 6.9 in the case of the lumbar spine - see the results below), then on the final result (frequency-amplitude distribution), coherent peaks will be as a rule, visually narrow (the ratio of the amplitude of the peak to its width), if the bone is not dense (with a low quality factor, with Q less than 6.9 in the case of the lumbar spine - see the results below), then the result will be the opposite (wide peaks).

For the diagnosis of osteopathy, the cutoff Q value for men aged 50 to 70 for the clavicle, wrist, hip, knee and ankle joints should be less than 6.4, 6.8, 7.2, 7.1, and 7, respectively.

For comparison, Table 1 shows the bone density (Q-factor) values in the lumbar spine (L1-L4) obtained by the resonance method, and the BMD values obtained using DEXA in a selected group of men. Four out of 15 patients were diagnosed with osteopathy.

TABLE I. Results of BMD assessment in the lumbar spine (L1-L4) and Q-factor in the resonance method in men aged 50 to 70 years.

The Q-factor in resonance showed a close positive correlation with the BMD obtained using DEXA (r = 0.92, p <0.00001, r is Pearson's correlation coefficient under the classical method of statistics, p is the probability).

Patients with osteopathy from Table 1 - 3,5,8 and 10 patients, by age 55, 56, 53 and 51, respectively. In the case of the presented category of subjects (from 50 to 70 years old men), it can be noted that if the value of the quality factor (Q) is on average higher than 6.9, then the bone density is good, if it is below 6.9, then it is worth paying attention and prescribing a complex of treatment.

The rest of the patients in whom the Q value turned out to be below 6.9, for example, 7 patient (68 years old) from Table 1 is on the upper edge of this considered age category and for him the value of the quality factor is considered the norm.

As a result of this study, a new method for assessing bone density based on the separation of standing waves from microseisms was developed, as well as its hardware implementation. The data show that the results of the bone density (Q-factor) assessment in the lumbar spine, obtained by the resonance method, are comparable to the results of DEXA. The advantages of the proposed method are low cost and no radiation exposure to the patient.

Claims (3)

1. A method for determining the density of bone tissue based on the isolation of standing waves from microseisms of the peripheral skeleton, consisting in the fact that noise records are recorded on the body surface at observation points, the recordings are divided into fragments, their amplitude spectra are calculated, then for each observation point, amplitude spectra of all fragments and the appearance of quasi-regular peaks in the averaged spectrum of fragments of noise records, the presence of standing waves is established, the figure of merit is calculated, and the density of bone tissue is estimated from its value. 2. The method according to claim 1, characterized in that continuous noise recordings at the observation points are made for at least 5 seconds at a sampling rate of 1000 kHz, after which the noise recordings are divided into fragments with a duration of 8192 samples. 3. The method according to claim 1, characterized in that the figure of merit is calculated by the formula Q = W / kA, where W is the value of the frequency of the coherent peak, kA is the width of the peak.

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