Multi-mode ultrasonic coupling analysis system for measuring bone mineral density

Abstract

The invention discloses a multi-mode ultrasonic coupling analysis system for measuring bone mineral density. The system comprises a shell, a foot placing groove, a sole supporting plate, a display screen, a first transducer, a second transducer, a clamping mechanism and a signal collecting and processing module, wherein the first transducer and the second transducer are oppositely arranged. A detachable double-state coupling piece is installed at the front end of the transducer, the coupling piece is provided with a first coupling face and a second coupling face which are equal in thickness but different in acoustic impedance, and the first coupling face and the second coupling face make contact with the skin in sequence when used. The device carries out bidirectional transmission measurement under multiple frequencies, the processing module averagely extracts transmission frequency dispersion characteristics through two-state difference and reciprocity, the center frequency, sharpness and sensitivity of a transmission window are obtained through fitting, and cortical-spongy transmission window indexes are formed and used for distinguishing osteoporosis phenotypes and longitudinal follow-up visit. According to the method, a traditional homogeneous model that QUS only depends on sound velocity and attenuation is broken through, frequency dispersion window characteristics of a cortical-cancellous double-layer structure are introduced into clinical quantitative indexes for the first time, and sensitivity to early osteoporosis and follow-up visit reliability are improved.

Description

Technical Field

[0001] This invention belongs to the field of ultrasound diagnostic technology, specifically a multi-mode ultrasound coupling analysis system for bone mineral density measurement. Background Technology

[0002] Osteoporosis is a common bone metabolic disease characterized by decreased bone mass, deterioration of trabecular bone structure, and increased bone fragility, seriously threatening the quality of life of the elderly. Current methods for detecting bone mineral density mainly include dual-energy X-ray absorptiometry (DXA), quantitative CT (QCT), and quantitative ultrasound (QUS). While DXA and QCT are considered the gold standards, their use is limited due to their expensive equipment, the presence of ionizing radiation, and unsuitability for large-scale screening. In contrast, QUS is widely used in physical examinations and primary care screenings because it is radiation-free, portable, and inexpensive.

[0003] However, existing ultrasound bone mineral density measurement techniques mainly use indicators such as sound velocity (SOS) and broadband attenuation (BUA), and their calculation models are generally based on the assumption of "single homogeneous bone tissue," without considering the true two-layer structure of bone. This simplification has led to many problems in clinical applications.

[0004] From an anatomical and acoustic propagation perspective, common testing sites such as the calcaneus and radius are covered by a thin layer of cortical bone over a large amount of cancellous bone, forming a typical "cortical-cancellous bilayer system." Cortical bone has a high sound velocity and low attenuation, while cancellous bone is porous and strongly scatters sound. During ultrasound transmission, some energy enters the cancellous bone as body waves, while some undergoes mode conversion to form guided waves. Due to individual differences in cortical bone thickness and cancellous bone porosity, this bilayer structure inevitably produces a dispersive transmission window: that is, transmitted energy is enhanced within specific frequency bands, while it is significantly suppressed in other frequency bands.

[0005] However, existing QUS devices and clinical indicators have not yet modeled this "cortical-spandex dispersion window" phenomenon. This results in the following clinical dilemmas: Risk of misdiagnosis and false negatives: In patients with thick cortical bone but significant osteoporosis of cancellous bone, SOS may "mask" the true bone degeneration due to the high sound velocity in the cortical layer, appearing as close to the normal value, leading to missed diagnosis.

[0006] Insufficient sensitivity to early lesions: In the early stages of osteoporosis, the degeneration of trabecular bone precedes the thinning of cortical bone, making it difficult for traditional SOS / BUA to detect in a timely manner, resulting in insufficient clinical sensitivity.

[0007] Longitudinal follow-up bias: With age, the cortical layer gradually thins, causing a shift in the center frequency of the transmission window. If only SOS or BUA is used, results from different years for the same patient often cannot be directly compared, seriously affecting the reliability of treatment follow-up.

[0008] Lack of parameterized phenotypic differentiation: The current QUS index cannot distinguish between the two clinical phenotypes of "normal cortex / cancellous degeneration" and "cortex degeneration / cancellous normal". Doctors often attribute it to "QUS is not as stable as DXA" without revealing the real physical root cause.

[0009] Therefore, despite the widespread application of QUS in screening, the clinical interpretability and longitudinal comparability of its results remain limited. The "dispersive transmission window" inherent in the cortical-cancellous bilayer structure has not yet been modeled and utilized, representing a key technological gap. Extracting and quantifying this window parameter through multi-frequency ultrasound and dual-state coupling, and establishing a new transmission window index, would provide a breakthrough improvement in the accuracy, sensitivity, and follow-up consistency of QUS in clinical practice. Summary of the Invention

[0010] The purpose of this invention is to provide a multi-mode ultrasound coupling analysis system for bone mineral density measurement. Through synergistic innovations in dual-state coupling differential, reciprocal bidirectional acquisition, multi-frequency fitting and windowing index, constant force clamping and quality control, this invention achieves superior effects compared to existing technologies in terms of diagnostic sensitivity, result repeatability, robustness to coupling thickness and environmental conditions, and long-term traceability.

[0011] The technical solution adopted in this invention is as follows: A multimodal ultrasound coupling analysis system for bone mineral density measurement, comprising: The housing serves to support and protect internal components, while also shaping the external appearance. A foot placement groove is provided on one side of the upper surface of the housing for placing and securing the feet; A display screen, located on one side of the upper surface of the housing, is used for display and operation; Foot support plate, located at the front of the foot placement slot, is used to support and position the foot; The first transducer and the second transducer are arranged opposite each other on both sides of the foot placement slot, serving as the transmitter and receiver respectively. A clamping mechanism, integrated with the first and second transducers, is used to fix the examined bone site under constant pressure; A dual-state coupling element is disposed on one of the first transducer and the second transducer. The dual-state coupling element has a first coupling surface and a second coupling surface with the same geometric thickness but different equivalent acoustic impedances, and switches between the first coupling surface and the second coupling surface by a mechanical switching mechanism. A signal acquisition and processing module is electrically connected to the first transducer and the second transducer. It is used to transmit and receive transmitted signals with at least three ultrasonic pulses at different center frequencies when the first coupling surface and the second coupling surface act respectively, and to perform reciprocal switching between the first transducer and the second transducer to obtain bidirectional data. The signal acquisition and processing module is further configured to calculate the bi-state difference and reciprocal average, fit the transmission radio frequency dispersion window, and output the cortical-cancellous transmission window index.

[0012] The dual-state coupling element is made of an elastic film layer of equal thickness, wherein: The first coupling surface is formed of a dense hydrophilic elastic material; The second coupling surface is formed from a composite material containing closed-pore microspheres or microporous structures.

[0013] The mechanical switching mechanism is a flipping or lateral movement structure, which allows the first coupling surface and the second coupling surface to alternately contact the skin without changing the geometric thickness.

[0014] The signal acquisition and processing module is configured as follows: Calculate the ratio of high-frequency to low-frequency transmission amplitude under the same coupling surface; Calculate the difference between different coupling surfaces; By performing quadratic curve fitting on the difference as a function of frequency, the center frequency fc of the transmission window and the sharpness Qwin are obtained. The sensitivity S is obtained by normalizing the differential amplitude at the mid-frequency point using the impedance difference.

[0015] The signal acquisition and processing module further includes a quality control unit, which monitors reciprocity consistency, energy stability, contact pressure and temperature, and prompts for retesting when the signal deviates from a preset threshold.

[0016] The equivalent acoustic impedances of the dual-state coupler are 0.8–1.2MRayl and 1.6–2.2MRayl, respectively, and the thickness tolerance is no greater than ±20μm.

[0017] The cortical-cancellous transmission window index includes: transmission window center frequency fc, transmission window sharpness Qwin, and sensitivity to impedance changes S; and is output as an indicator for differentiating bone health phenotypes and longitudinal follow-up in clinical reports.

[0018] It also includes a batch recording unit for storing batch information and impedance parameters of the dual-state coupler, and the signal acquisition and processing module performs automatic compensation and tracing based on the information.

[0019] A method for measuring bone mineral density using the aforementioned multimodal ultrasound coupling analysis system for bone mineral density measurement, comprising: S1. Place the subject's feet in the foot placement slot, and the clamping mechanism drives the first transducer and the second transducer to press against the feet, and the first coupling state is achieved through the dual-state coupling member; S2. Collect forward transmission data from the first transducer to the second transducer at three different frequencies; S3. Exchange the transmitting and receiving roles of the first transducer and the second transducer, and collect reverse transmission data; S4. Switch the mechanical switching mechanism to the second coupling state, and repeat steps S2 and S3. S5. The signal acquisition and processing module calculates the two-state difference and reciprocal average to obtain the difference function that varies with frequency. S6. Perform a second-order fitting on the difference function and extract fc, Qwin and S to form the cortical-cancellous transmission window index. S7. Output the index and use it to differentiate osteoporosis phenotypes or follow up on treatment effectiveness.

[0020] The ultrasonic bone mineral density measurement system provided by this invention has significant improvements over existing heel ultrasound measurement techniques in terms of overall structure and signal processing flow. Traditional heel ultrasound systems typically employ single-state coupling and unidirectional data acquisition, obtaining limited bone mineral density-related indicators based only on sound velocity or broadband attenuation. This approach suffers from insufficient sensitivity, large fluctuations in results, and high dependence on coupling fluid and operating environment in clinical practice, thus affecting the accurate assessment and follow-up of bone health status.

[0021] In contrast, this invention incorporates a dual-state coupling element at the transducer's front end. This coupling element provides two distinct equivalent acoustic impedances while maintaining a consistent geometric thickness. By acquiring data in both coupling states and performing differential analysis, the dependence of bone tissue on sound wave propagation can be effectively amplified, resulting in a more sensitive reflection of changes in bone condition. Furthermore, this invention introduces a reciprocal bidirectional acquisition strategy, where the transducer switches between transmitting and receiving roles, allowing for comparison and averaging of the acquired forward and reverse data. This not only offsets systematic errors caused by transducer differences and positional deviations but also improves the stability and reliability of the measurement results.

[0022] In terms of signal processing, this invention is no longer limited to amplitude or attenuation parameters at a single frequency point. Instead, it establishes an overall curve of transmission radio frequency dispersion through multi-frequency excitation, and then fits comprehensive indicators such as the center frequency, sharpness, and sensitivity of the cortical-cancellous transmission window. These indicators can more comprehensively reflect the structural and quality characteristics of bone, overcoming the shortcomings of traditional methods that can only reflect density changes and lack sensitivity to bone microstructure. In particular, the introduction of window sharpness allows for clearer capture of differences in trabecular arrangement and cortical state, thus enabling the differentiation of different bone phenotypes.

[0023] Furthermore, this invention also improves the clamping and quality control aspects. The transducer clamping mechanism can provide a constant clamping force under closed-loop control, ensuring that the contact pressure obtained by different subjects during the testing process remains stable. The system simultaneously monitors key parameters such as energy output, reciprocity consistency, contact pressure, and temperature in real time, and immediately prompts for retesting when abnormalities occur. This design significantly reduces interference caused by differences in the operating environment and operators, thereby improving repeatability across different populations and scenarios. At the same time, by setting up a batch recording unit, the system can compensate for the parameters of couplers in different batches, avoiding the impact of consumable batch differences on the consistency of results, making long-term follow-up and multi-center applications more comparable.

[0024] In summary, this invention achieves superior results compared to existing technologies in terms of diagnostic sensitivity, result repeatability, robustness to coupling thickness and environmental conditions, and long-term traceability through synergistic innovations in dual-state coupling differential, reciprocal bidirectional acquisition, multi-frequency fitting and windowing indicators, constant force clamping, and quality control. These improvements not only enhance the accuracy of osteoporosis screening and classification but also make the system more suitable for large-scale daily clinical use and longitudinal patient follow-up, demonstrating significant clinical application value and promising prospects for wider adoption. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the appearance of the present invention; Figure 2 This is a schematic diagram of the flip-type transducer structure of the present invention; Figure 3 This is a schematic diagram of the transverse-moving structure of the transducer of the present invention; Figure 4 This is a schematic flowchart of the bone mineral density measurement method of the present invention.

[0026] In the figure, 101 is the housing; 102 is the foot placement slot; 103 is the display screen; 104 is the foot support plate; 201 is the first transducer; 203 is the second transducer; 205 is the bracket; 206 is the anti-rotation telescopic rod; 207 is the linear motor; 208 is the slide rail; 209 is the slider; 210 is the stepper motor or servo motor; 211 is the first coupling surface; and 212 is the second coupling surface. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0028] See Figures 1 to 4 This invention relates to a multimodal ultrasound coupling analysis system for bone mineral density measurement. The system includes a housing 101 made of PC+ABS flame-retardant plastic, 2.5 mm thick, which serves both to support and protect internal components and to form the overall appearance. A foot placement groove 102 is provided on one side of the upper surface of the housing 101, the groove being approximately 160 mm long, 90 mm wide, and 60 mm deep, large enough to accommodate the feet of an adult subject. The bottom of the groove is covered with a 3 mm thick medical-grade silicone pad for anti-slip and cushioning purposes.

[0029] The front end of the foot placement slot 102 is provided with a foot support plate 104, which is made of aluminum alloy or plastic and covered with a non-slip rubber layer. The support plate is tilted forward at about 15° to support the subject's foot and ensure heel positioning.

[0030] On the other side of housing 101 is a display screen 103, which is a 7-inch LCD touch screen used to display real-time signals, prompts and final results.

[0031] A first transducer 201 and a second transducer 203 are installed on both sides of the foot placement slot 102, respectively, and are arranged opposite to each other to serve as the transmitter and receiver.

[0032] The transducer uses a piezoelectric ceramic plate with a diameter of 20mm and a thickness of 1.5mm, a center frequency of 1MHz, and can cover a frequency band of 0.5–2.0MHz. The front end is covered with a medical-grade polyurethane film, which ensures coupling and facilitates cleaning.

[0033] The two transducers are clamped and secured to the heel by a clamping mechanism. The clamping mechanism includes a linear drive unit (such as a linear motor or stepper screw) that drives the transducers to translate along the slide rail 208. Through a built-in force sensor or current closed-loop control, the clamping force of the two transducers is kept constant within the range of 5–8N, with fluctuations not exceeding ±0.2N.

[0034] A dual-state coupling element is installed on the emitting surface of the first transducer 201 or the second transducer 203. The dual-state coupling element is a circular diaphragm with a diameter of 22 mm and a thickness of 0.8 mm, with a thickness tolerance of no more than ±20 μm. The dual-state coupling element includes a first coupling surface 211 and a second coupling surface 212, which are used sequentially during operation.

[0035] First coupling surface 211: made of dense hydrophilic elastic material (such as TPU film), with an equivalent acoustic impedance of approximately 1.6–2.2 M ayl; The second coupling surface 212 is made of TPU + closed-cell microsphere composite material, with an equivalent acoustic impedance of approximately 0.8–1.2 MRayl.

[0036] For the first coupling surface 211 and the second coupling surface 212: Implementation Method 1: Removable and Replaceable The dual-state coupling element is fixed to the front end of the transducer via a snap-fit ​​annular groove or screw-in thread structure, and can be disassembled and replaced during use. For example, when measuring the first coupling state, the first coupling surface 211 is assembled with the first coupling surface facing outwards; after the measurement is completed, the dual-state coupling element is removed and flipped or replaced with another dual-state coupling element so that the second coupling surface 212 faces outwards.

[0037] Implementation Method 2: Flipping or Horizontal Movement See Figure 2 The flip-type coupling surface 211 and the second coupling surface 212 are fixed symmetrically on the support 205 with their center 211. The support 205 is driven to rotate by a stepper motor or servo motor 210 through an anti-rotation telescopic rod 206. A linear motor 207 drives the transducer to move. When the first coupling surface 211 or the second coupling surface 212 rotates to the corresponding position, it presses against the first coupling surface 211 or the second coupling surface 212 against the patient's heel.

[0038] See Figure 3 Horizontal movement type: The first transducer 201 and the second transducer 203 are arranged side by side along the length of the support 205 on one side of the support 205; a slide rail 208 is arranged along the length of the other side of the support 205; a slider 209 is arranged at the front end of the linear motor 207; the slider 209 slides in cooperation with the slide rail 208; when switching the coupling state, the first transducer 201 or the second transducer 203 is slid to be in a straight line with the linear motor 207.

[0039] The signal acquisition and processing module is electrically connected to the first transducer 201 and the second transducer 203, and includes: Transmitting circuit: High voltage pulse generator, output 50–150V, pulse width 0.2–2μs, used to drive the transducer; Receiver circuitry: low-noise amplifier (40–60dB), bandpass filter (0.3–3MHz); Data acquisition unit: ADC, sampling rate ≥20MS / s, resolution 12–14bit; Processing unit: microprocessor or FPGA, used to control transmission, acquisition, calculation and storage.

[0040] The software functions configured in the processing module include: Transmitted signals are transmitted and received at at least three center frequencies (e.g., 0.5, 1.0, 1.5 MHz) under different coupling states; A reciprocal switching is performed between the first transducer 201 and the second transducer 203 to collect bidirectional data; Calculate the high-frequency and low-frequency transmission amplitude ratio and the two-state difference; By performing a second-order fitting on the curve of the difference versus frequency, the center frequency fc of the transmission window and the sharpness Qwin are obtained. The sensitivity S is obtained by normalizing the impedance difference. Overall output cortical-cancellous transmission window index (CCWI).

[0041] The signal acquisition and processing module also includes a quality control unit for real-time monitoring of: reciprocity (error ≤3%); energy stability (fluctuation ≤5%); contact pressure (accuracy ±0.1N); and temperature (accuracy ±0.5℃). If any parameter exceeds the preset threshold, the system will prompt "Please retest".

[0042] Meanwhile, the system includes a batch recording unit for storing batch information and impedance parameters of the dual-state coupler, enabling the system to automatically compensate and ensure consistency of results across different batches of consumables.

[0043] See Figure 4 Methods for measuring bone mineral density using the above system include: S1: The subject places his foot in the foot placement slot 102, with the sole of the foot supported by the support plate 104 and the heel centered. The clamping mechanism drives the transducer to press the heel together, forming a first coupling state (the first coupling surface 211 faces the skin).

[0044] S2: Collect forward transmission data at three different frequencies (first transducer 201 → second transducer 203).

[0045] S3: Switch between transmitting and receiving roles, and collect reverse transmission data (second transducer 203 → first transducer 201).

[0046] S4: Replace or flip the dual-state coupling component so that the second coupling surface 212 contacts the skin to form the second coupling state; repeat S2 and S3.

[0047] S5: The processing module calculates the two-state difference and reciprocal average to obtain the difference function that varies with frequency.

[0048] S6: Perform a second-order fitting on the difference function to extract fc, Qwin, and S, forming the cortical-cancellous transmission window index.

[0049] S7: The system outputs an index, which is displayed and stored for osteoporosis phenotype differentiation and longitudinal follow-up.

[0050] In the system of this invention, the core task of the signal acquisition and processing module is to transform the complex ultrasound waveform into quantifiable bone conduction characteristics. To this end, this system employs a comprehensive approach combining multi-frequency transmission, bidirectional reciprocal acquisition, and two-state differential methods to make the measurement results more robust and clinically significant.

[0051] In practice, after the subject's heel bone is fixed, the system sequentially emits multiple ultrasound pulses at different center frequencies and receives the transmitted signals at corresponding transducers. Measurements at each frequency are acquired bidirectionally and reciprocally, i.e., transmitted by the first transducer and received by the second transducer, and transmitted by the second transducer and received by the first transducer. The two sets of data obtained in this way should theoretically be consistent. Therefore, by comparing the differences between the two sets, the stability of the measurement process can be monitored in real time, and averaging the data improves anti-interference capabilities.

[0052] The received ultrasonic signals typically contain noise and multiple echoes. The processing module first filters the signal and extracts the main transmitted waveform within the expected arrival time window to remove irrelevant interference. Within this time window, the system further extracts representative values ​​of energy or amplitude, simplifying the originally complex time-domain waveform into a comparable intensity index.

[0053] After completing the measurement in a single coupling state, the system replaces or flips the dual-state coupler to bring the coupling surface with a different equivalent acoustic impedance into contact with the skin, maintaining the same geometry to perform the same multi-frequency, bidirectional acquisition again. Because the two coupling surfaces have significant differences in impedance, their coupling effects with bone tissue also differ. By comparing the signal differences between the two coupling states, the frequency dependence of bone tissue on sound wave propagation can be effectively amplified. This "dual-state differential" method allows the sensitivity of bone to acoustic disturbances to be clearly demonstrated.

[0054] The system then connects the two-state difference results at different frequencies into a curve, which generally exhibits a window-like shape, with the difference maximizing at a certain frequency and gradually decreasing towards both sides. The signal processing module automatically determines the center frequency and sharpness of the window by fitting the curve. The center frequency reflects the main transmission characteristics of the cortical-cancellous structure, while sharpness reflects the clarity and distribution of the bone structure.

[0055] Simultaneously, the system utilizes the impedance difference between the two coupling surfaces provided by the batch recording unit to normalize the dual-state differential amplitude, obtaining a sensitivity index. This index represents the bone's response strength to different impedance loading, thereby eliminating the influence of different batches of consumables.

[0056] Finally, the signal processing module outputs a three-part cortical-cancellous transmission window index, including the window center frequency, sharpness, and sensitivity. This combined index can not only distinguish different bone health phenotypes but also be used to observe trends in bone changes during follow-up.

[0057] Throughout the process, the quality control unit continuously monitors reciprocity, energy stability, clamping pressure, and contact temperature during the measurement. If any parameter deviates from the preset threshold, the system will immediately prompt for a remeasurement, ensuring the reliability and repeatability of the final results.

[0058] Through the above signal processing procedure, the system of the present invention can achieve stable quantification of the acoustic properties of bone tissue with simple operation, providing an efficient and clinically feasible tool for osteoporosis screening and follow-up.

[0059] To verify the actual effectiveness of this invention under routine clinical conditions, a comparative experimental study was conducted with two currently mainstream commercially available devices (hereinafter referred to as Commercial A and Commercial B). The experiment was conducted in parallel under the same heel location and environmental conditions; the robustness and repeatability of the system were comprehensively evaluated through multiple scenario settings (including changes in coupling fluid volume, subject micro-movements, the effects of low temperature, and operator changes).

[0060] The core metrics of the experiment are: center frequency of the transmission window (fc), window sharpness (Qwin), sensitivity (S), and reciprocity consistency and repeatability (CV).

[0061] The test site was the heel (calcaneus); the number of subjects was n=24 heels; the table below shows the single case data of 6 representative scenarios (the rest are used for overall statistics).

[0062]

[0063] Overall statistics are as follows (n=24 heels; mean ± SD):

[0064] Results analysis: ① In all scenarios, the Qwin of this invention is always ≥2.3 and the CV is ≤3%; in the control model, the CV increases significantly to 7–10% under micro-motion (T4), low temperature (T5), and operator change (T6). Reciprocal averaging effectively suppresses directional deviation and ensures a stable fitting window (fc fluctuation ≤0.06MHz).

[0065] ② Under the conditions of 0.6 mL (thin) and 1.8 mL (thick) (T2 / T3), the variation of fc / Qwin / S in this invention is small; Qwin and S of the control machine decrease significantly, indicating that the single-state / unidirectional system is more sensitive to the thickness of the coupling layer.

[0066] ③ Low temperature and slight movements are common interferences in outpatient settings. This invention, with its force-controlled clamping and reciprocity verification, maintains a CV of approximately 2.6–2.8% at T4 / T5; the control machine exhibits repeatability degradation, with Qwin decreasing to 1.4–1.7.

[0067] Furthermore, in this embodiment, the dual-state coupling element includes a first coupling surface 211 and a second coupling surface 212, whose base materials are a dense hydrophilic elastic membrane and a microporous composite membrane, respectively. To solve the clinical inconvenience of traditional ultrasound measurement relying on coupling fluid, the present invention adds a "self-wetting surface layer" to the outermost layer of the dual-state coupling element.

[0068] The self-wetting surface layer is a microporous polymer film with a thickness of 20–50 μm, a pore size range controlled between 0.2–1.0 μm, and a porosity of approximately 30–50%. The material can be modified polyurethane (PU), polyvinylidene fluoride (PVDF), or plasma-treated medical-grade silicone film. This film undergoes surface hydrophilization treatment, resulting in a contact angle ≤30°.

[0069] During use, this microporous layer can form a stable ultrathin liquid film through the following mechanism: Air humidity adsorption: The microporous surface absorbs moisture and condenses water molecules in the air, quickly forming a uniform water film on the surface; Skin sweat activation: A small amount of sweat from the patient's soles enters the microporous structure and is rapidly diffused by capillary force to form a continuous water film; Water film stability: Due to the fine and uniform pore size, capillary action can maintain the stability of the liquid film locally, preventing rapid evaporation.

[0070] In this way, no additional coupling fluid is needed in actual clinical applications. The patient simply places their foot in the foot placement slot 102, and the self-wetting layer of the dual-state coupling element naturally forms an acoustic coupling interface with the skin. The equivalent acoustic impedance of this interface layer is maintained at 1.2–1.5 M ayl, which is between that of water and skin, ensuring effective transmission of ultrasound energy.

[0071] Furthermore, to prevent cross-infection, the self-wetting layer can be designed as a disposable, replaceable membrane with a thickness ≤0.05mm. After each measurement, it can be completely removed and replaced with a new membrane. The membrane is fixed to the dual-state coupling element substrate using annular micro-clamps or medical-grade adhesive.

[0072] Compared with traditional coupling fluid methods, the liquid-free self-lubricating coupling membrane of this invention has the following advantages: no external gel is required, reducing clinical operation time; disposable self-lubricating membranes avoid cross-contamination; patients do not need to come into contact with cold gel, resulting in greater comfort; and the liquid film thickness is uniform and does not fluctuate with differences in operator technique. Therefore, this self-lubricating coupling membrane not only maintains the dual-impedance characteristics of a dual-state coupler, but also addresses the clinical pain point by solving the problem of coupling fluid dependence, significantly improving the system's practicality and promotional value.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multi-mode ultrasound coupling analysis system for bone mineral density measurement, characterized in that, include: The housing (101) serves to support and protect the internal components while also forming the external shape; A foot placement groove (102) is provided on one side of the upper surface of the housing (101) for placing and fixing the feet; A display screen (103) is disposed on one side of the upper surface of the housing (102) for display and operation; A foot support plate (104) is provided at the front of the foot placement groove (102) to support and position the foot; The first transducer (201) and the second transducer (203) are arranged opposite each other on both sides of the foot placement slot (102), serving as the transmitter and receiver respectively; A clamping mechanism, integrated with the first transducer (201) and the second transducer (203), is used to fix the examined bone site under constant pressure; A dual-state coupling element is disposed on one of the first transducer (201) and the second transducer (203). The dual-state coupling element has a first coupling surface (211) and a second coupling surface (212) with the same geometric thickness but different equivalent acoustic impedances, and switches between the first coupling surface (211) and the second coupling surface (212). A signal acquisition and processing module is electrically connected to the first transducer (201) and the second transducer (203). It is used to transmit and receive transmitted signals with at least three ultrasonic pulses at different center frequencies when the first coupling surface (211) and the second coupling surface (212) are acting respectively. At the same time, it performs reciprocal switching between the first transducer (201) and the second transducer (203) to obtain bidirectional data. The signal acquisition and processing module is further configured to calculate the bi-state difference and reciprocal average, fit the transmission radio frequency dispersion window, and output the cortical-cancellous transmission window index.

2. The multi-mode ultrasound coupling analysis system for bone mineral density measurement according to claim 1, characterized in that, The dual-state coupling element is made of an elastic film layer of equal thickness, wherein: The first coupling surface (211) is formed of a dense hydrophilic elastic material; The second coupling surface (212) is formed of a composite material containing closed-pore microspheres or microporous structures.

3. The multi-mode ultrasound coupling analysis system for bone mineral density measurement according to claim 2, characterized in that, The dual-state coupling element is fitted onto the front end of the transducer via a snap-fit ​​annular groove or a screw-in fixing structure, facilitating quick disassembly and replacement during clinical use.

4. The multi-mode ultrasound coupling analysis system for bone mineral density measurement according to claim 2, characterized in that, By flipping or shifting the structure, the first coupling surface (211) and the second coupling surface (212) are switched.

5. The multi-mode ultrasound coupling analysis system for bone mineral density measurement according to claim 2, characterized in that, The equivalent acoustic impedances of the dual-state coupler are 0.8–1.2MRayl and 1.6–2.2MRayl, respectively, and the thickness tolerance is no greater than ±20μm.

6. The multi-mode ultrasound coupling analysis system for bone mineral density measurement according to claim 1, characterized in that, The signal acquisition and processing module is configured as follows: Calculate the ratio of high-frequency to low-frequency transmission amplitude under the same coupling surface; Calculate the difference between different coupling surfaces; By performing quadratic curve fitting on the difference as a function of frequency, the center frequency fc of the transmission window and the sharpness Qwin are obtained. The sensitivity S is obtained by normalizing the differential amplitude at the mid-frequency point using the impedance difference.

7. The multi-mode ultrasound coupling analysis system for bone mineral density measurement according to claim 6, characterized in that, The signal acquisition and processing module further includes a quality control unit for monitoring reciprocity consistency, energy stability, contact pressure and temperature, and prompting a retest when the signal deviates from a preset threshold.

8. The multi-mode ultrasound coupling analysis system for bone mineral density measurement according to claim 1, characterized in that, The cortical-cancellous transmission window index includes: transmission window center frequency fc, transmission window sharpness Qwin, and sensitivity to impedance changes S; and is output as an indicator for differentiating bone health phenotypes and longitudinal follow-up in clinical reports.

9. The multi-mode ultrasound coupling analysis system for bone mineral density measurement according to claim 1, characterized in that, It also includes a batch recording unit for storing batch information and impedance parameters of the dual-state coupler, and the signal acquisition and processing module performs automatic compensation and tracing based on the information.

10. A method for measuring bone mineral density using the multimodal ultrasound coupling analysis system for bone mineral density measurement according to any one of claims 1-9, characterized in that, include: S1. Place the subject's feet in the foot placement slot (102), and the clamping mechanism drives the first transducer (201) and the second transducer (203) to press against the feet, and realize the first coupling state through the dual-state coupling member; S2. Collect forward transmission data from the first transducer (201) to the second transducer (203) at three different frequencies; S3. Exchange the transmitting and receiving roles of the first transducer (201) and the second transducer (203) to collect reverse transmission data; S4. Switch the mechanical switching mechanism to the second coupling state, and repeat steps S2 and S3. S5. The signal acquisition and processing module calculates the two-state difference and reciprocal average to obtain the difference function that varies with frequency. S6. Perform a second-order fitting on the difference function and extract fc, Qwin and S to form the cortical-cancellous transmission window index. S7. Output the index and use it to differentiate osteoporosis phenotypes or follow up on treatment effectiveness.

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