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        It has recently been demonstrated that the use of ultrasound can improve tissue yield in ultrasound-enhanced fine needle aspiration biopsy (USeFNAB) compared to conventional fine needle aspiration biopsy (FNAB). The relationship between bevel geometry and needle tip action has not yet been investigated. In this study, we investigated the properties of needle resonance and deflection amplitude for various needle bevel geometries with different bevel lengths. Using a conventional lancet with a 3.9 mm cut, the tip deflection power factor (DPR) was 220 and 105 µm/W in air and water, respectively. This is higher than the axisymmetric 4mm bevel tip, which achieved a DPR of 180 and 80 µm/W in air and water, respectively. This study highlights the importance of the relationship between the bending stiffness of the bevel geometry in the context of different insertion aids, and thus may provide insight into methods for controlling cutting action after puncture by changing the needle bevel geometry, which is important for USeFNAB. Application matters.
        Fine needle aspiration biopsy (FNAB) is a technique in which a needle is used to obtain a sample of tissue when an abnormality is suspected1,2,3. Franseen-type tips have been shown to provide higher diagnostic performance than traditional Lancet4 and Menghini5 tips. Axisymmetric (i.e. circumferential) bevels have also been proposed to increase the likelihood of an adequate specimen for histopathology6.
        During a biopsy, a needle is passed through layers of skin and tissue to reveal suspicious pathology. Recent studies have shown that ultrasonic activation can reduce the puncture force required to access soft tissues7,8,9,10. Needle bevel geometry has been shown to affect needle interaction forces, eg longer bevels have been shown to have lower tissue penetration forces 11 . It has been suggested that after the needle has penetrated the tissue surface, i.e. after puncture, the cutting force of the needle may be 75% of the total needle-tissue interaction force12. Ultrasound (US) has been shown to improve the quality of diagnostic soft tissue biopsy in the post-puncture phase13. Other methods to improve bone biopsy quality have been developed for hard tissue sampling14,15 but no results have been reported that improve biopsy quality. Several studies have also found that mechanical displacement increases with increasing ultrasound drive voltage16,17,18. Although there are many studies of axial (longitudinal) static forces in needle-tissue interactions19,20, studies on the temporal dynamics and needle bevel geometry in ultrasonic enhanced FNAB (USeFNAB) are limited.
        The aim of this study was to investigate the effect of different bevel geometries on needle tip action driven by needle flexion at ultrasonic frequencies. In particular, we investigated the effect of the injection medium on needle tip deflection after puncture for conventional needle bevels (e.g., lancets), axisymmetric and asymmetric single bevel geometries (Fig. to facilitate the development of USeFNAB needles for various purposes such as selective suction access or soft tissue nuclei.
        Various bevel geometries were included in this study. (a) Lancets conforming to ISO 7864:201636 where \(\alpha\) is the primary bevel angle, \(\theta\) is the secondary bevel rotation angle, and \(\phi\) is the secondary bevel rotation Angle in degrees , in degrees (\(^\circ\)). (b) linear asymmetrical single step chamfers (called “standard” in DIN 13097:201937) and (c) linear axisymmetric (circumferential) single step chamfers.
        Our approach is to first model the change in the bending wavelength along the slope for conventional lancet, axisymmetric, and asymmetric single-stage slope geometries. We then calculated a parametric study to examine the effect of bevel angle and tube length on transport mechanism mobility. This is done to determine the optimal length for making a prototype needle. Based on the simulation, needle prototypes were made and their resonant behavior in air, water, and 10% (w/v) ballistic gelatin was experimentally characterized by measuring the voltage reflection coefficient and calculating the power transfer efficiency, from which the operating frequency was determined. . Finally, high-speed imaging is used to directly measure the deflection of the bending wave at the tip of the needle in air and water, and to estimate the electrical power transmitted by each tilt and the deflection power factor (DPR) geometry of the injected medium.
        As shown in Figure 2a, use No. 21 pipe (0.80 mm OD, 0.49 mm ID, 0.155 mm pipe wall thickness, standard wall as specified in ISO 9626:201621) made of 316 stainless steel ( Young’s modulus 205). \(\text {GN/m}^{2}\), density 8070 kg/m\(^{3}\), Poisson’s ratio 0.275).
        Determination of the bending wavelength and tuning of the finite element model (FEM) of the needle and boundary conditions. (a) Determination of bevel length (BL) and pipe length (TL). (b) Three-dimensional (3D) finite element model (FEM) using harmonic point force \(\tilde{F}_y\vec{j}\) to excite the needle at the proximal end, deflect the point, and measure velocity per tip (\( \tilde{u}_y\vec {j}\), \(\tilde{v}_y\vec {j}\)) to calculate the mechanistic transport mobility. \(\lambda _y\) is defined as the bending wavelength associated with the vertical force \(\tilde{F}_y\vec {j}\). (c) Determine the center of gravity, cross-sectional area A, and moments of inertia \(I_{xx}\) and \(I_{yy}\) around the x-axis and y-axis respectively.
        As shown in fig. 2b,c, for an infinite (infinite) beam with cross-sectional area A and at a large wavelength compared to the size of the cross-section of the beam, the bending (or bending) phase velocity \(c_{EI}\) is defined as 22:
        where E is Young’s modulus (\(\text {N/m}^{2}\)), \(\omega _0 = 2\pi f_0\) is the excitation angular frequency (rad/s), where \( f_0\ ) is the linear frequency (1/s or Hz), I is the moment of inertia of the area around the axis of interest \((\text {m}^{4})\) and \(m’=\ rho _0 A \) is the mass on unit length (kg/m), where \(\rho _0\) is the density \((\text {kg/m}^{3})\) and A is the cross-sectional area of ​​the beam (xy plane) (\ (\text {m}^{2}\)). Since in our case the applied force is parallel to the vertical y-axis, i.e. \(\tilde{F}_y\vec {j}\), we are only interested in the moment of inertia of the area around the horizontal x-axis, i.e. \(I_{xx} \), That’s why:
        For the finite element model (FEM), a pure harmonic displacement (m) is assumed, so the acceleration (\(\text {m/s}^{2}\)) is expressed as \(\partial ^2 \vec { u}/ \ partial t^2 = -\omega ^2\vec {u}\), e.g. \(\vec {u}(x, y, z, t) := u_x\vec {i} + u_y \vec {j }+ u_z\vec {k}\) is a three-dimensional displacement vector defined in spatial coordinates. Replacing the latter with the finitely deformable Lagrangian form of the momentum balance law23, according to its implementation in the COMSOL Multiphysics software package (versions 5.4-5.5, COMSOL Inc., Massachusetts, USA), gives:
        Where \(\vec {\nabla}:= \frac{\partial}}{\partial x}\vec {i} + \frac{\partial}}{\partial y}\vec {j} + \frac{ \partial }{\partial z}\vec {k}\) is the tensor divergence operator, and \({\underline{\sigma}}\) is the second Piola-Kirchhoff stress tensor (second order, \(\ text { N /m}^{2}\)), and \(\vec {F_V}:= F_{V_x}\vec {i}+ F_{V_y}\vec {j}+ F_{V_z}\vec {k} \) is the vector of the body force (\(\text {N/m}^{3}\)) of each deformable volume, and \(e^{j\phi }\) is the phase of the body force, has a phase angle \(\ phi\) (rad). In our case, the volume force of the body is zero, and our model assumes geometric linearity and small purely elastic deformations, i.e. \({\underline{\varepsilon}}^{el} = {\underline{\varepsilon}}\ ), where \({\underline{\varepsilon}}^{el}\) and \({\underline{ \varepsilon}}\) – elastic deformation and total deformation (dimensionless of the second order), respectively. Hooke’s constitutive isotropic elasticity tensor \(\underline {\underline {C))\) is obtained using Young’s modulus E(\(\text{N/m}^{2}\)) and Poisson’s ratio v is defined, so that \ (\underline{\underline{C}}:=\underline{\underline{C}}(E,v)\) (fourth order). So the stress calculation becomes \({\underline{\sigma}} := \underline{\underline{C}}:{\underline{\varepsilon}}\).
        The calculations were performed with 10-node tetrahedral elements with element size \(\le\) 8 µm. The needle is modeled in vacuum, and the mechanical mobility transfer value (ms-1 H-1) is defined as \(|\tilde{Y}_{v_yF_y}|= |\tilde{v}_y\vec { j} |/|\ tilde{F}_y\vec {j}|\)24, where \(\tilde{v}_y\vec {j}\) is the output complex velocity of the handpiece, and \( \tilde{F} _y\vec {j }\) is a complex driving force located at the proximal end of the tube, as shown in Fig. 2b. Transmissive mechanical mobility is expressed in decibels (dB) using the maximum value as a reference, i.e. \(20\log _{10} (|\tilde{Y}|/ |\tilde{Y}_{max}| )\ ) , All FEM studies were carried out at a frequency of 29.75 kHz.
        The design of the needle (Fig. 3) consists of a conventional 21 gauge hypodermic needle (catalog number: 4665643, Sterican\(^\circledR\), with an outer diameter of 0.8 mm, a length of 120 mm, made of AISI chromium-nickel stainless steel 304., B. Braun Melsungen AG, Melsungen, Germany) placed a plastic Luer Lock sleeve made of polypropylene proximal with a corresponding tip modification. The needle tube is soldered to the waveguide as shown in Fig. 3b. The waveguide was printed on a stainless steel 3D printer (EOS Stainless Steel 316L on an EOS M 290 3D printer, 3D Formtech Oy, Jyväskylä, Finland) and then attached to the Langevin sensor using M4 bolts. The Langevin transducer consists of 8 piezoelectric ring elements with two weights at each end.
        The four types of tips (pictured), a commercially available lancet (L), and three manufactured axisymmetric single-stage bevels (AX1–3) were characterized by bevel lengths (BL) of 4, 1.2, and 0.5 mm, respectively. (a) Close-up of the finished needle tip. (b) Top view of four pins soldered to a 3D printed waveguide and then connected to the Langevin sensor with M4 bolts.
        Three axisymmetric bevel tips (Fig. 3) (TAs Machine Tools Oy) were manufactured with bevel lengths (BL, determined in Fig. 2a) of 4.0, 1.2 and 0.5 mm, corresponding to \(\approx\) 2\ (^\circ\), 7\(^\circ\) and 18\(^\circ\). The waveguide and stylus weights are 3.4 ± 0.017 g (mean ± SD, n = 4) for bevel L and AX1–3, respectively (Quintix\(^\circledR\) 224 Design 2, Sartorius AG, Göttingen, Germany) . The total length from the tip of the needle to the end of the plastic sleeve is 13.7, 13.3, 13.3, 13.3 cm for the bevel L and AX1-3 in Figure 3b, respectively.
        For all needle configurations, the length from the tip of the needle to the tip of the waveguide (i.e., soldering area) is 4.3 cm, and the needle tube is oriented so that the bevel is facing up (i.e., parallel to the Y axis). ), as in (Fig. 2).
        A custom script in MATLAB (R2019a, The MathWorks Inc., Massachusetts, USA) running on a computer (Latitude 7490, Dell Inc., Texas, USA) was used to generate a linear sinusoidal sweep from 25 to 35 kHz in 7 seconds, converted to an analog signal by a digital-to-analog (DA) converter (Analog Discovery 2, Digilent Inc., Washington, USA). The analog signal \(V_0\) (0.5 Vp-p) was then amplified with a dedicated radio frequency (RF) amplifier (Mariachi Oy, Turku, Finland). The falling amplifying voltage \({V_I}\) is output from the RF amplifier with an output impedance of 50 \(\Omega\) to a transformer built into the needle structure with an input impedance of 50 \(\Omega)\) Langevin transducer (front and rear multilayer piezoelectric transducers , loaded with mass) are used to generate mechanical waves. The custom RF amplifier is equipped with a dual-channel standing wave power factor (SWR) meter that can detect incident \({V_I}\) and reflected amplified voltage \(V_R\) through a 300 kHz analog-to-digital (AD) converter (Analog Discovery 2). The excitation signal is amplitude modulated at the beginning and at the end to prevent overloading the amplifier input with transients.
        Using a custom script implemented in MATLAB, the frequency response function (AFC), i.e. assumes a linear stationary system. Also, apply a 20 to 40 kHz band pass filter to remove any unwanted frequencies from the signal. Referring to transmission line theory, \(\tilde{H}(f)\) in this case is equivalent to the voltage reflection coefficient, i.e. \(\rho _{V} \equiv {V_R}/{V_I} \)26 .Since the output impedance of the amplifier \(Z_0\) corresponds to the input impedance of the built-in transformer of the converter, and the reflection coefficient of electric power \({P_R}/{P_I}\) is reduced to \({V_R }^ 2/{V_I}^2\ ), then is \(|\rho _{V}|^2\). In the case where the absolute value of electrical power is required, calculate the incident \(P_I\) and reflected\(P_R\) power (W) by taking the root mean square (rms) value of the corresponding voltage, for example, for a transmission line with sinusoidal excitation, \(P = {V}^2/(2Z_0)\)26, where \(Z_0\) equals 50 \(\Omega\). The electrical power delivered to the load \(P_T\) (i.e. the inserted medium) can be calculated as \(|P_I – P_R |\) (W RMS) and the power transfer efficiency (PTE) can be defined and expressed as a percentage (%) thus gives 27:
       The frequency response is then used to estimate the modal frequencies \(f_{1-3}\) (kHz) of the stylus design and the corresponding power transfer efficiency, \(\text {PTE}_{1{-}3} \ ).FWHM (\(\text {FWHM}_{1{-}3}\), Hz) is estimated directly from \(\text {PTE}_{1{-}3}\), from Table 1 frequencies \(f_{1-3}\) described in .
        A method for measuring the frequency response (AFC) of an acicular structure. Dual-channel swept-sine measurement25,38 is used to obtain the frequency response function \(\tilde{H}(f)\) and its impulse response H(t). \({\mathcal {F}}\) and \({\mathcal {F}}^{-1}\) denote the numerical truncated Fourier transform and the inverse transform operation, respectively. \(\tilde{G}(f)\) means the two signals are multiplied in the frequency domain, e.g. \(\tilde{G}_{XrX}\) means inverse scan\(\tilde{X} r( f )\) and voltage drop signal \(\tilde{X}(f)\).
        As shown in fig. 5, high-speed camera (Phantom V1612, Vision Research Inc., New Jersey, USA) equipped with a macro lens (MP-E 65mm, \(f)/2.8, 1-5 \ (\times\), Canon Inc. ., Tokyo, Japan) were used to record the deflection of a needle tip subjected to flexural excitation (single frequency, continuous sinusoid) at a frequency of 27.5–30 kHz. To create a shadow map, a cooled element of a high intensity white LED (part number: 4052899910881, White Led, 3000 K, 4150 lm, Osram Opto Semiconductors GmbH, Regensburg, Germany) was placed behind the bevel of the needle.
        Front view of the experimental setup. Depth is measured from the media surface. The needle structure is clamped and mounted on a motorized transfer table. Use a high speed camera with a high magnification lens (5\(\times\)) to measure the deflection of the beveled tip. All dimensions are in millimeters.
        For each type of needle bevel, we recorded 300 high-speed camera frames of 128 \(\x\) 128 pixels, each with a spatial resolution of 1/180 mm (\(\approx) 5 µm), with a temporal resolution of 310,000 frames per second. As shown in Figure 6, each frame (1) is cropped (2) so that the tip is in the last line (bottom) of the frame, and then the histogram of the image (3) is calculated, so Canny thresholds 1 and 2 can be determined. Then apply Canny28(4) edge detection using the Sobel operator 3 \(\times\) 3 and calculate the pixel position of the non-cavitational hypotenuse (labeled \(\mathbf {\times }\)) for all 300-fold steps. To determine the span of the deflection at the end, the derivative is calculated (using the central difference algorithm) (6) and the frame containing the local extrema (ie peak) of the deflection (7) is identified. After visually inspecting the non-cavitating edge, a pair of frames (or two frames separated by half a time period) (7) was selected and the tip deflection measured (labeled \(\mathbf {\times} \ ) The above was implemented in Python (v3.8, Python Software Foundation, python.org) using the OpenCV Canny edge detection algorithm (v4.5.1, open source computer vision library, opencv.org). electrical power \ (P_T \) (W, rms).
       Tip deflection was measured using a series of frames taken from a high-speed camera at 310 kHz using a 7-step algorithm (1-7) including framing (1-2), Canny edge detection (3-4), pixel location edge calculation (5) and their time derivatives (6), and finally peak-to-peak tip deflection were measured on visually inspected pairs of frames (7).
        Measurements were taken in air (22.4-22.9°C), deionized water (20.8-21.5°C) and ballistic gelatin 10% (w/v) (19.7-23.0°C, \(\text {Honeywell}^{ \text { TM}}\) \(\text {Fluka}^{\text {TM}}\) Bovine and Pork Bone Gelatin for Type I Ballistic Analysis, Honeywell International, North Carolina, USA). Temperature was measured with a K-type thermocouple amplifier (AD595, Analog Devices Inc., MA, USA) and a K-type thermocouple (Fluke 80PK-1 Bead Probe No. 3648 type-K, Fluke Corporation, Washington, USA). From the medium Depth was measured from the surface (set as the origin of the z-axis) using a vertical motorized z-axis stage (8MT50-100BS1-XYZ, Standa Ltd., Vilnius, Lithuania) with a resolution of 5 µm. per step.
        Since the sample size was small (n = 5) and normality could not be assumed, a two-sample two-tailed Wilcoxon rank sum test (R, v4.0.3, R Foundation for Statistical Computing, r-project .org) was used to compare the amount of variance needle tip for different bevels. There were 3 comparisons per slope, so a Bonferroni correction was applied with an adjusted significance level of 0.017 and an error rate of 5%.
        Let us now turn to Fig.7. At a frequency of 29.75 kHz, the bending half-wave (\(\lambda_y/2\)) of a 21-gauge needle is \(\approximately) 8 mm. As one approaches the tip, the bending wavelength decreases along the oblique angle. At the tip \(\lambda _y/2\) \(\approximately\) there are steps of 3, 1 and 7 mm for the usual lanceolate (a), asymmetric (b) and axisymmetric (c) inclination of a single needle, respectively. Thus, this means that the range of the lancet is \(\approximately) 5 mm (due to the fact that the two planes of the lancet form a single point29,30), the asymmetric bevel is 7 mm, the asymmetric bevel is 1 mm. Axisymmetric slopes (the center of gravity remains constant, so only the pipe wall thickness actually changes along the slope).
        FEM studies and application of equations at a frequency of 29.75 kHz. (1) When calculating the variation of the bending half-wave (\(\lambda_y/2\)) for lancet (a), asymmetric (b) and axisymmetric (c) bevel geometries (as in Fig. 1a,b,c) . The average value \(\lambda_y/2\) of the lancet, asymmetric, and axisymmetric bevels was 5.65, 5.17, and 7.52 mm, respectively. Note that tip thickness for asymmetric and axisymmetric bevels is limited to \(\approx) 50 µm.
        Peak mobility \(|\tilde{Y}_{v_yF_y}|\) is the optimal combination of tube length (TL) and bevel length (BL) (Fig. 8, 9). For a conventional lancet, since its size is fixed, the optimal TL is \(\approximately) 29.1 mm (Fig. 8). For asymmetric and axisymmetric bevels (Fig. 9a, b, respectively), FEM studies included BL from 1 to 7 mm, so the optimal TL were from 26.9 to 28.7 mm (range 1.8 mm) and from 27.9 to 29 .2 mm (range 1.3 mm), respectively. For the asymmetric slope (Fig. 9a), the optimal TL increased linearly, reached a plateau at BL 4 mm, and then sharply decreased from BL 5 to 7 mm. For an axisymmetric bevel (Fig. 9b), the optimal TL increased linearly with increasing BL and finally stabilized at BL from 6 to 7 mm. An extended study of axisymmetric tilt (Fig. 9c) revealed a different set of optimal TLs at \(\approx) 35.1–37.1 mm. For all BLs, the distance between the two best TLs is \(\approx\) 8mm (equivalent to \(\lambda_y/2\)).
        Lancet transmission mobility at 29.75 kHz. The needle was flexibly excited at a frequency of 29.75 kHz and vibration was measured at the tip of the needle and expressed as the amount of transmitted mechanical mobility (dB relative to the maximum value) for TL 26.5-29.5 mm (in 0.1 mm increments).
        Parametric studies of the FEM at a frequency of 29.75 kHz show that the transfer mobility of an axisymmetric tip is less affected by a change in the length of the tube than its asymmetric counterpart. Bevel length (BL) and pipe length (TL) studies of asymmetric (a) and axisymmetric (b, c) bevel geometries in the frequency domain study using FEM (boundary conditions are shown in Fig. 2). (a, b) TL ranged from 26.5 to 29.5 mm (0.1 mm step) and BL 1–7 mm (0.5 mm step). (c) Extended axisymmetric tilt studies including TL 25–40 mm (in 0.05 mm increments) and BL 0.1–7 mm (in 0.1 mm increments) showing that \(\lambda_y/2\ ) must meet the requirements of the tip. moving boundary conditions.
        The needle configuration has three eigenfrequencies \(f_{1-3}\) divided into low, medium and high mode regions as shown in Table 1. The PTE size was recorded as shown in fig. 10 and then analyzed in Fig. 11. Below are the findings for each modal area:
        Typical recorded instantaneous power transfer efficiency (PTE) amplitudes obtained with swept-frequency sinusoidal excitation for a lancet (L) and axisymmetric bevel AX1-3 in air, water and gelatin at a depth of 20 mm. One-sided spectra are shown. The measured frequency response (sampled at 300 kHz) was low-pass filtered and then scaled down by a factor of 200 for modal analysis. The signal-to-noise ratio is \(\le\) 45 dB. PTE phases (purple dotted lines) are shown in degrees (\(^{\circ}\)).
        The modal response analysis (mean ± standard deviation, n = 5) shown in Fig. 10, for slopes L and AX1-3, in air, water and 10% gelatin (depth 20 mm), with (top) three modal regions (low, middle and high) and their corresponding modal frequencies\(f_{1-3 }\) (kHz), (average) energy efficiency \(\text {PTE}_{1{-}3}\) Calculated using equivalents . (4) and (bottom) full width at half maximum measurements \(\text {FWHM}_{1{-}3}\) (Hz), respectively. Note that the bandwidth measurement was skipped when a low PTE was registered, i.e. \(\text {FWHM}_{1}\) in case of AX2 slope. The \(f_2\) mode was found to be the most suitable for comparing slope deflections, as it showed the highest level of power transfer efficiency (\(\text {PTE}_{2}\)), up to 99%.
        First modal region: \(f_1\) does not depend much on the type of medium inserted, but depends on the geometry of the slope. \(f_1\) decreases with decreasing bevel length (27.1, 26.2 and 25.9 kHz in air for AX1-3, respectively). The regional averages \(\text {PTE}_{1}\) and \(\text {FWHM}_{1}\) are \(\approx\) 81% and 230 Hz respectively. \(\text {FWHM}_{1}\) has the highest gelatin content in the Lancet (L, 473 Hz). Note that \(\text {FWHM}_{1}\) AX2 in gelatin could not be evaluated due to the low recorded FRF amplitude.
        The second modal region: \(f_2\) depends on the type of media inserted and the bevel. Average values ​​\(f_2\) are 29.1, 27.9 and 28.5 kHz in air, water and gelatin, respectively. This modal region also showed a high PTE of 99%, the highest of any group measured, with a regional average of 84%. \(\text {FWHM}_{2}\) has a regional average of \(\approximately\) 910 Hz.
        Third mode region: frequency \(f_3\) depends on the media type and bevel. Average \(f_3\) values ​​are 32.0, 31.0 and 31.3 kHz in air, water and gelatin, respectively. The \(\text {PTE}_{3}\) regional average was \(\approximately\) 74%, the lowest of any region. The regional average \(\text {FWHM}_{3}\) is \(\approximately\) 1085 Hz, which is higher than the first and second regions.
        The following refers to Fig. 12 and Table 2. The lancet (L) deflected the most (with high significance to all tips, \(p<\) 0.017) in both air and water (Fig. 12a), achieving the highest DPR (up to 220 µm/W in air). 12 and Table 2. The lancet (L) deflected the most (with high significance to all tips, \(p<\) 0.017) in both air and water (Fig. 12a), achieving the highest DPR (up to 220 µm/ W in air). Следующее относится к рисунку 12 и таблице 2. Ланцет (L) отклонялся больше всего (с высокой значимостью для всех наконечников, \(p<\) 0,017) как в воздухе, так и в воде (рис. 12а), достигая самого высокого DPR. The following applies to Figure 12 and Table 2. Lancet (L) deflected the most (with high significance for all tips, \(p<\) 0.017) in both air and water (Fig. 12a), achieving the highest DPR . (do 220 μm/W in air). Smt. Figure 12 and Table 2 below.柳叶刀(L) 在空气和水中偏转最多（对所有尖端具有高显着性，\(p<\) 0.017）（图12a），实现最高DPR （在空气中高达220 µm/W）。柳叶刀(L) has the highest deflection in air and water (对所记尖端可以高电影性,\(p<\) 0.017) (图12a), and achieved the highest DPR (up to 220 µm/W in air). Ланцет (L) отклонялся больше всего (высокая значимость для всех наконечников, \(p<\) 0,017) в воздухе и воде (рис. 12а), достигая наибольшего DPR (до 220 мкм/Вт в воздухе). Lancet (L) deflected the most (high significance for all tips, \(p<\) 0.017) in air and water (Fig. 12a), reaching the highest DPR (up to 220 µm/W in air). In air, AX1 which had higher BL, deflected higher than AX2–3 (with significance, \(p<\) 0.017), while AX3 (which had lowest BL) deflected more than AX2 with a DPR of 190 µm/W. In air, AX1 which had higher BL, deflected higher than AX2–3 (with significance, \(p<\) 0.017), while AX3 (which had lowest BL) deflected more than AX2 with a DPR of 190 µm/W. В воздухе AX1 с более высоким BL отклонялся выше, чем AX2–3 (со значимостью \(p<\) 0,017), тогда как AX3 (с самым низким BL) отклонялся больше, чем AX2 с DPR 190 мкм/Вт. In air, AX1 with higher BL deflected higher than AX2–3 (with significance \(p<\) 0.017), whereas AX3 (with lowest BL) deflected more than AX2 with DPR 190 µm/W.在空气中，具有更高BL 的AX1 比AX2-3 偏转更高（具有显着性，\(p<\) 0.017），而AX3（具有最低BL）的偏转大于AX2，DPR 为190 µm/W。 In air, the deflection of AX1 with higher BL is higher than that of AX2-3 (significantly, \(p<\) 0.017), and the deflection of AX3 (with lowest BL) is greater than that of AX2, DPR is 190 µm/W . В воздухе AX1 с более высоким BL отклоняется больше, чем AX2-3 (значимо, \(p<\) 0,017), тогда как AX3 (с самым низким BL) отклоняется больше, чем AX2 с DPR 190 мкм/Вт. In air, AX1 with higher BL deflects more than AX2-3 (significant, \(p<\) 0.017), whereas AX3 (with lowest BL) deflects more than AX2 with DPR 190 μm/W. At 20 mm water, the deflection and PTE AX1–3 were not significantly different (\(p>\) 0.017). The levels of PTE in water (90.2–98.4%) were generally higher than in air (56–77.5%) (Fig. 12c), and the phenomenon of cavitation was noted during the experiment in water (Fig. 13 , see also additional information).
        The amount of tip deflection (mean ± SD, n = 5) measured for bevel L and AX1-3 in air and water (depth 20 mm) shows the effect of changing bevel geometry. The measurements were obtained using continuous single frequency sinusoidal excitation. (a) Peak to peak deviation (\(u_y\vec {j}\)) at the tip, measured at (b) their respective modal frequencies \(f_2\). (c) Power transfer efficiency (PTE, RMS, %) of the equation. (4) and (d) Deflection power factor (DPR, µm/W) calculated as deviation peak-to-peak and transmitted electrical power \(P_T\) (Wrms).
        A typical high-speed camera shadow plot showing the peak-to-peak deviation (green and red dotted lines) of a lancet (L) and axisymmetric tip (AX1–3) in water (20 mm depth) over a half cycle. cycle, at excitation frequency \(f_2\) (sampling frequency 310 kHz). The captured grayscale image has a size of 128×128 pixels and a pixel size of \(\approx\) 5 µm. Video can be found in additional information.
        Thus, we modeled the change in the bending wavelength (Fig. 7) and calculated the transferable mechanical mobility for combinations of pipe length and chamfer (Fig. 8, 9) for conventional lancet, asymmetric and axisymmetric chamfers of geometric shapes. Based on the latter, we estimated the optimal distance of 43 mm (or \(\approximately) 2.75\(\lambda _y\) at 29.75 kHz) from the tip to the weld, as shown in Fig. 5, and made Three axisymmetric bevels with different bevel lengths. We then characterized their frequency behavior in air, water, and 10% (w/v) ballistic gelatin compared to conventional lancets (Figures 10, 11) and determined the mode most suitable for bevel deflection comparison. Finally, we measured tip deflection by bending wave in air and water at a depth of 20 mm and quantified the power transfer efficiency (PTE, %) and deflection power factor (DPR, µm/W) of the insertion medium for each bevel. angular type (Fig. 12).
        Needle bevel geometry has been shown to affect the amount of needle tip deflection. The lancet achieved the highest deflection and the highest DPR compared to the axisymmetric bevel with lower average deflection (Fig. 12). The 4 mm axisymmetric bevel (AX1) with the longest bevel achieved a statistically significant maximum deflection in air compared to the other axisymmetric needles (AX2–3) (\(p < 0.017\), Table 2), but there was no significant difference. observed when the needle is placed in water. Thus, there is no obvious advantage to having a longer bevel length in terms of peak deflection at the tip. With this in mind, it appears that the bevel geometry studied in this study has a greater effect on deflection than the length of the bevel. This may be due to bending stiffness, for example depending on the overall thickness of the material being bent and the design of the needle.
        In experimental studies, the magnitude of the reflected flexural wave is affected by the boundary conditions of the tip. When the needle tip is inserted into water and gelatin, \(\text {PTE}_{2}\) is \(\approximately\) 95%, and \(\text {PTE}_{ 2}\) is \(\text {PTE}_{ 2}\) the values ​​are 73% and 77% for (\text {PTE}_{1}\) and \(\text {PTE}_{3}\), respectively (Fig. 11). This indicates that the maximum transfer of acoustic energy to the casting medium, i.e. water or gelatin, occurs at \(f_2\). Similar behavior was observed in a previous study31 using a simpler device configuration in the 41-43 kHz frequency range, in which the authors showed the dependence of the voltage reflection coefficient on the mechanical modulus of the embedding medium. The penetration depth32 and the mechanical properties of the tissue provide a mechanical load on the needle and are therefore expected to influence the resonant behavior of the UZEFNAB. Thus, resonance tracking algorithms (eg 17, 18, 33) can be used to optimize the acoustic power delivered through the needle.
        Simulation at bending wavelengths (Fig. 7) shows that the axisymmetric tip is structurally more rigid (i.e., more rigid in bending) than the lancet and asymmetric bevel. Based on (1) and using the known velocity-frequency relation, we estimate the bending stiffness at the tip of the needle as \(\about\) 200, 20 and 1500 MPa for lancet, asymmetric and axial inclined planes, respectively. This corresponds to \(\lambda_y\) of \(\approximately\) 5.3, 1.7, and 14.2 mm, respectively, at 29.75 kHz (Fig. 7a–c). Considering clinical safety during USeFNAB, the effect of geometry on the structural stiffness of the inclined plane should be assessed34.
        A study of the bevel parameters relative to the tube length (Fig. 9) showed that the optimal transmission range was higher for the asymmetric bevel (1.8 mm) than for the axisymmetric bevel (1.3 mm). In addition, the mobility is stable at \(\approximately) from 4 to 4.5 mm and from 6 to 7 mm for asymmetric and axisymmetric tilts, respectively (Fig. 9a, b). The practical significance of this discovery is expressed in manufacturing tolerances, for example, a lower range of optimal TL may mean that greater length accuracy is required. At the same time, the mobility plateau provides a greater tolerance for choosing the length of the dip at a given frequency without a significant impact on mobility.
        The study includes the following limitations. Direct measurement of needle deflection using edge detection and high-speed imaging (Figure 12) means that we are limited to optically transparent media such as air and water. We would also like to point out that we did not use experiments to test the simulated transfer mobility and vice versa, but used FEM studies to determine the optimal length for needle fabrication. With regard to practical limitations, the length of the lancet from tip to sleeve is \(\approximately) 0.4 cm longer than other needles (AX1-3), see fig. 3b. This can affect the modal response of the needle design. In addition, the shape and volume of solder at the end of a waveguide pin (see Figure 3) can affect the mechanical impedance of the pin design, introducing errors in the mechanical impedance and bending behavior.
        Finally, we have demonstrated that the experimental bevel geometry affects the amount of deflection in USeFNAB. If a larger deflection would have a positive effect on the effect of the needle on tissue, such as cutting efficiency after piercing, then a conventional lancet can be recommended in USeFNAB as it provides maximum deflection while maintaining adequate stiffness of the structural tip. . Moreover, a recent study35 has shown that greater tip deflection can enhance biological effects such as cavitation, which may contribute to the development of minimally invasive surgical applications. Given that increasing total acoustic power has been shown to increase biopsy yield in USeFNAB13, further quantitative studies of sample yield and quality are needed to evaluate the detailed clinical benefits of the studied needle geometry.