Local Area Tactile Stimulation Using Interference of Multi-Frequency Airborne Ultrasound.

In spatiotemporal modulation (STM) and lateral modulation (LM) used in conventional mid-air ultrasound tactile stimulation, single or multiple focuses are moved by switching the ultrasound transducer phases. A problem with the phase switching method is the limitation of the focus motion speed due to rapid phase switching that causes sound pressure fluctuations. This paper proposes an LM method using multiple-frequency ultrasound to shift the ultrasound focal point without switching the phase. This method can demonstrate a continuous and stable moving stimulus with high-frequency components, without producing unnecessary audible noise. Using the proposed broadband LM covering up to 400 Hz, we found that a high-frequency 400 Hz LM applied at a finger pad can display a stimulation area with the diameters comparable to or less than the half wavelength of 40 kHz ultrasound, where the perceptual size was evaluated as 4. 2 mm for the long axis diameter and 3. 4 mm for the short axis diameter.

Oocyte activation with phospholipase Cζ mRNA induces repetitive intracellular Ca2+ rises and improves the quality of pig embryos after intracytoplasmic sperm injection.

For the intracytoplasmic sperm injection (ICSI) procedure in pigs, an electrical pulse (EP) has been used as an effective method for oocyte stimulation, but unlike sperm, EP is unable to induce Ca2+ oscillations. In this study, we investigated the effects of generating artificial Ca2+ oscillations with phospholipase Cζ (PLCζ) mRNA, a candidate sperm factor, on fertilization, embryonic development, and gene expression after ICSI. Firstly, the concentration of PLCζ mRNA of a fixed volume (1.0 pl) that would induce a pattern of Ca2+ rise similar to that of in vitro fertilized (IVF) sperm was examined and determined to be 300 ng/µl. Secondly, the effects of oocyte stimulation methods on fertilization and embryonic development were investigated. ICSI-oocytes were activated by EP (EP group) or by PLCζ mRNA (PLCζ group). Furthermore, IVF-oocytes (IVF group) and ICSI-oocytes with and without an injection of buffer (buffer and untreated groups, respectively) were used as controls. It was found that the rates of normal fertilization in the PLCζ and EP groups were significantly higher than those in the buffer and untreated groups. The blastocyst formation rates did not differ among the groups. The embryo quality in the EP group was inferior to those in the PLCζ and IVF groups. Additionally, the expression level of a proapoptosis-related gene (Caspase-3) in the EP group was significantly higher than those in the PLCζ and IVF groups. Our data suggest that oocyte activation by PLCζ mRNA has the effect of improving embryo quality.

Is Common Trunk Anomaly Frequent in Hemifacial Spasm? Comparison with Normal Subjects Using Magnetic Resonance Imaging.

OBJECTIVE: Hemifacial spasm (HFS) results from vascular compression at the root exit of the facial nerve. Although the underlying etiology has yet to be identified, it has been suggested that congenital vascular anomalies are involved. We have hypothesized common trunk anomaly of the anterior inferior cerebellar artery (AICA) and posterior inferior cerebellar artery (PICA) which may play a role in HFS. However, no previous studies have directly compared the incidence of this anomaly between HFS patients and normal subjects. The present study was designed to address this gap in the literature. METHODS: This case-control study compared magnetic resonance angiography data from 65 HFS patients and 65 normal subjects. Dominant AICA/PICA is defined as the absence of PICA/AICA, with the remaining AICA/PICA supplying both vascular territories. The term "common trunk" encompasses both dominant AICA and dominant PICA. The frequency of common trunk and dominant AICA/PICA was compared between the 2 groups. RESULTS: There were no significant differences in the incidence of a common trunk (68.5% and 64.6%), dominant AICA (30.8% and 32.3%) and dominant PICA (37.7% and 32.3%) between the 2 groups. Additionally, no differences were found in the frequency of atherosclerosis risk factors. CONCLUSIONS: There was no apparent association between common trunk anomaly and HFS. It is suspected that some vascular anomalies other than a common trunk are involved in HFS.

A technique for reconstruction of a giant extracranial internal carotid artery aneurysm: A technical note.

Background: Surgery is effective for extracranial internal carotid artery (EICA) aneurysms. However, the risk of cranial nerve injury associated with surgical repair, such as graft-assisted resection and extracranial-intracranial bypass techniques, is relatively high. Here, we report two cases of surgical treatment for EICA aneurysms and describe the surgical techniques and strategies to avoid cranial nerve injury. Methods: Two patients presented to our facility with an increasing cervical pulsatile mass and no neurological symptoms. Angiography showed a large aneurysm in the cervical internal carotid artery. Surgical treatment was performed to prevent rupture of the aneurysm. In both patients, the aneurysm was strongly attached to the vagus nerve. The aneurysm and vagus nerve were carefully dissected using a low-power bipolar (20 Malis; 3 watts), leaving connective tissue on the vagus nerve side. Results: The aneurysm was detached from the vagus nerve without injury. Based on intraoperative findings, one patient underwent clipping, and the other underwent aneurysmectomy and primary closure for aneurysm obliteration and angioplasty. Both patients were discharged without any cranial nerve dysfunction. Conclusion: The selection of a strategy based on intraoperative findings and low-power bipolar cutting is important for the treatment of extracranial carotid artery aneurysms to preserve cranial nerves.

Sound Pressure Field Reconstruction for Airborne Ultrasound Tactile Display Encountering Obstacles.

Airborne ultrasound tactile display (AUTD) is used to provide non-contact tactile sensations with specific foci sound fields through the optimization of transducer phases. However, most existing optimization approaches are not directly applicable in case of an inhomogeneous medium, such as in the presence of obstacles between the AUTD and objective sound field. Certain methods can perform optimizations by considering the sound-scattering surfaces of the obstacles to compute the transmission matrix, which requires several complex measurements. This study proposed two methods to reconstruct the sound field under an inhomogeneous medium, wherein the need to calculate the impact of the obstacles was eliminated. The two methods are Bayesian optimization and greedy algorithm with brute-force search. Further, the process of the foci field generation was assumed as a black box. The proposed methods require only the pressure intensity at the control point generated by the input phases, discarding the need for transmission matrix in the presence of obstacles. Moreover, these methods offer the advantage of optimization of the phases in the presence of obstacles. This study explains the working of proposed methods in different forms of foci fields encountering obstacles.

Impact of the omicron phase on a highly advanced medical facility in Japan.

Background: Eight waves of the coronavirus disease 2019 (COVID-19) epidemic have been observed in Japan. This retrospective study was conducted to clarify the clinical characteristics of pediatric COVID-19 patients. Methods: We studied 121 patients admitted to the Jichi Children's Medical Center Tochigi between April 2020 and March 2023. Incidence of pediatric COVID-19 in Tochigi Prefecture was used to examine hospitalization and severe illness rates. Results: The mean age of the patients was 3 years and 8 months. One hundred and eleven patients (91.7%) were hospitalized after January 2022 (after the 6th wave), when the Omicron strain became endemic in Japan. Convulsions occurred in 30 patients (24.8%), all of whom were admitted after the 6th wave. Twenty-three of the 30 patients had no underlying disease. Eleven patients (9.1%) were diagnosed with acute encephalopathy. One patient died due to hemorrhagic shock and encephalopathy syndrome and two had sequelae after the 6th wave. The patient who died due to encephalopathy had hypercytokinemia. In the Tochigi Prefecture, the number of pediatric COVID-19 patients increased after the 6th wave, but the hospitalization rate declined. The rate of severe illness did not change before the end of 5th and after the 6th wave. Conclusion: Although the rate of severe illness in patients with pediatric COVID-19 did not increase after the 6th wave, some patients had complicated critical illnesses. Systemic inflammatory reaction was considered to have been associated with the severe encephalopathy.

Predictors of procedural complications in balloon pulmonary angioplasty for chronic thromboembolic pulmonary hypertension.

BACKGROUND: Balloon pulmonary angioplasty (BPA) is an effective treatment for inoperable chronic thromboembolic pulmonary hypertension, with good results reported for residual pulmonary hypertension (PH) after pulmonary endarterectomy (PEA). However, BPA is associated with complications, such as pulmonary artery perforation and vascular injury, which can lead to critical pulmonary hemorrhage requiring embolization and mechanical ventilation. Furthermore, the risk factors for occurrence of complications in BPA are unclear; therefore, this study aimed to evaluate predictors of procedural complications in BPA. METHODS: In this retrospective study, we collected clinical data (patient characteristics, details of medical therapy, hemodynamic parameters, and details of the BPA procedure) from 321 consecutive sessions involving 81 patients who underwent BPA. Procedural complications were evaluated as endpoints. RESULTS: BPA for residual PH after PEA was performed in 141 sessions (43.9 %), which involved 37 patients. Procedural complications were observed in 79 sessions (24.6 %), including severe pulmonary hemorrhage requiring embolization in 29 sessions (9.0 % of all sessions). No patients experienced severe complications requiring intubation with mechanical ventilation or extracorporeal membrane oxygenation. Age ≥ 75 years and mean pulmonary artery pressure ≥ 30 mmHg were independent predictors of procedural complications. Residual PH after PEA was a significant predictor of severe pulmonary hemorrhage requiring embolization (adjusted odds ratio, 3.048; 95 % confidence interval, 1.042-8.914, p = 0.042). CONCLUSIONS: Older age, high pulmonary artery pressure, and residual PH after PEA increase the risk of severe pulmonary hemorrhage requiring embolization in BPA.

Balloon pulmonary angioplasty followed by pulmonary endarterectomy: Combination treatment for high-surgical-risk patients with chronic thromboembolic pulmonary hypertension.

OBJECTIVES: Our goal was to evaluate the combined effects of balloon pulmonary angioplasty (BPA) followed by pulmonary endarterectomy (PEA) to treat high-surgical-risk patients with chronic thromboembolic pulmonary hypertension (CTEPH). METHODS: This study included 58 patients with CTEPH who had pulmonary vascular resistance of ≥1000 dyn·s/cm5, mean pulmonary arterial pressure (mPAP) of ≥45 mmHg or mPAP of 38-44 mmHg with comorbidities. Of these, 21 patients underwent the combined therapy of BPA followed by PEA (BPA group) and 37 underwent direct PEA (non-BPA group). Preoperative and postoperative results were compared between the 2 groups. An early postoperative composite event comprised the postoperative use of extracorporeal membrane oxygenation or intra-aortic balloon pump, in-hospital death, rescue BPA, prolonged ventilation, tracheostomy, prolonged stay in the intensive care unit, deep sternal wound infection and cerebral infarction. RESULTS: Before the first intervention (before BPA or direct PEA), patients in the BPA group had a higher mPAP than those in the non-BPA group. After undergoing BPA before PEA, the BPA group demonstrated significantly decreased mPAP and pulmonary vascular resistance (43 vs 52 mmHg, P < 0.001; 636 vs 965 dyn·s/cm5, P = 0.003, respectively) and significantly increased cardiac output (4.1 vs 3.5 l/min, P = 0.041). Notably, the number of patients with the early postoperative composite event was significantly lower in the BPA group than in the non-BPA group (4.8% vs 35.1%, P = 0.011). CONCLUSIONS: Compared with direct PEA, the combination therapy of BPA followed by PEA can be a feasible and effective risk-reduction strategy for high-surgical-risk patients with CTEPH.

Continuous cyclosporine a infusion in patients with severe Kawasaki disease.

BACKGROUND: The efficacy and safety of continuous intravenous infusion of cyclosporine A (CICsA) in patients with intravenous immunoglobulin-resistant Kawasaki disease are unclear. METHODS: Between 2010 and 2020, 83 patients with Kawasaki disease that was not responsive to intravenous immunoglobulin (total dose ≥ 4 g/kg) were enrolled. All patients were started on CICsA (3 mg/kg/day) and switched to oral cyclosporine A (CsA) (4-6 mg/kg/day). Treatment efficacy, occurrence of coronary artery lesions (CALs), and laboratory parameters were evaluated. Patients were divided into two groups according to CICsA response: the responder group (afebrile ≤24 h after CICsA without additional treatment) and the weak responder group (afebrile >24 h after CICsA requiring additional treatment). RESULTS: Fifty-five patients became afebrile within 24 and 74 h became afebrile in less than 72 h. Adverse events included hypertension in four and hyperkalemia in two patients. Thirty-nine patients were defined as responders and 44 patients as weak responders. There were no significant differences in CAL between the two groups. In weak responders, white blood cells, neutrophils, and C-reactive protein levels were higher, and albumin, immunoglobulin G, and CsA concentration were lower than in responders, indicating that weak responders had more severe inflammatory findings. However, there were no significant differences in CAL. Logistic regression analysis revealed that the response to treatment for CICsA was associated with immunoglobulin G levels at baseline and CsA concentrations the day after CICsA. CONCLUSION: Although CICsA required additional treatments in about half of the cases, a favorable clinical course was observed by using this strategy, especially for reducing CAL.

Screening of α-amino acid ester acyl transferase variant with improved activity by combining rational and random mutagenesis.

Random and rational mutagenesis of an α-amino acid ester acyl transferase from Sphingobacterium siyangensis AJ2458 (SAET) was conducted to examine the production of aspartame, an α-l-aspartyl-l-phenylalanine methyl ester. We previously reported aspartame production via combination of enzymatic and chemical methods. However, the productivity of the aspartame intermediate by SAET was approximately one-fifth that of l-alanyl-l-glutamine (Ala-Gln), whose production method has already been established. Here, to improve the enzymatic activity of SAET, we performed random mutagenesis in the gene encoding SAET and obtained 10 mutations that elevated the enzymatic activity (1.2- to 1.7-fold increase) relative to that of wild-type SAET. To further improve the activity, we performed mutagenesis to optimize the combination of the obtained mutations and finally selected one SAET variant with 10 amino acid substitutions (M35-4 SAET). An Escherichia coli strain overexpressing M35-4 SAET displayed a 5.7-fold higher activity than that of the wild-type SAET, which was almost equal to that of Ala-Gln by an E. coli strain overexpressing wild-type SAET. The Vmax value of M35-4 SAET was 2.0-fold greater, and its thermostability was higher than those of wild-type SAET. These results suggest that the obtained SAET variants contribute to improvement in aspartame production.

Successful Management in an Infant Patient of PHACE Syndrome with a Complicated Aortic Arch Anomaly.

PHACE syndrome is a congenital disorder often associated with a cervicofacial infantile hemangioma and complicated cardiovascular malformations. Patients with PHACE syndrome often have complex aortic arch anomalies, longer aortic stenosis or agenesis segments, and increased vascular tortuosity; therefore, perioperative management and surgical repair are challenging. We report a case of a female infant with PHACE syndrome and complex cardiovascular anomalies such as a double aortic arch associated with interruption of the left aortic arch, coarctation of the right aortic arch, patent ductus arteriosus, ventricular septal defect, and atrial septal defect. She was born at 36 weeks of gestation (birth weight, 2,150 g) and the diagnosis was confirmed by three-dimensional computed tomography. Because her patent ductus arteriosus did not close at first, her heart failure was managed preoperatively without prostaglandin E 1. We initially attempted to promote weight gain. Surgical planning and simulation were performed using the patient-specific three-dimensional cardiovascular model created from computed tomography data. She underwent a successful aortic arch reconstruction by an end-to-side anastomosis with anterior patch augmentation at the age of 56 days. Detailed planning and simulation before surgery were vital in achieving favorable outcomes. Careful management and surgical planning using a patient-specific three-dimensional model are vital, especially in patients with complex malformations, such as in our case.

Effects of 0.01% Atropine Instillation Assessed Using Swept-Source Anterior Segment Optical Coherence Tomography.

In this paper, we assessed the short-term effects of 0.01% atropine eye drops on anterior segment parameters by performing ocular biometry using a swept-source anterior segment optical coherence tomography system (AS-OCT). We recruited 17 healthy volunteers (10 men and 7 women aged 24-35 years) with no history of eye disease. Participants without accommodative demand demonstrated significant mydriasis 1 h after the atropine instillation (4.58 ± 0.77 to 5.41 ± 0.83 mm). Pupil diameters with a 5 diopter (D) accommodative stimulus at 1 h (4.70 ± 1.13 mm) and 24 h (4.05 ± 1.06 mm) after atropine instillation were significantly larger than those at baseline (3.71 ± 0.84 mm). Barring pupil diameter, no other biometric parameters significantly changed at any point in time after atropine instillation without accommodative demand. However, with an accommodative stimulus, anterior chamber depth (ACD) at 1 h and posterior curvature of the lens at 1 and 24 h were both significantly larger than those before atropine instillation. Using AS-OCT, we detected a slight decrease in the accommodation response of ocular biometric components evoked by 0.01% atropine instillation. Morphologically, our measurements suggested a change in the ACD and horizontal radius of the lens' posterior surface curvatures due to the subtle reduction of accommodation.

Radiation Pressure Field Reconstruction for Ultrasound Midair Haptics by Greedy Algorithm With Brute-Force Search.

Non-contact tactile presentation using ultrasound phased arrays is becoming a powerful method for providing haptic feedback on bare skin without restricting the user's movement. In such ultrasonic mid-air haptics, it is often necessary to generate multiple ultrasonic foci simultaneously, which requires solving the inverse problem of amplitudes and phases of the transducers in a phased array. Conventionally, matrix calculation methods have been used to solve this inverse problem. However, a matrix calculation requires a non-negligible amount of time when the number of control points and the number of transducers in the array are large. In this article, we propose a simple method based on a greedy algorithm and brute-force search to solve the field reconstruction problem. The proposed method directly optimizes the desired field without matrix calculation or target field phase optimization. The empirical results indicate that the proposed method can reproduce the target sound with an accuracy of more than 80%.

Efficacy and safety of balloon pulmonary angioplasty for residual pulmonary hypertension after pulmonary endarterectomy.

BACKGROUND: Pulmonary endarterectomy (PEA) is the standard treatment for chronic thromboembolic pulmonary hypertension (CTEPH), although some patients may experience residual pulmonary hypertension (PH). It is unclear whether balloon pulmonary angioplasty (BPA) is effective for residual PH after PEA. This study aimed to compare the BPA outcomes between patients with residual PH after PEA and those with inoperable CTEPH. METHODS: This retrospective study compared BPA for residual PH after PEA (25 patients, 101 BPA sessions) and BPA alone for inoperable CTEPH (21 patients, 89 BPA sessions). All patients underwent right heart catheterisation and functional and laboratory tests before PEA or before and after BPA. RESULTS: There was no difference in the number of BPA sessions per patient (4.0 ± 1.9 vs. 4.2 ± 1.9, p = 0.671). No significant differences were observed with respect to the mean pulmonary artery pressure (23.6 ± 9.1 vs. 21.9 ± 5.7 mmHg, p = 0.44), pulmonary vascular resistance (3.7 ± 0.5 vs. 2.8 ± 1.2 Wood units, p = 0.14), 6-min walking distance (392.1 ± 117.7 vs. 452.4 ± 90.1 m, p = 0.096), and World Health Organization functional class (I/II/III/IV: 14/11/0/0 vs. 9/12/0/0, p = 0.375). Severe haemoptysis requiring embolisation was more common in the PH after PEA group (16.0% vs. 5.4%, p = 0.018). However, no patients required mechanical ventilation or extracorporeal membrane oxygenation, and there were no procedural deaths. CONCLUSION: Although BPA might be effective for residual PH after PEA, it was associated with a high rate of haemoptysis.

AUTD3: Scalable Airborne Ultrasound Tactile Display.

Through nonlinear effects, airborne ultrasound phased arrays enable mid-air tactile presentations, as well as auditory presentation and acoustic levitation. To create workplaces flexibly, we have developed a scalable phased array system in which multiple modules can be connected via Ethernet cables and controlled from a PC or other host device. Each module has 249 transducers and the software used can individually specify the phase and amplitude of each of the connected transducers. Using EtherCAT for communication, the system achieves high accuracy synchronization among the connected modules. In this article, we describe the details of the hardware and software architecture of the developed system and evaluate it. We experimentally confirmed the synchronization of 20 modules within an accuracy of 0.1 µs and the phase and amplitude can be specified at 8 bits resolution. In addition, using nine modules, we confirmed that we could make a focal point of the size consistent with the theory at 500 mm above the array surface.

Supramolecular linear coordination polymers of human serum albumin and haemoglobin.

We describe the synthesis, structure, and functionalities of water-soluble linear coordination polymers of human serum albumin and haemoglobin, which are connected via a bis(terpyridyl)-Fe2+ complex. These protein fibres were self-assembled by lyophilisation and were transformed into single-wall nanotubes. The biological activities of the protein units were perfectly preserved in the long fibres.

Antiphospholipid syndrome with chronic thromboembolic pulmonary hypertension and coronary artery disease: a case report.

BACKGROUND: Antiphospholipid syndrome (APS) is characterized by the production of antiphospholipid antibodies associated with recurrent vascular thrombosis. There have been few reports of combination of chronic thromboembolic pulmonary hypertension (CTEPH) and coronary artery disease in APS, therefore, it is unclear about appropriate treatment strategy. CASE PRESENTATION: The patient was a 39 year-old-lady who had been suffering from hypoxia without chest pain. Transthoracic echocardiography showed severe pulmonary hypertension and mild hypokinesis of left ventricular anteroseptal wall. Simultaneously with the diagnosis of CTEPH, coronary angiography revealed severe stenosis of the left anterior descending artery. She underwent pulmonary endarterectomy (PEA) concomitant with coronary artery bypass grafting (CABG) successfully. CABG could be performed concomitantly during rewarming. During perioperative period, she was free from any thromboembolic and bleeding events despite receiving anticoagulant and antiplatelet therapies. CONCLUSIONS: PEA concomitant with coronary artery bypass grafting was feasible for APS patients complicated with CTEPH and coronary artery disease. APS patients with the presence of left ventricular dysfunction should be evaluated for coronary artery disease.

Rapid and Systematic Exploration of Chemical Space Relevant to Artemisinins: Anti-malarial Activities of Skeletally Diversified Tetracyclic Peroxides and 6-Aza-artemisinins.

To achieve both structural changes and rapid synthesis of the tetracyclic scaffold relevant to artemisinins, we explored two kinds of de novo synthetic approaches that generate both skeletally diversified tetracyclic peroxides and 6-aza-artemisinins. The anti-malarial activities of the tetracyclic peroxides with distinct skeletal arrays, however, were moderate and far inferior to artemisinins. Given the privileged scaffold of artemisinins, we next envisioned element implantation at the C6 position with a nitrogen without the trimmings of substituents and functional groups. This molecular design allowed the deep-seated structural modification of the hitherto unexplored cyclohexane moiety (C-ring) while keeping the three-dimensional structure of artemisinins. Notably, this approach induced dramatic changes of retrosynthetic transforms that allow an expeditious catalytic asymmetric synthesis with generation of substitutional variations at three sites (N6, C9, and C3) of the 6-aza-artemisinins. These de novo synthetic approaches led to the lead discovery with substantial intensification of the in vivo activities, which undermine the prevailing notion that the C-ring of artemisinins appears to be merely a structural unit but to be a functional area as the anti-malarial pharmacophore. Furthermore, we unexpectedly found that racemic 6-aza-artemisinin (33) exerted exceedingly potent in vivo efficacies superior to the chiral one and the first-line drug, artesunate.

Anterior Segment Biometry During Accommodation and Effects of Cycloplegics by Swept-Source Optical Coherence Tomography.

PURPOSE: We analyzed changes in the crystalline lens during accommodation and the effects of cycloplegics by swept-source anterior-segment optical coherence tomography (AS-OCT). MATERIALS AND METHODS: Twenty healthy volunteers (7 males and 13 females, aged 22-34 years), with no history of eye disease except for refractive errors, were recruited. Biometric parameters, including anterior chamber depth (ACD), lens thickness (LT), and anterior and posterior curvature of the lens (ACL and PCL), were measured using AS-OCT (CASIA2). The measurements were performed with or without an accommodative demand of 5.0 diopters (D). The same tests were repeated following the topical administration of 1% cyclopentolate or a compounding agent comprising 0.5% tropicamide and 0.5% phenylephrine. RESULTS: The AS-OCT system was capable of simultaneous visualization of all optical components of the anterior segment in a single frame. ACD, LAC, and LPC decreased and LT increased significantly during 5.0 D accommodative stimulation in both eyes. Both cyclopentolate and tropicamide/phenylephrine eyedrops led to deeper ACD, thinner LT, and flatter LAC. There were no significant differences in all lens parameters despite having 5.0 D accommodative stimulation in both eyes with cycloplegia. CONCLUSION: Our results suggest that both tropicamide/phenylephrine and cyclopentolate eyedrops have enough cycloplegic effects in young adults.

Reducing Amplitude Fluctuation by Gradual Phase Shift in Midair Ultrasound Haptics.

Ultrasound emitted from an array of transducers can produce various tactile sensations by temporally controlling the phase and amplitude of the transducers. However, the controllability in haptic applications has not been well examined. This article clarifies a phase shift of the driving signal causes amplitude fluctuation of emitted ultrasound, even under a constant driving amplitude. We demonstrate theoretically that this problem exists in general resonant systems with various quality factors, and point out that it produces radiation force decrease and audible noise. We also show a method to reduce the fluctuation and quantitatively evaluate the effectiveness. The results provide the measure of the displayed force fluctuation by a fast focus movement and enable silent haptic stimulation.