Investigation of feasibility of noise suppression method for cavitation-enhanced high-intensity focused ultrasound treatment.

In high-intensity focused ultrasound (HIFU) treatment, a method that monitors tissue changes while irradiating therapeutic ultrasound is needed to detect changes in the order of milliseconds due to thermal coagulation and the presence of cavitation bubbles. The new filtering method in which only the HIFU noise was reduced while the tissue signals remained intact was proposed in the conventional HIFU exposure in our preliminary study. However, HIFU was irradiated perpendicular to the direction of the imaging ultrasound in the preliminary experiment, which was believed to be impractical. This study investigated the efficacy of the proposed method a parallel setup, in which both HIFU and imaging beams have the same axis just as in a practical application. In addition, this filtering algorithm was applied to the "Trigger HIFU" sequence in which ultrasound-induced cavitation bubbles were generated in the HIFU focal region to enhance heating. In this setup and sequence, HIFU noise level was increased and the summation or difference tone induced by the interaction of HIFU waves with the imaging pulse has the potential to affect this proposed method. Ex-vivo experiments proved that the HIFU noise was selectively eliminated by the proposed filtering method in which chaotic acoustic signals were emitted by the cavitation bubbles at the HIFU focus. These results suggest that the proposed method was practically efficient for monitoring tissue changes in HIFU-induced cavitation bubbles.

Sonodynamically-induced Anticancer Effects of Polyethylene Glycol-Modified Carbon Nano Tubes.

BACKGROUND/AIM: Sonodynamic cancer therapy is based on the preferential uptake and/or retention of a sonosensitizing drug (sonosensitizer) in tumor tissues and the subsequent activation of the drug by ultrasound irradiation. In the present study, we investigated the sonodynamically-induced antitumoral effect with functionalized carbon nanotubes, such as poly-ethylene glycol-modified carbon nanotubes (PEG-modified CNTs). MATERIALS AND METHODS: Antitumor effects were evaluated using histological observation and assessing tumor growth following sonodynamic exposure to PEG-modified CNTs. RESULTS: The combined treatment of 100 µM PEG-modified CNT and ultrasound induced a 2-fold cytotoxicity. Sodium azide, which quenches singlet oxygen, significantly inhibited ultrasonication induced cell damage in the presence of PEG-modified CNTs. This suggests that singlet oxygen produced by the combined use of PEG-modified CNTs and ultrasound is involved in the induction of antitumoral effects. The destruction of tumor tissue was observed with the ultrasonic treatment in combination with PEG-modified CNTs, while neither the treatment with PEG-modified CNTs alone nor ultrasound alone caused any necrosis. CONCLUSION: These results indicate that PEG-modified CNT functions as a sonosensitizer and is effective for sonochemical treatment of solid tumors.

Ultrasound Sub-pixel Motion-tracking Method with Out-of-plane Motion Detection for Precise Vascular Imaging.

Ultrasound vascularity imaging provides important information for differential diagnosis of tumors. Peak-hold (PH) is a useful technique for precisely imaging small vessels by selecting a maximum brightness in each pixel through the frames obtained sequentially. To use PH successfully one needs motion compensation to reduce image blur, but out-of-plane motion cannot be avoided. To address this problem, we developed a sub-pixel motion-tracking method with out-of-plane motion detection (OPMD). It is a combination of the sum of the absolute differences (SAD) method and the Kanade-Lucas-Tomasi method and can be accurately applied to various motions. The value from OPMD (γ) is defined as a statistical value obtained from the distribution of residual values in the SAD procedure with the obtained frames. The value is ideally 0, and the frames having large γ are removed from the PH procedure. The accuracy of the proposed tracking method was found by a simulation study to be approximately 20 µm. We also found, through a phantom experiment, that the value of γ sensitively increased enough to detect out-of-plane motion. Most important, γ begins to increase before tracking errors occur. This suggests that OPMD can be used to predict tracking errors and effectively remove frames from the PH procedure. An in vivo experiment with a rabbit showed that the PH image obtained with motion tracking clearly revealed peripheral vessels that were blurred in the PH image obtained without motion tracking. We also found that the image quality becomes better when OPMD was used to remove frames including out-of-plane motion.

Sonodynamic Therapy: Advances and Challenges in Clinical Translation.

Sonodynamic therapy (SDT) consists of the synergetic interaction between ultrasound and a chemical agent. In SDT, the cytotoxicity is triggered by ultrasonic stimuli, notably through cavitation. The unique features of SDT are relevant in the clinical context more than ever: the need for efficacy, accuracy, and safety while being noninvasive and preserving the patient's quality of life. However, despite the promising results of this technique, only a few clinical reports describe the use of SDT. The objective of this article is to provide an extensive overview of the clinical and preclinical research conducted in vivo on SDT, to identify the limitations, and to detail the developed strategies to overcome them.

Evaluation of a Three Hydrophones Method for 2-Dimensional Cavitation Localization.

Cavitation is a critical parameter in various therapeutic applications involving ultrasound (US) such as histotrispy, lithothripsy, drug delivery, and cavitation-enhanced hyperthermia. A cavitation exposure outside the region of interest may lead to suboptimal treatment efficacy or in a worse case, to safety issues. Current methods of localizing cavitation are based on imaging approaches, such as beamforming the cavitation signals received passively by a US imager. These methods, although efficient, require expensive equipment, which may discourage potential future developments. We propose a threehydrophone method to localize the cavitation cloud source. Firstly, the delays between the three receptors are measured by detecting the maximum of their inter-correlations. Then, the position of the source is calculated by either minimizing a cost function or solving hyperbolic equations. After a numerical validation, the method was assessed experimentally. This method was able to track a source displacement with accuracy similar to the size of the cavitation cloud (2-4 millimeters). This light and versatile method provides interesting perspectives since localization can be executed in real time and the extension to three-dimensional localization seems straightforward.

Evaluation of a Three-Hydrophone Method for 2-D Cavitation Localization.

Cavitation is a critical parameter in various therapeutic applications involving ultrasound (US) such as histotripsy, lithotripsy, drug delivery, and cavitation-enhanced hyperthermia. A cavitation exposure outside the region of interest may lead to suboptimal treatment efficacy or in a worse case, to safety issues. Current methods of localizing cavitation are based on imaging approaches, such as beamforming the cavitation signals received passively by a US imager. These methods, although efficient, require expensive equipment, which may discourage potential future developments. We propose a three-hydrophone method to localize the cavitation cloud source. First, the delays between the three receptors are measured by detecting the maximum of their intercorrelations. Then, the position of the source is calculated by either minimizing a cost function or solving hyperbolic equations. After a numerical validation, the method was assessed experimentally. This method was able to track a source displacement with accuracy similar to the size of the cavitation cloud (2-4 mm). This light and versatile method provides interesting perspectives since localization can be executed in real time, and the extension to 3-D localization seems straightforward.

Cavitation-threshold Determination and Rheological-parameters Estimation of Albumin-stabilized Nanobubbles.

Nanobubbles (NBs) are of high interest for ultrasound (US) imaging as contrast agents and therapy as cavitation nuclei. Because of their instability (Laplace pressure bubble catastrophe) and low sensitivity to US, reducing the size of commonly used microbubbles to submicron-size is not trivial. We introduce stabilized NBs in the 100-250-nm size range, manufactured by agitating human serum albumin and perfluoro-propane. These NBs were exposed to 3.34- and 5.39-MHz US, and their sensitivity to US was proven by detecting inertial cavitation. The cavitation-threshold information was used to run a numerical parametric study based on a modified Rayleigh-Plesset equation (with a Newtonian rheology model). The determined values of surface tension ranged from 0 N/m to 0.06 N/m. The corresponding values of dilatational viscosity ranged from 5.10-10 Ns/m to 1.10-9 Ns/m. These parameters were reported to be 0.6 N/m and 1.10-8 Ns/m for the reference microbubble contrast agent. This result suggests the possibility of using albumin as a stabilizer for the nanobubbles that could be maintained in circulation and presenting satisfying US sensitivity, even in the 3-5-MHz range.

Visualization of murine lymph vessels using photoacoustic imaging with contrast agents.

Metastasis frequently occurs even in the early stage of breast cancer. This research studied the feasibility of using photoacoustic (PA) imaging for identifying metastasis in the lymph vessels of mice. The photoacoustic efficiency of various contrast agents was investigated, and the influence of scattered light was evaluated by using a lymph vessel phantom. The lymph vessels of mice were then visualized using the selected contrast agents: indocyanine green (ICG) and gold nanorods (AuNR). The attenuation of the PA imaging was -1.90 dB/mm, whereas that of the fluorescence imaging was -4.45 dB/mm. The results indicate the potential of identifying sentinel lymph nodes by using PA imaging with these contrast agents.

Development of Real-Time 3-D Photoacoustic Imaging System Employing Spherically Curved Array Transducer.

Photoacoustic (PA) imaging is a promising imaging modality to visualize specific living tissues based on the light absorption coefficients without dyeing. In this paper, a real-time PA imaging system with a tunable laser was newly developed with an originally designed spherically curved array transducer. Five different series of experiments were conducted to validate the PA measurement system. The peak frequency of the transducer response was 17.7 MHz, and a volume-imaging rate of 3-D volume imaging was 10-20 volumes per second. The spatial resolution of imaging was 90- [Formula: see text] along both the axial and lateral directions. The developed imaging system could measure a difference on an absorption coefficient of gold nanorods. Additionally, the PA imaging could visualize the in vivo microvasculatures of a human hand. This PA imaging system with higher spatial-temporal resolution and the tunable laser further should enhance our understanding of not only basic properties of the photo acoustics but also clinical applications.

Basic study of less invasive high-intensity focused ultrasound (HIFU) in fetal therapy for twin reversed arterial perfusion (TRAP) sequence.

PURPOSE: The objective of the present study was to develop a high-intensity focused ultrasound (HIFU) transducer more suitable for clinical use in fetal therapy for twin reversed arterial perfusion (TRAP) sequence. MATERIALS AND METHODS: We created a cooling and degassed water-circulating-type HIFU treatment device. HIFU was applied to renal branch vessels in three rabbits. Sequential HIFU irradiation contains a trigger wave, heating wave, and rest time. The duration of HIFU application was 10 s/course. Targeting could be achieved by setting the imaging probe in the center and placing the HIFU beam and imaging ultrasonic wave on the same axis. RESULT: We confirmed under sequential HIFU irradiation with a total intensity of 1.94 kW/cm(2) (spatial average temporal average intensity) that the vein and artery were occluded in all three rabbits. CONCLUSION: Simultaneous occluding of the veins and arteries was confirmed with trigger waves and a resting phase using the HIFU transducer treatment device created for this study. Clinical application appears possible and may represent a promising option for fetal therapy involving TRAP sequence.

Induction of Apoptosis by Functionalized Fullerene-based Sonodynamic Therapy in HL-60 cells.

Ultrasound has been widely utilized for medical diagnosis and therapy due to its ability to penetrate deep-seated tissue with less attenuation of energy and minimal undesirable side-effects. Functionalized fullerenes, such as polyhydroxy fullerene (PHF), have attracted particular attention due to their water solubility and potential application in tumor imaging and therapy as carbon nanomaterials. The present study investigated sonodynamically-induced apoptosis using PHF. Cell suspensions were treated with 2-MHz continuous ultrasound in the presence of PHF for 3 min and apoptosis was assessed by cell morphology using confocal microscopy, fragmentation of DNA (ladder pattern after agarose-gel electrophoresis) and caspase-3 activation. Cells were ultrasound-irradiated from the bottom of the culture dishes under the following condition: frequency, 2 MHz; output power, 3 W/cm(2) Electron spin resonance was used to measure reactive oxygen species. The number of apoptotic cells after sonodynamic exposure (ultrasound and PHF) was significantly higher than produced from other treatments, such as ultrasound alone and PHF alone. Furthermore, DNA fragmentation, caspase-3 activation and enhanced 2,2,6,6-tetramethyl-4-piperidinyloxy (4oxoTEMPO) formation were observed in the sonodynamically-treated cells. Histidine, a well-known reactive oxygen scavenger, significantly inhibited sonodynamically-induced apoptosis, caspase-3 activation and 4oxoTEMPO formation. Sonodynamic therapy with PHF induced apoptosis that was characterized by a series of typical morphological features, such as shrinkage of the cell and fragmentation into membrane-bound apoptotic bodies, in HL-60 cells. The significant inhibition of sonodynamically-induced apoptosis, caspase-3 activation, and 4oxoTEMPO formation due to histidine and tryptophan suggests that reactive oxygen species, such as singlet oxygen, are involved in the sonodynamic induction of apoptosis. These findings indicate that PHF-mediated sonodynamic therapy can trigger caspase-dependent apoptosis and oxidative injury, thus possibly playing a vital role in apoptotic signaling cascades.

Detection of tissue coagulation by decorrelation of ultrasonic echo signals in cavitation-enhanced high-intensity focused ultrasound treatment.

BACKGROUND: A noninvasive technique to monitor thermal lesion formation is necessary to ensure the accuracy and safety of high-intensity focused ultrasound (HIFU) treatment. The purpose of this study is to ultrasonically detect the tissue change due to thermal coagulation in the HIFU treatment enhanced by cavitation microbubbles. METHODS: An ultrasound imaging probe transmitted plane waves at a center frequency of 4.5 MHz. Ultrasonic radio-frequency (RF) echo signals during HIFU exposure at a frequency of 1.2 MHz were acquired. Cross-correlation coefficients were calculated between in-phase and quadrature (IQ) data of two B-mode images with an interval time of 50 and 500 ms for the estimation of the region of cavitation and coagulation, respectively. Pathological examination of the coagulated tissue was also performed to compare with the corresponding ultrasonically detected coagulation region. RESULTS: The distribution of minimum hold cross-correlation coefficient between two sets of IQ data with 50-ms intervals was compared with a pulse inversion (PI) image. The regions with low cross-correlation coefficients approximately corresponded to those with high brightness in the PI image. The regions with low cross-correlation coefficients in 500-ms intervals showed a good agreement with those with significant change in histology. CONCLUSIONS: The results show that the regions of coagulation and cavitation could be ultrasonically detected as those with low cross-correlation coefficients between RF frames with certain intervals. This method will contribute to improve the safety and accuracy of the HIFU treatment enhanced by cavitation microbubbles.

Personal Authentication Analysis Using Finger-Vein Patterns in Patients with Connective Tissue Diseases--Possible Association with Vascular Disease and Seasonal Change.

OBJECTIVE: To examine how connective tissue diseases affect finger-vein pattern authentication. METHODS: The finger-vein patterns of 68 patients with connective tissue diseases and 24 healthy volunteers were acquired. Captured as CCD (charge-coupled device) images by transmitting near-infrared light through fingers, they were followed up in once in each season for one year. The similarity of the follow-up patterns and the initial one was evaluated in terms of their normalized cross-correlation C. RESULTS: The mean C values calculated for patients tended to be lower than those calculated for healthy volunteers. In midwinter (February in Japan) they showed statistically significant reduction both as compared with patients in other seasons and as compared with season-matched healthy controls, whereas the values calculated for healthy controls showed no significant seasonal changes. Values calculated for patients with systemic sclerosis (SSc) or mixed connective tissue disease (MCTD) showed major reductions in November and, especially, February. Patients with rheumatoid arthritis (RA) and patients with dermatomyositis or polymyositis (DM/PM) did not show statistically significant seasonal changes in C values. CONCLUSIONS: Finger-vein patterns can be used throughout the year to identify patients with connective tissue diseases, but some attention is needed for patients with advanced disease such as SSc.

Focused ultrasound transducer for thermal treatment.

Air-backed transducers have been employed for thermal ultrasonic treatment including both ablation and hyperthermia because the power efficiency rather than the bandwidth is a main concern, unlike a typical imaging transducer working in a pulse mode. The characteristic of an air-backed piezoelectric transducer with a matching layer is analysed, and the role and choice of the matching layer is discussed. An element size of a focused array transducer, appropriate for such thermal treatment, is then estimated, and the characteristic of a piezoceramic transducer element of such a size was numerically analysed using a finite element code. The characteristic of a piezocomposite transducer element is also numerically analysed and its suitability to such a therapeutic array transducer is discussed.

Intrinsic elastography and its dependence on arterial flow volume.

We propose a new estimation method of tissues stiffness from deformation induced by arterial pulsation. The new method was named Intrinsic Elastography (IE). Under two assumptions that the deformation induced by pulsation propagates throughout the body, and the propagation velocity (PV) is closely related to the mechanical properties of tissues, the IE can evaluate the tissue stiffness based on the PV. However, this method has an issue that the observed PVs change with the changes of amounts of the flow. In this paper, we propose the new estimation method in order to estimate true shear elasticity in spite of the changes. The results was compared to the results of SWI. The results was almost identical to the result of SWI, or showed the similar results.

Measurement of regional pulse-wave velocity using spatial compound imaging of the common carotid artery in vivo.

Pulse-wave velocity (PWV) is an important index for diagnosing cardiovascular diseases. The pulse wave is volumetric change induced by heartbeat or inflowing blood, and significantly depends on the propagating path and stiffness of the artery. In this study, PWV of the propagating wave was visualized using spatial compound imaging with high temporal resolution. The frame rate was 1000 Hz, or a time interval of 1 ms. Subjects were four young healthy males and one young healthy female (n=5, age: 23.8±1.17 years old), and the measurement area was the right common carotid artery. PWVs in four phases (the four phases of heart valve opening and closing) were investigated during a cardiac cycle. In phase I, the heart pulsates. In phase II, the tricuspid and mitral valves close, and the aortic and pulmonic valves open. In phase III, the tricuspid and mitral valves open, and the aortic and pulmonic valves close. In phase IV, the propagating wave is reflected. PWVs in phases II and III were easily observed. PWVs were 3.52±1.11 m/s in phase I, 5.62±0.30 m/s in phase II, 7.94±0.85 m/s in phase III, and -4.60±0.99 m/s for the reflective wave. PWV was measured using Spatial Compound Imaging with high temporal resolution, and the PWV in each phase may be used as the index for diagnosing stages of arteriosclerosis progression.

Involvement of reactive oxygen species in the enhancement of membrane lipid peroxidation by sonodynamic therapy with functionalized fullerenes.

BACKGROUND/AIM: Sonodynamic cancer therapy is based on the preferential uptake and/or retention of a sonosensitizing drug (sonosensitizer) in tumor tissues and subsequent activation of the drug by ultrasound irradiation. In the present study, we investigated the participation of lipid peroxidation in the mechanism of the sonodynamically-induced antitumor effect with functionalized fullerenes, such as polyhydroxy fullerene (PHF. MATERIALS AND METHODS: Ultrasonically-induced cell damage and lipid peroxidation with PHF were compared in the same in vitro insonation setup. Sarcoma 180 cells suspended in PBS were exposed to 2 MHz ultrasound in the presence and absence of PHF. Cell viability was determined by the Trypan Blue exclusion test. Lipid peroxidation in cell membranes was estimated by measuring the amount of malondialdehyde as the thiobarbituric acid-reactive-substances. RESULTS: Significant enhancement of the rates of both ultrasonically-induced cell damage and lipid peroxidation was observed in the presence of PHF, both of which were positively correlated with PHF. The enhancement of cell damage and lipid peroxidation with PHF was suppressed by reactive oxygen scavengers such as histidine and tryptophan. CONCLUSION: The good correlation observed in the presence of PHF suggests that membrane lipid peroxidation is one of the important intermediary events in sonodynamically-induced cellular damage. The inhibitory effects of histidine and tryptophan also provide evidence that singlet oxygen plays an important role in PHF-mediated sonosensitization of membranes and that this moiety may be an important mediator of cell destruction in sonodynamic therapy associated with PHF and ultrasound.

High-speed observation of bubble cloud generation near a rigid wall by second-harmonic superimposed ultrasound.

Cavitation bubbles are known to accelerate therapeutic effects of ultrasound. Although negative acoustic pressure is the principle factor of cavitation, positive acoustic pressure has a role for bubble cloud formation at a high intensity of focused ultrasound when cavitation bubbles provide pressure release surfaces converting the pressure from highly positive to negative. In this study, the second-harmonic was superimposed onto the fundamental acoustic pressure to emphasize either peak positive or negative pressure. The peak negative and positive pressure emphasized waves were focused on a surface of an aluminum block. Cavitation bubbles induced near the block were observed with a high-speed camera by backlight and the size of the cavitation generation region was measured from the high-speed images. The negative pressure emphasized waves showed an advantage in cavitation inception over the positive pressure emphasized waves. In the sequence of the negative pressure emphasized waves immediately followed by the positive pressure emphasized waves, cavitation bubbles were generated on the block by the former waves and the cavitation region were expanded toward the transducer in the latter waves with high reproducibility. The sequence demonstrated its potential usefulness in enhancing the effects of therapeutic ultrasound at a high acoustic intensity.

Changes in backscatter of liver tissue due to thermal coagulation induced by focused ultrasound.

Ultrasonic imaging has advantages in its self-consistency in guiding and monitoring ultrasonic treatment such as high-intensity focused ultrasound (HIFU) treatment. Changes in ultrasonic backscatter of tissues due to HIFU treatment have been observed, but their mechanism is still under discussion. In this paper, ultrasonic backscatter of excised and degassed porcine liver tissue was observed before and after HIFU exposure using a diagnostic scanner, and its acoustic impedance was mapped using an ultrasonic microscope. The histology of its pathological specimen was also observed using an optical microscope. The observed decrease in backscatter intensity due to HIFU exposure was consistent with a spatial Fourier analysis of the histology, which also showed changes due to the exposure. The observed increase in acoustic impedance due to the exposure was also consistent with the histological change assuming that the increase was primarily caused by the increase in the concentration of hepatic cells.

Sonodynamically-induced anticancer effects by functionalized fullerenes.

BACKGROUND: Functionalized fullerenes, such as polyhydroxy fullerenes (PHF), have attracted particular attention due to their water solubility and their potential application in tumor imaging and therapy as carbon nanomaterials. In this study, the sonodynamically-induced antitumor effect of PHF was investigated. MATERIALS AND METHODS: Sonodynamically-induced antitumor effects of PHF in combination with ultrasound were investigated using isolated sarcoma 180 cells and solid tumor from colon 26 carcinoma cells. RESULTS: The cell damage induced by sonication was enhanced by two-fold in the presence of 80 µM PHF. Histidine significantly inhibited this enhancement. This inhibitory effect suggests that the sonodynamically-induced antitumor effect was mediated by sonodynamically-generated reactive oxygen species. The combined treatment of ultrasonic exposure with PHF suppressed the growth of implanted colon 26 tumors. The destruction of tumor tissue was observed with the ultrasonic treatment in combination with PHF, while neither the treatment with PHF alone nor that with ultrasound alone caused necrosis. CONCLUSION: These results suggest that PHF is a potential sonosensitizer for sonodynamic treatment of solid tumors.