To improve the cavitation-to-tissue ratio (CTR) of cavitation imaging during the treatment with high-intensity focused ultrasound (HIFU), we proposed a pulse inversion based broadband subharmonic cavitation imaging method (PIBSHI). Due to the fact that the subharmonic signal is a unique nonlinear vibration characteristic of cavitation bubbles, we extracted the broadband subharmonic signal to get a high-CTR cavitation imaging. The simulation showed that the subharmonic signal produced by cavitating bubbles with different sizes varied, and the signal was stronger than other subharmonics when the bubbles' resonant frequency was close to 1/2 subharmonic frequency. Further experiment results demonstrated that compared with the conventional B-mode images, broadband subharmonic cavitation imaging (BSHI) has improved the CTR by 5.7 dB, and the CTR was further improved by 3.4 dB when combined with pulse inversion (PI) technology. Moreover, when the bandwidth was set to 100%~140% of the 1/2 subharmonic frequency in PIBSHI, the CTR was the highest and the imaging showed the optimal quality. The study may have reference value for the development of precise cavitation imaging during HIFU treatment, and contribute to improve the safety of HIFU treatment.
High-Intensity Focused Ultrasound Ablation ; Ultrasonography

The FPGA-based phased-signal generator described in this paper meets the requirement of massive output channels and high resolution of HIFU. After experimental measurements, this phased-signal generator can output 256 channels of phase signals and each channel has a phase resolution of 2nS. The phased-signal generator also has many other advantages such as simple implementation method and high reliability.
Equipment Design ; High-Intensity Focused Ultrasound Ablation ; instrumentation

OBJECTIVETo investigate the accuracy of ultrasound monitoring during pulsed high intensity focused ultrasound (PHIFU) treatment and improve the sensitivity of ultrasound monitoring of tissue necrosis caused by PHIFU treatment.

METHODSBovine liver ex vivo was dot-exposed with HIFU at the therapeutic doses of 2000 J (group A) and 1440 J (group B). The two groups were further divided into groups A1 (power 100 W, duty cycle 100%, irradiate 20 s) A2 (power 100 W, duty cycle 50%, irradiate 40 s), A3 (power 100 W, duty cycle 40%, irradiate 50 s), B1 (power 120 W, duty cycle 100%, irradiate 12 s), B2 (power 100 W, duty cycle 50%, irradiate 24 s), and B3 (power 100 W, duty cycle 40%, irradiate 30 s). The gray scale changes in the ultrasonic images after the exposures were observed, and the correlation function of the image was calculated before and after the exposure. The accuracy of evaluations based on the correlation function and gray-scale changes was compared.

RESULTSThe correct rate of gray scale-based evaluation of tissue necrosis caused by PHIFU was only 51%, while that by correlation function-based evaluation reached 85%.

CONCLUSIONMonitoring of tissue necrosis caused by PHIFU treatment can not rely solely on evaluation of gray-scale change of the ultrasound images, and the correlation function-based evaluation can be more accurate and sensitive for that purpose.

OBJECTIVETo study the efficacy of B1 field shimming technique and evaluate the specific absorption rate (SAR) in ultra-high field magnetic resonance imaging (MRI) for MRI-guided high-intensity focused ultrasound (HIFU).

METHODSAn electromagnetic model of the female pelvis with a temperature gradient was established. B1 field homogeneity and local SAR were simulated and calculated using regular and optimized B1 shimming coefficients.

RESULTSThe maximum local SAR reached 10.24 W/kg, which exceeded the safe threshold of 10 W/kg, as calculated using regular B1 shimming coefficients in the normal model. Using the optimized B1 shimming coefficients, the maximum local SAR of the tissue was 9.65 W/kg, which was below the safe threshold.

CONCLUSIONThe temperature distributions in the body generated by ultrasound energy need to be considered in ultra-high field MRI-guided HIFU surgery. The proposed optimized B1 shimming strategy based on the temperature gradient can be used to control the local SAR levels.

BACKGROUNDIntravascular microbubble-enhanced acoustic cavitation is capable of disrupting the vascular walls of capillaries and small vessels. This study was designed to investigate the impact of microbubble-enhanced, pulsed and focused ultrasound (MEUS) on the blood perfusion of subcutaneous VX2 tumors in rabbits.

METHODSSubcutaneous VX2 cancers in twenty New Zealand rabbits were treated by combining high-pressure amplitude, pulsed and focused therapeutic ultrasound (TUS) and intravenous microbubble injections. The TUS transducer was operated with a peak negative pressure of 4.6 MPa and a duty cycle of 0.41%. Controls were subcutaneous VX2 cancers treated with TUS or microbubbles only. Contrast-enhanced ultrasound (CEUS) and intravenous Evans Blue (EB) perfusion were performed to assess the tumor circulation. The tumor microvascular disruption was assessed by histological examination.

RESULTSCEUS showed that the tumor circulation almost vanished after MEUS treatment. The average peak grayscale value (GSV) of tumor CEUS dropped significantly from 84.1±22.4 to 15.8±10.8 in the MEUS-treated tumors but no significant GSV changes were found in tumors in the two control groups. The mean tumor EB content of the MEUS-treated tumors was significantly lower than that of the controls. Histological examination found scattered tumor microvascular disruption with intercellular edema after MEUS treatment.

CONCLUSIONThe tumor circulation of VX2 cancers can be arrested or significantly reduced by MEUS due to microvascular disruption.

OBJECTIVETo compare the effect of low-dose focused ultrasound pre-irradiation and microbubbles for enhancing the ablation effect of high intensity focused ultrasound (HIFU) on VXhepatic tumor in rabbits.

METHODSFifty-five rabbits bearing VXhepatic tumor were randomly divided into low-dose pre-irradiation + HIFU ablation group, microbubbles+HIFU ablation group, and HIFU ablation group for corresponding treatments. The pathological changes in the tumors after low-dose irradiation, time for HIFU ablation, tumor volume with coagulative necrosis, energy efficiency factor (EEF), pathological changes in the ablated tumor, and sound channel of HIFU ablation were observed.

RESULTSTumor cell edema, vacuolar changes in the cytoplasm and tumor interstitial vascular congestion were observed 24 h after low-dose pre-irradiation. The ablation time were significantly shorter, coagulative necrosis volume was larger, and EEF was lower in low-dose irradiation + HIFU ablation group and microbubbles+HIFU ablation group than in simple HIFU ablation group (P<0.05), but the differences between the former two groups were not significant. The effectiveness and stability of the synergistic effect of low-dose pre-irradiation were inferior to microbubbles, but the former ensured a better safety of the sound channel.

CONCLUSIONLow-dose irradiation has comparable synergistic effect in HIFU with microbubbles with such advantages as non-invasiveness, high concentration and good safety, and can be a potentially new method to enhance the efficiency of HIFU.

High intensity focused ultrasound (HIFU) is a very complex transient process and can cause tissue coagulation necrosis. The cavitation and boiling behaviour of bubbles in the focal region play very important roles throughout an injury process. This paper reviews the research done by domestic and foreign scholars on behaviours of bubbles in HIFU irradiation process and summarizes in the focal region bubble cavitation and boiling generation, related detective means and relationships with hyperecho, temperature rise of the focus and injury shape.
Biophysical Phenomena ; High-Intensity Focused Ultrasound Ablation ; methods ; Humans ; Thermal Conductivity ; Thermodynamics

This paper introduces HIFU system software based on a phased-array HIFU device. Combined with the database and computer graphics technology, this HIFU system software can be used to develop the therapy planning semi-automatically, implement the pilot project efficiently and accelerate the clinical studies.
Computer Graphics ; High-Intensity Focused Ultrasound Ablation ; methods ; Software ; Software Design

We present a case of retained placenta accreta treated by high-intensity focused ultrasound (HIFU) ablation followed by hysteroscopic resection. The patient was diagnosed as submucosal myoma based on ultrasonography in local clinic. Pathologic examination of several pieces of tumor mass from the hysteroscopic procedure revealed necrotic chorionic villi with calcification. HIFU was performed using an ultrasound-guided HIFU tumor therapeutic system. The ultrasound machine had been used for real-time monitoring of the HIFU procedure. After HIFU treatment, no additional vaginal bleeding or complications were observed. A hysteroscopic resection was performed to remove ablated placental tissue 7 days later. No abnormal vaginal bleeding or discharge was seen after the procedure. The patient was stable postoperatively. We proposed HIFU and applied additional hysteroscopic resection for a safe and effective method for treating retained placenta accreta to prevent complications from the remaining placental tissue and to improve fertility options.
Chorionic Villi ; Fertility ; High-Intensity Focused Ultrasound Ablation ; Humans ; Methods ; Myoma ; Placenta, Retained* ; Ultrasonography* ; Uterine Hemorrhage

We present a case of retained placenta accreta treated by high-intensity focused ultrasound (HIFU) ablation followed by hysteroscopic resection. The patient was diagnosed as submucosal myoma based on ultrasonography in local clinic. Pathologic examination of several pieces of tumor mass from the hysteroscopic procedure revealed necrotic chorionic villi with calcification. HIFU was performed using an ultrasound-guided HIFU tumor therapeutic system. The ultrasound machine had been used for real-time monitoring of the HIFU procedure. After HIFU treatment, no additional vaginal bleeding or complications were observed. A hysteroscopic resection was performed to remove ablated placental tissue 7 days later. No abnormal vaginal bleeding or discharge was seen after the procedure. The patient was stable postoperatively. We proposed HIFU and applied additional hysteroscopic resection for a safe and effective method for treating retained placenta accreta to prevent complications from the remaining placental tissue and to improve fertility options.
Chorionic Villi ; Fertility ; High-Intensity Focused Ultrasound Ablation ; Humans ; Methods ; Myoma ; Placenta, Retained* ; Ultrasonography* ; Uterine Hemorrhage