Feasibility of magnetic resonance imaging-guided high intensity focused ultrasound therapy for ablating uterine fibroids in patients with bowel lies anterior to uterus

Purpose

To prospectively evaluate the feasibility of magnetic resonance (MR) imaging-guided high intensity focused ultrasound (HIFU) therapeutic ablation of uterine fibroids in patients with bowel lies anterior to uterus.

Materials and methods

Twenty-one patients with 23 uterine fibroids underwent MR imaging-guided high intensity focused ultrasound treatment, with a mean age of 39.4 ± 6.9 (20-49) years, with fibroids average measuring 6.0 ± 1.6 (range, 2.9-9.5) cm in diameter. After being compressed with a degassed water balloon on abdominal wall, MR imaging-guided high intensity focused ultrasound treatment was performed under conscious sedation by using fentanyl and midazolam. This procedure was performed by a Haifu^® JM focused ultrasound tumour therapeutic system (JM2.5C, Chongqing Haifu Technology Co., Ltd., China), in combination with a 1.5-Tesla MRI system (Symphony, Siemens, Germany), which provides real-time guidance and control. Contrast-enhanced MR imaging was performed to evaluate the efficacy of thermal ablation immediately and 3 months after HIFU treatment. The treatment time and adverse events were recorded.

Results

The mean fibroid volume was 97.0 ± 78.3 (range, 12.7-318.3) cm³. According to the treatment plan, an average 75.0 ± 11.4% (range, 37.8-92.4%) of the fibroid volume was treated. The mean fibroid volume immediately after HIFU was 109.7 ± 93.1 (range, 11.9-389.6) cm³, slightly enlarged because of edema. The average non-perfused volume was 83.3 ± 71.7 (range, 7.7-282.9) cm³, the average fractional ablation, which was defined as non-perfused volume divided by the fibroid volume immediately after HIFU treatment, was 76.9 ± 18.7% (range, 21.0-97.0%). There were no statistically significant differences between the treatment volume and the non-perfused volume. Follow-up magnetic resonance imaging (MRI) at 3 months obtained in 12 patients, the fibroid volume decreased by 31.4 ± 29.3% (range, −1.9 to 60.0%) in average, with paired t-test showing a statistically significant reduction (P = 0.002). The mean treatment time for ablating the average 83.3 ± 71.7 (range, 7.7-282.9) cm³ of fibroid volume was 2.5 ± 1.4 h (range, 27-390 min) in this study, which was relatively short and acceptable to patient and therapist. Four patients experienced mild skin burn (two with skin redness, two with blisters), the skin burn subsided within ∼2 days. No other adverse events were observed.

Conclusions

After the bowel was compressed with a degassed water balloon, MR imaging-guided high intensity focused ultrasound treatment is safe and feasible in ablating uterine fibroids in patients with bowel lies anterior to uterus.     

镇静止痛条件下聚焦超声治疗实体肿瘤的初步临床研究

目的初步评价镇静止痛条件下采用高强度聚焦超声(HIFU)对良性和晚期恶性肿瘤患者实施消融和姑息性消融治疗的安全性和有效性。方法静脉应用芬太尼(1μg/kg)及咪唑安定(0.03mg/kg)创建镇静止痛条件,应用JC型HIFU治疗系统对23例良性和58例晚期恶性肿瘤患者实施消融和姑息性消融治疗,观察镇静止痛药物及HIFU消融治疗的近期疗效、不良反应。结果在镇静止痛条件下,81例患者共进行112例次HIFU消融手术,其中23例良性肿瘤患者治疗26例次,58例恶性肿瘤患者姑息性治疗86例次,共治疗153个病灶。在可评价的疗效中,病灶体积消融率达到50%以上的病灶占81%(89/110),其中恶性肿瘤为72.2%(52/72),良性肿瘤为97.4%(37/38)。恶性肿瘤患者中81.3%(13/16)的患者肿瘤标志物下降>50%;肿瘤相关症状缓解率77%(30/39)。镇静止痛药物不良反应包括恶心、呼吸频率过缓、幻视等,HIFU治疗的主要副反应包括,治疗区疼痛及肿胀等。未出现三度以上镇静止痛药物或HIFU治疗的相关并发症。结论在镇静止痛条件下,HIFU消融治疗实体肿瘤具有较好的安全性、有效性和可操作性。     

Proton resonance frequency shift-weighted imaging for monitoring MR-guided high-intensity focused ultrasound transmissions

Purpose:

To combine temperature‐related information of phase images and magnitude images acquired from an MR spoiled gradient echo sequence using a postprocessing method referred to as PRF‐shift‐weighted imaging (PRFSWI).

Materials and Methods:

Phase images are capable of detecting shifts in proton resonance frequency (PRF) caused by local changes in temperature. Magnitude images provide anatomical information for treatment planning and positioning as well as temperature‐related contrast. We used PRFSWI to produce a phase‐mask and performed multiplication on the magnitude image to increase temperature‐related contrast.

Results:

Through MRI‐guided focused ultrasound (MRIgFUS) experiments (both ex vivo and in vivo), we determined that PRFSWI is capable of enhancing the contrast of a heated area even in the initial stages of transmitting high‐intensity focused ultrasound energy.

Conclusion:

The PRFSWI images are sensitive to changes in temperature and display the heated spot directly in the magnitude images. Although the images do not provide quantitative data related to temperature, this method could be used as a complement to the phase temperature mapping method in the real‐time monitoring of MRIgFUS experiments. J. Magn. Reson. Imaging 2011;33:1474–1481. © 2011 Wiley‐Liss, Inc.     

Renal ablation using magnetic resonance-guided high intensity focused ultrasound: Magnetic resonance imaging and histopathology assessment

AIM: To use magnetic resonance-guided high intensity focused ultrasound (MRg-HIFU), magnetic resonance imaging (MRI) and histopathology for noninvasively ablating, quantifying and characterizing ablated renal tissue.METHODS: Six anesthetized/mechanically-ventilated pigs underwent single/double renal sonication (n = 24) using a 3T-MRg-HIFU (1.1 MHz frequency and 3000J-4400J energies). T2-weighted fast spin echo (T2-W), perfusion saturation recovery gradient echo and contrast enhanced (CE) T1-weighted (T1-W) sequences were used for treatment planning, temperature monitoring, lesion visualization, characterization and quantification, respectively. Histopathology was conducted in excised kidneys to quantify and characterize cellular and vascular changes. Paired Student’s t-test was used and a P-value < 0.05 was considered statistically significant.RESULTS: Ablated renal parenchyma could not be differentiated from normal parenchyma on T2-W or non-CE T1-W sequences. Ablated renal lesions were visible as hypoenhanced regions on perfusion and CE T1-W MRI sequences, suggesting perfusion deficits and necrosis. Volumes of ablated parenchyma on CE T1-W images in vivo (0.12-0.36 cm³ for single sonication 3000J, 0.50-0.84 cm³, for double 3000J, 0.75-0.78 cm³ for single 4400J and 0.12-2.65 cm³ for double 4400J) and at postmortem (0.23-0.52 cm³, 0.25-0.82 cm³, 0.45-0.68 cm³ and 0.29-1.80 cm³, respectively) were comparable. The ablated volumes on 3000J and 4400J double sonication were significantly larger than single (P < 0.01), thus, the volume and depth of ablated tissue depends on the applied energy and number of sonication. Macroscopic and microscopic examinations confirmed the locations and presence of coagulation necrosis, vascular damage and interstitial hemorrhage, respectively.CONCLUSION: Contrast enhanced MRI provides assessment of MRg-HIFU renal ablation. Histopathology demonstrated coagulation necrosis, vascular damage and confirmed the volume of damage seen on MRI.     

High intensity focused ultrasound treatment of adenomyosis: The relationship between the features of magnetic resonance imaging on T2 weighted images and the therapeutic efficacy

ObjectivesTo investigate the relationship between the features of magnetic resonance imaging (MRI) on T2 weighted images (T2WI) and the therapeutic efficacy of high intensity focused ultrasound (HIFU) on adenomyosis.Materials and methodsFrom January 2011 to November 2015, four hundred and twenty-eight patients with symptomatic adenomyosis were treated with HIFU. Based on the signal intensity and the number of hyperintense foci in the adenomyotic lesions on T2WI, the patients were classified into groups. The day after HIFU ablation patients underwent contrast-enhanced MRI and a comparison was made of non-perfused volume (NPV) ratio, energy efficiency factor (EEF), treatment time, sonication time, and adverse effects.ResultsNo significant difference in terms of HIFU treatment settings and results was observed between the group of patients with hypointense adenomyotic lesions and the group with isointense adenomyotic lesions (P > 0.05). However, the sonication time and EEF were significantly higher in the group with multiple hyperintense foci compared to the group with few hyperintense foci. The NPV ratio achieved in the lesions with multiple hyperintenese foci was significantly lower than that in the lesions with few hyperintense foci (P < 0.05). No significant difference was observed in the rate of adverse effects between the two groups.ConclusionsBased on our results, the response of the adenomyotic lesions to HIFU treatment is not related to the signal intensity of adenomyotic lesions on T2WI. However, the number of the high signal intensity foci in the adenomyotic lesions on T2WI can be considered as a predictive factor to help select patients for HIFU treatment.     

Adapting MRI acoustic radiation force imaging for in vivo human brain focused ultrasound applications

A variety of magnetic resonance imaging acoustic radiation force imaging (MR‐ARFI) pulse sequences as the means for image guidance of focused ultrasound therapy have been recently developed and tested ex vivo and in animal models. To successfully translate MR‐ARFI guidance into human applications, ensuring that MR‐ARFI provides satisfactory image quality in the presence of patient motion and deposits safe amount of ultrasound energy during image acquisition is necessary. The first aim of this work was to study the effect of motion on in vivo displacement images of the brain obtained with 2D Fourier transform spin echo MR‐ARFI. Repeated bipolar displacement encoding configuration was shown less sensitive to organ motion. The optimal signal‐to‐noise ratio of displacement images was found for the duration of encoding gradients of 12 ms. The second aim was to further optimize the displacement signal‐to‐noise ratio for a particular tissue type by setting the time offset between the ultrasound emission and encoding based on the tissue response to acoustic radiation force. A method for measuring tissue response noninvasively was demonstrated. Finally, a new method for simultaneous monitoring of tissue heating during MR‐ARFI acquisition was presented to enable timely adjustment of the ultrasound energy aimed at ensuring the safety of the MR‐ARFI acquisition. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Volumetric MRI‐guided high‐intensity focused ultrasound for noninvasive,in vivo determination of tissue thermal conductivity: Initial experience in a pig model

Purpose:

To estimate the local thermal conductivity of porcine thigh muscle at temperatures required for magnetic resonance imaging (MRI)‐guided high‐intensity focused ultrasound (MRgHIFU) surgery (60–90°C).

Materials and Methods:

Using MRgHIFU, we performed 40 volumetric ablations in the thigh muscles of four pigs. Thirty‐five of the sonications were successful. We used MRI to monitor the resulting temperature increase. We then determined local thermal conductivity by analyzing the spatiotemporal spread of temperature during the cooling period.

Results:

The thermal conductivity of MRgHIFU‐treated porcine thigh muscle fell within a narrow range (0.52 ± 0.05 W/[m*K]), which is within the range reported for porcine thigh muscle at temperatures of <40°C (0.52 to 0.62 W/[m*K]). Thus, there was little change in the thermal conductivity of porcine thigh muscle at temperatures required for MRgHIFU surgery compared to lower temperatures.

Conclusion:

Our MRgHIFU‐based approach allowed us to estimate, with good reproducibility, the local thermal conductivity of in vivo deep tissue in real time at temperatures of 60°C to 90°C. Therefore, our method provides a valuable tool for quantifying the influence of thermal conductivity on temperature distribution in tissues and for optimizing thermal dose delivery during thermal ablation with clinical MRgHIFU. J. Magn. Reson. Imaging 2013;37:950–957. © 2012 Wiley Periodicals, Inc.     

Current status and future potential of MRI-guided focused ultrasound surgery

The combination of the imaging abilities of magnetic resonance imaging (MRI) with the ability to delivery energy to targets deep in the body noninvasively with focused ultrasound presents a disruptive technology with the potential to significantly affect healthcare. MRI offers precise targeting, visualization, and quantification of temperature changes and the ability to immediately evaluate the treatment. By exploiting different mechanisms, focused ultrasound offers a range of therapies, ranging from thermal ablation to targeted drug delivery. This article reviews recent preclinical and tests clinical of this technology.     

Estimation of thermal dose from MR thermometry during application of nonablative pulsed high intensity focused ultrasound

Purpose:

To evaluate whether MR thermometry is sufficiently fast, accurate, and spatially resolved for monitoring the thermal safety of nonablative pulsed high intensity ultrasound (pHIFU) treatments.

Materials and Methods:

A combination of real MR thermometry data and modeling was used to analyze the effects of temporal and spatial averaging as well as noise on the peak temperatures and thermal doses that would be measured by MR thermometry.

Results:

MR thermometry systematically underestimates the temperature and thermal doses during pHIFU treatment. Small underestimates of peak temperature can lead to large underestimates of thermal dose. Spatial averaging errors are small for ratios of pixel dimension to heating zone radius less than 0.25, which may be achieved by reducing the voxel size or steering the acoustic beam. Thermal dose might also be underestimated for very short, high power pulses due to temporal averaging. A simple correction factor based on the applied power and duty cycle may be applied to determine the upper bound of this effect.

Conclusion:

The temperature and thermal dose measured using MR thermometry during pulsed HIFU treatment is probably sufficient in most instances. Simple corrections may be used to calculate an upper bound where this is a critical factor. J. Magn. Reson. Imaging 2012;35:1169‐1178. © 2011 Wiley Periodicals, Inc.     

Effects of oxytocin on high intensity focused ultrasound (HIFU) ablation of adenomysis: A prospective study

Objective

To investigate the effects of oxytocin on high-intensity focused ultrasound (HIFU) ablation for the treatment of adenomyosis.

Materials and methods

Eighty-six patients with adenomyosis from three hospitals were randomly assigned to the oxytocin group or control group for HIFU treatment. During HIFU treatment, 80 units of oxytocin was added in 500 ml of 0.9% normal saline running at the rate of 2 ml/min (0.32 U/min) in the oxytocin group, while 0.9% normal saline was used in the control group. Both patients and HIFU operators were blinded to oxytocin or saline application. Treatment results, adverse effects were compared.

Results

When using oxytocin, the non-perfused volume (NPV) ratio was 80.7 ± 11.6%, the energy-efficiency factor (EEF) was 8.1 ± 9.9 J/mm³, and the sonication time required to ablate 1 cm³ was 30.0 ± 36.0 s/cm³. When not using oxytocin, the non-perfused volume ratio was 70.8 ± 16.7%, the EEF was 15.8 ± 19.6 J/mm³, and the sonication time required to ablate 1 cm³ was 58.2 ± 72.7 S/cm³. Significant difference in the NPV ratio, EEF, and the sonication time required to ablate 1 cm³ between the two groups was observed. No oxytocin related adverse effects occurred.

Conclusion

Oxytocin could significantly decrease the energy for ablating adenomyosis with HIFU, safely enhance the treatment efficiency.     

Tissue thermal conductivity by magnetic resonance thermometry and focused ultrasound heating

PURPOSE: To investigate the combined use of magnetic resonance (MR) temperature imaging and focused ultrasound (FUS) for the noninvasive determination of tissue thermal properties. MATERIALS AND METHODS: Brief, spatial impulses of temperature elevation were created in tissue using a spherical, air-backed transducer operating at 1.68 MHz and measured using MR temperature imaging in a 1.5-Tesla clinical scanner. A novel technique based on thermal washout is applied in an analysis of the acquired MR temperature images to estimate tissue thermal conductivity and perfusion. RESULTS: Numerical simulations and experiments in vitro and in vivo demonstrate that thermal conductivity can be measured to within 10% of the true value with MR thermometry at 1.5 Tesla. With the temperature precision available at 1.5 Tesla, however, robust perfusion estimation is feasible only in highly perfused organs or tumors. CONCLUSION: This study has developed a method for determining tissue thermal properties specific to the patient and organ at the site of interest, and allows repeated application. This capability is relevant in thermal therapy planning of tumor ablation using MR-guided FUS systems.     

An 11‐channel radio frequency phased array coil for magnetic resonance guided high‐intensity focused ultrasound of the breast

In this study, a radio frequency phased array coil was built to image the breast in conjunction with a magnetic resonance guided high‐intensity focused ultrasound (MRgHIFU) device designed specifically to treat the breast in a treatment cylinder with reduced water volume. The MRgHIFU breast coil was comprised of a 10‐channel phased array coil placed around an MRgHIFU treatment cylinder where nearest‐neighbor decoupling was achieved with capacitive decoupling in a shared leg. In addition a single loop coil was placed at the chest wall making a total of 11 channels. The radio frequency coil array design presented in this work was chosen based on ease of implementation, increased visualization into the treatment cylinder, image reconstruction speed, temporal resolution, and resulting signal‐to‐noise ratio profiles. This work presents a dedicated 11‐channel coil for imaging of the breast tissue in the MRgHIFU setup without obstruction of the ultrasound beam and, specifically, compares its performance in signal‐to‐noise, overall imaging time, and temperature measurement accuracy to that of the standard single chest‐loop coil typically used in breast MRgHIFU. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.