Development of an MRI-Compatible High-Intensity Focused Ultrasound Phased Array Transducer Dedicated for Breast Tumor Treatment.

High-intensity focused ultrasound (HIFU) under magnetic resonance imaging (MRI) guidance can achieve a noninvasive and precise ablation of the solid tumor. In the study, an MRI-compatible 1-MHz 16-channel ring-shaped transducer was developed to minimize the burn risk of breast skin and perform volumetric ablation for short treatment time. The measured electroacoustic conversion efficiency of the transducer was 50.90% ± 5. The transducer could produce a point and a quasi-hollow-cylinder lesion in a thermal-sensitive phantom or an ex vivo pork by tuning the phase of each element. It may achieve volumetric ablation of 1.5 cm3 when the point lesion is located inside the hollow lesion. Ex vivo ablation experiments showed that the transducer could cause a coagulative necrosis in the pork from the surrounded subcutaneous fat by 5 mm without fat damage. The temperature and region of the pork ablation were quantified by MRI technique. There was no MRI interference from HIFU and vice versa while both systems operated concurrently.

A Coaxial Dual-element Focused Ultrasound Probe for Guidance of Epidural Catheterization: An Experimental Study.

Ultrasound guidance for epidural block has improved clinical blind-trial problems but the design of present ultrasonic probes poses operating difficulty of ultrasound-guided catheterization, increasing the failure rate. The purpose of this study was to develop a novel ultrasonic probe to avoid needle contact with vertebral bone during epidural catheterization. The probe has a central circular passage for needle insertion. Two focused annular transducers are deployed around the passage for on-axis guidance. A 17-gauge insulated Tuohy needle containing the self-developed fiber-optic-modified stylet was inserted into the back of the anesthetized pig, in the lumbar region under the guidance of our ultrasonic probe. The inner transducer of the probe detected the shallow echo signals of the peak-peak amplitude of 2.8 V over L3 at the depth of 2.4 cm, and the amplitude was decreased to 0.8 V directly over the L3 to L4 interspace. The outer transducer could detect the echoes from the deeper bone at the depth of 4.5 cm, which did not appear for the inner transducer. The operator tilted the probe slightly in left-right and cranial-caudal directions until the echoes at the depth of 4.5 cm disappeared, and the epidural needle was inserted through the central passage of the probe. The needle was advanced and stopped when the epidural space was identified by optical technique. The needle passed without bone contact. Designs of the hollow probe for needle pass and dual transducers with different focal lengths for detection of shallow and deep vertebrae may benefit operation, bone/nonbone identification, and cost.

Synergistic Effects of Nanodrug, Ultrasound Hyperthermia, and Thermal Ablation on Solid Tumors-An Animal Study.

OBJECTIVE: Delivery barriers of nanodrug in large tumors due to heterogeneous blood supply, elevated interstitial pressure, and long transport distances can degrade the efficacy of cancer treatment. In this study, we proposed a therapeutic strategy to improve the tumor growth inhibition by injecting pegylated liposomal doxorubicin (PLD), and then applying a short time of ultrasound hyperthermia (HT) on the entire solid tumor, and inflicting ultrasound thermal ablation (Ab) in the low-perfused tumor region. METHODS: BALB/c female mice with an average weight of 20 g were adopted and murine breast cancer cells 4T1 were subcutaneously implanted into the flank. A 1.0-MHz planar and a 0.47-MHz focused ultrasound transducers were used, respectively, for the HT and Ab treatment. RESULTS: For a PLD dose of 5 mg/kg, the PLD + HT(42 °C, 10 min) group caused a significant decrease in the tumor size as compared with the control and the PLD group, but there were no significant differences between the PLD + HT group and the PLD + Ab(56 °C, 49 s) + HT group. For a PLD dose of 3 mg/kg, the tumor sizes among the four groups were mutually significant. The level of reduction in tumor was PLD + Ab + HT > PLD + HT > PLD > control. CONCLUSION: The combination of anticancer nanodrug and ultrasound thermal treatment could remarkably suppress cancer tumor growth with a minimum compromise of side effects. SIGNIFICANCE: The strategy of using thermal Ab in locations that are not reached by nanodrug with mild HT shows a promising potential for the entire tumor treatment.