Takashi Azuma

Real-time monitoring transcranial sub-megahertz ultrasound thrombolysis with phased array scanner

Transcranial ultrasonic thrombolytic system has been developed, for acute ischemic stroke (AIS) therapy during hyper acute phase. The system aims to have a higher potential for early recanalization in the thrombo-embolism by accelerating the effect of thrombolytic agent with transcranial ultrasonication. Sub MHz ultrasound has less attenuation by several orders through cranium than that of more than 2MHz, while it has higher risk of intracranial hemorrhage. In order to avoid the risk, the direction of therapeutic ultrasound (T) beam is targeted at an area around the embolic artery, and in order to minimize mechanical and thermal adverse biological effects, T-beam frequency is selected 500 kHz, the acoustic intensity limited less than the maximum regulation level of the diagnostic ultrasound equipment. The transcranial diagnostic (Doppler or color flow imaging) ultrasound (D) beam at 2MHz is used for monitoring the recanalization. The system irradiates both Tand D-beam alternately in the signal control subsystem through a phased array single compound probe. The images by the diagnostic array in the probe are comparable to those by the commercialized sector scanning diagnostic phased array. The probe also has supplied T-beam of the maximum acoustic intensity designated by the regulation for the diagnostic equipment. The margin of safety was confirmed through animal experiments. Keywordstranscranial ultrasound; thrombolysis; doppler; color flow imaging

Ultrasound-mediated gene transfection: A comparison between cells irradiated in suspension and attachment status

Sonoporation, in the presence of microbubbles, is a promising nonviral gene transfection method. Although the mechanism is not yet fully understood, shock waves emitted by cavitation bubbles have been known to play an important role in creating pores on cell membranes. This work investigates the gene transfection efficiency and influencing parameters of cells in two different statuses: attachment and suspension based on the fact that cells in suspension have more bubbles surrounding them and that shock wave has distinct effects on hit objects whether the object is attached to a rigid wall or not. Fibroblast cells (NIH3T3), both in attachment and suspension, and green fluorescent protein (GFP) plasmid were exposed to variations in acoustic pressure (0.6-1.2 MPa) and 10% duty cycle at fixed settings of 2 MHz central frequency, 5 kHz pulse repetition frequency and 1 minute insonation time, in the presence of 10% v/v microbubbles (Sonazoid, a commercialized product of ultrasound contrast agent). The transfect...