Creare interest in biomedical engineering has led to projects involving extremely high frequency ultrasound arrays for applications that require exceptionally high accuracy, but do not require deep surface penetration. Our ultrahigh frequency scanning acoustic microscopes, operating in frequencies of 50 – 100 MHz, offer sharp resolution and high definition, with magnification and image clarity almost fine enough to see inside individual cells. Our scanning microscopes permit the visualization of tissue typically only provided by invasive tissue biopsies viewed under light microscopy.

Clinical ultrasound systems operate at relatively low frequencies (resolution is inversely proportional to frequency). Ultrasound systems for general in vitro use operate with an imaging frequency of about 5 MHz, and echocardiogram and other specialty probes operate as high as 15 MHz. Currently, these systems cannot operate at higher frequencies for two reasons: 1) the attendant increase in sound absorption reduces sound wave penetration, interfering with image clarity; and (2) manufacturing processes have not been able to produce the necessary higher frequency probes and electronics. However, the improvement that high-frequency ultrasound arrays offer in image clarity can be used now in applications requiring minimal tissue penetration. Using Creare’s ultrahigh-frequency systems, physicians will be able to view the characteristics of tissues close to the surface of the body or in an easily accessible cavity.

Building ultrasound devices at frequencies higher than 25 MHz presents significant design challenges. As the operating frequency increases, the dimensions of the transducer elements get smaller. Consequently, the resulting probes become progressively more difficult to build, and traditional materials do not work as well. In order to create a device small enough to be used in situ, our design was based on a linear array of lithium niobate (LiNbO₃) ultrasonic transducers. The transducer comprises a thin, electroded wafer of bulk piezoelectric material that has been attached to the backside of an acoustic lens and machined into individual transducer elements. We also designed and built hardware to perform the very high-speed data acquisition required by the ultrasound RF signals. We have demonstrated the image formation potential of high-resolution arrays to be between 10 to 100 micrometers.

With image clarity at this level, scanning microscopes could be used in skin cancer detection, improving accuracy in diagnosis by allowing rapid visualization of cells over a large area in a single examination. In contrast, traditional biopsies examine tissue at only one or two spots, potentially missing abnormalities. Further, a high-frequency ultrasound system can image tissue blocked from view by scar tissue formed after either surgical or radiation treatment, making it possible to monitor the success of previous treatment with much greater accuracy.

Additional potential applications for Creare’s technology include mounting a scanning acoustic microscope on the tip of a catheter, gastroscope, colonoscope, bronchscope, or laparascope. Transducer arrays with these specifications will also likely have applications in nondestructive testing in the microelectronics industry.

Finally, we are developing an application of our scanning microscopes to improve visualization of the structure of the eye prior to corrective laser surgery. Approximately 10% of these surgeries need to be repeated, most likely due to an inaccurate measurement of the anatomy of the eye. Our technology will enable precise measurement of the internal structure of the cornea, as well as improving diagnosis and treatment of ocular scars and mass lesions.

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