High frequency ultrasonic imaging and its applications in skin

Utilizing transducers with center frequencies and bandwidths both up to 100 MHz high frequency ultrasound allows high resolution imaging in fluids and tissue with a resolution down to approximately 10 mu m. In addition to the increased resolution for medical imaging the backscatter properties of biological tissue are of considerable diagnostic advantage which change more rapidly with increasing frequency than the spatial resolution does. Because of the increasing attenuation of ultrasound in tissue at higher frequencies only small near surface areas can be imaged. For applications in dermatology recent research activities and instrument developments have included B-Scan systems (skin: thickness of layers, tumors, inflammatory diseases), flow visualization concepts (diagnosis of the cutaneous microcirculation), and tissue characterization (tumorous skin areas). As transducer and array technology has limitations high frequency imaging systems mainly utilize mechanically scanned single element transducers. They require special scanning procedures as well as signal processing techniques in order to optimize resolution, range, and signal-to-noise-ratio. The paper will give an overview of these techniques and will also present some examples of applications in dermatology.