Objective This paper describes development of a novel 500-MHz scanning acoustic microscope (SAM) for assessing the mechanical properties of ocular tissues at fine resolution. The mechanical properties of some ocular tissues, such as lamina cribrosa (LC) in the optic nerve head, are believed to play a pivotal role in eye pathogenesis. Methods A novel etching technology was used to fabricate silicon-based lens for a 500-MHz transducer. The transducer was tested in a custom designed scanning system on human eyes. Two-dimensional (2D) maps of bulk modulus (K), mass density (ρ) were derived using improved versions of current state-of-the-art signal processing approaches. Results The transducer employed a lens radius of 125 μm and had a center frequency of 479 MHz with a −6-dB bandwidth of 264 MHz and a lateral resolution of 4 μm. The LC, Bruch’s membrane (BM) at the interface of the retina and choroid, and Bowman’s layer (BL) at the interface of the corneal epithelium and stroma, were successfully imaged and resolved. Analysis of the 2D parameter maps revealed average values of LC, BM and BL with KLC = 2.81 ± 0.17; GPa, KBM = 2.89 ± 0.18; GPa, K BL = 2.6 ± 0.09; GPa, ρ LC = 0.96 ± 0.03 g/cm3; ρ BM = 0.97 ± 0.04 g/cm3; ρ BL = 0.98 ± 0.04g/cm3; Significance This novel SAM was shown to be capable of measuring mechanical properties of soft biological tissues at microscopic resolution; it currently is the only system that allows Simultaneous measurement of K, ρ, and attenuation in large lateral scales (field area > 9 mm2) and at fine resolutions.

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The knowledge of skull bone thickness would be helpful for a great variety of surgical interventions of the head. Ultrasound (US) can offer this information intraoperatively in real time. A-mode US measurements of skull bone thickness were performed with different pulse characteristics: 1) in water and 2) by directly coupling a 2.25-MHz US transducer integrated in a handpiece with a soft delay line using coded excitation (CE) (SonoPointer). Mechanical measurements by calipers served as controls. The specimen were 16 nonselected human cadaveric skull bones preserved with formaldehyde. The average difference between the bone thickness measured by the SonoPointer and the mechanical control measurements was 0.04 +/- 0.62 mm. The 95% limits of agreement between the two methods were -1.18 and 1.25 mm. However, even the gold standard of two repeated caliper measurements had limits of agreement of -0.4 and 0.42 mm. Using a standard US pulse in water, only 62.5% sample points were measurable, whereas the SonoPointer produced the thickness measurement in 97.9% of points. CE proved to be superior to single burst or needle US pulses. A-mode US measurements of skull bone thickness using the SonoPointer are feasible. It may provide valuable information on skull bone thickness, e.g., for osteosynthesis, calvarial split bone harvesting, implantation of hearing devices, osseointegrated titanium fixtures, and skull base surgery.

In this work we present the evaluation results of our 3D sonar camera system. The system consists of a matrix antenna array with 1024 single transducer elements and our in house developed DiPhAS sonar beamformer - a 128 channel FPGA-based beamforming system with a 1:8 multiplexing device for each channel. The system is designed to be applicable to ROV and AUV systems for real-time volumetric imaging in a deep sea environment. Defocused excitation of the transducer array is used to achieve a sound field opening angle of up to 40° in lateral and elevational direction. The antenna's sound field can be adjusted electronically in order to increase either the imaged area or the image contrast in a specific area of interest. Different filter algorithms working on a raw data basis have been implemented in order to suppress image artifacts which occur during the reconstruction process. Measurements on different phantoms have been performed in order to prove the real-time imaging as well as spatial resolution capabilities of the camera system

We present the newest application specific version of our beamformer platform “DiPhAS” that provides 256 parallel channels both for generation of ultrasound signals as well as digitalization of returned echos. Using ultrasound transducers with lots of elements requires high channel count electronics. Applications for such systems range from functional ultrafast imaging using high element count linear array transducers for imaging of a large field of view to real time volumetric imaging with matrix array transducers. To perform volumetric transmit beamforming with matrix transducers, lots of these matrix elements have to be controlled individually. Furthermore, many elements need to be excited in order to compensate for the small active element size and provide a sufficient overall active footprint to generate enough acoustic power for imaging with adequate SNR. The system is set up based on our platform concept with the common ultrasound research device components: mainboard, power supply, application-specific new front ends integrating 16 channels on each PCB and device software. Using 16 front ends results in a total channel count of 256. The new front ends are based on our existing 8 channel front end technology and share the same concepts with doubled channel count for both transmission and reception. The system generates transmit sequences with voltages up to 150 Vpp and digitizes with a sampling rate of up to 80 MHz. The beamformer implements the control for additional external multiplexers in the transducer probe. This has been tested with an external transducer matrix array and can be used to connect to our custom 1024 elements matrix array (32×32 elements) with a 1:4 multiplexer integrated into the probe head. Received data can be accessed as single element channel data of all 256 channels in parallel and transferred to a PC via PCI-Express. Beamforming can be done on a massively parallel computing graphics processor (GPU). The used software includes standard applications for measurements and interfaces for Matlab, C++ and C#. It is used to process, analyze and visualize data from the beamformer. This system will be scalable to an even higher channel count by connecting several beamformers to a single PC using multiple PCI-Express connections and additional synchronization over all single beamformer electronics. It is the basis of our 3D/4D ultrasound research system connected to our matrix arrays developed in-house