Development of a Handheld Scanning Transducer Probe for Ultrasound Imaging

The scanning transducer technique is a simple and cost effective approach to achieve ultrasound imaging. By mechanically scanning a single-element transducer with a motor stage, the time-variant ultrasound field at an array of locations can be recorded for image reconstruction. When compared with the use of conventional transducer arrays, the scanning transducer approach requires much less data acquisition electronics. However, conventional x-y motor stages used for scanning the transducer are complex, bulky and slow. As a result, the scanning transducer technique for image acquisition has been mainly limited for lab use and is not suitable for handheld imaging applications. The goal of this research is to achieve a new 2-axis scanning transducer probe for handheld ultrasound imaging operations, which is compact and light-weight. The approach is to develop and capitalize upon a miniaturized water-immersible 2-axis electromagnetic actuator to enable fast and agile scanning of a single-element transducer in a liquid filled probe case. The design and fabrication of a water-immersible 2-axis electromagnetic actuator has been achieved and its mechanical scanning performance has been characterized and optimized with finite-element simulation. Preliminary pulse-echo imaging experiments were performed to verify its ultrasound imaging capability with scanning in B-scan mode in multiple directions. The scan system built can be dynamically reconfigured to either 1D- B-Scan or even 2D C-Scan formats for conventional 2D as well as 3D ultrasound imaging. In addition, integrated optical light delivery with optic fiber cables was also investigated to extend its capability for photoacoustic imaging

An optimized ultrasound detector for photoacoustic breast tomography

Photoacoustic imaging has proven to be able to detect vascularization-driven optical absorption contrast associated with tumors. In order to detect breast tumors located a few centimeter deep in tissue, a sensitive ultrasound detector is of crucial importance for photoacoustic mammography. Further, because the expected photoacoustic frequency bandwidth (a few MHz to tens of kHz) is inversely proportional to the dimensions of light absorbing structures (0.5 to 10+ mm), proper choices of materials and their geometries, and proper considerations in design have to be made for optimal photoacoustic detectors. In this study, we design and evaluate a specialized ultrasound detector for photoacoustic mammography. Based on the required detector sensitivity and its frequency response, a selection of active material and matching layers and their geometries is made leading to a functional detector models. By iteration between simulation of detector performances, fabrication and experimental characterization of functional models an optimized implementation is made and evaluated. The experimental results of the designed first and second functional detectors matched with the simulations. In subsequent bare piezoelectric samples the effect of lateral resonances was addressed and their influence minimized by sub-dicing the samples. Consequently, using simulations, the final optimized detector could be designed, with a center frequency of 1 MHz and a -6 dB bandwidth of ~80%. The minimum detectable pressure was measured to be 0.5 Pa, which will facilitate deeper imaging compared to the currrent systems. The detector should be capable of detecting vascularized tumors with resolution of 1-2 mm. Further improvements by proper electrical grounding and shielding and implementation of this design into an arrayed detector will pave the way for clinical applications of photoacoustic mammography.Comment: Accepted for publication in Medical Physics (American Association of Physicists in Medicine

Printed Receive Coils with High Acoustic Transparency for Magnetic Resonance Guided Focused Ultrasound.

In magnetic resonance guided focused ultrasound (MRgFUS) therapy sound waves are focused through the body to selectively ablate difficult to access lesions and tissues. A magnetic resonance imaging (MRI) scanner non-invasively tracks the temperature increase throughout the tissue to guide the therapy. In clinical MRI, tightly fitted hardware comprised of multichannel coil arrays are required to capture high quality images at high spatiotemporal resolution. Ablating tissue requires a clear path for acoustic energy to travel but current array materials scatter and attenuate acoustic energy. As a result coil arrays are placed outside of the transducer, clear of the beam path, compromising imaging speed, resolution, and temperature accuracy of the scan. Here we show that when coil arrays are fabricated by additive manufacturing (i.e., printing), they exhibit acoustic transparency as high as 89.5%. This allows the coils to be placed in the beam path increasing the image signal to noise ratio (SNR) five-fold in phantoms and volunteers. We also characterize printed coil materials properties over time when submerged in the water required for acoustic coupling. These arrays offer high SNR and acceleration capabilities, which can address current challenges in treating head and abdominal tumors allowing MRgFUS to give patients better outcomes

Real-time 3D medical ultrasound : signal processing challenges

Real-time 2D ultrasound systems are used routinely in every hospital and are a huge success both technically and commercially. This paper discusses the signal processing problems that needs to be tackled in order to move from 2D to 3D real-time ultrasound systems. The first problem discussed is that of handling 2000 10000 elements in the transducer. Sparse array methods is a way to reduce the number of elements and cost without compromising quality. Examples of performance with sparse arrays are presented. The second important problem is that of frame-rate. In 3D the frame-rate will be so low that real-time acquisition will be impossible unless some form of parallelism is exploited. Various ways of doing that such as multiple receive beams, coded transmit excitation and limited diffraction beams are discussed

An annular array with fiber composite microstructure for far field NDT imaging applications

This paper describes the design and fabrication of a reduced element count annular array for far field NDT imaging applications, built with a random fiber piezoelectric composite microstructure. An annular array design is considered, spatially it offers axi-symmetric layout while reducing number of array elements, which could potentially result in a significant reduction in the cost and complexity of building an ultrasonic volumetric imaging system. Modelling and preliminary experimental results are presented to evaluate the feasibility of this approach