Increasing the field-of-view of row–column-addressed ultrasound transducers: implementation of a diverging compound lens

Abstract

The purpose of this work is to investigate compound lenses for row-column-addressed (RCA) ultrasound transducers for increasing the field-of-view (FOV) to a curvilinear volume region, while retaining a flat sole to avoid trapping air between the transducer sole and the patient, which would otherwise lead to unwanted reflections. The primary motivation behind this research is to develop a RCA ultrasound transducer for abdominal or cardiac imaging, where a curvilinear volume region is a necessity. RCA transducers provide 3-D ultrasound imaging with fewer channels than fully-addressed 2-D arrays (2N instead of N), but they have inherently limited FOV. By increasing the RCA FOV, these transducers can be used for the same applications as fully-addressed transducers while retaining the same price range as conventional 2-D imaging due to the lower channel count. Analytical and finite element method (FEM) models were employed to evaluate design options. Composite materials were developed by loading polymers with inorganic powders to satisfy the corresponding speed of sound and specific acoustical impedance requirements. A BiO powder with a density of 8.9g/cm was used to decrease the speed of sound of a room temperature vulcanizing (RTV) silicone, RTV615, from 1.03mm/μs to 0.792mm/μs. Using micro-balloons in RTV615 and a urethane, Hapflex 541, their speeds of sound were increased from 1.03mm/μs to 1.50mm/μs and from 1.52mm/μs to 1.93mm/μs, respectively. A diverging add-on lens was fabricated of a BiO loaded RTV615 and an unloaded Hapflex 541. The lens was tested using a RCA probe, and a FOV of 32.2° was measured from water tank tests, while the FEM model yielded 33.4°. A wire phantom with 0.15mm diameter wires was imaged at 3MHz down to a depth of 14cm using a synthetic aperture imaging sequence with single element transmissions. The beamformed image showed that wires outside the array footprint were visible, demonstrating the increased FOV.

A Row-Column-Addressed 2D Probe with an Integrated Compound Diverging Lens

“…A linear fit of the difference between the two frequency responses resulted in a slope of −4 dB/MHz, which is caused by the increased attenuation of the lens. The estimate of the one-way attenuation at 5 MHz at the center and at the edge of the lens is 9.9 dB and 18.9 dB, respectively [12]. Whereas the estimate of the one-way attenuation of the acoustic window of the probe without the lens is 3.2 dB at 5 MHz.…”

“…A mold of RTV664 was cast around a dummy nose piece where Teflon tape was applied on its surface to avoid the RTV adhering to the nose piece and also to make the cavity in the mold a little larger than the nose piece itself. RTV615 + Bi 2 O 3 was mixed, in a mass mix ratio (MMR) of 1:0.9, as described in [12]. The RTV664 mold was then placed on a glass plate, Fig.…”

“…To obtain a flat or convex surface without curving the stack, a compound lens of two or more different materials can be used [9]- [11]. We have earlier presented a compound diverging add-on lens for an RCA probe which obtained a FOV of 31 • [12]. The objective of this work is to integrate the developed compound lens into a fully functioning RCA probe and to compare it to a similar probe without a diverging lens.…”

Anatomic and Functional Imaging Using Row–Column Arrays

“…Our group in Denmark has worked extensively with RC arrays for the last ten years within anatomic and functional imaging primarily based on synthetic aperture (SA) sequences. We have also fabricated a range of RC probes including PZT and CMUT based devices [41] and developed fabrication schemes for diverging lenses and probes with integrated lenses [42,43]. The various results and possibilities will be presented below.…”

Preclinical study to improve microbubble-mediated drug delivery in cancer using an ultrasonic probe with an interchangeable acoustic lens

“…Thus, for drug delivery with UUS-MBs, the prevention of unexpected damage caused by widespread excessive ultrasonic irradiation is essential. Unlike conventional unfocused transducers, ultrasound with an acoustic lens can tune the pressure field depending on the type of interchangeable acoustic lens according to the purpose of the DDS 21 , 22 . Simple attachment of the inexpensive lens on the purchased diagnostic ultrasound probe can also reduce the tremendous cost for new therapeutic ultrasound probes.…”