Flexible integration of both high imaging resolution and high power arrays for Thermal Strain Imaging (TSI)

Thermal Strain Imaging (TSI) for carotid artery plaque characterization benefits from both high imaging resolution (<;75 μm) and sufficient heating to elevate tissue temperature (~1-3°C within 1-3 cardiac cycles) to produce a noticeable change in sound speed in the targeted tissues. Optimization of imaging and heating in a single array or set of arrays is challenging however. Our flexible approach utilizes independent ultrasound arrays which can be mechanically joined in a low cost, but high performance manner. The approach presented should enable the beginning of a new era in dual-arrays: high resolution dedicated arrays combined with high power custom arrays to produce a desired beam overlap function. Low cost and quick integration changes are possible which permit high investigational flexibility. The key innovations of this work utilize 3D printing in the creation of array manifolds, and a high efficiency RF power splitter. The 3D printer used is capable of 16 micron accuracy in the construction of rigid polymer manifold which supports the heating transducer array elements. For our particular application of TSI on carotid plaque characterization, the tissue target site is 15 to 30mm deep, with a typical target volume of 2mm (ele) X 5mm (azi) × 7mm (depth). The fully characterized early design comprises 6 high power PZT array elements, each at 8.8 mm in diameter, which can be integrated with a multitude of commercially available imaging probes; we have used the MS250 (13-24 MHz) on the Vevo 2100 VisualSonics imaging platform. Both analytical and simulation methods were used in the selection of the best heating frequency (3.5 MHz) to use at the tissue targeting depth. The custom heating array performance was compared against KLM modeling and can easily deliver 30W of total acoustic power which produces intensities beyond 100 W/cm2 in the 2mm by 5mm tissue target region resulting in a 3°C rise in 2 sec. Custom beam modeling software was used to optimize sets of beam shapes of the custom arrays, and then implemented in the desired array manifold configuration. This low cost, flexible, and very effective new method for combining very different array functions demonstrates a means for rapid growth in this research area as designs are refined towards eventual commercialization.