New Potassium Sodium Niobate Single Crystal with Thickness-independent High-performance for Photoacoustic Angiography of Atherosclerotic Lesion.

The synthesis of (K0.45Na0.55)0.96Li0.04NbO3 (KNLN) single crystals with a <100>-orientation, using a seed-free solid state crystal growth method, is described here. With the thickness of the crystals decreasing down to the order of tens of micrometers, this new lead-free single crystal exhibits thickness-independent electrical behavior, and maintains superior piezoelectric constant (d33 = 670 pC N-1) and electromechanical coupling factor (kt = 0.55). The successful fabrication of a tiny intravascular photoacoustic probe, with a 1 mm outside diameter, is achieved using a single crystal with a thickness of around 60 μm, in combination with a 200 μm core multimode fiber. Wire phantom photoacoustic images show that the axial resolution and lateral resolution of the single crystal based probe are 60 and 220 μm, respectively. In addition, intravascular photoacoustic imaging of the atherosclerotic lesion of a human artery is presented. In the time-domain and frequency-domain images, calcified regions are clearly distinguishable from surrounding tissue. These interesting results demonstrate that KNN-based lead-free piezoelectric single crystals are a promising candidate to substitute for lead-based piezoelectric materials for photoacoustic imaging in the future.