The physical properties of each transducer element play a vital role in the quality of images generated in optoacoustic (photoacoustic) tomography using transducer arrays. Thorough experimental characterization of such systems is often laborious and impractical. A shortcoming of the existing impulse response correction methods, however, is the assumption that all transducers in the array are identical and therefore share one electrical impulse response (EIR). In practice, the EIRs of the transducer elements in the array vary, and the effect of this element-to-element variability on image quality has not been investigated so far, to the best of our knowledge. We hereby propose a robust EIR derivation for individual transducer elements in an array using sparse measurements of the total impulse response (TIR) and by solving the linear system for temporal convolution. Thereafter, we combine a simulated spatial impulse response with the derived individual EIRs to obtain a full characterization of the TIR, which we call individual synthetic TIR. Correcting for individual transducer responses, we demonstrate significant improvement in isotropic resolution, which further enhances the clinical potential of array-based handheld transducers.
The morphology and thermal conductivity of injectionmolded polyamide 46 (PA46) samples were investigated in this study. It was found that injection molding parameters had no influence on the thermal conductivity. This was attributed to the high crystallization speed and therefore imperfect crystal structure of PA46. By annealing of some samples at 2608C for 24 h the thermal conductivity was increased by 30%. Polarization light microscopy revealed only minor changes of the visible morphological structure for the as molded and annealed samples. For the investigation of the sample crystallinity via Raman spectroscopy an analysis method was established and the term "Raman crystallinity" is introduced as the intensity ratio of characteristic Raman bands. Via Raman crystallinity it was possible to distinguish between different mold temperatures and the annealed PA46 samples showed a significantly increased Raman crystallinity. Our results show that the thermal conductivity of PA46 primarily depends on the crystal structure on a length scale of crystallites. The size of the visible spherulite-like structures did not correlate with the change in thermal conductivity. A correlation of the Raman crystallinity with the thermal conductivity of PA46 was shown. POLYM. ENG. SCI., 55:2231-2236, 2015
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