Optoacoustic determination of spatio- temporal responses of ultrasound sensors

Abstract

The characterization of the spatial and frequency response of acoustic detectors is important for enabling accurate optoacoustic imaging. In this work, we developed a hybrid method for the characterization of the spatially dependent response of ultrasound detectors. The method is based on the experimental determination of the receive-mode electrical impulse response (EIR) of the sensor, which is subsequently convolved with the corresponding spatial impulse response (SIR), computed numerically. The hybrid method is shown to have superior performance over purely experimental techniques in terms of accurate determination of the spatial and temporal responses of ultrasonic detectors, in high as well as low sensitivity regions of the sensor.

Adding fifth dimension to optoacoustic imaging: volumetric time-resolved spectrally enriched tomography

“…In order to provide quantitative values of the concentration of different chromophores, one must also account for the strong (and generally unknown) wavelength-dependent light fluence distribution 29 and the spatial distribution of the Grüneisen parameter, 30 as well as acoustic heterogeneities [31][32][33] and attenuation 34 in the object. Furthermore, a correct calibration of the space-and frequency-dependent sensitivity of the ultrasonic transducers 35,36 is needed to relate the collected voltage to the actual optoacoustic pressure. Even though in the current work we were clearly able to attain reasonable qualitative values regarding relative concentration of the different tissue chromophores and dynamics of the dye biodistribution, we are still restrained from claiming absolute quantification for imaging at a centimeter-scale depth.…”

Spatiospectral denoising framework for multispectral optoacoustic imaging based on sparse signal representation

“…Conversely, signal integration over large surfaces introduces a broadening in the impulse response of the system and may distort the reconstructed images. 23,24 When the imaging system is tomographic, the image reconstruction algorithm effectively offers noise suppression through the superposition of projection signals in the image domain. However, such noise suppression in the process of image formation has less impact in the case of nontomographic systems such as microscopes, endoscopes, or intravascular catheters.…”

A Constrained Variable Projection Reconstruction Method for Photoacoustic Computed Tomography Without Accurate Knowledge of Transducer Responses

“…It was suggested [16] that the impulse response could be measured by illuminating the transducer with an ultra-short laser pulse. However, the impulse response measured in this way represents the convolution of the photoacoustic pressure produced by parasitic sources on the surface of the transducer and the sought-after EIR [17]. Alternatively, the derivative of the EIR can be estimated by measuring the signal produced by optically illuminating an absorber that is small relative to the acoustic wavelength.…”

“…In practice, signals produced by small absorbers can be weak [14] and errors in their low frequencies can be amplified if the signals are integrated to estimate the EIR. Recently, an alternate method to estimate the EIR was proposed to circumvent this [14], [17]. All of these methods require precise alignment of the acoustic source with respect to the transducer axis.…”