Texture Generation for Photoacoustic Elastography

Abstract

Elastographic imaging is a widely used technique which can in principle be implemented on top of every imaging modality. In elastography, the specimen is exposed to a force causing local displacements in the probe, and imaging is performed before and during the displacement experiment. From the computed displacements material parameters can be deduced, which in turn can be used for clinical diagnosis. Photoacoustic imaging is an emerging image modality, which exhibits functional and morphological contrast. However, opposed to ultrasound imaging, for instance, it is considered a modality which is not suited for elastography, because it does not reveal speckle patterns. However, this is somehow counter-intuitive, because photoacoustic imaging makes available the whole frequency spectrum as opposed to single frequency standard ultrasound imaging. In this work, we show that in fact artificial speckle patterns can be introduced by using only a band-limited part of the measurement data. We also show that after introduction of artificial speckle patterns, deformation estimation can be implemented more reliably in photoacoustic imaging.

Photoacoustic elastography

“…In a second study, the volume-averaged Young’s modulus of soft tissue was measured by a photoacoustic sensing technique, which, however, possessed no spatial resolution [14]. Yet another study introduced speckles in photoacoustic images for sample displacement estimation, but demonstrated the concept only with simulation data [15]. So far, elastography has not been successfully implemented using photoacoustic imaging.…”

“…Compared to previous studies, our photoacoustic elastography technique based on a linear-array photoacoustic computed tomography has the following distinctive features [12–15]. First, photoacoustic elastography maps the Young’s modulus of biological tissue, but previous photoacoustic viscoelasticity studies are based on the contrast of the viscosity-elasticity ratio [12–13].…”

Challenges for Optical Flow Estimates in Elastography

“…[16]. This even lead to the introduction of additional [15] or virtual [8,14] speckle. Since speckle appears throughout the obtained images, and thus in particular also in otherwise featureless areas, their movement during an elastography experiment can also be used to estimate the internal displacement field more accurately.…”

Thermoacoustic elastography: recovery of bulk elastic modulus of heterogeneous media using tomographically measured thermoacoustic measurements

“…If the assume the microwave/mechanical property distributions are close to the true profiles, the left-hand side of Eq. [6] can be considered as the true data (observed or measured), and the relationship can be truncated to yield…”

“…Elastography for measuring tissue elastic modulus (2-9) is widely used as a supplementary diagnostic method for early detection and diagnosis of various diseases. At present, elastography has been implemented based on the contrast mechanism of ultrasound (US) imaging (3,10,11), optical coherence tomography (OCT) (4,12), magnetic resonance imaging (5,13) (MRI), or photoacoustic imaging (PAI) (6)(7)(8)(9)14,15). These elasticity imaging techniques have been applied for the detection of liver fibrosis (16), breast cancer (17), and prostate cancer (18).…”