8,652 research outputs found
Exploiting flow dynamics for super-resolution in contrast-enhanced ultrasound
Ultrasound localization microscopy offers new radiation-free diagnostic tools
for vascular imaging deep within the tissue. Sequential localization of echoes
returned from inert microbubbles with low-concentration within the bloodstream
reveal the vasculature with capillary resolution. Despite its high spatial
resolution, low microbubble concentrations dictate the acquisition of tens of
thousands of images, over the course of several seconds to tens of seconds, to
produce a single super-resolved image. %since each echo is required to be well
separated from adjacent microbubbles. Such long acquisition times and stringent
constraints on microbubble concentration are undesirable in many clinical
scenarios. To address these restrictions, sparsity-based approaches have
recently been developed. These methods reduce the total acquisition time
dramatically, while maintaining good spatial resolution in settings with
considerable microbubble overlap. %Yet, non of the reported methods exploit the
fact that microbubbles actually flow within the bloodstream. % to improve
recovery. Here, we further improve sparsity-based super-resolution ultrasound
imaging by exploiting the inherent flow of microbubbles and utilize their
motion kinematics. While doing so, we also provide quantitative measurements of
microbubble velocities. Our method relies on simultaneous tracking and
super-localization of individual microbubbles in a frame-by-frame manner, and
as such, may be suitable for real-time implementation. We demonstrate the
effectiveness of the proposed approach on both simulations and {\it in-vivo}
contrast enhanced human prostate scans, acquired with a clinically approved
scanner.Comment: 11 pages, 9 figure
Acoustical structured illumination for super-resolution ultrasound imaging.
Structured illumination microscopy is an optical method to increase the spatial resolution of wide-field fluorescence imaging beyond the diffraction limit by applying a spatially structured illumination light. Here, we extend this concept to facilitate super-resolution ultrasound imaging by manipulating the transmitted sound field to encode the high spatial frequencies into the observed image through aliasing. Post processing is applied to precisely shift the spectral components to their proper positions in k-space and effectively double the spatial resolution of the reconstructed image compared to one-way focusing. The method has broad application, including the detection of small lesions for early cancer diagnosis, improving the detection of the borders of organs and tumors, and enhancing visualization of vascular features. The method can be implemented with conventional ultrasound systems, without the need for additional components. The resulting image enhancement is demonstrated with both test objects and ex vivo rat metacarpals and phalanges
Super-resolution photoacoustic imaging via flow induced absorption fluctuations
In deep tissue photoacoustic imaging the spatial resolution is inherently
limited by the acoustic wavelength. We present an approach for surpassing the
acoustic diffraction limit by exploiting temporal fluctuations in the sample
absorption distribution, such as those induced by flowing particles. In
addition to enhanced resolution, our approach inherently provides background
reduction, and can be implemented with any conventional photoacoustic imaging
system. The considerable resolution increase is made possible by adapting
notions from super-resolution optical fluctuations imaging (SOFI) developed for
blinking fluorescent molecules, to flowing acoustic emitters. By generalizing
SOFI mathematical analysis to complex valued signals, we demonstrate
super-resolved photoacoustic images that are free from oscillations caused by
band-limited detection. The presented technique holds potential for
contrast-agent free micro-vessels imaging, as red blood cells provide a strong
endogenous source of naturally fluctuating absorption
Overcoming the acoustic diffraction limit in photoacoustic imaging by localization of flowing absorbers
The resolution of photoacoustic imaging deep inside scattering media is
limited by the acoustic diffraction limit. In this work, taking inspiration
from super-resolution imaging techniques developed to beat the optical
diffraction limit, we demonstrate that the localization of individual optical
absorbers can provide super-resolution photoacoustic imaging well beyond the
acoustic diffraction limit. As a proof-of-principle experiment, photoacoustic
cross-sectional images of microfluidic channels were obtained with a 15 MHz
linear CMUT array while absorbing beads were flown through the channels. The
localization of individual absorbers allowed to obtain super-resolved
cross-sectional image of the channels, by reconstructing both the channel width
and position with an accuracy better than . Given the discrete
nature of endogenous absorbers such as red blood cells, or that of exogenous
particular contrast agents, localization is a promising approach to push the
current resolution limits of photoacoustic imaging
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