An optimized ultrasound detector for photoacoustic breast tomography

Photoacoustic imaging has proven to be able to detect vascularization-driven optical absorption contrast associated with tumors. In order to detect breast tumors located a few centimeter deep in tissue, a sensitive ultrasound detector is of crucial importance for photoacoustic mammography. Further, because the expected photoacoustic frequency bandwidth (a few MHz to tens of kHz) is inversely proportional to the dimensions of light absorbing structures (0.5 to 10+ mm), proper choices of materials and their geometries, and proper considerations in design have to be made for optimal photoacoustic detectors. In this study, we design and evaluate a specialized ultrasound detector for photoacoustic mammography. Based on the required detector sensitivity and its frequency response, a selection of active material and matching layers and their geometries is made leading to a functional detector models. By iteration between simulation of detector performances, fabrication and experimental characterization of functional models an optimized implementation is made and evaluated. The experimental results of the designed first and second functional detectors matched with the simulations. In subsequent bare piezoelectric samples the effect of lateral resonances was addressed and their influence minimized by sub-dicing the samples. Consequently, using simulations, the final optimized detector could be designed, with a center frequency of 1 MHz and a -6 dB bandwidth of ~80%. The minimum detectable pressure was measured to be 0.5 Pa, which will facilitate deeper imaging compared to the currrent systems. The detector should be capable of detecting vascularized tumors with resolution of 1-2 mm. Further improvements by proper electrical grounding and shielding and implementation of this design into an arrayed detector will pave the way for clinical applications of photoacoustic mammography.Comment: Accepted for publication in Medical Physics (American Association of Physicists in Medicine

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

Dynamic Three-Dimensional Echocardiographic Imaging of Congenital Heart Defects in Infants and Children by Computer-Controlled Tomographic Parallel Slicing Using a Single Integrated Ultrasound Instrument

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73202/1/j.1540-8175.1994.tb01061.x.pd

Soft tissue absorption tomography with correction for scattering aberrations.

International audienceAmong the many factors involved in ultrasound attenuation phenomena, scattering effects play a major role, even in the unexpected case of soft tissues. It is proposed in this study to quantitatively evaluate the scattering affecting the measurements, before reconstructing the absorption parameter alone. The reconstruction procedure involves three steps: i/ estimating the sound speed map using a transmission tomography algorithm. This estimation procedure provides a numerical phantom of the organ probed, cleared of all dissipative components. This absorption free phantom mimics the (viscoacoustic) tissues imaged except for the density and absorption characteristics: the density a priori equals 1000 kg/m3, and the absorption is not taken into account. The impedance fluctuations in the object are therefore approximated on the basis of the sound speed contrast; ii/ synthesing the field scattered by the absorption free phantom; the attenuation observed here results solely from the scattering phenomenon. The synthesis is carried out using a finite-element time domain code simulating the ultrasonic propagation through the phantom. It provides the scattering distortion reference introduced into the log spectral absorption estimator; iii/ reducing the scattering distortions affecting the integrated absorption measured along the ray paths using a log spectral procedure. The corrected integrated absorption is then processed using a tomographic reconstruction procedure that provides an estimate of the absorption distribution. Simple numerical simulations show the improvement obtained in the absorption estimates with this approach

Photoacoustic tomography setup using LED illumination

Photoacoustic tomography (PAT) is a hybrid imaging modality that combines optical contrast with ultrasound resolution. Most of the PAT configurations are based on high-energy solid-state lasers such as Nd:YAG laser. In this work, a PAT system that uses light-emitting diode (LED) as a light source is introduced. The system is designed so that the imaged target can be stationary. The target is illuminated by a LED light source from one side and the pressure wave is measured using an acoustic transducer that is rotated around the target. Image reconstruction is based on Bayesian approach to illposed inverse problems. The system was tested with light absorbing targets also in limited-view and sparse angle measurement situations. The results show that LED-based instrumentation and advanced reconstruction methods can form a potential PAT system that can also be applied in limited-view and sparse angle photoacoustic tomography

Medical tomograph system using ultrasonic transmission

Ultrasonic energy transmission in rectilinear array scanning patterns of soft tissue provides projection density values of the tissue which are recorded as a function of scanning position and angular relationship, .theta., of the subject with a fixed coordinate system. A plurality of rectilinear scan arrays in the same plane for different angular relationships .theta..sub.1 . . . .theta..sub.n thus recorded are superimposed. The superimposition of intensity values thus yields a tomographic image of an internal section of the tissue in the scanning plane

Biomedical Photoacoustic Imaging and Sensing Using Affordable Resources

The overarching goal of this book is to provide a current picture of the latest developments in the capabilities of biomedical photoacoustic imaging and sensing in an affordable setting, such as advances in the technology involving light sources, and delivery, acoustic detection, and image reconstruction and processing algorithms. This book includes 14 chapters from globally prominent researchers , covering a comprehensive spectrum of photoacoustic imaging topics from technology developments and novel imaging methods to preclinical and clinical studies, predominantly in a cost-effective setting. Affordability is undoubtedly an important factor to be considered in the following years to help translate photoacoustic imaging to clinics around the globe. This first-ever book focused on biomedical photoacoustic imaging and sensing using affordable resources is thus timely, especially considering the fact that this technique is facing an exciting transition from benchtop to bedside. Given its scope, the book will appeal to scientists and engineers in academia and industry, as well as medical experts interested in the clinical applications of photoacoustic imaging