Two-dimensional photoacoustic imaging by use of Fourier-transform image reconstruction and a detector with an anisotropic response.
TL;DR: A 2D Fourier-transform-based reconstruction algorithm that is significantly faster and produces fewer artifacts than simple radial backprojection methods is described.
Abstract: Theoretical and experimental aspects of two-dimensional (2D) biomedical photoacoustic imaging have been investigated. A 2D Fourier-transform-based reconstruction algorithm that is significantly faster and produces fewer artifacts than simple radial backprojection methods is described. The image-reconstruction time for a 208 X 482 pixel image is similar to1 s. For the practical implementation of 2D photoacoustic imaging, a rectangular detector geometry was used to obtain an anisotropic detection sensitivity in order to reject out-of-plane signals, thereby permitting a tomographic image slice to be reconstructed. This approach was investigated by the numerical modeling of the broadband directional response of a rectangular detector and imaging of various spatially calibrated absorbing targets immersed in a turbid phantom. The experimental setup was based on a Q-switched Nd:YAG excitation laser source and a mechanically line-scanned Fabry-Perot polymer-film ultrasound sensor. For a 800 mum x 200 mum rectangular detector, the reconstructed image slice thickness was 0.8 mm up to a vertical distance of z = 3.5 mm from the detector, increasing thereafter to 2 mm at z = 10 mm. Horizontal and vertical spatial resolutions within the reconstructed slice were approximately 200 and 60 mum, respectively. (C) 2003 Optical Society of America.
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TL;DR: PAT holds the promise of in vivo imaging at multiple length scales ranging from subcellular organelles to organs with the same contrast origin, an important application in multiscale systems biology research.
Abstract: Photoacoustic tomography (PAT) is probably the fastest-growing area of biomedical imaging technology, owing to its capacity for high-resolution sensing of rich optical contrast in vivo at depths beyond the optical transport mean free path (~1 mm in human skin). Existing high-resolution optical imaging technologies, such as confocal microscopy and two-photon microscopy, have had a fundamental impact on biomedicine but cannot reach the penetration depths of PAT. By utilizing low ultrasonic scattering, PAT indirectly improves tissue transparency up to 1000-fold and consequently enables deeply penetrating functional and molecular imaging at high spatial resolution. Furthermore, PAT promises in vivo imaging at multiple length-scales; it can image subcellular organelles to organs with the same contrast origin — an important application in multiscale systems biology research.
1,276 citations
TL;DR: A brief recap of recent developments in photoacoustics in biomedicine, from basic principles to applications is provided, including the new imaging modalities, hybrid detection methods, photoac acoustic contrast agents and the photoacoustic Doppler effect.
Abstract: Photoacoustics has been broadly studied in biomedicine, for both human and small animal tissues. Photoacoustics uniquely combines the absorption contrast of light or radio frequency waves with ultrasound resolution. Moreover, it is non-ionizing and non-invasive, and is the fastest growing new biomedical method, with clinical applications on the way. This review provides a brief recap of recent developments in photoacoustics in biomedicine, from basic principles to applications. The emphasized areas include the new imaging modalities, hybrid detection methods, photoacoustic contrast agents and the photoacoustic Doppler effect, as well as translational research topics.
597 citations
Cites methods from "Two-dimensional photoacoustic imagi..."
...In comparison to the temporal frequency, the frequency-domain reconstruction can be implemented more efficiently by using k-space methods for a planar and a linear scanning geometry [72,86,87]....
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TL;DR: In this paper, the fundamentals of photoacoustics are first introduced and then, scanning photoacoustic microscopy and reconstruction-based photo-acoustic computed tomography (or photo acoustics computed tomograph) are covered.
Abstract: The field of photoacoustic tomography has experienced considerable growth in the past few years. Although several commercially available pure optical imaging modalities, including confocal microscopy, two-photon microscopy, and optical coherence tomography, have been highly successful, none of these technologies can provide penetration beyond ~1 mm into scattering biological tissues, because they are based on ballistic and quasi-ballistic photons. Heretofore, there has been a void in high-resolution optical imaging beyond this penetration limit. Photoacoustic tomography, which combines high ultrasonic resolution and strong optical contrast in a single modality, has broken through this limitation and filled this void. In this paper, the fundamentals of photoacoustics are first introduced. Then, scanning photoacoustic microscopy and reconstruction-based photoacoustic tomography (or photoacoustic computed tomography) are covered.
550 citations
TL;DR: It is considered that this type of instrument may provide a practicable alternative to piezoelectric-based photoacoustic systems for high-resolution structural and functional imaging of the skin microvasculature and other superficial structures.
Abstract: A multiwavelength backward-mode planar photoacoustic scanner for 3D imaging of soft tissues to depths of several millimeters with a spatial resolution in the tens to hundreds of micrometers range is described. The system comprises a tunable optical parametric oscillator laser system that provides nanosecond laser pulses between 600 and 1200 nm for generating the photoacoustic signals and an optical ultrasound mapping system based upon a Fabry-Perot polymer film sensor for detecting them. The system enables photoacoustic signals to be mapped in 2D over a 50 mm diameter aperture in steps of 10 microm with an optically defined element size of 64 microm. Two sensors were used, one with a 22 microm thick polymer film spacer and the other with a 38 mum thick spacer providing -3 dB acoustic bandwidths of 39 and 22 MHz, respectively. The measured noise equivalent pressure of the 38 microm sensor was 0.21 kPa over a 20 MHz measurement bandwidth. The instrument line-spread function (LSF) was measured as a function of position and the minimum lateral and vertical LSFs found to be 38 and 15 microm, respectively. To demonstrate the ability of the system to provide high-resolution 3D images, a range of absorbing objects were imaged. Among these was a blood vessel phantom that comprised a network of blood filled tubes of diameters ranging from 62 to 300 microm immersed in an optically scattering liquid. In addition, to demonstrate the applicability of the system to spectroscopic imaging, a phantom comprising tubes filled with dyes of different spectral characteristics was imaged at a range of wavelengths. It is considered that this type of instrument may provide a practicable alternative to piezoelectric-based photoacoustic systems for high-resolution structural and functional imaging of the skin microvasculature and other superficial structures.
531 citations
TL;DR: The prospects of photoacoustic tomography are envisaged in the following aspects:photoacoustic microscopy of optical absorption emerging as a mainstream technology, melanoma detection using photoac acoustic microscopy, and multiscale photoacoust imaging in vivo with common signal origins.
Abstract: Commercially available high-resolution three-dimensional optical imaging modalities—including confocal microscopy, two-photon microscopy, and optical coherence tomography—have fundamentally impacted biomedicine. Unfortunately, such tools cannot penetrate biological tissue deeper than the optical transport mean free path (∼1mm in the skin). Photoacoustictomography, which combines strong optical contrast and high ultrasonic resolution in a single modality, has broken through this fundamental depth limitation and achieved superdepth high-resolution optical imaging. In parallel, radio frequency-or microwave-induced thermoacoustic tomography is being actively developed to combine radio frequency or microwave contrast with ultrasonic resolution. In this Vision 20/20 article, the prospects of photoacoustictomography are envisaged in the following aspects: (1) photoacoustic microscopy of optical absorption emerging as a mainstream technology, (2) melanoma detection using photoacoustic microscopy, (3) photoacoustic endoscopy, (4) simultaneous functional and molecular photoacoustictomography, (5) photoacoustictomography of gene expression, (6) Doppler photoacoustictomography for flow measurement, (7) photoacoustictomography of metabolic rate of oxygen, (8) photoacoustic mapping of sentinel lymph nodes, (9) multiscale photoacoustic imagingin vivo with common signal origins, (10) simultaneous photoacoustic and thermoacoustic tomography of the breast, (11) photoacoustic and thermoacoustic tomography of the brain, and (12) low-background thermoacoustic molecular imaging.
513 citations
References
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TL;DR: The sensitivity of the technique is demonstrated by photoacoustic detection of single red blood cells upon a glass plate byPhotoacoustics as a tissue tomography technique for the detection of blood concentrations, e.g., angiogenesis around tumors.
Abstract: We applied photoacoustics as a tissue tomography technique for the detection of blood concentrations, e.g., angiogenesis around tumors. We imaged blood vessels in highly scattering samples, using 532-nm light, to depths of ,1 cm. The samples were real tissue (chicken breast) or 10% dilutions of Intralipid-10%. The blood flowed through nylon capillaries. Polyvinylidene difluoride (PVdF) piezoelectric detectors were used in a surface-scanning mode. We demonstrate the sensitivity of the technique by photoacoustic detection of single red blood cells upon a glass plate. Lateral resolution is limited by the detector diameter s200 mmd. The depth resolution is ,10 mm.
473 citations
TL;DR: An analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatialcompounding, frequency compounding, and parallel processing.
Abstract: The principles and techniques of real-time imaging with phased array ultrasound scanners are reviewed. Topics include 1) the geometric optics of beam steering and focusing with a linear array in the transmit and receive modes; 2) limitations on image data acquisition due to ultrasound propagation velocity; 3) optical diffraction theory for linear arrays including effects of amplitude grating lobes. Limitations on the image quality of phased array imaging systems are also discussed, including 1) nonideal response of array transducers; 2) target ambiguities caused by phase error grating lobes; 3) refraction errors; 4) delay line design. Finally, an analysis is presented of current techniques for improving ultrasound image quality using phased array methods including phase compensation, spatial compounding, frequency compounding, and parallel processing.
260 citations
TL;DR: A novel computational algorithm is presented, which, at least in principle, yields an exact reconstruction of the absorbing structures in three-dimensional space inside the tissue based on 2D pressure distributions captured outside at different delay times.
Abstract: In medical imaging different techniques have been developed to gain information from inside a tissue. Optoacoustics is a method to generate tomography pictures of tissue using Q-switched laser pulses. Due to thermal and pressure confinement, a short light pulse generates a pressure distribution inside tissue, which mirrors absorbing structures and can be measured outside the tissue. Using a temporal back-projection method, the pressure distribution measured on the tissue surface allows us to gain a tomography picture of the absorbing structures inside tissue. This study presents a novel computational algorithm, which, at least in principle, yields an exact reconstruction of the absorbing structures in three-dimensional space inside the tissue. The reconstruction is based on 2D pressure distributions captured outside at different delay times. The algorithm is tested in a simulation and back-projection of pressure transients of a small absorber and a single point source.
254 citations
TL;DR: The authors evaluated images obtained with a prototypic thermoacoustic computed tomographic (CT) scanner constructed for use at 434 MHz, a promising radio frequency for detecting breast cancer, and found the renal outline, parenchyma, and collecting system were clearly delineated on the thermoACoustic CT images.
Abstract: The authors evaluated images obtained with a prototypic thermoacoustic computed tomographic (CT) scanner constructed for use at 434 MHz, a promising radio frequency for detecting breast cancer. In one excised porcine kidney, acoustic energy emanating from the kidney was detected with transducers. The resultant electric signals were used to create a three-dimensional data set. Two-dimensional images reconstructed in multiple planes were compared with state-of-the-art T1- and T2-weighted magnetic resonance images. The renal outline, parenchyma, and collecting system were clearly delineated on the thermoacoustic CT images.
210 citations
TL;DR: The transduction mechanisms of a wideband (30 MHz) contact ultrasound sensor based upon the use of a thin polymer film acting as a Fabry-Perot interferometer have been investigated and a model of frequency response that incorporates the effect of an adhesive layer between the sensor film and backing material has been developed and validated.
Abstract: The transduction mechanisms of a wideband (30 MHz) contact ultrasound sensor based upon the use of a thin polymer film acting as a Fabry-Perot interferometer have been investigated. Polyethylene terepthalate (PET) sensing elements, illuminated by the free-space collimated output of a wavelength-tunable DBR laser diode, have been used to study the sensor transfer function, sensitivity, the effect of water absorption, and frequency response characteristics. Acoustic performance was evaluated by comparing the sensor output with that of a calibrated PVDF membrane hydrophone using laser-generated acoustic transients as a source of broadband ultrasound. An ultrasonic acoustic phase sensitivity of 0.1 rad/MPa, a linear operating range to 5 MPa, and a noise-equivalent-pressure of 20 kPa over a 25 MHz measurement bandwidth were obtained using a water-backed 50 /spl mu/m PET sensing film. A model of frequency response that incorporates the effect of an adhesive layer between the sensor film and backing material has been developed and validated for different sensing film thicknesses, backing configurations, and adhesive layer thicknesses.
192 citations