The feasibility of air-coupled ultrasound transducers to detect laser-induced ultrasound from artificial blood vessels embedded in an optically scattering phantom is demonstrated. These air-coupled transducers allow new applications in biomedical photoacoustic imaging where contact with tissue is not preferred. One promising application of such transducers is the addition of photoacoustic imaging to the regular x-ray mammographic screening procedure.
A real-time photoacoustic imaging system was designed and built. This system is based on a commercially available
ultrasound imaging system. It can achieve a frame rate of 8 frames/sec. This system has been characterized in phantom
experiments. In addition, vasculature in the hand of a human volunteer was imaged.
A real-time photoacoustic imaging system is designed and built. This system is based on a commercially available ultrasound imaging system. It can achieve a frame rate of 8 frames/sec. Vasculature in the hand of a human volunteer is imaged, and the resulting photoacoustic image is combined with the ultrasound image. The real-time photo acoustic imaging system with a hybrid ultrasound probe is demonstrated by imaging the branching of subcutaneous blood vessels in the hand.
Photoacoustic imaging is used to obtain a range of three-dimensional images representing tumor neovascularization
over a 10-day period after subcutaneous inoculation of pancreatic tumor cells in a rat. The images are
reconstructed from data measured with a double-ring photoacoustic detector. The ultrasound data originates
from the optical absorption by hemoglobin of 14 ns laser pulses at a wavelength of 1064 nm. Three-dimensional
data is obtained by using two dimensional linear scanning. Scanning and motion artifacts are reduced using a
correction method. The data is used to visualize the development of the individual blood vessels around the
growing tumor, blood concentration changes inside the tumor and growth in depth of the neovascularized region.
The three-dimensional vasculature reconstruction is created using VTK, which enables us to create a composition
of the vasculature on day seven, eight and ten and to interactively measure tumor growth in the near future.
Photoacoustic imaging is a hybrid imaging modality that is based on the detection of acoustic waves generated
by absorption of pulsed light by tissue chromophores such as hemoglobin in blood. Serial photoacoustic imaging has
been performed over a 10-day period after subcutaneous inoculation of pancreatic tumor cells in a rat. The images were
obtained from ultrasound generated by absorption in hemoglobin of short laser pulses at a wavelength of 1064 nm. The
ultrasound signals were measured in reflection mode using a
double-ring photoacoustic detector. A correction algorithm
has been developed to correct for scanning and movement artifacts during the measurements. Three-dimensional data
visualize the development and quantify the extent of individual blood vessels around the growing tumor, blood
concentration changes inside the tumor and growth in depth of the neovascularized region.
Photoacoustic imaging is a hybrid imaging modality that is based on the detection of acoustic waves generated
by absorption of pulsed light by tissue chromophores such as hemoglobin in blood. We show that photoacoustic imaging
can be used to image blood concentrations in a port-wine stain.
We report results of a feasibility study regarding the question whether or not venous valves can be imaged using photoacoustics, and how they will appear in the images. First an in vitro study was made on tissue phantoms consisting of blood filled rubber tubes with discontinuities in the inner tube wall. We also have studied superficial veins on the ventral side of the wrist. For excitation, an Nd:YAG laser at 1064 nm was used. Detection of acoustic signals was performed with a PVdF sensor consisting of two concentric rings. Measurements were performed on valves which where first localized by palpation. The phantom studies showed that irregular structures of the tube walls could clearly be identified from the photoacoustic images. Furthermore, in a photoacoustic image of a vein at the dorsal side of the wrist, the presence of a valve could be identified from a region of increased signal intensity within the vessel lumen.
We present a laboratory version of a photoacoustic mammoscope, based on a parallel plate geometry. The instrument is built around a flat high-density ultrasound detector matrix. The light source is a Q-switched Nd:YAG laser with a pulse duration of 5 ns. To test the instrument, a novel photoacoustic phantom is developed using poly(vinyl alcohol) gel, prepared by a simple procedure that imparts optical scattering suggestive of breast tissue to it without the requirement for extraneous scattering particles. Tumor simulating poly(vinyl alcohol) gel spheres appropriately dyed at the time of preparation are characterized for optical absorption coefficients. These are then embedded in the phantom to serve as tumors with absorption contrasts ranging from 2 to 7, with respect to the background. Photoacoustic studies in transmission mode are performed, by acquiring the laser-induced ultrasound signals from regions of interest in the phantom. Image reconstruction is based on a delay-and-sum beamforming algorithm. The results of these studies provide an insight into the capabilities of the prototype. Various recommendations that will guide the evolving of our laboratory prototype into a clinical version are also discussed.
Photoacoustic imaging is demonstrated in imaging blood vessels of a chicken embryo. Using a weighted sum-and-delay beamforming algorithm we were able to reconstruct two- and three-dimensional images of these blood vessels.
In laser Doppler flowmetry (LDF) deep perfusion measurements can be realized by using a large separation between the fibers used for illumination and detection. In order to achieve a sufficient signal-to-noise ratio, the power of the laser light can be increased, but only to the limit indicated by the safety regulations. In this paper, pulsed laser Doppler flowmetry (pLDF) is presented as a manner to increase the SNR without exceeding the safety limits. The method is based on the principle that light is needed only when the signal is being sampled. The setup is presented, and we will show results that indicate that equivalent results are obtained for a pulsed and continuous wave setup (cwLDF), however with a much smaller tissue exposure. Furthermore, the limits encountered in realizing a pulsed system will be discussed.
A double-ring photoacoustic sensor to image and monitor blood content in tissue has been developed. This sensor has a very small opening angle. Using this sensor we are able to image artifical blood vessels, as well as vessels in a rabbit ear. Furthermore, the feasibility of <i>in vivo</i> imaging is demonstrated with a photoacoustic reconstruction of the joining of two palmar veins a few centimeter proximal to the wrist in a human arm.
To localize and monitor the blood content in tissue we developed very sensitive photoacoustical detectors. In these detectors a PVdF-layer has been used as piezo-electric material and also fibers for the illumination of the sample are integrated. The resolution is about 20 im in depth and about 50-100 im laterally. The wavelengths ofthe laser light were 532and 1064 nm. With these colors we can measure at different depths in tissue. We will report measurements on real tissue: vessels in chicken breast, in the human arm, and in test animals at various positions.
Using very sensitive photoacoustical detectors we localized and monitored the blood content in tissue. In these detectors a PVdF-layer has been used as piezo-electric material and also fibers for the illumination of the sample are integrated. The resolution is about 20micrometers in depth and about 50-100micrometers laterally. The wavelengths of the laser light were 532 and 1064 nm. With these colors we can measure at different depths in tissue. The measurements concerned blood perfusion in real tissue: vessels in chicken breast, in test animals at various positions and in the human arm.
Measurements have been carried out using a pulsed laser-Doppler setup. The main advantage of pulsing a laser-diode is that much higher peak powers can be used, allowing a larger source-detector separation, resulting in a larger penetration depth. The method enables e.g. monitoring of cerebral perfusion as well as monitoring perfusion through organs (e.g. kidney).
To localize and monitor the blood content in tissue we developed a very sensitive photo-acoustical detector. PVDF has been used as piezo-electric material. In this detector also fibers for the illumination of the sample are integrated. Resolution is about 20 (m in depth and about 50-100 m laterally). We use 532 nm light. We will show how photoacoustics can be used for measuring the thickness of tissue above bone. We will also report measurements on tissue phantoms: e.g. a vessel delta from the epigastric artery branching of a Wistar rat, filled with an artificial blood-resembling absorber. The measurements have been carried out on phantoms containing vessels at several depths. Signal processing was enhanced by Fourier processing of the data.
An experimental facility has been developed that allows for the determination of the scattering cross section and the scattering phase function of thin layers of undiluted blood. The layer is formed between to flat glass plates. By rotating one of the plates, a simple shear can be imposed onto the blood. Experiments have been performed with 633 nm light on layers with a thickness between 20 and 60 micrometer. It was shown that for shear rates in the range 150 - 500 s<SUP>-1</SUP>, the scattering coefficient has a constant value of 115 mm<SUP>-1</SUP>. Also, the scattering anisotropy for single scattering g ranges from 0.95 at lower shear rates, to 0.975 at higher shear rates. The value of g increases with the shear, both in a direction parallel to and perpendicular to the shear direction.
Our goal is the development of a photo-acoustic instrument for 3D imaging of the microvascular structure in tissue, in real time. A photo-acoustic multi-element detector has been designed, which measures in reflection mode. The light source is a pulsed laser with a wavelength of 532nm and the active piezo-material is PVdF. Using a disk detector we have achieved to reconstruction 3D images with a depth and lateral resolution of 10-20 micrometers and 200 micrometers respectively. With the new probe we expect to reduce the measuring time and to sped up the signal and image processing.
To localize and monitor the blood content in tissue we developed a very sensitive double-ring photo-acoustical detector. PvdF has been used as piezo-electric material. In this detector also a fiber for illumination of the sample is integrated. This detector has the advantage that it is very sensitive in the forward direction. A ratio of FWHM to depth of 1:70 can be obtained with this detector.
We developed Photoacoustic Tissue Scanning to tomografically image optically absorbing structures in tissue. With 532 nm light depths down to 6-9 mm were reached. As the samples we used capillaries with blood, human hairs or a variable dilution of Evans blue, embedded in real tissue (chicken breast) or a 10 % solution of Intralipid-10%. Small PVdF piezoelectric hydrophones were used for detection, in scanning mode for imaging purposes. The depth resolution is about 10 ?m, and the lateral resolution is limited by the diameter of the detector (200 ?m in our case).