We have demonstrated a novel microbubbles methylene blue solution, called to “MB2” solution for a dual modality contrast. We have photoacoustically and ultrasonically imaged and quantified aqueous solutions of MB2 by varying the concentration of either microbubbles or methylene blue to investigate the dual modal imaging capability. Interestingly, as the microbubbles concentration increased with the constant methylene blue concentration, photoacoustic (PA) signal was greatly attenuated in the MB2 solution. Conversely, when methylene blue concentration increased with the fixed microbubbles concentration, no interference was observed in ultrasound (US) signals. To further confirm our findings, we switched the PA and ultrasound (US) signals using conventional ultrasound. We compared the PA and US signals of the MB2 solution before and after sonication. The PA amplitude increased 2.5 times. Conversely, the US signals were initially strong, but decreased 2.5 times following sonication. Moreover, we used a clinically modified PA/US imaging system to disrupt the microbubbles in MB2 and recover the PA signals.
Ultrasound and photoacoustic imaging are highly complementary modalities since both use ultrasonic detection for operation. Increasingly, photoacoustic and ultrasound have been integrated in terms of hardware instrumentation. To generate a broadly accessible dual-modality contrast agent, we generated microbubbles (a standard ultrasound contrast agent) in a solution of methylene blue (a standard photoacoustic dye). This MB 2 solution was formed effectively and was optimized as a dual-modality contrast solution. As microbubble concentration increased (with methylene blue concentration constant), photoacoustic signal was attenuated in the MB 2 solution. When methylene blue concentration increased (with microbubble concentration held constant), no ultrasonic interference was observed. Using an MB 2 solution that strongly attenuated all photoacoustic signal, high powered ultrasound could be used to burst the microbubbles and dramatically enhance photoacoustic contrast (>800 -fold increase), providing a new method for spatiotemporal control of photoacoustic signal generation.
We demonstrate that changes in the degree of polarization (DOP) depend on changes in the scattering coefficient, and they can be quantified by using a polarization-sensitive optical coherence tomography (PS-OCT) system. We test our hypothesis using liquid and solid phantoms made from Intralipid suspensions and gelatin, respectively. We also quantify the DOP changes with depth caused by changes in the concentration of scatterers in the liquid and solid phantoms. It is clearly shown that the DOP change has a linear relationship with the scattering change. In our previous study, we showed that the axial slope of the DOP is different between normal and pathologic cervical tissues. Our results demonstrate that the quantification of the axial DOP slope can be used for the systematic diagnosis of certain tissue pathology.
We use polarization-sensitive optical coherence tomography (PS-OCT) to monitor the wound healing process in vitro and in vivo, which are affected by various drugs. Five rabbit subjects are used for in vitro studies and another five are used for in vivo studies. The in vitro studies are conducted to compare the PS-OCT images with histopathology. For each subject, three biopsy lesions are created on each ear: one site is not treated (control); the second site is treated with sphingosylphosphorylcholine, which is expected to promote healing; and the last is administered with tetraacetylphytosphingosine, which negatively affects the healing process. Each site is examined with a PS-OCT system at 1, 4, 7, 10, and 14- days after wound generation. The variations of phase retardation values caused by the collagen morphology changes on wound sites are quantified for all cases. Our results suggest that PS-OCT may be a useful tool for visualization of collagen fiber regeneration and for quantification of various drug effects during the wound healing process.
KEYWORDS: Melanoma, Skin, Photoacoustic spectroscopy, 3D image processing, Absorption, In vivo imaging, Tissue optics, Visible radiation, Near infrared, 3D photoacoustic microscopy
Dual-wavelength reflection-mode photoacoustic microscopy is used to noninvasively obtain three-dimensional (3-D) images of subcutaneous melanomas and their surrounding vasculature in nude mice in vivo. The absorption coefficients of blood and melanin-pigmented melanomas vary greatly relative to each other at these two optical wavelengths (764 and 584 nm). Using high-resolution and high-contrast photoacoustic imaging in vivo with a near-infrared (764-nm) light source, the 3-D melanin distribution inside the skin is imaged, and the maximum thickness of the melanoma (~0.5 mm) is measured. The vascular system surrounding the melanoma is also imaged with visible light (584 nm) and the tumor-feeding vessels found. This technique can potentially be used for melanoma diagnosis, prognosis, and treatment planning.
We present a study of the functional photoacoustic imaging of tumor hypoxia in mice in vivo. Based on spectroscopic photoacoustic tomography that detects the optical absorption of oxy- and deoxy-hemoglobins, the blood oxygen saturation and the vascularization of brain tumors were visualized. U87 glioblastoma tumor cells were inoculated intracranially at a 3-mm depth from the surface of the nude mouse head seven days before the experiment. Increased blood content and hypoxia inside the tumor vasculature were detected through the intact skin and skull. This technique will be useful for future studies on tumor metabolic activities in the brain and hypoxia-related therapeutic resistance.
Functional photoacoustic microscopy is a hybrid imaging technique that detects laser induced photoacoustic waves to image biological tissues in three dimensions. Its imaging depth exceeds the fundamental depth limit of the existing high resolution optical imaging modalities while maintaining a comparable ratio of imaging depth to axial resolution. The amplitude of photoacoutic waves is related to tissue's optical absorption and, therefore, functional imaging can be achieved by acquiring spectroscopic information. We demonstrate here the capabilities of functional photoacoustic microscopy by volumetric imaging a skin melanoma tumor and functional imaging of hemoglobin oxygen saturation in single vessels in vivo.
KEYWORDS: Tumors, Molecular imaging, Spectroscopy, Brain, Imaging spectroscopy, Acquisition tracking and pointing, In vivo imaging, Photoacoustic spectroscopy, Neuroimaging, Near infrared
Molecular imaging is a newly emerging field in which the modern tools of molecular and cell biology have been
married to state-of-the-art technologies for noninvasive imaging. The study of molecular imaging will lead to better
methods for understanding biological processes as well as diagnosing and managing disease. Here we present
noninvasive in vivo spectroscopic photoacoustic tomography (PAT)-based molecular imaging of αvβ3 integrin in a
nude mouse U87 brain tumor. PAT combines high optical absorption contrast and high ultrasonic resolution by
employing short laser pulses to generate acoustic waves in biological tissues through thermoelastic expansion.
Spectroscopic PAT-based molecular imaging offers the separation of the contributions from different absorbers based
on the differences in optical absorption spectra among those absorbers. In our case, in the near infrared (NIR) range,
oxy-heamoglobin (O2Hb), deoxy-heamoglobin (HHb) and the injected αvβ3-targeted peptide-ICG conjugated NIR
fluorescent contrast agent are the three main absorbers. Therefore, with the excitation by multiple wavelength laser
pulses, spectroscopic PAT-based molecular imaging not only provides the level of the contrast agent accumulation in
the U87 glioblastoma tumor, which is related to the metabolism and angiogenesis of the tumor, but also offers the
information on tumor angiogenesis and tumor hypoxia.
In this study, we demonstrate the potential of photoacoustic tomography for the study of traumatic brain injury (TBI) in rats in vivo. Based on spectroscopic photoacoustic tomography that can detect the absorption rates of oxy- and deoxy-hemoglobins, the blood oxygen saturation and total blood volume in TBI rat brains were visualized. Reproducible cerebral trauma was induced using a fluid percussion TBI device. The time courses of the hemodynamic response following the trauma initiation were imaged with multi-wavelength photoacoustic tomography with bandwidth-limited spatial resolution through the intact skin and skull. In the pilot set of experiments, trauma induced hematomas and blood oxygen saturation level changes were detected, a finding consistent with the known physiological responses to TBI. This new imaging method will be useful for future studies on TBI-related metabolic activities and the effects of therapeutic agents.
KEYWORDS: Tumors, Luminescence, Acquisition tracking and pointing, In vivo imaging, Brain, Photoacoustic tomography, Neuroimaging, Near infrared, Head, Signal detection
We present a dual modality imaging technique by combining photoacoustic tomography (PAT) and near-infrared (NIR) fluorescence imaging for the study of animal model tumors. PAT provides high-resolution structural images of tumor angiogenesis, and fluorescence imaging offers high sensitivity to molecular probes for tumor detection. Coregistration of the PAT and fluorescence images was performed on nude mice with M21 human melanoma cell lines with αvβ3 integrin expression. An integrin αvβ3-targeted peptide-ICG conjugated NIR fluorescent contrast agent was used as the molecular probe for tumor detection. PAT was employed to noninvasively image the brain structures and the angiogenesis associated with tumors in nude mice. Coregistration of the PAT and fluorescence images was used in this study to visualize tumor location, angiogenesis, and brain structure simultaneously.
We present a new computational algorithm for complex frequency domain optical coherence tomography (FD-OCT) that can effectively suppress artifacts, which are caused by uncertainty in phase shift due to errors in reference phases. The algorithm treats the phase shifting values as additional unknowns and we can determine their exact values by analyzing interference fringes using numerical least square technique. A series of simulation and experiments prove that this algorithm can effectively remove strong mirror image artifacts because it is unaffected by random phase fluctuation.
We use polarization sensitive optical coherence tomography (PS-OCT) to monitor wound healing processes in-vitro and in-vivo, which are affected by various drugs. Five rabbit subjects are used for the in-vitro studies and another five are used for in-vivo studies. The in-vitro studies are conducted to compare the PS-OCT images with histopathology. For each subject, three biopsy lesions are created on each ear: one site is not treated (control), the second site is treated with sphingosyl phosphoryl choline (SPC), which is known to promote healing, and the last is administered with tetra acetyl phytosphingo sine (TAPS), which negatively affects the healing process. Each site is examined with a PS-OCT system and conventional histopathology at 1-, 4-, 7-, 10-, and 14-days after wound generation. The phase retardation values are quantified for all cases and our results suggest that PS-OCT may be a useful tool for visualization of collagen fiber regeneration during the healing process; therefore, various drug effects can be noninvasively monitored.
We measure the skin wrinkle topology by means of low coherence interferometry (LCI), which forms the basis of the optical coherence tomography (OCT). The skin topology obtained using LCI and corresponding 2-D fast Fourier transform allow quantification of skin wrinkles. It took approximately 2 minutes to obtain 2.1 mm x 2.1 mm topological image with 4 um and 16 um resolutions in axial and transverse directions, respectively. Measurement examples show the particular case of skin contour change after-wrinkle cosmeceutical treatments and atopic dermatitis
The method of scattering media probing with the use of low-coherent light source with the controllable width of emission spectrum is considered. The contrast of partially coherent speckles is suggested as the diagnostical parameter. The additional polarization discrimination of detected speckles gives the possibility to select the components of scattered field which propagate in probed medium at different distances. Experimental results obtained for weakly ordered systems characterized by non-diffuse scattering regimes are presented.
We tried to probe photon path statistics by analyzing the change of speckle contrast with different coherence length of source. The speckle contrast is strong function of both photon path statistics inside scattering media and coherence function of a source. By introducing explicit formula for speckle contrast, we can relate photon path statistics with measured speckle contrast and coherence of source in reverse manner. To realize this idea, we formulated this relationship and performed several MC simulations and basic experiments for various scattering media. Although the present result is very rough, it shows some possibility of using this method to find photon propagation statistics inside turbid media such as tissues and thin polymer film.
One problem with moire topography for 3D surface metrology is the so-called 2(pi) -ambiguity limiting the maximum step height difference between two neighboring samples points to be less than half the equivalent wavelength of moire fringes. To cope with the ambiguity problem, a special scheme of scanning moire technique is proposed by resorting to the frequency domain fringe analysis that is in fact originated from white light scanning interferometry. This new more principle of 3D measurement allows determining the absolute height of the surface without information on absolute fringe orders so that largely stepped surfaces are measured with a great improvement in accuracy.
Adopting phase-shifting technique in moire topography provides many advantages in measuring complex surface profiles with varying reflectance. However, still the so- called 2(pi) -ambiguity problem remains, which limits the maximum measurable step height difference between two neighboring sample points to be less than half the equivalent wavelength of moire fringes. To cope with the problem in this investigation, a two-wavelength scheme of projection moire topography is proposed along with necessary hardware design considerations. Test results prove that the proposed scheme is capable of finding absolute fringe orders automatically, so that the 2(pi) -ambiguity problem can be effectively overcome so as to treat large step discontinuities in measured surfaces.
We present a method of projection moire specially devised for the three-dimensional inspection of printed circuit boards. This method incorporates phase-shifting technique in analyzing moire fringes so as to achieve a fine resolution of 1 micron in height measurement. Further a synchronous grating translation scheme enhances the lateral measuring resolution by inherently removing the original pattern of the reference grating in resulting moire fringes. Finally we discuss the advantages of the proposed method using several measurement results performed on the various types of solder paste silk-screened on printed circuit boards.
An industrial application of phase-shifting shadow moire interferometry for automatic 3D inspection of fine objects is presented. A line grating is used to generate shadow type moire fringes whose relative phases are readily determined by implementing the principle of phase shifting so that the surface height of the object can be measured. A special phase-measuring algorithm, named the A-bucket algorithm, is used which can precisely computes the relative phases even though there exists a significant level of errors in phase shifting due to miscalibration and external vibration. Finally, several experimental cases are discussed to demonstrate that a measuring accuracy in the order of 0.001 mm can practically be achieved.
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