SignificanceCollagen and lipid are important components of tumor microenvironments (TME) and participates in tumor development and invasion. It has been reported that collagen and lipid can be used as a hallmark to diagnosis and differentiate tumors.AimWe aim to introduce photoacoustic spectral analysis (PASA) method that can provide both the content and structure distribution of endogenous chromophores in biological tissues to characterize the tumor-related features for identifying different types of tumors.ApproachEx vivo human tissues with suspected squamous cell carcinoma (SCC), suspected basal cell carcinoma (BCC), and normal tissue were used in this study. The relative lipid and collagen contents in the TME were assessed based on the PASA parameters and compared with histology. Support vector machine (SVM), one of the simplest machine learning tools, was applied for automatic skin cancer type detection.ResultsThe PASA results showed that the lipid and collagen levels of the tumors were significantly lower than those of the normal tissue, and there was a statistical difference between SCC and BCC (p < 0.05), consistent with the histopathological results. The SVM-based categorization achieved diagnostic accuracies of 91.7% (normal), 93.3% (SCC), and 91.7% (BCC).ConclusionsWe verified the potential use of collagen and lipid in the TME as biomarkers of tumor diversity and achieved accurate tumor classification based on the collagen and lipid content using PASA. The proposed method provides a new way to diagnose tumors.
Transrectal ultrasound (TRUS) guided biopsy is the standard procedure for evaluating the presence of prostate cancer. TRUS, however, has limited sensitivity to prostate tumors, nor can it differentiate aggressive cancer from non-aggressive ones. The emerging photoacoustic (PA) imaging combined with TRUS offers a great promise to solve this overarching issue, especially when powered by tumor-targeting contrast agent. In this work, we studied the feasibility of PA imaging to cover the entire prostate by using light illumination via the urethral track. Experiment was conducted on whole human prostates ex vivo. The light source was an array of light emitting diodes (LED) which has many advantages compared to solid state laser. The LED array was placed in the urethra, delivering light with fluence within the ANSI safety limit. A PA and ultrasound (US) dual modality system acquired the images in the same way as in TRUS. The imaging target was a 1-mm tube filled with ICG solution, mimicking the situation of a prostate tumor labeled with ICG contrast agent. The imaging results demonstrated that PA imaging can detect the ICG-filled tube at any place in the prostate, with an imaging depth over 20 mm. This study validated that PA imaging, when performed in a transrectal manner and combined with transurethral light illumination, is capable of molecular level imaging of the entire prostate noninvasively. The high sensitivity offered by PA imaging in detecting aggressive prostate cancer may contribute to prostate cancer management, e.g., enabling more accurate guidance for needle biopsy.
Port-wine stain (PWS) is a discoloration of human skin caused by a vascular anomaly (i.e., capillary malformation in the skin). In the past years, several techniques have been developed for characterization and treatment evaluation of PWS. However, each of them has some limitations. Optical methods working in the ballistic regime, such as dermoscopy and VISIA, do not have sufficient penetration to cover the entire scale of PWS. High frequency ultrasound, although with better imaging depth, does not offer sufficient contrast to differentiate PWS and normal skin tissue. Therefore, current endpoint clinical assessment for PWS still relies on physicians’ subjective judgement. In this study, photoacoustic (PA) imaging utilizing light emitting diodes (LED) as the light source was adapted to the evaluation of PWS and response to photodynamic therapy (PDT). PA images as well as US images of the targeted skin area before and at different time points after the treatment were acquired. The imaging results from adults and children were also compared. The imaging findings demonstrate that the PWS levels of adult patients are significantly higher than children (p<0.01), which fits well with the knowledge that the vessel malefaction degree develops with patients’ age. The 2-month follow-up study on four children shows that the average PWS level reduced for 33.60%onstrat (p<0.01) as a result of 3-4 times of PDT treatment. This initial clinical trial on patients suggests PA imaging holds potential for quantitative assessment of PWS in clinical settings.
We have developed a safe, noninvasive imaging-guided localized antivascular method, namely photo-mediated ultrasound therapy (PUT), by applying synchronized laser and ultrasound pulses. Through our experimental and theoretical studies, we demonstrate that cavitation plays a key role in PUT. PUT promotes cavitation activity in blood vessels by concurrently applying ultrasound bursts and nanosecond laser pulses. The collapse of cavitation can induce damage to blood vessel endothelial cells, resulting in occlusion of microvessels. This study presents the effect of laser pulse energy, laser pulse length, ultrasound intensity, and synchronization time between laser and ultrasound. We found that, in order to produce controllable blood vessel occlusion, linear oscillation of cavitation (or non-inertial cavitation) might be the key, while strong collapse of cavitation (inertial cavitation) might induce bleeding. Under the guidance an optical coherence tomography (OCT) system, we utilized PUT to remove microvessels in the rabbit choroid. We were able to monitor cavitation activity in real-time in vivo during PUT treatment, and predict treatment outcome. Histology findings confirmed that fibrin clots were developed in the microvessels in the treated region, while no damage was found in the surrounding tissue.
Wet age-related macular degeneration (AMD) is a leading cause of vision loss in the United States. Choroidal neovascularization (CNV), the creation of new blood vessels in the choroid layer of the eye, plays a central role in the pathophysiology of wAMD. Despite advanced anti-VEGF therapy, 20% of patients become legally blind and other 30% suffer significant vision loss after 5 years. Given the significant burden imposed by wAMD on a growing aging population, there is an urgent need for developing new therapeutic techniques to remove microvessels induced by CNV. We developed a safe, noninvasive imaging-guided photo-mediated ultrasound therapy (PUT) technique as a localized antivascular method, and applied it to remove microvessels in the rabbit choroid. This technique promotes cavitation activity in blood vessels by concurrently applying ultrasound bursts and nanosecond laser pulses. The collapse of cavitation can induce damage to blood vessel endothelial cells, resulting in occlusion of microvessels. PUT takes advantages of the high native optical contrast among biological tissues, and has the unique capability to self-target microvessels without causing surrounding damages. Under the guidance of a fundus camera and an optical coherence tomography (OCT) system, our PUT system now has the capability to precisely target the treating area before the treatment procedure (through the fundus camera), and real-time intra-treatment cavitation monitor to evaluate the therapeutic effect (through the OCT system). Additionally, the safety of PUT technique is confirmed by histopathological studies.
Retinal and choroidal neovascularization play a pivotal role in the leading causes of blindness including macular degeneration and diabetic retinopathy (DR). Current therapy by focal laser photocoagulation can damage the normal surrounding cells, such as the photoreceptor inner and outer segments which are adjacent to the retinal pigment epithelium (RPE), due to the use of high laser energy and millisecond pulse duration. Therapies with pharmaceutical agents involve systemic administration of drugs, which can cause adverse effects and patients may become drug-resistant.
We have developed a noninvasive photo-mediated ultrasound therapy (PUT) technique as a localized antivascular method, and applied it to remove micro blood vessels in the retina. PUT takes advantage of the high native optical contrast among biological tissues, and has the unique capability to self-target microvessels without causing unwanted damages to the surrounding tissues. This technique promotes cavitation activity in blood vessels by synergistically applying nanosecond laser pulses and ultrasound bursts. Through the interaction between cavitation and blood vessel wall, blood clots in microvessels and vasoconstriction can be induced. As a result, microvessels can be occluded. In comparison with other techniques that involves cavitation, both laser and ultrasound energy needed in PUT is significantly lower, and hence improves the safety in therapy.
We developed a novel localized antivascular method, namely photo-mediated ultrasound therapy (PUT), by applying synchronized laser and ultrasound pulses. PUT relies on high optical contrast among biological tissues. Taking advantage of the high optical absorption of hemoglobin, PUT can selectively target microvessels without causing unwanted damages to the surrounding tissue. Moreover, PUT working at different optical wavelengths can selectively treat veins or arteries by utilizing the contrast in the optical spectra between deoxy- and oxy-hemoglobin. Through our experiments, we demonstrated that cavitation might have played a key role in PUT. The addition of a laser pulse to an existing ultrasound field can significantly improve the likelihood of inertial cavitation, which can induce microvessel damage through its mechanical effect. In comparison with conventional laser therapies, such as photothermolysis and photocoagulation, the laser energy level needed in PUT is significantly lower. When a nanosecond laser was used, our in vivo experiments showed that the needed laser fluence was in the range of 4 to 40 mJ/cm2.
Laser-induced thermotherapy (LITT), i.e. tissue destruction induced by a local increase of temperature by means of laser light energy transmission, has been frequently used for minimally invasive treatments of various diseases such as benign thyroid nodules and liver cancer. The emerging photoacoustic (PA) imaging, when integrated with ultrasound (US), could contribute to LITT procedure. PA can enable a good visualization of percutaneous apparatus deep inside tissue and, therefore, can offer accurate guidance of the optical fibers to the target tissue. Our initial experiment demonstrated that, by picking the strong photoacoustic signals generated at the tips of optical fibers as a needle, the trajectory and position of the fibers could be visualized clearly using a commercial available US unit. When working the conventional US Bscan mode, the fibers disappeared when the angle between the fibers and the probe surface was larger than 60 degree; while working on the new PA mode, the fibers could be visualized without any problem even when the angle between the fibers and the probe surface was larger than 75 degree. Moreover, with PA imaging function integrated, the optical fibers positioned into the target tissue, besides delivering optical energy for thermotherapy, can also be used to generate PA signals for on-line evaluation of LITT. Powered by our recently developed PA physio-chemical analysis, PA measurements from the tissue can provide a direct and accurate feedback of the tissue responses to laser ablation, including the changes in not only chemical compositions but also histological microstructures. The initial experiment on the rat liver model has demonstrated the excellent sensitivity of PA imaging to the changes in tissue temperature rise and tissue status (from native to coagulated) when the tissue is treated in vivo with LITT.
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