1. Photoacoustic Imaging (Microscopy & Tomography)
5050 Anthony Wayne Dr. Detroit, MI 48202 313-577-3780 Directions
Photoacoustic imaging is a high-resolution method that is suited for deep tissue imaging. As opposed to optical imaging where the attenuation of the backscattered light reaching the detector limits the penetration depth, in photoacoustic imaging an acoustic detection scheme is used which dramatically increases the penetration depth. In OPIRA lab, we design varous photoacoustic imaging systems (both microscopy & tomography) for unmet clinical needs. A list of active projects in OPIRA is given in the followings.
Optical Coherence Tomography (OCT) delivers three-dimensional images of tissue microstructures. Although OCT imaging offers a promising high-resolution method, OCT images experience some artefacts that lead to misapprehension of tissue structures. In OPIRA we propose novel image enhancement algorithms for OCT images to address the abovementioned artifacts. We also develop new instrumentation based on optical coherence tomography to assist specialists in the diagnosis of skin and brain tumors.
3. Wavefront Engineering & Adaptive Optics
Light propagation and high resolution optical imaging in turbid media, such as biological tissues, experience scattering due to inhomogeneous distributions of refractive indexes of media. Control of light scattering is important for focusing the light or image through biological tissues, and it can improve the diagnosis and treatment of several human diseases. By spatially shaping the wave-front of the incident laser beam in tissue it can cause the scattered light to converge to a focus. Using spatial light modulators is one of the best methods to address the phase of light to change its direction of propagation. Due to stochastic property of scattered light, one of the best methods of controlling the light is using optimization algorithms.
2. Optical Coherence Tomography Instrumentaion and Image Anlaysis & Processing
In OPIRA, we study a broad range of activities that can roughly be divided into three major themes:
1. Photoacoustic Imaging (Microscopy & Tomography)
2. Optical Coherence Tomography Image Anlaysis & Processing
3. Wavefront Engineering & Adaptive Optics
1. Development of Low-Cost Photoacoustic Imaging Systems Using Very Low Energy Pulsed Laser Diodes:
With the growing application of photoacoustic imaging (PAI) in medical fields, there is a need to make them more compact, portable and affordable. Therefore, we designed very low-cost PAI systems by replacing the expensive and sophisticated laser with a very low energy laser diode. We implemented PA microscopy, both reflection and transmission modes, as well as PA computed tomography systems. Images obtained from tissue mimicking phantoms and biological samples determine the feasibility of using very low energy laser diode in these configurations
1. Transfontanelle Photoacoustic Imaging (TFPAI) in Neonates
TFPAI is a functional imaging technique to image preterm newborns brain. For intellectual property protection, the description of this project is not available online. However interested readers can contact us through for more information.
5. Modeling Skull’s Acoustic Attenuation and Dispersion on Photoacoustic Signal: Towards Neonatal Brain Imaging
It has been demonstrated that the presence of the skull severely affects the performance of photoacoustic (PA) imaging.We investigate the effects of acoustic heterogeneity induced by skull on the PA signals generated from single particles, with firstly developing a mathematical model for this phenomenon and then explore experimental validation of the results. The model takes into account the frequency dependent attenuation and dispersion effects occur with wave reflection, refraction and mode conversion at the skull surfaces. Numerical simulations based on the developed model are performed for calculating the propagation of photoacoustic waves through the skull. We anticipate that such quantification and modeling of the skull transmission effects will ultimately allow for aberration correction in transcranial PA human brain imaging.
2. Photoacoustic Signal Enhancement: towards Utilization of Very Low-Cost Laser Diodes in Photoacoustic Imaging
In practice, photoacoustic (PA) waves generated with cost-effective, low-energy laser diodes, are weak and almost buried in noise. Reconstruction of an artifact-free PA image from noisy measurements requires an effective denoising technique. Averaging is widely used to increase the Signal-to-Noise Ratio (SNR) of PA signals, however it is time-consuming and in the case of very low SNR signals, hundreds/thousands of data acquisition epochs are needed. We introduce an adaptive algorithm to improve the SNR of PA signals. Our results show that the proposed method increases the SNR of the PA signals more efficiently and with much fewer number of acquisitions, compared to common averaging techniques. Consequently, PA imaging is conducted considerably faster.
4. Development of a Skull Phantom for Photoacoustic Neonatal Imaging
There is a need for continued research into the diagnosis, prevention and cure of neonatal brain diseases and disorders. Non-invasive imaging techniques are being researched to facilitate detection, diagnosis, and treatment monitoring of brain diseases. Photoacoustic imaging (PAI) has successfully proved its capability in functional and structural brain imaging in small animals. Skull has been the major obstacle in translating PAI into the clinic. Infants with fontanels and thinner skull are the first translational application in human for PAI. Since the availability of neonatal skull samples is very low, an easy-to-make neonatal skull phantom can be used for simulation and optimization of the imaging system. Based on specified theoretical framework, experimental and simulation results, this study suggests a phantom made of polyurethane and titanium dioxide (TiO2) and proves its value as a replacement for neonatal skull in research. The methods used for this proof are validation of choice against the literature for Mie scattering, transmissivity, and acoustic attenuation. At the end, the photoacoustic characteristics of the final choice is presented.
6. A new Dictionary-based Image Reconstruction for PACT: Towards a Practical Neonatal Brain Imager
One of the major concerns in Photoacoustic Computed Tomography (PACT) is to obtain a high-quality image using a minimum number of ultrasound transducers/view angles. This issue is especially important when a cost-effective PACT is needed. However, analytical reconstruction algorithms such as back projection and time reversal whe a limited number of view angles used cause streak-type artifacts in the reconstructed image. Iterative sparsifying algorithms offer a solution via signal sparsification. We introduce a novel sparse dictionary to capture important features of the photoacoustic signal and eliminate the artifacts using a fewer number of transducers. Our dictionary is an optimum combination of Wavelet Transform (WT), Discrete Cosine Transform (DCT), and Total Variation (TV) transform. Based on the magnitude of desired features in the image, the transform domains of the signals multiplied by different weights in the combined dictionary. Edges, singular points, and homogenous texture are the most prominent diagnostically features in a medical image. In order to quantify such features, canny filter, Harris operator, and Gray-Level Co-occurrence Matrix (GLCM) are used, respectively.
3. A Numerical Study of Temperature Rise on Infant’s Head in Photoacoustic Computed Tomography
A numerical method has been developed to analyze the temperature rise on the scalp of an infant in a semi-dry coupling configuration of a Photoacoustic Computed Tomography (PACT) system used for infant brain imaging. The configuration consists of a cap with two layers: an outer layer that consists of optical fibers and transducers placed throughout the entire layer of the cap, and a thin elastomeric inner layer that has desirable acoustic properties. These two layers have water or ultrasound gel between them to comprise the semi-dry coupling configuration. The temperature rise is calculated from the Mimics, Geomagic, and COMSOL Multiphysics software programs for static and dynamic structural analysis when a hemispherical illumination scheme with optical fibers is used to show that the proposed illumination scheme is safe for infant brain imaging.
I. Photoacoustic Tomography of Neonatal Brain
In the application of photoacoustic human infant brain imaging, debubbled ultrasound gel or water is commonly used as a couplant for ultrasonic transducers due to their acoustic properties. The main challenge in using such a couplant is its discomfort for the patient. We explore the feasibility of a semi-dry coupling configuration to be used in photoacoustic computed tomography (PACT) systems. The coupling system includes an inflatable container consisting of a thin layer of Aqualene with ultrasound gel or water inside of it. Finite element method (FEM) is used for static and dynamic structural analysis of the proposed configuration to be used in PACT for infant brain imaging. The outcome of the analysis is an optimum thickness of Aqualene in order to meet the weight tolerance requirement with the least attenuation and best impedance match to recommend for an experimental setting.
II. Photoacoustic Imaging of Skin
III. Low-cost Photoacoustic Imaging Systems
IV. Hybrid Imaging Systems
1. Hybrid Co-planar Diffuse Optical Tomography and Photoacoustic Imaging:
Diffuse optical tomography (DOT) has successfully been demonstrated for functional imaging of biological tissues. We present the results of the combination of a high-resolution photoacoustic tomography (PAT) with DOT to improve the spatial resolution of DOT. PAT and DOT systems are co-planar, hence their images are inherently co-registered. The images obtained by PAT are used as a priori information reflecting light-absorbing structure of the tissue to improve the quantification accuracy during DOT image reconstruction. Our results show that the resolution of the reconstructed DOT images is significantly enhanced.
2. Hybrid Optical Coherence Tomography, Fluorescent imaging and Photoacoustic Microscopy:
Hybrid OCT/FI/PAM is a microscopy modality to assist oncologists in their office. For intellectual property protection, the description of this project is not available online. However interested readers can contact us through for more information.
1. Localization of Dermal Epidermal Junction in OCT Images of Skin
Identifying the location of the Dermal Epidermal Junction (DEJ) in skin images is essential in several clinical applications of dermatology such as epidermal thickness determination in healthy versus un-healthy skins, e.g., basal cell carcinoma (BCC). Optical coherence tomography (OCT) facilitates the visual detection of DEJ in-vivo. However, due to the granular texture of speckle and a low contrast between dermis and epidermis, a skin border detection method is required for DEJ localization. Current DEJ algorithms work well for skins with visible differentiable epidermal layer but not for the skins of different body sites. We develop a semi-automated DEJ localization algorithm based on graph theory for OCT images of skin. The proposed algorithm is performed in an interactive framework by a graphical representation of an attenuation coefficient map through a uniform-cost search method. For border thinning, a fuzzy-based nonlinear smoothing technique is used.
1. Development of Dynamic Focus OCT
Optical coherence tomography (OCT) is capable to image microstructures within translucid samples. We develop dynamic focus (DF) on time domain (TD) version of the OCT technology. DF means moving the confocal gate in synchronism with the depth scanning via the coherence gate. The DF-OCT set-up is implemented for imaging samples at 1300 nm.
4. Cluster-based Filtering Framework for Speckle Reduction in OCT Images
To date, a variety of filtering techniques have been introduced to reduce speckle in OCT images. However, further improvement is required to reduce edge smoothing and the deterioration of small structures in OCT images after despeckling. We develop a novel cluster-based speckle reduction framework (CSRF) which consists of a clustering method, followed by a despeckling method.
2. Quantitative Analysis of OCT Images
OCT images offer morphological information about microstructures within the tissue. Utilizing image analysis methods, some numerical information (optical properties) can be extracted from the image that are closely related to the cell structure and tissue architecture. An optical properties extraction (OPE) algorithm is developed based on enhanced Huygens–Fresnel light propagation theorem, to extract the scattering and absorption coefficients of a specific region in an OCT image. The aim is to quantitatively analyze the OCT images.
1. S.M.A.R.T. – PAI of Skin Melanoma
The gold standard for diagnosing melanoma, a deadly skin cancer, is the biopsy. However, this procedure can cause skin trauma and is not always reliable. Photoacoustic imaging (PAI) has a great potential to noninvasively image the skin by combining the high contrast of optical imaging with the depth potential of ultrasound imaging. Previous PAI studies on melanoma use melanin as an endogenous contrast agent. However, melanin is found in both benign nevi and melanoma. Thus, we have developed an exogenous contrast agent using an organic fluorescent dye conjugated to a melanoma-specific biomarker for better specificity and sensitivity. The fluorescent dye is an indocyanine based dye (IRDye800cw) that is nontoxic, is small enough to penetrate through tumor bulk, and can effectively be cleared from the body. The biomarker is a galectin-3 antibody that binds to galectin-3, a protein that has been shown to be significantly higher in primary cutaneous melanoma cells. We call this approach the Specific Melanoma Antigen Radiomics of Tumors with PhotoAcoustic Imaging (S.M.A.R.T. – PAI).
3. In vivo Textural Model for Human Skin based on Optical Coherence Tomograms
Currently, diagnosis of skin diseases is based primarily on visual pattern recognition skills and expertise of the physician observing the lesion. Even though dermatologists are trained to recognize patterns of morphology, it is still a subjective visual assessment. Tools for automated pattern recognition can provide objective information to support clinical decision-making. Noninvasive skin imaging techniques provide complementary information to the clinician. In recent years, optical coherence tomography has become a powerful skin imaging technique. According to specific functional needs, skin architecture varies across different parts of the body, as do the textural characteristics in OCT images. There is, therefore, a critical need to systematically analyze OCT images from different body sites, to identify their significant qualitative and quantitative differences. Sixty-three optical and textural features extracted from OCT images of healthy and diseased skin are analyzed and in conjunction with decision-theoretic approaches used to create computational models of the diseases. We demonstrate that these models provide objective information to the clinician to assist in the diagnosis of abnormalities of cutaneous microstructure, and hence, aid in the determination of treatment. Specifically, we demonstrate the performance of this methodology on differentiating basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) from healthy tissue.
2. Hand-held spatula-integrated OCT device for oncologic neurosurgery
We develop a novel imaging probe integrated with a retractor spatula that can be used for image-guidance of surgery. The probe is designed based on bundled full-field swept source OCT technology. The technology will be utilized for the assessment of resection margins in brain tumor removal procedure. For intellectual property protection, the description of this project is not available online. However interested readers can contact us through for more information.
I. Hardware / Instrumentation
II. Software / Image processing