Research

Join us to become a key player for innovations in optical physics, imaging, inverse problems and image science with applications to medical, biological and materials science problems. Some important problems currently being addressed in our lab are summarized here :

Measuring phase changes in x-rays and their applications in quantitative imaging. With smaller wavelength in comparison to visible or IR regime, instrumentation and quantitative measurements become challenging for x-ray phase measurements. Theoretical, analytical and computational methods go hand-in-hand with instrumentations to address these problems.
Optical phase retrieval - light transport models, instrumentation and algorithms
Single photon detection- Significantly higher information can be achieved from each detected photon with smart photon counting detectors. How can this be effectively used in various areas of fundamental, applied physics, imaging and investigations in biology and medicine?
Science and mathematical models behind human perception of scenes, images and how we make signal detection in a complex background. Psychophysics and human perception is a complex process with significant applications in a wide range of areas such as machine learning, artificial intelligence, defense and security medical imaging device and algorithm optimization, microscopy and general image analysis.
Energy resolved x-ray detection and color x-ray imaging. Monte Carlo simulations and experimental feedback from current prototypes will advance the design for these next generation direct detection semiconducting detectors.
Among applications, we are working towards methods for early cancer detection, fast x-ray microscopes, fast and low dose x-ray micro computed tomography, lens free wide-area microscopes, building blocks for machine learning in imaging, mathematical models for human observers.
Extensive computational imaging platforms for virtual clinical trials.
Inverse problems and advanced tomographic image reconstruction.

Single Photon Counting Detectors: Advancements in single photon counting detectors can maximize the information obtained from each recorded photon. These direct detection semiconductor detectors for high energy photons are still in the early stages of development. Understanding the physics and engineering aspects of these advanced detectors involve Monte Carlo simulations, experimental analysis with early prototypes and analytical models. We have shown robust correction and calibration methods for these along with some innovative applications using these detectors. We work closely with industrial collaborators as well as Medipix collaboration (CERN, Geneva) for advancing these investigations.

Current X-ray Imaging in clinical settings utilize energy integrating detectors along with incoherent polychromatic X-ray tubes. Applications of photon counting spectral detectors include separating material maps of a complex object non-invasively and non-destructively. Advanced algorithms that enable accurate quantitation with fewer detected photons are being developed.

Spectral CT and material decomposition showing (3D rendered) image of quantitive maps of iodine, Gadolinium and calcium and water tubes in plastic cylinder. Several applications including drug delivery and contrast enhanced imaging in micro CT.

This novel system developed in-house uses photon counting x-ray detectors and advanced algorithms. Image shows 1cm diameter outer plastic cylinder with 3mm diameter tubes of contrast materials.

Phase Contrast X-Ray Imaging: X-ray phase changes can yield significantly higher image contrast than a simple absorption imaging. However extracting this phase information from these high frequency EM waves can be challenging. This often involves cumbersome instrumentation and algorithms.

Our group has developed a novel phase retrieval approach that is strengthened by the spectral data obtained from single photon counting detectors.

Light Transport Models for Optical and X-Ray Phase Retrieval: Transport of intensity models can be analytically derived for any phase enhanced geometry. These models allow an intuitive understanding of the detected intensity in an imaging setup with propagation distances, system geometry and the object phase and absorption properties. With these models one can then pursue an efficient phase retrieval algorithm. Effective measures to simplify these models are required for phase retrieval involving complex geometries.

Tomographic breast imaging - Acquisition and Reconstruction Strategies: Digital Breast Tomosynthesis (DBT) is a partial angle breast tomographic imaging and starting to enter the clinical setting. Dedicated breast CT (bCT) which is a fully 3D imaging of breast is also being investigated. Bothe DBT and bCT are aimed to reduce structural overlap that is present in conventional mammography while bCT has the added advantage of providing quantitative accuracy. Several groups are investigating optimal acquisition and reconstruction strategies for improving DBT and bCT image quality as measured by improved sensitivity and specificity for breast mass and micro calcification detection. One example is a variable-dose acquisition scheme in DBT that we are investigating which may combine the advantages of planar mammography and tomographic imaging. Other aspects of interest are the DBT acquisition arc and number of projection angles.

Besides novel acquisition strategies, another avenue that is being explored is improved tomographic reconstruction methods. Conventionally used linear image reconstruction methods like filtered back projection yields noisy image when a low dose acquisition protocol is used. We are investigating utility of statistical iterative reconstruction methods to mitigate this problem. These advanced image reconstruction methods allow modeling of imaging physics allowing for reduced noise images that have shown to improve detectability in tomographic imaging.

We use rigorous computer simulations and work closely with our clinical collaborators (Dr. Gary Whitman and Dr. Bill Geiser) are M. D. Anderson Cancer Center to investigate these aspects

Combining Light/Radiation and Acoustics: Radiological (x-ray/gamma), optical and ultrasound imaging methods employed for in-vivo imaging of cancers or other malignancies have limitations when used as stand alone modalities. Our group is interested in modulating the effect of each one of these or combining the advantages offered by these modalities for efficient and novel detection schemes.

EM Wave Propagation in Biological Tissue: We use a combination of experiments, Monte Carlo methods and analytical methods to understand the forward propagation of EM waves (ionizing and non-ionizing radiation) in various tissue structures. This approach helps us with proving a feedback mechanism based design of efficient imaging techniques.

Psychophysics, Image Perception and Pre-Clinical Optimization: Our goal of devising methodologies for reduced dose imaging makes it imperative that we understand the signal detection and perception science involved in radiology. Psychophysical methods using human observer studies are the gold standard for optimizing various acquisition and reconstruction methods. These can be extremely time consuming and expensive. A mathematical model that mimics the human vision and perception will speed up such optimization techniques. In a collaborative project with the Biomedical Engineering department and radiologists at M. D. Anderson, we are developing a robust and clinically relevant mathematical model observer for tomographic breast imaging.

Innovative aspects of this research include the utility of a “visual search” mathematical model observer and use of eye tracking equipment to understand human perception of complex images and signal detection in complex backgrounds.

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