Publications by Type: Conference Paper

2013
L. Mensah, S. Mallidi, I. Massodi, S. Anbil, Z. Mai, and T. Hasan, “Environmental effects on molecular biomarkers expression in pancreatic and brain cancer,” in Proc. SPIE, 2013, vol. 8568, pp. 856803-856803-8. Publisher's VersionAbstract

A complete understanding of the biological mechanisms regulating devastating disease such as cancer remains elusive. Pancreatic and brain cancers are primary among the cancer types with poor prognosis. Molecular biomarkers have emerged as group of proteins that are preferentially overexpressed in cancers and with a key role in driving disease progression and resistance to chemotherapy. The epidermal growth factor receptor (EGFR), a cell proliferative biomarker is particularly highly expressed in most cancers including brain and pancreatic cancers. The ability of EGFR to sustain prolong cell proliferation is augmented by biomarkers such as Bax, Bcl-XL and Bcl-2, proteins regulating the apoptotic process. To better understand the role and effect of the microenvironment on these biomarkers in pancreatic cancer (PaCa); we analysed two pancreatic tumor lines (AsPc-1 and MiaPaCa-2) in 2D, 3D in-vitro cultures and in orthotopic tumors at different growth stages. We also investigated in patient derived glioblastoma (GBM) tumor cultures, the ability to utilize the EGFR expression to specifically deliver photosensitizer to the cells for photodynamic therapy. Overall, our results suggest that (1) microenvironment changes affect biomarker expression; thereby it is critical to understand these effects prior to designing combination therapies and (2) EGFR expression in tumor cells indeed could serve as a reliable and a robust biomarker that could be used to design targeted and image-guided photodynamic therapy.

S. Mallidi, H. - C. Huang, J. Liu, Z. Mai, and T. Hasan, “Towards image-guided photodynamic therapy of Glioblastoma,” in Proc. SPIE, 2013, vol. 8568, pp. 85681C-85681C-7. Publisher's VersionAbstract

Glioblastoma (GBM) is an aggressive cancer with dismal survival rates and few new treatment options. Fluorescence guided resection of GBM followed by photodynamic therapy (PDT) has shown promise in several chemo- or radiotherapy non-responsive GBM treatments clinically. PDT is an emerging light and photosensitizer (PS) mediated cytotoxic method. However, as with other therapeutic modalities, the outcomes are variable largely due to the nonpersonalization of dose parameters. The variability can be attributed to the differences in heterogeneous photosensitizer accumulation in tumors. Building upon our previous findings on utilizing PS fluorescence for designing tumor-specific PDT dose, we explore the use of photoacoustic imaging, a technique that provides contrast based on the tissue optical absorption properties, to obtain 3D information on the tumoral photosensitizer accumulation. The findings of this study will form the basis for customized photodynamic therapy for glioblastoma and have the potential to serve as a platform for treatment of other cancers.

2010
M. Qu, et al., “Combined photoacoustic and magneto-motive ultrasound imaging,” in Proc. SPIE, 2010, vol. 7564, pp. 756433-756433-7. Publisher's VersionAbstract

Ultrasound imaging can provide excellent resolution at reasonable depths while retaining the advantages of being nonionizing, cost-effective and portable. However, the contrast in ultrasound imaging is limited, and various ultrasoundbased techniques such as photoacoustic (PA) and magneto-motive ultrasound (MMUS) imaging have been developed to augment ultrasound imaging. Photoacoustic imaging enhances imaging contrast by visualizing the optical absorption of either tissue or injected contrast agents (e.g., gold or silver nanoparticles). MMUS imaging enhances the sensitivity and specificity of ultrasound based on the detection of magnetic nanoparticles perturbed by an external magnetic field. This paper presents integrated magneto-photo-acoustic (MPA) imaging - a fusion of complementary ultrasound-based imaging techniques. To demonstrate the feasibility of MPA imaging, porcine ex-vivo tissue experiments were performed using a dual contrast (magnetic/plasmonic) agent. Spatially co-registered and temporally consecutive ultrasound, photoacoustic, and magneto-motive ultrasound images of the same cross-section of tissue were obtained. Our ex-vivo results indicate that magneto-photo-acoustic imaging can be used to detect magnetic/plasmonic nanoparticles with high resolution, sensitivity and contrast. Therefore, our study suggests that magneto-photo-acoustic images can identify the morphological properties, molecular information and complementary functional information of the tissue.

2009
S. Y. Nam, S. Mallidi, G. Zhang, L. J. Suggs, and S. Emelianov, “Ultrasound and photoacoustic imaging to monitor vascular growth in tissue engineered constructs,” in Proc. SPIE, 2009, vol. 7179, pp. 71790G-71790G-7. Publisher's VersionAbstract

Quantitative and qualitative monitoring of neovascular growth is required in many vascular tissue engineering applications. For example, the contribution of progenitor cells in growing microvasculature has been demonstrated; however, the process of vascularization from progenitor cells is not well understood. Therefore, there is a need for an imaging technique that is consistent, easy to use, and can quantitatively assess the dynamics of vascular growth or regression in a three-dimensional environment. In this study, we evaluate the ability of combined ultrasound and photoacoustic imaging to assess the dynamics of vascular growth. The experiments were performed using hydrogels that spontaneously promote tube formation from implanted mesenchymal stem cells (MSCs). Specifically, PEGylated fibrin gels, supporting the development of capillary growth were implanted in a Lewis rat. After one week, the rat was euthanized and the gel implants were excised and positioned in water cuvettes for imaging. Simultaneous ultrasound and photoacoustic images were obtained using single-element, focused ultrasound transducers interfaced with a nanosecond pulsed laser source. To image samples, ultrasound transducers operating at either 25 MHz or 48 MHz and interfaced with laser sources operating at either 532 nm or within 680-800 nm wavelengths were used. The 3-D ultrasound and photoacoustic images were acquired by mechanically scanning the transducer over the region of interest and capturing spatially co-registered and temporally consecutive photoacoustic transients and ultrasound pulse-echo signals. The ultrasound and photoacoustic images agree well with the overall anatomy and vascular structure in the gel samples. The results suggest that the photoacoustic and ultrasound imaging could be used to sequentially monitor the growth of neovasculature in-vivo.

S. Mallidi, et al., “Ultrasound-based imaging of nanoparticles: from molecular and cellular imaging to therapy guidance,” in IEEE Ultrasonics Symposium, 2009, pp. 27-36. Publisher's VersionAbstract

The effectiveness of an imaging technique is often based on the ability to image quantitatively both morphological and physiological functions of the tissue. Here we present several ultrasound-based imaging techniques capable of visualizing both structural and functional properties of living tissue. Each imaging system utilizes custom-made, targeted nanoparticles developed to probe specific molecular events. Therefore, images of these nanoparticles display molecular processes in the body. Furthermore, the developed nanoparticle contrast agents can also be used for image-guided molecular therapy. For each imaging system, the basic physics and principles behind each approach are described. Experimental aspects of each imaging system including fabrication of integrated imaging probes and associated imaging hardware, and design of targeted contrast agents are discussed. Finally, biomedical and clinical applications of the developed imaging approaches ranging from microscopic to macroscopic imaging of cardiovascular diseases, cancer detection, diagnosis, therapy and therapy monitoring are demonstrated and discussed.

2008
S. Mallidi, E. Yantsen, T. Larson, K. Sokolov, and S. Emelianov, “Molecular specific photoacoustic imaging with plasmonic nanosensors,” in Proc. SPIE, 2008, vol. 6856, pp. 685616-685616-7. Publisher's VersionAbstract

Gold nanoparticles functionalized with anti-EGFR antibodies undergo molecular specific aggregation on the cellular membrane and later within the cell that leads to a red shift in the plasmon resonance frequency of the gold nanoparticles. Capitalizing on this effect, we previously demonstrated on tissue phantoms that highly sensitive and selective detection of cancer cells can be achieved using the combination of photoacoustic imaging and molecular specific gold nanoparticles. To further evaluate the efficacy of molecular specific photoacoustic imaging technique in detecting deeply situated tumors, small animal experiments were performed. In this study, two gelatin solutions mixed with cells labeled with gold nanoparticles and cells mixed with polyethylene glycol-thiol (mPEG-SH) coated gold nanoparticles were injected in a mouse abdomen ex-vivo. The photoacoustic and ultrasound images from the same crosssection of the region before and after the injections were obtained using a 25 MHz single element ultrasound transducer interfaced with pulsed laser system. The results of our study suggest that the molecular specific photoacoustic imaging with plasmonic nanosensors could be used to detect deeply embedded tumors.

2007
S. Sethuraman, et al., “Intravascular photoacoustic imaging of atherosclerotic plaques: ex-vivo study using a rabbit model of atherosclerosis,” in Proc. SPIE, 2007, vol. 6437, pp. 643729-643729-9. Publisher's VersionAbstract

Diagnosis and treatment of atherosclerosis necessitates the detection and differentiation of rupture prone plaques. In principle, intravascular photoacoustic (IVPA) imaging has the ability to simultaneously visualize the structure and composition of atherosclerotic plaques by utilizing the difference in optical absorption. Extensive studies are required to validate the utility of IVPA imaging in detecting vulnerable plaques and address issues associated with the clinical implementation of the technique. In this work, we performed ex vivo imaging studies using a rabbit model of atherosclerosis. The intravascular photoacoustic (IVPA) and ultrasound (IVUS) images of the normal aorta and aorta with plaque were obtained and compared with histological slices of the tissue. The results indicate that IVPA imaging is capable of detecting plaques and showed potential in determining the composition. Furthermore, we initially addressed several aspects of clinical implementation of the IVPA imaging. Specifically, the configuration of combined IVPA and IVUS catheter was investigated and the effect of the optical absorption of the luminal blood on the IVPA image quality was evaluated. Overall, this study suggests that IVPA imaging can become a unique and important clinical tool.

S. Mallidi, A. B. Karpiouk, S. R. Aglyamov, S. Sethuraman, and S. Y. Emelianov, “Measurement of blood perfusion using photoacoustic, ultrasound, and strain imaging,” in Proc. SPIE, 2007, vol. 6437, pp. 643707-643707-9. Publisher's VersionAbstract

In many clinical and research applications including cancer diagnosis, tumor response to therapy, reconstructive surgery, monitoring of transplanted tissues and organs, and quantitative evaluation of angiogenesis, sequential and quantitative assessment of microcirculation in tissue is required. In this paper we present an imaging technique capable of spatial and temporal measurements of blood perfusion through microcirculation. To demonstrate the developed imaging technique, studies were conducted using phantoms with modeled small blood vessels of various diameters positioned at different depths. A change in the magnitude of the photoacoustic signal was observed during vessel constriction and subsequent displacement of optically absorbing liquid present in the vessels. The results of the study suggest that photoacoustic, ultrasound and strain imaging could be used to sequentially monitor and qualitatively assess blood perfusion through microcirculation.

S. Park, S. Mallidi, A. B. Karpiouk, S. Aglyamov, and S. Y. Emelianov, “Photoacoustic imaging using array transducer,” in Proc. SPIE, 2007, vol. 6437, pp. 643714-643714-7. Publisher's VersionAbstract

To perform ultrasound imaging using an array transducer, a focused ultrasound beam is transmitted in a particular direction within the tissue and the received backscattered ultrasound wave is then dynamically focused at every position along the beam. The ultrasound beam is scanned over the desired region to form an image. The photoacoustic imaging, however, is distinct from conventional ultrasound imaging. In photoacoustic imaging the acoustic transients are generated simultaneously in the entire volume of the irradiated tissue - no transmit focusing is possible due to light scattering in the tissue. The photoacoustic waves are then recorded on every element of the ultrasound transducer array at once and processed to form an image. Therefore, compared to ultrasound imaging, photoacoustic imaging can utilize dynamic receive focusing only. In this paper, we describe the image formation algorithms of the array-based photoacoustic and ultrasound imaging system and present methods to improve the quality of photoacoustic images. To evaluate the performance of photoacoustic imaging using an array transducer, numerical simulations and phantom experiments were performed. First, to evaluate spatial resolution, a point source was imaged using a combined ultrasound and photoacoustic imaging system. Next, image quality was assessed by imaging tissue imaging phantoms containing a circular inclusion. Finally, the photoacoustic and ultrasound images from the combined imaging system were analyzed.

M. Mehrmohammadi, et al., “Imaging of Iron Oxide Nanoparticles Using Magneto-Motive Ultrasound,” in Ultrasonics Symposium, 2007. IEEEUltrasonics Symposium, 2007. IEEE, 2007, vol. 8B-2, pp. 652-655.Abstract

Due to its excellent spatial resolution, fast and reliable performance, cost and wide availability, ultrasound should be considered the imaging modality of choice for many applications including molecular imaging. However, ultrasound imaging cannot image molecular content of tissue due to trade-off between spatial resolution and penetration depth. Consequently, contrast agents have been developed both to enhance the contrast of ultrasound images and to make the images molecularly specific. Most ultrasound contrast agents, however, are micrometer sized and may not be applicable to wide range of pathology-specific cellular and molecular imaging. We have developed an imaging technique - magneto-motive ultrasound (MMUS) imaging, capable of imaging magnetic nanoparticles subjected to time-varying magnetic field. The result of our studies indicate that magnetically excited nanoparticles can be used as contrast agents in magneto-motive ultrasound imaging thus expanding the role of ultrasound imaging to cellular scales and molecular sensitivity. View full abstract

2006
S. Mallidi, S. R. Aglyamov, A. B. Karpiouk, S. Park, and S. Y. Emelianov, “Functional and morphological ultrasonic biomicroscopy for tissue engineers,” in Proc. SPIE, 2006, vol. 6147, pp. 61470Y-61470Y-7. Publisher's VersionAbstract

Tissue engineering is an interdisciplinary field that combines various aspects of engineering and life sciences and aims to develop biological substitutes to restore, repair or maintain tissue function. Currently, the ability to have quantitative functional assays of engineered tissues is limited to existing invasive methods like biopsy. Hence, an imaging tool for non-invasive and simultaneous evaluation of the anatomical and functional properties of the engineered tissue is needed. In this paper we present an advanced in-vivo imaging technology - ultrasound biomicroscopy combined with complementary photoacoustic and elasticity imaging techniques, capable of accurate visualization of both structural and functional changes in engineered tissues, sequential monitoring of tissue adaptation and/or regeneration, and possible assistance of drug delivery and treatment planning. The combined imaging at microscopic resolution was evaluated on tissue mimicking phantoms imaged with 25 MHz single element focused transducer. The results of our study demonstrate that the ultrasonic, photoacoustic and elasticity images synergistically complement each other in detecting features otherwise imperceptible using the individual techniques. Finally, we illustrate the feasibility of the combined ultrasound, photoacoustic and elasticity imaging techniques in accurately assessing the morphological and functional changes occurring in engineered tissue.

S. Park, et al., “Integrated system for ultrasonic, photoacoustic and elasticity imaging,” in Proc. SPIE, 2006, vol. 6147, pp. 61470H-61470H-8. Publisher's VersionAbstract

A hybrid imaging system is proposed for cancer detection, diagnosis and therapy monitoring by integrating three complementary imaging techniques - ultrasound, photoacoustic and elasticity imaging. Indeed, simultaneous imaging of the anatomy (ultrasound imaging), cancer-induced angiogenesis (photoacoustic imaging) and changes in biomechanical properties (elasticity imaging) of tissue is based on many synergistic features of these modalities and may result in a unique and important imaging tool. To facilitate the design and development of a real-time imaging system for clinical applications, we have investigated the core components of the imaging system using numerical simulations. Differences and similarities between each imaging technique were considered and contrasted. The results of our study suggest that the integration of ultrasound, photoacoustic and elasticity imaging is possible using a custom designed imaging system.