Combined Ultrasound and Photoacoustic Imaging of Pancreatic Cancer Using Nanocage Contrast Agents Kimberly Homan 1 , Jignesh Shah 1 , Sobeyda Gomez 1 , Heidi Gensler 1 , Andrei Karpiouk 1 , L. Brannon-Peppas 2 and Stanislav Emelianov 1 1 Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78712 2 Appian Labs LLC, Austin, TX 78738 ABSTRACT A new metallodielectric nanoparticle consisting of a silica core and silver outer cage was developed for the purpose of enhancing photoacoustic imaging contrast in pancreatic tissue. These nanocages were injected into an ex vivo porcine pancreas and imaged using a combined photoacoustic and ultrasound (PAUS) assembly. This custom-designed PAUS assembly delivered 800 nm light through a fiber optical light delivery system integrated with 128 element linear array transducer operating at 7.5 MHz center frequency. Imaging results prove that the nanocage contrast agents have the ability to enhance photoacoustic imaging contrast. Furthermore, the value of the combined PAUS imaging modality was demonstrated as the location of nanocages against background native tissue was evident. Future applications of these nanocage contrast agents could include targeting them to pancreatic cancer for enhancement of photoacoustic imaging for diagnosis and therapy. Keywords: photoacoustic and ultrasound imaging; silver nanocages, silica nanoparticles, pancreatic cancer 1. INTRODUCTION Pancreatic cancer represents the 4 th leading cause of cancer-related deaths in the United States [1, 2]. This year over 37,000 will be diagnosed with pancreatic adenocarcinoma. Unfortunately, the yearly death rate at over 33,000 people is painfully close to its incidence [3]. In fact, for all stages of pancreatic cancer combined, the 5 year survival rate remains at a low 5%, making it arguably the most lethal of all solid tumors [4]. Patients who present with a metastatic form of this disease suffer a life expectancy of just 3-6 months [3], and over 50% of pancreatic cancer patients are diagnosed metastatic [5]. Furthermore, patients whose disease is localized upon diagnosis still only retain a 15% long term survival rate [4]. These survival rates represent the lowest of all major cancer types [2]. In addition, the number of patients diagnosed with pancreatic cancer each year is rising [6]; this rise is in contrast to other diseases such as colorectal cancer, where a decrease in incidences can be attributed to investments in early detection [7]. Pancreatic cancer is particularly difficult to diagnose and treat for several reasons. Unfortunately, diagnosis of pancreatic cancer in late developmental phases is very common because symptoms do not present early. Furthermore, the types of symptoms presented (fatigue, weight loss, etc) are nebulous and could be associated with many other diseases [8]. Secondly, the positioning of the pancreas (between the stomach and spine) in the human body makes it difficult to access and image. Preferred imaging modalities currently include helical computed tomography CT and endoscopic ultrasound (EUS). Helical CT is generally used to initially detect the presence of a pancreatic mass and any distant metastasis, while EUS is used for tumor staging and predicting vascular invasion. EUS is a fine art and only highly experienced Invited Paper Photons Plus Ultrasound: Imaging and Sensing 2009, edited by Alexander A. Oraevsky, Lihong V. Wang, Proc. of SPIE Vol. 7177, 71771M · © 2009 SPIE · CCC code: 1605-7422/09/$18 · doi: 10.1117/12.807520 Proc. of SPIE Vol. 7177 71771M-1