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Am J Nucl Med Mol Imaging 2013;3(4):336-349
Original Article
In vivo validation and 3D visualization of broadband ultrasound molecular imaging
Xiaowen Hu, Charles F Caskey, Lisa M Mahakian, Dustin E Kruse, Julie R Beegle, Anne-Emilie Declèves, Joshua J Rychak, Patrick L 
Sutcliffe, Kumar Sharma, Katherine W Ferrara
Department of Biomedical Engineering, University of California, Davis, One Shields Ave, Davis, CA 95616, USA; Center for Renal 
Translational Medicine, Division of Nephrology-Hypertension, Department of Medicine, University of California, San Diego, La Jolla, 
CA 92093, USA; Targeson Inc., 3550 General Atomics Court, MS 02-444, San Diego, CA 92121, USA. These authors contributed 
equally to this manuscript.
Received March 7, 2013; Accepted April 11, 2013; Epub July 10, 2013; Published July 15, 2013
Abstract: Ultrasound can selectively and specifically visualize upregulated vascular receptors through the detection of bound 
microbubbles. However, most current ultrasound molecular imaging methods incur delays that result in longer acquisition times and 
reduced frame rates. These delays occur for two main reasons: 1) multi-pulse imaging techniques are used to differentiate 
microbubbles from tissue and 2) acquisition occurs after free bubble clearance (>6 minutes) in order to differentiate bound from 
freely circulating microbubbles. In this paper, we validate tumor imaging with a broadband single pulse molecular imaging method 
that is faster than the multi-pulse methods typically implemented on commercial scanners. We also combine the single pulse 
method with interframe filtering to selectively image targeted microbubbles without waiting for unbound bubble clearance, thereby 
reducing acquisition time from 10 to 2 minutes. The single pulse imaging method leverages non-linear bubble behavior by 
transmitting at low and receiving at high frequencies (TLRH). We implemented TLRH imaging and visualized the accumulation of 
intravenously administrated integrin-targeted microbubbles in a phantom and a Met-1 mouse tumor model. We found that the TLRH 
contrast imaging has a ~2-fold resolution improvement over standard contrast pulse sequencing (CPS) imaging. By using interframe 
filtering, the tumor contrast was 24.8±1.6 dB higher after the injection of integrin-targeted microbubbles than non-targeted control 
MBs, while echoes from regions lacking the target integrin were suppressed by 26.2±2.1 dB as compared with tumor echoes. Since 
real-time three-dimensional (3D) molecular imaging provides a more comprehensive view of receptor distribution, we generated 3D 
images of tumors to estimate their volume, and these measurements correlated well with expected tumor sizes. We conclude that 
TLRH combined with interframe filtering is a feasible method for 3D targeted ultrasound imaging that is faster than current 
multi-pulse strategies. (ajnmmi1303004).
Keywords: Targeted microbubbles, ultrasound molecular imaging, angiogenesis, 3D visualization
Address correspondence to: Katherine Ferrara, Department of Biomedical Engineering, University of California, Davis, 451 E Health 
Sciences Dr, Davis, CA 95616. Phone: 530-754-9436; Fax: 530-754-5739; E-mail: kwferrara@ucdavis.edu