Advancing small-animal molecular imaging through multifaceted innovation.

Lihong V. Wang: Photoacoustic tomography (PAT), combining non‐ionizing optical and ultrasonic waves via the photoacoustic effect, provides in vivo multiscale functional, metabolic, and molecular imaging. Broad applications include imaging of the breast, brain, skin, esophagus, colon, vascular system, and lymphatic system in humans or animals. Light offers rich contrast but does not penetrate biological tissue in straight paths as x‐rays do. Consequently, high‐resolution pure optical imaging (e.g., confocal microscopy, two‐photon microscopy, and optical coherence tomography) is limited to penetration within the optical diffusion limit (∼1 mm in the skin). Ultrasonic imaging, on the contrary, provides fine spatial resolution but suffers from both poor contrast in early‐stage tumors and strong speckle artifacts. In PAT, pulsed laser light penetrates tissue and generates a small but rapid temperature rise, which induces emission of ultrasonic waves due to thermoelastic expansion. The ultrasonic waves, orders of magnitude less scattering than optical waves, are then detected to form high‐resolution images of optical absorption at depths up to 7 cm, conquering the optical diffusion limit. PAT is the only modality capable of imaging across the length scales of organelles, cells, tissues, and organs (up to whole‐body small animals) with consistent contrast. This rapidly growing technology promises to enable multiscale biological research and accelerate translation from microscopic laboratory discoveries to macroscopic clinical practice. PAT may also hold the key to label‐free early detection of cancer by in vivo quantification of hypermetabolism, the quintessential hallmark of malignancy. Learning Objectives: To understand the contrast mechanism of PAT To understand the multiscale applications of PATBenjamin M. W. Tsui: Multi‐modality molecular imaging instrumentation and techniques have been major developments in small animal imaging that has contributed significantly to biomedical research during the past decade. The initial development was an extension of clinical PET/CT and SPECT/CT from human to small animals and combine the unique functional information obtained from PET and SPECT with anatomical information provided by the CT in registered multi‐modality images. The requirements to image a mouse whose size is an order of magnitude smaller than that of a human have spurred advances in new radiation detector technologies, novel imaging system designs and special image reconstruction and processing techniques. Examples are new detector materials and designs with high intrinsic resolution, multi‐pinhole (MPH) collimator design for much improved resolution and detection efficiency compared to the conventional collimator designs in SPECT, 3D high‐resolution and artifact‐free MPH and sparse‐view image reconstruction techniques, and iterative image reconstruction methods with system response modeling for resolution recovery and image noise reduction for much improved image quality. The spatial resolution of PET and SPECT has improved from ∼6–12 mm to ∼1 mm a few years ago to sub‐millimeter today. A recent commercial small animal SPECT system has achieved a resolution of ∼0.25 mm which surpasses that of a state‐of‐art PET system whose resolution is limited by the positron range. More recently, multimodality SA PET/MRI and SPECT/MRI systems have been developed in research laboratories. Also, multi‐modality SA imaging systems that include other imaging modalities such as optical and ultrasound are being actively pursued. In this presentation, we will provide a review of the development, recent advances and future outlook of multi‐modality molecular imaging of small animals. Learning Objectives: To learn about the two major multi‐modality molecular imaging techniques of small animals. To learn about the spatial resolution achievable by the molecular imaging systems for small animal today. To learn about the new multi‐modality imaging instrumentation and techniques that are being developed.Sang Hyun Cho; X‐ray fluorescence (XRF) imaging, such as x‐ray fluorescence computed tomography (XFCT), offers unique capabilities for accurate identification and quantification of metals within the imaging objects. As a result, it has emerged as a promising quantitative imaging modality in recent years, especially in conjunction with metal‐based imaging probes. This talk will familiarize the audience with the basic principles of XRF/XFCT imaging. It will also cover the latest development of benchtop XFCT technology. Additionally, the use of metallic nanoparticles such as gold nanoparticles, in conjunction with benchtop XFCT, will be discussed within the context of preclinical multimodal multiplexed molecular imaging. Learning Objectives: To learn the basic principles of XRF/XFCT imaging To learn the latest advances in benchtop XFCT development for preclinical imagingFunding support received from NIH and DOD; Funding support received from GE Healthcare; Funding support received from Siemens AX; Patent royalties received from GE Healthcare; L. Wang, Funding Support: NIH; COI: Microphotoacoustics; S. Cho, Yes:;NIH/NCI grant R01CA155446 DOD/PCRP grant W81XWH‐12‐1‐0198

The advent of optical molecular probes has taken optical imaging beyond approaches limited to intrinsic optical contrast mechanisms. Fluorophores are typically used as the source of contrast for optical molecular probes and the field of optical molecular imaging is concerned with measuring and quantifying their in vivo biodistribution and pharmacokinetics. Most optical molecular imaging systems are based on Continuous Wave (CW) approaches which enable rapid, full-body imaging of small animals and readily yield images of probe location, however quantification of probe concentration is challenging. Time Domain (TD) approaches, although more expensive and complicated than CW, provide more information to assist in determining the probe location and concentration. Moreover, the TD approach permits access to measuring the fluorophore lifetime which can be indicative of the probe's environment. The eXplore Optix^TM system, developed by ART (Canada) and distributed by GE Healthcare, has enabled TD optical molecular imaging of small animals in vivo and preliminary studies conducted with the system will be presented. In addition, the initial research and development of a full-field TD optical molecular imaging system incorporating a high-power laser for area illumination and a gated-intensified CCD camera for area detection will be presented.

Small animal imaging with high resolution single photon emission tomography

Fluorescence-based molecular imaging in small animals is having a major impact on drug development and disease research and the ability to detect multiple molecular species at once is becoming increasingly important. Unlike bioluminescence, in fluorescence, ubiquitous autofluorescent signals from the skin need to be separated from that of labeled fluorophores to ensure proper quantitative data. Since its introduction in 2004, spectral imaging methods have become an important part of in vivo fluorescence imaging of small animals by enabling easy multiplexed imaging methods and through the quantitative removal of interfering skin autofluorescence signals. This article is a review of the literature on spectral imaging methods and applications in fluorescence imaging of small animals.

Small animal imaging has recently been focused on basic nuclear medicine. We have designed and built a small animal SPECT imaging system using a semiconductor camera and a newly designed collimator. We assess the performance of this system for small object imaging. We employed an MGC 1500 (Acrorad Co.) camera including a CdTe semiconductor. The pixel size was 1.4 mm/pixel. We designed and produced a parallel-hole collimator with 20-mm hole length. Our SPECT system consisted of a semiconductor camera with the subject holder set on an electric rotating stage controlled by a computer. We compared this system with a conventional small animal SPECT system comprising a SPECT-2000H scanner with four Anger type cameras and pinhole collimators. The count rate linearity for estimation of the scatter was evaluated for a pie-chart phantom containing different concentrations of 99mTc. We measured the FWHM of the 99mTc SPECT line source along with scatter. The system volume sensitivity was examined using a flood source phantom which was 35 mm long with a 32-mm inside diameter. Additionally, an in vivo myocardial perfusion SPECT study was performed with a rat. With regards to energy resolution, the semiconductor camera (5.6%) was superior to the conventional Anger type camera (9.8%). In the count rate linearity evaluation, the regression lines of the SPECT values were y = 0.019x + 0.031 (r2 = 0.999) for our system and y = 0.018x + 0.060 (r2 = 0.997) for the conventional system. Thus, the scatter count using the semiconductor camera was less than that using the conventional camera. FWHMs of our system and the conventional system were 2.9 +/- 0.1 and 2.0 +/- 0.1 mm, respectively. Moreover, the system volume sensitivity of our system [0.51 kcps/(MBq/ ml)/cm] was superior to that of the conventional system [0.44 kcps/(MBq/ml)/cm]. Our system provided clear images of the rat myocardium, sufficient for practical use in small animal imaging. Our SPECT system, utilizing a semiconductor camera, permits high quantitative analysis by virtue of its low scatter radiation and high sensitivity. Therefore, this system may contribute to molecular imaging of small animals and basic medical research.

Day two of the Molecular Imaging Symposium (MI-2) will focus on the applications of molecular imaging in small animals and humans. The session will begin with a discussion of a recent trans-agency announcement that addresses molecular imaging as a biomarker for drug response (DHHS New Federal Health Initiative to Improve Cancer Therapy). Opportunities for imaging physicists to engage in the development of physical performance standards for dual modality imaging platforms (anatomical and molecular imaging) during the course of therapy treatment will be discussed. Similarly the development of standardized methods to evaluate change analysis tools will be addressed. A case for creation of a new AAPM task group to address this topic will be presented. The following links are of interest: http://www.fda.gov/oc/mous/domestic/FDA-NCI-CMS.html http://www.nist.gov/public_affairs/factsheet/bioimaging.htm http://imaging.nci.nih.gov/i3/ The second lecture will review the clinical research use of existing contrast agents in dynamic contrast MRI for early assessment of therapy-induced microvascular changes, pre-clinical use of novel high molecular weight and/or targeted or enzymatically activated MR contrast agents, endogenous contrast agent techniques, such a blood oxygen level dependent (BOLD), for assessing changes in tissue oxygenation, and other techniques for assessing treatment response or improving lesion characterization, including quantitative diffusion and spectroscopy techniques. The session will conclude with an introduction of the new combined modality instrumentation now available in PET/CT and SPECT/CT, discuss clinical examples of radiotracers that are being used in oncologic imaging (FDG, amino acids, peptide, hormones, antibodies, cell proliferation and hypoxia tracers), techniques to evaluate whether radiotracers actually localize at the intended site (i.e., autoradiographic correlation with tumor immunohistochemistry in rodent models and on clinical biopsy tissue), and the use of functional images to determine features of tumor biology, to monitor treatment response, and for radiotherapy treatment planning.

The limitations on the sensitivity for detecting small changes in MRI, CT, and ultrasound pulse-echo images are used to estimate the practical requirements for molecular imaging and targeted contrast enhancement for these modalities. These types of imaging are highly unlikely to approach the sensitivity for detecting molecular processes of radionuclear methods, and the prospects for achieving sufficient concentrations of appropriate agents in vivo are poor for several types of applications such as small-molecule targeting of specific receptors. However, using relatively large carrier systems such as particles and liposomes, sufficient concentrations of paramagnetic agents may be delivered to achieve MR-signal changes adequate for detection. The use of higher-resolution MR images will aid the prospects for molecular imaging in small animals. Theoretic considerations also predict that a similar approach, using rather large particles or carriers of materials with a high atomic number, may also be successful for CT, especially with additional developments such as the use of monochromatic x-rays. The prospects of molecular imaging by x-ray imaging may not be as bleak as has been predicted. For ultrasound detection, gas-filled bubbles can provide a sufficient backscattered sound intensity to be detectable at concentrations and sizes not much different from agents designed for these other modalities.

Recent developments in radiochemistry have opened new vistas for investigations of nicotinergic acetylcholine receptors (nAChRs) in living brain by positron emission tomography (PET) and by single photon emission computed tomography (SPECT). In parallel, dedicated instrumentation for molecular imaging in small animals has facilitated preclinical investigations in a number of models in which perturbations in nAChR signalling are implicated, notably Alzheimer’s disease and other neurodegenerative conditions, schizophrenia and other neuropsychiatric disorders, substance abuse and traumatic brain injury. The nAChRs are members of a family of ligand-gated ion channels composed of five subunits, most commonly occurring in the central nervous system as heteropentamers designated α4β2, with lesser amounts of the α7 homopentamer. We present a systematic review of preclinical findings with the diverse nAChR ligands which have been investigated to date. Molecular imaging of the α4β2 nAChR subtype by PET has been successfully achieved by 2-[18F]fluoro-A-85380. Newer agents such as (−)-[18F]flubatine permit quantitation of α4β2 receptors with PET recordings not exceeding 90 min, without the toxicity characteristic of earlier epibatidine derivatives. Imaging studies of α7 nAChRs have been hampered by inadequate pharmacological specificity of available ligands and by the low natural abundance of this receptor subtype in the brain. However, a continued search for optimal ligands is justified by the particular association of α7 nAChRs with aspects of cognitive function. We note that no molecular imaging ligands have been developed for α6-containing nAChRs, despite their importance for the psychopharmacology of nicotine actions in the basal ganglia. Finally, we review the competitive binding model, in which the availability of α4β2 binding sites is altered by competition from endogenous acetylcholine, noting that this approach has yet to be applied for monitoring acetylcholine release in disease models.

Optical molecular imaging in small animals harnesses the power of highly specific and biocompatible contrast agents for drug development and disease research1-7. However, the widespread adoption of in vivo optical imaging has been inhibited by its inability to clearly resolve and identify targeted internal organs. Optical tomography8-11 and combined X-ray and micro-computed tomography (micro-CT)12 approaches developed to address this problem are generally expensive, complex or incapable of true anatomical co-registration. Here, we present a remarkably simple all-optical method that can generate co-registered anatomical maps of a mouse's internal organs, while also acquiring in vivo molecular imaging data. The technique uses a time series of images acquired after injection of an inert dye. Differences in the dye's in vivo biodistribution dynamics allow precise delineation and identification of major organs. Such co-registered anatomical maps permit longitudinal organ identification irrespective of repositioning or weight gain, thereby promising greatly improved accuracy and versatility for studies of orthotopic disease, diagnostics and therapies.

Imaging technologies for in vivo functional and molecular imaging in small animals have undergone a very fast development in the last years with very intense competition to further develop resolution and molecular sensitivity. Among the imaging technologies available, ultrasound-based molecular imaging methods are of particular interest, since the use of ultrasound contrast agents allows specific and sensitive depiction of molecular targets. Together with new developments in quantification methods of targeted microbubbles, sonography represents a dynamic and seminal tool for molecular imaging.

Objectives: We have developed a portable system compatible with various clinical gamma cameras to perform three-dimensional (3D) small-animal molecular imaging. The spatial resolution of this system is close to that of commercial animal imaging systems, although its cost is much lower. Methods: The portable system consists of a rotating stage, a leveling plate, a line source phantom, and a calibration phantom. To obtain high-resolution single-photon emission computed tomography (SPECT) images, we developed several methods for system alignment and applied geometric calibration. The projections of the subject were reimaged according to the calibration parameters and reconstructed by the 3D ordered subsets expectation maximization (OS-EM) algorithm. Results: The resulting images of the microdeluxe phantom showed 2.4-mm cold rods. The image quality of phantom scanning was stable when the portable system was applied to various gamma cameras from different manufacturers. The resultant images of a 99mTc-MDP bone scan of a mouse showed details of the spine, femur, pelvis, and tail. Furthermore, a radiopharmaceutical study of 99mTc-HYNIC-Annexin V on a liver inflammation-induced mouse was carried out to demonstrate the feasibility of this system for small-animal molecular imaging. Conclusions: The newly developed portable system was compatible with various gamma cameras and enabled successful performance of small-animal molecular imaging.

Lihong V. Wang: Photoacoustic tomography (PAT), combining non‐ionizing optical and ultrasonic waves via the photoacoustic effect, provides in vivo multiscale functional, metabolic, and molecular imaging. Broad applications include imaging of the breast, brain, skin, esophagus, colon, vascular system, and lymphatic system in humans or animals. Light offers rich contrast but does not penetrate biological tissue in straight paths as x‐rays do. Consequently, high‐resolution pure optical imaging (e.g., confocal microscopy, two‐photon microscopy, and optical coherence tomography) is limited to penetration within the optical diffusion limit (∼1 mm in the skin). Ultrasonic imaging, on the contrary, provides fine spatial resolution but suffers from both poor contrast in early‐stage tumors and strong speckle artifacts. In PAT, pulsed laser light penetrates tissue and generates a small but rapid temperature rise, which induces emission of ultrasonic waves due to thermoelastic expansion. The ultrasonic waves, orders of magnitude less scattering than optical waves, are then detected to form high‐resolution images of optical absorption at depths up to 7 cm, conquering the optical diffusion limit. PAT is the only modality capable of imaging across the length scales of organelles, cells, tissues, and organs (up to whole‐body small animals) with consistent contrast. This rapidly growing technology promises to enable multiscale biological research and accelerate translation from microscopic laboratory discoveries to macroscopic clinical practice. PAT may also hold the key to label‐free early detection of cancer by in vivo quantification of hypermetabolism, the quintessential hallmark of malignancy. Learning Objectives: To understand the contrast mechanism of PAT To understand the multiscale applications of PATBenjamin M. W. Tsui: Multi‐modality molecular imaging instrumentation and techniques have been major developments in small animal imaging that has contributed significantly to biomedical research during the past decade. The initial development was an extension of clinical PET/CT and SPECT/CT from human to small animals and combine the unique functional information obtained from PET and SPECT with anatomical information provided by the CT in registered multi‐modality images. The requirements to image a mouse whose size is an order of magnitude smaller than that of a human have spurred advances in new radiation detector technologies, novel imaging system designs and special image reconstruction and processing techniques. Examples are new detector materials and designs with high intrinsic resolution, multi‐pinhole (MPH) collimator design for much improved resolution and detection efficiency compared to the conventional collimator designs in SPECT, 3D high‐resolution and artifact‐free MPH and sparse‐view image reconstruction techniques, and iterative image reconstruction methods with system response modeling for resolution recovery and image noise reduction for much improved image quality. The spatial resolution of PET and SPECT has improved from ∼6–12 mm to ∼1 mm a few years ago to sub‐millimeter today. A recent commercial small animal SPECT system has achieved a resolution of ∼0.25 mm which surpasses that of a state‐of‐art PET system whose resolution is limited by the positron range. More recently, multimodality SA PET/MRI and SPECT/MRI systems have been developed in research laboratories. Also, multi‐modality SA imaging systems that include other imaging modalities such as optical and ultrasound are being actively pursued. In this presentation, we will provide a review of the development, recent advances and future outlook of multi‐modality molecular imaging of small animals. Learning Objectives: To learn about the two major multi‐modality molecular imaging techniques of small animals. To learn about the spatial resolution achievable by the molecular imaging systems for small animal today. To learn about the new multi‐modality imaging instrumentation and techniques that are being developed.Sang Hyun Cho; X‐ray fluorescence (XRF) imaging, such as x‐ray fluorescence computed tomography (XFCT), offers unique capabilities for accurate identification and quantification of metals within the imaging objects. As a result, it has emerged as a promising quantitative imaging modality in recent years, especially in conjunction with metal‐based imaging probes. This talk will familiarize the audience with the basic principles of XRF/XFCT imaging. It will also cover the latest development of benchtop XFCT technology. Additionally, the use of metallic nanoparticles such as gold nanoparticles, in conjunction with benchtop XFCT, will be discussed within the context of preclinical multimodal multiplexed molecular imaging. Learning Objectives: To learn the basic principles of XRF/XFCT imaging To learn the latest advances in benchtop XFCT development for preclinical imagingFunding support received from NIH and DOD; Funding support received from GE Healthcare; Funding support received from Siemens AX; Patent royalties received from GE Healthcare; L. Wang, Funding Support: NIH; COI: Microphotoacoustics; S. Cho, Yes:;NIH/NCI grant R01CA155446 DOD/PCRP grant W81XWH‐12‐1‐0198

Lihong V. Wang: Photoacoustic tomography (PAT), combining non‐ionizing optical and ultrasonic waves via the photoacoustic effect, provides in vivo multiscale functional, metabolic, and molecular imaging. Broad applications include imaging of the breast, brain, skin, esophagus, colon, vascular system, and lymphatic system in humans or animals. Light offers rich contrast but does not penetrate biological tissue in straight paths as x‐rays do. Consequently, high‐resolution pure optical imaging (e.g., confocal microscopy, two‐photon microscopy, and optical coherence tomography) is limited to penetration within the optical diffusion limit (∼1 mm in the skin). Ultrasonic imaging, on the contrary, provides fine spatial resolution but suffers from both poor contrast in early‐stage tumors and strong speckle artifacts. In PAT, pulsed laser light penetrates tissue and generates a small but rapid temperature rise, which induces emission of ultrasonic waves due to thermoelastic expansion. The ultrasonic waves, orders of magnitude less scattering than optical waves, are then detected to form high‐resolution images of optical absorption at depths up to 7 cm, conquering the optical diffusion limit. PAT is the only modality capable of imaging across the length scales of organelles, cells, tissues, and organs (up to whole‐body small animals) with consistent contrast. This rapidly growing technology promises to enable multiscale biological research and accelerate translation from microscopic laboratory discoveries to macroscopic clinical practice. PAT may also hold the key to label‐free early detection of cancer by in vivo quantification of hypermetabolism, the quintessential hallmark of malignancy. Learning Objectives: To understand the contrast mechanism of PAT To understand the multiscale applications of PATBenjamin M. W. Tsui: Multi‐modality molecular imaging instrumentation and techniques have been major developments in small animal imaging that has contributed significantly to biomedical research during the past decade. The initial development was an extension of clinical PET/CT and SPECT/CT from human to small animals and combine the unique functional information obtained from PET and SPECT with anatomical information provided by the CT in registered multi‐modality images. The requirements to image a mouse whose size is an order of magnitude smaller than that of a human have spurred advances in new radiation detector technologies, novel imaging system designs and special image reconstruction and processing techniques. Examples are new detector materials and designs with high intrinsic resolution, multi‐pinhole (MPH) collimator design for much improved resolution and detection efficiency compared to the conventional collimator designs in SPECT, 3D high‐resolution and artifact‐free MPH and sparse‐view image reconstruction techniques, and iterative image reconstruction methods with system response modeling for resolution recovery and image noise reduction for much improved image quality. The spatial resolution of PET and SPECT has improved from ∼6–12 mm to ∼1 mm a few years ago to sub‐millimeter today. A recent commercial small animal SPECT system has achieved a resolution of ∼0.25 mm which surpasses that of a state‐of‐art PET system whose resolution is limited by the positron range. More recently, multimodality SA PET/MRI and SPECT/MRI systems have been developed in research laboratories. Also, multi‐modality SA imaging systems that include other imaging modalities such as optical and ultrasound are being actively pursued. In this presentation, we will provide a review of the development, recent advances and future outlook of multi‐modality molecular imaging of small animals. Learning Objectives: To learn about the two major multi‐modality molecular imaging techniques of small animals. To learn about the spatial resolution achievable by the molecular imaging systems for small animal today. To learn about the new multi‐modality imaging instrumentation and techniques that are being developed.Sang Hyun Cho; X‐ray fluorescence (XRF) imaging, such as x‐ray fluorescence computed tomography (XFCT), offers unique capabilities for accurate identification and quantification of metals within the imaging objects. As a result, it has emerged as a promising quantitative imaging modality in recent years, especially in conjunction with metal‐based imaging probes. This talk will familiarize the audience with the basic principles of XRF/XFCT imaging. It will also cover the latest development of benchtop XFCT technology. Additionally, the use of metallic nanoparticles such as gold nanoparticles, in conjunction with benchtop XFCT, will be discussed within the context of preclinical multimodal multiplexed molecular imaging. Learning Objectives: To learn the basic principles of XRF/XFCT imaging To learn the latest advances in benchtop XFCT development for preclinical imagingFunding support received from NIH and DOD; Funding support received from GE Healthcare; Funding support received from Siemens AX; Patent royalties received from GE Healthcare; L. Wang, Funding Support: NIH; COI: Microphotoacoustics; S. Cho, Yes:;NIH/NCI grant R01CA155446 DOD/PCRP grant W81XWH‐12‐1‐0198

Lihong V. Wang: Photoacoustic tomography (PAT), combining non‐ionizing optical and ultrasonic waves via the photoacoustic effect, provides in vivo multiscale functional, metabolic, and molecular imaging. Broad applications include imaging of the breast, brain, skin, esophagus, colon, vascular system, and lymphatic system in humans or animals. Light offers rich contrast but does not penetrate biological tissue in straight paths as x‐rays do. Consequently, high‐resolution pure optical imaging (e.g., confocal microscopy, two‐photon microscopy, and optical coherence tomography) is limited to penetration within the optical diffusion limit (∼1 mm in the skin). Ultrasonic imaging, on the contrary, provides fine spatial resolution but suffers from both poor contrast in early‐stage tumors and strong speckle artifacts. In PAT, pulsed laser light penetrates tissue and generates a small but rapid temperature rise, which induces emission of ultrasonic waves due to thermoelastic expansion. The ultrasonic waves, orders of magnitude less scattering than optical waves, are then detected to form high‐resolution images of optical absorption at depths up to 7 cm, conquering the optical diffusion limit. PAT is the only modality capable of imaging across the length scales of organelles, cells, tissues, and organs (up to whole‐body small animals) with consistent contrast. This rapidly growing technology promises to enable multiscale biological research and accelerate translation from microscopic laboratory discoveries to macroscopic clinical practice. PAT may also hold the key to label‐free early detection of cancer by in vivo quantification of hypermetabolism, the quintessential hallmark of malignancy. Learning Objectives: To understand the contrast mechanism of PAT To understand the multiscale applications of PATBenjamin M. W. Tsui: Multi‐modality molecular imaging instrumentation and techniques have been major developments in small animal imaging that has contributed significantly to biomedical research during the past decade. The initial development was an extension of clinical PET/CT and SPECT/CT from human to small animals and combine the unique functional information obtained from PET and SPECT with anatomical information provided by the CT in registered multi‐modality images. The requirements to image a mouse whose size is an order of magnitude smaller than that of a human have spurred advances in new radiation detector technologies, novel imaging system designs and special image reconstruction and processing techniques. Examples are new detector materials and designs with high intrinsic resolution, multi‐pinhole (MPH) collimator design for much improved resolution and detection efficiency compared to the conventional collimator designs in SPECT, 3D high‐resolution and artifact‐free MPH and sparse‐view image reconstruction techniques, and iterative image reconstruction methods with system response modeling for resolution recovery and image noise reduction for much improved image quality. The spatial resolution of PET and SPECT has improved from ∼6–12 mm to ∼1 mm a few years ago to sub‐millimeter today. A recent commercial small animal SPECT system has achieved a resolution of ∼0.25 mm which surpasses that of a state‐of‐art PET system whose resolution is limited by the positron range. More recently, multimodality SA PET/MRI and SPECT/MRI systems have been developed in research laboratories. Also, multi‐modality SA imaging systems that include other imaging modalities such as optical and ultrasound are being actively pursued. In this presentation, we will provide a review of the development, recent advances and future outlook of multi‐modality molecular imaging of small animals. Learning Objectives: To learn about the two major multi‐modality molecular imaging techniques of small animals. To learn about the spatial resolution achievable by the molecular imaging systems for small animal today. To learn about the new multi‐modality imaging instrumentation and techniques that are being developed.Sang Hyun Cho; X‐ray fluorescence (XRF) imaging, such as x‐ray fluorescence computed tomography (XFCT), offers unique capabilities for accurate identification and quantification of metals within the imaging objects. As a result, it has emerged as a promising quantitative imaging modality in recent years, especially in conjunction with metal‐based imaging probes. This talk will familiarize the audience with the basic principles of XRF/XFCT imaging. It will also cover the latest development of benchtop XFCT technology. Additionally, the use of metallic nanoparticles such as gold nanoparticles, in conjunction with benchtop XFCT, will be discussed within the context of preclinical multimodal multiplexed molecular imaging. Learning Objectives: To learn the basic principles of XRF/XFCT imaging To learn the latest advances in benchtop XFCT development for preclinical imagingFunding support received from NIH and DOD; Funding support received from GE Healthcare; Funding support received from Siemens AX; Patent royalties received from GE Healthcare; L. Wang, Funding Support: NIH; COI: Microphotoacoustics; S. Cho, Yes:;NIH/NCI grant R01CA155446 DOD/PCRP grant W81XWH‐12‐1‐0198

Recent reports revealed that endothelial progenitor cells (EPCs) isolated from bone marrow, cord blood or embryos have been experimentally utilized to deliver therapeutic agents for cancer treatment. Their potential in cancer therapy highlights the need for a consistent and renewable source of endothelial cells for clinical applications. Moreover, one of the most critical issues for ensuring success of endothelial therapy is the development of technologies for non-invasive monitoring of the distribution of transplanted cells and kinetic of tumor progression or regression. We generated human embryonic stem cell-derived endothelial cells (hESC-ECs) from H9 cell line. The hESC-ECs resemble adult endothelial cells HUVEC in endothelial markers and angiogenesis potential. In vitro study revealed the paracrine effects of hESC-ECs on tumor cells using conditioned medium (EC-CM). After treated with EC-CM, human breast cancer cells MDA-MB-231 proliferated slower and exhibited a higher apoptosis rate in low-serum condition, and the migration ability was impaired. Furthermore, we introduced a multitude of non-invasive, quantitative, functional imaging techniques with reporter gene methods to probe breast cancer model processes, and to track the hESC-ECs for targeting therapy in vivo by firefly luciferase (Fluc)/renilla luciferase (Rluc) imaging. We transduced hESC-ECs with triple fusion (TF) reporter gene containing the herpes simplex virus truncated thymidine kinase (HSV-ttk), renilla luciferase (Rluc) and RFP (RL-RFP-HSV-ttk). The NOD/SCID mice breast cancer metastasis model was established by tail vein injection of 1.5×106 MDA-MB-231 cells, which carry a reporter system encoding the gene of Fluc and GFP. Bioluminescence imaging (BLI) revealed that hESC-ECs can be sequenced in tumor sites for more than 72 hours. When given pro-drug ganciclovir (GCV), targeting HSV-ttk gene, the MDA-MB-231 tumor was inhibited by the indication of Fluc imaging. And immunofluorescence staining also confirmed that hESC-EC can exclusively home to tumor lesions instead of normal lung tissue. Taken together, our results revealed that hESC-ECs can specifically target tumor sites and kill nearby tumor cells by bystander effect when GCV is given. These finds suggest that hESC-ECs are attractive targeting vehicles for cancer therapy, and molecular imaging in small animals is an invaluable part of cancer diagnosis, prediction of tumor response to available therapies and monitoring response to therapy as well as developing drugs prior to clinical translation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 415. doi:1538-7445.AM2012-415