Small Animal Imaging System Research Articles

Multi-modal molecular diffuse optical tomography system for small animal imaging

A multi-modal optical imaging system for quantitative 3D bioluminescence and functional diffuse imaging is presented, which has no moving parts and uses mirrors to provide multi-view tomographic data for image reconstruction. It is demonstrated that through the use of trans-illuminated spectral near-infrared measurements and spectrally constrained tomographic reconstruction, recovered concentrations of absorbing agents can be used as prior knowledge for bioluminescence imaging within the visible spectrum. Additionally, the first use of a recently developed multi-view optical surface capture technique is shown and its application to model-based image reconstruction and free-space light modelling is demonstrated. The benefits of model-based tomographic image recovery as compared to two-dimensional (2D) planar imaging are highlighted in a number of scenarios where the internal luminescence source is not visible or is confounding in 2D images. The results presented show that the luminescence tomographic imaging method produces 3D reconstructions of individual light sources within a mouse-sized solid phantom that are accurately localized to within 1.5 mm for a range of target locations and depths, indicating sensitivity and accurate imaging throughout the phantom volume. Additionally the total reconstructed luminescence source intensity is consistent to within 15%, which is a dramatic improvement upon standard bioluminescence imaging. Finally, results from a heterogeneous phantom with an absorbing anomaly are presented, demonstrating the use and benefits of a multi-view, spectrally constrained coupled imaging system that provides accurate 3D luminescence images.

Effect of Liposomes on the Absorption of Water-soluble Active Pharmaceutical Ingredients via Oral Administration

The objective of this study was to investigate the effect of liposomes on the absorption of water-soluble active pharmaceutical ingredients. Salbutamol sulfate (SBS) has been widely used for treatment of bronchospasm in conditions such as asthma. Using SBS as the model drug in this study, we developed SBS-loaded liposomes for oral administration and explored the relationship between their bioavailability and anti-asthmatic efficacy. SBS was entrapped in liposomes with encapsulation efficiency as high as 70%. The in vitro transport profile of SBS across a dialysis membrane for liposome suspension was compared with that for free SBS solution. Oral administration of liposomes labeled with the fluorescent dye 1,1'-dioctadecyltetramethyl indotricarbocyanine iodide (DiR) in a mouse model was assessed by a small animal imaging system. Pharmacokinetic and pharmacodynamic studies on SBS liposome suspension and free SBS solution were performed using animal models via oral administration. The results showed that liposomes could sustain the release of SBS in vitro and decrease the transport rate of SBS across the dialysis membrane. In vivo fluorescence imaging analysis demonstrated DiR liposome distribution in mouse stomach for at least 24 hr. The mean residence time of SBS from liposomes was found to be longer than that of free SBS, suggesting that the relative bioavailability of SBS was higher when liposome delivery was used. The pharmacokinetic data also showed that the drug absorption rate was relatively slower for treatment with liposomal SBS when compared to free SBS. Moreover, SBS liposome suspension was shown to give a prolonged anti-asthmatic effect after oral administration when compared to free SBS solution. Overall, this study demonstrated that use of liposomes as delivery vehicles for sustained drug release and controlled absorption could be a promising approach for improving the therapeutic potency of active pharmaceutical ingredients.

Investigating line- versus point-laser excitation for three-dimensional fluorescence imaging and tomography employing a trimodal imaging system

The adoption of axially oriented line illumination patterns for fluorescence excitation in small animals for fluorescence surface imaging (FSI) and fluorescence optical tomography (FOT) is being investigated. A trimodal single-photon-emission-computed-tomography/computed-tomography/optical-tomography (SPECT-CT-OT) small animal imaging system is being modified for employment of point- and line-laser excitation sources. These sources can be arbitrarily positioned around the imaged object. The line source is set to illuminate the object along its entire axial direction. Comparative evaluation of point and line illumination patterns for FSI and FOT is provided involving phantom as well as mouse data. Given the trimodal setup, CT data are used to guide the optical approaches by providing boundary information. Furthermore, FOT results are also being compared to SPECT. Results show that line-laser illumination yields a larger axial field of view (FOV) in FSI mode, hence faster data acquisition, and practically acceptable FOT reconstruction throughout the whole animal. Also, superimposed SPECT and FOT data provide additional information on similarities as well as differences in the distribution and uptake of both probe types. Fused CT data enhance further the anatomical localization of the tracer distribution in vivo. The feasibility of line-laser excitation for three-dimensional fluorescence imaging and tomography is demonstrated for initiating further research, however, not with the intention to replace one by the other.

Comparison of photon counting and conventional scintillation detectors in a pinhole SPECT system for small animal imaging: Monte carlo simulation studies

The photon counting detector based on cadmium telluride (CdTe) or cadmium zinc telluride (CZT) is a promising imaging modality that provides many benefits compared to conventional scintillation detectors. By using a pinhole collimator with the photon counting detector, we were able to improve both the spatial resolution and the sensitivity. The purpose of this study was to evaluate the photon counting and conventional scintillation detectors in a pinhole single-photon emission computed tomography (SPECT) system. We designed five pinhole SPECT systems of two types: one type with a CdTe photon counting detector and the other with a conventional NaI(Tl) scintillation detector. We conducted simulation studies and evaluated imaging performance. The results demonstrated that the spatial resolution of the CdTe photon counting detector was 0.38 mm, with a sensitivity 1.40 times greater than that of a conventional NaI(Tl) scintillation detector for the same detector thickness. Also, the average scatter fractions of the CdTe photon counting and the conventional NaI(Tl) scintillation detectors were 1.93% and 2.44%, respectively. In conclusion, we successfully evaluated various pinhole SPECT systems for small animal imaging.

Design and performance of a small-animal imaging system using synthetic collimation

This work outlines the design and construction of a single-photon emission computed tomography imaging system based on the concept of synthetic collimation. A focused multi-pinhole collimator is constructed using rapid-prototyping and casting techniques. The collimator projects the centre of the field of view (FOV) through 46 pinholes when the detector is adjacent to the collimator, with the number reducing towards the edge of the FOV. The detector is then moved further from the collimator to increase the magnification of the system. The object distance remains constant, and each new detector distance is a new system configuration. The level of overlap of the pinhole projections increases as the system magnification increases, but the number of projections subtended by the detector is reduced. There is no rotation in the system; a single tomographic angle is used in each system configuration. Image reconstruction is performed using maximum-likelihood expectation–maximization and an experimentally measured system matrix. The system matrix is measured for each configuration on a coarse grid, using a point source. The pinholes are individually identified and tracked, and a Gaussian fit is made to each projection. The coefficients of these fits are used to interpolate the system matrix. The system is validated experimentally with a hot-rod phantom. The Fourier crosstalk matrix is also measured to provide an estimate of the average spatial resolution along each axis over the entire FOV. The 3D synthetic-collimator image is formed by estimating the activity distribution within the FOV and summing the activities in the voxels along the axis perpendicular to the collimator face.

Abstract 4138: Fluorescence laparoscopy with an LED light source enables fluorescence-guided resection of pancreatic cancer, labeled with fluorophore-conjugated antibodies, in mouse models.

Abstract Orthotopic mouse models of human pancreatic cancer were established with the BxPC-3 RFP pancreatic cancer cell line. Two weeks after implantation, mice were randomized to undergo bright light laparoscopic resection (BLR) (n=19) or fluorescence-guided laparoscopic resection (FLR) (n=19). Fluorescence laparoscopy was performed with a 495-nm emission filter and a Stryker L9000 LED light source 24 hours after tail vein injection of anti-CEA-Alexa 488 antibodies. Bright light laparoscopy was performed with a Stryker X8000 xenon light source. Pre- and postoperative images were taken with the Olympus OV-100 Small Animal Imaging System to assess completeness of resection. Postoperatively, whole body images were obtained to assess for recurrence and follow tumor progression. Intravital and ex vivo images were obtained at termination to evaluate tumor burden. FLS enabled real-time identification and localization of brightly-fluorescent BxPC-3 RFP tumor labeled with anti-CEA-Alexa 488. Furthermore, there was adequate background illumination for surgical navigation permitting improved resection. At termination at 12 weeks, mice in the FLS group had a smaller pancreatic tumor burden compared to mice from the BLS group (5.75 mm2 vs 28.43 mm2; p=0.012). Mice in the FLS group also experienced decreased local recurrence (47.4% vs 78.9%, p=0.046) and distant recurrence (68.4% vs 94.7%, p=0.045) compared to mice in the BLS group. Fluorescence-guided surgery has significant potential to improve laparoscopic approaches in the treatment of pancreatic cancer. Citation Format: Cristina A. Metildi, Sharmeela Kaushal, George A. Luiken, Mark A. Talamini, Robert M. Hoffman, Michael Bouvet. Fluorescence laparoscopy with an LED light source enables fluorescence-guided resection of pancreatic cancer, labeled with fluorophore-conjugated antibodies, in mouse models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4138. doi:10.1158/1538-7445.AM2013-4138

Abstract 726: Fluorophore-conjugated antibodies improve surgical resection of pancreatic cancer leading to prolonged disease-free survival and overall survival in orthotopic mouse models.

Abstract We established orthotopic mouse models of human pancreatic cancer with fragments of BxPC-3-RFP tumor. Two weeks after implantation, mice were randomized to FGS or bright-field surgery (BS). FGS was performed 24 hrs after tail vein injection of anti-CEA-Alexa 488. Completeness of resection was assessed from pre- and postoperative images obtained with the OV-100 Small Animal Imaging System. Whole body images of mice were obtained postoperatively to assess for recurrence and mice were followed until premorbid to measure survival. We achieved a complete resection of pancreatic cancers in 92% of mice in the FGS group as compared to 58% in the BS group (p=0.002). Preoperative tumor burden was not significantly different between groups (p=0.424). However, FGS afforded a significantly smaller mean postoperative tumor burden compared to BS: 0.0004 ± SE 0.0003 mm2 vs. 0.0841 ± SE 0.027 mm2, p=0.004. On average, mice in the FGS experienced a greater reduction in tumor burden: 99.99% vs 97.72%, p=0.01. FGS reduced recurrence rates from 95% to 50% (p=0.002) and lengthened mean disease-free survival from 7 weeks to 30.5 weeks (p<0.001). The FGS group experienced longer overall survival compared to the BS group: 16.5 weeks vs. 37 weeks (p=0.001). Cure rate was improved with FGS from 5% to 50% (p=0.003). Furthermore, FGS more than doubled the one-year postoperative survival rate from 3 mice in the BLS group to 8 mice in the FGS group (p=0.005). This novel approach has potential to improve outcomes in the surgical treatment of pancreatic cancer. Survival and recurrence according to surgical mode. Surgical Mode Disease-Free Survival Overall Survival Recurrence Rate Bright-Field Surgery 7 weeks 16.5 weeks 95% Fluorescence-Guided Surgery 30.5 weeks 37 weeks 50% Citation Format: Cristina A. Metildi, Sharmeela Kaushal, Mark A. Talamini, George A. Luiken, Robert M. Hoffman, Michael Bouvet. Fluorophore-conjugated antibodies improve surgical resection of pancreatic cancer leading to prolonged disease-free survival and overall survival in orthotopic mouse models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 726. doi:10.1158/1538-7445.AM2013-726

Regulatory T Cells (Tregs) in Neonatal Tolerance: Allogeneic Tregs Regulate the Neonatal Immune System and Prolong Heart Graft Survival

Purpose Semi-allogeneic (F1; H-2k/b) splenocytes (SC) injected into newborn mice (H-2k) induce immunological tolerance whereas allogeneic SC (H-2b) lead to graft- vs -host disease (GVHD). This study tested injection of purified allogeneic Tregs in our model of neonatal tolerance to cardiac allografts. Methods and Materials CD4 + CD25 + Tregs were isolated using StemCell Technologies EasySep® purification kits. Injected labeled syngeneic, F1 or allogeneic SC, or purified allogeneic Tregs, were tracked in newborn mice for 6 days by OV100 small animal imaging system. Treg interactions and fates were studied by confocal microscopy, and their ability to prolong heart allograft survival in adults. Results By whole body and organ imaging syngeneic and F1 SC tracked to lymphoid organs while allogeneic SC initially tracked there but then proliferated and distributed throughout the mice consistent with GVHD. Injected Tregs also trafficked to lymphoid organs but unlike allogeneic SC did not proliferate. Allogeneic Tregs survived post-injection in spleen suggesting they were not being attacked by the host immune system. In neonatal spleen, allogeneic Tregs interacted with host Tregs either directly or via host dendritic cells indicating a possible role in iTreg formation. Injected allogeneic Tregs prolonged survival of both donor-type and third-party heart grafts to 100 days in 50% of transplanted mice (n=6). A >100 day functioning donor-type heart graft showed mild-moderate cellular infiltrate of macrophages and T cells including CD8+ T cells, with focal regions of myocyte damage. Conclusions Injection of neonates with purified allogeneic Tregs prolongs survival of donor-type and third party heart grafts transplanted as adults. Prolonged third-party graft survival suggests suppression of the host immune system in a localized “non-specific” manner; alternatively given the presumed clonal diversity of allogeneic Tregs, some form of specific/cross-reactive suppression may be occurring.

Simultaneous multiple view high resolution surface geometry acquisition using structured light and mirrors

Knowledge of the surface geometry of an imaging subject is important in many applications. This information can be obtained via a number of different techniques, including time of flight imaging, photogrammetry, and fringe projection profilometry. Existing systems may have restrictions on instrument geometry, require expensive optics, or require moving parts in order to image the full surface of the subject. An inexpensive generalised fringe projection profilometry system is proposed that can account for arbitrarily placed components and use mirrors to expand the field of view. It simultaneously acquires multiple views of an imaging subject, producing a cloud of points that lie on its surface, which can then be processed to form a three dimensional model. A prototype of this system was integrated into an existing Diffuse Optical Tomography and Bioluminescence Tomography small animal imaging system and used to image objects including a mouse-shaped plastic phantom, a mouse cadaver, and a coin. A surface mesh generated from surface capture data of the mouse-shaped plastic phantom was compared with ideal surface points provided by the phantom manufacturer, and 50% of points were found to lie within 0.1mm of the surface mesh, 82% of points were found to lie within 0.2mm of the surface mesh, and 96% of points were found to lie within 0.4mm of the surface mesh.

<italic>In vivo</italic> study of biodistribution and urinary excretion of silica nanoparticles with different size

The biodistribution and urinary excretion of fluorescent silica nanoparticles (FSiNPs) with different sizes were investigated in situ and real-time in mice using small animal imaging system. In addition, in vitro organ imaging, organization slice imaging and urine fluorescence imaging were also investigated. In vivo imaging results showed that the smaller the size of FSiNPs, the longer the blood circulation, and the more obvious in whole body distribution. Finally, these particles gradually accumulated in the liver and bladder. These results were well confirmed by in vitro organ imaging and organization slice imaging. At the same time, the kidney tissue sections and urine imaging results showed that the smaller the particle the more easily excreted through the urinary system. The results of this study would be helpful for future application of fluorescent silica nanoparticles with different sizes in vivo .

Multimodal Fluorescence-Mediated Tomography and SPECT/CT for Small-Animal Imaging

Spatial and temporal coregistration of nuclear and optical images can enable the fusion of the information from these complementary molecular imaging modalities. A critical challenge is in integrating the optical and nuclear imaging hardware. Flexible fiber-based fluorescence-mediated tomography (FMT) systems provide a viable solution. The various bore sizes of small-animal nuclear imaging systems can potentially accommodate the FMT fiber imaging arrays. In addition, FMT imaging facilitates coregistration of the nuclear and optical contrasts in time. Herein, we combine a fiber-based FMT system with a preclinical SPECT/CT platform. Feasibility of in vivo imaging is demonstrated by tracking a monomolecular multimodal imaging agent (MOMIA) during transport from the forepaw to the axillary lymph node region of a rat. The fiber-based, video-rate FMT imaging system is composed of 12 sources (785- and 830-nm laser diodes) and 13 detectors. To maintain high temporal sampling, the system simultaneously acquires ratio-metric data at each detector. A 3-dimensional finite element model derived from CT projections provides anatomically based light propagation modeling. Injection of a MOMIA intradermally into the forepaw of rats provided spatially and temporally coregistered nuclear and optical contrasts. FMT data were acquired concurrently with SPECT and CT data. The incorporation of SPECT data as a priori information in the reconstruction of FMT data integrated both optical and nuclear contrasts. Accurate depth localization of phantoms with different thicknesses was accomplished with an average center-of-mass error of 4.1 ± 2.1 mm between FMT and SPECT measurements. During in vivo tests, fluorescence and radioactivity from the MOMIA were colocalized in spatially coincident regions with an average center-of-mass error of 2.68 ± 1.0 mm between FMT and SPECT for axillary lymph node localization. Intravital imaging with surgical exposure of the lymph node validated the localization of the optical contrast. The feasibility of integrating a fiber-based, video-rate FMT system with a commercial preclinical SPECT/CT platform was established. These coregistered FMT and SPECT/CT results with MOMIAs may facilitate the development of the next generation of preclinical and clinical multimodal optical-nuclear platforms for a broad array of imaging applications and help elucidate the underlying biologic processes relevant to cancer diagnosis and therapy monitoring.

Scanning linear estimation: improvements over region of interest (ROI) methods

In tomographic medical imaging, a signal activity is typically estimated by summing voxels from a reconstructed image. We introduce an alternative estimation scheme that operates on the raw projection data and offers a substantial improvement, as measured by the ensemble mean-square error (EMSE), when compared to using voxel values from a maximum-likelihood expectation–maximization (MLEM) reconstruction. The scanning-linear (SL) estimator operates on the raw projection data and is derived as a special case of maximum-likelihood estimation with a series of approximations to make the calculation tractable. The approximated likelihood accounts for background randomness, measurement noise and variability in the parameters to be estimated. When signal size and location are known, the SL estimate of signal activity is unbiased, i.e. the average estimate equals the true value. By contrast, unpredictable bias arising from the null functions of the imaging system affect standard algorithms that operate on reconstructed data. The SL method is demonstrated for two different tasks: (1) simultaneously estimating a signal’s size, location and activity; (2) for a fixed signal size and location, estimating activity. Noisy projection data are realistically simulated using measured calibration data from the multi-module multi-resolution small-animal SPECT imaging system. For both tasks, the same set of images is reconstructed using the MLEM algorithm (80 iterations), and the average and maximum values within the region of interest (ROI) are calculated for comparison. This comparison shows dramatic improvements in EMSE for the SL estimates. To show that the bias in ROI estimates affects not only absolute values but also relative differences, such as those used to monitor the response to therapy, the activity estimation task is repeated for three different signal sizes.

Identification of the optimal therapeutic antibody for fluorescent imaging of cutaneous squamous cell carcinoma

Intraoperative, real-time fluorescence imaging may significantly improve tumor visualization and resection and postoperatively, in pathological assessment. To this end, we sought to determine the optimal FDA approved therapeutic monoclonal antibody for optical imaging of human cutaneous squamous cell carcinoma (cSCC). A near-infrared (NIR) fluorescent probe (IRDye800) was covalently linked to bevacizumab, panitumumab or tocilizumab and injected systemically into immunodeficient mice bearing either cutaneous tumor cell lines (SCC13) or cutaneous human tumor explants. Tumors were then imaged and resected under fluorescent guidance with the SPY, an FDA-approved intraoperative imaging system, and the Pearl Impulse small animal imaging system. All fluorescently labeled antibodies delineated normal tissue from tumor in SCC13 xenografts based on tumor-to-background (TBR) ratios. The conjugated antibodies produced TBRs of 1.2–2 using SPY and 1.6–3.6 using Pearl; in comparison, isotype control antibody IgG-IRDye produced TBRs of 1.0 (SPY) and 0.98 (Pearl). Comparison between antibodies revealed them to be roughly equivalent for imaging purposes with both the SPY and Pearl (p = 0.89 SPY, p = 0.99 Pearl; one way ANOVA). Human tumor explants were also imaged and tumor detection was highest with panitumumab-IRDye800 when using the SPY (TBR 3.0) and Pearl (TBR 4.0). These data suggest that FDA approved antibodies may be clinically used for intraoperative detection of cSCC.

In vivovalidation of quantitative frequency domain fluorescence tomography

We have developed a hybrid frequency domain fluorescence tomography and magnetic resonance imaging system (MRI) for small animal imaging. The main purpose of this system is to obtain quantitatively accurate fluorescence concentration and lifetime images using a multi-modality approach. In vivo experiments are undertaken to evaluate the system. We compare the recovered fluorescence parameters with and without MRI structural a priori information. In addition, we compare two optical background heterogeneity correction methods: Born normalization and utilizing diffuse optical tomography (DOT) functional a priori information. The results show that the concentration and lifetime of a 4.2-mm diameter indocyanine green inclusion located 15 mm deep inside a rat can be recovered with less than a 5% error when functional a priori information from DOT and structural a priori information from MRI are utilized.

SMALL-ANIMAL MOLECULAR IMAGING WITH PORTABLE DEVICES ON CLINICAL PINHOLE SINGLE-PHOTON EMISSION COMPUTED TOMOGRAPHY SYSTEMS

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.

Development of an ultrahigh-resolution Si-PM-based dual-head GAGG coincidence imaging system

A silicon photomultiplier (Si-PM) is a promising photodetector for high resolution PET systems due to its small channel size and high gain. Using Si-PMs, it will be possible to develop a high resolution imaging systems. For this purpose, we developed a small field-of-view (FOV) ultrahigh-resolution Si-PM-based dual-head coincidence imaging system for small animals and plant research. A new scintillator, Ce doped Gd3Al12Ga3O12 (GAGG), was selected because of its high light output and its emission wavelength matched with the Si-PM arrays and contained no radioactivity. Each coincidence imaging block detector consists of 0.5×0.5×5mm3 GAGG pixels combined with a 0.1-mm thick reflector to form a 20×17 matrix that was optically coupled to a Si-PM array (Hamamatsu MPPC S11064-050P) with a 1.5-mm thick light guide. The GAGG block size was 12.0×10.2mm2. Two GAGG block detectors were positioned face to face and set on a flexible arm based detector stand. All 0.5mm GAGG pixels in the block detectors were clearly resolved in the 2-dimensional position histogram. The energy resolution was 14.4% FWHM for the Cs-137 gamma ray. The spatial resolution was 0.7mm FWHM measured using a 0.25mm diameter Na-22 point source. Small animal and plant images were successfully obtained. We conclude that our developed ultrahigh-resolution Si-PM-based dual-head coincidence imaging system is promising for small animal and plant imaging research.

Fluorescence-guided surgery of human colon cancer increases complete resection resulting in cures in an orthotopic nude mouse model

BackgroundWe inquired if fluorescence-guided surgery (FGS) could improve surgical outcomes in fluorescent orthotopic nude mouse models of human colon cancer. MethodsWe established fluorescent orthotopic mouse models of human colon cancer expressing a fluorescent protein. Tumors were resected under bright light surgery (BLS) or FGS. Pre- and post-operative images with the OV-100 Small Animal Imaging System (Olympus Corp, Tokyo Japan) were obtained to assess the extent of surgical resection. ResultsAll mice with primary tumor that had undergone FGS had complete resection compared with 58% of mice in the BLS group (P = 0.001). FGS resulted in decreased recurrence compared with BLS (33% versus 62%, P = 0.049) and lengthened disease-free median survival from 9 to >36 wk. The median overall survival increased from 16 wk in the BLS group to 31 weeks in the FGS group. FGS resulted in a cure in 67% of mice (alive without evidence of tumor at >6 mo after surgery) compared with only 37% of mice that underwent BLS (P = 0.049). ConclusionsSurgical outcomes in orthotopic nude mouse models of human colon cancer were significantly improved with FGS. The present study can be translated to the clinic by various effective methods of fluorescently labeling tumors.

Hyperpolarized singlet NMR on a small animal imaging system

Nuclear spin hyperpolarization makes a significant advance toward overcoming the sensitivity limitations of in vivo magnetic resonance imaging, particularly in the case of low-gamma nuclei. The sensitivity may be improved further by storing the hyperpolarization in slowly relaxing singlet populations of spin-1/2 pairs. Here, we report hyperpolarized (13) C spin order transferred into and retrieved from singlet spin order using a small animal magnetic resonance imaging scanner. For spins in sites with very similar chemical shifts, singlet spin order is sustained in high magnetic field without requiring strong radiofrequency irradiation. The demonstration of robust singlet-to-magnetization conversion, and vice versa, on a small animal scanner, is promising for future in vivo and clinical deployments.

Fluorescence-Guided Surgery Allows for More Complete Resection of Pancreatic Cancer, Resulting in Longer Disease-Free Survival Compared with Standard Surgery in Orthotopic Mouse Models

Negative surgical margins are vital to achieve cure and prolong survival in patients with pancreatic cancer. We inquired if fluorescence-guided surgery (FGS) could improve surgical outcomes and reduce recurrence rates in orthotopic mouse models of human pancreatic cancer. A randomized active-control preclinical trial comparing bright light surgery (BLS) to FGS was used. Orthotopic mouse models of human pancreatic cancer were established using the BxPC-3 pancreatic cancer cell line expressing red fluorescent protein (RFP). Two weeks after orthotopic implantation, tumors were resected with BLS or FGS. Pre- and postoperative images were obtained with the OV-100 Small Animal Imaging System to assess completeness of surgical resection in real time. Postoperatively, noninvasive whole body imaging was done to assess recurrence and follow tumor progression. Six weeks postoperatively, mice were sacrificed to evaluate primary pancreatic and metastatic tumor burden at autopsy. A more complete resection of pancreatic cancer was achieved using FGS compared with BLS: 98.9% vs 77.1%, p = 0.005. The majority of mice undergoing BLS (63.2%) had evidence of gross disease with no complete resections; 20% of mice undergoing FGS had complete resection and an additional 75% had only minimal residual disease (p = 0.0001). The mean postoperative tumor burden was significantly less with FGS compared with BLS: 0.08 ± 0.06 mm(2) vs 2.64 ± 0.63 mm(2), p = 0.001. The primary tumor burden at termination was significantly less with FGS compared with BLS: 19.3 ± 5.3 mm(2) vs 6.2 ± 3.6 mm(2), p = 0.048. FGS resulted in significantly longer disease-free survival than BLS (p = 0.02, hazard ratio = 0.39, 95% CI 0.17, 0.88). Surgical outcomes were improved in pancreatic cancer using fluorescence-guidance. This novel approach has significant potential to improve surgical treatment of cancer.

Whole-body ring-shaped confocal photoacoustic computed tomography of small animals in vivo

We report a novel small-animal whole-body imaging system called ring-shaped confocal photoacoustic computed tomography (RC-PACT). RC-PACT is based on a confocal design of free-space ring-shaped light illumination and 512-element full-ring ultrasonic array signal detection. The free-space light illumination maximizes the light delivery efficiency, and the full-ring signal detection ensures a full two-dimensional view aperture for accurate image reconstruction. Using cylindrically focused array elements, RC-PACT can image a thin cross section with 0.10 to 0.25 mm in-plane resolutions and 1.6 s/frame acquisition time. By translating the mouse along the elevational direction, RC-PACT provides a series of cross-sectional images of the brain, liver, kidneys, and bladder.