In human prostate to bone metastases and in a novel rodent model that recapitulates prostate tumor-induced osteolytic and osteogenic responses, we found that osteoclasts are a major source of the proteinase, matrix metalloproteinase (MMP)-9. Because MMPs are important mediators of tumor-host communication, we tested the effect of host-derived MMP-9 on prostate tumor progression in the bone. To this end, immunocompromised mice that were wild-type or null for MMP-9 received transplants of osteolytic/osteogenic-inducing prostate adenocarcinoma tumor tissue to the calvaria. Surprisingly, we found that that host MMP-9 significantly contributed to prostate tumor growth without affecting prostate tumor-induced osteolytic or osteogenic change as determined by microcomputed tomography, microsingle-photon emission computed tomography, and histomorphometry. Subsequent studies aimed at delineating the mechanism of MMP-9 action on tumor growth focused on angiogenesis because MMP-9 and osteoclasts have been implicated in this process. We observed (a) significantly fewer and smaller blood vessels in the MMP-9 null group by CD-31 immunohistochemistry; (b) MMP-9 null osteoclasts had significantly lower levels of bioavailable vascular endothelial growth factor-A 164 ; and (c) using an aorta sprouting assay, conditioned media derived from wild-type osteoclasts was significantly more angiogenic than conditioned media derived from MMP-9 null osteoclasts. In conclusion, these studies show that osteoclast-derived MMP-9 affects prostate tumor growth in the bone microenvironment by contributing to angiogenesis without altering prostate tumor-induced osteolytic or osteogenic changes. Mol Cancer Res; 8(4); 459-70. ©2010 AACR.

The majority of breast cancer and prostate cancer patients with metastatic disease will go on to develop bone metastases, which contribute largely to patient morbidity and mortality. Numerous small animal models of cancer metastasis to bone have been developed in order to study tumorinduced bone destruction, but the advancement of imaging modalities utilized for these models has lagged significantly behind clinical imaging. Therefore, there is a significant need for improvements to live small animal imaging, particularly when obtaining high resolution images for longitudinal quantitative analyses. Recently, live animal micro-Computed Tomography (μCT) has gained popularity due to the ability to obtain high resolution, 3-dimensional images. However, the utility of μCT in bone metastasis models has been limited to end-point analyses due to offtarget radiation effects on tumor cells. We hypothesized that live animal in vivo μCT can be utilized to perform reproducible and quantitative longitudinal analyses of bone volume in tumor bearing mice, particularly in a drug treatment model of breast cancer metastasis to bone. To test this hypothesis we utilized the MDA-MB-231 osteolytic breast cancer model in which the tumor cells are inoculated directly into the tibia of athymic nude mice and imaged mice weekly by Faxitron (radiography), Imtek μCT (in vivo), and Maestro (GFP-imaging). Ex-vivo μCT and histology were performed at end-point for validation. After establishing a high resolution scanning protocol for the Imtek CT, we determined whether clear, measurable differences in bone volume were detectable in mice undergoing bisphosphonate drug treatments. We found that in vivo μCT can be used to obtain quantifiable and longitudinal images of the progression of bone destruction over time without altering tumor cell growth. Additionally, we found that we could detect lesions as early as week one and that this approach could be used to monitor the effect of drug treatment on bone. Taken together, these data indicate in vivo μCT is an effective and reproducible method Corresponding Author: Julie A. Sterling, PhD, Vanderbilt Center for Bone Biology, 2215B Garland Avenue, 1235 MRBIV, Nashville, TN 37232, P. 1+ (615) 322-4364 F. 1+ (615) 343-2611, julie.sterling@vanderbilt.edu. * These authors contributed equally to this work.Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errorsmaybe discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptBone. Author manuscript; available in PMC 2012 January 1. BackgroundNearly 70% of breast cancer and 90% of prostate cancer patients with metastatic disease will develop bone meta...

We present an initial evaluation of a mechanically-cooled, high-purity germanium double-sided strip detector as a potential gamma camera for small-animal SPECT. It is 90 mm in diameter and 10 mm thick with two sets of 16 orthogonal strips that have a 4.5 mm width with a 5 mm pitch. We found an energy resolution of 0.96% at 140 keV, an intrinsic efficiency of 43.3% at 122 keV and a FWHM spatial resolution of approximately 1.5 mm. We demonstrated depth-of-interaction estimation capability through comparison of pinhole acquisitions with a point source on and off axis. Finally, a flood-corrected-flood image exhibited a strip-level uniformity of less than 1%. This high-purity germanium offers many desirable properties for small-animal SPECT.

We present an initial evaluation of a mechanically cooled, high-purity germanium double-sided strip detector as a potential gamma camera for small-animal SPECT. It is 90 mm in diameter and 10 mm thick with two sets of 16 orthogonal strips that have a 4.75 mm width with a 5 mm pitch. A sub-strip interpolation method is used to bin the data at a pixel size of 0.53mm x 0.53mm, while it is also possible to estimate the depth of interaction based on CFD time differences between the anode and cathode. The system has an energy resolution of 0.92% at 140 keY and an intrinsic efficiency of 55.40% at 122 keY.Simulations suggest that increases in the efficiency should be possible by altering signal processing to include Compton events in which charge is collected on more than one strip. Integral uniformity in the central field of view for strips was found to be less than 1 % in a flood-corrected flood while pixel-level uniformity was 2.98%. Due to the excellent energy resolution, the presence of a scattering medium did not greatly alter the FWHM or FWTM of a pinhole projection when compared to an acquisition without a scattering medium. This high-purity germanium system offers many desirable properties for small animal SPECT.

Myocardial blood flow and myocardial blood flow reserve (MBFR) measurements are often used clinically to quantify coronary microvascular function. Developing imaging-based methods to measure MBFR for research in mice would be advantageous for evaluating new treatment methods for coronary microvascular disease, yet this is more challenging in mice than in humans. This work investigates microSPECT's quantitative capabilities of cardiac imaging by utilizing a multipart cardiac phantom and applying a known kinetic model to synthesize kinetic data from static data, allowing for assessment of kinetic modeling accuracy. The phantom was designed with four main components: two left-ventricular (LV) myocardial sections and two LV blood-pool sections, sized for end-systole and end-diastole. Each section of the phantom was imaged separately while acquiring list-mode data. These static, separate-compartment data were manipulated into synthetic dynamic data using a kinetic model representing the myocardium and blood-pool activity concentrations over time and then combined into a set of dynamic image frames and reconstructed. Regions of interest were drawn on the resulting images, and kinetic parameters were estimated. This process was performed for three tracer uptake values (K 1), three myocardial wall thicknesses, 10 filter parameters, and 20 iterations for 25 noise ensembles. The degree of filtering and iteration number were optimized to minimize the root mean-squared error (RMSE) of K 1 values, with the largest number of iterations and minimal filtering yielding the lowest error. Using the optimized parameters, K 1 was determined with reasonable error (~3% RMSE) over all wall thicknesses and K 1 input values. This work demonstrates that accurate and precise measurements of K 1 are possible for the U-SPECT+ system used in this study, for several different uptake rates and LV dimensions. Additionally, it allows for future investigation utilizing other imaging systems, including PET studies with any radiotracer, as well as with additional phantom parts containing lesions.

In pinhole SPECT, multi-pinhole collimators can increase sensitivity but may lead to projection overlap, or multiplexing, which can cause image artifacts. In this work we explore whether a stacked-detector configuration with a germanium and a silicon detector, used with 123I (27–32, 159 keV), where little multiplexing occurs in the Si projections, can reduce image artifacts caused by highly-multiplexed Ge projections. Simulations are first used to determine a reconstruction method that combines the Si and Ge projections to maximize image quality. Next, simulations of different pinhole configurations (varying projection multiplexing) in conjunction with digital phantoms are used to examine whether additional Si projections mitigate artifacts from the multiplexing in the Ge projections. Reconstructed images using both Si and Ge data are compared to those using Ge data alone. Normalized mean-square error and normalized standard deviation provide a quantitative evaluation of reconstructed images’ error and noise, respectively, and are used to evaluate the impact of the additional non-multiplexed data on image quality. For a qualitative comparison, the differential point response function is used to examine multiplexing artifacts. Results show that in cases of highly-multiplexed Ge projections, the addition of low-multiplexed Si projections helps to reduce image artifacts both quantitatively and qualitatively.

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Advances in fabrication techniques, electronics, and mechanical cooling systems have given rise to germanium detectors suitable for biomedical imaging. We are developing a small-animal SPECT system that uses a double-sided Ge strip detector. The detector’s excellent energy resolution may help to reduce scatter and simplify processing of multi-isotope imaging, while its ability to measure depth of interaction has the potential to mitigate parallax error in pinhole imaging. The detector’s energy resolution is <1% FWHM at 140 keV and its spatial resolution is approximately 1.5 mm FWHM. The prototype system described has a single-pinhole collimator with a 1-mm diameter and a 70-degree opening angle with a focal length variable between 4.5 and 9 cm. Phantom images from the gantry-mounted system are presented, including the NEMA NU-2008 phantom and a hot-rod phantom. Additionally, the benefit of energy resolution is demonstrated by imaging a dual-isotope phantom with 99mTc and 123I without cross-talk correction.