Combination of single-photon emission computed tomography and magnetic resonance imaging to track 111in-oxine-labeled human mesenchymal stem cells in neuroblastoma-bearing mice.

Homing is an inherent, complex, multistep process performed by cells such as human bone marrow mesenchymal stem cells (hMSCs) to travel from a distant location to inflamed or damaged tissue and tumors. This ability of hMSCs has been exploited as a tumor-targeting strategy in cell-based cancer therapy. The purpose of this study was to investigate the applicability of 111In-oxine for tracking hMSCs in vivo by combining single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI). 111In-labeled hMSCs (106 cells) were infused intraperitoneally in neuroblastoma-bearing mice, whereas a control group received a dose of free 111In-oxine. SPECT and MRI studies were performed 24 and 48 hours afterwards. Initially, the images showed similar activity in the abdomen in both controls and hMSC-injected animals. In general, abdominal activity decreases at 48 hours. hMSC-injected animals showed increased uptake in the tumor area at 48 hours, whereas the control group showed a low level of activity at 24 hours, which decreased at 48 hours. In conclusion, tracking 111In-labeled hMSCs combining SPECT and MRI is feasible and may be transferable to clinical research. The multimodal combination is essential to ensure appropriate interpretation of the images.

Chemoenzymatic radiosynthesis of 2-deoxy-2-[18F]fluoro-d-trehalose ([18F]-2-FDTre): A PET radioprobe for in vivo tracing of trehalose metabolism.

Trehalose analogues bearing fluorescent and click chemistry tags have been developed as probes of bacterial trehalose metabolism, but these tools have limitations with respect to in vivo imaging applications. Here, we report the radiosynthesis of the 18F-modified trehalose analogue 2-deoxy-2-[18F]fluoro-d-trehalose ([18F]-2-FDTre), which in principle can be used in conjunction with positron emission tomography (PET) imaging to allow in vivo imaging of trehalose metabolism in various contexts. A chemoenzymatic method employing the thermophilic TreT enzyme from Thermoproteus tenax was used to rapidly (15-20 min), efficiently (70% radiochemical yield; ≥ 95% radiochemical purity), and reproducibly convert the commercially available radiotracer 2-deoxy-2-[18F]fluoro-d-glucose ([18F]-2-FDG) into the target radioprobe [18F]-2-FDTre in a single step; both manual and automated syntheses were performed with similar results. Cellular uptake experiments showed that radiosynthetic [18F]-2-FDTre was metabolized by Mycobacterium smegmatis but not by various mammalian cell lines, pointing to the potential future use of this radioprobe for selective PET imaging of infections caused by trehalose-metabolizing bacterial pathogens such as M. tuberculosis.

Improving PET Quantification of Small Animal [68Ga]DOTA-Labeled PET/CT Studies by Using a CT-Based Positron Range Correction.

PURPOSE: Image quality of positron emission tomography (PET) tracers that emits high-energy positrons, such as Ga-68, Rb-82, or I-124, is significantly affected by positron range (PR) effects. PR effects are especially important in small animal PET studies, since they can limit spatial resolution and quantitative accuracy of the images. Since generators accessibility has made Ga-68 tracers wide available, the aim of this study is to show how the quantitative results of [68Ga]DOTA-labeled PET/X-ray computed tomography (CT) imaging of neuroendocrine tumors in mice can be improved using positron range correction (PRC). PROCEDURES: Eighteen scans in 12 mice were evaluated, with three different models of tumors: PC12, AR42J, and meningiomas. In addition, three different [68Ga]DOTA-labeled radiotracers were used to evaluate the PRC with different tracer distributions: [68Ga]DOTANOC, [68Ga]DOTATOC, and [68Ga]DOTATATE. Two PRC methods were evaluated: a tissue-dependent (TD-PRC) and a tissue-dependent spatially-variant correction (TDSV-PRC). Taking a region in the liver as reference, the tissue-to-liver ratio values for tumor tissue (TLRtumor), lung (TLRlung), and necrotic areas within the tumors (TLRnecrotic) and their respective relative variations (ΔTLR) were evaluated. RESULTS: All TLR values in the PRC images were significantly different (p < 0.05) than the ones from non-PRC images. The relative differences of the tumor TLR values, respect to the case with no PRC, were ΔTLRtumor 87 ± 41 % (TD-PRC) and 85 ± 46 % (TDSV-PRC). TLRlung decreased when applying PRC, being this effect more remarkable for the TDSV-PRC method, with relative differences respect to no PRC: ΔTLRlung = - 45 ± 24 (TD-PRC), - 55 ± 18 (TDSV-PRC). TLRnecrotic values also decreased when using PRC, with more noticeable differences for TD-PRC: ΔTLRnecrotic = - 52 ± 6 (TD-PRC), - 48 ± 8 (TDSV-PRC). CONCLUSION: The PRC methods proposed provide a significant quantitative improvement in [68Ga]DOTA-labeled PET/CT imaging of mice with neuroendocrine tumors, hence demonstrating that these techniques could also ameliorate the deleterious effect of the positron range in clinical PET imaging.

Functional segmentation of dynamic PET studies: Open source implementation and validation of a leader-follower-based algorithm.

UNLABELLED: We present a novel segmentation algorithm for dynamic PET studies that groups pixels according to the similarity of their time-activity curves. METHODS: Sixteen mice bearing a human tumor cell line xenograft (CH-157MN) were imaged with three different (68)Ga-DOTA-peptides (DOTANOC, DOTATATE, DOTATOC) using a small animal PET-CT scanner. Regional activities (input function and tumor) were obtained after manual delineation of regions of interest over the image. The algorithm was implemented under the jClustering framework and used to extract the same regional activities as in the manual approach. The volume of distribution in the tumor was computed using the Logan linear method. A Kruskal-Wallis test was used to investigate significant differences between the manually and automatically obtained volumes of distribution. RESULTS: The algorithm successfully segmented all the studies. No significant differences were found for the same tracer across different segmentation methods. Manual delineation revealed significant differences between DOTANOC and the other two tracers (DOTANOC - DOTATATE, p=0.020; DOTANOC - DOTATOC, p=0.033). Similar differences were found using the leader-follower algorithm. CONCLUSION: An open implementation of a novel segmentation method for dynamic PET studies is presented and validated in rodent studies. It successfully replicated the manual results obtained in small-animal studies, thus making it a reliable substitute for this task and, potentially, for other dynamic segmentation procedures.

Meningiomas: a comparative study of 68Ga-DOTATOC, 68Ga-DOTANOC and 68Ga-DOTATATE for molecular imaging in mice.

PURPOSE: The goal of this study was to compare the tumor uptake kinetics and diagnostic value of three (68)Ga-DOTA-labeled somatostatin analogues ((68)Ga-DOTATOC, (68)Ga-DOTANOC, and (68)Ga-DOTATATE) using PET/CT in a murine model with subcutaneous meningioma xenografts. METHODS: The experiment was performed with 16 male NUDE NU/NU mice bearing xenografts of a human meningioma cell line (CH-157MN). (68)Ga-DOTATOC, (68)Ga-DOTANOC, and (68)Ga-DOTATATE were produced in a FASTLab automated platform. Imaging was performed on an Argus small-animal PET/CT scanner. The SUVmax of the liver and muscle, and the tumor-to-liver (T/L) and tumor-to-muscle (T/M) SUV ratios were computed. Kinetic analysis was performed using Logan graphical analysis for a two-tissue reversible compartmental model, and the volume of distribution (Vt) was determined. RESULTS: Hepatic SUVmax and Vt were significantly higher with (68)Ga-DOTANOC than with (68)Ga-DOTATOC and (68)Ga-DOTATATE. No significant differences between tracers were found for SUVmax in tumor or muscle. No differences were found in the T/L SUV ratio between (68)Ga-DOTATATE and (68)Ga-DOTATOC, both of which had a higher fraction than (68)Ga-DOTANOC. The T/M SUV ratio was significantly higher with (68)Ga-DOTATATE than with (68)Ga-DOTATOC and (68)Ga-DOTANOC. The Vt for tumor was higher with (68)Ga-DOTATATE than with (68)Ga-DOTANOC and relatively similar to that of (68)Ga-DOTATOC. CONCLUSIONS: This study demonstrates, for the first time, the ability of the three radiolabeled somatostatin analogues tested to image a human meningioma cell line. Although Vt was relatively similar with (68)Ga-DOTATATE and (68)Ga-DOTATOC, uptake was higher with (68)Ga-DOTATATE in the tumor than with (68)Ga-DOTANOC and (68)Ga-DOTATOC, suggesting a higher diagnostic value of (68)Ga-DOTATATE for detecting meningiomas.