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Background: Fucosyl-GM1 (FucGM1) is a monosialoganglioside highly expressed in 50%-70% of small cell lung cancer (SCLC) cells, supporting it as a potential biomarker. BMS-986012 is a nonfucosylated, first-in-class, fully human immunoglobulin G1 monoclonal antibody that binds to FucGM1 with high affinity and specificity. Understanding how FucGM1+ tumor expression correlates with response to BMS-986012 may improve patient selection and therapeutic efficacy. Objective: Evaluate ability of imaging agents built on BMS-986012 to detect tumor FucGM1 expression. Methods: BMS-986012 was labeled with a near-infrared fluorophore. Binding to human H520 (FucGM1−) and DMS79 (FucGM1+) xenografts was assessed in vivo via optical imaging. BMS-986012 was labeled with deferoxamine and radiolabeled to produce 89Zr-BMS-986279, which was evaluated in vitro with H520 and DMS79 cells. Tracer distribution and tumor accumulation was assessed by positron emission tomography (PET) imaging in mice bearing bilateral H520 and DMS79 xenografts and analyzed with ex vivo autoradiography (ARG). Results: Optical imaging with fluorescent BMS-986012 showed statistically significant accumulation in DMS79 vs H520 tumors at all time points (P Conclusions: In vitro cell binding, in vivo fluorescence and PET imaging, and ex vivo ARG studies demonstrated that 89Zr-BMS-986279 was sensitive and specific for detecting FucGM1 expression in tumor cells. Specificity to the intended target in animal disease models coupled with kinetics typical of antibody-based tracers further support the utility of 89Zr-BMS-986279 as a potential FucGM1 imaging agent. A phase 2 study is evaluating safety and efficacy of BMS-986012 combined with carboplatin, etoposide, or nivolumab in patients with newly diagnosed extensive-stage SCLC (NCT04702880). Citation Format: R. Adam Smith, Erin L. Cole, Andrea Olga Shorts, Thomas Petrone, Joonyoung Kim, Daniel Cohen, Paul Morin, Samuel J. Bonacorsi, Patrick L. Chow. Preclinical assessment of imaging agents for identification of fucosyl-GM1 expression in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2479.

Major depressive disorder is a leading cause of disability globally. Improvements in the efficacy of antidepressant therapy are needed as a high proportion (>40%) of individuals with major depressive disorder fail to respond adequately to current treatments. The non-selective N-methyl-D-aspartate receptor channel blocker, (±)-ketamine, has been reported to produce a rapid and long-lasting antidepressant response in treatment-resistant major depressive disorder patients, which provides a unique opportunity for investigation of mechanisms that mediate its therapeutic effect. Efforts have also focused on the development of selective N-methyl-D-aspartate receptor subtype 2B antagonists which may retain antidepressant activity but have lower potential for dissociative/psychotomimetic effects. In the present study, we examined the central nervous system effects of acute, intravenous administration of (±)-ketamine or the N-methyl-D-aspartate receptor subtype 2B antagonist, traxoprodil, in awake rats using pharmacological magnetic resonance imaging. The study contained five treatment groups: vehicle, 3 mg/kg (±)-ketamine, and three doses of traxoprodil (0.3 mg/kg, 5 mg/kg, and 15 mg/kg). Non-linear model fitting was performed on the temporal hemodynamic pharmacological magnetic resonance imaging data to generate brain activation maps as well as regional responses based on blood oxygen level dependent signal changes for group analysis. Traxoprodil at 5 mg/kg and 15 mg/kg produced a dose-dependent pharmacological magnetic resonance imaging signal in rat forebrain regions with both doses achieving >80% N-methyl-D-aspartate receptor subtype 2B occupancy determined by ex vivo [3H]Ro 25-6981 binding. The middle dose of traxoprodil (5 mg/kg) generated region-specific activations in medial prefrontal cortex, ventral orbital cortex, and anterior cingulate cortex whereas the high dose (15 mg/kg) produced a widespread pharmacological magnetic resonance imaging response in both cortical and subcortical brain regions which was similar to that produced by (±)-ketamine (3 mg/kg, intravenous).

The programmed death protein (PD-1) and its ligand (PD-L1) play critical roles in a checkpoint pathway cancer cells exploit to evade the immune system. A same-day PET imaging agent for measuring PD-L1 status in primary and metastatic lesions could be important for optimizing drug therapy. Herein, we have evaluated the tumor targeting of an anti-PD-L1 adnectin after 18F-fluorine labeling. Methods: An anti-PD-L1 adnectin was labeled with 18F in 2 steps. This synthesis featured fluorination of a novel prosthetic group, followed by a copper-free click conjugation to a modified adnectin to generate 18F-BMS-986192. 18F-BMS-986192 was evaluated in tumors using in vitro autoradiography and PET with mice bearing bilateral PD-L1-negative (PD-L1(-)) and PD-L1-positive (PD-L1(+)) subcutaneous tumors. 18F-BMS-986192 was evaluated for distribution, binding, and radiation dosimetry in a healthy cynomolgus monkey. Results:18F-BMS-986192 bound to human and cynomolgus PD-L1 with a dissociation constant of less than 35 pM, as measured by surface plasmon resonance. This adnectin was labeled with 18F to yield a PET radioligand for assessing PD-L1 expression in vivo. 18F-BMS-986192 bound to tumor tissues as a function of PD-L1 expression determined by immunohistochemistry. Radioligand binding was blocked in a dose-dependent manner. In vivo PET imaging clearly visualized PD-L1 expression in mice implanted with PD-L1(+), L2987 xenograft tumors. Two hours after dosing, a 3.5-fold-higher uptake (2.41 ± 0.29 vs. 0.82 ± 0.11 percentage injected dose per gram, P < 0.0001) was observed in L2987 than in control HT-29 (PD-L1(-)) tumors. Coadministration of 3 mg/kg ADX_5322_A02 anti-PD-L1 adnectin reduced tumor uptake at 2 h after injection by approximately 70%, whereas HT-29 uptake remained unchanged, demonstrating PD-L1-specific binding. Biodistribution in a nonhuman primate showed binding in the PD-L1-rich spleen, with rapid blood clearance through the kidneys and bladder. Binding in the PD-L1(+) spleen was reduced by coadministration of BMS-986192. Dosimetry estimates indicate that the kidney is the dose-limiting organ, with an estimated human absorbed dose of 2.20E-01 mSv/MBq. Conclusion:18F-BMS-986192 demonstrated the feasibility of noninvasively imaging the PD-L1 status of tumors by small-animal PET studies. Clinical studies with 18F-BMS-986192 are under way to measure PD-L1 expression in human tumors.

Cancer immunotherapy, unlike traditional cytotoxic chemotherapeutic treatments, engages the immune system to identify cancer cells and stimulate immune responses. The Programmed Death-1 (PD-1) protein is an immunoinhibitory receptor expressed by activated cytotoxic T-lymphocytes (CTL) that seek out and destroy cancer cells. Multiple cancer types express and upregulate the Programmed Death-Ligand 1 (PD-L1) and 2 (PD-L2) which bind to PD-1 as an immune escape mechanism. Nivolumab is a fully human IgG4 anti-PD-1 monoclonal antibody (mAb) approved for treatment of multiple cancer types. This study reports the preparation and in vivo evaluation of 89Zr labeled nivolumab in healthy non-human primates (NHP) as a preliminary study of biodistribution and clearance. The radiochemical and in vivo stabilities of the 89Zr complex were shown to be acceptable for imaging. Three naive NHPs were intravenously injected with tracer only or tracer co-injected with nivolumab followed by co-registered by positron emission tomography (PET) and magnetic resonance imaging (MRI), acquired for eight days following injection. Image-derived standardized uptake values (SUV) were quantified by region of interest (ROI) analysis. Radioactivity in the spleen was significantly reduced by addition of excess nivolumab compared to the tracer only study at all imaging time points. Liver uptake of the radiotracer was consistent as a clearance organ with minimal signal from other tissues: lung, muscle, brain, heart, and kidney. The results indicate specific biodistribution to the spleen, which can be blocked by co-administration of excess nivolumab. Distribution to other organs is consistent with elimination pathways of antibodies, with primary clearance through the liver.

Rationale and Aim: Studies linking the lysophosphatidic acid 1 receptor (LPA1) to the pathogenesis of lung and kidney fibrosis have identified LPA1 as a potential clinical target for idiopathic pulmonary fibrosis (IPF). LPA1 antagonism has shown efficacy in a Phase 2 clinical IPF trial. Here we report the evaluation of BMS-986327 as a PET ligand to detect LPA1 expression and assess engagement and occupancy of LPA1-targeted drugs. Methods: BMS-986327 binding was measured in competition with LPA1 antagonists in a whole-cell binding assay. PET imaging was performed in wild-type (WT) and pulmonary fibrosis (PF) rat models to determine target expression and drug target engagement. Similar PET studies were carried out in healthy non-human primates (NHPs) as a prelude to clinical studies. Results: In vitro studies showed tracer binding to LPA1 and concentration-dependent inhibition with LPA1 antagonists. In vivo, preferential tracer accumulation was measured in the lungs of PF rats compared to WT controls. Drug competition studies showed a correlation between tracer signal in the lungs of PF rats and the plasma concentration of LPA1 antagonist. PET studies in NHPs confirmed lung tracer localization and dose-dependent blockade with LPA1 antagonist, with test-retest variability within typical limits of PET. Conclusions: In vitro and in vivo studies demonstrated specific binding of BMS-986327 to LPA1. Increased lung tracer accumulation in PF compared to WT animals and displacement with LPA1 antagonists showed the ability of BMS-986327 to assess LPA1 expression and drug target engagement in vivo in both rat and NHP models. Minimal test-retest variability supports the translatability of this tracer to clinical study.

Cancer immunotherapy, unlike traditional cytotoxic chemotherapeutic treatments, engages the immune system to identify cancer cells and stimulate immune responses. The Programmed Death-1 (PD-1) protein is an immunoinhibitory receptor expressed by activated cytotoxic T-lymphocytes (CTL) that seek out and destroy cancer cells. Multiple cancer types express and upregulate the Programmed Death-Ligand 1 (PD-L1) and 2 (PD-L2) which bind to PD-1 as an immune escape mechanism. Nivolumab is a fully human IgG4 anti-PD-1 monoclonal antibody (mAb) approved for treatment of multiple cancer types. This study reports the preparation and in vivo evaluation of

The ability to reproducibly and repeatedly image rodents in noninvasive imaging systems, such as small-animal positron emission tomography (PET) and computed tomography (CT), requires a reliable method for anesthetizing, positioning, and heating animals in a simple reproducible manner. In this paper, we demonstrate that mice and rats can be reproducibly and repeatedly imaged using an imaging chamber designed to be rigidly mounted on multiple imaging systems.Mouse and rat imaging chambers were made of acrylic plastic and aluminum. MicroCT scans were used to evaluate the positioning reproducibility of the chambers in multimodality and longitudinal imaging studies. The ability of the chambers to maintain mouse and rat body temperatures while anesthetized with gas anesthesia was also evaluated.Both the mouse and rat imaging chambers were able to reproducibly position the animals in the imaging systems with a small degree of error. Placement of the mouse in the mouse imaging chamber resulted in a mean distance of 0.23 mm per reference point in multimodality studies, whereas for longitudinal studies the mean difference was 1.11 mm. The rat chamber resulted in a mean difference of 0.46 mm in multimodality studies and a mean difference of 4.31 mm in longitudinal studies per reference point. The chambers maintained rodent body temperatures at the set point temperature of 38 degrees C.The rodent imaging chambers were able to reproducibly position rodents in tomographs with a small degree of variability and were compatible with routine use. The embedded anesthetic line and heating system was capable of maintaining the rodent's temperature and anesthetic state, thereby enhancing rodent health and improving data collection reliability.

The X-ray spectrum from a small-animal computed tomography (CT) device directly influences the dose delivered to the animal as well as the image quality. For any given imaging task, the spectrum needs to be optimized. The aim of this study is to present a model of a small animal microCT X-ray source and to calculate practical spectra for different anode and filter combinations by using the Monte Carlo method. The GATE simulation package was used for this work. The X-ray source of the MicroCAT II scanner was modeled as a tungsten enclosure containing the X-ray tube with dielectric oil and a thin carbon exit window. The anode was a tungsten or molybdenum cylinder block tilted with respect to the electron-beam axis. Beam filtration was achieved through a disk of variable thickness and composition positioned at the exit window. Photon detection was performed with a thick (1 cm) cylindrical tungsten plate (20 cm diameter). Simulated spectra were compared with spectra measured with a CdTe detector for three beams: 50, 70 and 80 kVp with 2 mm of aluminum filtration. There was a reasonable agreement between measurements and calculations. Identified features of the measured spectra were: K absorption edges of Cd and Te (from the detector itself) and characteristic X-rays from Te (Kα and Kβ) and possibly Sb (Kα). Discrepancies between simulations and measurements can be attributed to elements that have been left out of simulations, imperfect detector alignment, and uncertainty in elemental composition of simulated materials. The Monte Carlo method is a convenient and fast tool allowing the calculation of spectra possessing the essential features of real spectra. These and other spectra will be used in future work to study the influence of X-ray spectrum on dose and image quality for various X-ray CT system configurations.

Many research institutions have a full suite of preclinical tomographic scanners to answer biomedical questions in vivo. Routine multi-modality imaging requires robust registration of images generated by various tomographs. We have implemented a hardware registration method for preclinical imaging that is similar to that used in the combined positron emission tomography (PET)/computed tomography (CT) scanners in the clinic. We designed an imaging chamber which can be rigidly and reproducibly mounted on separate microPET and microCT scanners. We have also designed a three-dimensional grid phantom with 1288 lines that is used to generate the spatial transformation matrix from software registration using a 15-parameter perspective model. The imaging chamber works in combination with the registration phantom synergistically to achieve the image registration goal. We verified that the average registration error between two imaging modalities is 0.335 mm using an in vivo mouse bone scan. This paper also estimates the impact of image misalignment on PET quantitation using attenuation corrections generated from misregistered images. Our technique is expected to produce PET quantitation errors of less than 5%. The methods presented are robust and appropriate for routine use in high throughput animal imaging facilities.

Objectives Inhibition of the Programmed Death Ligand-1 (PD-L1)/PD-1 interaction allows for potent anti-tumor activity and antibodies that disrupt this interaction have been approved for the treatment of multiple cancer types. PD-L1 expression has been investigated clinically as a potential biomarker to predict response to anti-PD-1/PD-L1 therapy. BMS-986192, an Adnectin with high affinity and specificity for human PD-L1, was selected in vitro from a complex library. Here we report the discovery and first preclinical evaluation of [18F]BMS-986192 as a PET imaging agent to detect PD-L1 expression in vivo. Methods [18F]BMS-986192 was radiolabeled via copper-free click chemistry and assessed for its ability to detect PD-L1 expression. Tracer binding to human L2987 (PD-L1+) and HT-29 (PD-L1-) xenografts as well as human non-small cell lung cancer (NSCLC) tissue samples was assessed by autoradiography (ARG). Tracer binding was compared to PD-L1 expression assessed independently with anti-PD-L1 immunohistochemistry (IHC). In vivo performance of the tracer was also assessed by PET imaging in mice bearing bilateral L2987 and HT-29 xenografts, and tracer biodistribution was further assayed in these animals ex vivo by gamma counter. Finally, initial in vivo biodistribution and radiation dosimetry was measured by PET in cynomolgus monkey. Results ARG studies showed increased [18F]BMS-986192 total binding to PD-L1(+) L2987 xenograft compared to PD-L1(-) HT-29 xenograft tissue. Radiotracer binding was higher in all tested human NSCLC tissue samples compared to xenografts. Dose-dependent blockade was seen in all PD-L1(+) tissues co-incubated with cold BMS-986192, and binding was unaffected by co-incubation with cold non-PD-L1 binding control. Visual comparison of tracer binding aligns closely with PD-L1 IHC both spatially as well as in intensity. Preferential accumulation of [18F]BMS-986192 was noted in PD-L1(+) L2987 compared to PD-L1(-) HT-29 xenografts in tumor-bearing mice. PET studies in cynomolgus monkeys confirmed binding to PD-L1(+) tissue (e.g. spleen) with minimal nonspecific background signal exclusive of primary clearance organs. Radiation dosimetry of [18F]BMS-986192 indicates an estimated single administration dose limit of 6.2 mCi for an average human subject. Conclusions ARG, PET studies, and ex vivo measurements in rodent and cynomolgus monkey demonstrated sensitive and specific [18F]BMS-986192 binding to PD-L1. Low background signal in cynomolgus monkey in the context of endogenous PD-L1 expression further supports the potential of this tracer for sensitive detection of PD-L1(+) lesions in vivo. Radiation dosimetry suggests that [18F]BMS-986192 can be safely administered in human trials, with estimated absorbed radiation doses well within safe parameters for human administration. [18F]BMS-986192 has potential as a sensitive PD-L1 imaging agent for same-day imaging in patients. Citation Format: Ralph A. Smith, David Donnelly, Paul E. Morin, Dasa Lipovsek, Jochem Gokemeijer, Daniel Cohen, Joonyoung Kim, Adrienne Pena, Olufemi Adelakun, Xi-Tao Wang, Patrick Chow, Samuel J. Bonacorsi, Wendy Hayes. [18F]BMS-986192 as a novel PET imaging agent for assessment of PD-L1 expression in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 871. doi:10.1158/1538-7445.AM2017-871

The purpose of this work was to calculate radiation dose and its organ distribution in a realistic mouse phantom from micro-computed tomography (microCT) imaging protocols. CT dose was calculated using GATE and a voxelized, realistic phantom. The x-ray photon energy spectra used in simulations were precalculated with GATE and validated against previously published data. The number of photons required per simulated experiments was determined by direct exposure measurements. Simulated experiments were performed for three types of beams and two types of mouse beds. Dose-volume histograms and dose percentiles were calculated for each organ. For a typical microCT screening examination with a reconstruction voxel size of 200 μm, the average whole body dose varied from 80 mGy (at 80 kVp) to 160 mGy (at 50 kVp), showing a strong dependence on beam hardness. The average dose to the bone marrow is close to the soft tissue average. However, due to dose nonuniformity and higher radiation sensitivity, 5% of the marrow would receive an effective dose about four times higher than the average. If CT is performed longitudinally, a significant radiation dose can be given. The total absorbed radiation dose is a function of milliamperes-second, beam hardness, and desired image quality (resolution, noise and contrast). To reduce dose, it would be advisable to use the hardest beam possible while maintaining an acceptable contrast in the image.

Biological research in recent years has generated significant interest for in vivo small animal imaging technologies. 3D small animal X-ray computed tomography (CT) provides anatomical images with high spatial resolution and good bone-to-soft tissue contrast. Radiation doses to the subject can be significant when soft tissue contrast and high-resolution images are desired. We have used the MCNP Monte Carlo simulation, and calibrated thermoluminescent dosimeters (TLD's), in combination with high resolution X-ray spectra obtained with a cadmium zinc telluride (CZT) detector, to calculate the depth dependent dose in 3D high resolution X-ray CT. Three spectra (30 kVp with 0.25 mm of aluminum filtration, 40 kVp with 0.50 mm Al, and 50 kVp with 1.00 mm Al) were chosen as representative of soft, medium, and hard beams. MCNP was used to simulate the dose from these X-ray spectra incident upon a cylindrical mouse-sized phantom (2.54/spl times/6.1cm). The same phantom was also constructed from solid lucite material with thermo-luminescent dosimeters (TLD's) placed at the positions where we sampled the dose with MCNP. The maximum and minimum dose observed in this study is 19.7 /spl plusmn/ 1.7 cGy from the soft beam measured nearest the surface, and 5.2 /spl plusmn/ 0.1 cGy from the hard beam measured furthest from the source, for a typical data acquisition with 196 angles.

Attenuation correction is one of the important corrections required for quantitative positron emission tomography (PET). This work will compare the quantitative accuracy of attenuation correction using a simple global scale factor with traditional transmission-based methods acquired either with a small animal PET or a small animal x-ray computed tomography (CT) scanner. Two phantoms (one mouse-sized and one rat-sized) and two animal subjects (one mouse and one rat) were scanned in CTI Concorde Microsystem's MicroPET(R) Focus(TM) for emission and transmission data and in ImTek's MicroCAT(TM) II for transmission data. PET emission image values were calibrated against a scintillation well counter. Results indicate that the scale factor method of attenuation correction places the average measured activity concentration about the expected value, without correcting for the cupping artefact from attenuation. Noise analysis in the phantom studies with the PET-based method shows that noise in the transmission data increases the noise in the corrected emission data. The CT-based method was accurate and delivered low-noise images suitable for both PET data correction and PET tracer localization.

The microPET Focus is the latest generation microPET system dedicated to high-resolution animal imaging and incorporates several changes to enhance its performance. This study evaluated the basic performance of the scanner and compared it with the Primate (P4) and Rodent (R4) models.The system consists of 168 lutetium oxyorthosilicate (LSO) detectors arranged in 4 contiguous rings, with a 25.8-cm diameter and a 7.6-cm axial length. Each detector consists of a 12 x 12 LSO crystal array of 1.51 x 1.51 x 10.00 mm3 elements. The scintillation light is transmitted to position-sensitive photomultiplier tubes via optical fiber bundles. The system was evaluated for its energy and spatial resolutions, sensitivity, and noise equivalent counting rate. Phantoms and animals of varying sizes were scanned to evaluate its imaging capability.The energy resolution averages 18.5% for the entire system. Reconstructed image resolution is 1.3-mm full width at half maximum (FWHM) at the center of field of view (CFOV) and remains under 2 mm FWHM within the central 5-cm-diameter FOV in all 3 dimensions. The absolute sensitivity of the system is 3.4% at the CFOV for an energy window of 250-750 keV and a timing window of 10 ns. The noise equivalent counting-rate performance reaches 645 kcps for a mouse-size phantom using 250- to 750-keV and 6-ns settings. Emission images of a micro-Derenzo phantom demonstrate the improvement in image resolution compared with previous models. Animal studies exhibit the capability of the system in studying disease models using mouse, rat, and nonhuman primates.The Focus has significantly improved performance over the previous models in all areas evaluated. This system represents the state-of-the-art scintillator-based animal PET scanner currently available and is expected to advance the potential of small animal PET.

Imaging with Positron Emission Tomography (PET) requires compensation for attenuation of the annihilation photons in subject tissues. Although the magnitude of this correction for small subjects is significantly smaller than for humans, it Is important for a quantitatively accurate representation of the tracer distribution. Attenuation correction (AC) has been implemented on the Concorde microPET/spl reg/ P4 scanner using a Ge-68 point source (PS) that spirals through the field of view under computer control. Transmission (TX) scans of a rat-sized phantom were acquired with this PS and this tomograph by varying acquisition parameters including: acquisition mode (coincidence vs. singles), energy window, coincidence timing window, PS radius, PS activity, and acquisition time. We also evaluated the quality of post-injection TX images. Transmission data were processed by reconstruction of the log of the attenuation sinograms with 3D filtered backprojection. The attenuation coefficient images were subsequently analyzed with regions of interest in the uniform region of the phantom. Despite a significant amount of scatter contribution, singles data acquisition was found to have the best signal-to-noise ratio (SNR). We found that using higher PS activity or smaller PS radius resulted in a dramatic improvement in the SNR. A combination of both could lead to short acquisition times appropriate for TX imaging in a high throughput imaging facility. Attenuation correction sinograms were created by forward projecting through a smoothed TX image, in which the water-equivalent tissues were scaled to the appropriate /spl mu/-values. Noise levels in the corrected and uncorrected emission images indicate that no significant noise was introduced from the correction. A rat was imaged postinjection in the heart region. Singles TX images were used to create AC sinograms after emission contamination subtraction using a mock scan. The results are encouraging and demonstrate the feasibility of using PET TX images in AC.

MAP (maximum a posteriori) reconstructions of transmission images produce more accurate ACFs (attenuation correction factors) than smoothed division of blank and transmission scans and analytical methods. Also, for highly specific tracers, transmission images can provide useful anatomical cues for use in localizing structures and image coregistration. The resolution of MAP images reconstructed with a spatially invariant smoothing prior is known to be nonuniform. Spatially variant smoothing parameters are used to achieve uniform resolution throughout the transmission image. We also investigate the relationship between resolution and the global smoothing parameter through computer simulations. The resulting calibration curve can be used to select the smoothing parameter to achieve a desired spatial resolution. The tractability and feasibility of our method is demonstrated through an application to phantom transmission data collected using a Concorde P4 microPET system.