Multi-modality imaging provides coregistered PET-CT and SPECT-CT images; however such multi-modality workflows usually consist of sequential scans from the individual imaging components for each modality. This typical workflow may result in long scan times limiting throughput of the imaging system. Conversely, acquiring multi-modality data simultaneously may improve correlation and registration of images, improve temporal alignment of the acquired data, increase imaging throughput, and benefit the scanned subject by minimizing time under anesthetic. In this work, we demonstrate the feasibility and procedure for modifying a commercially available preclinical SPECT-CT platform to enable simultaneous SPECT-CT acquisition. We also evaluate the performance of simultaneous SPECT-CT tomographic imaging with this modified system. Performance was accessed using a (57)Co source and image quality was evaluated with (99m)Tc phantoms in a series of simultaneous SPECT-CT scans.

In this work, a method of generating normalization maps by scanning a large uniform cylindrical object in standard tomography mode (with the collimator on) has been investigated. This method may have several advantages over point-source approaches: First, since the object is not attached to the collimator, the normalization map generated may be less sensitivity to the geometric changes than the point-source-atpinhole approach. Second, it represents the typical photon incident angles during imaging. Third, it can be applied to single-pinhole and multi-pinhole collimators. Combined with the point-source normalization at 360 mm distance, a normalization correction map (to correct for the 360 mm point-source normalization) can be generated for the specific isotope and collimator and thus applied to different scanners of the same type.

A previously developed method derives co-registration parameters from PET and CT images of a four-point-source calibration phantom by manually adjusting the offsets and orientation of the CT image to achieve alignment with the PET image in a graphic viewer. This manual process is tedious and can be inaccurate, especially when rotational offsets exist. An automated segmentation method has been developed, based on thresholding and application of constraints on the sizes of point sources in the images. After point sources are identified on PET and CT images, co-registration is performed using an analytic rigid-body registration algorithm which is based on singular value decomposition and minimization of the co-registration error. The co-registration parameters thus derived can then be applied to co-register other PET and CT images from the same system. Twenty PET-CT images of the calibration phantom at various locations and/or orientations were obtained on a Siemens Inveon® Multi-Modality scanner. We tested the use of from 1 to 10 data sets to derive the co-registration parameters, and found that the co-registration accuracy improves with increasing number of data sets until it stabilizes. Co-registration of PET-CT images with an accuracy of 0.33±0.11 mm has been achieved by this method on the Inveon Multi-Modality scanner.

We recently reported a numerical ray-tracing algorithm for calculating the point-spread function (PSF) used in 3-D ordered subsets expectation maximization (OSEM) reconstruction of single and multi-pinhole collimated single photon emission computed tomography (SPECT) images. In this work, we evaluated the performance of our PSF reconstruction method with and without X-ray CT-based attenuation correction (AC) and dual energy window scatter correction (SC). X-ray CT data was acquired to create the attenuation maps. SPECT data was acquired using 99mTc phantoms and 5-pinhole tungsten collimators with 1.0 mm diameter pinholes. With no corrections applied, an axial image slice of a 3 cm diameter cylinder uniformly filled with mTc showed a 13% dip near the center of the phantom. When AC and SC were applied, the cross-section through an axial slice showed a desirable flattened profile that dipped only 3%. We also scanned a mouse with 99mTc implantable sources that had negligible self-attenuation. The sources were first scanned in air for calibration. Our results show that the reconstructed SPECT images with no corrections underestimated the activity for each mTc implanted source by 12% on average, while the image with AC and SC underestimated the activity by only 3.3% on average. We repeated all of the experiments with 125I phantoms but did not apply SC to the 125I data. With no correction applied, an axial slice of a 3 cm diameter cylinder uniformly filled with 125I dipped 25 % near the center of the phantom. After applying AC, the 125I image profile no longer dipped but rather was overcorrected by 4.5%. Similarly, the reconstructed image of the 125I implants with no correction underestimated the activity of each source by 23% on average, while the 125I image with AC overestimated the activity in the sources by 4.6% on average. These results have shown that our PSF- - reconstruction method with CT-based attenuation correction improved the quantitative accuracy of SPECT images for representative 99mTc and 125I studies.

The Quicksilver event processing module (EPM) designed for the Siemens Inveon Dedicated PET (Positron Emission Tomography) preclinical scanner, has been leveraged in the development of a new SPECT (Single Photon Emission Computed Tomography) EPM module. This new module is used in Inveon SPECT systems and provides 16 channels of high speed data acquisition and event processing functions. Fifteen of these channels are used for processing 7 X signals, 7 Y signals and a SUM signal all received from the SPECT detector electronics. Custom mixed-signal CMOS ASICs and high speed ADCs are utilized to provide the front-end analog portion of the data acquisition. A high performance FPGA provides the digital portion of the data acquisition running at 100 MHz and the subsequent event processing. This FPGA also provides multiple high speed serial data channels for external interconnection. These interconnections allow the module to be replicated as needed in a distributed parallel processing architecture for flexible, high performance SPECT imaging. The module also provides controllable high voltage needed to bias the SPECT detectors. A four head Nal(Tl) based SPECT system is currently being built using one SPECT EPM per SPECT head.

Multi-pinhole SPECT collimators can provide sub-millimeter resolution and improved sensitivity over single-pinhole and parallel-beam collimators. Attenuation and scatter will degrade the quantitative accuracy of reconstruction for lower energy emitters like I-125 and therefore both effects should be accounted for during reconstruction. We implemented an OSEM MAP reconstruction which incorporated attenuation, scatter and detector intrinsic resolution for a multi-pinhole detector designed for whole-body mouse imaging. The ray- driven projector/backprojector implemented considerably reduced the calculation of attenuation factors and decreased reconstruction time compared to a voxel-driven approach. The multi-pinhole SPECT system simulated consists of 2 or 4 cameras, with a 5-pinhole collimator plate for each. The attenuation map would be obtained from a CT system mounted on the same gantry. Scatter is estimated from scatter windows using a triple energy window (TEW) method and applied during the iterative reconstruction. A quadratic smoothness prior is implemented to control noise. Simulations with the MOBY mouse phantom show that modeling of the pinhole sensitivity, attenuation and detector intrinsic resolution results in a more accurate reconstruction. Preliminary Monte Carlo simulations showed the importance of determining and correcting the attenuation and scatter for I-125 imaging. Further investigations will be performed towards accurate estimation of the point-spread-function or sensitivity model of the multi-pinhole collimator plate.

Summary form only given. In recent years, fluorescence microscopy and constructed reporter strains have been applied to investigate the stochastic behavior of gene expression in single cells. While many of these studies have focused on the magnitude of the fluctuations as measured by variance, a great deal of additional information concerning the timing of the fluctuations is contained in the autocorrelation function. Here we calibrate a stochastic model of gene expression that explicitly accounts for the effects of intrinsic and extrinsic noise using comparisons of the experimental and simulated autocorrelation function as basis of the goodness of fit. The experimental data set includes unregulated and negative auto regulation cases of similar gene circuits. The calibration process is computationally demanding because it requires many evaluations of the stochastic simulation model. We demonstrate how a combination of computational techniques can be employed to make the problem tractable. The calibrated model demonstrates how feedback affects the manner in which extrinsic noise sources at the transcription and translation level are propagated through the circuit

A new detector for single photon emission computed tomography (SPECT) has been developed for the Siemens microCATreg II and Inveon Multimodality preclinical imaging systems. The detector provides an active imaging area of 15 cm times 15 cm. We review the design of this new SPECT detector and present some key performance characteristics. Integral and differential uniformity were 3.7% and 3.0%, respectively. Mean energy resolution for 99mTc (140 keV) was 12.5%. Sensitivity as high as 1400 cps/MBq was measured for 99mTc on a dual-detector system, and a spatial resolution of 0.7 mm (FWHM) was obtained using 0.5 mm single pinhole collimators. Additionally, we present data from representative preclinical SPECT studies acquired with single and multi-pinhole collimators and multiple isotopes. Reconstructed images demonstrate that this detector is capable of high-resolution SPECT for multimodality small animal imaging.

A new, highly versatile multi-modality small animal imaging platform, the Siemens Inveon Multimodality (MM) scanner, has been developed. This platform supports any combination of x-ray micro-CT, single-photon computed tomography (SPECT) and positron emission tomography (PET) modalities on a single gantry. Each modality within the system is designed to be configured with a different level of imaging performance based on the needs of the application. From a single control workstation, the end-user has the ability to tune the system configuration for each modality in terms of resolution, field-of-view (FOV), sensitivity, etc., as needed for the target application. The scanner platform is ergonomically designed to allow efficient access to the animal and employs a unique cable management device to allow more effective use of physiologic monitoring and anesthesia systems within a user-accessible x-ray shielded cabinet. The motivation for this versatile platform design is to accommodate a wide range of multi-modality imaging applications from mouse to small primate, each with performance parameters that can be tuned as driven by the target anatomy or biological process being studied within the animal.

We report four-probe I–V measurements on individual vertically aligned carbon nanofibers (VACNFs). These measurements were enabled by the fabrication of multiple Ti/Au ohmic contacts on individual fibers that exhibited resistance of only a few kilohms. These measurements demonstrate that VACNFs exhibit linear I–V behavior at room temperature, with a resistivity of approximately 4.2×10−3 Ω cm. Our measurements are consistent with a dominant transport mechanism of electrons traveling through intergraphitic planes in the VACNFs.

We report on the fabrication and electrical characterization of active nanoscale electronic devices using single vertically aligned carbon nanofibers (VACNFs). A rectifying behavior consistent with a 0.3 eV Schottky barrier was found. Experimental results indicate that a region of semiconducting SiC is formed directly beneath the VACNF during the growth process, creating the Schottky-barrier junction between this semiconductor material and the metallic carbon nanofibers.

We have fabricated active nanoscale electronic devices based on Vertically Aligned Carbon Nanofiber (VACNF) in a way that will be practical for large-scale manufacturing using conventional fabrication technology. The VACNFs are synthesized in a high-density Plasma-Enhanced Chemical Vapor Deposition (PECVD) process. that provides a high degree of control of the growth conditions and consequently, the resultant electronic properties. Rectifying devices containing metal-semiconductor (Schottky) junctions will be presented in this paper and we calculate the barrier height of about 300mV from the temperature sweep measurements. The VACNF devices can operate at current levels of I 100uA current without any sign of damage.

A dedicated small animal x-ray computed tomography system has been developed to screen mutagenized mice for anatomical phenotypes. The key components of the data acquisition instrumentation are described along with the system performance parameters. Image reconstruction, visualization and segmentation software algorithms are described. Two contrast media regimens are described and representative studies of mice with adipose, soft and skeletal tissue abnormalities are presented.