Publications (4)6.01 Total impact

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    ABSTRACT: Considering the high cost of dedicated small-animal positron emission tomography/computed tomography (PET/CT), an acceptable alternative in many situations might be clinical PET/CT. However, spatial resolution and image quality are of concern. The utility of clinical PET/CT for small-animal research and image quality improvements from super-resolution (spatial subsampling) were investigated. National Electrical Manufacturers Association (NEMA) NU 4 phantom and mouse data were acquired with a clinical PET/CT scanner, as both conventional static and stepped scans. Static scans were reconstructed with and without point spread function (PSF) modeling. Stepped images were postprocessed with iterative deconvolution to produce super-resolution images. Image quality was markedly improved using the super-resolution technique, avoiding certain artifacts produced by PSF modeling. The 2 mm rod of the NU 4 phantom was visualized with high contrast, and the major structures of the mouse were well resolved. Although not a perfect substitute for a state-of-the-art small-animal PET/CT scanner, a clinical PET/CT scanner with super-resolution produces acceptable small-animal image quality for many preclinical research studies.
    Molecular Imaging 06/2012; 11(3):210-9. DOI:10.2310/7290.2011.00041 · 1.96 Impact Factor
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    Frank P Difilippo · Sven L Gallo · Ryan S Klatte · Sagar Patel ·
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    ABSTRACT: The lesion detection performance of SPECT and PET scanners is most commonly evaluated with a phantom containing hollow spheres in a background chamber at a specified radionuclide contrast ratio. However, there are limitations associated with a miniature version of a hollow sphere phantom for small-animal SPECT and PET scanners. One issue is that the 'wall effect' associated with zero activity in the sphere wall and fill port causes significant errors for small diameter spheres. Another issue is that there are practical difficulties in fabricating and in filling very small spheres (<3 mm diameter). The need for lesion detection performance assessment of small-animal scanners has motivated our development of a micro-hollow sphere phantom that utilizes the principle of superposition. The phantom is fabricated by stereolithography and has interchangeable sectors containing hollow spheres with volumes ranging from 1 to 14 microL (diameters ranging from 1.25 to 3.0 mm). A simple 60 degrees internal rotation switches the positions of three such sectors with their corresponding background regions. Raw data from scans of each rotated configuration are combined and reconstructed to yield superposition images. Since the sphere counts and background counts are acquired separately, the wall effect is eliminated. The raw data are subsampled randomly prior to summation and reconstruction to specify the desired sphere-to-background contrast ratio of the superposition image. A set of images with multiple contrast ratios is generated for visual assessment of lesion detection thresholds. To demonstrate the utility of the phantom, data were acquired with a multi-pinhole SPECT/CT scanner. Micro-liter syringes were successful in filling the small hollow spheres, and the accuracy of the dispensed volume was validated through repeated filling and weighing of the spheres. The phantom's internal rotation and the data analysis process were successful in producing the expected superposition images. Visual inspection of the multi-contrast images provided simple determination of lesion detection thresholds for this scanner (4:1 ratio for 1.5 mm spheres and 3:1 ratio for 2.0 mm spheres) at a specified cumulated background concentration (30 kBq-min microL(-1)). In summary, the micro-hollow sphere phantom demonstrated its practical utility for lesion detection evaluation and is well suited for comparing the task-based performance of small-animal SPECT and PET scanners.
    Physics in Medicine and Biology 09/2010; 55(18):5363-81. DOI:10.1088/0031-9155/55/18/007 · 2.76 Impact Factor
  • F.P. DiFilippo · Sagar Patel ·
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    ABSTRACT: Multi-pinhole collimation is commonly used to improve image quality in small animal SPECT. However multiplexed pinhole projections may introduce ambiguity in image reconstruction and may cause image artifacts and inaccurate quantification. We investigated strategies to optimize data sampling and minimize artifacts, including varying the pinhole configuration and providing a CT-based seed for iterative image reconstruction. Through computer simulations, we assessed the merits of these strategies in terms of quantitative accuracy, image noise, and lesion detection. Use of the CT-based seed for reconstruction significantly reduced multiplexing artifact and improved quantitative accuracy. Overall image quality was best with an imbalanced and irregular multiplexed pinhole configuration, which provided better lesion detection than the non-multiplexed configuration and with negligible artifact. Irregular pinhole patterns also appeared less sensitive to artifacts from unshielded background counts. Ultimately, the optimal pinhole configuration depends on the actual activity distribution. Having a collimator design where some pinholes may be selectively blocked may provide optimal flexibility for various mouse imaging applications.
    Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE; 12/2009
  • Frank P. DiFilippo · Sagar Patel ·
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    ABSTRACT: A multi-pinhole collimation device for small animal single photon emission computed tomography (SPECT) uses the gamma camera detectors of a standard clinical SPECT scanner. The collimator and animal bed move independently of the detectors, and therefore their motions must be synchronized. One approach is manual triggering of the SPECT acquisition simultaneously with a programmed motion sequence for the device. However, some data blurring and loss of image quality result, and true electronic synchronization is preferred. An off-the-shelf digital gyroscope with integrated Bluetooth interface provides a wireless solution to device synchronization. The sensor attaches to the SPECT gantry and reports its rotational speed to a notebook computer controlling the device. Software processes the rotation data in real-time, averaging the signal and issuing triggers while compensating for baseline drift. Motion commands are sent to the collimation device with minimal delay, within approximately 0.5 second of the start of SPECT gantry rotation. Test scans of a point source demonstrate an increase in true counts and a reduction in background counts compared to manual synchronization. The wireless rotation sensor provides robust synchronization of the collimation device with the clinical SPECT scanner and enhances image quality.
    IEEE Transactions on Nuclear Science 07/2009; 56(3-56):640 - 645. DOI:10.1109/TNS.2009.2018843 · 1.28 Impact Factor