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Nuclear Science, IEEE Transactions on

Issue 1  Part 1 • Date Feb. 2006

 This issue contains several parts.Go to:  Part 2 

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Displaying Results 1 - 25 of 40
  • [Front cover]

    Publication Year: 2006 , Page(s): c1
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  • IEEE Transactions on Nuclear Science publication information

    Publication Year: 2006 , Page(s): c2
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  • Table of contents

    Publication Year: 2006 , Page(s): 1
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  • Performance of scintillating waveguides for CCD-based X-ray detectors

    Publication Year: 2006 , Page(s): 3 - 8
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB) |  | HTML iconHTML  

    Scintillating films are usually used to improve the sensitivity of CCD-based X-ray imaging detectors. For an optimal spatial resolution and detection efficiency, a tradeoff has to be made on the film thickness. However, these scintillating layers can also be structured to provide a pixellated screen. In this paper, the study of CsI(Tl)-filled pore arrays is reported. The pores are first etched in silicon, then oxidized and finally filled with CsI(Tl) to form scintillating waveguides. The dependence of the detector sensitivity on pore depth, varied from 40 to 400 μm here, follows rather well theoretical predictions. Most of the detectors produced in this work have a detective quantum efficiency of the incoming X-ray photons of about 25%. However, one detector shows that higher efficiency can be achieved approaching almost the theoretical limit set by Poisson statistics of the incoming X-rays. Thus, we conclude that it is possible to fabricate scintillating waveguides with almost ideal performance. Imaging capabilities of the detectors are demonstrated. View full abstract»

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  • Investigation of scintillator coated CCDs for medical imaging

    Publication Year: 2006 , Page(s): 9 - 13
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1256 KB) |  | HTML iconHTML  

    We describe the development of a scintillator-coated charge coupled device (CCD) based camera for imaging small volumes of radionuclide uptake in tissues. The high-resolution gamma imager (HRGI) is a collimated, scintillator-coated, low cost, imager using low noise CCDs. The HRGI operates in photon counting mode using a peltier cooler to achieve an operating temperature of -5°C. We have measured the spatial resolution and efficiency of a prototype CCD from e2v Technologies Ltd coated with a 500-μm-thick Gadox (Gd2O2S(Tb)) layer using 59.5 keV radiation from a 241Am source and 140 keV gamma-rays from a 99 mTc source. We also describe our first images using 99 mTc phantoms. View full abstract»

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  • Scintillation Properties of Lu _0.4 Gd _1.6 SiO _5 :Ce (LGSO) Crystal

    Publication Year: 2006 , Page(s): 14 - 17
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    We have developed Lu _0.4 Gd _1.6 SiO _5 :Ce (LGSO) crystals as a new scintillator for medical applications. Scintillation properties of LGSO crystal of various Ce concentrations and their dependence on annealing effect were studied. Its absorption coefficient at 511 KeV gamma rays is 0.70 cm ^-1 . We observed that the light output and decay time are dependent on the Ce concentration in the crystal. Decay constant decreases with increasing Ce. Annealing of the colored crystal having 2.0 mol% Ce makes it colorless with better scintillation properties: large light output (40% of NaI:Tl), good energy resolution (8.3% for 4 ,\times, 6 ,\times, 20 mm ^3 crystal) and fast decay constant (65 ns of primary component and 180 ns of secondary component). View full abstract»

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  • New approach to obtain high resolution using conventional block designs in PET

    Publication Year: 2006 , Page(s): 18 - 24
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1824 KB) |  | HTML iconHTML  

    High spatial resolution is essential to image small lesions in positron emission tomography. Traditional methods suggest using small crystals to obtain high resolution. In this study, a new method is introduced to achieve high spatial resolution by using scintillators with different decay times arranged in a checkerboard pattern. Pulse shape discrimination was implemented to determine which crystal the gamma energy was deposited. In this work, a 13×13 LSO crystal array and a 13×13 LSO-GSO checkerboard crystal array using 4×4×20 mm3 crystals were built and optimized using light sharing techniques. Similarly, using 2.5×2.5×19 mm3 LSO and LYSO crystals, a 17×17 LSO-LYSO checkerboard crystal array was built as a high-resolution application. The average pixel energy resolution for the 13×13 LSO was measured to be 14.5%. Similarly, the average pixel resolutions for the GSO part of the 13×13 LSO-GSO crystal array and the LSO part of the same array were measured to be 13.9% and 18.5%, respectively. The average crystal energy resolutions for the LSO and LYSO parts of the 17×17 LSO-LYSO crystal array were measured to be 23.5% and 24.2%, respectively. The average peak-to-valley ratios in the position profiles were measured to be 2.1 for the 13×13 LSO crystal array, 7.2 for the LSO part of the 13×13 LSO-GSO crystal array and 4.3 for the GSO part of the 13×13 LSO-GSO crystal array. Similarly, the average peak-to-valley ratios in the position profiles were measured to be 2.5 for the LSO part of the 17×17 LSO-LYSO crystal array and 2.7 for the LYSO part of the 17×17 LSO-LYSO crystal array. View full abstract»

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  • Development of an optimized LSO/LuYAP phoswich detector head for the Lausanne ClearPET demonstrator

    Publication Year: 2006 , Page(s): 25 - 29
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1288 KB) |  | HTML iconHTML  

    This paper describes the LSO/LuYAP phoswich detector head developed for the ClearPET small animal PET scanner demonstrator that is under construction in Lausanne within the Crystal Clear Collaboration. The detector head consists of a dual layer of 8×8 LSO and LuYAP crystal arrays coupled to a multi-anode photomultiplier tube (Hamamatsu R7600-M64). Equalistion of the LSO/LuYAP light collection is obtained through partial attenuation of the LSO scintillation light using a thin aluminum deposit of 20-35 nm on LSO and appropriate temperature regulation of the phoswich head between 30°C to 60°C. At 511keV, typical FWHM energy resolutions of the pixels of a phoswich head amounts to (28±2)% for LSO and (25±2)% for LuYAP. The LSO versus LuYAP crystal identification efficiency is better than 98%. Six detector modules have been mounted on a rotating gantry. Axial and tangential spatial resolutions were measured up to 4 cm from the scanner axis and compared to Monte Carlo simulations using GATE. FWHM spatial resolution ranges from 1.3 mm on axis to 2.6 mm at 4 cm from the axis. View full abstract»

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  • Preliminary evaluation of four-layer BGO DOI-detector for PET

    Publication Year: 2006 , Page(s): 30 - 34
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1360 KB) |  | HTML iconHTML  

    We found that Bi4Ge3 O12 (BGO) scintillator can be elements of a four-layer depth of interaction (DOI) detector and it was proved with a 12×12×4 array of BGO crystals in dimensions of 2.9 mm×2.9 mm×7.5 mm coupled to a 256-channel flat panel position sensitive photomultiplier tube. Appropriate reflector insertion in the array makes all crystal identification possible on one position histogram. Despite the large refractivity and small light output of BGO, the four-layer BGO detector showed no significant variation in the full energy peaks among all crystal elements. When no optical grease was used in the construction of the BGO DOI-block and irradiated with gamma-rays from 137Cs, a top layer crystal has 80% of light output relative to the bottom layer. The obtained two-dimensional position histogram by the irradiation was clear enough to allow identification of the crystals of interaction. Profiles of the histogram show peak-to-valley ratio of 1.9:1 for the top layer crystals and larger ratio for other layer crystals in the experiment. View full abstract»

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  • Performance evaluation of a subset of a four-layer LSO detector for a small animal DOI PET scanner: jPET-RD

    Publication Year: 2006 , Page(s): 35 - 39
    Cited by:  Papers (29)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB) |  | HTML iconHTML  

    Previously, we proposed a new depth of interaction (DOI) encoding method and proved that it worked successfully with four-layered Gd2SiO5 crystals for a small animal positron emission tomography (PET) detector. We are now planning to develop a small animal PET scanner, jPET-RD (for rodents with DOI detectors), which has both high resolution and high sensitivity by the use of a DOI detector with a 32×32×4 crystal array. The scintillator for the detector will be Lu2(1-x)Y2xSiO5 (LYSO). In this work, we evaluated performance of a DOI detector composed of four layers of a 12×12 LYSO (Lu: 98%, Y: 2%) crystal array by irradiating 511 keV gamma rays uniformly. The new encoding method was used for crystal identification. The size of each crystal was 1.46 mm×1.46 mm×4.5 mm. The crystal block was coupled to a 256-channel flat panel position sensitive photomultiplier tube, which has 16×16 multi anodes at intervals of 3.04 mm. As we expected, all crystals are expressed on a single two-dimensional position histogram without overlapping. Energy resolution of all events is 21.8% and time resolution of all events is 0.69 ns in FWHM. When layers are counted from the top, the energy resolutions of the first, second, third, and fourth layer events are 11.6%, 12.3%, 13.3%, and 19.1% and the time resolutions are 0.60ns, 0.59ns, 0.60ns, and 0.66ns, respectively. View full abstract»

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  • High resolution GSO block detectors using PMT-quadrant-sharing design for small animal PET

    Publication Year: 2006 , Page(s): 40 - 43
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    GSO position-sensitive block detectors have been developed using the PMT-Quadrant -Sharing (PQS) technology for animal PET imaging. Two prototype block detectors with dimensions of 1.51 mm×1.51 mm×10 mm (12×12 array) and 1.66 mm×1.66 mm×10 mm (11×11 array) were built using 19 mm round PMTs. The Enhanced Specular Reflector mirror-film (98% reflectance, 0.065 mm thickness, 3M Co.) was used to control the light collection and distribution in the PQS design. The detector pitches are 1.59 (12×12) and 1.74 mm (11×11) and the crystal-packing fractions 95.0 and 95.4%, respectively. List-mode measurements with Cs-137 sources were carried out to investigate the crystal decoding and analyzed to extract the individual crystal spectra. All the crystals in both the detectors were clearly identified and well isolated. The light-collection efficiency is lowest in the central crystals and highest in the crystals of the four corners, with a ratio of 0.76 for the 11×11 array. The overall energy resolution of the 11×11 array is 13.5% (15.4% at 511 keV) with a standard deviation of 1.2%, which indicates that the individual energy resolutions of the detector are high and uniformly distributed. From this study, we achieved a high decodable crystals/PMT ratio of 144:1 for the 19 mm PQS GSO detector technology with crystals 10 mm deep. It is believed that these detectors would be useful for high resolution animal PET imaging. View full abstract»

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  • Development of a one-dimensional sharing block detector using dual PMTs for PET

    Publication Year: 2006 , Page(s): 44 - 48
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB) |  | HTML iconHTML  

    We propose and test a one-dimensional (1-D) sharing block detector using dual photo-multiplier tubes (PMT). The detector consists of scintillator blocks and dual PMTs. The dual PMTs are optically coupled on the scintillator blocks and overlap in one dimensional. With this configuration, the scintillator size of the block detector can be reduced to half that of a conventional block detector in one direction, and isotropic spatial resolution can be obtained in transaxial and axial directions using commercially available dual PMTs. First, we measure the position and energy response for minimum configuration; one GSO block and two dual PMTs. The size of a single GSO is 2.9 mm×2.9 mm×20 mm. The scintillators are arranged in an 8×8 matrix with multi-layer optical film inserted partly between scintillators to obtain the resolved position response. We obtain good position and energy responses with this configuration. Next, we fabricate a 1-D sharing block detector with five GSO blocks and six dual PMTs. With this configuration, we also obtain reasonable position and energy responses. These results indicate that the proposed 1-D sharing block detector is a promising solution for developing high-resolution and low cost PET systems. View full abstract»

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  • Resolution improvement using a fiber optic plate for a small field-of-view NaI(Tl) gamma camera

    Publication Year: 2006 , Page(s): 49 - 53
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    To improve the spatial resolution of a small field-of-view gamma camera composed of a NaI(Tl) scintillator and a position sensitive photo-multiplier tube (PSPMT), the performance of an NaI(Tl) scintillator with a fiber optic plate for a light output was compared with that of such a scintillator using a conventional glass plate. Since the fiber optic plate limits the light distribution and makes it narrower, spatial resolution is improved. Using 20×20 mm, 2-mm-thick NaI(Tl) scintillators with a glass plate and with a fiber optic plate, performance was measured and compared. Using the fiber optic plate, the scintillation light output was 35% less than with a glass plate. The average spatial resolution with the fiber optic plate was 0.98-mm full width at half maximum (FWHM) while that with the glass plate was 1.48 mm FWHM for 122-keV, Co-57 gamma photons. Although light output decreased, spatial resolution dramatically improved. These results indicate that the NaI(Tl) with a fiber optic plate for light output is promising for PSPMT-based small field-of-view gamma cameras. View full abstract»

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  • A CCD-based detector for SPECT

    Publication Year: 2006 , Page(s): 54 - 58
    Cited by:  Papers (19)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB) |  | HTML iconHTML  

    We are investigating the use of a CCD for high-resolution radionuclide imaging. The use of a CCD has the potential to provide very high spatial resolution on the order of 200 to 400 μm, while significantly simplifying the readout electronics. The detector is based on a special CCD with on-chip multiplication gain that allows high-speed operation while maintaining the read noise at a very low level of <1 electron. To achieve high detection efficiency and excellent spatial resolution for incident gamma flux, a specially fabricated thick microcolumnar CsI(Tl) scintillator was optically coupled to the CCD. A prototype SPECT imaging system was assembled by incorporating pinhole/parallel hole collimators in the design. The use of this system for radionuclide imaging has been demonstrated through tomographic imaging of a test phantom filled with 99mTc. View full abstract»

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  • A compact gamma camera for biological imaging

    Publication Year: 2006 , Page(s): 59 - 65
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (984 KB) |  | HTML iconHTML  

    A compact detector, sized particularly for imaging a mouse, is described. The active area of the detector is approximately 46 mm × 96 mm. Two flat-panel Hamamatsu H8500 position-sensitive photomultiplier tubes (PSPMTs) are coupled to a pixellated NaI(Tl) scintillator which views the animal through a copper-beryllium (CuBe) parallel-hole collimator specially designed for 125I. Although the PSPMTs have insensitive areas at their edges and there is a physical gap, corrections for scintillation light collection at the junction between the two tubes results in a uniform response across the entire rectangular area of the detector. The system described has been developed to optimize both sensitivity and resolution for in-vivo imaging of small animals injected with iodinated compounds. We demonstrate an in-vivo application of this detector, particularly to SPECT, by imaging mice injected with approximately 10-15 μCi of 125I. View full abstract»

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  • Tri-modality small animal imaging system

    Publication Year: 2006 , Page(s): 66 - 70
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1728 KB) |  | HTML iconHTML  

    Our group is developing a scanner that combines x-ray, single gamma, and optical imaging on the same rotating gantry. Two functional modalities (SPECT and optical) are included because they have different strengths and weaknesses in terms of spatial and temporal decay lengths in the context of in vivo imaging, and because of the recent advent of multiple reporter gene constructs. The effect of attenuation by biological tissue on the detected intensity of the emitted signal was measured for both gamma and optical imaging. Attenuation by biological tissue was quantified for both the bioluminescent emission of luciferace and for the emission light of the near infrared fluorophore cyanine 5.5, using a fixed excitation light intensity. Experiments were performed to test the feasibility of using either single gamma or x-ray imaging to make depth-dependent corrections to the measured optical signal. Our results suggest that significant improvements in quantitation of optical emission are possible using straightforward correction techniques based on information from other modalities. Development of an integrated scanner in which data from each modality are obtained with the animal in a common configuration will greatly simplify this process. View full abstract»

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  • Design and evaluation of the clear-PEM scanner for positron emission mammography

    Publication Year: 2006 , Page(s): 71 - 77
    Cited by:  Papers (36)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    The design and evaluation of the imaging system Clear-PEM for positron emission mammography, under development by the PEM Consortium within the framework of the Crystal Clear Collaboration at CERN, is presented. The proposed apparatus is based on fast, segmented, high atomic number radiation sensors with depth-of-interaction measurement capabilities, and state-of-the-art data acquisition techniques. The camera consists of two compact and planar detector heads with dimensions 16.5×14.5 cm2 for breast and axilla imaging. Low-noise integrated electronics provide signal amplification and analog multiplexing based on a new data-driven architecture. The coincidence trigger and data acquisition architecture makes extensive use of pipeline processing structures and multi-event memories for high efficiency up to a data acquisition rate of one million events/s. Experimental validation of the detection techniques, namely the basic properties of the radiation sensors and the ability to measure the depth-of-interaction of the incoming photons, are presented. System performance in terms of detection sensitivity, count-rates and reconstructed image spatial resolution were also evaluated by means of a detailed Monte Carlo simulation and an iterative image reconstruction algorithm. View full abstract»

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  • Factors influencing timing resolution in a commercial LSO PET camera

    Publication Year: 2006 , Page(s): 78 - 85
    Cited by:  Papers (26)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    The CPS Accel is a commercial PET camera based on a block detector with 64 LSO scintillator crystals (each 6.75×6.75×25 mm) read out with 4 photomultiplier tubes. The excellent timing resolution of LSO suggests that this camera might be used for time-of-flight (TOF) PET, thereby reducing the statistical noise significantly. Although the Accel achieves 3 ns coincidence resolution (a factor of two better than BGO-based PET cameras), its timing resolution is nearly an order of magnitude worse than that demonstrated with individual LSO crystals. This paper quantifies the effect on the timing of each component in the Accel timing chain to identify which components most limit the camera's timing resolution. The components in the timing chain are: the scintillator crystal, the photomultiplier tube (PMT), the constant fraction discriminator (CFD), and the time to digital converter (TDC). To measure the contribution of each component, we construct a single crystal test system with high-performance versions of these components. This system achieves 221 ps FWHM coincidence timing resolution, which is used as a baseline measurement. One of the high-performance components is replaced by a production component, the coincidence timing resolution is re-measured, and the difference between measurements is the contribution of that (production) component. We find that the contributions of the TDC, CFD, PMT, and scintillator are 2000 ps, 1354 ps, 422 ps, and 326 ps FWHM, respectively, and that the overall timing resolution scales like the square root of the amount of scintillation light detected by the PMT. Based on these measurements we predict that the limit for the coincidence timing resolution in a practical, commercial, LSO-based PET camera is 528 ps FWHM. View full abstract»

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  • Generation of the Acquisition-Specific NEC (AS-NEC) Curves to Optimize the Injected Dose in 3D ^18 F-FDG Whole Body PET Studies

    Publication Year: 2006 , Page(s): 86 - 92
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    Aim of this work was the implementation and validation, for the Discovery-ST PET/CT (GE Medical Systems) system, of the acquisition-specific noise equivalent counts (AS-NEC) method to establish the amount of tracer to be injected in 3D ^18 F-FDG whole body (WB) PET studies to achieve the peak of the NEC (NEC-p) at the acquisition time. The AS-NEC method uses prompts, delayed events and detector dead-time of a single reference PET scan to calculate the full shape of the NEC curve. The method was implemented using a 3D decay series of the 70 cm NEMA 2001 (line source in a 20 cm diameter solid polyethylene cylinder) phantom and validated with the cylindrical NEMA 1994 (diameter, 20 cm; length, 20 cm) and NEMA 2001 IEC body phantoms. The NEC curves generated by the single frames of the phantom series, using the AS-NEC method, well correlated with the experimental NEC curves proving the validity of the method and the possible application to clinical studies. The AS-NEC model was then retrospectively applied on 40 3D ^18 F-FDG WB studies in a range of body mass index (BMI) between 16 and 30 (kg/m ^2 ) (6 under-weight (uw), 18 normal-weight (nw), 16 over-weight (ow)). For each acquisition frame of each patient study, the activity at the acquisition time, corresponding to the NEC-p was identified on the NEC curves. Furthermore, as the NEC curves show a region around the NEC-p with small variations (nearly a plateau), the values of radioactivity corresponding to a reduction of 1%, 3% and 5% with respect to NEC-p were also calculated to assess a possible reduction of the doses to be injected in clinical studies. The results show that the average activities at the acquisition time corresponding to the NEC-p were comparable for the three BMI classes: 336.7 MBq ( sd=22.2), 329.3 MBq ( sd=33.3), 344.1 MBq ( sd=48.1) for uw, nw and ow, respectively. Therefore, the total average NEC-p activity for the three BMI classes was 336.7 MBq ( sd=40.7) . The mean values of the radioactivity at a reduction of 1%, 3% and 5% with respect to the NEC-p were: 284.9 MBq ( sd=40.7), 247.9 MBq ( sd=33.3) and 225.7 MBq ( sd=29.6) respectively. These results indicate the possibi- lity to use, for the Discovery-ST, a single injection protocol of 448 MBq (for the range of BMI here considered) to have an activity at the acquisition time (after 45 min of uptake) of 336.7 MBq (NEC-p). Nevertheless, the plateau near the NEC-p suggests the possibility to reduce significantly the dose to be injected in clinical studies down to about 330 MBq, while preserving suitable NEC performance ( -3 %) with respect to the NEC-p. This result was supported by image quality assessment performed on reconstructed images of the NEMA 2001 IEC body phantom. View full abstract»

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  • Performance Evaluation of the Philips “Gemini” PET/CT System

    Publication Year: 2006 , Page(s): 93 - 101
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    Methods to test the practical performance of the Philips Gemini PET/CT system during clinical imaging are described and results presented. The test methods used were based on the NEMA standards and those suggested by a task group of the Commission of European Communities (EEC). These were performed using the EEC emission phantom, and phantoms provided by Philips. Scans were acquired using the routine clinical protocols. Images were reconstructed using a 3D row action maximum likelihood algorithm (RAMLA). Attenuation correction (AC) was applied using CT data (CTAC) and Cs-137 source transmission scans (CsAC). Images can be acquired with the PET and CT gantries closed or open. Results of tests on the gantry alignment show that the static offsets varied by a maximum of 4.5 mm when the system was first installed, but as the floor has settled these variations have decreased to a maximum of 2.5 mm. The mean negative nonuniformity was -4.8 \pm 1.1\hbox {\%} and -5.3 \pm 1.1\hbox {\%} for CsAC and CTAC respectively and the mean positive nonuniformity was 4.7 \pm 1.4\hbox {\%} and 5.5 \pm 1.6\hbox {\%} . Scatter fraction measurements were made in the EEC body phantom. The reconstructed scatter fractions were 0.18 and 0.16 with and without out-of-field-of-view activity respectively ( \pm OFOVA) for both CsAC and CTAC images. The sinogram-derived (NEMA NU 2-1994) scatter fraction was 0.44 and 0.43 \pm OFOVA. At the centre of the field of view (FOV) the transverse spatial resolution (SR) was 5.0 mm in air (5.0 mm in water) and the axial SR was 6.0 mm (6.8 mm). 10 cm away from the centre the transverse radial SR was 5.4 mm (5.3 mm), the transverse tangential SR was 5.2 mm (5.4 mm) and the axial SR was 6.6 mm (7.2 mm). The recovery coefficients demonstrate the partial volume effect. The AC accuracy was similar in water (both 0.2 \pm 0.1 \hbox {%} ) and Teflon [ 10.9 \pm 1.9\hbox {\%} (CTAC) and 10.0 \pm 2.0\hbox {\%} (CsAC)], for both types of AC, but very different in air [ 14.3 \pm 2.2\hbox {\%} (CTAC) and 31.3 \pm 1.5\hbox {\%} (CsAC)]. If the transmission maps were not segmented prior to AC these gave much higher and very different residual AC errors. The peak noise equivalent count rate was 45.2 kcps at - 184 MBq and 25.2 kcps at 127 MBq \pm OFOVA. The system sensitivity to true and scattered counts was 34.1 kcps/(kBq/cm ^3 ) and to true counts was 19.4 kcps/(kBq/cm ^3 ). View full abstract»

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  • A method for calibrating the CT-based attenuation correction of PET in human tissue

    Publication Year: 2006 , Page(s): 102 - 107
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    The use of x-ray computed tomography (CT)-based attenuation correction for positron emission tomography (PET) in PET/CT systems requires the transformation of CT Hounsfield units (HU) to linear attenuation coefficients at 511 keV (LAC511). This cannot be done perfectly from a single peak kilovolt (kVp) CT scan due to variability in Compton and photoelectric composition and, thus, an approximate transformation must be employed. One difficulty in this lies in accurately determining the linear attenuation coefficients (LAC) in actual human tissue. Typically, phantoms consisting of synthetic materials thought to be approximate human tissue equivalents are employed instead. A potentially more accurate approach would be to use dual kVp CT scans to estimate LAC511 in actual human tissue and then base the single kVp transformation on these data. This approach would also permit an assessment of the dispersion of actual tissue values about the two-component trend lines typically used for the single kVp transformation. In this paper, we develop and assess this methodology. View full abstract»

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  • PET Detector Quality Assurance Using ^137 Cs Singles Transmission Imaging

    Publication Year: 2006 , Page(s): 108 - 112
    Cited by:  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    Daily quality assurance of positron emission tomography detectors, to ensure accurate efficiency calibration of the system, typically requires the acquisition of coincidence data from a flood source. To obtain sufficient counts, long scan times on the order of an hour are required. The long acquisition time and necessity of an external activity source may make such a protocol impractical for daily use. A new protocol has been demonstrated for the ECAT ART scanner, using the two ^137 Cs transmission sources. The new protocol produces a map of the counts per detector, as well as plots of the mean and standard deviation of the detector counts in a given block. Graphical outputs allow for quick recognition of problematic areas. The factory protocol requires 90 min to obtain a 1% statistical error on the individual detector counts. Due to the high activity of the ^137 Cs sources, a 1% statistical error is obtained with an 8 min scan using the new protocol. The new protocol provides information regarding the status of all blocks, reduces acquisition time, and alleviates the need for an external activity source. The protocol presented in this study can be implemented on other ^137 Cs transmission based scanners, and with coincidence flood sources if detector-specific singles histogramming is available. View full abstract»

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  • Simultaneous multi-head calibration for pinhole SPECT

    Publication Year: 2006 , Page(s): 113 - 120
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    Pinhole collimation is used as a magnifying geometry to overcome the resolution constraints of the gamma cameras used in SPECT. It is very sensitive to the mechanical position of the aperture relative to the axis of rotation. It is also sensitive to the axial position of the aperture. When one camera head is used, there is no intrinsic reference point for determining the axial mechanical shift. However, when multiple heads are used, the axial origin can be defined as the center of the first aperture. The other apertures can be measured relative to the first. A procedure has been developed for simultaneously calibrating multiple heads by using a single point source in the field of view of all heads. The gantry is rotated through 360 degrees. The centroids are fit using a maximum-likelihood method to an equation that describes the axial and transaxial geometry. The three coordinates of the point source are determined along with the mechanical and electronic shifts in the axial and transaxial directions; the axial mechanical shift of the first aperture is set to zero by definition. Another advantage of multi-head calibration is that a further constraint on the position of the point source is made. We apply the calibration information to a sub-micro disk phantom with 1.6 mm disks. View full abstract»

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  • Initial study of an asymmetric PET system dedicated to breast cancer imaging

    Publication Year: 2006 , Page(s): 121 - 126
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    We are developing a positron emission tomography (PET) system dedicated to breast cancer imaging and based on a pseudo-pinhole PET geometry. The system consists of a small half-ring (r=153 mm) of high-resolution LSO detectors and a large half-ring (R=413 mm) of medium-resolution LSO detectors. The coincidence detection profile between a small LSO crystal and a large LSO crystal reveals that, when the object imaged is located close to the small detector, the image resolution is primarily determined by the intrinsic spatial resolution of the small detector, and is only slightly affected by the resolution of the large detector. The dimensions of the crystals are 1.6×1.6×20 mm3 for the small half-ring and 4.3×4.3×25 mm3 for the large half-ring. Monte Carlo simulation of the system was performed using a modified SimSET package. The detectors in the small half ring are modeled as 2- or 4-layer detectors with DOI capability. One-mm point sources were simulated to measure the image resolution of the system at 0, 2, 6, and 10 cm offset along the +X, +Y and -Y directions. Results suggest image resolutions of 1.7-2.5 mm FWHM for breast tissues and 1.8-3.1 mm FWHM for tissues near the chest wall, including internal and axillary lymph nodes. Sensitivity of the system ranges from 5.4% to 7.8% and can be significantly increased if two planar detectors are attached to the system along the axial direction. View full abstract»

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  • Observations regarding scatter fraction and NEC measurements for small animal PET

    Publication Year: 2006 , Page(s): 127 - 132
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    The goal of this study was to evaluate the magnitude and origin of scattered radiation in a small-animal PET scanner and to assess the impact of these findings on noise equivalent count rate (NECR) measurements, a metric often used to optimize scanner acquisition parameters and to compare one scanner with another. The scatter fraction (SF) was measured for line sources in air and line sources placed within a mouse-sized phantom (25 mm φ×70 mm) and a rat-sized phantom (60 mm φ×150 mm) on the microPET II small-animal PET scanner. Measurements were performed for lower energy thresholds ranging from 150-450 keV and a fixed upper energy threshold of 750 keV. Four different methods were compared for estimating the SF. Significant scatter fractions were measured with just the line source in the field of view, with the spatial distribution of these events consistent with scatter from the gantry and room environment. For mouse imaging, this component dominates over object scatter, and the measured SF is strongly method dependent. The environmental SF rapidly increases as the lower energy threshold decreases and can be more than 30% for an open energy window of 150-750 keV. The object SF originating from the mouse phantom is about 3-4% and does not change significantly as the lower energy threshold increases. The object SF for the rat phantom ranges from 10 to 35% for different energy windows and increases as the lower energy threshold decreases. Because the measured SF is highly dependent on the method, and there is as yet no agreed upon standard for animal PET, care must be exercised when comparing NECR for small objects between different scanners. Differences may be methodological rather than reflecting any relevant difference in the performance of the scanner. Furthermore, these results have implications for scatter correction methods when the majority of the detected scatter does not arise from the object itself. View full abstract»

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