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See detailPerformance Measurements of the microPET FOCUS 120 for Iodine-124 Imaging
Taleb, Dounia ULg; Bahri, Mohamed Ali ULg; Seret, Alain ULg et al

in IEEE Transactions on Nuclear Science (2012), PP

This study aimed to evaluate the performance of the microPET FOCUS 120 for 124I in terms of counting rate capability and image quality using the NEMA NU 4-2008 methodology. Scanner sensitivity was ... [more ▼]

This study aimed to evaluate the performance of the microPET FOCUS 120 for 124I in terms of counting rate capability and image quality using the NEMA NU 4-2008 methodology. Scanner sensitivity was measured for 124I for comparison and reached 75 cps/kBq, respectively, with the usual 350-650 keV energy window (EW) and 6 ns time window (TW). The noise equivalent count rate (NECR) index was defined as: NECR = RT2/(RP+RGP) (T = true, P = prompt, GP = γ-prompt). A rat phantom maximum NECR of 48 kcps was obtained for the 250-590 keV EW with 6 ns TW. An almost identical maximum NECR of 43 kcps was recorded for 350-590 and 350-650 keV EW and 6 ns TW. The 2 ns TW reduced the sensitivity and NECR by 40-50% for all EW. The mouse phantom NECR study was limited because of the maximum available activity concentration of 124I. The 250-590 keV EW showed the largest scatter and γ-prompt plus scatter fractions with 25.7% and 43%, respectively, for the rat phantom and 12.2% and 27% for the mouse phantom. With the 350-590 keV EW, these fractions decreased to 20% and 33.5% for the rat phantom and to 10% and 21% for the mouse phantom. The image quality was investigated with the NEMA NU 4-2008 dedicated phantom for four (two analytic and two iterative) 2D or 3D reconstruction methods. The lowest spillover ratios (SOR) for the phantom non-emitting regions were obtained for the 350-590 and 350-650 keV EWs. Recovery coefficients (RC) of the hot rods were the highest for the 350-590 keV EW except for the 1 mm rod. Scatter correction led to a large decrease in RC. The combination of the 350-590 keV EW with 6 ns TW appeared to be a good compromise between counting rate capability and image quality for the FOCUS 120, especially when maximum a posteriori reconstruction was used without scatter correction. Moreover this combination enabled the best quantification with an error as low as 0.36%. [less ▲]

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See detailMicroPET Focus 120 scanner use at high-­‐count rate
Bahri, Mohamed Ali ULg; Warnock, Geoffrey ULg; Taleb, Dounia ULg et al

Poster (2012, September)

Kinetic modeling of physiological processes using imaging techniques requires an accurate measurement of the time-activity curve of the tracer in plasma, known as the arterial input function (IF). The IF ... [more ▼]

Kinetic modeling of physiological processes using imaging techniques requires an accurate measurement of the time-activity curve of the tracer in plasma, known as the arterial input function (IF). The IF can be obtained by manual blood sampling, can be derived from PET images, or continuously measured by the use of small counting systems such as beta microprobes [1]. However, some beta microprobe systems can suffering from high background counts and low sensitivity compared to PET can obligate the use of activities higher than those typical for the imaging system. In the present study, the NEMA NU4-2008 image quality (IQ) phantom [2] was used to evaluate the image quality of the microPET Focus 120 at high activity values. Attenuation correction was obtained from transmission measurement using 57Co point source. Eight emission scans of 20 minutes were performed at decreasing activity starting from 109 MBq to 3.7 MBq (total activity in the field-of-view). To study the effect of normalization in high count rate studies, several normalization scans were performed using activities ranging between 18 and 212 MBq. Images were reconstructed with all corrections using Fourier rebinning and filtered backprojection. The mean activity and the coefficients of variation of the uniform slices were measured. All high activity reconstructed images showed a detector-block-patterned artifact with an overestimation of the counts when normalization activity is higher than that used in the IQ phantom and underestimation of the counts when normalization activity is below the activity used in the IQ phantom. Using the same high activity for acquisition and normalization considerably reduces the patterned-artifact but does not eliminate it entirely. The observed artifact is due to pulse pile-up in the detectors at high count-rates. A dedicated rejection of the pulse pile-up does not appear to have been implemented for the microPET Focus 120. An alternative would be to re-calibrate the detectors with higher activity values to prevent any pile-up effect or to create an attenuation volume into which phantoms or small animals could be inserted thus decreasing the artifact. This latter option is under development. References: [1] G. Warnock et al, European Journal of Nuclear Medicine and Molecular Imaging Research, 1-13 (2011) [2] NEMA Standards Publication NU4-2008. Rosslyn, VA: National Electrical Manufacturers Association; (2008). [less ▲]

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See detailSmall animal imaging with human PET
Bahri, Mohamed Ali ULg; Tombuloglu, S; Warnock, Geoffrey ULg et al

Poster (2012, September)

PET studies provide valuable information in the assessment of animal models for human diseases. MicroPET systems provide the high resolution needed to explore small organs but suffer from a reduced axial ... [more ▼]

PET studies provide valuable information in the assessment of animal models for human diseases. MicroPET systems provide the high resolution needed to explore small organs but suffer from a reduced axial FOV. Multiple bed positions are then used to obtain whole body scans resulting in increased scan time and incomplete dynamic data. In contrast, human PET systems have larger axial FOV but a lower resolution. In this study, an image-based model of the scanner spatial response function combined with a 3D-OSEM reconstruction algorithm were used to improve spatial resolution of the Siemens ECAT EXACT HR+ PET scanner. A stationary double Gaussian model [1] of the ECAT EXACT HR+ point spread function was derived from 18F point source measurements performed at different radial and axial locations in the scanner FOV. This model was used in a 3D-OSEM reconstruction (3D-OSEM-RM). Sinograms were normalized and attenuation and scatter corrected using the Siemens ECAT tools before reconstruction. Both NEMA NU 2-1994 performance phantoms and NEMA NU4-2008 image quality phantom mimicking small animals were used to evaluate the accuracy of corrections for physical effects and the overall image quality. A 50 min dynamic FDG rat study was conducted on the ECAT HR+ and reconstructed with 3D-OSEM-RM. The images were used to compute the metabolic rate of glucose (MRglu) in multiple brain structures. These images were also visually compared to the static image obtained with a FOCUS 120 microPET immediately after the HR+ dynamic scan. The standard deviations of the two Gaussians used to model the transaxial (axial) resolution in a central FOV of 5 cm radius were σ1 = 1.6 (2.75) mm and σ2 = 3.66 (4.16) mm, and the ratio of the weights between the first and second Gaussians was ρ = 0.2 (0.7). Image uniformity and accuracy of scatter and attenuation corrections, evaluated following NEMA NU 2-1994, were found to be very similar between 3D-OSEM, 3D-OSEM-RM, 2D- and 3D-FBP reconstructed images. When using the NEMA NU4-2008 image quality phantom a significant increase of the hot rod recovery coefficient was observed. This effect was rod size dependent and amounted to 17-35% for the 3D-OSEM-RM compared to the 3D-OSEM and to 35-62% compared to the FBP reconstructions. Nevertheless the values obtained with 3D-OSEM-RM were around 20-35% lower than those obtained with the FOCUS 120 microPET scanner. Most of the small brain structures observed on microPET images were also visible on the images obtained with the HR+ scanner and 3D-OSEM-RM. Rat cerebral MRglu values calculated on 3D-OSEM-RM images were in the range of published values [2] (e.g. whole brain = 25.34 μmol/min/100g). Using an approximate model of the ECAT EXACT HR+ spatial response in 3D-OSEM resulted in sufficient image quality for dynamic whole body scans of small rodents, despite the large FOV, and resulted in improved contrast compared to images generated using the built-in software. This methodology will be applied for future small animal dosimetry and modeling studies in our laboratory. [1] Comtat et al. IEEE Nucl Sci Symp Conf Record. pp. 4120-4123 (2008) [2] Schiffer et al. J Nucl Med 48:277-287 (2007) [less ▲]

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See detailNEMA NU4-2008 Performance Evaluation for the MicroPET FOCUS 120 and Iodine-124
Taleb, Dounia ULg; Bahri, Mohamed Ali ULg; Warnock, Geoffrey ULg et al

in IEEE proceedings of ANIMMA 2011 (2012, March 12)

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See detailNEMA NU4-2008 performance evaluation for the microPET Focus 120 and iodine-124
Taleb, Dounia ULg

Conference (2011, June 09)

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See detailMonte Carlo modelling in Positron Emission Tomography
Taleb, Dounia ULg

Scientific conference (2011, February 04)

Gate (Geant4 Application for Tomographic Emission), based on Monte Carlo methods allows simulation of full PET-acquisition processes. Gate results for one of CRC’s tomographs, the HR+, are in good ... [more ▼]

Gate (Geant4 Application for Tomographic Emission), based on Monte Carlo methods allows simulation of full PET-acquisition processes. Gate results for one of CRC’s tomographs, the HR+, are in good agreement with real data, with a maximum mean difference of 6%. Monte Carlo simulations are highly CPU-consuming, so we had to parallelize simulations on the recently setup cluster. In order to use Gate properly on the cluster, the optimal number of CPU was determined. We studied the performances of the small animal microPET FOCUS 120 in terms of counting rate capability (NECR index) for comparison with future simulated results. [less ▲]

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See detailImage Quality evaluation for 124I in the microPET Focus 120 scanner using the NEMA NU4-2008 phantom
Bahri, Mohamed Ali ULg; Warnock, Geoffrey ULg; Taleb, Dounia ULg et al

Conference (2011, January 17)

Physical properties of iodine-124 such as its high positron energy, corresponding large positron range in tissue and the fraction of the single γ-photons emitted may have detrimental effects on the PET ... [more ▼]

Physical properties of iodine-124 such as its high positron energy, corresponding large positron range in tissue and the fraction of the single γ-photons emitted may have detrimental effects on the PET image quality. The purpose of this work was to evaluate the image quality for iodine-124 in the small animal microPET Focus 120 scanner using the NEMA NU4-2008 image quality phantom. Although the 2 ns timing window gives higher recovery coefficients and slightly lower spill-over ratios and combined with the 350-590 keV energy window gives the lowest spill-over ratio, the combination of the 350-650 keV and 6 ns windows seems to be the best compromise to obtain images with high contrast and low noise content. [less ▲]

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See detailUtilisation optimisée de GATE sur un cluster Sun Grid Engine
Taleb, Dounia ULg; Seret, Alain ULg

Poster (2010, May)

Detailed reference viewed: 45 (12 ULg)