D Ros

University of Barcelona, Barcino, Catalonia, Spain

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Publications (72)163.96 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work a comparison between experimental and simulated data using GATE and PeneloPET Monte Carlo simulation packages is presented. All simulated setups, as well as the experimental measurements, followed exactly the guidelines of the NEMA NU 4-2008 standards using the microPET R4 scanner. The comparison was focused on spatial resolution, sensitivity, scatter fraction and counting rates performance. Both GATE and PeneloPET showed reasonable agreement for the spatial resolution when compared to experimental measurements, although they lead to slight underestimations for the points close to the edge. High accuracy was obtained between experiments and simulations of the system's sensitivity and scatter fraction for an energy window of 350-650 keV, as well as for the counting rate simulations. The latter was the most complicated test to perform since each code demands different specifications for the characterization of the system's dead time. Although simulated and experimental results were in excellent agreement for both simulation codes, PeneloPET demanded more information about the behavior of the real data acquisition system. To our knowledge, this constitutes the first validation of these Monte Carlo codes for the full NEMA NU 4-2008 standards for small animal PET imaging systems.
    Physics in Medicine and Biology 12/2014; 60(1):151-162. · 2.92 Impact Factor
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    ABSTRACT: It is well-known that in pinhole SPECT (single-photon-emission computed tomography), iterative reconstruction methods including accurate estimations of the system response matrix can lead to submillimeter spatial resolution. There are two different methods for obtaining the system response matrix: those that model the system analytically using an approach including an experimental characterization of the detector response, and those that make use of Monte Carlo simulations. Methods based on analytical approaches are faster and handle the statistical noise better than those based on Monte Carlo simulations, but they require tedious experimental measurements of the detector response. One suggested approach for avoiding an experimental characterization, circumventing the problem of statistical noise introduced by Monte Carlo simulations, is to perform an analytical computation of the system response matrix combined with a Monte Carlo characterization of the detector response. Our findings showed that this approach can achieve high spatial resolution similar to that obtained when the system response matrix computation includes an experimental characterization. Furthermore, we have shown that using simulated detector responses has the advantage of yielding a precise estimate of the shift between the point of entry of the photon beam into the detector and the point of interaction inside the detector. Considering this, it was possible to slightly improve the spatial resolution in the edge of the field of view.
    Physics in Medicine and Biology 11/2014; 59:7573-7585. · 2.92 Impact Factor
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    ABSTRACT: Middle cerebral artery occlusion (MCAO) in rodents causes brain infarctions of variable sizes that depend on multiple factors, particularly in models of ischemia/reperfusion. This is a major problem for infarct volume comparisons between different experimental groups since unavoidable variability can induce biases in the results and imposes the use of large number of subjects. MRI can help to minimize these difficulties by ensuring that the severity of ischemia is comparable between groups. Furthermore, several studies showed that infarct volumes can be predicted with MRI data obtained soon after ischemia onset. However, such predictive studies require multiparametric MRI acquisitions that cannot be routinely performed, and data processing using complex algorithms that are often not available. The aim here was to provide a simplified method for infarct volume prediction using apparent diffusion coefficient (ADC) data in a model of transient MCAO in rats. ADC images were obtained before, during MCAO and after 60 min of reperfusion. Probability histograms were generated using ADC data obtained either during MCAO, after reperfusion, or both combined. The results were compared to real infarct volumes, i.e.T2 maps obtained at day 7. Assessment of the performance of the estimations showed better results combining ADC data obtained during occlusion and at reperfusion. Therefore, ADC data alone can provide sufficient information for a reasonable prediction of infarct volume if the MRI information is obtained both during the occlusion and soon after reperfusion. This approach can be used to check whether drug administration after MRI acquisition can change infarct volume prediction.
    Brain Research 10/2014; · 2.83 Impact Factor
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    ABSTRACT: SPECT studies with 123I-ioflupane facilitate the diagnosis of Parkinson's disease (PD). The effect on quantification of image degradations has been extensively evaluated in human studies but their impact on studies of experimental PD models is still unclear. The aim of this work was to assess the effect of compensating for the degrading phenomena on the quantification of small animal SPECT studies using 123I-ioflupane. This assessment enabled us to evaluate the feasibility of quantitatively detecting small pathological changes using different reconstruction methods and levels of compensation for the image degrading phenomena. Monte Carlo simulated studies of a rat phantom were reconstructed and quantified. Compensations for point spread function (PSF), scattering, attenuation and partial volume effect were progressively included in the quantification protocol. A linear relationship was found between calculated and simulated specific uptake ratio (SUR) in all cases. In order to significantly distinguish disease stages, noise-reduction during the reconstruction process was the most relevant factor, followed by PSF compensation. The smallest detectable SUR interval was determined by biological variability rather than by image degradations or coregistration errors. The quantification methods that gave the best results allowed us to distinguish PD stages with SUR values that are as close as 0.5 using groups of six rats to represent each stage.
    Physics in Medicine and Biology 07/2014; 59(16):4567. · 2.92 Impact Factor
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    ABSTRACT: The 6-hydroxydopamine (6-OHDA) rodent model of Parkinson's disease (PD) has been used to evaluate the nigrostriatal pathway. The aim of this work was to explore the relationship between the degree of 6-OHDA-induced dopaminergic degeneration and [(123) I]FP-CIT binding using single photon emission computed tomography (SPECT). Fourteen rats received a 6-OHDA injection (4 or 8 µg) into the left medial forebrain bundle. After 3 weeks, magnetic resonance imaging and scans with a small-animal SPECT system were performed. Finally, the nigrostriatal lesion was assessed by immunohistochemical analysis. Immunohistochemical analysis confirmed two levels of dopaminergic degeneration. Lesions induced by 6-OHDA diminished the ipsilateral [(123) I]FP-CIT binding by 61 and 76%, respectively. The decrease in tracer uptake between control and lesioned animals was statistically significant, as was the difference between the two 6-OHDA lesioned groups. Results concluded that [(123) I]FP-CIT SPECT is a useful technique to discriminate the degree of dopaminergic degeneration in a rat model of PD. Copyright © 2014 John Wiley & Sons, Ltd.
    Contrast Media & Molecular Imaging 05/2014; · 3.33 Impact Factor
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    ABSTRACT: Purpose: To assess the performance of two approaches to the system response matrix (SRM) calculation in pinhole single photon emission computed tomography (SPECT) reconstruction.Methods: Evaluation was performed using experimental data from a low magnification pinhole SPECT system that consisted of a rotating flat detector with a monolithic scintillator crystal. The SRM was computed following two approaches, which were based on Monte Carlo simulations (MC-SRM) and analytical techniques in combination with an experimental characterization (AE-SRM). The spatial response of the system, obtained by using the two approaches, was compared with experimental data. The effect of the MC-SRM and AE-SRM approaches on the reconstructed image was assessed in terms of image contrast, signal-to-noise ratio, image quality, and spatial resolution. To this end, acquisitions were carried out using a hot cylinder phantom (consisting of five fillable rods with diameters of 5, 4, 3, 2, and 1 mm and a uniform cylindrical chamber) and a custom-made Derenzo phantom, with center-to-center distances between adjacent rods of 1.5, 2.0, and 3.0 mm.Results: Good agreement was found for the spatial response of the system between measured data and results derived from MC-SRM and AE-SRM. Only minor differences for point sources at distances smaller than the radius of rotation and large incidence angles were found. Assessment of the effect on the reconstructed image showed a similar contrast for both approaches, with values higher than 0.9 for rod diameters greater than 1 mm and higher than 0.8 for rod diameter of 1 mm. The comparison in terms of image quality showed that all rods in the different sections of a custom-made Derenzo phantom could be distinguished. The spatial resolution (FWHM) was 0.7 mm at iteration 100 using both approaches. The SNR was lower for reconstructed images using MC-SRM than for those reconstructed using AE-SRM, indicating that AE-SRM deals better with the projection noise than MC-SRM.Conclusions: The authors' findings show that both approaches provide good solutions to the problem of calculating the SRM in pinhole SPECT reconstruction. The AE-SRM was faster to create and handle the projection noise better than MC-SRM. Nevertheless, the AE-SRM required a tedious experimental characterization of the intrinsic detector response. Creation of the MC-SRM required longer computation time and handled the projection noise worse than the AE-SRM.Nevertheless, the MC-SRM inherently incorporates extensive modeling of the system and therefore experimental characterization was not required.
    Medical Physics 03/2014; 41(3):032501. · 3.01 Impact Factor
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    ABSTRACT: Purpose: The Software for Tomographic Image Reconstruction (STIR, http://stir.sourceforge.net) package is an open source object-oriented library implemented in C++. Although its modular design is suitable for reconstructing data from several modalities, it currently only supports Positron Emission Tomography (PET) data. In this work, the authors present results for Single Photon Emission Computed Tomography (SPECT) imaging.Methods: This was achieved by the complete integration of a 3D SPECT system matrix modeling library into STIR.Results: The authors demonstrate the flexibility of the combined software by reconstructing simulated and acquired projections from three different scanners with different iterative algorithms of STIR.Conclusions: The extension of the open source STIR project with advanced SPECT modeling will enable the research community to study the performance of several algorithms on SPECT data, and potentially implement new algorithms by expanding the existing framework.
    Medical Physics 09/2013; 40(9):092502. · 3.01 Impact Factor
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    ABSTRACT: Very recent clinical research has investigated whether obstructive sleep apnea (OSA) may modulate bone homeostasis but the few data available are conflicting. Here we report novel data obtained in a mouse study specifically designed to determine whether chronic intermittent hypoxia realistically mimicking OSA modifies bone mineral density (BMD). Normal male and female mice and orchidectomized mice (N=10 each group) were subjected to a pattern of high-frequency intermittent hypoxia (20 s at 5% and 40 s at 21%, 60 cycles/h) for 6h/day. Identical groups breathing room air (normoxia) were the controls. After 32 days of intermittent hypoxia/normoxia the trabecular bone mineral density (BMD) in the peripheral femora were measured by micro-CT scanning. When compared with normoxia (two-way ANOVA), intermittent hypoxia did not significantly modify BMD in the three animal groups tested. Data in this study suggest that the type of intermittent hypoxia characterizing OSA, applied as a single challenge, preserves bone homeostasis.
    Respiratory Physiology & Neurobiology 08/2013; · 1.97 Impact Factor
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    ABSTRACT: The purpose of this work was to evaluate the performance of the microPET R4 system for rodents according to the NU 4-2008 standards of the National Electrical Manufacturers Association (NEMA) for small-animal positron emission tomography (PET) systems and to compare it against its previous evaluation according the adapted clinical NEMA NU 2-2001. The performance parameters evaluated here were spatial resolution, sensitivity, scatter fraction, counting rates for rat- and mouse-sized phantoms, and image quality. Spatial resolution and sensitivity were measured with a 22Na point source, while scatter fraction and count rate performance were determined using a mouse and rat phantoms with an 18F line source. The image quality of the system was assessed using the NEMA image quality phantom. Assessment of attenuation correction was performed using γ-ray transmission and computed tomography (CT)-based attenuation correction methods. At the center of the field of view, a spatial resolution of 2.12 mm at full width at half maximum (FWHM) (radial), 2.66 mm FWHM (tangential), and 2.23 mm FWHM (axial) was measured. The absolute sensitivity was found to be 1.9% at the center of the scanner. Scatter fraction for mouse-sized phantoms was 8.5 %, and the peak count rate was 311 kcps at 153.5 MBq. The rat scatter fraction was 22%, and the peak count rate was 117 kcps at 123.24 MBq. Image uniformity showed better results with 2-D filtered back projection (FBP), while an overestimation of the recovery coefficients was observed when using 2-D and 3-D OSEM MAP reconstruction algorithm. All measurements were made for an energy window of 350-650 keV and a coincidence window of 6 ns. Histogramming and reconstruction parameters were used according to the manufacturer's recommendations. The microPET R4 scanner was fully characterized according to the NEMA NU 4-2008 standards. Our results diverge considerably from those previously reported with an adapted version- of the NEMA NU 2-2001 clinical standards. These discrepancies can be attributed to the modifications in NEMA methodology, thereby highlighting the relevance of specific small-animal standards for the performance evaluation of PET systems.
    IEEE Transactions on Nuclear Science 10/2012; 54(5):1879 - 1886. · 1.46 Impact Factor
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    ABSTRACT: Subtraction of Ictal SPECT Co-registered to MRI (SISCOM) is an imaging technique used to localize the epileptogenic focus in patients with intractable partial epilepsy. The aim of this study was to determine the accuracy of registration algorithms involved in SISCOM analysis using FocusDET, a new user-friendly application. To this end, Monte Carlo simulation was employed to generate realistic SPECT studies. Simulated sinograms were reconstructed by using the Filtered BackProjection (FBP) algorithm and an Ordered Subsets Expectation Maximization (OSEM) reconstruction method that included compensation for all degradations. Registration errors in SPECT-SPECT and SPECT-MRI registration were evaluated by comparing the theoretical and actual transforms. Patient studies with well-localized epilepsy were also included in the registration assessment. Global registration errors including SPECT-SPECT and SPECT-MRI registration errors were less than 1.2 mm on average, exceeding the voxel size (3.32 mm) of SPECT studies in no case. Although images reconstructed using OSEM led to lower registration errors than images reconstructed with FBP, differences after using OSEM or FBP in reconstruction were less than 0.2 mm on average. This indicates that correction for degradations does not play a major role in the SISCOM process, thereby facilitating the application of the methodology in centers where OSEM is not implemented with correction of all degradations. These findings together with those obtained by clinicians from patients via MRI, interictal and ictal SPECT and video-EEG, show that FocusDET is a robust application for performing SISCOM analysis in clinical practice.
    Neuroinformatics 08/2012; · 3.14 Impact Factor
  • Iranian Journal of Nuclear Medicine 01/2012; 20(1):11-18.
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    ABSTRACT: Serial dopamine transporter (DAT) imaging in patients with Parkinson's disease (PD) and other synucleinopathies shows progressive nigrostriatal dopaminergic dysfunction. Because idiopathic rapid-eye-movement (REM) sleep behaviour disorder (IRBD) can precede the classic symptoms of PD and other synucleinopathies, we postulated that serial DAT imaging in patients with IRBD could be used to detect decline in striatal tracer uptake, indicating progressive nigrostriatal cell degeneration. In a prospective study, 20 patients with IRBD (mean age 70·55 years [SD 6·02]) underwent serial DAT imaging with (123)I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl)-nortropane ((123)I-FP-CIT) SPECT at baseline and again after 1·5 years and 3 years; 20 age-matched and sex-matched control participants (69·50 years [6·77]) underwent imaging at baseline and 3 years. The striatum to occipital cortex uptake ratios were calculated for the putamen and caudate nucleus in each hemisphere. In patients, the ratio was judged to be reduced when it was less than two SD of the mean ratio in controls at the same timepoint. Differences in (123)I-FP-CIT uptake between patients and controls in each striatal region and rates of decline were assessed by use of multivariate ANOVA (MANOVA). Compared with controls, patients had significantly reduced mean (123)I-FP-CIT binding in all four striatal regions at baseline and after 3 years. Striatal (123)I-FP-CIT uptake was reduced compared with that in controls in ten patients at baseline and in 13 patients after 3 years. In patients, the mean reduction in (123)I-FP-CIT uptake from baseline to 3 years was 19·36% (95% CI 15·14 to 23·59) in the left putamen, 15·57% (10·87 to 20·28) in the right putamen, 10·81% (6·49 to 15·18) in the left caudate nucleus, and 7·14% (2·74 to 11·56) in the right caudate nucleus. After adjustment for the baseline (123)I-FP-CIT uptake ratios, the decline in (123)I-FP-CIT binding at baseline to 3 years was significantly greater in patients than in controls in the left putamen (9·78% difference between groups, 95% CI 3·22 to 16·32), right putamen (5·43%, 1·99 to 12·86), and left caudate nucleus (8·07%, 1·44 to 14·70), but not in the right caudate nucleus (4·16%, -3·00 to 11·34). At the 3-year assessment, three patients were diagnosed with PD. These patients had the lowest (123)I-FP-CIT uptake at baseline and a mean reduction in (123)I-FP-CIT uptake at 3 years of 32·81% in the left putamen, 30·40% in the right putamen, 26·51% in the left caudate nucleus, and 23·75% in the right caudate nucleus. In patients with IRBD, serial (123)I-FP-CIT SPECT shows decline in striatal tracer uptake that reflects progressive nigrostriatal dopaminergic dysfunction. Serial (123)I-FP-CIT SPECT can be used to monitor the progression of nigrostriatal deficits in patients with IRBD, and could be useful in studies of potential disease-modifying compounds in these patients. Fondo de Investigaciones Sanitarias of Spain.
    The Lancet Neurology 09/2011; 10(9):797-805. · 21.82 Impact Factor
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    ABSTRACT: Nigrostriatal involvement is considered an additional feature in the new consensus criteria for the diagnosis of the cerebellar variant of multiple system atrophy (MSA-C). However, so far, only a few studies, which include a relative small number of patients, give support to this criterion. Our objective was to assess nigrostriatal dopaminergic innervation in patients with MSA-C without parkinsonism by use of dopamine transporter single photon emission computed tomography (DAT SPECT). Thirteen patients that fulfilled criteria for possible or probable MSA-C and presented no parkinsonian signs, and 12 age-matched healthy controls underwent ((123)I-2-β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane ([(123)I]FP-CIT) SPECT. Patients were also evaluated through the Unified Multiple System Atrophy Rating Scale (UMSARS) and brain magnetic resonance imaging (MRI). The mean duration of the cerebellar syndrome was 3.8 ± 1.7 years. DAT SPECT showed a significant decrease of striatal [(123)I]FP-CIT uptake ratios in patients (p < 0.001). Radiotracer uptake reduction was 21% in the entire striatum, 19% in putamen, and 24% in caudate nuclei. Striatal binding ratios were within the normal range in 3 patients. We did not find correlation between striatal uptake and disease duration, age of patients, UMSARS-II score, and pontine diameter. [(123)I]FP-CIT SPECT shows that most but not all MSA-C patients without parkinsonism have subclinical nigrostriatal dopaminergic denervation which is not related to disease duration, cerebellar dysfunction, or pontine atrophy.
    Journal of Neurology 06/2011; 258(12):2248-53. · 3.84 Impact Factor
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    ABSTRACT: To develop a small-animal SPECT system using a low cost commercial portable gamma camera equipped with a pinhole collimator, a continuous scintillation crystal and a position-sensitive photomultiplier tube. The gamma camera was attached to a variable radius system, which enabled us to optimize sensitivity and resolution by adjusting the radius of rotation to the size of the object. To investigate the capability of the SPECT system for small animal imaging, the dependence of resolution and calibration parameters on radius was assessed and acquisitions of small phantoms and mice were carried out. Resolution values, ranging from 1.0mm for a radius of 21.4mm and 1.4mm for a radius of 37.2mm were obtained, thereby justifying the interest of a variable radius SPECT system. The image quality of phantoms and animals were satisfactory, thus confirming the usefulness of the system for small animal SPECT imaging.
    Revista española de medicina nuclear. 06/2011; 30(5):286-91.
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    ABSTRACT: Auditory verbal hallucinations (AVHs) are a core symptom of schizophrenia. Previous reports on neural activity patterns associated with AVHs are inconsistent, arguably owing to the lack of an adequate control group (i.e., patients with similar characteristics but without AVHs) and neglect of the potential confounding effects of medication. The current study was conducted in a homogeneous group of patients with schizophrenia to assess whether the presence or absence of AVHs was associated with differential regional cerebral glucose metabolic patterns. We investigated differences between patients with commenting AVHs and patients without AVHs among a group of dextral antipsychotic-naive inpatients with acute first-episode schizophrenia examined with [(18)F]fluoro-deoxyglucose positron emission tomography (FDG-PET) at rest. Univariate and multivariate approaches were used to establish between-group differences. We included 9 patients with AVHs and 7 patients without AVHs in this study. Patients experiencing AVHs during FDG uptake had significantly higher metabolic rates in the left superior and middle temporal cortices, bilateral superior medial frontal cortex and left caudate nucleus (cluster level p < 0.005, family wise error-corrected, and bootstrap ratio > 3.3, respectively). Additionally, the multivariate method identified hippocampal-parahippocampal, cerebellar and parietal relative hypoactivity during AVHs in both hemispheres (bootstrap ratio < -3.3). The FDG-PET imaging technique does not provide information regarding the temporal course of neural activity. The limited sample size may have increased the risk of false-negative findings. Our results indicate that AVHs in patients with schizophrenia may be mediated by an alteration of neural pathways responsible for normal language function. Our findings also point to the potential role of the dominant caudate nucleus and the parahippocampal gyri in the pathophysiology of AVHs. We discuss the relevance of phenomenology-based grouping in the study of AVHs.
    Journal of psychiatry & neuroscience: JPN 01/2011; 36(5):312-21. · 7.49 Impact Factor
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    ABSTRACT: A tool for the MC simulation of pinhole SPECT cameras that includes the main calibration parameters has been developed and validated.
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    ABSTRACT: Small-animal molecular imaging is a prominent field of research, and SPECT plays an important role within it. Evaluation of imaging systems and reconstruction algorithms in SPECT imaging often involves Monte Carlo simulations, and SimSET is a widely used code for emission tomography simulation. 123I is a frequently used radionuclide in human and small animal studies. It emits a main yield of 159 keV photons, which are used for imaging, but it also has a low contribution of higher energy photons, which generate non-negligible noise in SPECT studies. The aim of this work was to implement experiment-based high- and low-energy response functions for a small animal SPECT system, to incorporate them into SimSET and to carry out a preliminary validation of the simulator obtained for 123I labeled radiotracers. Experimental measurements with 99mTc were carried out to characterize 159 keV detection of 123I. Since most of the relevant high-energy (HE) lines of 123I are close to 511 keV, the detector response to HE photons was characterized with the 511 keV photons from positron-electron annihilation subsequent to 18F decay. Once the obtained response functions were incorporated into SimSET, experimental and simulated images of capillaries and small spheres containing 123I were generated at various distances. Efficiency and spatial resolution were estimated from these images. The values from simulated images are close to the experimental ones, with deviations of under 10% in efficiency and under 6% in spatial resolution.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2011 IEEE; 01/2011
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    ABSTRACT: We developed a cost-effective SPECT scanner prototype (rSPECT) for in vivo imaging of rodents based on small-area gamma cameras. Each detector consists of a position-sensitive photomultiplier tube (PS-PMT) coupled to a 30 x 30 Nal(Tl) scintillator array and electronics attached to the PS-PMT sockets for adapting the detector signals to an in-house developed data acquisition system. The detector components are enclosed in a lead-shielded case with a receptacle to insert the collimators. System performance was assessed using 99mTc for a high-resolution parallel-hole collimator, and for a 0.75-mm pinhole collimator with a 60° aperture angle and a 42-mm collimator length. The energy resolution is about 10.7% of the photopeak energy. The overall system sensitivity is about 3 cps/μCi/detector and planar spatial resolution ranges from 2.4 mm at 1 cm source-to-collimator distance to 4.1 mm at 4.5 cm with parallel-hole collimators. With pinhole collimators planar spatial resolution ranges from 1.2 mm at 1 cm source-to-collimator distance to 2.4 mm at 4.5 cm; sensitivity at these distances ranges from 2.8 to 0.5 cps/μCi/detector. Tomographic hot-rod phantom images are presented together with images of bone, myocardium and brain of living rodents to demonstrate the feasibility of preclinical small-animal studies with the rSPECT.
    IEEE Transactions on Nuclear Science 11/2010; · 1.46 Impact Factor
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    ABSTRACT: In the present work, the authors compare geometrical and Monte Carlo projectors in detail. The geometrical projectors considered were the conventional geometrical Siddon ray-tracer (S-RT) and the orthogonal distance-based ray-tracer (OD-RT), based on computing the orthogonal distance from the center of image voxel to the line-of-response. A comparison of these geometrical projectors was performed using different point spread function (PSF) models. The Monte Carlo-based method under consideration involves an extensive model of the system response matrix based on Monte Carlo simulations and is computed off-line and stored on disk. Comparisons were performed using simulated and experimental data of the commercial small animal PET scanner rPET. The results demonstrate that the orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions yield better images in terms of contrast and spatial resolution than those obtained after using the conventional method and the multiray-based S-RT. Furthermore, the Monte Carlo-based method yields slight improvements in terms of contrast and spatial resolution with respect to these geometrical projectors. The orthogonal distance-based ray-tracer and Siddon ray-tracer using PSF image-space convolutions represent satisfactory alternatives to factorizing the system matrix or to the conventional on-the-fly ray-tracing methods for list-mode reconstruction, where an extensive modeling based on Monte Carlo simulations is unfeasible.
    Medical Physics 11/2010; 37(11):5691-702. · 3.01 Impact Factor
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    ABSTRACT: Reported values of D(2) receptor occupancy (RO) achieved by antipsychotic drugs tend to be lower when measured with (123)I-IBZM SPECT than with (11)C-Raclopride PET. Image degrading factors such as attenuation, distance-dependent collimator response and scatter could account for this difference. While attenuation correction is routinely applied to SPECT images, the other degradations are not usually accounted for. The aim of this work was to assess the impact of scatter correction on D(2) RO quantification with (123)I-IBZM SPECT, and to compare the results of both corrected and un-corrected SPECT values with (11)C-Raclopride PET measurements. Phantom experiments as well as within-subject human data from a previous study were used for this purpose. SPECT images were reconstructed using filtered back-projection including attenuation correction (FBP(A)), ordered subsets expectation maximization including attenuation and point spread function corrections (OSEM(A+PSF)) and ordered subsets expectation maximization including attenuation, point spread function and scatter corrections (OSEM(A+PSF+SCT)). PET images were reconstructed using the FBP algorithm and corrected for attenuation, scatter, random coincidences and dead time. Quantification of receptor availability was performed using the tissue ratio at pseudoequilibrium for SPECT, and the simplified reference tissue model (SRTM) for PET. Analysis was performed using both occipital cortex (occ) and cerebellum (cer) as reference regions for both modalities. When images were reconstructed using FBP(A), SPECT D(2) RO values were significantly lower as compared with PET leading to a D(2) RO difference of -20% (CI(95%): -13, -27%) (occ) and -23% (CI(95%): -14, -31%) (cer). When images were reconstructed using OSEM(A+PSF), SPECT D(2) RO values were also lower as compared with PET leading to a D(2) RO difference of -21% (CI(95%): -14, -27%) (occ) and -24% (CI(95%): -18, -30%) (cer). When images were reconstructed using OSEM(A+PSF+SCT), the D(2) RO bias was reduced to -6% (CI(95%): 0, -13%) (occ) and -11% (CI(95%): -4, -18%) (cer). These data suggest that the scatter correction plays a major role in explaining the differences between D(2) RO measurements using (123)I-IBZM SPECT and (11)C-Raclopride PET.
    NeuroImage 05/2010; 50(4):1511-8. · 6.13 Impact Factor

Publication Stats

416 Citations
163.96 Total Impact Points


  • 1981–2014
    • University of Barcelona
      • • Department of Physiological Sciences I
      • • Departament de Física Aplicada i Òptica
      • • Departament de Medicina
      • • Facultad de Física
      • • Facultad de Medicina
      Barcino, Catalonia, Spain
  • 2011
    • Catalan Institute of Oncology
      Badalona, Catalonia, Spain
  • 1998–2011
    • IDIBAPS August Pi i Sunyer Biomedical Research Institute
      Barcino, Catalonia, Spain
  • 2010
    • University of Santiago de Compostela
      Santiago, Galicia, Spain
  • 2008
    • CRC Corporació Sanitária
      Barcino, Catalonia, Spain
    • GlaxoSmithKline plc.
      • Clinical Pharmacology and Discovery Medicine
      London, ENG, United Kingdom
  • 2001–2006
    • Polytechnic University of Catalonia
      • Department of Physics and Nuclear Engineering (FEN)
      Barcino, Catalonia, Spain
  • 1991
    • Hospital Clínic de Barcelona
      • Servicio de Medicina Nuclear
      Barcelona, Catalonia, Spain
  • 1988
    • Hospital Universitari de Bellvitge
      l'Hospitalet de Llobregat, Catalonia, Spain