Judith Gallego - Academia.edu (original) (raw)
Papers by Judith Gallego
![Research paper thumbnail of Striatal dopamine D 2 receptor occupancy measurements using [123I]IBZM SPECT and [11C]Raclopride PET: A within-subject comparison study](https://attachments.academia-assets.com/48384537/thumbnails/1.jpg)
](Neuroimage, 2008
Introduction: There is extensive literature on antipsychotic induced striatal dopamine D 2 recept... more Introduction: There is extensive literature on antipsychotic induced striatal dopamine D 2 receptor occupancy (D 2 RO) measured either by PET or SPECT. However, a meta analysis of these data reveals that for any given dose of medication, [123I]IBZM SPECT estimates of D 2 RO tend to be lower than those measured with [11C]Raclopride PET. To clarify this issue, D 2 RO was measured in the same subjects using both [123I]IBZM SPECT and [11C]Raclopride PET.
Neuroimage, 2010
Reported values of D 2 receptor occupancy (RO) achieved by antipsychotic drugs tend to be lower w... more 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.
Journal of Neurology
Nigrostriatal involvement is considered an additional feature in the new consensus criteria for t... more 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 (123I-2-β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane ([123I]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 [123I]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. [123I]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.
European Journal of Nuclear Medicine and Molecular Imaging, 2008
Purpose 123I-labelled radioligands are commonly used for single-photon emission computed tomograp... more Purpose 123I-labelled radioligands are commonly used for single-photon emission computed tomography (SPECT) imaging of the dopaminergic system to study the dopamine transporter binding. The aim of this work was to compare the quantitative capabilities of two different SPECT systems through Monte Carlo (MC) simulation. Methods The SimSET MC code was employed to generate simulated projections of a numerical phantom for two gamma cameras equipped with a parallel and a fan-beam collimator, respectively. A fully 3D iterative reconstruction algorithm was used to compensate for attenuation, the spatially variant point spread function (PSF) and scatter. A post-reconstruction partial volume effect (PVE) compensation was also developed. Results For both systems, the correction for all degradations and PVE compensation resulted in recovery factors of the theoretical specific uptake ratio (SUR) close to 100%. For a SUR value of 4, the recovered SUR for the parallel imaging system was 33% for a reconstruction without corrections (OSEM), 45% for a reconstruction with attenuation correction (OSEM-A), 56% for a 3D reconstruction with attenuation and PSF corrections (OSEM-AP), 68% for OSEM-AP with scatter correction (OSEM-APS) and 97% for OSEM-APS plus PVE compensation (OSEM-APSV). For the fan-beam imaging system, the recovered SUR was 41% without corrections, 55% for OSEM-A, 65% for OSEM-AP, 75% for OSEM-APS and 102% for OSEM-APSV. Conclusion Our findings indicate that the correction for degradations increases the quantification accuracy, with PVE compensation playing a major role in the SUR quantification. The proposed methodology allows us to reach similar SUR values for different SPECT systems, thereby allowing a reliable standardisation in multicentric studies.
Psychiatry Research-neuroimaging, 2011
Alterations in the dopaminergic system have long been implicated in schizophrenia. A key componen... more Alterations in the dopaminergic system have long been implicated in schizophrenia. A key component in dopaminergic neurotransmission is the striatal dopamine transporter (DAT). To date, there have been no longitudinal studies evaluating the course of DAT in schizophrenia. A 4-year follow-up study was therefore conducted in which single photon emission computed tomography was used to measure DAT binding in 14 patients and 7 controls. We compared the difference over time in [123I] FP-CIT striatal/occipital uptake ratios (SOUR) between patients and controls and the relationship between this difference and both symptomatology and functional outcome at follow-up. We also calculated the relationship between baseline SOUR, symptoms and functional outcome at follow-up. There were no statistically significant differences between patients' SOUR changes over time and those of controls. A significant negative correlation was observed between patients' SOUR changes over time and negative symptomatology at follow-up. A significant negative correlation was also found between baseline SOUR in patients and negative symptomatology, and there was a significant association between lower SOUR at baseline and poor outcome. Although the study found no overall differences in DAT binding during follow-up between schizophrenia patients and controls, it demonstrated that differences in DAT binding relate to patients' characteristics at follow-up.
Lancet Neurology, 2010
Background Patients with idiopathic rapid-eye-movement sleep behaviour disorder (IRBD) may develo... more Background Patients with idiopathic rapid-eye-movement sleep behaviour disorder (IRBD) may develop neurodegenerative conditions associated with substantia nigra dysfunction such as Parkinson's disease. In patients with Parkinson's disease, ¹²³I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fl uoropropyl)-nortropane (¹²³I-FP-CIT) SPECT detects striatal dopamine dysfunction resulting from nigral pathology whereas transcranial sonography (TCS) shows increased substantia nigra echogenic size, even before parkinsonism is clinically evident. We postulated that these neuroimaging changes could occur in a proportion of IRBD individuals who might then be at increased risk for development of a neurodegenerative disorder associated with substantia nigra dysfunction.
Neuroimage, 2008
Introduction: There is extensive literature on antipsychotic induced striatal dopamine D 2 recept... more Introduction: There is extensive literature on antipsychotic induced striatal dopamine D 2 receptor occupancy (D 2 RO) measured either by PET or SPECT. However, a meta analysis of these data reveals that for any given dose of medication, [123I]IBZM SPECT estimates of D 2 RO tend to be lower than those measured with [11C]Raclopride PET. To clarify this issue, D 2 RO was measured in the same subjects using both [123I]IBZM SPECT and [11C]Raclopride PET.
Neuroimage, 2010
Reported values of D 2 receptor occupancy (RO) achieved by antipsychotic drugs tend to be lower w... more 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.
Journal of Neurology
Nigrostriatal involvement is considered an additional feature in the new consensus criteria for t... more 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 (123I-2-β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fluoropropyl) nortropane ([123I]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 [123I]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. [123I]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.
European Journal of Nuclear Medicine and Molecular Imaging, 2008
Purpose 123I-labelled radioligands are commonly used for single-photon emission computed tomograp... more Purpose 123I-labelled radioligands are commonly used for single-photon emission computed tomography (SPECT) imaging of the dopaminergic system to study the dopamine transporter binding. The aim of this work was to compare the quantitative capabilities of two different SPECT systems through Monte Carlo (MC) simulation. Methods The SimSET MC code was employed to generate simulated projections of a numerical phantom for two gamma cameras equipped with a parallel and a fan-beam collimator, respectively. A fully 3D iterative reconstruction algorithm was used to compensate for attenuation, the spatially variant point spread function (PSF) and scatter. A post-reconstruction partial volume effect (PVE) compensation was also developed. Results For both systems, the correction for all degradations and PVE compensation resulted in recovery factors of the theoretical specific uptake ratio (SUR) close to 100%. For a SUR value of 4, the recovered SUR for the parallel imaging system was 33% for a reconstruction without corrections (OSEM), 45% for a reconstruction with attenuation correction (OSEM-A), 56% for a 3D reconstruction with attenuation and PSF corrections (OSEM-AP), 68% for OSEM-AP with scatter correction (OSEM-APS) and 97% for OSEM-APS plus PVE compensation (OSEM-APSV). For the fan-beam imaging system, the recovered SUR was 41% without corrections, 55% for OSEM-A, 65% for OSEM-AP, 75% for OSEM-APS and 102% for OSEM-APSV. Conclusion Our findings indicate that the correction for degradations increases the quantification accuracy, with PVE compensation playing a major role in the SUR quantification. The proposed methodology allows us to reach similar SUR values for different SPECT systems, thereby allowing a reliable standardisation in multicentric studies.
Psychiatry Research-neuroimaging, 2011
Alterations in the dopaminergic system have long been implicated in schizophrenia. A key componen... more Alterations in the dopaminergic system have long been implicated in schizophrenia. A key component in dopaminergic neurotransmission is the striatal dopamine transporter (DAT). To date, there have been no longitudinal studies evaluating the course of DAT in schizophrenia. A 4-year follow-up study was therefore conducted in which single photon emission computed tomography was used to measure DAT binding in 14 patients and 7 controls. We compared the difference over time in [123I] FP-CIT striatal/occipital uptake ratios (SOUR) between patients and controls and the relationship between this difference and both symptomatology and functional outcome at follow-up. We also calculated the relationship between baseline SOUR, symptoms and functional outcome at follow-up. There were no statistically significant differences between patients' SOUR changes over time and those of controls. A significant negative correlation was observed between patients' SOUR changes over time and negative symptomatology at follow-up. A significant negative correlation was also found between baseline SOUR in patients and negative symptomatology, and there was a significant association between lower SOUR at baseline and poor outcome. Although the study found no overall differences in DAT binding during follow-up between schizophrenia patients and controls, it demonstrated that differences in DAT binding relate to patients' characteristics at follow-up.
Lancet Neurology, 2010
Background Patients with idiopathic rapid-eye-movement sleep behaviour disorder (IRBD) may develo... more Background Patients with idiopathic rapid-eye-movement sleep behaviour disorder (IRBD) may develop neurodegenerative conditions associated with substantia nigra dysfunction such as Parkinson's disease. In patients with Parkinson's disease, ¹²³I-2β-carbomethoxy-3β-(4-iodophenyl)-N-(3-fl uoropropyl)-nortropane (¹²³I-FP-CIT) SPECT detects striatal dopamine dysfunction resulting from nigral pathology whereas transcranial sonography (TCS) shows increased substantia nigra echogenic size, even before parkinsonism is clinically evident. We postulated that these neuroimaging changes could occur in a proportion of IRBD individuals who might then be at increased risk for development of a neurodegenerative disorder associated with substantia nigra dysfunction.