Publications by authors named "Pim Pullens"

17 Publications

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Editorial for "Evaluating High Spatial Resolution Diffusion Kurtosis Imaging at 3T: Reproducibility and Quality of Fit".

Authors:
Pim Pullens

J Magn Reson Imaging 2021 04 9;53(4):1188-1189. Epub 2020 Nov 9.

Department of Radiology, University Hospital Ghent, Ghent, Belgium.

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http://dx.doi.org/10.1002/jmri.27428DOI Listing
April 2021

Consensus-based technical recommendations for clinical translation of renal T1 and T2 mapping MRI.

MAGMA 2020 Feb 22;33(1):163-176. Epub 2019 Nov 22.

Department of Radiology, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands.

To develop technical recommendations on the acquisition and post-processing of renal longitudinal (T1) and transverse (T2) relaxation time mapping. A multidisciplinary panel consisting of 18 experts in the field of renal T1 and T2 mapping participated in a consensus project, which was initiated by the European Cooperation in Science and Technology Action PARENCHIMA CA16103. Consensus recommendations were formulated using a two-step modified Delphi method. The first survey consisted of 56 items on T1 mapping, of which 4 reached the pre-defined consensus threshold of 75% or higher. The second survey was expanded to include both T1 and T2 mapping, and consisted of 54 items of which 32 reached consensus. Recommendations based were formulated on hardware, patient preparation, acquisition, analysis and reporting. Consensus-based technical recommendations for renal T1 and T2 mapping were formulated. However, there was considerable lack of consensus for renal T1 and particularly renal T2 mapping, to some extent surprising considering the long history of relaxometry in MRI, highlighting key knowledge gaps that require further work. This paper should be regarded as a first step in a long-term evidence-based iterative process towards ever increasing harmonization of scan protocols across sites, to ultimately facilitate clinical implementation.
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http://dx.doi.org/10.1007/s10334-019-00797-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7021750PMC
February 2020

Consensus-based technical recommendations for clinical translation of renal diffusion-weighted MRI.

MAGMA 2020 Feb 1;33(1):177-195. Epub 2019 Nov 1.

Department of Radiology, Center for Biomedical Imaging (CBI), Center for Advanced Imaging Innovation and Research (CAI2R), NYU Langone Health, New York, NY, USA.

Objectives: Standardization is an important milestone in the validation of DWI-based parameters as imaging biomarkers for renal disease. Here, we propose technical recommendations on three variants of renal DWI, monoexponential DWI, IVIM and DTI, as well as associated MRI biomarkers (ADC, D, D*, f, FA and MD) to aid ongoing international efforts on methodological harmonization.

Materials And Methods: Reported DWI biomarkers from 194 prior renal DWI studies were extracted and Pearson correlations between diffusion biomarkers and protocol parameters were computed. Based on the literature review, surveys were designed for the consensus building. Survey data were collected via Delphi consensus process on renal DWI preparation, acquisition, analysis, and reporting. Consensus was defined as ≥ 75% agreement.

Results: Correlations were observed between reported diffusion biomarkers and protocol parameters. Out of 87 survey questions, 57 achieved consensus resolution, while many of the remaining questions were resolved by preference (65-74% agreement). Summary of the literature and survey data as well as recommendations for the preparation, acquisition, processing and reporting of renal DWI were provided.

Discussion: The consensus-based technical recommendations for renal DWI aim to facilitate inter-site harmonization and increase clinical impact of the technique on a larger scale by setting a framework for acquisition protocols for future renal DWI studies. We anticipate an iterative process with continuous updating of the recommendations according to progress in the field.
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http://dx.doi.org/10.1007/s10334-019-00790-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7021760PMC
February 2020

Technical recommendations for clinical translation of renal MRI: a consensus project of the Cooperation in Science and Technology Action PARENCHIMA.

MAGMA 2020 Feb 18;33(1):131-140. Epub 2019 Oct 18.

Imaging Biomarkers Group, Department of Biomedical Imaging Sciences, University of Leeds, Leeds, UK.

Purpose: The potential of renal MRI biomarkers has been increasingly recognised, but clinical translation requires more standardisation. The PARENCHIMA consensus project aims to develop and apply a process for generating technical recommendations on renal MRI.

Methods: A task force was formed in July 2018 focused on five methods. A draft process for attaining consensus was distributed publicly for consultation and finalised at an open meeting (Prague, October 2018). Four expert panels completed surveys between October 2018 and March 2019, discussed results and refined the surveys at a face-to-face meeting (Aarhus, March 2019) and completed a second round (May 2019).

Results: A seven-stage process was defined: (1) formation of expert panels; (2) definition of the context of use; (3) literature review; (4) collection and comparison of MRI protocols; (5) consensus generation by an approximate Delphi method; (6) reporting of results in vendor-neutral and vendor-specific terms; (7) ongoing review and updating. Application of the process resulted in 166 consensus statements.

Conclusion: The process generated meaningful technical recommendations across very different MRI methods, while allowing for improvement and refinement as open issues are resolved. The results are likely to be widely supported by the renal MRI community and thereby promote more harmonisation.
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http://dx.doi.org/10.1007/s10334-019-00784-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7021737PMC
February 2020

Central versus Local Radiological Reading of Acute Computed Tomography Characteristics in Multi-Center Traumatic Brain Injury Research.

J Neurotrauma 2019 04 11;36(7):1080-1092. Epub 2018 Dec 11.

1 Department of Radiology, Antwerp University Hospital and University of Antwerp, Antwerp, Belgium.

Observer variability in local radiological reading is a major concern in large-scale multi-center traumatic brain injury (TBI) studies. A central review process has been advocated to minimize this variability. The aim of this study is to compare central with local reading of TBI imaging datasets and to investigate the added value of central review. A total of 2050 admission computed tomography (CT) scans from subjects enrolled in the Collaborative European NeuroTrauma Effectiveness Research in Traumatic Brain Injury (CENTER-TBI) study were analyzed for seven main CT characteristics. Kappa statistics were used to calculate agreement between central and local evaluations and a center-specific analysis was performed. The McNemar test was used to detect whether discordances were significant. Central interobserver and intra-observer agreement was calculated in a subset of patients. Good agreement was found between central and local assessment for the presence or absence of structural pathology (CT+, CT-, κ = 0.73) and most CT characteristics (κ = 0.62 to 0.71), except for traumatic axonal injury lesions (κ = 0.37). Despite good kappa values, discordances were significant in four of seven CT characteristics (i.e., midline shift, contusion, traumatic subarachnoid hemorrhage, and cisternal compression; p = 0.0005). Central reviewers showed substantial to excellent interobserver and intra-observer agreement (κ = 0.73 to κ = 0.96), contrasted by considerable variability in local radiological reading. Compared with local evaluation, a central review process offers a more consistent radiological reading of acute CT characteristics in TBI. It generates reliable, reproducible data and should be recommended for use in multi-center TBI studies.
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http://dx.doi.org/10.1089/neu.2018.6061DOI Listing
April 2019

Diffusion kurtosis imaging with free water elimination: A bayesian estimation approach.

Magn Reson Med 2018 08 2;80(2):802-813. Epub 2018 Feb 2.

imec-Vision Lab, Department of Physics, University of Antwerp, Antwerp, Belgium.

Purpose: Diffusion kurtosis imaging (DKI) is an advanced magnetic resonance imaging modality that is known to be sensitive to changes in the underlying microstructure of the brain. Image voxels in diffusion weighted images, however, are typically relatively large making them susceptible to partial volume effects, especially when part of the voxel contains cerebrospinal fluid. In this work, we introduce the "Diffusion Kurtosis Imaging with Free Water Elimination" (DKI-FWE) model that separates the signal contributions of free water and tissue, where the latter is modeled using DKI.

Theory And Methods: A theoretical study of the DKI-FWE model, including an optimal experiment design and an evaluation of the relative goodness of fit, is carried out. To stabilize the ill-conditioned estimation process, a Bayesian approach with a shrinkage prior (BSP) is proposed. In subsequent steps, the DKI-FWE model and the BSP estimation approach are evaluated in terms of estimation error, both in simulation and real data experiments.

Results: Although it is shown that the DKI-FWE model parameter estimation problem is ill-conditioned, DKI-FWE was found to describe the data significantly better compared to the standard DKI model for a large range of free water fractions. The acquisition protocol was optimized in terms of the maximally attainable precision of the DKI-FWE model parameters. The BSP estimator is shown to provide reliable DKI-FWE model parameter estimates.

Conclusion: The combination of the DKI-FWE model with BSP is shown to be a feasible approach to estimate DKI parameters, while simultaneously eliminating free water partial volume effects. Magn Reson Med 80:802-813, 2018. © 2018 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
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http://dx.doi.org/10.1002/mrm.27075DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5947598PMC
August 2018

The effect of adipose tissue-derived stem cells in a middle cerebral artery occlusion stroke model depends on their engraftment rate.

Stem Cell Res Ther 2017 04 26;8(1):96. Epub 2017 Apr 26.

Department of Neurology, Universitätsmedizin Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, D-68167, Mannheim, Germany.

Background: In the field of experimental stem cell therapy, intra-arterial (IA) delivery yields the best results concerning, for example, migrated cell number at the targeted site. However, IA application also appears to be associated with increased mortality rates and infarction. Since many rodent studies systemically apply 1 × 10 cells, this could also be a consequence of engrafted cell number. The aim of this study was therefore to investigate the effect of different doses of adipose tissue-derived stem cells (ASCs) on engraftment rates and stroke outcome measured in vivo using 9.4-T high-field magnetic resonance imaging (MRI).

Methods: Male Wistar rats (n = 43) underwent a middle cerebral artery occlusion (MCAo) for 45 or 90 min, followed by IA delivery of either saline or 1 × 10, 3 × 10, or 5 × 10 ASCs pre-labelled with very small superparamagnetic iron oxide particles (VSOPs). MRI (9.4-T) analysis was performed 48 h and 9 days post-MCAo. Lesion volumes were assessed by analysis of T2-weighted images and cell signal tracking showing cell engraftment and active cell migration by an improved T2*-analysis.

Results: The ASC-derived signal intensity increased in the affected hemisphere 48 h post MCAo with injected cell number (p < 0.05). The analysis of stroke volumes revealed an increased infarction after injection of 1 × 10 ASCs compared to controls or application of 5 × 10 ASCs (p < 0.05). At 9 days post-MCAo, injection of 3 × 10 ASCs resulted in reduced infarct volumes (p < 0.05). Correspondingly, MRI analysis revealed no changes in cell numbers between both MRI examinations but showed active ASC migration to the site of infarction.

Conclusion: Our results confirm that IA injection is an efficient way of targeting damaged brain tissue but its usefulness strongly depends on the right dose of delivered stem cells since this factor has a strong influence on migration rate and infarct volume, with better results for doses below 1 × 10 cells. Future challenges will include the determination of therapeutic doses for best cellular engraftment and stroke outcome.
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http://dx.doi.org/10.1186/s13287-017-0545-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5407025PMC
April 2017

Diffusion tensor imaging of the anterior cruciate ligament graft.

J Magn Reson Imaging 2017 11 14;46(5):1423-1432. Epub 2017 Feb 14.

Imec/Vision Lab, Department of Physics, University of Antwerp, Wilrijk, Belgium.

Purpose: A great need exists for objective biomarkers to assess graft healing following ACL reconstruction to guide the time of return to sports. The purpose of this study was to evaluate the feasibility and reliability of diffusion tensor imaging (DTI) to delineate the anterior cruciate ligament (ACL) graft and to investigate its diffusion properties using a clinical 3T scanner.

Materials And Methods: DTI of the knee (b = 0, 400, and 800 s/mm , 10 diffusion directions, repeated 16 times for a total of 336 diffusion-weighted volumes) was performed at 3T in 17 patients between 3 and 7 months (mean, 4 months) following ACL reconstruction. Tractography was performed by two independent observers to delineate the ACL graft. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were calculated within the graft. Interrater reliability was assessed using the intraclass correlation coefficient (ICC) and the scan-rescan reproducibility was evaluated based on the percentage coefficient of variance (%CV) across 20 repetition bootknife samples.

Results: In all subjects, tractography of the ACL graft was feasible. Quantitative evaluation of the diffusion properties of the ACL graft yielded the following mean ± SD values: FA = 0.23 ± 0.04; MD = 1.30 ± 0.11 × 10 mm /s; AD = 1.61 ± 0.12 × 10 mm /s, and RD = 1.15 ± 0.11 × 10 mm /s. Interrater reliability for the DTI parameters was excellent (ICC = 0.91-0.98). Mean %CVs for FA, MD, AD, and RD were 4.6%, 3.5%, 3.7%, and 4.4%, respectively.

Conclusion: We demonstrated the feasibility and reliability of DTI for the visualization and quantitative evaluation of the ACL graft at 3T.

Level Of Evidence: 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2017;46:1423-1432.
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http://dx.doi.org/10.1002/jmri.25666DOI Listing
November 2017

Technical Note: A safe, cheap, and easy-to-use isotropic diffusion MRI phantom for clinical and multicenter studies.

Med Phys 2017 Mar 28;44(3):1063-1070. Epub 2017 Feb 28.

Department of Radiology, University Hospital Antwerp & University of Antwerp, 2650, Edegem, Belgium.

Purpose: Since Diffusion Weighted Imaging (DWI) data acquisition and processing are not standardized, substantial differences in DWI derived measures such as Apparent Diffusion Coefficient (ADC) may arise which are related to the acquisition or MRI processing method, but not to the sample under study. Quality assurance using a standardized test object, or phantom, is a key factor in standardizing DWI across scanners.

Methods: Current diffusion phantoms are either complex to use, not available in larger quantities, contain substances unwanted in a clinical environment, or are expensive. A diffusion phantom based on a polyvinylpyrrolidone (PVP) solution, together with a phantom holder, is presented and compared to existing diffusion phantoms for use in clinical DWI scans. An ADC vs. temperature calibration curve was obtained.

Results: ADC of the phantom (808 to 857 ± 0.2 mm /s) is in the same range as ADC values found in brain tissue. ADC measurements are highly reproducible across time with an intra-class correlation coefficient of > 0.8. ADC as function of temperature (in Kelvin) can be estimated as ADCm(T)=[exp(-7.09)·exp-2903.81T-1293.55] with a total uncertainty (95% confidence limit) of ± 1.7%.

Conclusion: We present an isotropic diffusion MRI phantom, together with its temperature calibration curve, that is easy-to-use in a clinical environment, cost-effective, reproducible to produce, and that contains no harmful substances.
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http://dx.doi.org/10.1002/mp.12101DOI Listing
March 2017

Diffusion Tensor Imaging: A Possible Biomarker in Severe Traumatic Brain Injury and Aneurysmal Subarachnoid Hemorrhage?

Neurosurgery 2016 Dec;79(6):786-793

*Department of Neurosurgery, Antwerp University Hospital, Edegem, Belgium; ‡Department of Radiology, Antwerp University Hospital, Edegem, Belgium; §Department of Intensive Care, Antwerp University Hospital, Edegem, Belgium; ¶University of Antwerp, Edegem, Belgium.

Background: A great need exists in traumatic brain injury (TBI) and aneurysmal subarachnoid hemorrhage (aSAH) for objective biomarkers to better characterize the disease process and to serve as early endpoints in clinical studies. Diffusion tensor imaging (DTI) has shown promise in TBI, but much less is known about aSAH.

Objective: To explore the use of whole-brain DTI tractography in TBI and aSAH as a biomarker and early endpoint.

Methods: Of a cohort of 43 patients with severe TBI (n = 20) or aSAH (n = 23) enrolled in a prospective, observational, multimodality monitoring study, DTI data were acquired at approximately day 12 (median, 12 days; interquartile range, 12-14 days) after injury in 22 patients (TBI, n = 12; aSAH, n = 10). Whole-brain DTI tractography was performed, and the following parameters quantified: average fractional anisotropy, mean diffusivity, tract length, and the total number of reconstructed fiber tracts. These were compared between TBI and aSAH patients and correlated with mortality and functional outcome assessed at 6 months by the Glasgow Outcome Scale Extended.

Results: Significant differences were found for fractional anisotropy values (P = .01), total number of tracts (P = .03), and average tract length (P = .002) between survivors and nonsurvivors. A sensitivity analysis showed consistency of results between the TBI and aSAH patients for the various DTI measures.

Conclusion: DTI parameters, assessed at approximately day 12 after injury, correlated with mortality at 6 months in patients with severe TBI or aSAH. Similar patterns were found for both TBI and aSAH patients. This supports a potential role of DTI as early endpoint for clinical studies and a predictor of late mortality.

Abbreviations: aSAH, aneurysmal subarachnoid hemorrhageDTI, diffusion tensor imagingFA, fractional anisotropyGOSE, Glasgow Outcome Scale ExtendedTBI, traumatic brain injuryTE, echo timeTR, repetition time.
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http://dx.doi.org/10.1227/NEU.0000000000001325DOI Listing
December 2016

Reproducibility of hormone-driven regional grey matter volume changes in women using SPM8 and SPM12.

Brain Struct Funct 2016 12 9;221(9):4631-4641. Epub 2016 Feb 9.

Department of Radiology, Antwerp University Hospital, University of Antwerp, Wilrijkstraat 10, 2650, Antwerp, Belgium.

Aim of this work was to evaluate the reproducibility of hormone driven regional grey matter volume differences in women, and their correlations with premenstrual symptoms, as determined by voxel-based morphometry (VBM). After data quality control, a total of 138 T1-weighted MR images were included in this longitudinal study, and were analyzed as three different subgroups. Women with a natural menstrual cycle were scanned at three time-points: follicular, ovulatory and luteal phase. Two groups of women, using androgenic and anti-androgenic hormonal contraceptives, respectively, were scanned twice: during the pill-free week and during pill intake. Additionally, subjects were asked to complete a "daily rating of severity of problems" questionnaire, to quantify premenstrual symptoms. All data were analyzed using SPM8 and SPM12 with identical parameter settings. In the natural menstrual cycle group, the regional grey matter volume of the insula is larger at ovulation, as compared to the luteal phase. Premenstrual symptoms correlate differently with regional grey matter volumes between women with a natural cycle and hormonal contraceptive users. Changes in hormonal environment can to various extents affect VBM findings in women. We suggest that researchers take these confounding factors into account while applying this technique, to avoid heterogeneity in data acquisition and to safeguard the sensitivity of findings. Additionally, we suggest validating the consistency of results using more than one software package.
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http://dx.doi.org/10.1007/s00429-016-1193-1DOI Listing
December 2016

Stability of resting state networks in the female brain during hormonal changes and their relation to premenstrual symptoms.

Brain Res 2015 Oct 4;1624:275-285. Epub 2015 Aug 4.

Department of Radiology, Antwerp University Hospital & University of Antwerp Belgium, Belgium. Electronic address:

Resting-state fMRI is a promising imaging technique to evaluate functions in the human brain in health and disease. Different hormonal stages of the female menstrual cycle and hormonal contraceptives use affect results in task-based fMRI; it is however not yet clarified whether resting state networks are also altered. A population of 18 women with a natural cycle, and 19 women using hormonal contraceptives was examined in a longitudinal study-design. The natural cycle group was scanned at 3 time-points (follicular phase, ovulation, luteal phase), and the contraceptives group was scanned twice (inactive pill-phase, active pill-phase). Blood samples were acquired to evaluate hormonal concentrations, and premenstrual symptoms were assessed through daily record of severity of problems questionnaires. Results show no major alterations in the default mode network and the executive control network between different hormonal phases, across or within groups. A positive correlation of functional connectivity in the posterior part of the default mode network (DMN) was found with premenstrual-like symptoms in the hormonal contraceptives group. Using the current methodology, the studied resting state networks seem to show a decent stability throughout menstrual cycle phases. Also, no effect of hormonal contraceptive use is found. Interestingly, we show for the first time an association of DMN alterations with premenstrual-like symptoms, experienced during the inactive pill-phase by a sub-population of women.
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http://dx.doi.org/10.1016/j.brainres.2015.07.045DOI Listing
October 2015

Evidence for normal letter-sound integration, but altered language pathways in a case of recovered Landau-Kleffner Syndrome.

Brain Cogn 2015 Oct 29;99:32-45. Epub 2015 Jul 29.

Maastricht University, Maastricht Brain Imaging Center, Faculty of Psychology and Neuroscience, Oxfordlaan 55, 6229 EV Maastricht, Netherlands; Brain Innovation BV, Research & Development, Oxfordlaan 55, 6229 EV Maastricht, Netherlands.

Landau-Kleffner Syndrome (LKS) is a rare form of acquired aphasia in children, characterized by epileptic discharges, which occur mostly during sleep. After normal speech and language development, aphasia develops between the ages of 3-7 years in a period ranging from days to months. The epileptic discharges usually disappear after reaching adulthood, but language outcomes are usually poor if no treatment focused on restoration of (non-) verbal communication is given. Patients often appear deaf-mute, but sign language, as part of the treatment, may lead to recovery of communication. The neural mechanisms underlying poor language outcomes in LKS are not yet understood. In this detailed functional MRI study of a recovered LKS patient - that is, a patient no longer suffering from epileptic discharges, audiovisual multi-sensory processing was investigated, since LKS patients are often proficient in reading, but not in speech perception. In the recovered LKS patient a large difference in the neural activation to auditory stimuli was found in the left versus the right auditory cortex, which cannot be attributed to hearing loss. Compared to healthy proficient readers investigated earlier with the same fMRI experiment, the patient demonstrated normal letter-sound integration in the superior temporal gyrus as demonstrated by the multi-sensory interaction index, indicating intact STG function. Diffusion Tensor Imaging (DTI) based fiber tracking in the LKS patient showed fibers originating from Heschl's gyrus that seem to be left-right inverted with respect to HG fiber pattern described in the literature for healthy controls. In the patient, in both hemispheres we found arcuate fibers projecting from (homologues of) Broca's to Wernicke's areas, and a lack of fibers from arcuate left inferior parietal and sylvian areas reported in healthy subjects. We observed short arcuate segments in the right hemisphere. Although speculative, our results suggest intact temporal lobe processing but an altered temporal to frontal connectivity. The altered connectivity might explain observed short-term verbal memory problems, disturbed (speech) sound-motor interaction and online feedback of speech and might be one of the neuronal factors underlying LKS.
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http://dx.doi.org/10.1016/j.bandc.2015.07.003DOI Listing
October 2015

Subcortical connections to human amygdala and changes following destruction of the visual cortex.

Curr Biol 2012 Aug 28;22(15):1449-55. Epub 2012 Jun 28.

Cognitive and Affective Neuroscience Laboratory, Tilburg University, 5000 LE Tilburg, The Netherlands.

Nonconscious [1-6], rapid [7, 8], or coarse [9] visual processing of emotional stimuli induces functional activity in a subcortical pathway to the amygdala involving the superior colliculus and pulvinar. Despite evidence in lower mammals [10, 11] and nonhuman primates [12], it remains speculative whether anatomical connections between these structures exist in the human brain [13-15]. It is also unknown whether destruction of the visual cortex, which provides a major input to the amygdala, induces modifications in anatomical connections along this subcortical pathway. We used diffusion tensor imaging to investigate in vivo anatomical connections between human amygdala and subcortical visual structures in ten age-matched controls and in one patient with early unilateral destruction of the visual cortex. We found fiber connections between pulvinar and amygdala and also between superior colliculus and amygdala via the pulvinar in the controls as well as in the patient. Destruction of the visual cortex led to qualitative and quantitative modifications along the pathways connecting these three structures and the changes were confined to the patient's damaged hemisphere. The present findings thus show extensive neural plasticity in the anatomical connections between subcortical visual structures of old evolutionary origin involved in the processing of emotional stimuli.
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http://dx.doi.org/10.1016/j.cub.2012.06.006DOI Listing
August 2012

Ground truth hardware phantoms for validation of diffusion-weighted MRI applications.

J Magn Reson Imaging 2010 Aug;32(2):482-8

Maastricht Brain Imaging Center, Faculty of Psychology and Neuroscience, Maastricht University, The Netherlands.

Purpose: To quantitatively validate diffusion-weighted MRI (DW-MRI) applications, a hardware phantom containing crossing fibers at a sub-voxel level is presented. It is suitable for validation of a large spectrum of DW-MRI applications from acquisition to fiber tracking, which is an important recurrent issue in the field.

Materials And Methods: Phantom properties were optimized to resemble properties of human white matter in terms of anisotropy, fractional anisotropy, and T(2). Sub-voxel crossings were constructed at angles of 30, 50, and 65 degrees, by wrapping polyester fibers, with a diameter close to axon diameter, into heat shrink tubes. We show our phantoms are suitable for the acquisition of DW-MRI data using a clinical protocol.

Results: The phantoms can be used to successfully estimate both the diffusion tensor and non-Gaussian diffusion models, and perform streamline fiber tracking. DOT (Diffusion Orientation Transform) and q-ball reconstruction of the diffusion profiles acquired at b = 3000 s/mm(2) and 132 diffusion directions reveal multimodal diffusion profiles in voxels containing crossing yarn strands.

Conclusion: The highly purpose adaptable phantoms provide a DW-MRI validation platform: applications include optimisation of acquisition schemes, validation of non-Gaussian diffusion models, comparison and validation of fiber tracking algorithms, and quality control in multi-center DWI studies.
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http://dx.doi.org/10.1002/jmri.22243DOI Listing
August 2010

Quantifying the spatial resolution of the gradient echo and spin echo BOLD response at 3 Tesla.

Magn Reson Med 2005 Dec;54(6):1465-72

F. C. Donders Centre for Cognitive Neuroimaging, University of Nijmegen, the Netherlands.

The blood oxygen level dependent (BOLD) response, as measured with fMRI, offers good spatial resolution compared to other non-invasive neuroimaging methods. The use of a spin echo technique rather than the conventional gradient echo technique may further improve the resolution by refocusing static dephasing effects around the larger vessels, so sensitizing the signal to the microvasculature. In this work the width of the point spread function (PSF) of the BOLD response at a field strength of 3 Tesla is compared for these two approaches. A double echo EPI pulse sequence with simultaneous collection of gradient echo and spin echo signal allows a direct comparison of the techniques. Rotating multiple-wedge stimuli of different spatial frequencies are used to estimate the width of the BOLD response. Waves of activation are created on the surface of the visual cortex, which begin to overlap as the wedge separation decreases. The modulation of the BOLD response decreases with increasing spatial frequency in a manner dependent on its width. The spin echo response shows a 13% reduction in the width of the PSF, but at a cost of at least 3-fold reduction in contrast to noise ratio.
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http://dx.doi.org/10.1002/mrm.20712DOI Listing
December 2005