Skills and Expertise
Research Items (56)
Background: Axonal degeneration is related to long-term disability in patients with multiple sclerosis (MS). The underlying mechanism remains ill understood but appears to involve axonal energetic dysfunction. A globally impaired cerebral blood flow (CBF) has been observed in the normal-appearing white matter (NAWM) of patients with MS, which is probably related to astrocytic overexpression of endothelin-1 (ET-1). Cerebral hypoperfusion has been associated with reduced mitochondrial activity and disabling symptoms (e.g. fatigue and cognitive decline) of MS. Countering this process could therefore be beneficial in the disease course. Short-term CBF restoration with a single 62.5-mg dose of the ET-1 receptor antagonist bosentan has already been demonstrated in patients with MS. Methods: The ROCHIMS study is a proof-of-concept double-blind randomized clinical trial in which patients with relapsing-remitting MS will receive either 62.5 mg bosentan or matching placebo twice daily during 28 ± 2 days. Clinical evaluation and brain magnetic resonance imaging (MRI) will be performed at baseline and treatment termination. Based on previous work, we expect a global increase of CBF in the individuals treated with bosentan. The primary outcome measure is the change of N-acetyl aspartate in centrum semiovale NAWM, which is a marker of regional axonal mitochondrial activity. Other parameters of interest include changes in fatigue, cognition, motor function, depression, and brain volume. Discussion: We hypothesize that restoring cerebral hypoperfusion in MS patients improves axonal metabolism. Early positive effects on fatigue and cognitive dysfunction related to MS might additionally be detected. There is a medical need for drugs that can slow down the progressive axonal degeneration in MS, making this an important topic of interest.
- Dec 2018
Although in treatment-resistant depression (TRD) subgenual anterior cingulate cortex (sgACC) functional connectivity (FC) is frequently used to examine deregulated brain networks, neurobiological data from other sources may be required to interpret these FC findings. In 16 melancholic TRD patients with a high level of treatment resistance and 16 closely matched healthy never-depressed individuals we verified whether sgACC FC patterns were related to regional metabolic activity (CMRglc) with ¹⁸FDG PET imaging. Notwithstanding that TRD patients displayed stronger sgACC FC with the right lateral frontotemporal cortex, metabolically they exhibited the opposite pattern. Our results indicate that the sgACC seed and its functionally connected regions not automatically follow a similar metabolic pattern in TRD, possibly reflecting the refractory state of the sample. Multimodal brain imaging may help to increase our insight into the pathophysiology of TRD.
Background and purpose: Failed back surgery syndrome (FBSS) is a common and devastating chronic neuropathic pain disorder. Conventional spinal cord stimulation (SCS) applies electrical suprathreshold pulses to the spinal cord at a frequency of 40–60 Hz and relieves pain in FBSS patients. During the last decade, two major changes have emerged in the techniques of stimulating the spinal cord: paresthesia-free or subthreshold stimulation and administration of higher frequency or higher amounts of energy to the spinal cord. Despite the positive clinical results, the mechanism of action remains unclear. A functional MRI (fMRI) study was conducted to investigate the brain alterations during subthreshold and suprathreshold stimulation at different frequencies. Methods: Ten subjects with FBSS, treated with externalized SCS, received randomly four different stimulation frequencies (4 Hz, 60 Hz, 500 Hz, and 1 kHz) during four consecutive days. At every frequency, the patient underwent sub-and suprathreshold stimulation. Cerebral activity was monitored and assessed using fMRI. Results: Suprathreshold stimulation is generally accompanied with more activity than subthreshold SCS. Suprathreshold SCS resulted in increased bilateral activation of the frontal cortex, thalamus, pre-and postcentral gyri, basal ganglia, cingulate gyrus, insula, thalamus, and claustrum. We observed deactivation of the bilateral parahippocampus, amygdala, precuneus, posterior cingulate gyrus, postcentral gyrus, and unilateral superior temporal gyrus. Conclusion: Suprathreshold stimulation resulted in greater activity (both activation and deactivation) of the frontal brain regions; the sensory, limbic, and motor cortices; and the diencephalon in comparison with subthreshold stimulation. Each type of frequency at suprathreshold stimulation was characterized by an individual activation pattern.
Background: Smoking is a common phenomenon and kills over 6 million people every year. Many smokers try to quit smoking by using nicotine replacement therapy (NRT). Most of the time, relapse occurs in less than six months after finishing the program of NRT. We performed a single blinded study in which our aim was to figure out what the effect of the nicotine patch is on craving in the brain of smokers deprived from smoking. Methods: Five heavy smokers (Fagerström Test for Nicotine Dependence ≥4) underwent a functional magnetic resonance imaging (fMRI) in 4 random conditions: smoking (S); smoking deprivation (SD); SD combined with a NP (SD + NP); SD combined with a placebo patch (SD + PP). Visual stimulation provoked craving in block design by randomly displaying images of smoking related scenes. After image preprocessing, a fixed-effect analysis was performed to compare average group activations. The Questionnaire for Smoking Urges (QSU) was obtained before and after each scan. Results: The fMRI results showed higher activation in areas involved in craving in S compared with SD + NP, SD + PP, and SD. In the SD + NP, limbic circuit and attention area were higher activated compared with SD and SD + PP. The SD + PP and SD showed higher activation in the frontal cortex and limbic system compared with S and SD + NP. Nonsmokers showed higher limbic activation compared with SD.The QSU increased significantly after the fMRI experiment in S (P = .036).The SD had higher QSU scores compared with the S before (P = .002), and also after (P = .022) the fMRI experiment. The NP showed lower scores than the SD before the experiment (P = .046). Conclusion: The fMRI experiment revealed lower activity in areas associated with attention when subjects were nicotine deprived (SD + PP and SD). Areas involved with craving showed less activity when nicotine is present (S and SD + NP). The QSU showed a significant difference between SD and when nicotine is present (S and SD + NP).
- Aug 2018
The application of repetitive transcranial magnetic stimulation (rTMS) to prevent relapse in alcohol addiction is currently being evaluated. However, how rTMS may influence the related brain processes is far from clear. Here we wanted to investigate whether baseline grey matter volume (GMV) can predict relapse and whether 15 accelerated high-frequency (HF)- rTMS sessions may influence GMV in areas related to relapse. Voxel-based morphometric (VBM) measurements were used to compare baseline GMV of 22 detoxified, hospitalized, alcohol-dependent patients with 22 age and gender matched healthy control subjects. Only patients received 15 accelerated HF-rTMS sessions at the right dorsolateral prefrontal cortex (DLPFC) followed by VBM measurements. Relapse rates were assessed four weeks after the end of the stimulation protocol. At baseline, alcohol-dependent patients overall showed less GMV in diffuse brain areas compared to healthy controls. Relapsers compared to abstainers displayed larger GMV decreases, especially in brain midline structures, insular, hippocampal, and amygdalar areas. Accelerated HF-rTMS treatment had no significant effect on GMV in alcohol-dependent patients, regardless of the relapse state. Although an accelerated HF-rTMS treatment protocol did not influence GMV in alcohol-dependent patients, baseline GMV predicted future relapse.
- Jun 2018
Introduction: With the development of new neuroimaging tools it has become possible to assess neurochemical alterations in patients experiencing chronic pain and to determine how these factors change during pharmacological treatment. The goal of this study was to examine the exact neurochemical mechanism underlying pregabalin treatment, utilizing magnetic resonance spectroscopy (1H-MRS), in a population of patients with painful diabetic polyneuropathy (PDN), with the overall aim to ultimately objectify the clinical effect of pregabalin. Methods: A double blind, randomized, placebo-controlled study was conducted. A total of 27 patients with PDN were enrolled in the study, of whom 13 received placebo treatment (control group) and 14 received pregabalin (intervention group). Pregabalin treatment consisted of stepwise dose escalation over the study period from 75 mg daily ultimately to 600 mg daily. 1H-MRS was performed at 3T on four regions of interest in the brain: the rostral anterior cingulate cortex (rACC), left and right thalamus and prefrontal cortex. The absolute concentrations of N-acetyl aspartate, glutamate, glutamine, gamma-amino-butyric-acid (GABA), glucose (Glc) and myo-inositol (mINS) were determined using LCModel. Results: The concentration of most neurometabolites in the placebo and pregabalin group did not significantly differ over time, with only a small significant difference in Glc level in the left thalamus (p = 0.049). Comparison of the effects of the different doses revealed significant differences for mINS in the rACC (baseline 2.42 ± 1.21 vs. 450 mg 1.58 ± 0.94; p = 0.022) and dorsolateral prefrontal cortex (75 mg 2.38 ± 0.89 vs. 450 mg 1.59 ± 0.85; p = 0.042) and also for GABA in the rACC (75 mg 0.53 ± 0.51 vs. 225 mg 0.28 ± 0.19; p = 0.014). Conclusion: No differences were found in metabolite concentrations between the placebo (control) and intervention groups, but some differences, although small, were found between the different doses. Trial registration: This study is registered at ClinicalTrials.gov (NCT01180608). Funding: Lyrica Independent Investigator Research Award (LIIRA) 2010 (Pfizer) funded the study.
- Dec 2017
Purpose: Besides chiasmal hemidecussation, interhemispheric connections are likely important in human binocularity. The corpus callosum (CC) is the major fiber bundle in the mammalian brain which mostly connects homologous cortical areas in the two hemispheres. Visual interhemispheric connections were found abnormal in strabismic cats. No studies have investigated these pathways in humans with infantile strabismus. Methods: Diffusion tensor imaging was used in four subjects with infantile esotropia (IE) and nine control subjects with normal binocularity, in order to study interhemispheric fibers in the CC connecting the right and left primary visual cortical areas. Results: The number of callosal fibers linking both visual cortical areas between the hemispheres was found to be higher in subjects with IE. Also in IE, the amount of visual callosal fibers found after analysis from the primary visual cortical areas on one side appeared significantly different from the amount starting from the contralateral primary visual areas. The distribution area on one side is wider. Conclusion: We show callosal visual fibers to be abnormal in human IE. Subjects with IE showed abnormal numbers of transcallosal fibers connecting the visual cortical areas on both sides which likely results from an abnormal elimination process during development. Pruning of these fibers in IE favors the side of the visual cortex ipsilateral to the dominant eye. This study underlines the likely role of the CC in the development of human binocularity.
- Jul 2017
Objective Although accelerated repetitive transcranial magnetic stimulation (rTMS) designs seem to be able to alleviate mood over a relatively short period of time, no studies yet examined the cellular effects on neurochemicals with regard to working mechanisms, safety and neural integrity. Methods Eighteen right-handed antidepressant-free unipolar treatment resistant depressed (TRD) patients participated in this sham-controlled accelerated high frequency (aHF)-rTMS ¹H MR spectroscopy study applied to the left dorsolateral prefrontal cortex (DLPFC). Baseline measurements were compared to eighteen age- and gender-matched healthy controls. We explicitly focused on neurochemical concentrations in the bilateral DLPFC and rostral anterior cingulate cortex (rACC). Results Compared to healthy individuals, TRD patients displayed significantly lower baseline glutamatergic (sum absolute concentrations glutamate and glutamine) concentrations in the left DLPFC. aHF-rTMS does not significantly alter neurochemical concentrations in the three predefined brain regions. Clinical improvement was related to significant GABA concentration increases in the left DLPFC. Conclusions Accelerated HF-rTMS treatment did not affect neural integrity in the examined regions. The observed GABA concentration increases suggest that the immediate therapeutic effects of aHF-rTMS could be mediated through a locally increased GABAergic inhibitory neurotransmission. Significance Although more statistical power is needed for reaching firm conclusions, aHF-rTMS does not appear to negatively influence neural integrity.
Concerns are raising about the large variability in reported correlations between gray matter morphology and affective personality traits as 'Harm Avoidance' (HA). A recent review study (Mincic 2015) stipulated that this variability could come from methodological differences between studies. In order to achieve more robust results by standardizing the data processing procedure, as a first step, we repeatedly analyzed data from healthy females while changing the processing settings (voxel-based morphology (VBM) or region-of-interest (ROI) labeling, smoothing filter width, nuisance parameters included in the regression model, brain atlas and multiple comparisons correction method). The heterogeneity in the obtained results clearly illustrate the dependency of the study outcome to the opted analysis settings. Based on our results and the existing literature, we recommended the use of VBM over ROI labeling for whole brain analyses with a small or intermediate smoothing filter (5-8mm) and a model variable selection step included in the processing procedure. Additionally, it is recommended that ROI labeling should only be used in combination with a clear hypothesis and that authors are encouraged to report their results uncorrected for multiple comparisons as supplementary material to aid review studies.
Background: The application of accelerated high-frequency (HF) repetitive transcranial magnetic stimulation (rTMS) could be a potential treatment option for alcohol-dependent patients and may result in a faster clinical response. In this open-label HF-rTMS feasibility study, we wanted to replicate previous findings of baseline brain activation as a predictor of relapse, and to evaluate how this intervention influences the relapse neurocircuit of "treatment-seeking" alcohol-dependent patients, by means of functional magnetic resonance imaging (fMRI) cue-exposure paradigms. Because relapsing patients have a diminished resilience of the emotion regulation/cognitive control system, before HF-rTMS treatment, we expected lower neuronal activation of especially the ventromedial prefrontal cortex and anterior cingulate cortex (ACC) during the presentation of alcohol-related cues in these patients. The relapse neurocircuit should be modified after accelerated HF-rTMS treatment, only in those patients who did not relapse. Methods: After being administered a single sham-controlled HF-rTMS session (20 Hz to 110% motor threshold), 19 alcohol-dependent patients received an accelerated HF-rTMS protocol, consisting of 14 right dorsolateral prefrontal cortical sessions spread over 3 days. Before and after stimulation, during fMRI patients were confronted with a block and an event-related alcoholic cue-exposure paradigm. Relapse was defined as the consumption of any amount of alcohol within 4 weeks after the stimulation. A region of interest analysis was performed to evaluate how HF-rTMS exerts its effect. Results: After 4 weeks, 13 of 19 patients had already consumed alcohol. When abstainers were compared to patients who had relapsed, we found higher dorsal ACC (dACC) activation at baseline, but only during the blocked cue-exposure paradigm. The effects of HF-rTMS on dACC blood oxygen level-dependent response were negatively correlated with the baseline dACC activation. Due to susceptibility artifacts located at the ventral cortical aspects in 6 of our participants, reliable data were only obtained for the ACC. Conclusions: Our data indicate that higher baseline dACC activation may serve as a protective mechanism regarding relapse. For the first time, it is demonstrated that accelerated HF-rTMS treatment influences dACC activation in a rate-dependent manner: the lower the baseline dACC activation, the more dACC activity was increased after HF-rTMS treatment.
In alcohol-dependent patients craving is a difficult-to-treat phenomenon. It has been suggested that high-frequency (HF) repetitive transcranial magnetic stimulation (rTMS) may have beneficial effects. However, exactly how this application exerts its effect on the underlying craving neurocircuit is currently unclear. In an effort to induce alcohol craving and to maximize detection of HF-rTMS effects to cue-induced alcohol craving, patients were exposed to a block and event-related alcohol cue-reactivity paradigm while being scanned with fMRI. Hence, we assessed the effect of right dorsolateral prefrontal cortex (DLPFC) stimulation on cue-induced and general alcohol craving, and the related craving neurocir-cuit. Twenty-six recently detoxified alcohol-dependent patients were included. First, we evaluated the impact of one sham-controlled stimulation session. Second, we examined the effect of accelerated right DLPFC HF-rTMS treatment: here patients received 15 sessions in an open label accelerated design, spread over 4 consecutive days. General craving significantly decreased after 15 active HF-rTMS sessions. However, cue-induced alcohol craving was not altered. Our brain imaging results did not show that the cue-exposure affected the underlying craving neurocircuit after both one and fifteen active HF-rTMS sessions. Yet, brain activation changes after one and 15 HF-rTMS sessions, respectively, were observed in regions associated with the extended reward system and the default mode network, but only during the presentation of the event-related paradigm. Our findings indicate that accelerated HF-rTMS applied to the right DLPFC does not manifestly affect the craving
Although numerous people grow up speaking more than one language, the impact of bilin-gualism on brain developing neuroanatomy is still poorly understood. This study aimed to determine whether the changes in the mean fractional-anisotropy (MFA) of language pathways are different between bilingual and monolingual children. Simultaneous-bilinguals, sequential -bilinguals and monolingual, male and female 10–13 years old children participated in this longitudinal study over a period of two years. We used diffusion tensor tractography to obtain mean fractional-anisotropy values of four language related pathways and one control bundle: 1-left-inferior-occipitofrontal fasciculus/lIFOF, 2-left-arcuate fasciculus/lAF/ lSLF, 3-bundle arising from the anterior part of corpus-callosum and projecting to orbital lobe/AC-OL, 4-fibres emerging from anterior-midbody of corpus-callosum (CC) to motor cor-tices/AMB-PMC, 5-right-inferior-occipitofrontal fasciculus rIFOF as the control pathway unrelated to language. These values and their rate of change were compared between 3 groups. FA-values did not change significantly over two years for lAF/lSLF and AC-OL. Sequential -bilinguals had the highest degree of change in the MFA value of lIFOF, and AMB-PMC did not present significant group differences. The comparison of MFA of lIFOF yielded a significantly higher FA-value in simultaneous bilinguals compared to monolinguals. These findings acknowledge the existing difference of the development of the semantic processing specific pathway between children with different semantic processing procedure. These also support the hypothesis that age of second language acquisition affects the maturation and myelination of some language specific white-matter pathways.
Background In their daily communication, bilinguals switch between two languages, a process that involves the selection of a target language and minimization of interference from a nontarget language. Previous studies have uncovered the neural structure in bilinguals and the activation patterns associated with performing verbal conflict tasks. One question that remains, however is whether this extra verbal switching affects brain function during nonverbal conflict tasks.Methods In this study, we have used fMRI to investigate the impact of bilingualism in children performing two nonverbal tasks involving stimulus–stimulus and stimulus–response conflicts. Three groups of 8–11-year-old children – bilinguals from birth (2L1), second language learners (L2L), and a control group of monolinguals (1L1) – were scanned while performing a color Simon and a numerical Stroop task. Reaction times and accuracy were logged.ResultsCompared to monolingual controls, bilingual children showed higher behavioral congruency effect of these tasks, which is matched by the recruitment of brain regions that are generally used in general cognitive control, language processing or to solve language conflict situations in bilinguals (caudate nucleus, posterior cingulate gyrus, STG, precuneus). Further, the activation of these areas was found to be higher in 2L1 compared to L2L.Conclusion The coupling of longer reaction times to the recruitment of extra language-related brain areas supports the hypothesis that when dealing with language conflicts the specialization of bilinguals hampers the way they can process with nonverbal conflicts, at least at early stages in life.
Brain imaging studies have consistently shown subgenual Anterior Cingulate Cortical (sgACC) involvement in emotion processing. catechol-O-methyltransferase (COMT) Val(158) and Met(158) polymorphisms may influence such emotional brain processes in specific ways. Given that resting-state fMRI (rsfMRI) may increase our understanding on brain functioning, we integrated genetic and rsfMRI data and focused on sgACC functional connections. No studies have yet investigated the influence of the COMT Val(158)Met polymorphism (rs4680) on sgACC resting-state functional connectivity (rsFC) in healthy individuals. A homogeneous group of 61 Caucasian right-handed healthy female university students, all within the same age range, underwent rsfMRI. Compared to Met(158) homozygotes, Val(158) allele carriers displayed significantly stronger rsFC between the sgACC and the left parahippocampal gyrus, ventromedial parts of the inferior frontal gyrus (IFG), and the nucleus accumbens (NAc). On the other hand, compared to Val(158) homozygotes, we found in Met(158) allele carriers stronger sgACC rsFC with the medial frontal gyrus (MFG), more in particular the anterior parts of the medial orbitofrontal cortex. Although we did not use emotional or cognitive tasks, our sgACC rsFC results point to possible distinct differences in emotional and cognitive processes between Val(158) and Met(158) allele carriers. However, the exact nature of these directions remains to be determined.
The affective personality trait ‘harm avoidance’ (HA) from Cloninger’s psychobiological personality model determines how an individual deals with emotional stimuli. Emotional stimuli are processed by a neural network that include the left and right amygdalae as important key nodes. Explicit, implicit and passive processing of affective stimuli are known to activate the amygdalae differently reflecting differences in attention, level of detailed analysis of the stimuli and the cognitive control needed to perform the required task. Previous studies revealed that implicit processing or passive viewing of affective stimuli, induce a left amygdala response that correlates with HA. In this new study we have tried to extend these findings to the situation in which the subjects were required to explicitly process emotional stimuli. A group of healthy female participants was asked to rate the valence of positive and negative stimuli while undergoing fMRI. Afterwards the neural responses of the participants to the positive and to the negative stimuli were separately correlated to their HA scores and compared between the low and high HA participants. Both analyses revealed increased neural activity in the left laterobasal (LB) amygdala of the high HA participants while they were rating the positive and the negative stimuli. Our results indicate that the left amygdala response to explicit processing of affective stimuli does correlate with HA.
The left and right amygdalae are key regions distinctly involved in emotion-regulation processes. Individual differences, such as personality features, may affect the implicated neurocircuits. The lateralized amygdala affective processing linked with the temperament dimension Harm Avoidance (HA) remains poorly understood. Resting state functional connectivity imaging (rsFC) may provide more insight into these neuronal processes. In 56 drug-naive healthy female subjects, we have examined the relationship between the personality dimension HA on lateralized amygdala rsFC. Across all subjects, left and right amygdalae were connected with distinct regions mainly within the ipsilateral hemisphere. Females scoring higher on HA displayed stronger left amygdala rsFC with ventromedial prefrontal cortical (vmPFC) regions involved in affective disturbances. In high HA scorers, we also observed stronger right amygdala rsFC with the dorsomedial prefrontal cortex (dmPFC), which is implicated in negative affect regulation. In healthy females, left and right amygdalae seem implicated in distinct mPFC brain networks related to HA and may represent a vulnerability marker for sensitivity to stress and anxiety (disorders).
Objectives. Intensified repetitive transcranial magnetic stimulation (rTMS) applied to the left dorsolateral prefrontal cortex (DLPFC) may result in fast clinical responses in treatment resistant depression (TRD). In these kinds of patients, subgenual anterior cingulate cortex (sgACC) functional connectivity (FC) seems to be consistently disturbed. So far, no de novo data on the relationship between sgACC FC changes and clinical efficacy of accelerated rTMS were available. Methods. Twenty unipolar TRD patients, all at least stage III treatment resistant, were recruited in a randomized sham-controlled crossover high-frequency (HF)-rTMS treatment study. Resting-state (rs) functional MRI scans were collected at baseline and at the end of treatment. Results. HF-rTMS responders showed significantly stronger resting-state functional connectivity (rsFC) anti-correlation between the sgACC and parts of the left superior medial prefrontal cortex. After successful treatment an inverted relative strength of the anti-correlations was observed in the perigenual prefrontal cortex (pgPFC). No effects on sgACC rsFC were observed in non-responders. Conclusions. Strong rsFC anti-correlation between the sgACC and parts of the left prefrontal cortex could be indicative of a beneficial outcome. Accelerated HF-rTMS treatment designs have the potential to acutely adjust deregulated sgACC neuronal networks in TRD patients.
- May 2013
Introduction: Although spinal cord stimulation (SCS) is a widely used treatment for chronic neuropathic pain secondary to spinal surgery, little is known about the underlying physiological mechanisms. Methods: The primary aim of this study is to investigate the neural substrate underlying short-term SCS by means of (1)H MR spectroscopy with short echo time, in 20 patients with failed back surgery syndrome. Results: Marked increase of γ-aminobutyric acid (GABA) and decrease in glucose in the ipsilateral thalamus were found between baseline situation without SCS and after 9' of SCS, indicating the key role of the ipsilateral thalamus as a mediator of chronic neuropathic pain. In addition, this study also showed a progressive decrease in glucose in the ipsilateral thalamus over time, which is in line with the findings of previous studies reporting deactivation in the ipsilateral thalamic region. Conclusions: The observation of GABA increase and glucose decrease over time in the ipsilateral thalamus may be the causal mechanism of the pain relief due to SCS or an epiphenomenon.
- Apr 2013
Depressive brooding - a passive ruminative focus on one's problems, negative mood and their consequences - is a thinking style that places individuals at a greater risk to develop future psychopathology. In this study, we investigated whether inter-individual differences in depressive brooding are related to neural differences underlying the inhibition of a dominant response towards negative information in favor of the concurrent (positive) response. To exclude the possibility that information processes would be confounded by sustained negative mood or enhanced stress responses, a sample of thirty never-depressed healthy individuals was selected. The Cued Emotional Control Task (CECT) was used to index the ability to enhance cognitive control when encountering a negative stimulus associated with an incompatible stimulus-response mapping. Individual brooding scores were not related to behavioral performances on the CECT. On the other hand, whole brain analyses demonstrated that trait depressive brooding scores were positively associated with activation in the posterior parts of the dorsal anterior cingulate cortex (pdACC) while successfully inhibiting a response to negative relative to positive information. These findings demonstrate that brooding minds need to recruit more pdACC activation when inhibiting a dominant response towards negative information (in favor of a response towards positive), although they are performing similarly as low brooders at the behavioral level. Future research should investigate whether and how these brooding related neural adjustments in healthy volunteers are related to future psychopathology.
- Feb 2013
Diffusion weighted imaging sequences are now widely available on Magnetic Resonance Imaging (MRI) scanners. Diffusion Tensor Imaging (DTI) of the brain is able to show white matter tracts and is now commonly used in human medicine to study brain anatomy, tumors, structural pathways,… The purpose of this study was to show the interest of DTI to reveal the white matter fibers in the dogs' brain. DTI MR Images for this study were obtained with a 3 T system of 4 dogs euthanized for other reasons than neurological disorders. Combined fractional anisotropic (FA) and directional maps were obtained in the first 2 hours after death. The heads were amputated immediately after scanning and stored in 10% formalin until preparation for dissection. An experienced anatomist tracked white matter tracts with clinical relevance using the scanner software. The selected tracts were REFVIDume rendered and correlated with gross dissection. Using DTI we were able to track relevant neurological connections, such as the corticospinal tract, the optic and the cerebellar tract. The three dimensional anatomy is better presented using modern visualization techniques. DTI seems to be a valuable tool in order to present clinically relevant white matter tracts to neurological clinicians and researchers. Anat Rec, 296:340-349, 2013. © 2013 Wiley Periodicals, Inc.
- Sep 2012
Introduction: Although spinal cord stimulation (SCS) is widely used for chronic neuropathic pain after failed spinal surgery, little is known about the underlying physiological mechanisms. This study aims to investigate the neural substrate underlying short-term (30 s) SCS by means of functional magnetic resonance imaging in 20 patients with failed back surgery syndrome (FBSS). Methods: Twenty patients with FBSS, treated with externalized SCS, participated in a blocked functional magnetic resonance imaging design with stimulation and rest phases of 30 s each, repeated eight times in a row. During scanning, patients rated pain intensity over time using an 11-point numerical rating scale with verbal anchors (0 = no pain at all to 10 = worst pain imaginable) by pushing buttons (left hand, lesser pain; right hand, more pain). This scale was back projected to the patients on a flat screen allowing them to manually direct the pain indicator. To increase the signal-to-noise ratio, the 8-min block measurements were repeated three times. Results: Marked deactivation of the bilateral medial thalamus and its connections to the rostral and caudal cingulate cortex and the insula was found; the study also showed immediate pain relief obtained by short-term SCS correlated negatively with activity in the inferior olivary nucleus, the cerebellum, and the rostral anterior cingulate cortex. Conclusions: Results indicate the key role of the medial thalamus as a mediator and the involvement of a corticocerebellar network implicating the modulation and regulation of averse and negative affect related to pain. The observation of a deactivation of the ipsilateral antero-medial thalamus might be used as a region of interest for further response SCS studies.
The amygdalae are key players in the processing of a variety of emotional stimuli. Especially aversive visual stimuli have been reported to attract attention and activate the amygdalae. However, as it has been argued that passively viewing withdrawal-related images could attenuate instead of activate amygdalae neuronal responses, its role under passive viewing conditions remains unclear. Furthermore, because individual sensitivity to stress reactions has been shown to modulate amygdalae processing, the aim of the current event-related fMRI study was to investigate whether individual differences in stress proneness could influence amygdala responses while passively viewing withdrawal and approach-related visual images. We presented 14 healthy female subjects with a random sequence of images of happy 'healthy' baby faces (approach-related) and baby faces disfigured by severe dermatological conditions (withdrawal-related). No instructions were given other than to watch the images attentively. We integrated individual perceived stress (PSS) scores in our analysis. The processing of withdrawal-related pictures resulted in less left amygdala activity in females scoring higher on perceived stress. Our findings suggest that stress-sensitive healthy females are less able to fully attend to withdrawal-related visual material and in essence avoid exposure to such images in an effort to reduce strong psychophysiological responses. Although the relatively small number of participants limits drawing firm conclusions, we suggest that in passive viewing emotional brain imaging paradigms, individual information on stress proneness should be included in the interpretation of amygdala neuronal processes.
Events coupled with an emotional context seem to be better retained than non-emotional events. The aim of our study was to investigate whether an emotional context could influence the neural substrates of memory associations with novel portrait art stimuli. In the current prospective fMRI study, we have investigated for one specific visual art form (modern artistic portraits with a high degree of abstraction) whether memory is influenced by priming with emotional facial pictures. In total forty healthy female volunteers in the same age range were recruited for the study. Twenty of these women participated in a prospective brain imaging memory paradigm and were asked to memorize a series of similar looking, but different portraits. After randomization, for twelve participants (Group 1), a third of the portraits was emotionally primed with approach-related pictures (smiling baby faces), a third with withdrawal-related pictures (baby faces with severe dermatological conditions), and another third with neutral images. Group 2 consisted of eight participants and they were not primed. Then, during an fMRI session 2h later, these portraits were viewed in random order intermixed with a set of new (previously unseen) ones, and the participants had to decide for each portrait whether or not they had already been seen. In a separate experiment, a different sample of twenty healthy females (Group 3) rated their mood after being exposed to the same art stimuli, without priming. The portraits did not evoke significant mood changes by themselves, supporting their initial neutral emotional character (Group 3). The correct decision on whether the portraits were Familiar of Unfamiliar led to similar neuronal activations in brain areas implicated in visual and attention processing for both groups (Groups 1 and 2). In contrast, whereas primed participants showed significant higher neuronal activities in the left midline superior frontal cortex (Brodmann area (BA) 6), unprimed volunteers displayed higher right medial frontal cortical (BA 10) activities. Furthermore, specifically in Group 1, correct retrieval of negatively primed portraits evoked increased neuronal activity in the left medial orbitofrontal cortex (BA 11) and in the right (posterior) insula, suggesting enhanced stress-related responses to the memory of withdrawal-related primed modern artistic portraits in this group. Our prospective memory data in healthy females indicate that, to reach a correct retrieval decision, different midline anterior neuronal networks are recruited for portraits that were emotionally primed than for the unprimed ones. Importantly, our results also suggest that the negative emotional context leads to the formation of associations that are reactivated during memory retrieval processes of the initially neutral art portraits. When correctly recognized, the portraits evoke neuronal activities consistent with the withdrawal-related character of the emotional visual stimuli with which they have been associated. Although our results show that abstract portrait art can be associated with emotional primes this doesn't mean that this effect is specific for art images.
Two different emotion regulation strategies, cognitive reappraisal and expressive suppression, are strongly associated with increased neural activity in the prefrontal cognitive control network. In this event-related fMRI study, we investigated whether individual differences in habitual reappraisal and suppression tendencies are related to differences in prefrontal cognitive control processes for emotional information. In order to measure cognitive control over inhibiting a dominant response to happy or sad stimuli (in favor of the opposite valence), thirty-one healthy female participants performed the Cued Emotional Conflict Task (CECT). The Emotion Regulation Questionnaire was used to measure individual differences in everyday use of emotion regulation. Results demonstrate that high reappraisers are behaviorally faster and exert more fronto-cingulate activity when inhibiting a response to sad faces (compared to happy faces, FDR corrected). On the other hand, suppression scores are not correlated with performance to CECT trials. Interestingly, suppression scores are associated with higher amygdala activation during the inhibition of a response to sad faces (compared to happy faces). These data suggest that habitual reappraisal is associated with underlying functional cognitive control processes to inhibit a dominant response to negative material. In contrast, the effort to control negative material has negative consequences in individuals who have a tendency to suppress emotions.
Spinal cord stimulation (SCS) is a well-known treatment option for intractable neuropathic pain after spinal surgery, but its pathophysiological mechanisms are poorly stated. The goal of this study is to analyse the feasibility of using brain MRI, functional MRI (fMRI) and Magnetic Resonance Spectroscopy (MRS) as tools to analyse these mechanisms in patients with externalised neurostimulators during trial period. The authors conducted in an in vitro and in vivo study analysing safety issues when performing brain MRI, fMRI and MRS investigations in human subjects with externalised SCS. Temperature measurements in vitro were performed simulating SCS during MRI sequences using head transmit-receive coils in 1.5 and 3 T MRI systems. 40 Patients with externalised SCS were included in the in vivo study. 20 patients underwent brain MRI, fMRI and another 20 patients underwent brain MRI and MRS. A maximal temperature increase of 0.2°C was measured and neither electrode displacements nor hardware failures were observed. None of the patients undergoing the MRS sequences at the 1.5 or 3 T MRI scanners described any discomfort or unusual sensations. We can conclude that brain MRI, fMRI and MRS studies performed in patients with externalised SCS can be safely executed.
Although repetitive Transcranial Magnetic Stimulation (rTMS) is currently used to investigate neural connections in the living human brain, it remains largely unclear as to how rTMS can alter emotional processing. We examined in 'uniform' samples of healthy female volunteers whether a single high frequency (HF)-rTMS session applied to the DLPFC could influence the processing of positively and negatively valenced emotional stimuli. In our earlier research, we developed a specially adapted fMRI paradigm with only baby faces as 'emotional' visual stimuli. We especially focused on lateralized anterior hemispheric functioning while these salient emotional visual stimuli were being processed. In essence, one active high frequency session (left or right) attenuates stress-related responses in the cortico-subcortical regions of the right anterior hemisphere, such as the insula and the amygdala. Furthermore, active left-sided HF-rTMS results in enhanced task-related processing caused by the neuronal activation of the left DLPFC, which could indicate that females are more able to empathize with the depicted happy baby faces, possibly by the integration of different high-order cognitive processes. Our findings confirm the involvement of the left anterior hemisphere in the processing of positively valenced emotional stimuli and the right anterior hemisphere in the processing of withdrawal-related ones.
The impact of bilingualism on the microstructure of the white matter pathways related to language processing is assessed in elementary school children by magnetic resonance diffusion tensor imaging (MR-DTI). Forty children, 8-11 years old, subdivided into 3 different groups (15 simultaneous bilinguals, 15 sequential bilinguals and 10 monolinguals), were scanned. The hypothesis was that the starting age and the manner of second language acquisition would affect the characteristics of language circuitry. In each subject the mean fractional anisotropy (FA) was obtained for four major white matter pathways: 1 - the left arcuate fasciculus/superior longitudinal fasciculus (lAF/lSLF) that connects Broca's area in the opercular and triangular regions of the left inferior frontal gyrus to the posterior language zone, 2 - the left inferior occipitofrontal fasciculus (lIFOF), connecting anterior regions in the frontal lobe with posterior regions in the temporal occipital lobes, 3 - the bundle arising from the anterior part of the corpus callosum projecting to the orbital lobe (AC-OL) and 4 - the fibers emerging from the anterior midbody (AMB) of the corpus callosum that associate with the premotor and supplementary motor cortices (AMB-PMC). The three groups did not show significant differences in mean FA over the lAF/lSLF or AMB-PMC tracts. In simultaneous bilingual subjects the lIFOF tracts had higher mean FA value compared to monolinguals and also sequential bilinguals, whereas the comparison for the AC-OL fibers yielded a significantly lower mean FA value in simultaneous bilingual subjects compared to monolinguals. In both cases the FA value for sequential bilinguals was intermediate to that of the other two groups. To our knowledge, this study provides the first evidence of bilingualism related adaptation of white matter microstructure in the human brain.
- Jun 2011
- 66th Society of Biological Psychiatry Annual Meeting 2011
Background / Purpose: High frequency Repetitive Transcranial Magnetic Stimulation (HF-rTMS) of the left dorsolateral prefrontal cortex (DLPFC) is currently used as a promising treatment strategy for depression, but the working mechanisms of this technique remain poorly understood. Recent models of depression suggest that dysfunctional top-down processes biasing attentional control over emotional information may contribute to the onset and development of depression.Because neuroimaging studies have provided support for a central role of the DLPFC in emotional control, rTMS might be effective through an enhancement of attentional control for emotional material.To test this hypothesis, we used HF-rTMS over the left or right DLPFC in thirty seven right handed healthy female participants (mean age 22.6 + 2.6 yrs.) within a single-blind placebo controlled randomized design, and examined changes in attentional processing of emotional information using an exogenous cueing paradigm with angry versus neutral faces during event-related fMRI. Main conclusion: Left HF-rTMS resulted in diminished attentional engagement by angry faces associated with increased activity within the right DLPFC, dACC, right superior parietal gyrus and left orbitofrontal cortex. Right prefrontal HF-rTMS resulted in impaired disengagement from angry faces, associated with decreased activation within the right DLPFC, dorsal anterior cingulate cortex and left superior parietal gyrus, combined with increased activity within the right amygdala.The present study contributes to the existing evidence of a functionally interactive network of cortical-limbic pathways that play a central role in emotion regulation and increases our insight in the possible working mechanisms of rTMS as a treatment strategy for depression.
- May 2011
Although repetitive Transcranial Magnetic Stimulation (rTMS) is frequently used to examine emotional changes in healthy volunteers, it remains largely unknown how rTMS is able to influence emotion. In this sham-controlled, single-blind crossover study using fMRI, we examined in 20 right-handed healthy females whether a single high frequency (HF)-rTMS session applied to the left dorsolateral prefrontal cortex could influence emotional processing while focussing on blocks of positively and negatively valenced baby faces. While positive information was being processed, we observed after one active HF-rTMS session enhanced neuronal activity in the left superior frontal cortex and right inferior parietal cortex. After sham HF-rTMS, we found significant decreases in neuronal activity in the left superior frontal cortex, the left inferior prefrontal cortex, as well as in the right posterior cingulate gyrus. When negative information was processed, one active stimulation attenuated neuronal activity in the right insula only. Our findings suggest that during the processing of positive information one active session enhanced the ability to empathize with the depicted emotional stimuli, while during the processing of negative information it resulted in decreased psychophysiological reactions. These results provide new information on the working mechanism of left-sided HF-rTMS.
- Jan 2011
The psychobiological personality model of Cloninger distinguishes four heritable temperament traits (harm avoidance (HA), novelty seeking (NS), reward dependence (RD) and persistence (P)) and three character traits (self-directedness (SD), cooperativeness (CO) and self-transcendence (ST)) which develop during lifetime. Prior research already showed that individual differences in temperament are reflected in structural variances in specific brain areas. In this study, we used voxel-based morphometry (VBM) to correlate the different temperament and character traits with local gray and white matter volumes (GMV and WMV) in young healthy female volunteers. We found correlations between the temperament traits and GMV and WMV in the frontal, temporal and limbic regions involved in controlling and generating the corresponding behavior as proposed in Cloninger's theory: anxious for HA, impulsive for NS, reward-directed for RD and goal-directed for P. The character traits correlated with GMV and WMV in the frontal, temporal and limbic regions involved in the corresponding cognitive tasks: self-reflection for SD, mentalizing and empathizing with others for CO and religious belief for ST. This study shows that individual variations in brain morphology can be related to the temperament and character dimensions, and lends support to the hypothesis of a neurobiological basis of personality traits.
Repetitive transcranial magnetic stimulation (rTMS) studies investigating brain imaging correlates of emotion modulation in healthy volunteers can improve our understanding of the 'affective' impact of this application. In this fMRI study, we focused on lateralized amygdala functioning when processing salient emotional visual stimuli after one high-frequency (HF)-rTMS session. In a 'uniform sample' of 20 right-handed, non-depressed, healthy female subjects we examined whether one HF-rTMS session applied to the left (n=10) or right (n=10) dorsolateral prefrontal cortex (DLPFC) would influence amygdala responses to positively and negatively valenced baby faces. Subjects were given no other instructions than to focus on the emotion the visual stimuli elicited during scanning. One HF-rTMS session did not result in a conscious mood change. Whereas one left-sided HF-rTMS session did not affect amygdala processing of the positive or negative stimuli, after a single right-sided HF-rTMS session we found a significant right amygdala activity attenuation during the processing of negatively valenced baby faces. This finding provides additional evidence supporting the role of the right anterior hemisphere in the processing of negative emotional information, and increases our understanding of HF-rTMS treatment effects in mental disorders.
Research regarding the neurocircuitry in mood disorders suggests an important role for affective information processing of the subgenual part of the anterior cingulate cortex (Cg25: Brodmann area 25). In this study, we focused on Cg25 neuronal responses in depressed females using a paradigm in which emotions are elicited without explicit cognitive control, relying on the salient nature of the mood inducing stimuli eliciting approach-related emotions (like happiness) or withdrawal-related emotions (like disgust). Twelve treatment-resistant melancholic depressed women and 12 healthy female control subjects were asked to passively view blocks of emotionally valenced baby faces while undergoing functional magnetic resonance imaging (fMRI). Compared to the healthy females, the depressed patients displayed significantly higher bilateral Cg25 neuronal activities in both emotional conditions. In melancholically depressed women, we found significantly less left-sided than right-sided Cg25 neuronal activity during the withdrawal-related emotions, while right-sided Cg25 activity was comparable for both emotional responses. Our results indicate that in depressed women the left Cg25 modulates intense visceral emotional responses to aversive visual stimuli. This could help explain why the left Cg25 provides a valid target region for antidepressant treatment strategies in unipolar melancholic depression.
- Nov 2010
Although repetitive Transcranial Magnetic Stimulation (rTMS) is frequently used to examine emotional changes in healthy volunteers, it remains largely unknown how rTMS is able to influence emotion.We carried out a sham-controlled single-blind crossover study using fMRI, we examined in 20 right-handed healthy female volunteers whether a single high frequency (HF)-rTMS session applied to the left dorsolateral prefrontal cortex (DLPFC) could influence emotional processing while focussing on blocks of positively and negatively valenced baby faces. A single HF-rTMS session selectively influenced the processing of positively and negatively valenced baby faces. In essence, our results indicate that the effects of one left-sided HF-rTMS sessions results in improved processing of positive emotions and reduced negative emotional processing in never depressed female subjects.
- Oct 2010
Current evidence concerning the neurocircuitry underlying the interplay between attention and emotion is mainly correlational. We used high-frequency repetitive Transcranial Magnetic Stimulation (HF-rTMS) to experimentally manipulate activity within the right or left dorsolateral prefrontal cortex (DLPFC) of healthy women and examined changes in attentional processing of emotional information using an emotional modification of the exogenous cueing task during event-related fMRI. Right prefrontal HF-rTMS resulted in impaired disengagement from angry faces, associated with decreased activation within the right DLPFC, dorsal anterior cingulate cortex (dACC) and left superior parietal gyrus, combined with increased activity within the right amygdala. Left prefrontal HF-rTMS resulted in diminished attentional engagement by angry faces and was associated with increased activity within the right DLPFC, dACC, right superior parietal gyrus and left orbitofrontal cortex. The present observations are in line with reports of a functionally interactive network of cortical-limbic pathways that play a central role in emotion regulation.
- Jul 2010
The amygdalae play an important role in the evaluation and processing of emotionally salient visual stimuli. However, individual differences in personality traits, such as Harm Avoidance (HA), have been reported to influence emotional amygdalae responses. To trigger strong approach and withdrawal-related emotions in 'never depressed' young female subjects under fMRI, we presented them with blocks of happy 'healthy' baby faces and baby faces disfigured by severe dermatological conditions and we integrated the temperament dimension HA into our analysis. No other instructions were given than to watch the images attentively. Only in withdrawal-related emotional experience, we observed a negative correlation between HA and left amygdala activity, suggesting that during passive viewing females scoring higher on HA 'avoid' images with highly aversive content. When investigating the amygdala's emotional role in passive viewing paradigms, personality features such as HA should be taken into account.
The participation of pregnant women in radiology can be an emotional experience. The word "radiation" understandably invokes fear and uncertainty. Irradiation of a foetus should be avoided whenever possible. However, radiological examinations of pregnant women are often justified and unintended exposures do occur. Also pregnant radiology staff may remain working in the department. Lack of knowledge about the effects of both ionising (X-rays) and non-ionising (MRI) radiation is responsible for anxiety of patients and workers. If foetal exposures occur, they must be quantitatively evaluated and the risk put into perspective. This paper is intended to inform radiology managers, radiologists, technologists and referring clinicians in their management with pregnant patients and co-workers. The paper describes conceptus doses for both patient and worker that are associated with radiology practice, reviews the risks and effects of in utero irradiation, and discusses current national policies, international guidelines and practical aspects.
Research regarding the lateralization of processing emotional visual stimuli suggests various roles for affective information-processing by the amygdalae. However, individual differences seem to influence outcome results. In this study we re-investigate this question, paying special attention to the salient nature of the mood inducing stimuli. We presented blocks of happy looking baby faces and sad looking baby faces (disfigured by severe dermatological conditions), as well as blurred isoluminescent neutral pictures to a 'homogeneous' group of 40 healthy female subjects during fMRI. We used the temperament dimension harm avoidance (HA), extracted from the Temperament and Character Inventory (TCI), to evaluate the impact of this personality feature on 'emotional' amygdala responses. HA is related to behavioral inhibition and it implies a genetically determined bias towards being cautious, apprehensive and overly pessimistic. Because emotional valence and arousal may be controlled by different neural systems, the positively and negatively valenced baby faces were selected to be equal in arousal levels. Viewing blocks of negatively valenced baby faces evoked bilateral amygdala activity, whereas viewing positively valenced ones resulted in left amygdala activity only. Globally, we found no evidence of lateralized amygdala specialization. When taking into account individual differences in HA, only in female subjects who score high on this dimension did we find predominantly left amygdala activation when viewing blocks of negatively valenced baby faces. HA did not influence amygdala activity when processing positively valenced images. Our results might indicate that personality features, such as HA, could be of importance in 'emotional' fMRI paradigms examining amygdala lateralization patterns.
Postmastectomy edema is a current complication after axillary lymph node dissection in cases of breast cancer treatment. Staging is important in order to select those patients who can benefit from complex physical therapy (CPT). Different imaging techniques can be used to evaluate the edema. Ultrasonography (US) is a harmless, cheap, and easily applicable technique to visualize the dermal and subcutaneous tissue, but interpretation of the obtained images is not always evident. The aim of this study was to compare ultrasound images of irreversible edema with tissue histology, magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). Ultrasonographic images of the edematous dermis show an homogeneous hypoechogenic dermal layer that appears on tissue histology to be less compact, due to the excess of fluid in the interstitium separating the collagen fibres and making it more transparent on light microscopy. MRI of the dermis gives a hyperintense signal, indicating the presence of fluid. In the subcutis, increase of the adipose tissue could be observed on US, MRI, and tissue histology. In the case of lymphedema, the area and perimeter of fat cells is significantly (p < 0.05) increased. Hypoechogenic areas near the muscle fascia are registered on US corresponding with epifascial fluid on MRI, and hyperechogenic branches are embedded within the adipose tissue, on tissue histology seen as large fibrotic septa enclosing adipose cells. MRI has a honeycomb picture corresponding with fluid bound to fibrosis.
Transcranial magnetic stimulation (TMS) is currently used as a non-invasive treatment for depression. In most clinical trials, the left dorsolateral prefrontal cortex (DLPFC) has been selected as the target site for TMS treatment and this region is commonly determined by a "standard procedure", using a fixed position with respect to the motor cortex. In this study, to evaluate the relevance of using individual anatomical data during coil positioning, we used a more individualized localization method, based on three-dimensional magnetic resonance imaging of the head (3D-MRI). We wanted to examine the intra-individual variability of the localization of the stimulation area using a method taking into account individual brain anatomy by 3D-MRI, by comparing this method to the "standard procedure". As expected, even in a gender-controlled sample, our results demonstrate that the difference between the anatomical localization and the standard procedure of a well-defined part of the prefrontal cortex varies within subjects. Therefore, our results confirm the need for a TMS-coil positioning method which incorporates individual anatomical information.
- Oct 2006
Estimates of the incidence of arm swelling after axillary lymph node dissection for breast cancer range from 10 to 37%. Yet the subjective sensation of edema is described in at least 54% of patients. The purpose of this research was to examine the structural changes occurring in the subcutaneous tissue that might explain these subjective complaints using multiple imaging modalities. Two female cadavers with unilateral breast amputation and axillary dissection were studied. The dermal and subcutaneous layers of both arms were visualized with high frequency ultrasonography, and magnetic resonance imaging and spectroscopy (MRS), and tissue biopsies were taken for histological evaluation. On the operated side, ultrasound imaging showed a hyperechogenic subcutis and the fat-to-water relationship in adipose cells was higher as measured by MRS. Dissection of the arms revealed structural adipose tissue changes, which were confirmed by microscopic evaluation.
- Aug 2004
Truncated singular value decomposition (TSVD) is an effective method for the deconvolution of dynamic contrast enhanced (DCE) MRI. Two robust methods for the selection of the truncation threshold on a pixel-by-pixel basis--generalized cross validation (GCV) and the L-curve criterion (LCC)--were optimized and compared to paradigms in the literature. GCV and LCC were found to perform optimally when applied with a smooth version of TSVD, known as standard form Tikhonov regularization (SFTR). The methods lead to improvements in the estimate of the residue function and of its maximum, and converge properly with SNR. The oscillations typically observed in the solution vanish entirely, and perfusion is more accurately estimated at small mean transit times. This results in improved image contrast and increased sensitivity to perfusion abnormalities, at the cost of 1-2 min in calculation time and hyperintense clusters in the image. Preliminary experience with clinical data suggests that the latter problem can be resolved using spatial continuity and/or hybrid thresholding methods. In the simulations GCV and LCC are equivalent in terms of performance, but GCV thresholding is faster.
- Jul 2004
Truncated singular value decomposition (TSVD) is an effective method for the deconvolution of dynamic contrast-enhanced MRI. Two robust methods for the selection of the truncation threshold on a pixel-by-pixel basis--generalized cross validation (GCV) and the L-curve criterion (LCC)--were optimized and compared to paradigms in the literature. The methods lead to improvements in the estimate of the residue function and of its maximum and converge properly with SNR. The oscillations typically observed in the solution vanish entirely and perfusion is more accurately estimated at small mean transit times. This results in improved image contrast and increased sensitivity to perfusion abnormalities, at the cost of 1-2 min in calculation time and isolated instabilities in the image. It is argued that the latter problem may be resolved by optimization. Simulated results for GCV and LCC are equivalent in terms of performance, but GCV is faster.