Using Magnetic Resonance for Predicting Femoral Strength: Added Value with respect to Bone Densitometry.

BACKGROUND AND PURPOSE: To evaluate the added value of MRI with respect to peripheral quantitative computed tomography (pQCT) and dual energy X-ray absorptiometry (DXA) for predicting femoral strength. MATERIAL AND METHODS: Bone mineral density (BMD) of eighteen femur specimens was assessed with pQCT, DXA, and MRI (using ultrashort echo times (UTE) and the MicroView software). Subsequently biomechanical testing was performed to assess failure load. Simple and multiple linear regression were used with failure load as the dependent variable. RESULTS: Simple linear regression allowed a prediction of failure load with either pQCT, DXA, or MRI in an r(2) range of 0.41-0.48. Multiple linear regression with pQCT, DXA, and MRI yielded the best prediction (r(2) = 0.68). CONCLUSIONS: The accuracy of MRI, using UTE and MicroView software, to predict femoral strength compares well with that of pQCT or DXA. Furthermore, the inclusion of MRI in a multiple-regression model yields the best prediction.

White-matter development is different in bilingual and monolingual children: a longitudinal DTI study.

Although numerous people grow up speaking more than one language, the impact of bilingualism 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 cortices/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.

Age of second language acquisition affects nonverbal conflict processing in children: an fMRI study.

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. RESULTS: Compared 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.

COMT Val(158)Met genotypes differentially influence subgenual cingulate functional connectivity in healthy females.

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.

Does the amygdala response correlate with the personality trait 'harm avoidance' while evaluating emotional stimuli explicitly?

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: Our results indicate that the left amygdala response to explicit processing of affective stimuli does correlate with HA.

Left and right amygdala - mediofrontal cortical functional connectivity is differentially modulated by harm avoidance.

BACKGROUND: 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. METHODS: In 56 drug-naive healthy female subjects, we have examined the relationship between the personality dimension HA on lateralized amygdala rsFC. RESULTS: 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. CONCLUSIONS: 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).

Accelerated HF-rTMS in treatment-resistant unipolar depression: Insights from subgenual anterior cingulate functional connectivity.

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.

Cylinders or walls? A new computational model to estimate the MR transverse relaxation rate dependence on trabecular bone architecture.

OBJECTIVE: Bone density is distributed in a complex network of interconnecting trabecular plates and rods that are interspersed with bone marrow. A computational model to assess the dependence of the relaxation rate on the geometry of bone can consider the distribution of bone material in the form of two components: cylinders and open walls (walls with gaps). We investigate whether the experimentally known dependence of the transverse relaxation rate on the trabecular bone structure can be usefully interpreted in terms of these two components. MATERIALS AND METHODS: We established a computer model based on an elementary computational cell. The model includes a variable number of open walls and infinitely long cylinders as well as multiple geometric parameters. The transverse relaxation rate is computed as a function of these parameters. Within the model, increasing the trabecular spacing with a fixed trabecular radius is equivalent to thinning the trabeculae while maintaining constant spacing. RESULTS: Increasing the number of cylinder and wall gap elements beyond their nearest neighbors does not change the transverse relaxation rate. Although the absolute contribution to the relaxation due to open walls is on average more important than that due to cylinders, the latter drops off rapidly. The change on transverse relaxation rate is larger for changing cylinder geometry than for changing wall geometry, as it can be seen from the effect on the relaxation rate when trabecular spacing is varied, compared to varying the size of wall gaps. CONCLUSION: Our results provide strong evidence that trabecular thinning, which is associated with increasing age, decreases the relaxation rates. The effect of thinning plates and rods on the transverse relaxation can be understood in terms of simple cylinders and open walls. A reduction in the relaxation rate can be seen as an indication of thinning cylinders, corresponding to reduced bone stability and ultimately, osteoporosis.

Stress sensitive healthy females show less left amygdala activation in response to withdrawal-related visual stimuli under passive viewing conditions.

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.

The Akaike information criterion in DCE-MRI: does it improve the haemodynamic parameter estimates?

The Akaike information criterion and the associated Akaike weights (AW) rank pharmacokinetic models on the basis of goodness-of-fit and number of parameters. The usefulness of this information for improving the haemodynamic parameter estimates from DCE-MRI was investigated through two examples. In each of these, the estimates from the two-compartment exchange model (2CXM) were combined on the basis of the AW with those of a simplified model (either the uptake model or the extended Tofts model). Data were simulated using the 2CXM for a range of experimental and tissue conditions. Two multimodel approaches exploiting the AW were investigated: the 'bestmodel' approach which selects the parameter estimates from the model with highest AW and the 'weighted model' approach in which AW-weighted averages of the estimates from the competing models are calculated. Although these approaches were shown to be beneficial in some cases, they were found to frequently lead to unexpected increases in the bias and/or uncertainty of the resulting parameter estimates. Within the limited scope of this simulation study, the use of the Akaike criterion showed no systematic benefit over a fitting strategy involving only the more complex model.

The influence of emotional priming on the neural substrates of memory: a prospective fMRI study using portrait art stimuli.

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.

Quantification of cerebral tumour blood flow and permeability with T1-weighted dynamic contrast enhanced MRI: a feasibility study.

OBJECTIVES: Recently, T1-weighted DCE-MRI was proposed as an alternative to T2*-weighted DSC-MRI for the quantification of perfusion and permeability in brain tumors. The aim of the present feasibility study was to explore the clinical potential of the technique in different tumor types using a case-based review of initial results. PATIENTS AND METHODS: The method for data analysis was adapted from cerebral perfusion CT and applied in this study to a small group of patients with grade IV glioma and other brain tumors. The possible use of the proposed methodology was also explored for characterizing, following-up and planning the therapy of brain tumors. RESULTS: Parametric maps clearly differentiated tumor from the surrounding brain tissue, and also distinguished areas within the tumor presenting with different characteristics, thereby allowing identification of significant target areas for biopsy and/or treatment. Differences in cerebral blood flow (CBF) and lower extraction fractions (E) were observed in various tumors. Progression from a grade II to grade IV glioma over the course of a year was characterized by an increase in CBF and a decrease in E. CONCLUSION: DCE-MRI-based quantitative perfusion and permeability may be helpful for tumor-grade characterization, biopsy guidance, radiotherapy planning, radiotherapy monitoring and clinical follow-up, thereby improving the non-invasive characterization of brain tumors.

DTI reveals structural differences in white matter tracts between bilingual and monolingual children.

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.

Feasibility of cerebral magnetic resonance imaging in patients with externalised spinal cord stimulator.

OBJECT: 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. METHODS: 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. RESULTS: 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. CONCLUSION: We can conclude that brain MRI, fMRI and MRS studies performed in patients with externalised SCS can be safely executed.

Validity of perfusion parameters obtained using the modified Tofts model: a simulation study.

The two-compartment Tofts model (2CTM) has had widespread use in research and clinical practice. It assumes there is no broadening associated with the bolus transit through the capillary bed of the tissue under study. This assumption is often violated, with consequences that are hard to predict intuitively. The two-compartment exchange model is a generalization of 2CTM obtained by dropping the zero-broadening hypothesis, making it suitable for estimating the impact of violating this assumption. Using data simulated on the basis of the two-compartment exchange model, the correspondence between the hemodynamic parameters serving as input for the two-compartment exchange model and the parameters resulting from fitting the data with the 2CTM was investigated. The influence of tissue type and experimental setup was studied. Generally, a large tissue and setup dependent bias of the 2CTM fitting results with respect to the two-compartment exchange model input was observed. Extreme caution is needed when interpreting 2CTM data.

The effect of one left-sided dorsolateral prefrontal cortical HF-rTMS session on emotional brain processes in women.

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.

Passively viewing negatively valenced baby faces attenuates left amygdala activity in healthy females scoring high on 'Harm Avoidance'.

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.

Accuracy of peripheral quantitative computed tomography and magnetic resonance imaging in assessing cortical bone cross-sectional area: a cadaver study.

OBJECTIVE: The present study aimed to assess the accuracy of peripheral quantitative computed tomography (pQCT) and magnetic resonance imaging (MRI) in assessing the cortical cross-sectional area (CCSA) at the level of the tibia. METHODS: Nine human whole-leg specimens were scanned with pQCT and MRI (T1-weighted and ultrashort echo-time [UTE] images) at 2 diaphyseal levels, 1 distal and the other 1 proximal. Subsequently, the bones were cut, and the CCSA was measured using digitized planimetry on the transverse sections. The correlation between CCSAs assessed via pQCT and MRI (T1 and UTE images) and assessed via planimetry, taken as a criterion standard, was evaluated using the Spearman rank correlation method. RESULTS: The mean (SD) CCSA with pQCT was 237.3 (54.3) mm2; T1-MRI, 228.8 (63.2) mm2; UTE-MRI, 178.5 (54.8) mm2; and planimetry, 250.17 (59.3) mm2. The CCSA measured with pQCT and T1-MRI was highly correlated with the planimetric CCSA (rho = 0.868 and rho = 0.880, respectively, P < 0.001). The correlation involving UTE-MRI was somewhat weaker (rho = 0.664, P = 0.003). CONCLUSIONS: Peripheral quantitative computed tomography and MRI (T1-weighted images) are accurate for the assessment of the CCSA at the tibial shaft.

Assessment of tumor blood flow in breast tumors with T1-dynamic contrast-enhanced MR imaging: impact of dose reduction and the use of a prebolus technique on diagnostic efficacy.

PURPOSE: To prospectively evaluate whether dose reduction and the application of a prebolus technique can effectively alleviate signal saturation effects in T1 dynamic contrast enhanced (T1-DCE) magnetic resonance imaging (MRI) data in breast tumors and lead to increased diagnostic efficacy of the regional tumor blood flow (TBF) values obtained with deconvolution of T1-DCE MRI data. MATERIALS AND METHODS: After obtaining informed consent, 23 women (32-80 years) with histologically proven breast tumors underwent MR mammography that included a whole-breast T1 DCE sequence. In the slice where the tumor enhanced maximally, a prebolus protocol was applied. One mL of Gd-DTPA solution at 2 mL/s was injected at the beginning of a dynamic axial single slice inversion-prepared turbo field echo acquisition. At the 400th dynamic, a high dose of either 20 mL (15 patients) or 10 mL (8 patients) of contrast agent was injected at 2 mL/s and a further 400 dynamics were acquired. From the aortic prebolus curve an arterial input function (AIF) was reconstructed by time-shifting and adding the prebolus data. The relative enhancement time course from the tumor region of interest was deconvolved with the reconstructed AIF to generate the impulse response function, the maximum of which yielded the TBF. The institutional ethical committee approved the study. RESULTS: Reducing the contrast dose by a factor of 2 led to an increase in diagnostic contrast for the TBF values of malignant and benign tumors by a factor of slightly more than 2. Addition of the prebolus technique improved this further by 45%. receiver operating characteristic analysis showed a significant increase of diagnostic yield related to the combined use of a prebolus and minimal dose. CONCLUSION: Using a prebolus approach provides an estimate of the unsaturated AIF, while reduction of the high-dose bolus minimizes possible saturation effects in the tumor time course.

Using 3D-MRI to localize the dorsolateral prefrontal cortex in TMS research.

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.