Biomedical subjects

Matthias J P van Osch

Publications and source records attributed to Matthias J P van Osch.

17 recordsLinked to original sources

PubMed2007

Sensitivity comparison of multiple vs. single inversion time pulsed arterial spin labeling fMRI.

PURPOSE: To study the sensitivity for detection of activation for multiple vs. single inversion time (TI) pulsed arterial spin labeling (PASL). MATERIALS AND METHODS: The number of activated voxels and the mean t-statistic over activated voxels was measured by means of multiple and single TI PASL sequences in five volunteers during visual stimulation by means of an alternating checkerboard. Acquisition was performed by means of the transfer insensitive labeling technique (TILT) and TURBO-TILT. RESULTS: It was found that the sensitivity for the detection of activation was lower for an individual TI out of a multiple TI sequence than for the corresponding single TI acquisition of equal duration. After averaging over all TIs between and including 600 and 1400 msec, the number of activated voxels and mean t-statistic were no longer statistically lower for the multiple TI sequence than for the single TI experiment. CONCLUSION: Multiple TI PASL can be used for functional MRI (fMRI) studies, when performing the detection of activated brain regions on data that is averaged over all TIs between 600 and 1400 msec. Subsequently the multi-TI data can be used to quantify cerebral blood flow (CBF) changes upon activation. Additionally, we have shown that single TI PASL fMRI overestimates the CBF changes upon activation due to transit time changes.

Adult↗

PubMed2006

Effect of satiety on brain activation during chocolate tasting in men and women.

BACKGROUND: The brain plays a crucial role in the decision to eat, integrating multiple hormonal and neural signals. A key factor controlling food intake is selective satiety, ie, the phenomenon that the motivation to eat more of a food decreases more than does the motivation to eat foods not eaten. OBJECTIVE: We investigated the effect of satiation with chocolate on the brain activation associated with chocolate taste in men and women. DESIGN: Twelve men and 12 women participated. Subjects fasted overnight and were scanned by use of functional magnetic resonance imaging while tasting chocolate milk, before and after eating chocolate until they were satiated. RESULTS: In men, chocolate satiation was associated with increased taste activation in the ventral striatum, insula, and orbitofrontal and medial orbitofrontal cortex and with decreased taste activation in somatosensory areas. Women showed increased taste activation in the precentral gyrus, superior temporal gyrus, and putamen and decreased taste activation in the hypothalamus and amygdala. Sex differences in the effect of chocolate satiation were found in the hypothalamus, ventral striatum, and medial prefrontal cortex (all P < 0.005). CONCLUSIONS: Our results indicate that men and women differ in their response to satiation and suggest that the regulation of food intake by the brain may vary between the sexes. Therefore, sex differences are a covariate of interest in studies of the brain's responses to food.

Adult↗

PubMed2005

Association between supine cerebral perfusion and symptomatic orthostatic hypotension.

The goal of this study was to investigate whether the supine resting perfusion of brain tissue in symptomatic patients suffering from orthostatic hypotension (OH) is changed compared to control subjects and whether an association exists between the resting perfusion and the severity of OH. Ten symptomatic OH patients and 8 control subjects were included in this study. One patient was retrospectively excluded because he suffered from multiple system atrophy. Systolic and diastolic blood pressure changes were measured during a tilting bed procedure. Cerebral blood flow, cerebral blood volume and mean transit time were determined by bolus-tracking perfusion MRI and correlated with blood pressure changes. Cerebral blood volume was significantly increased in OH patients compared with control subjects for white matter (P = 0.019) and the mean transit time was significantly increased for gray (P = 0.010) and white matter (P = 0.015). The cerebral blood flow of the gray (r = 0.74, P = 0.022) and white matter (r = 0.75, P = 0.020) was significantly, positively correlated with systolic blood pressure changes. The mean transit time in white matter was significantly, negatively correlated with systolic blood pressure changes (r = -0.68, P = 0.045). This study suggests that in symptomatic patients with OH the cerebral perfusion of the brain in the resting, supine position correlates with the severity of OH as measured by postural changes in blood pressure.

Aged↗

PubMed2005

Probabilistic segmentation of brain tissue in MR imaging.

A new method has been developed for probabilistic segmentation of five different types of brain structures: white matter, gray matter, cerebro-spinal fluid without ventricles, ventricles and white matter lesion in cranial MR imaging. The algorithm is based on information from T1-weighted (T1-w), inversion recovery (IR), proton density-weighted (PD), T2-weighted (T2-w) and fluid attenuation inversion recovery (FLAIR) scans. It uses the K-Nearest Neighbor classification technique that builds a feature space from spatial information and voxel intensities. The technique generates for each tissue type an image representing the probability per voxel being part of it. By application of thresholds on these probability maps, binary segmentations can be obtained. A similarity index (SI) and a probabilistic SI (PSI) were calculated for quantitative evaluation of the results. The influence of each image type on the performance was investigated by alternately leaving out one of the five scan types. This procedure showed that the incorporation of the T1-w, PD or T2-w did not significantly improve the segmentation results. Further investigation indicated that the combination of IR and FLAIR was optimal for segmentation of the five brain tissue types. Evaluation with respect to the gold standard showed that the SI-values for all tissues exceeded 0.8 and all PSI-values exceeded 0.7, implying an excellent agreement.

Aged↗

PubMed2005

In vivo flow territory mapping of major brain feeding arteries.

The ability to visualize the perfusion territories of major feeding arteries to the brain is important for many clinical applications. Since the work of Duret in 1874 on vascularization of the brain, many textbooks and atlases have shown schematic drawings of the supply areas of the major cerebral arteries. Recent postmortem studies demonstrated that the variability of the cerebral vascular territories is significantly greater than previously assumed. The aim of the present study was to investigate in vivo, the variability of flow territories of major brain feeding arteries. Flow territory mapping of the anterior (internal carotid arteries) and posterior (basilar artery) circulation was performed in 115 (58 +/- 9 years of age) subjects with selective arterial spin labeling MRI. Flow territory maps for the entire population indicated significant variation in flow territories. However, when the subjects are further categorized into groups with a complete circle of Willis, with a missing A1 segment and with a unilateral or bilateral fetal-type posterior cerebral artery, the results showed considerably lower variation within groups. It is therefore concluded that, the variation observed from the entire population is mainly caused by anatomical variants of the circle of Willis. To relate focal brain lesions to underlying flow territories in individual cases, knowledge of the anatomy of the circle of Willis is essential.

Aged↗

PubMed2005

Non-invasive visualization of collateral blood flow patterns of the circle of Willis by dynamic MR angiography.

The circle of Willis plays an important role in the distribution of blood flow in the brain. To obtain dynamic information of the blood flow through the circle of Willis, a dynamic MRA technique based on arterial spin labeling (ASL) is introduced as a non-invasive technique. When the ASL labeling slab is restricted to a single artery, it is possible to visualize selectively the flow distribution of that specific artery. However, because of the decay of the label and the presence of noise it is difficult to extract functional information from these images. In the present study we propose three visualization and post-processing methods for the interpretation of these images. Firstly, the passage of labeled blood was corrected for decay of the label and hereafter shown as a movie. Secondly, by calculating the time of arrival at every location in the arteries of the circle of Willis, a 2D image was reconstructed summarizing the information of the movie. Finally, quantitative flow values were obtained by relating the arterial input function to the passage of labeled blood through a region of interest encompassing the vessel under investigation. Experiments in a circle of Willis phantom showed a high linear relation between measured flow and true flow, although the measured values were 10-15% lower than the true flow values. Measurements in healthy volunteers showed the potential to quantify the flow in all major arteries of the circle of Willis.

Circle of Willis↗

PubMed2005

Functional MRI of human hypothalamic responses following glucose ingestion.

The hypothalamus is intimately involved in the regulation of food intake, integrating multiple neural and hormonal signals. Several hypothalamic nuclei contain glucose-sensitive neurons, which play a crucial role in energy homeostasis. Although a few functional magnetic resonance imaging (fMRI) studies have indicated that glucose consumption has some effect on the neuronal activity levels in the hypothalamus, this matter has not been investigated extensively yet. For instance, dose-dependency of the hypothalamic responses to glucose ingestion has not been addressed. We measured the effects of two different glucose loads on neuronal activity levels in the human hypothalamus using fMRI. After an overnight fast, the hypothalamus of 15 normal weight men was scanned continuously for 37 min. After 7 min, subjects ingested either water or a glucose solution containing 25 or 75 g of glucose. We observed a prolonged decrease of the fMRI signal in the hypothalamus, which started shortly after subjects began drinking the glucose solution and lasted for at least 30 min. Moreover, the observed response was dose-dependent: a larger glucose load resulted in a larger signal decrease. This effect was most pronounced in the upper anterior hypothalamus. In the upper posterior hypothalamus, the signal decrease was similar for both glucose loads. No effect was found in the lower hypothalamus. We suggest a possible relation between the observed hypothalamic response and changes in the blood insulin concentration.

Adult↗

PubMed2005

Partial volume effects on arterial input functions: shape and amplitude distortions and their correction.

For quantification of perfusion values from a bolus-tracking MRI experiment, the measurement of an arterial input function (AIF) is necessary. Gradient-echo (GE) sequences are commonly used for this type of experiment because they offer a high signal-to-noise ratio (SNR) and the potential to quantify the concentration of contrast agent. Measurements of calibration curves for Gd-DTPA in human blood have shown a quadratic relation between the DeltaR(2)* and the concentration of contrast agent, and a linear relationship between phase changes and the concentration of contrast agent. However, for in vivo studies the spatial resolution is usually limited, which leads to partial volume effects. Partial volume effects result in a complex sum of signal arising from the tissue outside the vessel and a contrast agent concentration-dependent blood signal. Ignoring the presence of partial volume effects can lead to an overestimation or underestimation of the contrast agent concentration, depending on the experimental conditions. Correction for partial volume effects is feasible in arteries that are parallel to the main magnetic field by estimation and subtraction of the static signal of the surrounding tissue. Patient studies showed a large variation due to the AIF measurements, but it has also been shown that this influence can be minimized by correction for partial volume effects.

Arteries↗

PubMed2005

The effect of B1 field inhomogeneity and the nonselective inversion profile on the kinetics of FAIR-based perfusion MRI.

Perfusion imaging with pulsed arterial spin labeling techniques, like flow-sensitive alternating inversion recovery (FAIR), may suffer from inflow of fresh, i.e., unlabeled, spins. Inflow of fresh spins is caused by the arrival of unlabeled spins in the image slice and can lead to underestimation of the perfusion if not taken into account. In this study it was shown that a decrease in B(1) field strength toward the edge of the transmit coil and the consequent reduction in the inversion efficiency leads to a narrowing of the arterial delivery function and a reduction in FAIR signal. Increasing the B(1) amplitude of the adiabatic inversion pulse from 2.3 to 5.7 times its minimum amplitude requirement resulted in an observed increase of 40 to 80% in the rat brain FAIR signal at inflow times longer than 0.65 s. For coils with limited dimensions and significant B(1) inhomogeneity over the perfusion labeling slab, the application of an excessively large B(1) amplitude in combination with adiabatic inversion is recommended to optimize the FAIR perfusion contrast.

Animals↗

PubMed2005

Functional magnetic resonance imaging of human hypothalamic responses to sweet taste and calories.

BACKGROUND: Evidence exists that beverages do not trigger appropriate anticipatory physiologic responses, such as cephalic phase insulin release. Therefore, it is of interest to elucidate the food properties necessary for triggering adaptive responses. Previously, we found a prolonged dose-dependent decrease in the hypothalamic functional magnetic resonance imaging signal after ingestion of a glucose solution. OBJECTIVES: The aims of the present study were to measure the effects of sweet taste and energy content on the hypothalamic response to glucose ingestion and to measure the concomitant changes in blood glucose and insulin concentrations. DESIGN: Five healthy, normal-weight men participated in a randomized crossover design trial. The subjects were scanned 4 times for 37 min on separate days with functional magnetic resonance imaging. After 7 min, they ingested 1 of the following 4 stimuli (300 mL of each): water (control), a glucose solution, an aspartame (sweet taste) solution, or a maltodextrin (nonsweet carbohydrate) solution. RESULTS: Glucose ingestion resulted in a prolonged and significant signal decrease in the upper hypothalamus (P < 0.05). Water, aspartame, and maltodextrin had no such effect. Glucose and maltodextrin ingestions resulted in similar increases in blood glucose and insulin concentrations. However, only glucose triggered an early rise in insulin concentrations. Aspartame did not trigger any insulin response. CONCLUSIONS: Our findings suggest that both sweet taste and energy content are required for a hypothalamic response. The combination of sweet taste and energy content could be crucial in triggering adaptive responses to sweetened beverages.

Adult↗

PubMed2005

Altered flow territories after extracranial-intracranial bypass surgery.

OBJECTIVE: To prevent stroke after carotid sacrifice and to augment cerebral perfusion in patients with internal carotid artery (ICA) occlusion, high-flow extracranial-intracranial (EC-IC) bypass operations are performed. Although the function and efficacy of the bypass is monitored during surgery, the postoperative flow through the bypass is significantly lower than the flow in the contralateral ICA. Thus far, it is unknown whether decreased bypass flow is caused by a low tissue perfusion or by a relatively small flow territory. METHODS: Seven patients, four with an atherosclerotic ICA occlusion and three with a giant aneurysm of the ICA, were investigated; each underwent a high-flow EC-IC bypass and permanent occlusion of the ICA. Cerebral blood flow was measured with arterial spin labeling perfusion magnetic resonance imaging. Separate flow territory mapping of the EC-IC bypass, contralateral ICA, and posterior circulation was performed with selective arterial spin labeling magnetic resonance imaging. RESULTS: No significant difference was found in cerebral blood flow between the hemisphere ipsilateral to the EC-IC bypass (70.9 +/- 11.3 ml/min/100 g tissue), contralateral to the EC-IC bypass (71.9 +/- 14.3 ml/min/100 g tissue), and comparable findings in 50 healthy control participants (69.1 +/- 17.5 ml/min/100 g tissue). Paired analysis of the individual flow territories demonstrated a 15% volume reduction (P = 0.018) in flow territory of the EC-IC bypass compared with the contralateral side. CONCLUSION: In the present study, we demonstrate the feasibility of selective arterial spin labeling magnetic resonance imaging for clinical follow-up of patients after high-flow EC/IC bypass surgery, providing both information on flow territories and the level of regional cerebral blood flow.

Adult↗

PubMed2004

Internal carotid artery occlusion assessed at pulsed arterial spin-labeling perfusion MR imaging at multiple delay times.

Magnetic resonance (MR) imaging with pulsed arterial spin labeling (ASL) was performed at six different inversion times in nine patients with internal carotid artery (ICA) occlusion and in 11 control subjects. The hospital's commission on scientific research on human subjects approved the study protocol, and all study subjects gave informed consent. Cerebral blood flow (CBF) in the middle cerebral artery territories was calculated from the combined signal intensities measured with ASL at the multiple inversion times. In the patients with ICA occlusion, mean CBF values were decreased in the gray matter of the hemisphere ipsilateral to the occlusion, as compared with values in the gray matter of the contralateral hemisphere (P < .05) and with values in the gray matter of the control subjects (P < .05). Quantification of CBF with ASL at multiple inversion times can compensate for the blood transit delays in patients with ICA occlusion.

Adult↗

PubMed2004

Comparison of FAIR perfusion kinetics with DSC-MRI and functional histology in a model of transient ischemia.

Flow-sensitive alternating inversion recovery (FAIR) is a noninvasive method for perfusion imaging. It has been shown that the FAIR signal may depend on hemodynamic parameters other than perfusion, the most important one being transit delays of labeled spins to the observed tissue. These parameters are expected to change with ischemia. The goal of this study was to assess the effect of these changes on the interpretation of FAIR results in the case of altered perfusion. This was investigated in a rat model of transient cerebral ischemia. It was shown that the ratio of FAIR signal in the infarct compared to the contralateral side was lower at short inflow times, which suggests that transit times affected the effective FAIR signal. The FAIR results were compared with those from functional histology and dynamic susceptibility contrast MRI, and the findings indicated that the altered kinetics of the FAIR signal were related to reduced and delayed inflow in the infarct region--not to a decrease in the number of functional vessels.

Animals↗

PubMed2004

Automatic segmentation of different-sized white matter lesions by voxel probability estimation.

A new method for fully automated segmentation of white matter lesions (WMLs) on cranial MR imaging is presented. The algorithm uses five types of regular MRI-scans. It is based on a K-Nearest Neighbor (KNN) classification technique, which builds a feature space from voxel intensity features and spatial information. The technique generates images representing the probability per voxel being part of a WML. By application of thresholds on these probability maps binary segmentations can be produced. ROC-curves show that the segmentations achieve a high sensitivity and specificity. Three similarity measures, the similarity index (SI), the overlap fraction (OF) and the extra fraction (EF), are calculated for evaluation of the results and determination of the optimal threshold on the probability map. Investigation of the relation between the total lesion volume and the similarity measures shows that the method performs well for lesions larger than 2 cc. The maximum SI per patient is correlated to the total WML volume. No significant relation between the lesion volume and the optimal threshold has been observed. The probabilistic equivalents of the SI, OF en EF (PSI, POF and PEF) allow direct evaluation of the probability maps, which provides a strong tool for comparison of different classification results. A significant correlation between the lesion volume and the PSI and the PEF has been noticed. This method for automated WML segmentation is applicable to lesions of different sizes and shapes, and reaches an accuracy that is comparable to existing methods for multiple sclerosis lesion segmentation. Furthermore, it is suitable for detection of WMLs in large and longitudinal population studies.

Aged↗

PubMed2004

Probabilistic segmentation of white matter lesions in MR imaging.

A new method has been developed for fully automated segmentation of white matter lesions (WMLs) in cranial MR imaging. The algorithm uses information from T1-weighted (T1-w), inversion recovery (IR), proton density-weighted (PD), T2-weighted (T2-w) and fluid attenuation inversion recovery (FLAIR) scans. It is based on the K-Nearest Neighbor (KNN) classification technique that builds a feature space from voxel intensities and spatial information. The technique generates images representing the probability per voxel being part of a WML. By application of thresholds on these probability maps, binary segmentations can be obtained. ROC curves show that the segmentations achieve both high sensitivity and specificity. A similarity index (SI), overlap fraction (OF) and extra fraction (EF) are calculated for additional quantitative analysis of the result. The SI is also used for determination of the optimal probability threshold for generation of the binary segmentation. Using probabilistic equivalents of the SI, OF and EF, the probability maps can be evaluated directly, providing a powerful tool for comparison of different classification results. This method for automated WML segmentation reaches an accuracy that is comparable to methods for multiple sclerosis (MS) lesion segmentation and is suitable for detection of WMLs in large and longitudinal population studies.

Aged↗

PubMed2003

Measuring the arterial input function with gradient echo sequences.

The measurement of the arterial input function by use of gradient echo sequences was investigated by in vitro and in vivo experiments. First, calibration curves representing the influence of the concentration of Gd-DTPA on both the phase and the amplitude of the MR signal were measured in human blood by means of a slow-infusion experiment. The results showed a linear increase in the phase velocity and a quadratic increase in DeltaR(*) (2) as a function of the Gd-DTPA concentration. Next, the resultant calibration curves were incorporated in a partial volume correction algorithm for the arterial input function determination. The algorithm was tested in a phantom experiment and was found to substantially improve the accuracy of the concentration measurement. Finally, the reproducibility of the arterial input function measurement was estimated in 16 patients by considering the input function of the left and the right sides as replicate measurements. This in vivo study showed that the reproducibility of the arterial input function determination using gradient echo sequences is improved by employing a partial volume correction algorithm based on the calibration curve for the contrast agent used.

Algorithms↗

PubMed2003

Model of the human vasculature for studying the influence of contrast injection speed on cerebral perfusion MRI.

Simulations of dynamic susceptibility contrast (DSC) MRI are frequently performed by assuming a certain shape for the input function and the microvascular response function. However, to investigate the influence of parameters that will affect the shape of the input function, a more complex model of the human vasculature is required. In this study, a model of the human vasculature is proposed that consists of a network of vascular operators based on physiological data typical of a 35-year-old male subject. The simulated contrast passage curves were found to be within the range of observed contrast passage curves in a population of patients without vascular disease. The model was used to predict the effect of different injection speeds of the contrast agent on the accuracy of the perfusion experiment. It was found that injection speeds of <3 ml/s lead to an underestimation of the observed cerebral blood flow (CBF). Additionally, it was determined that decreasing the temporal resolution of the acquisition results in an underestimation of the CBF values, and an increase of the standard deviation (SD) of CBF measurements.

Adult↗