Jeroen van der Grond

Probability of Regaining Dexterity in the Flaccid Upper Limb Impact of Severity of Paresis and Time Since Onset in Acute Stroke

BACKGROUND AND PURPOSE To improve the accuracy of early postonset prediction of motor recovery in the flaccid hemiplegic arm, the effects of change in motor function over time on the accuracy of prediction were evaluated, and a prediction model for the probability of regaining dexterity at 6 months was developed. METHODS In 102 stroke patients, dexterity and paresis were measured with the Action Research Arm Test, Motricity Index, and Fugl-Meyer motor evaluation. For model development, 23 candidate determinants were selected. Logistic regression analysis was used for prognostic factors and model development. RESULTS At 6 months, some dexterity in the paretic arm was found in 38%, and complete functional recovery was seen in 11.6% of the patients. Total anterior circulation infarcts, right hemisphere strokes, homonymous hemianopia, visual gaze deficit, visual inattention, and paresis were statistically significant related to a poor arm function. Motricity Index leg scores of at least 25 points in the first week and Fugl-Meyer arm scores of 11 points in the second week increasing to 19 points in the fourth week raised the probability of developing some dexterity (Action Research Arm Test >or=10 points) from 74% (positive predictive value [PPV], 0.74; 95% confidence interval [CI], 0.63 to 0.86) to 94% (PPV, 0.83; 95% CI, 0.76 to 0.91) at 6 months. No change in probabilities of prediction dexterity was found after 4 weeks. CONCLUSIONS Based on the Fugl-Meyer scores of the flaccid arm, optimal prediction of arm function outcome at 6 months can be made within 4 weeks after onset. Lack of voluntary motor control of the leg in the first week with no emergence of arm synergies at 4 weeks is associated with poor outcome at 6 months.

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.

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.

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 ΔR  *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. Magn Reson Med 49:1067–1076, 2003.

Cerebral lactate and N-acetyl-aspartate/choline ratios in asphyxiated full-term neonates demonstrated in vivo using proton magnetic resonance spectroscopy.

ABSTRACT: The purpose of this study was to test the hypothesis that a high lactate signal and a low N-acetyl-aspartate/choline ratio in neonates with postasphyxial encephalopathy indicated a high chance of an adverse outcome in vivo when proton magnetic resonance spectroscopy was used. Twenty-one full-term asphyxiated neonates were examined at a mean postnatal age of 7.1 d. Five patients died, and five survivors had handicaps. Eleven of the 16 survivors (seven without handicaps and four with handicaps) had a second examination at 3 mo of age. After magnetic resonance imaging, spectra were obtained at 1.5 tesla. A 20-mm-thick slice was selected through the basal ganglia. After optimizing the B-0 field, we used a double spin-echo pulse sequence (90–180-180°) with a time to repeat of 2000 ms and a time to echo of 272 ms. Two-dimensional spectroscopic imaging was performed by 32 ± 32 phase encoding steps in two directions in a 225-mm field of view, resulting in 1-mL volumes, followed by computerized processing. Neuromotor development was examined at 6 wk, 3 mo, and every 3 mo thereafter. Lactate resonances were seen only in the five patients with grade 3 postasphyxial encephalopathy. Lactate was distributed diffusely (n = 4), or localized in areas of infarction (n = 1). N-acetyl-aspartate/choline ratios were significantly lower in the patients with an adverse outcome than in the survivors without handicaps, both neonatally (p < 0.005, Wilcoxons rank sum test) and at 3 mo (p < 0.05). In conclusion, the presence of cerebral lactate and a low N-acetyl-aspartate/choline ratio demonstrated in vivo using proton magnetic resonance spectroscopy in full-term neonates with postasphyxial encephalopathy indicate a poor outcome.

Flow territory mapping of the cerebral arteries with regional perfusion MRI.

Background and Purpose— Conventional contrast-enhanced angiography is the gold standard for visualization of the vascular tree supplied by the major cerebral arteries and assessment of collateral flow. Thus far, however, no methods are available to assess the actual flow territories of the individual cerebral arteries. In the present study, we evaluate a noninvasive arterial spin labeling MRI method for selective mapping of the flow territories of the left and right internal carotid arteries and posterior circulation (basilar artery and vertebral arteries). Methods— A spatially selective labeling approach, regional perfusion imaging, was developed on the basis of selective slab inversion of the arterial water with a pulsed arterial spin labeling sequence. The selectivity of this method was demonstrated. Results— Regional perfusion imaging enables assessment of the perfusion territories of the major cerebral arteries. With selective labeling of an internal carotid artery, signal is present in both the ipsilateral anterior cerebral artery and ipsilateral middle cerebral artery flow territory. With labeling of the basilar artery, perfusion-weighted signal is symmetrically present in both posterior cerebral artery flow territories. Cerebral blood flow values measured with regional perfusion imaging in the complete hemisphere (40.1 mL · min−1 · 100 g−1 tissue), white matter (22.1 mL · min−1 · 100 g−1 tissue), and gray matter (65.8 mL · min−1 · 100 g−1 tissue) are in agreement with data in the literature. Conclusions— We present the first imaging method capable of evaluating both quantitatively and qualitatively the flow territories of the individual brain-feeding arteries in vivo.

Circle of Willis Collateral Flow Investigated by Magnetic Resonance Angiography

BACKGROUND AND PURPOSE The circle of Willis (CW) is considered an important collateral pathway in maintaining adequate cerebral blood flow in patients with internal carotid artery (ICA) obstruction. We aimed to investigate the anatomic variation of the CW in patients with severe symptomatic carotid obstructive disease and to analyze diameter changes of its components in relation to varying grades of ICA obstruction and in relation to the presence or absence of (retrograde) collateral flow. METHODS Seventy-five patients with minor disabling neurological deficits and with ICA stenoses or occlusions were categorized into 4 groups according to the severity of ICA obstruction. This patient population reflected a relatively favorable subgroup of cerebral infarction (considering their minor neurological deficits). All subjects underwent magnetic resonance angiography, including magnetic resonance angiography sensitive to flow direction. CW morphology and the size of its components were determined and compared with those values in control subjects (n=100). RESULTS Compared with control subjects, patients demonstrated a significantly higher percentage of entirely complete CW configurations (55% versus 36%, P=0.02), complete anterior configurations (88% versus 68%, P=0.002), and complete posterior CW configurations (63% versus 47%, P=0.04). Patients with severe ICA stenosis did not show significantly increased CW vessel diameters. Patients with ICA occlusion demonstrated a high prevalence of collateral flow through the anterior CW and significantly increased diameters of the communicating channels. Patients with bilateral ICA occlusion relied on collateral flow via the posterior CW and demonstrated a bilateral increase in posterior communicating artery diameters (P<0.05). CONCLUSIONS The anatomic and functional configuration of the CW reflects the degree of ICA obstruction.

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.

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.

Brain Perfusion Territory Imaging: Methods and Clinical Applications of Selective Arterial Spin-labeling MR Imaging

The ability to visualize perfusion territories in the brain is important for many clinical applications. The aim of this overview is to highlight the possibilities of selective arterial spin-labeling (ASL) magnetic resonance (MR) imaging techniques in the assessment of the perfusion territories of the cerebral arteries. In the past decade, the optimization of selective ASL MR techniques to image the cerebral perfusion territories has resulted in numerous labeling approaches and an increasing number of clinical applications. In this article, the methods and clinical applications of selective ASL MR imaging are described and the importance of perfusion territory information in studying cerebral hemodynamic changes in patients with cerebrovascular disease is shown. In specific patient groups with cerebrovascular disease, such as acute stroke, large artery steno-occlusive disease, and arteriovenous malformation, selective ASL MR imaging provides valuable hemodynamic information when added to current MR protocols. As a noninvasive tool for perfusion territory measurements, selective ASL may contribute to a better understanding of the relation between the vasculature, perfusion, and brain function.