Parietal lobe critically supports successful paired immediate and single-item delayed memory for targets.

The parietal lobe is important for successful recognition memory, but its role is not yet fully understood. We investigated the parietal lobes' contribution to immediate paired-associate memory and delayed item-recognition memory separately for hits (targets) and correct rejections (distractors). We compared the behavioral performance of 56 patients with known parietal and medial temporal lobe dysfunction (i.e. early Alzheimer's Disease) to 56 healthy control participants in an immediate paired and delayed single item object memory task. Additionally, we performed voxel-based morphometry analyses to investigate the functional-neuroanatomic relationships between performance and voxel-based estimates of atrophy in whole-brain analyses. Behaviorally, all participants performed better identifying targets than rejecting distractors. The voxel-based morphometry analyses associated atrophy in the right ventral parietal cortex with fewer correct responses to familiar items (i.e. hits) in the immediate and delayed conditions. Additionally, medial temporal lobe integrity correlated with better performance in rejecting distractors, but not in identifying targets, in the immediate paired-associate task. Our findings suggest that the parietal lobe critically supports successful immediate and delayed target recognition memory, and that the ventral aspect of the parietal cortex and the medial temporal lobe may have complementary preferences for identifying targets and rejecting distractors, respectively, during recognition memory.

Hematocrit and Serum Hemoglobin Do Not Influence Values in Computed Tomography Perfusion of Patients With Acute Ischemic Stroke.

OBJECTIVE: There is a correlation between both serum hemoglobin (HGB) and hematocrit (HCT) and attenuation values of vessels in noncontrast-enhanced computed tomography (NECT), which could influence calculated perfusion maps in CT perfusion. METHODS: We retrospectively included 45 patients, who presented with acute new neurological symptoms and underwent NECT and CT perfusion (128-row multi detector scanner, coverage: 6.9 cm craniocaudally; 80 kV; 200 mAs; temporal resolution: 2 seconds using 40 mL Ultravist 370 at a flow rate of 5 mL/s) on admission and a follow-up MRI within 1 week of admission. RESULTS: Hematocrit, HGB, and attenuation values did not differ between patients with stroke and controls. A statistically significant correlation was found between HCT and HGB and attenuation values in the internal carotid artery or middle cerebral artery on NECT (P < 0.05). No statistically significant correlation was observed between HCT and HGB and perfusion maps. CONCLUSIONS: Hematocrit and HGB do not influence calculated perfusion maps. There is no need for HCT/HGB-adjusted cerebral blood volume thresholds in stroke patients.

Spontaneous dissections of the anterior cerebral artery: a meta-analysis of the literature and three recent cases.

INTRODUCTION: Spontaneous dissections of intracranial arteries are rare, but important causes of stroke, especially in younger patients. Dissections of the anterior cerebral artery (ACA) have been reported only very rarely in the European and North American populations but might be more prevalent than previously thought. METHODS: This paper describes the presenting pattern of the disease, the clinical and imaging findings, as well as endovascular therapeutical options with respect to a meta-analysis of cases reported in the literature. Additionally, own observations in three recent representative cases are discussed. RESULTS: Overall, 80 cases from recent literature were included to the meta-analysis. The median age was 51 (35-82) years. Ischemia alone was described in 58 cases (73 %), subarachnoid hemorrhage (SAH) in 8 cases (10 %), and a combination of both in 14 cases (17 %). Radiological diagnosis including use of thin-layered 3T-MRI vessel wall imaging with black blood technique was verified by double lumen, by a string sign or string and pearl sign, or by a vessel wall hematoma in 23 (32 %), 62 (89 %), and 14 (20 %) cases, respectively. Interventional or surgical treatment was performed in 7 cases. A good clinical recovery was achieved in 77 % of cases. CONCLUSION: Dissections of the ACA mostly cause ischemia, but can cause SAH or a combination of both in a relatively young population. Detailed neuroradiological diagnosis including 3T-MRI vessel wall imaging is required as a double lumen, isolated stenosis due to vessel wall hematoma, or the secondary development of a pseudoaneurysm might occur. Interventional therapy is the primary therapy for these vascular complications.

Basic Principles and Clinical Applications of Magnetic Resonance Spectroscopy in Neuroradiology.

Magnetic resonance spectroscopy is a powerful tool to assist daily clinical diagnostics. This review is intended to give an overview on basic principles of the technology, discuss some of its technical aspects, and present typical applications in daily clinical routine in neuroradiology.

Perturbation of the left inferior frontal gyrus triggers adaptive plasticity in the right homologous area during speech production.

The role of the right hemisphere in aphasia recovery after left hemisphere damage remains unclear. Increased activation of the right hemisphere has been observed after left hemisphere damage. This may simply reflect a release from transcallosal inhibition that does not contribute to language functions. Alternatively, the right hemisphere may actively contribute to language functions by supporting disrupted processing in the left hemisphere via interhemispheric connections. To test this hypothesis, we applied off-line continuous theta burst stimulation (cTBS) over the left inferior frontal gyrus (IFG) in healthy volunteers, then used functional MRI to investigate acute changes in effective connectivity between the left and right hemispheres during repetition of auditory and visual words and pseudowords. In separate sessions, we applied cTBS over the left anterior IFG (aIFG) or posterior IFG (pIFG) to test the anatomic specificity of the effects of cTBS on speech processing. Compared with cTBS over the aIFG, cTBS over the pIFG suppressed activity in the left pIFG and increased activity in the right pIFG during pseudoword vs. word repetition in both modalities. This effect was associated with a stronger facilitatory drive from the right pIFG to the left pIFG during pseudoword repetition. Critically, response became faster as the influence of the right pIFG on left pIFG increased, indicating that homologous areas in the right hemisphere actively contribute to language function after a focal left hemisphere lesion. Our findings lend further support to the notion that increased activation of homologous right hemisphere areas supports aphasia recovery after left hemisphere damage.

Increased facilitatory connectivity from the pre-SMA to the left dorsal premotor cortex during pseudoword repetition.

Previous studies have demonstrated that the repetition of pseudowords engages a network of premotor areas for articulatory planning and articulation. However, it remains unclear how these premotor areas interact and drive one another during speech production. We used fMRI with dynamic causal modeling to investigate effective connectivity between premotor areas during overt repetition of words and pseudowords presented in both the auditory and visual modalities. Regions involved in phonological aspects of language production were identified as those where regional increases in the BOLD signal were common to repetition in both modalities. We thus obtained three seed regions: the bilateral pre-SMA, left dorsal premotor cortex (PMd), and left ventral premotor cortex that were used to test 63 different models of effective connectivity in the premotor network for pseudoword relative to word repetition. The optimal model was identified with Bayesian model selection and reflected a network with driving input to pre-SMA and an increase in facilitatory drive from pre-SMA to PMd during repetition of pseudowords. The task-specific increase in effective connectivity from pre-SMA to left PMd suggests that the pre-SMA plays a supervisory role in the generation and subsequent sequencing of motor plans. Diffusion tensor imaging-based fiber tracking in another group of healthy volunteers showed that the functional connection between both regions is underpinned by a direct cortico-cortical anatomical connection.

Sellar and supra-sellar glioblastoma masquerading as a pituitary macroadenoma.

A few number of suprasellar gliomas have been reported thus far of which, some of them developed several years after radiation therapy for pituitary adenomas or craniopharyngiomas. Herein, we report a case of sellar glioblastoma with suprasellar extension with no prior radiation history who mimicked clinical and radiologic findings of a pituitary macroadenoma.

Phonological decisions require both the left and right supramarginal gyri.

Recent functional imaging studies demonstrated that both the left and right supramarginal gyri (SMG) are activated when healthy right-handed subjects make phonological word decisions. However, lesion studies typically report difficulties with phonological processing after left rather than right hemisphere damage. Here, we used a unique dual-site transcranial magnetic stimulation (TMS) approach to test whether the SMG in the right hemisphere contributes to modality-independent (i.e., auditory and visual) phonological decisions. To test task-specificity, we compared the effect of real or sham TMS during phonological, semantic, and perceptual decisions. To test laterality and anatomical specificity, we compared the effect of TMS over the left, right, or bilateral SMG and angular gyri. The accuracy and reaction times of phonological decisions were selectively disrupted relative to semantic and perceptual decisions when real TMS was applied over the left, right, or bilateral SMG. These effects were not observed for TMS over the angular gyri. A follow-up experiment indicated that the threshold-intensity for inducing a disruptive effect on phonological decisions was identical for unilateral TMS over the right or left SMG. Taken together, these findings provide converging evidence that the right SMG contributes to accurate and efficient phonological decisions in the healthy brain, with no evidence that the left and right SMG can compensate for one another during TMS. Our findings motivate detailed studies of phonological processing in patients with acute or long-term damage of the right SMG.

A review of brain regions and associated post-concussion symptoms.

The human brain is an exceptionally complex organ that is comprised of billions of neurons. Therefore, when a traumatic event such as a concussion occurs, somatic, cognitive, behavioral, and sleep impairments are the common outcome. Each concussion is unique in the sense that the magnitude of biomechanical forces and the direction, rotation, and source of those forces are different for each concussive event. This helps to explain the unpredictable nature of post-concussion symptoms that can arise and resolve. The purpose of this narrative review is to connect the anatomical location, healthy function, and associated post-concussion symptoms of some major cerebral gray and white matter brain regions and the cerebellum. As a non-exhaustive description of post-concussion symptoms nor comprehensive inclusion of all brain regions, we have aimed to amalgamate the research performed for specific brain regions into a single article to clarify and enhance clinical and research concussion assessment. The current status of concussion diagnosis is highly subjective and primarily based on self-report of symptoms, so this review may be able to provide a connection between brain anatomy and the clinical presentation of concussions to enhance medical imaging assessments. By explaining anatomical relevance in terms of clinical concussion symptom presentation, an increased understanding of concussions may also be achieved to improve concussion recognition and diagnosis.

Thin-slice reconstructions of nonenhanced CT images allow for detection of thrombus in acute stroke.

BACKGROUND AND PURPOSE: The purpose of this study was to investigate whether thin-slice image reconstructions of cranial nonenhanced CT scans could be used to significantly increase sensitivity for detecting intraluminal thrombus in patients with acute ischemic stroke due to proximal occlusion of the middle cerebral artery. METHODS: In a prospective case series, the raw data of nonenhanced CT scans from 54 patients presenting with acute ischemic stroke and proven vascular obliteration of the middle cerebral artery were collected along with the same data from patients not having a stroke but the same sex and age. All raw data were reconstructed with a slice thickness of 5 mm and as thin slices with a thickness of 0.625 mm. Three observers independently evaluated the 5-mm nonenhanced CT reconstructions and 5-mm maximum intensity projections of the thin slices and rated the likelihood of a clot obliterating the middle cerebral artery trunk or first-order branches using a 5-point scale. The results were evaluated in comparison with base data using receiver operating curve analysis. Interobserver agreement was measured using Cohen κ for every pair of observers. RESULTS: The area under the curve for the receiver operating curve analysis for the thick slices ranged from 0.63 to 0.67, whereas for the maximum intensity projection images of the thin slice reconstructions, receiver operating curve analysis revealed areas under the curve between 0.94 and 0.97. Interobserver agreement was higher for thin-slice (κ, 0.69-0.83) versus thick-slice nonenhanced CT reconstructions (κ, 0.38-0.45). CONCLUSIONS: Thin-slice reconstructions of standard cranial nonenhanced CT raw data allow for more sensitive and reliable detection of clots occluding the proximal middle cerebral artery.

Measurements of Functional Network Connectivity Using Resting State Arterial Spin Labeling During Neurosurgery.

In neurosurgery, an exact delineation of functional areas is of great interest to spare important regions to ensure the best possible outcome for the patient (i.e., maximum removal while maintaining the highest possible quality of life). Preoperative imaging is routinely performed, including the visualization of not only structural but also functional information. During surgery, however, brain shift can occur, leading to an offset between the previously defined and the real position. Real-time imaging during the procedure is therefore desired to obtain this information while performing surgery. In this study 15 patients suffering from glioblastoma multiforme were included. These patients underwent structural and perfusion imaging using arterial spin labeling during the procedure. The latter has been used for gathering information about tumor residual perfusion. However, special postprocessing of this data allows for additional mapping of resting state networks and is intended to be used to gather deeper insights to aid the surgeon in planning the procedure. The data of each patient could be successfully postprocessed and used to map different resting state networks alongside the default mode network. On the basis of this study, it is feasible to use the information obtained from perfusion imaging to visualize not only vascular signal but also functional activation of resting state networks without acquiring any additional data besides the already available information. This may help guide the neurosurgeon in real time to adjust the surgical plan.

Assessment of thrombus in acute middle cerebral artery occlusion using thin-slice nonenhanced Computed Tomography reconstructions.

BACKGROUND AND PURPOSE: We sought to evaluate how accurately length and volume of thrombotic clots occluding cerebral arteries of patients with acute ischemic stroke can be assessed from nonenhanced CT (NECT) scans reconstructed with different slice widths. METHODS: NECT image data of 58 patients with acute ischemic stroke with vascular occlusion proven by CT angiography were reconstructed with slice widths of 1.25 mm, 2.5 mm, 3.75 mm, and 5 mm. Thrombus lengths and volumes were quantified based on these NECT images by detecting and segmenting intra-arterial hyperdensities. The results were compared with reference values of thrombus length and volume obtained from CT angiography images using Bland-Altman analysis and predefined levels or tolerance to find NECT slice thicknesses that allow for sufficiently accurate thrombus quantification. RESULTS: Thrombus length can be measured with high accuracy using the hyperdense middle cerebral artery sign detected in NECT images with slice thicknesses of 1.25 mm and 2.5 mm. We found mean deviations from the reference values and limits of agreement of -0.1 mm+/-0.6 mm with slice widths of 1.25 mm and 0.1 mm+/-0.7 mm for slice widths of 2.5 mm. Thrombus length measurements in NECT images with higher slice width and all evaluated thrombus volume measurements exhibited severe dependence on the level and did not match the accuracy criteria. CONCLUSIONS: The length of the hyperdense middle cerebral artery sign as detected on thin-slice NECT reconstructions in patients with acute ischemic stroke can be used to quantify thrombotic burden accurately. Thus, it might qualify as a new diagnostic parameter in acute stroke management that indicates and quantifies the extent of vascular obliteration.

Intraoperative dynamic susceptibility contrast MRI (iDSC-MRI) is as reliable as preoperatively acquired perfusion mapping.

DSC-MRI was applied intraoperatively during human brain tumor removal. Immediately after complete tumor resection was presumed, MRI including a dynamic susceptibility contrast T2-weighted EPI sequence was performed in 30 patients while the skull was still open using a flexible two-channel coil system at an intraoperative 1.5-Tesla MR scanner. Maps of relative regional blood flow (rCBF), blood volume (rCBV), and mean transit time (MTT) were calculated, and ratios of these maps were compared to preoperatively acquired DSC-MRI data. The extent of the resection was compared with the postoperative MRI performed 24 h after the operation. In 8 of these patients residual tumor tissue was depicted at the time of intraoperative MRI. In corresponding regions ratios for rCBV and rCBF did not differ significantly between pre- and intraoperatively acquired data (two-tailed t-test). Furthermore, we found a high correlation between ratios created from pre- and intraoperatively measured data for both rCBV and rCBF, respectively (Pearson correlation; r(2)(rCBV)=0.86, p

Incidental findings are frequent in young healthy individuals undergoing magnetic resonance imaging in brain research imaging studies: a prospective single-center study.

OBJECTIVE: There is an ongoing debate about how to handle incidental findings (IF) detected in healthy individuals who participate in research-driven magnetic resonance imaging (MRI) studies. There are currently no established guidelines regarding their management. METHODS: We prospectively assessed the frequency of IF in 206 young healthy volunteers who additionally underwent structural MRIs of the whole brain as part of a scientific MRI protocol. RESULTS: Assessment of the structural MRI by 2 board-certified neuroradiologists revealed IF in 19% of the subjects (n = 39). In approximately half of these subjects (n = 21), these findings were of potential clinical relevance (eg, arteriovenous malformations, cavernomas, pituitary abnormalities) and required further diagnostic investigations. None of these potentially relevant IF prompted immediate active medical treatment. CONCLUSIONS: Incidental findings are very frequent in young healthy volunteers. Because many of the IF require further diagnostic workup, standardized procedures for MRI and the handling of these images are mandatory to ensure competent clinical management.

Intraoperative dynamic susceptibility contrast weighted magnetic resonance imaging (iDSC-MRI) - Technical considerations and feasibility.

DSC-MRI was applied intraoperatively during brain tumor removal. Immediately after presumed complete tumor resection an MRI including a dynamic susceptibility contrast T2-weighted EPI sequence was performed in 6 patients while the skull was still open using a flexible two-channel coil system at an intraoperative 1.5-Tesla MR scanner. After an initial baseline period of this iDSC-MRI sequence a bolus of contrast agent was administered intravenously. Maps of relative regional blood flow (rCBF), blood volume (rCBV) and the mean transit time (MTT) were calculated. These maps were compared to preoperatively acquired DSC-MRI data. The extent of the resection was compared with the postoperative MRI performed 24 h after the operation. In five patients complete tumor removal was already achieved at the time of iDSC-MRI and no areas of elevated perfusion values adjacent to the resection cavity were found. Complete removal was again documented on the postoperatively performed MRI. In one case there was residual tumor that showed both contrast enhancement and identical perfusion ratios as in the preoperatively acquired data. Removal of the remaining tumor was performed. iDSC-MRI is technically feasible as there are no significant susceptibility artifacts. DSC-MRI has been used to distinguish different tumor entities preoperatively and recurrent disease from radiation necrosis. Despite brain shift and thus invalidated preoperative image data or contrast leakage caused by intraoperative manipulation, iDCS-MRI furthermore reliably detects residual tumor intraoperatively at a timepoint where further resection is still possible and thus enables the neurosurgeon to complete the resection during the same procedure.

The correlation between quantitative T2' and regional cerebral blood flow after acute brain ischemia in early reperfusion as demonstrated in a middle cerebral artery occlusion/reperfusion model of the rat.

INTRODUCTION: qT2'-maps are calculated by subtracting T2- from T2*-relaxation rates. They are oxygen-sensitive and depict oxygen extraction. In several studies they have been used to describe the penumbra in patients with acute ischemic stroke. No correlation between rCBF and qT2' has been performed to date. In this study a correlation between rCBF and qT2' was performed in a temporary middle cerebral occlusion-reperfusion model of the rat. MATERIALS AND METHODS: Temporary middle cerebral artery occlusion was performed on seven Sprague-Dawley rats. After 60 min of occlusion and 90 min of reperfusion MRI was performed including DWI, dynamic susceptibility contrast-weighted MR imaging (DSC-MRI) and qT2'. ROIs were placed inside the DWI lesion and transferred to rCBF- and qT2'-maps. rCBF and qT2' were compared to corresponding tissue in the contralateral hemisphere. RESULTS: qT2' was lower in the infarcted areas when compared to the contralateral hemisphere. Correlation between rCBF and qT2' was r = 0.41, p = 0.14 (Pearson's correlation coefficient), when corrected for outliers it was r = 0.58, p = 0.04. CONCLUSION: Our results show that there is a moderate correlation between rCBF and qT2'. qT2'-maps could be used to explore cerebral perfusion without the application of contrast agent or radiation.

Dynamic contrast-enhanced susceptibility-weighted perfusion MRI (DSC-MRI) in a glioma model of the rat brain using a conventional receive-only surface coil with a inner diameter of 47 mm at a clinical 1.5 T scanner.

Magnetic resonance (MR) imaging in animal models is usually performed in expensive dedicated small bore animal scanners of limited availability. In the present study a standard clinical 1.5 T MR scanner was used for morphometric and dynamic contrast-enhanced susceptibility-weighted MR imaging (DSC-MRI) of a glioma model of the rat brain. Ten male Wistar rats were examined with coronal T2-weighted, and T1-weighted images (matrix 128 x 128, FOV 64 mm) after implantation of an intracerebral tumor xenografts (C6) using a conventional surface coil. For DSC-MRI a T2*-weighted sequence (TR/TE=30/14 ms, matrix 64 x 64, FOV 90 mm; slice thickness of 1.5mm) was performed. Regions of interest were defined within the tumor and the non-affected contralateral hemisphere and the mean transit time (MTT) was determined. Tumor dimensions in MR predicted well its real size as proven by histology. The MTT of contrast agent passing through the brain was significantly decelerated in the tumor compared to the unaffected hemisphere (p<0.001, paired t-test), which is most likely due to the leakage of contrast agent through the disrupted blood brain barrier. This setup offers advanced MR imaging of small animals without the need for dedicated animal scanners or dedicated custom-made coils.

A comparison of arterial spin labeling and dynamic susceptibility perfusion imaging for resection control in glioblastoma surgery.

Resection control using magnetic resonance imaging during neurosurgical interventions increases confidence regarding the extent of tumor removal already during the procedure. In addition to morphological imaging, functional information such as perfusion might become an important marker of the presence and extent of residual tumor mass. The aim of this study was to implement arterial spin labeling (ASL) perfusion imaging as a noninvasive alternative to dynamic susceptibility contrast (DSC) perfusion imaging in patients suffering from intra-axial tumors for resection control already during surgery. The study included 15 patients suffering from glioblastoma multiforme in whom perfusion imaging using DSC and ASL was performed before, during, and after surgery. The data obtained from intraoperative scanning were analyzed by two readers blinded to any clinical information, and the presence of residual tumor mass was evaluated using a ranking scale. Similarity of results was analyzed using the intraclass correlation coefficient and Pearson's correlation coefficient. The results show that intraoperative ASL is as reliable as DSC when performing intraoperative perfusion imaging. According to the results of this study, intraoperative imaging using ASL represents an attractive alternative to contrast agent-based perfusion imaging.

Intraoperative resection control using arterial spin labeling - Proof of concept, reproducibility of data and initial results.

OBJECTIVES: Intraoperative magnetic resonance imaging is a unique tool for visualizing structures during resection and/or for updating any kind of neuronavigation that might be hampered as a result of brain shift during surgery. Advanced MRI techniques such as perfusion-weighted imaging have already proven to be important in the initial diagnosis preoperatively, but can also help to differentiate between tumor and surgically induced changes intraoperatively. Commonly used methods to visualize brain perfusion include contrast agent administration and are therefore somewhat limited. One method that uses blood as an internal contrast medium is arterial spin labeling (ASL), which might represent an attractive alternative. MATERIALS AND METHODS: Ten healthy volunteers were examined using three different scanners and coils within 1 h (3T Achieva MRI using 32-channel head coil, 1.5T Achieva MRI using a 6-channel head coil, 1.5 Intera Scanner using 2 surface coils, Philips, Best, The Netherlands) and quantitative CBF values were calculated and compared between the different setups. Additionally, in eight patients with glioblastoma multiforme, ASL was used pre-, intra-, and postoperatively to define tumor tissue and the extent of resection in comparison to structural imaging. RESULTS: A high correlation (r = 0.91-0.96) was found between MRI scanners and coils used. ASL was as reliable as conventional MR imaging if complete resection was already achieved, but additionally provided valuable information regarding residual tumor tissue in one patient. CONCLUSIONS: Intraoperative arterial spin-labeling is a feasible, reproducible, and reliable tool to map CBF in brain tumors and seems to give beneficial information compared to conventional intraoperative MR imaging in partial resection.