No abstract

No abstract

This study examines the value of spin-echo-based fMRI for cognitive studies at the main magnetic field strength of 3 T using a spin-echo EPI (SE-EPI) sequence and a Stroop color-word matching task. SE-EPI has the potential advantage over conventional gradient-echo EPI (GE-EPI) that signal losses caused by dephasing through the slice are not present, and hence although image distortion will be the same as for an equivalent GE-EPI sequence, signal voids will be eliminated. The functional contrast in SE-EPI will be lower than for GE-EPI, as static dephasing effects do not contribute. As an auxiliary experiment interleaved diffusion-weighted and non-diffusion-weighted SE-EPI was performed in the visual cortex to further elucidate the mechanims of functional contrast. In the Stroop experiment activation was detected in all areas previously found using GE-EPI. Additional frontopolar and ventral frontomedian activations were also found, which could not be detected using GE-EPI. The experiments from visual cortex indicated that at 3 T the BOLD signal change has contributions from the extravascular space and larger blood vessels in roughly equal amounts. In comparison with GE-EPI the absence of static dephasing effects would seem to result in a superior intrinsic spatial resolution. In conclusion the sensitivity of SE-EPI at 3 T is sufficient to make it the method of choice for fMR studies that require a high degree of spatial localization or where the requirement is to detect activation in regions affected by strong susceptibility gradients. © 2002 Elsevier Science (USA)

The entorhinal cortex lies in the mediotemporal lobe and has major functional, structural, and clinical significance. The entorhinal cortex has a unique cytoarchitecture with large stellate neurons in layer II that form clusters. The entorhinal cortex receives vast sensory association input, and its major output arises from the layer II and III neurons that form the perforant pathway. Clinically, the neurons in layer II are affected with neurofibrillary tangles, one of the two pathological hallmarks of Alzheimer's disease. We describe detection of the entorhinal layer II islands using magnetic resonance imaging. We scanned human autopsied temporal lobe blocks in a 7T human scanner using a solenoid coil. In 70 and 100m isotropic data, the entorhinal islands were clearly visible throughout the anterior-posterior extent of entorhinal cortex. Layer II islands were prominent in both the magnetic resonance imaging and corresponding histological sections, showing similar size and shape in two types of data. Area borders and island location based on cytoarchitectural features in the mediotemporal lobe were robustly detected using the magnetic resonance images. Our ex vivo results could break ground for high-resolution in vivo scanning that could ultimately benefit early diagnosis and treatment of neurodegenerative disease. Neurol 2005;57:489 -494 Ann

No abstract

Successful survival in a competitive world requires the employment of efficient procedures for selecting new in preference to old information. Recent behavioral studies have shown that efficient selection is dependent not only on properties of new stimuli but also on an intentional bias that we can introduce against old stimuli. Event-related analysis of functional magnetic resonance imaging data from a task involving visual search across time as well as space indicates that the superior parietal lobule is specifically involved in processes leading to the efficient segmentation of old from new items, whereas the temporoparietal junction area and the ascending limb of the right intraparietal sulcus are involved in the detection of salient new items and in response preparation. The study provides evidence for the functional segregration of brain regions within the posterior parietal lobe.

PurposeIn order to fully benefit from the improved signal‐to‐noise and contrast‐to‐noise ratios at 9.4T, the challenges of normalB1+ inhomogeneity and the long acquisition time of high‐resolution 2D gradient‐recalled echo (GRE) imaging were addressed.Theory and MethodsFlip angle homogenized excitations were achieved by parallel transmission (pTx) of 3‐spoke pulses, designed by magnitude least‐squares optimization in a slice‐by‐slice fashion; the acquisition time reduction was achieved by simultaneous multislice (SMS) pulses. The slice‐specific spokes complex radiofrequency scaling factors were applied to sinc waveforms on a per‐channel basis and combined with the other pulses in an SMS slice group to form the final SMS‐pTX pulse. Optimal spokes locations were derived from simulations.ResultsFlip angle maps from presaturation TurboFLASH showed improvement of flip angle homogenization with 3‐spoke pulses over CP‐mode excitation (normalized root‐mean‐square error [NRMSE] 0.357) as well as comparable excitation homogeneity across the single‐band (NRMSE 0.119), SMS‐2 (NRMSE 0.137), and SMS‐3 (NRMSE 0.132) 3‐spoke pulses. The application of the 3‐spoke SMS‐3 pulses in a 48‐slice GRE protocol, which has an in‐plane resolution of 0.28 × 0.28 mm, resulted in a 50% reduction of scan duration (total acquisition time 6:52 min including reference scans).ConclusionTime‐efficient flip angle homogenized high‐resolution GRE imaging at 9.4T was accomplished by using slice‐specific SMS‐pTx spokes excitations. Magn Reson Med 78:1050–1058, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.

Functional perfusion imaging with a separate labeling coil located above the common carotid artery was demonstrated in human volunteers at 3 T. A helmet resonator and a spin-echo echo-planar imaging (EPI) sequence were used for imaging, and a circular surface coil of 6 cm i.d. was employed for labeling. The subjects performed a finger-tapping task. Signal differences between the condition of finger tapping and the resting state were between -0.5% and -1.1 % among the subjects. Functional perfusion imaging using magnetically labeled water as an endogenous tracer has proven to be a valuable tool for investigating task-related brain activity (1,2). The advantages of perfusion-based functional imaging in comparison to the widely used blood oxygenation level-dependent (BOLD) technique include a potentially better localized area of activation (3) and the feasibility of quantification (4 -6). This study shows that functional perfusion imaging with continuous arterial spin labeling (CASL) can be performed with a separate labeling coil located above the common carotid artery in humans. For functional imaging, the temporal resolution of CASL is poor because it requires labeling periods of several seconds prior to image acquisition. A quantification of the cerebral blood flow (CBF) during task activation requires the acquisition of images with and without CASL, and would further increase the effective sampling interval. Therefore, in this study, labeling was applied for all repetitions of the functional run, and as a result the temporal resolution and the sensitivity of the functional study were increased by factors of 2 and ͌2 (7), respectively, while the ability to quantify blood flow changes was maintained.CASL approaches (8,9) for measuring the CBF are in principle more sensitive than methods based on pulsed labeling, but their use in humans is confronted with two major problems (10). First, the application of long offresonance radiofrequency (RF) pulses causes magnetization-transfer (MT) effects. Second, the transit time from the labeling plane to the imaging slice results in a loss of sensitivity due to the relaxation of spins in the arterial blood. Finally, at 3 T RF power deposition may also be an issue of concern. The first problem can be addressed by keeping the MT influence constant for the labeling and control experiments (11,12). Complete elimination of MT effects is achieved by using separate labeling and imaging coils, which additionally removes the need for RF pulsing during the control acquisition (13,14), and in general reduces the total RF-power requirement. Multislice perfusion imaging can easily be implemented by this method. However, influences from transit-time differences in the brain are increased if labeling is performed at the neck, and quantitative maps of CBF cannot easily be obtained. Alsop and Detre (15) showed that the introduction of a post-label delay (PLD) markedly reduces transit-time effects, provided that the longitudinal relaxation times of arterial blood and brain tissue are nearly ...