Understanding the relationship between fMRI signal changes and activated cortex is paramount to successful mapping of neuronal activity. To this end, the relative extravascular and intravascular contribution to fMRI signal change from capillaries (localized), venules (less localized) and macrovessels (remote, draining veins) must be determined. In this work, the authors assessed both the extravascular and intravascular contribution to blood oxygenation level-dependent gradient echo signal change at 1.5 T by using a Monte Carlo model for susceptibility-based contrast in conjunction with a physiological model for neuronal activation-induced changes in oxygenation and vascular volume fraction. The authors compared our Model results with experimental fMRI signal changes with and without velocity sensitization via bipolar gradients to null the intravascular signal. The model and experimental results are in agreement and suggest that the intravascular spins account for the majority of fMRI signal change on T2*-weighted images at 1.5 T.

Considerable evidence exists to support the hypothesis that the hippocampus and related medial temporal lobe structures are crucial for the encoding and storage of information in long-term memory. Few human imaging studies, however, have successfully shown signal intensity changes in these areas during encoding or retrieval. Using functional magnetic resonance imaging (fMRI), we studied normal human subjects while they performed a novel picture encoding task High-speed echo-planar imaging techniques evaluated fMRI signal changes throughout the brain. During the encoding of novel pictures, statistically significant increases in fMRI signal were observed bilaterally in the posterior hippocampal formation and parahippocampal gyrus and in the lingual and fusiform gyri. To our knowledge, this experiment is the first fMRI study to show robust signal changes in the human hippocampal region. It also provides evidence that the encoding of novel, complex pictures depends upon an interaction between ventral cortical regions, specialized for object vision, and the hippocampal formation and parahippocampal gyrus, specialized for long-term memory.The structures that are important for encoding and storage of novel information have been the focus of extensive research since the pioneering work of Scoville, Milner, and Penfield (1-4). A convergence of research in animals and humans has led to the hypothesis that the hippocampus and related medial temporal lobe structures are critical for the encoding of novel information for subsequent storage in the neocortex (2, 5-7). In humans, anterograde amnesia-the inability to learn new information-is associated with bilateral lesions of medial temporal lobe structures (2,8). In nonhuman primates, singleunit recordings have identified neurons that respond preferentially to novel or familiar stimuli. These neurons are found in structures that receive output from the hippocampus [such as the anterior thalamus (9) and nucleus accumbens (10)] and in structures that provide afferent input to the hippocampus [such as the entorhinal cortex (11)]. Lesion studies in animals have provided extensive data on the role of medial temporal lobe structures in the performance of behavioral tasks requiring storage of novel information. For example, lesions of hippocampus and adjacent cortical structures, such as the perirhinal and entorhinal cortices, impair performance on delayed nonmatching to sample tasks in nonhuman primates (12) and rats (13). Controversies remain about the exact structures that are most important for the performance of explicit memory tasks (12-16).Functional brain imaging studies have attempted to demonstrate the role of the hippocampus and related medial temporal lobe structures in the encoding and retrieval of long-term memories in the intact human brain. Several studies using positron emission tomography have shown no evidence of a medial temporal lobe contribution to encoding and recognition (17-19); however, more recent reports have shown changes in the hippocampus in re...

Results of functional magnetic resonance imaging were consistent with past studies of obsessive-compulsive disorder that used other functional neuroimaging modalities. However, paralimbic and limbic activations were more prominent in the present study.

There is a lack of physiological data pertaining to how listening humans process auditory information. Functional magnetic resonance imaging (fMRI) has provided some data for the auditory cortex in awake humans, but there is still a paucity of comparable data for subcortical auditory areas where the early stages of processing take place, as amply demonstrated by single-unit studies in animals. It is unclear why fMRI has been unsuccessful in imaging auditory brain-stem activity, but one problem may be cardiac-related, pulsatile brain-stem motion. To examine this, a method eliminating such motion (using cardiac gating) was applied to map sound-related activity in the auditory cortices and inferior colliculi in the brain stem. Activation in both the colliculi and cortex became more discernible when gating was used. In contrast with the cortex, the improvement in the colliculi resulted from a reduction in signal variability, rather than from an increase in percent signal change. This reduction is consistent with the hypothesis that motion or pulsatile flow is a major factor in brain-stem imaging. The way now seems clear to studying activity throughout the human auditory pathway in listening humans.

Objective: To compare accuracy of ultrasound and MRI for detecting focal peripheral nerve pathology, excluding idiopathic carpal or cubital tunnel syndromes.Methods: We performed a retrospective review of patients referred for neuromuscular ultrasound to identify patients who had ultrasound and MRI of the same limb for suspected brachial plexopathy or mononeuropathies, excluding carpal/cubital tunnel syndromes. Ultrasound and MRI results were compared to diagnoses determined by surgical or, if not performed, clinical/electrodiagnostic evaluation. Results:We identified 53 patients who had both ultrasound and MRI of whom 46 (87%) had nerve pathology diagnosed by surgical (n 5 39) or clinical/electrodiagnostic (n 5 14) evaluation. Ultrasound detected the diagnosed nerve pathology (true positive) more often than MRI (43/46 vs 31/46, p , 0.001). Nerve pathology was correctly excluded (true negative) with equal frequency by MRI and ultrasound (both 6/7). In 25% (13/53), ultrasound was accurate (true positive or true negative) when MRI was not. These pathologies were typically (10/13) long (.2 cm) and only occasionally (2/13) outside the MRI field of view. MRI missed multifocal pathology identified with ultrasound in 6 of 7 patients, often (5/7) because pathology was outside the MRI field of view.Conclusions: Imaging frequently detects peripheral nerve pathology and contributes to the differential diagnosis in patients with mononeuropathies and brachial plexopathies. Ultrasound is more sensitive than MRI (93% vs 67%), has equivalent specificity (86%), and better identifies multifocal lesions than MRI. In sonographically accessible regions ultrasound is the preferred initial imaging modality for anatomic evaluation of suspected peripheral nervous system lesions. Neurology â 2013;80: [1634][1635][1636][1637][1638][1639][1640] Nerve imaging augments patient management by providing information regarding lesion morphology, anatomic location, relationship of lesions to surrounding soft tissue, and evaluation of areas difficult to evaluate by electrodiagnostic testing. Imaging can also identify peripheral nerve lesions that are not apparent on electrodiagnostic testing. Types of peripheral nerve abnormalities suited to visualization by imaging include changes in nerve caliber, continuity, and echogenicity or magnetic resonance signal characteristics.1-3 Imaging can identify peripheral nerve tumors, traumatic neuromas, lacerations, entrapments with nerve damage, inflammation, demyelinating features, and infections. [4][5][6][7][8][9][10][11][12][13][14][15] Ultrasound and MRI are the most commonly used methods for visualizing peripheral nerves. Ultrasonography of nerve lesions impacts management beyond the electrodiagnostic findings in as many as 43% of patients 16 and, by identifying nerve continuity, can change surgical decisions after traumatic neuropathies.17 MRI visualizes nerves, characterizes soft tissue structures when evaluating atypical sites of compression, identifies features of malignancy in peripheral ner...

Subject motion present during the time course of functional activation studies is a pervasive problem in mapping the spatial and temporal characteristics of brain activity. In functional MRI (fh4RI) studies, the observed signal changes are small. Therefore, it is crucial to reduce the effect of subject motion during the acquisition of image data in order to differentiate true brain activation from artifactual signal changes due to subject motion. We have adapted a technique for automatic motion detection and correction which is based on the ratio-variance minimization algorithm to the fh4RI subject motion problem. This method was used for retrospective correction of subject motion in the acquired data and resulted in improved functional maps. In this paper we have designed and applied a series of tests to evaluate the performance of this technique which span the classes of image characteristics common to fh4RI. These areas include tests of the accuracy and range of motion as well as measurement of the effect of image signal to noise ratio, focal activation, image resolution, and image coverage on the motion detection system. Also, we have evaluated the amount of residual motion remaining after motion correction, and the ability of this technique to reduce the motion-induced artifacts and restore regions of activation lost due to subject motion. In summary, this method performed well in the range of image characteristics common for N R I experiments, reducing residual motion to under 0.5 mm, and removed significant motion-induced artifacts while restoring true regions of activation. Motion correction is expected to become a routine requirement in the analysis of fMRI experiments. D 1996 Wiley-Liss, inc.

Diabetes mellitus is increasingly prevalent and results in various clinically important musculoskeletal disorders affecting the limbs, feet, and spine as well as in widely recognized end-organ complications such as neuropathy, nephropathy, and retinopathy. Diabetic muscle ischemia-a self-limited disorder-may be confused with infectious or inflammatory myositis, venous thrombosis, or compartment syndrome. The absence of fever and leukocytosis, combined with the presence of bilaterally distributed lesions in multiple and often noncontiguous muscles in the legs, including the thighs, is suggestive of ischemia; by contrast, the presence of well-defined intramuscular abscesses with rimlike enhancement favors a diagnosis of infectious pyomyositis. In the diabetic foot, an ulcer, sinus tract, or abscess with an adjacent region of abnormal signal intensity in bone marrow favors the diagnosis of pedal osteomyelitis over that of neuropathic arthropathy. Contrast material-enhanced magnetic resonance imaging is important when planning the treatment of foot infections in diabetic patients because it allows the differentiation of viable tissue from necrotic regions that require surgical débridement in addition to antibiotic therapy. Subtraction images are particularly useful for visualizing nonviable tissue. Dialysis-associated spondyloarthropathy characteristically occurs in diabetic patients with a long history of hemodialysis. Intervertebral disk space narrowing without T2 signal hyperintensity, extensive endplate erosions without endplate remodeling, and facet joint involvement are suggestive of spondyloarthropathy instead of infectious diskitis or degenerative disk disease. Although the clinical features of these conditions may overlap, knowledge of the patient's medical history, coupled with recognition of key imaging characteristics, allows the radiologist to make a prompt and correct diagnosis that leads to appropriate management.

The purpose of this study was to develop a method for obtaining simultaneous electrophysiological and functional magnetic resonance imaging data. Using phantom experiments and tests on several of the investigators, a method for obtaining simultaneous electrophysiological and fMRI data was developed and then tested in three volunteers including two task activation experiments. It was then applied in a sleep experiment (n = 12). Current limiting resistance and low-pass filtering were added to the electrophysiological circuit. Potential high frequency current loops were avoided in the electrical layout near the subject. MRI was performed at 1.5 T using conventional and echo planar imaging sequences. There was no evidence of subject injury. Expected correlations were observed between the electrophysiological and fMIU data in the task activation experiments. The fMRI data were not sigruficantly degraded by the electrophysiological apparatus. Alpha waves were detected from within the magnet in seven of the 15 experimental sessions. There was degradation of the electrophysiological data due to ballistocardiographic artifacts (pulsatile whole body motion time-locked to cardiac activity) which vaned between subjects from being minimal to becoming large enough to make detection of alpha waves difficult. We concluded that simultaneous fMRI and electrophysiological recording is possible with minor modifications of standard electrophysiological equipment. Our initial results suggest this can be done safely and without compromise of the fMRI data. The usefulness of this technique for studies of such things as sleep and epilepsy is promising. Applications requiring higher precision electrophysiological data, such as evoked response measurements, may require modifications based on ballistocardiographic effects. Address reprint requests to Bruce R. Rosen, M.D., Ph.D., Department of Radiology, Massachusetts General Hospital, MGH-NMR Within the last few years, several magnetic resowhich are sensitive to local changes in cerebral hemo-nance imaging (MRI) techniques have been developed Center,