人脑视皮质功能MRI的初步研究及临床应用

目的：本实验应用功能磁共振成像（fMRI）的回波平面（EPI）技术,着重研究了人脑视皮质的血氧水平依赖（BOLD）的功能磁共振成像。方法：本实验包括对36名正常健康志愿者及17例具有枕区病变患者的fMRI研究。在刺激和静止2种对比条件下采集枕区的回波平面图像。结果：主要视皮质位于双侧距状裂两侧 ,属于布劳德曼（Brodmann)17区。3例具有距状裂附近病变的患者的视皮质由于病变的占位效应而发生移位。结论：fMRI可用于在活体上脑上研究各功能区活动。视觉刺激下的fMRI可对人脑视皮质初步定位。由于病变占位效应的影响,病变周围的功能活动区常发生变形或移位。     

Organization of the human motor system as studied by functional magnetic resonance imaging.

Blood oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI), because of its superior resolution and unlimited repeatability, can be particularly useful in studying functional aspects of the human motor system, especially plasticity, and somatotopic and temporal organization. In this survey, while describing studies that have reliably used BOLD fMRI to examine these aspects of the motor system, we also discuss studies that investigate the neural substrates underlying motor skill acquisition, motor imagery, production of motor sequences; effect of rate and force of movement on brain activation and hemispheric control of motor function. In the clinical realm, in addition to the presurgical evaluation of neurosurgical patients, BOLD fMRI has been used to explore the mechanisms underlying motor abnormalities in patients with neuropsychiatric disorders and the mechanisms underlying reorganization or plasticity of the motor system following a cerebral insult.     

PACS-based functional magnetic resonance imaging.

The picture archiving and communication system (PACS) technology reaches its 10th anniversary. Retrospectively no one could foresee the impact the PACS would have to the health care enterprise, but it is common consent today, that PACS is the key technology crucial to daily clinical image operations and especially to image related basic and clinical research. During the past 10 years the PACS has been matured from a research and developmental stage into commercial products which are provided by all major modality and health care equipment vendors. The PACS, originally implemented in the Radiology Department, needs to grow and has already carried well beyond departmental limits conquering all image relevant areas inside the hospital. During the past 10 years a dramatic development in imaging techniques especially within MRI emerged. Advanced 3D- and 4D-MR imaging techniques result in much more images and more complex data objects than ever before which need to be implemented into the existing PACS. These new imaging techniques require intensive post-processing apart from the imaging modality which need to be integrated into the image workflow and the PACS implementation. Along with these new imaging techniques new clinical applications, e.g. stroke detection, and research applications, e.g. study of heart and brain function, in Neurology and Cardiology require changes to the traditional PACS concept. Therefore inter-disciplinary image distribution will become the high-water mark for the next 10 years in the PACS endeavor. This paper focuses on one new advanced imaging technique, functional magnetic resonance imaging (fMRI), and discusses how fMRI data is defined, what fMRI requires in terms of clinical and research applications and how to implement fMRI in the existing PACS.     

Assessment of cerebral blood flow reserve using functional magnetic resonance imaging

Imaging of activated brain areas based on changes of blood deoxyhemoglobin levels is now possible with MRI. Acetazolamide (ACZ) increases cerebral blood flow (CBF) without changing cerebral oxygen consumption; this results in signal changes observed in gradient echo MR images from the areas with an increase in CBF. We assessed signal changes after ACZ application in seven healthy subjects with a conventional 1.5-T MRI scanner. The susceptibility-sensitized three-dimensional fast low-angle shot (FLASH) sequence was used to visualize signal changes induced by ACZ. We analyzed anatomic localization of different ranges of detected signal changes. ACZ caused significant signal changes in the gray matter and at the edge of the cerebral cortex, the latter corresponding to draining surface veins. No significant differences were seen among different brain areas within the same slice. Using the maximum intensity projection technique, we were able to partially separate signal changes originating in draining veins from signal originating in the gray matter microvasculature. Signal changes from the microvessels reflect cerebrovascular reserve. Blood-oxygen-level-dependent (BOLD) based MRI can evaluate CBF reserve with high spatial and temporal resolution. To assess cerebrovascular reserve, it is necessary to separate signal changes originating in large vessels from signal from brain microvasculature.     

Combined magnetic resonance tractography and functional magnetic resonance imaging in evaluation of brain tumors involving the motor system

The goal of neuro-oncologic surgery is to maximize tumor resection while preserving vital brain functions. Identification of the relation between the tumor and adjacent functional cortical areas as well as efferent subcortical white matter tracts is important for preservation of function. Combined diffusion tensor imaging with magnetic resonance (MR) tractography and functional blood oxygen level-dependent MR imaging were applied successfully for preoperative planning and guidance in 2 patients with tumors near the motor cortex. The combination of these novel functional imaging techniques can provide new information for presurgical planning.     

Clinical applications of functional magnetic resonance imaging

Despite its immediate success as a tool for basic research, the clinical application of functional MRI(fMRI) is still limited. FMRI has proven useful for presurgical functional mapping of the eloquent cortices. Localization of the sensorimotor cortex by fMRI may be of relatively limited value because the sensorimotor cortex can often be readily localized by means of anatomical methods. In contrast, the language cortices may not be localized anatomically and the language dominant hemisphere has been determined by invasive Wada test. Previous reports have shown that fMRI can be a promising alternative to the Wada test. A recent clinical trial has suggested that fMRI can be used to diagnose Alzheimer's disease in its earliest stage, detecting subclinical deterioration of the memory function. FMRI may be useful to predict the future decline of memory in people with genetic risks. Monitoring of the functional recovery of post-stroke brains may be another promising clinical application of fMRI. FMRI has demonstrated functional reorganization of the brain that may be related to the restoration of motor and language functions.     

BOLD and CBV-weighted functional magnetic resonance imaging of the rat somatosensory system.

A multislice spin echo EPI sequence was used to obtain functional MR images of the entire rat brain with blood oxygenation level dependent (BOLD) and cerebral blood volume (CBV) contrast at 11.7 T. Maps of activation incidence were created by warping each image to the Paxinos rat brain atlas and marking the extent of the activated area. Incidence maps for BOLD and CBV were similar, but activation in draining veins was more prominent in the BOLD images than in the CBV images. Cerebellar activation was observed along the surface in BOLD images, but in deeper regions in the CBV images. Both effects may be explained by increased signal dropout and distortion in the EPI images after administration of the ferumoxtran-10 contrast agent for CBV fMRI. CBV-weighted incidence maps were also created for 10, 20, and 30 mg Fe/kg doses of ferumoxtran-10. The magnitude of the average percentage change during stimulation increased from 4.9% with the 10 mg Fe/kg dose to 8.7% with the 30-mg Fe/kg dose. Incidence of activation followed a similar trend.     

Spatially filtering functional magnetic resonance imaging data

When constructing MR images from acquired spatial frequency data, it can be beneficial to apply a low-pass filter to remove high frequency noise from the resulting images. This amounts to attenuating high spatial frequency fluctuations that can affect detected MR signal. A study is presented of spatially filtering MR data and possible ramifications on detecting regionally specific activation signal. It is shown that absolute activation levels are strongly dependent on the parameters of the filter used in image construction and that significance of an activation signal can be enhanced through appropriate filter selection. A comparison is made between spatially filtering MR image data and applying a Gaussian convolution kernel to statistical parametric maps.     

Retrospective coregistration of functional magnetic resonance imaging data using external monitoring.

Coregistration is essential for correcting head motion artifacts in functional magnetic resonance imaging (fMRI). Coregistration algorithms typically realign images through optimization of a similarity measure based on voxel signal intensities. However, coregistration can also be performed through external monitoring, whereby a tracking device measures head motion directly and independently of the imaging data. This paper describes development of external monitoring using fMRI-compatible infrared cameras. Three subjects participated in block-design fMRI experiments consisting of bilateral finger tapping alone and tapping combined with visuomotor tracking to produce controlled task-correlated head motion. Functional MRI time-series were coregistered using the external monitoring technique and a known image-based algorithm for comparison. Over various performance characteristics, external monitoring and image-based coregistration exhibited good agreement, in particular reducing signals correlated with millimeter task-correlated motions by 50-100%, with a 5% difference between the two techniques. These results promise future applications and refinements of external monitoring in patient populations where head motion is especially problematic. Possibilities include 3D prospective coregistration during real-time fMRI, coregistration of individual slices, and motion correction in anatomic MRI.     

Breast imaging and reporting data system (BIRADS) magnetic resonance imaging illustrated cases

Illustrated cases are presented here, for training the reader to BIRADS MRI. This article offers guidance in integrating findings from the different MR sequences, morphology and kinetics of an abnormal enhancement: report organization, use of lexicon for describing the detected lesion, final assessment with BI-RADS assessment categories.     

Cardiac magnetic resonance imaging using an open 0.35 T system

OBJECTIVE: To evaluate cardiac magnetic resonance imaging (MRI) using a 0.35 T magnetic resonance system with open design. METHODS: Eleven patients were examined in an open MRI system with a field strength of 0.35 T. Myocardial function was assessed with cine true fast imaging with steady-state precession sequences in 2 planes. Perfusion images were acquired with a T1-weighted gradient echo sequence. Late enhancement was performed using an inversion recovery-prepared fast gradient echo technique. Image quality was assessed using a 4-point score in consensus. Signal-noise ratio was measured. RESULTS: For functional imaging, average score was 1.65 (SD, 0.6). For perfusion imaging, the value was 2.25 (SD, 0.68). For late enhancement, quality score was 2.6 (SD, 0.82). Average value of signal-noise ratio for functional, perfusion, and late enhancement imaging was 50.6 (SD, 16.4), 91.8 (SD, 52.8), and 33.2 (SD, 20.4), respectively. CONCLUSIONS: Open MRI with lower field strength can be used for functional imaging of the heart. For perfusion and viability imaging (late enhancement), higher field strength is needed. Open low-field cardiac MRI may provide a helpful alternative for obese or claustrophobic patients or patients who are difficult to move.     

The clinical potential of functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) has had a huge impact on understanding the healthy human brain. To date it has had much less impact in clinical neuroscience or clinical practice. The reasons for this are in part that the image acquisition, paradigm design, and data analysis strategies used presently are not sufficiently standardized. This makes the comparison of results across individuals, scanning sessions, and centers difficult. Nevertheless, there are emerging applications for clinical fMRI, and as the field matures the number of applications is likely to grow. It seems certain that fMRI has an important role to play in helping us understand the mechanisms of neuropsychiatric diseases and in helping to identify effective therapeutic strategies.     

Applications of functional magnetic resonance imaging in psychiatry

While the use of MRI techniques has become a cornerstone of the neurology clinic, the application of such methods in psychiatry was rather limited until the advent of functional magnetic resonance imaging (fMRI). Over the past decade fMRI has superseded radionuclide-imaging techniques and blossomed into a widely used psychiatric research tool. This review focuses on the neurobiological findings from fMRI research in three less well-documented psychiatric disorders: attention deficit hyperactivity disorder (ADHD), depression, and obsessive-compulsive disorder (OCD). Although there was some disparity in early findings, greater standardization of image acquisition, analysis, and paradigms, and improved clinical classification are leading to a greater convergence of observations from different laboratories. fMRI is also beginning to realize its potential as an important mediator between genes and phenotypes, and may thus contribute to a better understanding of the pathophysiology of major neuropsychiatric diseases. The role of fMRI in the objective assessment of therapeutic intervention and early prediction of response to treatment is also discussed.     

Probabilistic analysis of functional magnetic resonance imaging data

Probability theory is applied to the analysis of fMRI data. The posterior distribution of the parameters is shown to incorporate all the information available from the data, the hypotheses, and the prior information. Under appropriate simplifying conditions, the theory reduces to the standard statistical test, including the general linear model. The theory is particularly suited to handle the spatial variations in the noise present in fMRI, allowing the comparison of activated voxels that have different, and unknown, noise. The theory also explicitly includes prior information, which is shown to be critical in the attainment of reliable activation maps.     

Cardiac imaging using gated magnetic resonance

To overcome the limitations of magnetic resonance (MR) cardiac imaging using nongated data acquisition, three methods for acquiring a gating signal, which could be applied in the presence of a magnetic field, were tested: an air-filled plethysmograph, a laser-Doppler capillary perfusion flowmeter, and an electrocardiographic gating device. The gating signal was used for timing of MR imaging sequences (IS). Application of each gating method yielded significant improvements in structural MR image resolution of the beating heart, although with both plethysmography and laser-Doppler velocimetry it was difficult to obtain cardiac images from the early portion of the cardiac cycle due to an intrinsic delay between the ECG R wave and peripheral detection of the gating signal. Variations in the temporal relationship between the R wave and plethysmographic and laser-Doppler signals produced inconsistencies in the timing of IS. Since the ECG signal is virtually free of these problems, the preferable gating technique is IS synchronization with an electrocardiogram. The gated images acquired with this method provide sharp definition of internal cardiac morphology and can be temporarily referenced to end diastole and end systole or intermediate points.     

Functional magnetic resonance imaging using PROPELLER-EPI

Periodically rotated overlapping parallel lines with enhanced reconstruction-echo-planar imaging (PROPELLER-EPI) is a multishot technique that samples k-space by acquisition of narrow blades, which are subsequently rotated until the entire k-space is filled. It has the unique advantage that the center of k-space, and thus the area containing the majority of functional MRI signal changes, is sampled with each shot. This continuous refreshing of the k-space center by each acquired blade enables not only sliding-window but also keyhole reconstruction. Combining PROPELLER-EPI with a fast gradient-echo readout scheme allows for high spatial resolutions to be achieved while maintaining a temporal resolution, which is suitable for functional MRI experiments. Functional data acquired with a novel interlaced sequence that samples both single-shot EPI and blades in an alternating fashion suggest that PROPELLER-EPI can achieve comparable functional MRI results. PROPELLER-EPI, however, features different spatiotemporal characteristics than single-shot EPI, which not only enables keyhole reconstruction but also makes it an interesting alternative for many functional MRI applications.