Hemodynamically independent analysis of cerebrospinal fluid and brain motion observed with dynamic phase contrast MRI

Brain and cerebrospinal fluid (CSF) movements are influenced by the anatomy and mechanical properties of intracranial tissues, as well as by the waveforms of driving vascular pulsations. The authors analyze these movements so that the purely hemodynamic factors are removed and the underlying mechanical couplings between brain, CSF, and the vasculature are characterized in global fashion. These measurements were used to calculate a set of impulse response functions or modulation transfer functions, characterizing global aspects of the vasculature's mechanical coupling to the intracranial tissues, the cervical CSF, and the cervical spinal cord. These functions showed that a sudden influx of blood into the head was rapidly accommodated by some type of intracranial reserve or capacity. After this initial response, an equal volume of CSF was driven through the foramen magnum over the next 200-300 ms as the intracranial reserve relaxed to its base-line state.     

颅内肿瘤脑脊液播散的 MRI 表现及影响因素

目的：分析颅内肿瘤脑脊液播散的 MRI 表现及影响脑脊液播散的因素。方法回顾性分析经临床和(或)手术病理证实的33例颅内肿瘤脑脊液播散患者 MRI 资料。所有患者均进行平扫和增强 MRI 检查。结果按播散病灶的分布进行分类：软脑脊膜-蛛网膜型平扫显示2例阳性,增强8例阳性;室管膜下型平扫显示9例阳性,增强8例阳性;混合型平扫显示8例阳性,增强17例阳性。按播散病灶的大小进行分类：线状增厚型平扫显示均为阴性,增强9例阳性;结节型平扫显示18例阳性,增强9例阳性;混合型平扫显示1例阳性,增强15例阳性。结论MRI 增强扫描能够充分显示颅内肿瘤脑脊液播散的特点,并可对播散灶按分布及大小进行分型。手术、原发肿瘤部位与级别等是影响脑脊液播散的主要因素。高、低级别的颅内肿瘤均可发生脑脊液播散,以高级别肿瘤多见。     

Simultaneous MRI acquisition of blood volume, blood flow, and blood oxygenation information during brain activation.

Simultaneous acquisition of complementary functional hemodynamic indices reflecting different aspects of brain activity would be a valuable tool for functional brain-imaging studies offering enhanced detection power and improved data interpretation. As such, a new MRI technique is presented that is able to achieve concurrent acquisition of three hemodynamic images based primarily on the changes of cerebral blood volume, blood flow, and blood oxygenation, respectively, associated with brain activation. Specifically, an inversion recovery pulse sequence has been designed to measure VASO (vascular space occupancy), ASL (arterial spin labeling) perfusion, and BOLD (blood-oxygenation-level-dependent) signals in a single scan. The MR signal characteristics in this sequence were analyzed, and image parameters were optimized for the simultaneous acquisition of these functional images. The feasibility and efficacy of the new technique were assessed by brain activation experiments with visual stimulation paradigms. Experiments on healthy volunteers showed that this technique provided efficient image acquisition, and thus higher contrast-to-noise ratio per unit time, compared with conventional techniques collecting these functional images separately. In addition, it was demonstrated that the proposed technique was able to be utilized in event-related functional MRI experiments, with potential advantages of obtaining accurate transient information of the activation-induced hemodynamic responses.     

Intracranial oscillations of cerebrospinal fluid and blood flows: analysis with magnetic resonance imaging

PURPOSE: To detect oscillations of the cerebrospinal fluid (CSF) flow related to the heartbeat and frequencies lower than 0.6 Hz and to compare these oscillations of CSF and blood flow in cerebral vessels by using echo planar imaging in real time mode. The existence of such waves has been well known but has not yet been shown by MRI. MATERIALS AND METHODS: In a slice perpendicular to the aqueduct, CSF flow as well as CBF, could be determined in sagittal sinus, basilar artery, and capillary vessels. After Fourier analysis, four frequency bands were assigned. RESULTS: In the very high-frequency (heart rate) range, the integrals under the CSF curves were more closely related to arterial CBF than to changes in the sinus. Also, in the high-frequency (respiration rate), low-frequency (0.05-0.15 Hz), and very-low-frequency (0.008-0.05 Hz) ranges, the integrals under the CSF curves corresponded with arterial and capillary CBF. CONCLUSION: Slow and fast oscillations in CSF flow are detectable in healthy persons with a proportional allotment to arterial and capillary CBF.     

Precision of the CASL-perfusion MRI technique for the measurement of cerebral blood flow in whole brain and vascular territories

PURPOSE: To analyze the precision of cerebral blood flow (CBF) measurements made with continuous arterial spin labeling(CASL) perfusion magnetic resonance imaging (MRI) over experimentally relevant intervals. MATERIALS AND METHODS: CASL perfusion MRI measurements of CBF on a 1.5-T GE Signa magnet were repeated in young healthy male and female subjects at one hour and one week. Precision of the measurement was evaluated at both time intervals. RESULTS: CASL perfusion MRI measurements of CBF yielded within-subject coefficients of variation (wsCV) of 5.8% for global and 13% for individual vascular regions when measurements were repeated within one hour. Differences in these values represent the error in post-processing. Global and regional CBF measurements over one week yielded wsCVs of 13% and 14%, respectively. At one week, error secondary to physiologic variability affected global and regional measurements to the same degree and masked the software post-processing error seen at one hour. The magnitude of the difference in repeated measures correlated with the magnitude of the measurement. CONCLUSION: CASL perfusion MRI CBF measurements are accurate and precise. Variability over longer periods of time appears attributable to physiologic factors. Repeatability of the CASL measurement is sensitive to the magnitude of the measurement. This should be taken into account when studies requiring repeated measures involve subjects with significant variability in CBF.     

颅内压检测及脑脊液乳酸水平对重型颅脑损伤患者预后预测研究

目的研究颅内压检测及脑脊液乳酸水平对重型颅脑损伤患者预后的预测价值。方法 2014年5月—2018年1月蚌埠市第一人民医院重症医学科收治重型颅脑损伤并进行手术患者68例,其中男性38例,女性30例;年龄40～78岁,平均61.28岁;受伤至入院时间(4.61±1.34)h;致伤原因:高血压脑出血60例,道路交通伤4例,高处坠落伤4例。患者均在术后采用无创颅内压检测仪连续监测并记录颅内压同时设定预警值,并根据变化情况给予适当的干预。同时对患者行腰椎穿刺收集脑脊液检测乳酸水平。将患者颅内压变化情况与GCS评分及CT复查结果进行比对,采用格拉斯评价量表对患者的预后进行评估,比较预后不同组别间患者脑脊液乳酸水平的差异,并分析颅内压预警结果与预后的关系。结果术后2h后颅内压轻度增高患者21例(30.88%),GCS评分降低0～1分,CT复查结果显示未发现挫裂伤与迟发性血肿;中度增高患者32例(47.09%),GCS评分下降2～3分,CT复查结果显示颅内挫伤与迟发性水肿均有一定程度的增大;重度增高患者15例(22.06%),GCS评分降低>3分,CT复查结果显示颅内挫伤与迟发性水肿均明显增大;随着颅内压增高程度上升,患者的恢复良好率、轻度缺陷残疾率越低,而重度残疾率、植物生存率与病死率越高(P<0.05);随着脑脊液乳酸水平增加,患者的恢复良好率、轻度缺陷残疾率越低,而重度残疾率、植物生存率与病死率越高(P<0.05)。结论随着颅内压和脑脊液乳酸水平的增加,重症颅脑损伤患者的预后越差,可见在重症颅脑损伤患者治疗过程中对上述两种指标的观察和控制,对于重症颅脑损伤患者的恢复具有积极的作用。     

Measurement of brain perfusion,blood volume,and blood‐brain barrier permeability,using dynamic contrast‐enhanced T1‐weighted MRI at 3 tesla

Assessment of vascular properties is essential to diagnosis and follow‐up and basic understanding of pathogenesis in brain tumors. In this study, a procedure is presented that allows concurrent estimation of cerebral perfusion, blood volume, and blood‐brain permeability from dynamic T₁‐weighted imaging of a bolus of a paramagnetic contrast agent passing through the brain. The methods are applied in patients with brain tumors and in healthy subjects. Perfusion was estimated by model‐free deconvolution using Tikhonov's method (gray matter/white matter/tumor: 72 ± 16/30 ± 8/56 ± 45 mL/100 g/min); blood volume (6 ± 2/4 ± 1/7 ± 6 mL/100 g) and permeability (0.9 ± 0.4/0.8 ± 0.3/3 ± 5 mL/100 g/min) were estimated by using Patlak's method and a two‐compartment model. A corroboration of these results was achieved by using model simulation. In addition, it was possible to generate maps on a pixel‐by‐pixel basis of cerebral perfusion, cerebral blood volume, and blood‐brain barrier permeability. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Principles of T2*‐weighted dynamic susceptibility contrast MRI technique in brain tumor imaging

Dynamic susceptibility contrast magnetic resonance imaging (DSC‐MRI) is used to track the first pass of an exogenous, paramagnetic, nondiffusible contrast agent through brain tissue, and has emerged as a powerful tool in the characterization of brain tumor hemodynamics. DSC‐MRI parameters can be helpful in many aspects, including tumor grading, prediction of treatment response, likelihood of malignant transformation, discrimination between tumor recurrence and radiation necrosis, and differentiation between true early progression and pseudoprogression. This review aims to provide a conceptual overview of the underlying principles of DSC‐MRI of the brain for clinical neuroradiologists, scientists, or students wishing to improve their understanding of the technical aspects, pitfalls, and controversies of DSC perfusion MRI of the brain. Future consensus on image acquisition parameters and postprocessing of DSC‐MRI will most likely allow this technique to be evaluated and used in high‐quality multicenter studies and ultimately help guide clinical care. J. Magn. Reson. Imaging 2015;41:296–313. © 2013 Wiley Periodicals, Inc .     

Sequential dynamic susceptibility contrast MR experiments in human brain: Residual contrast agent effect,steady state,and hemodynamic perturbation

The stability and reproducibility of the dynamic susceptibility contrast (DSC) MRI method for sequential relative cerebral blood volume (relCBV) measurements was evaluated to validate the method for use in quantitative studies of cerebral hemodynamics in humans. A spin echo echo planar imaging protocol was used in conjunction with multiple bolus injections of the susceptibility contrast agent gadoteridol (GD). The effects of variation in interbolus interval (10 min to 4 h), the number of injections (two to four), and the effect of the cerebral vasodilating agent acetazolamide (ACZ) were evaluated in 44 experiments performed with 22 normal subjects. Two fundamental observations were made. First, with multiple injections of GD, the change in MR signal over time was not consistent from first to subsequent boluses. A second bolus administered 10 min to 2 h after an initial bolus resulted in signal change of greater amplitude and duration, resulting in artifactually elevated estimates of relCBV, consistent with a residual effect of GD. Second, a relative steady state could be reached with serial injections of GD, such that the profile of subsequent boluses closely paralleled those of previous ones. This facilitates the reliable measurement of relCBV during activation, as demonstrated by use of ACZ.