缺血再灌注SD大鼠脑表羟基自由基产生的可视化检测

目的对缺血再灌注SD大鼠脑皮质区域羟基自由基(.OH)的产生进行可视化检测。方法多普勒血流检测脑表血流变化。用HPF(.OH荧光标记探针)标记大鼠脑表区域神经细胞,共焦点激光显微镜活体观察在缺血(10min)再灌注(30min)过程中,脑表区域.OH产生的情况。结果缺血时脑血流下降至基线-的20%,缺血开始3min后,O2,.OH产生开始增加,并一直持续到再灌注后10min,后未继续增加。缺血时HPF.OH荧光强度上升至189%,且动脉附近区域.OH产生量要多于其他区域。结论在缺血期及再灌注早期.OH生成增加,且动脉附近区域.OH产生量要多于其他区域。     

LSCI检测不同缺血期对大鼠缺血再灌注过程脑血流的影响

目的　考察不同缺血期对大鼠缺血再灌注过程脑血流的影响。 方法　通过激光散斑成像技术（LSCI）检测大鼠大脑中动脉不同栓塞时间后,对再灌注过程中脑血流的影响,并对再灌注过程中的低灌注状态、无复流现象、血流流速及管径变化进行研究分析。 结果　2 h的栓塞后,大鼠脑部血流量趋向低灌注状态,约为栓塞前血流基值的(35±10)%;栓塞时间越长,无复流现象越多;在再灌注期间,缺血2 h组的血流比0.5 h组的低灌注水平低10%。 结论　长时间的脑缺血期再灌注过程可能是造成脑损伤程度加重的主要原因之一。LSCI可应用于脑部血流实时监测,操作简便,成像灵敏、稳定,结果可靠。     

脑逆灌注血液动力学数学模型研究

脑逆灌注方法是指在脑梗塞患者发病后最短时间内从股动脉引出动脉血经血泵由颈内静脉逆行灌入大脑缺血部位从而缓解缺血程度 ,减轻缺血损伤 ,提高患者预后质量。目的是建立脑逆灌注血液动力学模型 ,研究逆灌注血流速度与颅内压、静脉窦压及脑血管床压的关系 ,从理论上验证脑逆灌注的可行性。     

磁共振弥散成像和血流灌注成像指导尿激酶溶栓治疗的安全性评价

目的应用磁共振弥散成像和血流灌注成像指导尿激酶溶栓治疗急性脑梗死 ,观察其安全性。方法25例急性脑梗死病人 ,发病时间为6～12h,均进行磁共振弥散成像 (DWI)和血流灌注成像(PWI) ,并且PWI体积>DWI体积 ,给予尿激酶100万U一次静滴溶栓治疗 ,观察溶栓治疗后凝血酶原时间变化及出血并发症发生情况。结果25例急性脑梗死病人尿激酶溶栓治疗无一例颅内出血 ,凝血酶原时间延长后很快恢复。结论磁共振弥散成像和血流灌注成像可以指导发病6～12h的急性脑梗死的尿激酶溶栓 ,临床疗效安全肯定。     

冠状动脉狭窄时主动脉内气囊反搏对心内膜下动脉的影响

测量了左冠状动脉狭窄前后，主动脉内气囊反搏时，各项血流动力学参数，并用超声多普勒血流仪测量了室间隔动脉血流的变化。结果表明，当ＩＡＢＰ反搏时，加强了冠脉系统血流的脉动变化，在左冠状动脉主干狭窄时，对心内膜下小动脉的灌注产生不良影响。     

磁共振3D-ASL定量评估儿童病毒性脑炎脑灌注特征

目的:探讨儿童病毒性脑炎的磁共振三维动脉自旋标记（3D-ASL）成像的灌注特征。方法:回顾性收集25例急性病毒性脑炎患儿和25名年龄相仿的健康对照组。在脑血流量（CBF）伪彩图上对每个患者进行视觉评估，定量分析病变区与对照组CBF值差异，确定儿童病毒性脑炎的脑灌注特征。结果:25例病毒性脑炎患儿在急性期灌注显著增高，急性病变的CBF值、标准化CBF值显著高于对照组，其ROC-AUC值分别为0.971和0.992。9例患儿在治疗好转后进行复查，病变区血流灌注随病情好转而减低。结论:儿童病毒性脑炎的3D-ASL成像表现有一定特征，病灶在急性期灌注显著增高，病情好转后减低。3D-ASL可以为儿童病毒性脑炎诊断和随访提供一种新的影像学参考。     

电阻抗断层成像技术在肺灌注中的研究进展

电阻抗断层成像技术（EIT）是根据人体不同组织器官阻抗差异来进行实时监测的一种新兴技术,目前已被初步运用于临床研究和疾病诊疗。肺灌注是指肺组织的血流灌注功能,许多疾病的发生发展都和肺灌注情况密切相关,所以实时监测肺灌注显得尤为重要,而EIT的应用和发展进一步促进了肺灌注的监测,相关研究已取得极大进展。针对近几年相关研究,本文从EIT成像原理、肺灌注成像方法及其在临床中的应用等几个方面进行综述,以期对临床及科研工作者有所帮助。     

原发性肝癌的CT灌注成像研究进展

灌注(perfusion)是血流通过毛细血管网将携带的氧和营养物质输送给组织细胞的重要功能。通过影像学技术直观显示活体灌注过程和作定量或半定量分析的方法称为灌注成像(perfusion imaging)。近年来,现代影像学的发展已经从单纯反映组织解剖形态改变向着能够将宏观形态学和微观揭示组织代谢和功能演变相结合的方向发展。CT灌注成像空间分辨率高、扫描速度快,可以在一次扫描中显示良好的解剖细节和组织的灌注信息,已经成为影像学研究的热点。本文主要对CT灌注成像的基本原理、操作技术及在原发性肝癌诊断中的应用进行综述。一、肝脏CT灌注成…     

血流灌注对高强度聚焦超声消融子宫肌瘤的影响

高强度聚焦超声（HIFU）治疗时,血流灌注会带走部分组织热量。为了保证治疗的安全性和有效性并提高治疗效率,需要在HIFU治疗过程中考虑血流灌注的影响。目前临床治疗已观察到血流灌注会降低HIFU疗效,但针对血流灌注的量化及如何控制血流灌注以提高HIFU疗效仍不明确。本研究以HIFU消融子宫肌瘤为例,分别从血流灌注对HIFU疗效的影响、子宫肌瘤血流灌注的检测、如何控制血流灌注以提高HIFU疗效这几个方面进行综述,旨在明晰血流灌注对HIFU疗效的影响,为临床控制并利用血流灌注提高HIFU疗效提供参考。     

鼻咽癌3D pCASL与Ki-67指数相关性及临床分期价值

目的:探讨鼻咽癌三维动脉自旋标记（3D pCASL）与Ki-67指数的相关性及其对临床分期的价值。方法:收集病理证实的鼻咽癌首诊患者48例,其中36例经免疫组化检测Ki-67指数,并对患者以T、N及临床分期分为低、高级别组。所有患者均行鼻咽部MR平扫及增强和3D-ASL序列扫描,并测量肿瘤实质内的血流图平均值（BFmean）、最小值（BFmin）及最大值（BFmax）,利用秩和检验比较高、低级别组间ASL的3个定量参数的差异。分析3个定量参数与Ki-67之间相关性。结果:T、N及临床分期的高级别组BFmean、BFmax及BFmin值均高于低级别组;Ki-67指数与BFmax显著相关（r=0.408, P=0.014）,具有统计学意义（P<0.05）。结论:3D pCASL作为一种无创的功能磁共振灌注成像,可以评估鼻咽癌的血流灌注信息;BFmax可以评价鼻咽癌的增殖程度,有利于评估鼻咽癌患者预后。     

Characterizing pulmonary blood flow distribution measured using arterial spin labeling

The arterial spin labeling (ASL) method provides images in which, ideally, the signal intensity of each image voxel is proportional to the local perfusion. For studies of pulmonary perfusion, the relative dispersion (RD, standard deviation/mean) of the ASL signal across a lung section is used as a reliable measure of flow heterogeneity. However, the RD of the ASL signals within the lung may systematically differ from the true RD of perfusion because the ASL image also includes signals from larger vessels, which can reflect the blood volume rather than blood flow if the vessels are filled with tagged blood during the imaging time. Theoretical studies suggest that the pulmonary vasculature exhibits a lognormal distribution for blood flow and thus an appropriate measure of heterogeneity is the geometric standard deviation (GSD). To test whether the ASL signal exhibits a lognormal distribution for pulmonary blood flow, determine whether larger vessels play an important role in the distribution, and extract physiologically relevant measures of heterogeneity from the ASL signal, we quantified the ASL signal before and after an intervention (head‐down tilt) in six subjects. The distribution of ASL signal was better characterized by a lognormal distribution than a normal distribution, reducing the mean squared error by 72% (p < 0.005). Head‐down tilt significantly reduced the lognormal scale parameter (p = 0.01) but not the shape parameter or GSD. The RD increased post‐tilt and remained significantly elevated (by 17%, p < 0.05). Test case results and mathematical simulations suggest that RD is more sensitive than the GSD to ASL signal from tagged blood in larger vessels, a probable explanation of the change in RD without a statistically significant change in GSD. This suggests that the GSD is a useful measure of pulmonary blood flow heterogeneity with the advantage of being less affected by the ASL signal from tagged blood in larger vessels. Copyright © 2009 John Wiley & Sons, Ltd.     

Anteroposterior perfusion heterogeneity in human hippocampus measured by arterial spin labeling MRI

Measurements of blood flow in the human hippocampus are complicated by its relatively small size, unusual anatomy and patterns of blood supply. Only a handful of arterial spin labeling (ASL) MRI articles have reported regional cerebral blood flow (rCBF) values for the human hippocampus. Numerous reports have found heterogeneity in a number of other physiological and biochemical parameters along the longitudinal hippocampal axis. There is, however, only one ASL study of perfusion properties as a function of anteroposterior location in the hippocampus, reporting that rCBF is lower and the arterial transit time (ATT) is longer in the anterior hippocampus than in the posterior hippocampus of the rat brain. The purpose of this article was to measure ATT and rCBF in anterior, middle and posterior normal adult human hippocampus. To better distinguish anteroposterior perfusion heterogeneity in the hippocampus, a modified ASL method, called Orthogonally Positioned Tagging Imaging Method for Arterial Labeling with Flow‐sensitive Alternating Inversion Recovery (OPTIMAL FAIR), was developed that provides high in‐plane resolution with oblique coronal imaging slices perpendicular to the long axis of the hippocampus to minimize partial volume effects. Perfusion studies performed with this modified FAIR method at 3 T indicated that anterior, middle and posterior human hippocampus segments have unique transit time and rCBF values. Of these three longitudinal hippocampal regions, the middle hippocampus has the highest perfusion and the shortest transit time and the anterior hippocampus has the lowest perfusion and the longest transit time. Copyright © 2013 John Wiley & Sons, Ltd.     

Measurement of cerebral perfusion territories using arterial spin labelling

The ability to assess the perfusion territories of major cerebral arteries can be a valuable asset to the diagnosis of a number of cerebrovascular diseases. Recently, several arterial spin labeling (ASL) techniques have been proposed for determining the cerebral perfusion territories of individual arteries by three different approaches: (1) using a dedicated labeling radio frequency (RF) coil; (2) applying selective inversion of spatially confined areas; (3) employing multidimensional RF pulses. Methods that use a separate labeling RF coil have high signal-to-noise ratio (SNR), low RF power deposition, and unrestricted three-dimensional coverage, but are mostly limited to separation of the left and right circulation, and do require extra hardware, which may limit their implementation in clinical systems. Alternatively, methods that utilize selective inversion have higher flexibility of implementation and higher arterial selectivity, but suffer from imaging artifacts resulting from interference between the labeling slab and the volume of interest. The goal of this review is to provide the reader with a critical survey of the different ASL approaches proposed to date for determining cerebral perfusion territories, by discussing the relative advantages and disadvantages of each technique, so as to serve as a guide for future refinement of this promising methodology.     

Comparative analysis of arterial spin labeling and dynamic susceptibility contrast perfusion imaging for quantitative perfusion measurements of brain tumors

We comparatively analyzed the difference between three-dimensional arterial spin labeling (3D-ASL) and the conventional dynamic susceptibility contrast (DSC) perfusion imaging in the setting of assessing brain tumor perfusion in 28 patients with proved brain tumors. All patients were scheduled with standard MRI, 3D-ASL and DSC scannings on a GE DISCOVERY MR 750 system. Maximal relative tumor perfusion was obtained based on the region of interest (ROI) method. A close correlation between 3D-ASL and DSC perfusion imaging was noted as manifested by the absence of significant differences between ASL nTBF and DSC nTBF when normalized to M (mirror region) and GM (contralateral gray matter). However, ASL nTBF was found to be highly correlated with DSC nTBF and DSC nTBV when normalized to M, GM and WM (contralateral normal white matter). Together, our data support that 3D-ASL possesses the potential to be a noninvasive alternate for DSC-MRI in assessing brain tumor perfusion in the setting of treatment prognosis and metastasis, particularly for those patients with renal failure and patients required for collection of follow up information.     

Background suppression in arterial spin labeling MRI with a separate neck labeling coil

In arterial spin labeling (ASL) MRI to measure cerebral blood flow (CBF), pair-wise subtraction of temporally adjacent non-labeled and labeled images often can not completely cancel the background static tissue signal because of temporally fluctuating physiological noise. While background suppression (BS) by inversion nulling improves CBF temporal stability, imperfect pulses compromise CBF contrast. Conventional BS techniques may not be applicable in small animals because the arterial transit time is short. This study presents a novel approach of BS to overcome these drawbacks using a separate 'neck' radiofrequency coil for ASL and a 'brain' radiofrequency coil for BS with the inversion pulse placed before spin labeling. The use of a separate 'neck' coil for ASL should also improve ASL contrast. This approach is referred to as the inversion-recovery BS with the two-coil continuous ASL (IR-cASL) technique. The temporal and spatial contrast-to-noise characteristics of basal CBF and CBF-based fMRI of hypercapnia and forepaw stimulation in rats at 7 Tesla were analyzed. IR-cASL yielded two times better temporal stability and 2.0-2.3 times higher functional contrast-to-noise ratios for hypercapnia and forepaw stimulation compared with cASL without BS in the same animals. The Bloch equations were modified to provide accurate CBF quantification at different levels of BS and for multislice acquisition where different slices have different degree of BS and residual degree of labeling. Improved basal CBF and CBF-based fMRI sensitivity should lead to more accurate CBF quantification and should prove useful for imaging low CBF conditions such as in white matter and stroke.     

FAWSETS perfusion measurements in exercising skeletal muscle

Arterial spin labeling (ASL) techniques are now recognized as valid tools for providing accurate measurements of cerebral and cardiac perfusion. The labeling process used with most ASL techniques creates two problems, magnetization transfer (MT) effects and arterial transit time effects, that require compensation. The compensation process limits time resolution and hinders absolute quantification. MT effects are particularly problematic in skeletal muscle because they are large and change rapidly during exercise. The protocol presented here was developed specifically for quantification of perfusion in exercising skeletal muscle. The ASL technique that was implemented, FAWSETS, eliminates MT effects and arterial transit times. Localized, single-voxel perfusion measurements were acquired from rat hind limbs at rest, during ischemia and during three different levels of stimulated exercise. The results demonstrate sufficient sensitivity to determine the time constants for perfusion changes at onset of, and during recovery from, exercise and to distinguish the differences in the amplitude of the perfusion response to different levels of exercise. Additional measurements were conducted to demonstrate insensitivity to MT effects. The exercise protocol is easily adaptable to phosphorous magnetic resonance measurements, allowing the possibility to acquire local measurements of perfusion and metabolism from the same tissue in future experiments.     

Evaluation of segmented 3D acquisition schemes for whole‐brain high‐resolution arterial spin labeling at 3 T

Recent technical developments have significantly increased the signal‐to‐noise ratio (SNR) of arterial spin labeled (ASL) perfusion MRI. Despite this, typical ASL acquisitions still employ large voxel sizes. The purpose of this work was to implement and evaluate two ASL sequences optimized for whole‐brain high‐resolution perfusion imaging, combining pseudo‐continuous ASL (pCASL), background suppression (BS) and 3D segmented readouts, with different in‐plane k‐space trajectories. Identical labeling and BS pulses were implemented for both sequences. Two segmented 3D readout schemes with different in‐plane trajectories were compared: Cartesian (3D GRASE) and spiral (3D RARE Stack‐Of‐Spirals). High‐resolution perfusion images (2 × 2 × 4 mm³) were acquired in 15 young healthy volunteers with the two ASL sequences at 3 T. The quality of the perfusion maps was evaluated in terms of SNR and gray‐to‐white matter contrast. Point‐spread‐function simulations were carried out to assess the impact of readout differences on the effective resolution. The combination of pCASL, in‐plane segmented 3D readouts and BS provided high‐SNR high‐resolution ASL perfusion images of the whole brain. Although both sequences produced excellent image quality, the 3D RARE Stack‐Of‐Spirals readout yielded higher temporal and spatial SNR than 3D GRASE (spatial SNR = 8.5 ± 2.8 and 3.7 ± 1.4; temporal SNR = 27.4 ± 12.5 and 15.6 ± 7.6, respectively) and decreased through‐plane blurring due to its inherent oversampling of the central k‐space region, its reduced effective T_E and shorter total readout time, at the expense of a slight increase in the effective in‐plane voxel size. Copyright © 2014 John Wiley & Sons, Ltd.     

一站式多模态平扫MR动态成像在急性脑卒中的应用及对缺血半暗带的早期干预效果

目的:探讨一站式多模态平扫MR动态成像在急性脑卒中的应用及对缺血半暗带的早期干预效果。方法:回顾性分析34例急性脑卒中患者影像资料。对比患者正常区域及病变区域的脑组织血流量（CBF）、造影剂平均峰值时间等参数。结果:弥散加权成像显示所有患者均有不同程度的高信号梗死灶,其中28例成像显示存在不同程度的狭窄与闭塞。在评价缺血半暗带方面,26例动态磁敏感对比增强（DSC）与磁共振动脉自旋标记（ASL）结果高度一致。8例患者两种检测结果不一致,ASL显示高灌注,而DSC显示正常灌注,DSC与ASL显示缺血半暗带无明显差异（P>0.05）。与正常对照区域各灌注成像参数相比,半暗带及梗死区域的中枢血容量（CBV）及CBF水平更低（P<0.05）,平均通过时间（MTT）水平更高（P<0.05）;与半暗带区域相比,梗死区域的CBF及CBV水平更低（P<0.05）,MTT水平更高（P<0.05）。结论:一站式平扫MR可快速准确评价急性缺血性脑卒中,为临床个性化治疗提供客观的影像学依据。     

A statistical clustering approach to discriminating perfusion from conduit vessel signal contributions in a pulmonary ASL MR image

The measurement of pulmonary perfusion (blood delivered to the capillary bed within a voxel) using arterial spin labeling (ASL) magnetic resonance imaging is often complicated by signal artifacts from conduit vessels that carry blood destined for voxels at a distant location in the lung. One approach to dealing with conduit vessel contributions involves the application of an absolute threshold on the ASL signal. While useful for identifying a subset of the most dominant high signal conduit image features, signal thresholding cannot discriminate between perfusion and conduit vessel contributions at intermediate and low signal. As an alternative, this article discusses a data‐driven statistical approach based on statistical clustering for characterizing and discriminating between capillary perfusion and conduit vessel contributions over the full signal spectrum. An ASL flow image is constructed from the difference between a pair of tagged magnetic resonance images. However, when viewed as a bivariate projection that treats the image pair as independent measures (rather than the univariate quantity that results from the subtraction of the two images), the signal associated with capillary perfusion contributions is observed to cluster independently of the signal associated with conduit vessel contributions. Analyzing the observed clusters using a Gaussian mixture model makes it possible to discriminate between conduit vessel and capillary‐perfusion‐dominated signal contributions over the full signal spectrum of the ASL image. As a demonstration of feasibility, this study compares the proposed clustering approach with the standard absolute signal threshold strategy in a small number of test images. Copyright © 2015 John Wiley & Sons, Ltd.     

ASL‐MRICloud: An online tool for the processing of ASL MRI data

Arterial spin labeling (ASL) MRI is increasingly used in research and clinical settings. The purpose of this work is to develop a cloud‐based tool for ASL data processing, referred to as ASL‐MRICloud, which may be useful to the MRI community. In contrast to existing ASL toolboxes, which are based on software installation on the user's local computer, ASL‐MRICloud uses a web browser for data upload and results download, and the computation is performed on the remote server. As such, this tool is independent of the user's operating system, software version, and CPU speed. The ASL‐MRICloud tool was implemented to be compatible with data acquired by scanners from all major MRI manufacturers, is capable of processing several common forms of ASL, including pseudo‐continuous ASL and pulsed ASL, and can process single‐delay and multi‐delay ASL data. The outputs of ASL‐MRICloud include absolute and relative values of cerebral blood flow, arterial transit time, voxel‐wise masks indicating regions with potential hyper‐perfusion and hypo‐perfusion, and an image quality index. The ASL tool is also integrated with a T₁‐based brain segmentation and normalization tool in MRICloud to allow generation of parametric maps in standard brain space as well as region‐of‐interest values. The tool was tested on a large data set containing 309 ASL scans as well as on publicly available ASL data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study.