MRI assessment of cerebral blood volume in patients with brain infarcts

MRI perfusion studies have focussed mainly on acute ischaemia and characterisation in ischaemia. Our purpose was to analyse regional brain haemodynamic information in acute, subacute, and chronic ischaemia. We performed 16 examinations of 11 patients on a 1.5 T MR images. Conventional and dynamic contrast-enhanced imaging were employed in all examinations. For the dynamic susceptibility sequences, a bolus (0.2 mmol/kg) of gadopentetate dimeglumine was injected. Reconstructed regional relative cerebral blood volume (rCBV) maps, bolus maps, and conventional images were analysed by consensus reading. In all examinations decreases in rCBV were observed in the lesions. The distribution of regional rCBV in lesions was heterogeneous. The rCBV of the periphery of the lesions was higher than that at their center. There was a correlation between the time since onset and abnormalities on the rCBV map and T2-weighted images (T2WI). In the early stage of acute stroke, the abnormalities tended to be larger on the rCBV than on T2WI. Many patterns of bolus passage were observed in ischaemic regions. rCBV maps provide additional haemodynamic information in patients with brain infarcts. Received: 15 September 1997 Accepted: 22 December 1997     

Continuous assessment of relative cerebral blood volume in transient ischemia using steady state susceptibility-contrast MRI

The utility of a noninvasive steady state susceptibility-contrast MRI technique for continuous measurement of relative cerebral blood volume (rCBV) during global transient ischemia and subsequent hyperemia in a feline ischemia model is demonstrated. The measurements were obtained during a 10-min period of occlusion and 1-h period of reperfusion. Maximal hyperemic responses in gray matter, basal ganglia, and white matter (observed at 7,7, and 5 min, respectively) were 1.9 ± 0.5,1.8 ± 0.3, and 1.7 ± 0.6 times greater than baseline CBV (mean ± SEM). Thirty to forty minutes after onset of reperfusion, CBV returned to normal. Thereafter, it decreased below baseline, nearing the control level by 1 h after onset of reperfusion. Steady state susceptibility-contrast MRI permits continuous, in vivo mapping of alterations in CBV.     

Cerebral blood volume measurements by rapid contrast infusion and T2*-weighted echo planar MRI.

Cerebral blood volume (CBV) provides information complementary to that of cerebral blood flow in cerebral ischemia, tumors, and other conditions. We have developed an alternative theory and method for measuring CBV based on dynamic imaging by MRI or CT during a short contrast infusion. This method avoids several limitations of traditional approaches that involve waiting for steady state or measuring the area under the curve (AUC) during bolus contrast injection. Anesthetized dogs were studied by T2*-weighted echo planar imaging during gadolinium-DTPA infusions lasting 30-60 sec. CBV was calculated from the ratio of the signal changes in tissue and artery. Method responsiveness was compared to AUC measurements using the vasodilator acepromazine. The ratio of signal change in tissue to that in artery rapidly approached an asymptotic value even while the amount of contrast in artery continued to increase. Using 30-sec infusions, the mean (+/- SD) of CBV for control animals was 3.6 +/- 0.9 ml blood/100 g tissue in gray matter and 2.3 +/- 0.8 ml blood/100 g tissue in white matter (ratio = 1.6). Acepromazine increased CBV to 5.7 +/- 1.5 ml blood/100 g tissue in gray matter and 3.1 +/- 0.8 ml blood/100 g tissue in white matter (ratio = 2.0). AUC measurements after bolus injection yielded similar values for control animals but failed to demonstrate any change after acepromazine. It is possible to measure CBV using dynamic MRI or CT during 30-60-sec contrast infusions. This method may be more sensitive to changes in CBV than traditional AUC methods.     

MRI评价亚急性硬化性脑脊髓病患儿的脑灌注特点

目的探讨亚急性硬化性脑脊髓病患儿的脑血流灌注特点。方法对12例亚急性硬化性脑脊髓病患儿和无代谢性脑病或脑血管性疾病的13例对照组患儿进行了流速敏感交替反转恢复免除独立T1测量序列扫描，通过后处理生成脑血流量图，分别测量双侧基底节区和丘脑的相对脑血流量比值（rCBF），进行统计学比较，并对双侧基底节区的rCBF进行受试者工作曲线（ROC）分析。结果亚急性硬化性脑脊髓病组和对照组的右侧基底节区的rCBF分别为0．432±0．158和0．619±0．125，左侧基底节区的rCBF分别为0．478±0．186和0．621±0．123，右侧丘脑的rCBF分别为0．630±0．189和0．833±0．160，差异具有统计学意义（分别为t=3．26，P=0．002；t=2．25，P=0．018；t=2．88，P=0．004）。右侧和左侧基底节区rCBF的受试者工作曲线下面积分别为0．833和0．756。结论MR灌注成像能够显示亚急性硬化性脑脊髓病患儿的脑血流改变，提示患儿双侧基底节区脑灌注的异常，为临床提供新的参考信息。     

Repeat cerebral blood volume assessment with first-pass MR imaging

The feasibility of performing multiple first-pass studies with dynamic, contrast material-enhanced magnetic resonance (MR) imaging was evaluated in a cat model of acute middle cerebral artery (MCA) ischemia. Two dynamic series of SSFP (steady-state free precession) images were acquired in each animal (n = 5) with a conventional 1.5-T imager. The initial first-pass study was acquired at 60 minutes after MCA occlusion, and the second study at 70 minutes, with each performed during an intravenous bolus injection of a 0.5 mmol/kg dose of gadoteridol. In both first-pass studies, differentiation of normal and ischemic gray and white matter was highly statistically significant. At a threshold of P<.01, no statistically significant difference in the peak signal intensity between the first and second studies was noted. A difference between the two studies in the recovery to baseline was seen, presumably due to T1 effects. First-pass MR studies can be repeated within the time frame of a single clinical examination, expanding their utility.     

Quantification of cerebral arterial blood volume and cerebral blood flow using MRI with modulation of tissue and vessel (MOTIVE) signals.

Regional cerebral arterial blood volume (CBVa) and blood flow (CBF) can be quantitatively measured by modulation of tissue and vessel (MOTIVE) signals, enabling separation of tissue signal from blood. Tissue signal is selectively modulated using magnetization transfer (MT) effects. Blood signal is changed either by injection of a contrast agent or by arterial spin labeling (ASL). The measured blood volume represents CBVa because the contribution from venous blood was insignificant in our measurements. Both CBVa and CBF were quantified in isoflurane-anesthetized rats at 9.4T. CBVa obtained using a contrast agent was 1.1 +/- 0.5 and 1.3 +/- 0.6 ml/100 g tissue (N = 10) in the cortex and caudate putamen, respectively. The CBVa values determined from ASL data were 1.0 +/- 0.3 ml/100 g (N = 10) in both the cortex and the caudate putamen. The match between CBVa values determined by both methods validates the MOTIVE approach. In ASL measurements, the overestimation in calculated CBF values increased with MT saturation levels due to the decreasing contribution from tissue signals, which was confirmed by the elimination of blood with a contrast agent. Using the MOTIVE approach, accurate CBF values can also be obtained.     

Can cerebrovascular reactivity be assessed by dynamic susceptibility contrast-enhanced MRI?

The acetazolamide (ACZ) test is performed to evaluate the decrease in cerebral perfusion pressure (CPP) by investigation of vasomotor reactivity (VMR). Our aim was to study cerebral blood flow and blood volume changes induced by the ACZ test in healthy control subjects using dynamic susceptibility contrast-enhanced gradient-echo MRI (DSC-MRI). A FLASH sequence was used to produce susceptibility-weighted images during an intravenous injection of 0.1 mmol/kg gadopentetate dimeglumine (Gd-DTPA). After the first dynamic study, 1 g acetazolamide was given intravenously and 10 min later a second bolus of Gd-DTPA was injected. Using the indicator-dilution theory, relative cerebral blood volume and relative cerebral blood flow were estimated. In healthy subjects the ACZ test induced a significant increase in relative blood volume (from 80.5 ± 10.7 to 113.4 ± 11.9) and relative blood flow (from 5.73 ± 0.96 to 7.5 ± 0.97), symmetrically in the cerebral hemispheres. This approach might be promising in the understanding of cerebral haemodynamics in patients with vascular disorders. Received: 14 October 1996 Accepted: 2 May 1997     

Perfusion-weighted MRI to evaluate cerebral autoregulation in aneurysmal subarachnoid haemorrhage

Introduction  The aim of this study was to evaluate autoregulatory mechanisms in different vascular territories within the first week after aneurysmal subarachnoid haemorrhage (SAH) by perfusion-weighted magnetic resonance imaging (PW-MRI). For this purpose, regional cerebral blood flow and volume (rCVF and rCBV) were measured in relation to different degrees of angiographically visible cerebral vasospasm (CVS). Materials and methods  In 51 SAH patients, PW-MRI and digital subtraction angiography were performed about 5 days after onset of SAH. Regional CBF and rCBV were analysed in the territories of the anterior cerebral artery (ACA), the middle cerebral artery (MCA) and the basal ganglia of each hemisphere in relationship to the degree of CVS in the particular territory. Correlations between rCBF, rCBV and CVS were analysed. Results  CVS was found in 22 out of 51 patients in at least one territory. In all territories, rCBV decreased with increasing degree of CVS, correlated with a decrease of rCBF. In the ACA territories, SAH patients with severe CVS had significantly lower rCBF compared to healthy subjects and to SAH patients without CVS. In the basal ganglia, rCBF and rCBV of the control group were significantly higher compared to the patients without and with moderate vasospasms. Conclusion  PW-MRI showed simultaneous decrease of rCBF and rCBV in patients with SAH. The fact that rCBV did not increase in territories with CVS to maintain rCBF reveals dysfunctional vascular autoregulation. Vasospasms in the microvasculature are most evident in the basal ganglia, showing decreased rCBV and rCBF even in SAH patients without CVS.     

Estimating cerebral blood volume with expanded vascular space occupancy slice coverage

A model for quantifying cerebral blood volume (CBV) based on the vascular space occupancy (VASO) technique and varying the extent of blood nulling yielding task‐related signal changes with various amounts of blood oxygenation level‐dependent (BOLD) and VASO weightings was previously described. Challenges associated with VASO include limited slice coverage and the confounding inflow of fresh blood. In this work, an approach that extends the previous model to multiple slices and accounts for the inflow effect is described and applied to data from a multiecho sequence simultaneously acquiring VASO, cerebral blood flow (CBF), and BOLD images. This method led to CBV values (7.9 ± 0.3 and 5.6 ± 0.3 ml blood/100 ml brain during activation [CBV_ACT] and rest [CBV_REST], respectively) consistent with previous studies using similar visual stimuli. Furthermore, an increase in effective blood relaxation (0.65 ± 0.01) compared to the published value (0.62) was detected, likely reflecting inflow of fresh blood. Finally, cerebral metabolic rate of oxygen (CMRO₂) estimates using a multiple compartment model without assumption of CBV_REST led to estimates (18.7 ± 17.0%) that were within published ranges. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

MRI of sickle cell cerebral infarction

Summary Eleven patients with sickle cell disease and neurological symptoms underwent MRI examination. Cerebral infarcts of two types were found, those in the vascular distribution of the middle cerebral artery and those in the deep white matter. In the patient whose hydration and whose oxygenation of erythrocytes has been treated, MRI offers diagnostic advantages over arteriography and CT.     

Magnetic resonance angiography of supratentorial tumours: comparison with selective digital subtraction angiography

We compared magnetic resonance angiography (MRA) and intra-arterial digital subtraction angiography (IADSA) in the study of brain tumours and assessed the utility of gadolinium-enhanced MRA. We studied 17 patients with supratentorial brain tumors. The entire brain was imaged with multiple overlapping thin volume acquisitions. After IV injection of gadolinium-DTPA, a single thick-slab MRA acquisition was performed. Standard three-dimensional (3D-TOF) acquisitions (in six patients) and 3D-TOF with magnetization transfer prepulse and tilted optimisation nonsaturing radiofrequency excitation pulses (in 11 patients) were used. Displacement of the anterior cerebral artery, main stem and insular branches of the middle cerebral artery was seen well on unenhanced and contrast-enhanced MRA. Displacement of the lenticulostriate and anterior choroidal arteries was seen only once, after Gadolinium. Tumour encasement of the middle cerebral artery was demonstrated in one patient. Tumour vessels were seen in 2 of 8 cases before and 3 of 8 after gadolinium; Tumour hypervascularity was seen only after gadolinium, in 3 of 8 cases. Study of the veins was possible only on gadolinium-enhanced MRA. Displacement of the venous angle was seen in 4 of 7 patients in the frontal, and in all of 8 patients on the lateral projections. Early venous drainage was not seen. Patency of the dural venous sinuses was demonstrated in all patients, but in one neoplastic occlusion of a cortical vein was recognised.     

Contrast between white and grey matter: MRI appearance with ageing

MRI contrast between white and grey matter appears to be higher in young normal subjects than in older patients. The aim of the present study was to investigate the possible relationships between these changes in contrast and ageing. It consisted of two parts. In the first part we retrospectively evaluated 140 MRI brain examinations of healthy subjects, 20 per decade (age range 20–90 years), in whom the contrast was subjectively scored. In the second part we prospectively measured the actual T1, spin density (SD) and T2 values of white and grey matter in another 22 healthy subjects (age range 20–80 years). In the first group of subjects a progressive decrease in white/grey matter contrast was observed with ageing. In the second group of subjects the T1, SD and T2 values of white matter were always shorter than those of grey matter. There is a close relation among T1, SD and T2 values of white and grey matter with ageing. We suggest that there is a progressive loss of white/grey matter contrast with ageing. Such a phenomenon is possibly due to an increased water content in the white matter and the progressive neuronal loss in the grey matter that occurs with age. Correspondence to: S. Magnaldi     

Measurement of cerebral blood volume in humans using hyperoxic MRI contrast

PURPOSE: To develop a new method of measuring quantitative regional cerebral blood volume (CBV) using epochs of hyperoxia as an intravenous contrast agent with T2*-weighted MRI. MATERIALS AND METHODS: Images were acquired from six subjects (four male, two female, mean age 29 +/- 3.7 years) using a sequence combining pulsed arterial spin labeling interleaved with a gradient echo echo-planar imaging (EPI) blood oxygenation level-dependent (BOLD) sequence at 3T. The hyperoxia paradigm lasted 28 minutes consisting of 4 minutes of normoxia, two 6-minute blocks of hyperoxia separated by 6 minutes of normoxia. During the hyperoxic blocks the subjects were delivered a fractional oxygen concentration of 0.5. RESULTS: The mean CBV was calculated to be 3.77 +/- 1.05 mL/100 g globally, 3.93 +/- 0.90 mL/100 g in gray matter (GM), and 2.52 +/- 0.78 mL/100 g in white matter (WM). The mean GM/WM ratio was thus found to be 1.56. These values are comparable to those obtained in other studies. CONCLUSION: The hyperoxia technique for measuring CBV may be particularly useful for patient groups where an injected bolus of contrast agent is contraindicated. As more functional studies are employing epochs of inspired gases for calibration purposes, this method is easily incorporated into existing paradigms to produce a noninvasive, repeatable, easily tolerated, and quantitative measurement of regional CBV.     

Noninvasive measurement of arterial cerebral blood volume using Look-Locker EPI and arterial spin labeling.

This paper describes a method of noninvasively measuring regional arterial cerebral blood volume fractions (CBV(a)) in vivo using the combination of Look-Locker echo-planar imaging (LL-EPI) with arterial spin labeling (ASL). Using this technique the arterial inflow curve is rapidly sampled and the regional CBV(a) is measured, while tissue perfusion signals are suppressed. Two methods of spin labeling (LL-EPI flow-sensitive alternating inversion recovery (LL-EPI-FAIR) and LL-EPI signal targeting using alternating radiofrequency (LL-EPI-STAR)) are assessed and their advantages discussed. The application of vascular crushing to LL-EPI-FAIR is described and used to validate the insensitivity of the sequence to the perfusion difference signal. LL-EPI-STAR is used to assess changes in CBV(a) in response to a finger-tapping task. LL-EPI-STAR signal difference curves are shown to have a shortened vascular transit delay and increased peak signal change on activation. A 33 +/- 14% increase in CBV(a) on activation is found. CBV(a) is measured with a 6-s temporal resolution and the temporal response is compared with the BOLD signal change. CBV(a) is shown to increase more rapidly and return to baseline significantly faster than the BOLD signal change, which supports the suggestion that a change in CBV(a) is an input to the BOLD response.     

Perfusion MRI in cerebral infarction

Purpose: To investigate the hemodynamic changes in patients with acute cerebral stroke by perfusion MRI. Materials and methods: In 12 patients with acute stroke in the territory of the middle cerebral artery, perfusion MRI was performed. Peak time, mean transit time, regional cerebral blood volume and regional cerebral blood flow were calculated in the infarction, the peri-infarction area and the contralateral hemisphere. Results: In the infarction the mean blood flow was 29 ml/100 g/min, compared to about 40 ml/100 g/min in the peri-infarction area and the contralateral hemisphere. In two patients increased cortical blood flow was found in the infarction due to luxury perfusion. The cerebral blood volume was reduced in the infarction, but significantly increased, to 7.3 ml/100 g, in the peri-infarction tissue. Conclusion: Perfusion MRI allows one to differentiate various patterns of perfusion disorders in patients with acute cerebral stroke. The resulting data may be helpful in describing the pathophysiologic mechanisms of compensation.      

Regional cerebral blood flow and blood volume in patients with subcortical arteriosclerotic encephalopathy (SAE)

The aim of the present study was a detailed analysis of the regional cerebral blood flow and blood volume in patients with subcortical arteriosclerotic encephalopathy (SAE) by means of functional magnetic resonance imaging (MRI). A group of 26 patients with SAE and a group of 16 age-matched healthy volunteers were examined. Using a well-established dynamic susceptibility contrast-enhanced MRI method, the regional cerebral blood flow (rCBF) and blood volume (rCBV) were quantified for each subject in 12 different regions in the brain parenchyma. As compared to healthy volunteers, patients with SAE showed significantly reduced rCBF and rCBV values in white matter regions and in the occipital cortex. Regions containing predominantly grey matter show almost normal rCBF and rCBV values. In conclusion, quantitative analysis of rCBF and rCBV values demonstrates clearly that SAE is a disease that is associated with a reduced microcirculation predominantly in white matter.     

针刺太冲穴的脑功能MRI研究

目的采用功能MRI（fMm）方法研究与针刺太冲穴（Liv3）有关的脑功能区，以及可能的针刺后效应。方法健康右利手志愿者18例参加本次实验。实验采用单组块设计，包括静息期、刺激期和针刺后效应期。每名被试只接受1种针刺，即针刺右侧Liv3或针刺相邻假穴位，其中，10例被试者参加穴位针刺，其余8例参加假穴位针刺，同时进行全脑的fMRI。采用统计参数图（SPM99）进行统计学分析，用t检验分析获得刺激期、后效应期状态分别与静息期状态信号对比的脑功能图像，以P〈0．001的像素构成统计参数图，最后利用SPM的掩盖（Mask）功能，从针刺激活区中排除假穴位针刺的干扰激活区，得出针刺激活的特异性脑区图。结果排除8例假穴位针刺期激活脑区后，与静息状态比较，针刺10例被试右侧太冲穴激活的脑区主要包括左右小脑（t值分别为10．06、9．82）、前额叶、顶上小叶（t值分别为4．36、4．53）和顶下小叶（t值分别为3．94、4．95）、枕叶、海马旁回（t值分别为5．63、6．32）、岛叶（t值分别为3．82、5．51）、丘脑、豆状核（t值分别为3．24、4．40）以及对侧颞极和前、后扣带回（P值均〈0．01）。排除8例假穴位针刺“后效应期”激活区后，针刺10例被试太冲穴后效应期激活的脑区主要包括双侧小脑、前额叶、顶上小叶和顶下小叶、枕叶、豆状核、海马旁回，同侧颞极、海马、岛叶和丘脑，对侧尾状核头和胼胝体以及前、后扣带回。结论针刺Liv3激活视区、边缘系统和皮层下灰质结构，可能是脑内调整的特异性脑区，而且这些区域在后效应期仍有激活，为针刺后效应的存在提供了一定的客观证据，这将为以后针刺实验的科学设计奠定基础工作。     

Estimate of vascular permeability and cerebral blood volume using Gd-DTPA contrast enhancement and dynamic T2*-weighted MRI

PURPOSE: To develop a numerical approach for estimation of vascular permeability from dynamic T2*-weighted imaging, a technique routinely used to measure cerebral blood volume (CBV) and flow in gliomas. MATERIALS AND METHODS: This study describes a process for estimating both the gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) transvascular transfer constant and CBV from dynamic T2*-weighted images. The algorithm was applied to data from the brains of 12 patients with grade IV gliomas. The stability of the method was assessed. Estimates of CBV by this technique were compared to those of the conventional method. RESULTS: The algorithm was found to be insensitive to noise and to generate stable voxel-by-voxel estimates of permeability and CBV. CONCLUSION: Using a single imaging acquisition, the three most important vascular properties, CBV, cerebral blood flow (CBF), and permeability, can be estimated. This approach may have potential in clinical evaluation of patients with brain tumor or acute ischemic stroke.     

脑膜瘤相对血流量MR定量检测:梯度回波与平面回波序列法的比较

目的通过对梯度回波序列法与平面回波(echoplanerimaging,EPI)序列法重建脑膜瘤相对血流量图的比较,对脑膜瘤相对血流量的定量检测进行评价。方法应用西门子1.5TMR仪对18例脑膜瘤病人进行检查,获取常规的T1WI、T2WI和增强T1WI,以及动态的磁顺应敏感图像(T2WI梯度回波序列或SEEPI序列)。在采集动态的磁顺应敏感图像期间(梯度回波法12例,EPI法6例),应用程控注射器以每秒5ml的流率注入钆喷替酸葡甲胺(GdDTPA)(0.2mmol/kg)。应用优视系统(advancedvisualsystem,AVS)软件逐点处理动态的磁顺应敏感资料,对重建的全部相对血流量图作感兴趣区分析,通过借鉴文献中脑灰质血流量数值,定量计算脑膜瘤的相对血流量。结果肿瘤相对血流量与脑灰质相对血流量的比率是3.01±1.18(梯度回波序列法为3.07±1.39;EPI序列法为2.84±0.94)。脑膜瘤的平均相对血流量为(14.47±5.96)ml/100g:梯度回波序列法为(14.85±6.72)ml/100g,EPI序列法为(13.72±4.54)ml/100g;梯度回波序列法与EPI序列法的结果比较差异无统计学意义(t=0.42,P=0.68)。结论应用脑灰质血流量数值法可便捷地定量检测脑膜瘤的相对血流量,脑膜瘤的相对血流量明显增高而且非均匀性;血脑屏障破坏情况下,仍可估算相对血流量值;尽管EPI序列法更具有效应,梯度回波序列法和EPI序列法均能有效地应用于相对血流量的测定。     

MR relative cerebral blood flow mapping of Alzheimer disease: correlation with Tc-99m HMPAO SPECT

RATIONALE AND OBJECTIVES: To evaluate the value of magnetic resonance (MR) perfusion imaging for diagnosis of Alzheimer disease (AD), the authors compared relative cerebral blood flow (CBF) maps obtained with MR perfusion imaging and technetium-99m hexamethyl-propyleneamine oxime (HMPAO) single photon emission computed tomography (SPECT) in patients with AD. MATERIALS AND METHODS: Eight patients with AD were studied with MR perfusion imaging and HMPAO SPECT. The relative CBF maps from the two techniques were spatially coregistered, and relative CBF values in 13 cerebral gray matter regions (total, 26 regions of interest) were compared with regression analysis. To evaluate the degree of deviation of each brain region from the regression line, a P value for the residual was calculated for each region. RESULTS: A significant overall correlation was seen between the relative CBF values produced by the two techniques (r = .68, P < .0001). Smaller P values for the residuals were obtained in the anterior cingulate cortex (P = .05) and posterior cingulate cortex (P < .001), indicating larger deviations in these regions. When data from these two regions were eliminated, the correlation coefficient rose to 0.80 (P < .0001). CONCLUSION: Despite fairly large discrepancies in the anterior and posterior cingulate cortices, the relative CBF map obtained with MR imaging is generally in close agreement with the HMPAO SPECT map, suggesting that MR perfusion imaging can provide clinically useful information regarding CBF abnormalities in patients with AD.