MR fingerprinting ASL: Sequence characterization and comparison with dynamic susceptibility contrast (DSC) MRI

MR Fingerprinting (MRF)‐based Arterial‐Spin‐Labeling (ASL) has the potential to measure multiple parameters such as cerebral blood flow (CBF), bolus arrival time (BAT), and tissue T₁ in a single scan. However, the previous reports have only demonstrated a proof‐of‐principle of the technique but have not examined the performance of the sequence in the context of key imaging parameters. Furthermore, there has not been a study to directly compare the technique to clinically used perfusion method of dynamic‐susceptibility‐contrast (DSC) MRI. The present report consists of two studies. In the first study (N = 8), we examined the dependence of MRF‐ASL sequence on TR time pattern. Ten different TR patterns with a range of temporal characteristics were examined by both simulations and experiments. The results revealed that there was a significance dependence of the sequence performance on TR pattern (p < 0.001), although there was not a single pattern that provided dramatically improvements. Among the TR patterns tested, a sinusoidal pattern with a period of 125 TRs provided an overall best estimation in terms of spatial consistency. These experimental observations were consistent with those of numerical simulations. In the second study (N = 8), we compared MRF‐ASL results with those of DSC MRI. It was found that MRF‐ASL and DSC MRI provided highly comparable maps of cerebral blood flow (CBF) and bolus‐arrival‐time (BAT), with spatial correlation coefficients of 0.79 and 0.91, respectively. However, in terms of quantitative values, BAT obtained with MRF‐ASL was considerably lower than that from DSC (p < 0.001), presumably because of the differences in tracer characteristics in terms of diffusible versus intravascular tracers. Test–retest assessment of MRF‐ASL MRI revealed that the spatial correlations of parametric maps were 0.997, 0.962, 0.746 and 0.863 for B₁⁺, T₁, CBF, and BAT, respectively. MRF‐ASL is a promising technique for assessing multiple perfusion parameters simultaneously without contrast agent.     

Application of arterial spin labeling and susceptibility weighted imaging in the diagnosis of ischemic cerebrovascular diseases

Objective: To investigate the application value of arterial spin labeling (ASL) and susceptibility weighted imaging (SWI) in the diagnosis of acute ischemic cerebrovascular disease (CVDs). Methods: A total of 124 patients who received fluid attenuated inversion recovery (FLAIR), diffusion weighted imaging (DWI), ASL, time of flight magnetic resonance angiography (TOF-MRA) and SWI scan sequentially were included in this study. The area of the abnormal perfusion region was compared with that of the restricted diffusion region. The cerebral blood flow (CBF) value and apparent diffusion coefficient (ADC) value were compared in ischemic penumbra (IP), infarct core and mirror region. The susceptibility vessel sign (SVS) detection rate was compared with the major vessel severe stenosis or occlusion rate as revealed by MRA. A receiver operating characteristic curve (ROC) was used to analyze the value of SVS as revealed by SWI. Results: In total, 124 cases were included in this study, and 77 cases showed acute cerebral infarction. Among the 77 cases, 59 cases showed an IP. There were significant differences in ADC and CBF values between the infarct core and mirror region (P < 0.01). There was no significant difference in ADC value between IP and mirror region (P = 0.176), but there was significant difference in CBF value between IP and mirror region (P < 0.01). There was no significant difference in SVS detection rate compared with the vessel severe stenosis or occlusion rate in MRA (P = 0.111). Based on the MRA standards, the area under curve (AUC) of ROC for the SVS as revealed by SWI was 0.86 (95% CI: 0.753-0.962). Conclusions: ASL combined with DWI contributed to IP evaluation of acute cerebral infarction. SWI showed higher diagnostic value for intravascular thrombus in acute cerebral infarction.     

Whole‐brain perfusion imaging with balanced steady‐state free precession arterial spin labeling

Recently, balanced steady‐state free precession (bSSFP) readout has been proposed for arterial spin labeling (ASL) perfusion imaging to reduce susceptibility artifacts at a relatively high spatial resolution and signal‐to‐noise ratio (SNR). However, the main limitation of bSSFP‐ASL is the low spatial coverage. In this work, methods to increase the spatial coverage of bSSFP‐ASL are proposed for distortion‐free, high‐resolution, whole‐brain perfusion imaging. Three strategies of (i) segmentation, (ii) compressed sensing (CS) and (iii) a hybrid approach combining the two methods were tested to increase the spatial coverage of pseudo‐continuous ASL (pCASL) with three‐dimensional bSSFP readout. The spatial coverage was increased by factors of two, four and six using each of the three approaches, whilst maintaining the same total scan time (5.3 min). The number of segments and/or CS acceleration rate (R) correspondingly increased to maintain the same bSSFP readout time (1.2 s). The segmentation approach allowed whole‐brain perfusion imaging for pCASL‐bSSFP with no penalty in SNR and/or total scan time. The CS approach increased the spatial coverage of pCASL‐bSSFP whilst maintaining the temporal resolution, with minimal impact on the image quality. The hybrid approach provided compromised effects between the two methods. Balanced SSFP‐based ASL allows the acquisition of perfusion images with wide spatial coverage, high spatial resolution and SNR, and reduced susceptibility artifacts, and thus may become a good choice for clinical and neurological studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Partial volume correction of brain perfusion estimates using the inherent signal data of time‐resolved arterial spin labeling

Quantitative perfusion MRI based on arterial spin labeling (ASL) is hampered by partial volume effects (PVEs), arising due to voxel signal cross‐contamination between different compartments. To address this issue, several partial volume correction (PVC) methods have been presented. Most previous methods rely on segmentation of a high‐resolution T₁‐weighted morphological image volume that is coregistered to the low‐resolution ASL data, making the result sensitive to errors in the segmentation and coregistration. In this work, we present a methodology for partial volume estimation and correction, using only low‐resolution ASL data acquired with the QUASAR sequence. The methodology consists of a T₁‐based segmentation method, with no spatial priors, and a modified PVC method based on linear regression. The presented approach thus avoids prior assumptions about the spatial distribution of brain compartments, while also avoiding coregistration between different image volumes. Simulations based on a digital phantom as well as in vivo measurements in 10 volunteers were used to assess the performance of the proposed segmentation approach. The simulation results indicated that QUASAR data can be used for robust partial volume estimation, and this was confirmed by the in vivo experiments. The proposed PVC method yielded probable perfusion maps, comparable to a reference method based on segmentation of a high‐resolution morphological scan. Corrected gray matter (GM) perfusion was 47% higher than uncorrected values, suggesting a significant amount of PVEs in the data. Whereas the reference method failed to completely eliminate the dependence of perfusion estimates on the volume fraction, the novel approach produced GM perfusion values independent of GM volume fraction. The intra‐subject coefficient of variation of corrected perfusion values was lowest for the proposed PVC method. As shown in this work, low‐resolution partial volume estimation in connection with ASL perfusion estimation is feasible, and provides a promising tool for decoupling perfusion and tissue volume. Copyright © 2014 John Wiley & Sons, Ltd.     

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。     

全脑容积灌注动脉自旋标记成像用于缺血性脑血管疾病的初步研究

目的 探讨全脑容积灌注动脉自旋标记成像（3DASL）应用于缺血性脑血管病诊断中的可行性和价值.方法 实验1：全部患者（对照组30例、脑栓塞组20例）行头部MRI增强检查,加扫3DASL及动态磁敏感对比增强（DSC）序列.对照组计算3DASL及DSC得到的大脑左右半球半卵圆中心镜像感兴趣区（ROI）的脑血流量（CBF）比,脑栓塞组计算2种方法得到的病灶区域与对侧镜像ROI的CBF比,配对分析数据.实验2：急性及亚急性脑栓塞组和短暂脑缺血发作（TIA）组患者各30例,全部行常规头部MRI检查,加扫3DASL序列,对比分析弥散成像（DWI）及3DASL 2种技术显示病变的阳性率及面积大小.结果 实验1：2种灌注方法获得了一致的灌注结果.对照组左右侧镜像ROI的CBF比值：3DASL为1.02±0.18,DSC为1.06±0.24,2者间差异无统计学意义（P＞0.05）;脑栓塞组病灶区域与对侧镜像ROI的CBF比值：3DASL为0.50±0.12,DSC为0.48±0.18,2者间差异无统计学意义（P＞0.05）.实验2：急性及亚急性脑栓塞的检出率：DWI和3DASL均为100％.同一病例相同病变显示面积的大小：SDwI＜S3DASL,n=22; SDW1≈S3DASL,n=8;SDWI＞S3DASL,n=0.TIA的检出率：DWI为0％,3DASL为70％.结论 3DASL和DSC相比,测量脑血流量有相似的敏感性,且具有三维成像扫描范围广、无需注射对比剂和可重复性强等优势.3DASL较DWI有更高的TIA阳性检出率,有助于TIA的早期诊断,全面准确地评估缺血半暗带及急性缺血性脑血管病的血流灌注情况,可作为急诊检查方法之一,为临床治疗提供科学依据.     

Feasibility of measuring prostate perfusion with arterial spin labeling

Prostate perfusion has the potential to become an important pathophysiological marker for the monitoring of disease progression or the assessment of the therapeutic response of prostate cancer. The feasibility of arterial spin labeling, an MRI approach for the measurement of perfusion without an exogenous contrast agent, is demonstrated in the prostate for the first time. Although various arterial spin labeling methods have been demonstrated previously in highly perfused organs, such as the brain and kidneys, the prospect of obtaining such measurements in the prostate is challenging because of the relatively low blood flow, long transit times, susceptibility‐induced image distortion and local motion. However, despite these challenges, this study demonstrates that, with a whole‐body transmit coil and external receiver array, global prostate perfusion can be measured with arterial spin labeling at 3 T. In five healthy subjects with a mean age of 44 years, the mean total prostate blood flow was measured to be 25.8 ± 7.1 mL/100 cm³/min, with an estimated bolus duration and arterial transit time of 884 ± 209 ms and 721 ± 131 ms, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

A comparison of arterial spin labeling perfusion MRI and DCE‐MRI in human prostate cancer

Perfusion MRI has the potential to provide pathophysiological biomarkers for the evaluating, staging and therapy monitoring of prostate cancer. The objective of this study was to explore the feasibility of noninvasive arterial spin labeling (ASL) to detect prostate cancer in the peripheral zone and to investigate the correlation between the blood flow (BF) measured by ASL and the pharmacokinetic parameters K^trans (forward volume transfer constant), k_ep (reverse reflux rate constant between extracellular space and plasma) and v_e (the fractional volume of extracellular space per unit volume of tissue) measured by dynamic contrast‐enhanced (DCE) MRI in patients with prostate cancer. Forty‐three consecutive patients (ages ranging from 49 to 86 years, with a median age of 74 years) with pathologically confirmed prostate cancer were recruited. An ASL scan with four different inversion times (TI = 1000, 1200, 1400 and 1600 ms) and a DCE‐MRI scan were performed on a clinical 3.0 T GE scanner. BF, K^trans, k_ep and v_e maps were calculated. In order to determine whether the BF values in the cancerous area were statistically different from those in the noncancerous area, an independent t‐test was performed. Spearman's bivariate correlation was used to assess the relationship between BF and the pharmacokinetic parameters K^trans, k_ep and v_e. The mean BF values in the cancerous areas (97.1 ± 30.7, 114.7 ± 28.7, 102.3 ± 22.5, 91.2 ± 24.2 ml/100 g/min, respectively, for TI = 1000, 1200, 1400, 1600 ms) were significantly higher (p < 0.01 for all cases) than those in the noncancerous regions (35.8 ± 12.5, 42.2 ± 13.7, 53.5 ± 19.1, 48.5 ± 13.5 ml/100 g/min, respectively). Significant positive correlations (p < 0.01 for all cases) between BF and the pharmacokinetic parameters K^trans, k_ep and v_e were also observed for all four TI values (r = 0.671, 0.407, 0.666 for TI = 1000 ms; 0.713, 0.424, 0.698 for TI = 1200 ms; 0.604, 0.402, 0.595 for TI = 1400 ms; 0.605, 0.422, 0.548 for TI = 1600 ms). It can be seen that the quantitative ASL measurements show significant differences between cancerous and benign tissues, and exhibit strong to moderate correlations with the parameters obtained using DCE‐MRI. These results show the promise of ASL as a noninvasive alternative to DCE‐MRI. Copyright © 2014 John Wiley & Sons, Ltd.     

动态增强MRI定量与半定量分析在直肠癌术前T、N分期中的应用价值

目的 评估动态增强MRI(DCE-MRI)定量、半定量分析在直肠癌术前T、N分期诊断中的应用价值。方法 回顾性分析山西省肿瘤医院MR室2014年7月—2014年11月经肠镜病理证实的27 例直肠癌患者影像资料。其中男18例,女9例,年龄45～73岁,此前均未经任何治疗。均于术前行DCE-MRI,用Omni-Kinetics专用灌注软件进行后处理,同时获得容量转移常数(K^trans)、速率常数(K_ep)、细胞外血管外间隙容积比(V_e)等定量参数,以及达峰时间(TTP)、曲线下面积(AUC)、最大浓度(Max Conc)、最大斜率(Max Slope)等半定量参数。对正常肠壁与病变段肠壁的定量、半定量参数行独立样本t检验;采用秩和检验比较各定量、半定量参数在直肠癌术后病理T、N分期的差异,判断各参数的诊断价值。应用ROC曲线分析定量参数在T、N分期中的最佳诊断界点及敏感性、特异性。根据TNM对患者进行分期。结果 正常肠壁与病变段肠壁的K^trans值[(0.28±0.14)min^-1 vs (1.33±0.86)min^-1]、K_ep值[(1.41±0.67)min^-1 vs (3.56±0.72)min^-1]、Max Conc(0.17±0.02 vs 0.29±0.09)、AUC(0.11±0.07 vs 0.23±0.11)比较,差异均具有统计学意义(t=-6.270、-11.359、-2.487、-2.803,P值均＜0.05)。在T分期为T1～2的早期组与T3～4的晚期组间K^trans值[0.66(0.12～1.35)min^-1 vs 2.15(0.84～2.96) min^-1]、K_ep值[2.51(0.12～5.65)min^-1 vs 4.05(3.18～6.68) min^-1]比较,差异均有统计学意义(Z值分别为-4.077、-2.281,P值均＜0.05)。N分期中,淋巴结无转移组的K^trans值(1.01±0.73)、V_e值(0.29±0.18)、TPP(0.93±0.35)均低于转移组(1.75±0.84、0.54±0.29、1.14±0.15,差异均有统计学意义(Z值分别为-2.433、-2.832、-2.496,P值均＜0.05)。结论 DCE-MRI定量及半定量参数在判断正常肠壁与病变段肠壁、直肠癌的术前T、N分期方面和病理有较高的相关性,对诊断有一定参考价值。定量参数K^trans值、V_e值最佳诊断界点为直肠癌T、N分期提供了较高的敏感性与特异性。     

Assessment of vessel permeability by combining dynamic contrast‐enhanced and arterial spin labeling MRI

The forward volumetric transfer constant (K^trans), a physiological parameter extracted from dynamic contrast‐enhanced (DCE) MRI, is weighted by vessel permeability and tissue blood flow. The permeability × surface area product per unit mass of tissue (PS) in brain tumors was estimated in this study by combining the blood flow obtained through pseudo‐continuous arterial spin labeling (PCASL) and K^trans obtained through DCE MRI. An analytical analysis and a numerical simulation were conducted to understand how errors in the flow and K^trans estimates would propagate to the resulting PS. Fourteen pediatric patients with brain tumors were scanned on a clinical 3‐T MRI scanner. PCASL perfusion imaging was performed using a three‐dimensional (3D) fast‐spin‐echo readout module to determine blood flow. DCE imaging was performed using a 3D spoiled gradient‐echo sequence, and the K^trans map was obtained with the extended Tofts model. The numerical analysis demonstrated that the uncertainty of PS was predominantly dependent on that of K^trans and was relatively insensitive to the flow. The average PS values of the whole tumors ranged from 0.006 to 0.217 min^?1, with a mean of 0.050 min^?1 among the patients. The mean K^trans value was 18% lower than the PS value, with a maximum discrepancy of 25%. When the parametric maps were compared on a voxel‐by‐voxel basis, the discrepancies between PS and K^trans appeared to be heterogeneous within the tumors. The PS values could be more than two‐fold higher than the K^trans values for voxels with high K^trans levels. This study proposes a method that is easy to implement in clinical practice and has the potential to improve the quantification of the microvascular properties of brain tumors. Copyright © 2015 John Wiley & Sons, Ltd.     

Comparison of relative cerebral blood flow maps using pseudo-continuous arterial spin labeling and single photon emission computed tomography

Pseudo‐continuous arterial spin labeling (PCASL) MRI is a relatively new arterial spin labeling technique and has the potential to extend the cerebral blood flow (CBF) measurement to all tissue types, including white matter. However, the arterial transit time (δ_a) for white matter is not well established and a limited number of reports using multi‐delay methods have yielded inconsistent findings. In this study, we used a different approach and measured white matter δ_a (mean ± standard deviation, 1541 ± 173 ms) by determining the arrival times of exogenous contrast agent in a bolus tracking experiment. The data also confirmed δ_a of gray matter to be 912 ± 209 ms. In the second part of this study, we used these parameters in PCASL kinetic models and compared relative CBF (rCBF, with respect to the whole brain) maps with those measured using a single photon emission computed tomography (SPECT) technique. It was found that the use of tissue‐specific δ_a in the PCASL model was helpful in improving the correspondence between the two modalities. On a regional level, the gray/white matter CBF ratios were 2.47 ± 0.39 and 2.44 ± 0.18 for PCASL and SPECT, respectively. On a single‐voxel level, the variance between the modalities was still considerable, with an average rCBF difference of 0.27. Copyright © 2011 John Wiley & Sons, Ltd.     

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.     

磁共振灌注成像在高级别脑胶质瘤与单发脑转移瘤鉴别诊断中的 价值

【摘要】目的:观察和分析磁共振灌注成像对高级别脑胶质瘤的诊断价值。方法:选取经病理证实的84例高级别脑胶质瘤 患者和60例单发脑转移瘤患者,采用磁共振动态增强灌注成像,测算肿瘤实质区与瘤周水肿区的相对脑血容量（rCBV） 值,并进行统计学分析。结果:高级别脑胶质瘤和单发脑转移瘤的时间-信号曲线不同。在肿瘤实质区,单发脑转移瘤的 rCBV值为4.03±0.79,低于高级别脑胶质瘤的5.48±1.32,差异有统计学意义（P<0.05）;瘤周水肿区,单发脑转移瘤的rCBV 值为0.74±0.35,低于高级别脑胶质瘤的1.48±0.26,差异有统计学意义（P<0.05）。结论:磁共振动态增强灌注成像在鉴别 单发脑转移瘤和高级别脑胶质瘤中具有较高的临床价值。     

Perfusion deficits in patients with mild traumatic brain injury characterized by dynamic susceptibility contrast MRI

Perfusion deficits in patients with mild traumatic brain injury (TBI) from a military population were characterized by dynamic susceptibility contrast perfusion imaging. Relative cerebral blood flow (rCBF) was calculated by a model‐independent deconvolution approach from the tracer concentration curves following a bolus injection of gadolinium diethylenetriaminepentaacetate (Gd‐DTPA) using both manually and automatically selected arterial input functions (AIFs). Linear regression analysis of the mean values of rCBF from selected regions of interest showed a very good agreement between the two approaches, with a regression coefficient of R = 0.88 and a slope of 0.88. The Bland–Altman plot also illustrated the good agreement between the two approaches, with a mean difference of 0.6 ± 12.4 mL/100 g/min. Voxelwise analysis of rCBF maps from both approaches demonstrated multiple clusters of decreased perfusion (p < 0.01) in the cerebellum, cuneus, cingulate and temporal gyrus in the group with mild TBI relative to the controls. MRI perfusion deficits in the cerebellum and anterior cingulate also correlated (p < 0.01) with neurocognitive results, including the mean reaction time in the Automated Neuropsychological Assessment Metrics and commission error and detection T‐scores in the Continuous Performance Test, as well as neurobehavioral scores in the Post‐traumatic Stress Disorder Checklist–Civilian Version. In conclusion, rCBF calculated using AIFs selected from an automated approach demonstrated a good agreement with the corresponding results using manually selected AIFs. Group analysis of patients with mild TBI from a military population demonstrated scattered perfusion deficits, which showed significant correlations with measures of verbal memory, speed of reaction time and self‐report of stress symptoms. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Detecting early response to cyclophosphamide treatment of RIF-1 tumors using selective multiple quantum spectroscopy (SelMQC) and dynamic contrast enhanced imaging

The purpose of this study was to develop a reliable, noninvasive method for early detection of tumor response to therapy that would facilitate optimization of treatment regimens to the needs of the individual patient. In the present study, the effects of cyclophosphamide (Cp, a widely used alkylating agent) were monitored in a murine radiation induced fibrosarcoma (RIF-1) using in vivo (1)H NMR spectroscopy and imaging to evaluate the potential of these techniques towards early detection of treatment response. Steady-state lactate levels and Gd-DTPA uptake kinetics were measured using selective multiple quantum coherence (Sel-MQC) transfer spectroscopy and dynamic contrast enhanced imaging, respectively in RIF-1 tumors before, 24 and 72 h after 300 mg/kg of Cp administration. High-resolution (1)H NMR spectra of perchloric acid extracts of the tumor were correlated with lactate and glucose concentrations determined enzymatically. In vivo NMR experiments showed a decrease in steady-state lactate to water ratios (5.4 +/- 1.6 to 0.6 +/- 0.5, p < 0.05) and an increase in Gd-DTPA uptake kinetics following treatment response. The data indicate that decreases in lactate result from decreased glycolytic metabolism and an increase in tumor perfusion/permeability. Perchloric acid extracts confirmed the lower lactate levels seen in vivo in treated tumors and also indicated a higher glycerophosphocholine/phosphocholine (GPC/PC) integrated intensity ratio (1.39 +/- 0.09 vs 0.97 +/- 0.04, p < 0.01), indicative of increased membrane degradation following Cp treatment. Steady-state lactate levels provide metabolic information that correlates with changes in tumor physiology measured by Gd-DTPA uptake kinetics with high spatial and temporal resolution. Both of these parameters may be useful for monitoring early tumor response to therapy.     

Reliability and precision of pseudo‐continuous arterial spin labeling perfusion MRI on 3.0 T and comparison with 15O‐water PET in elderly subjects at risk for Alzheimer's disease

Arterial spin labeling (ASL) offers MRI measurement of cerebral blood flow (CBF) in vivo, and may offer clinical diagnostic utility in populations such as those with early Alzheimer's disease (AD). In the current study, we investigated the reliability and precision of a pseudo‐continuous ASL (pcASL) sequence that was performed two or three times within one hour on eight young normal control subjects, and 14 elderly subjects including 11 with normal cognition, one with AD and two with Mild Cognitive Impairment (MCI). Six of these elderly subjects including one AD, two MCIs and three controls also received ¹⁵O‐water positron emission tomography (PET) scans 2 h before their pcASL MR scan. The instrumental reliability of pcASL was evaluated with the intraclass correlation coefficient (ICC). The ICCs were greater than 0.90 in pcASL global perfusion measurements for both the young and the elderly groups. The cross‐modality perfusion imaging comparison yielded very good global and regional agreement in global gray matter and the posterior cingulate cortex. Significant negative correlation was found between age and the gray/white matter perfusion ratio (r = –0.62, p < 0.002). The AD and MCI patients showed the lowest gray/white matter perfusion ratio among all the subjects. The data suggest that pcASL provides a reliable whole brain CBF measurement in young and elderly adults whose results converge with those obtained with the traditional ¹⁵O‐water PET perfusion imaging method. pcASL perfusion MRI offers an alternative method for non‐invasive in vivo examination of early pathophysiological changes in AD. Copyright © 2009 John Wiley & Sons, Ltd.     

磁共振全脑容积动脉自旋标记成像评价单侧颈动脉狭窄患者脑血流动力学的初步研究

目的探讨磁共振全脑容积灌注3D动脉自旋标记（3DASL）成像在单侧颈动脉狭窄或闭塞中的应用价值。方法对连续36例单侧颈动脉狭窄患者（经数字减影血管造影（DSA）验证）行颈部磁共振血管成像（MRA）与头部MR3DASL检查。检验颈部MRA与DSA在狭窄程度上诊断的一致性。以DSA诊断的狭窄程度为标准,将36例患者分成轻、中、重3组,对3DASL所测得的患侧,健侧脑血流量（CBF）比率进行方差分析。以临床症状为标准,将重度狭窄的患者分为有症状组和无症状组,分析2组患侧,踺侧CBF比率的统计学意义。结果颈部MRA与DSA在动脉血管狭窄程度上的诊断,经Kappa行一致性检验,有很强的一致性（Kappa〉0．75,P〈0．05）。轻、中度狭窄组间患侧楗侧CBF比率差别无统计学意义（P〉O．05）;重度狭窄组与轻、中度狭窄组患侧健侧CBF比率差别均有统计学意义（P〈0．01）。重度狭窄患者的有症状组与无症状组患侧,睦侧CBF比率差别有统计学意义（P〈0．01）。结论3DASL技术作为一种安全、无创和可重复的检查方式,配合颈部MRA,对评价单侧颈动脉狭窄患者脑血流动力学状况在临床诊治方面有重要意义。     

B0 field inhomogeneity considerations in pseudo-continuous arterial spin labeling (pCASL): effects on tagging efficiency and correction strategy

Pseudo-continuous arterial spin labeling (pCASL) is a very powerful technique to measure cerebral perfusion, which circumvents the problems affecting other continuous arterial spin labeling schemes, such as magnetization transfer and duty cycle. However, some variability in the tagging efficiency of the pCASL technique has been reported. This article investigates the effect of B(0) field inhomogeneity on the tagging efficiency of the pCASL pulse sequence as a possible cause of this variability. Both theory and simulated data predict that the efficiency of pseudo-continuous labeling pulses can be degraded in the presence of off-resonance effects. These findings are corroborated by human in vivo measurements of tagging efficiency. On the basis of this theoretical framework, a method utilizing B(0) field map information is proposed to correct for the possible loss in tagging efficiency of the pCASL pulse sequence. The efficiency of the proposed correction method is evaluated using numerical simulations and in vivo implementation. The data show that the proposed method can effectively recover the lost tagging efficiency and signal-to-noise ratio of pCASL caused by off-resonance effects.     

Combination of feature-reduced MR spectroscopic and MR imaging data for improved brain tumor classification

The purpose of this paper is to evaluate the effect of the combination of magnetic resonance spectroscopic imaging (MRSI) data and magnetic resonance imaging (MRI) data on the classification result of four brain tumor classes. Suppressed and unsuppressed short echo time MRSI and MRI were performed on 24 patients with a brain tumor and four volunteers. Four different feature reduction procedures were applied to the MRSI data: simple quantitation, principal component analysis, independent component analysis and LCModel. Water intensities were calculated from the unsuppressed MRSI data. Features were extracted from the MR images which were acquired with four different contrasts to comply with the spatial resolution of the MRSI. Evaluation was performed by investigating different combinations of the MRSI features, the MRI features and the water intensities. For each data set, the isolation in feature space of the tumor classes, healthy brain tissue and cerebrospinal fluid was calculated and visualized. A test set was used to calculate classification results for each data set. Finally, the effect of the selected feature reduction procedures on the MRSI data was investigated to ascertain whether it was more important than the addition of MRI information. Conclusions are that the combination of features from MRSI data and MRI data improves the classification result considerably when compared with features obtained from MRSI data alone. This effect is larger than the effect of specific feature reduction procedures on the MRSI data. The addition of water intensities to the data set also increases the classification result, although not significantly. We show that the combination of data from different MR investigations can be very important for brain tumor classification, particularly if a large number of tumors are to be classified simultaneously.     

The impact of white matter fiber orientation in single‐acquisition quantitative susceptibility mapping

The aim of this work was to assess the impact of tissue structural orientation on quantitative susceptibility mapping (QSM) reliability, and to provide a criterion to identify voxels in which measures of magnetic susceptibility (χ) are most affected by spatial orientation effects. Four healthy volunteers underwent 7‐T magnetic resonance imaging (MRI). Multi‐echo, gradient‐echo sequences were used to obtain quantitative maps of frequency shift (FS) and χ. Information from diffusion tensor imaging (DTI) was used to investigate the relationship between tissue orientation and FS measures and QSM. After sorting voxels on the basis of their fractional anisotropy (FA), the variations in FS and χ values over tissue orientation were measured. Using a K‐means clustering algorithm, voxels were separated into two groups depending on the variability of measures within each FA interval. The consistency of FS and QSM values, observed at low FA, was disrupted for FA > 0.6. The standard deviation of χ measured at high FA (0.0103 ppm) was nearly five times that at low FA (0.0022 ppm). This result was consistent through data across different head positions and for different brain regions considered separately, which confirmed that such behavior does not depend on structures with different bulk susceptibility oriented along particular angles. The reliability of single‐orientation QSM anticorrelates with local FA. QSM provides replicable values with little variability in brain regions with FA < 0.6, but QSM should be interpreted cautiously in major and coherent fiber bundles, which are strongly affected by structural anisotropy and magnetic susceptibility anisotropy.