Masthead,Volume 69, Issue 3

Manganese (Mn)‐enhanced MRI (MEMRI) has found a growing number of applications in anatomical and functional imaging in small animals, based on the cellular uptake of Mn ions in the brain, heart, and other organs. Previous studies have relied on endogenous mechanisms of paramagnetic Mn ion uptake and enhancement. To genetically control MEMRI signals, we reverse engineered a major component of the molecular machinery involved in Mn uptake, the divalent metal transporter, DMT1. DMT1 provides positive cellular enhancement in a manner that is highly sensitive and dynamic, allowing greater spatial and temporal resolution for MRI compared to previously proposed MRI reporters such as ferritin. We characterized the MEMRI signal enhancement properties of DMT1‐expressing cells, both in vitro and in vivo in mouse models of cancer and brain development. Our results show that DMT1 provides an effective genetic MRI reporter for a wide range of biological and preclinical imaging applications. Magn Reson Med 70:842–850, 2013. © 2012 Wiley Periodicals, Inc.     

Effects of blood flow modifiers on tumor metabolism observed in vivo by proton magnetic resonance spectroscopic imaging

Perfusion plays a key role in tumor proliferation and therapeutic response. Tumor heterogeneity necessitates use of the highest spatial resolution to monitor metabolic correlates of blood flow changes. This is best achieved with ¹H NMR spectroscopy, which permits noninvasive acquisition of high resolution spectroscopic images (SI) of subcutaneous tumors in a relatively short scan time (e.g., 12-25 μl voxels with signal-to-noise ratio 7:1 in 30 min at 4.7 T). This study seeks to identify ¹H spectroscopic indices of tumor blood flow. Proton SI of subcutaneous murine RIF-1 tumors were recorded (a) before and after administration of nicotinamide (1 g/kg) to increase blood flow, and (b) before and after hydralazine (10 mg/kg) to decrease flow. Nicotinamide produced a significant decrease in the total choline peak amplitudes, which subsequent high resolution NMR spectroscopy of tumor extracts revealed to be due to decreases in phosphocholine and glycerophosphocholine. The deamidation of nicotinamide to nicotinic acid, which is known to have hypolipidemic effects and to stimulate the formation of prostaglandins, may have sufficiently altered lipid metabolism to affect the in vivo concentration of the NMR-visible choline-containing compounds. The main effect of hydralazine was a significant increase of lactate, which is consistent with a reduction of tumor blood flow.     

Comparison of k-space sampling schemes for multidimensional MR spectroscopic imaging

For clinical ³¹P MR spectroscopic imaging (MRSI) studies, where signal averaging is necessary, some improvement of sensitivity and spatial response function may be achieved by acquiring data over a spherical k-space volume and varying the number of averages acquired in proportion to the desired spatial filter. Eight different k-space sampling schemes are compared through simulations that provide graphs of the spatial response functions (SRF), and tabulations of voxel volumes, relative signal-to-noise ratios (SNR), and relative data collection efficiencies (SNR per unit volume over the same time). All schemes were based on practical experiments, each of which could be implemented in the same length of time. The results show that in comparison with cubic k-space sampling with the same number of signal averages at each point, spherical and acquisition-weighted k-space sampling can be used to achieve reduced Gibbs ringing along the principal axes directions, and thus reduced contamination from adjacent tissue in these directions, without degradation of voxel volume or SNR.     

Motion detection and compensation in infrared retinal image sequences

Infrared image data captured by non-mydriatic digital retinography systems often are used in the diagnosis and treatment of the diabetic macular edema (DME). Infrared illumination is less aggressive to the patient retina, and retinal studies can be carried out without pupil dilation. However, sequences of infrared eye fundus images of static scenes, tend to present pixel intensity fluctuations in time, and noisy and background illumination changes pose a challenge to most motion detection methods proposed in the literature. In this paper, we present a retinal motion detection method that is adaptive to background noise and illumination changes. Our experimental results indicate that this method is suitable for detecting retinal motion in infrared image sequences, and compensate the detected motion, which is relevant in retinal laser treatment systems for DME.     

短暂性脑缺血发作时磁共振血管成像病变特点

 目的 探讨短暂性脑缺血发作（transient ischemic attacks,TIA）时磁共振血管成像病变特点。方法 选取我院收治的60例TIA患者,行磁共振血管成像检查颅内动脉、颈部动脉,分析患者颅颈部供血动脉病变特点、狭窄情况。结果 磁共振检查发现脑供血动脉狭窄患者53例(88.33%),未见异常者7例（11.67%）。其中,颈内动脉系统发现病变者40例(75.47%),椎基底动脉系统发现病变者13例（24.53%）。不同动脉系统的病变在颅内外的分布无统计学差异（χ²=4.94,P=0.08470）。53例发生狭窄病例中,共有病变动脉92支,其中轻度狭窄20支,中度32支,重度38支,2支闭塞;按发生支数依次排序为颈内动脉、大脑中动脉、椎动脉、颈总动脉、基底动脉、大脑前动脉起始段、大脑后动脉。结论 磁共振技术诊断TIA客观,综合患者临床情况对于制定治疗方案具有重要的临床意义。     

儿童脑干胶质瘤的MRI诊断

目的：探讨脑干胶质瘤的ＭＲＩ特征。方法：收集经证实的脑干胶质瘤１２例。结果：ＭＲＩ表现有以下３个特征;（１）肿瘤使脑干的外形增大,通过不同序列和断面显示肿瘤的精确部位,矢状面对于显示胶质瘤的早期改变、顶盖部位及延髓颈髓联合部位的胶质瘤具有独特作用。（２）肿瘤的Ｔ１加权像呈低信号或低等混合信号,Ｔ２加权像呈高信号,注射造影剂（ＧＤ－ＤＴＰＡ）后除少数不增强外有３种强化方式：弥漫型、结节型、环状。（３     

急性脑梗塞早期MRI表现与病理对照研究

目的阻断狗大脑中动脉建立急性脑梗塞动物模型,观察早期MRI表现及其病理改变。材料与方法将16只成年狗随机分为实验组(10只)和对照组(6只)。经颞开颅阻断一侧大脑中动脉(MCA),造成其供应区急性缺血性脑梗塞,只成年狗随机分为实验组(10只)和对照组(6只)。经颞开颅阻断一侧大脑中动脉(MCA),造成其供应区急性缺血性脑梗塞,术后2,4,6,8,12小时行MRI薄层扫描;取出动物大脑观察病理改变,测定不同时相梗塞区T2时间和组织水含量。结果MRI最早2小时表现异常,T2加权像可见尾状核头部、豆状核信号增高;梗塞6小时,MRI可见尾状核、豆状核形成明确梗塞,并出现占位征象。梗塞2小时,电镜下已有缺血水肿改变,4小时光镜下出现脑缺血水肿改变,电镜下见血脑屏障受损。相关分析表明病灶区T2时间变化与组织水含量变化在时序上有密切关系,经t检验差别具显著意义(P＜0．01)。结论本项实验结果表明,MRI可用于脑梗塞早期的诊断,在显示病灶方面,MRIT2加权像优于T1加权像。急性脑梗塞早期MRI表现的病理基础是脑水肿。     

磁共振胰胆管造影诊断胆管系统结石

目的：评价磁共振胰胆管造影在胆管系统结石中的诊断价值。材料和方法：对１００例胆管系统结石的患者进行了ＭＲＣＰ检查,采用不屏气快速自旋回波（ＦＳＥ）序列重Ｔ２加权成像,并用呼吸触发、脂肪抑制和最大信号强度投影（ＭＩＰ）的三维重建方法。对ＭＲＣＰ的诊断结果与手术或临床作了对照分析。结果：本组病例均获得了诊断质量的ＭＲＣＰ图像;１００例胆道结石的患者共有１５８处结石：肝内胆管结石２６例次,胆囊结石５６例次,总胆管结石７３例次和总肝管结石３例次。胆管系统结石的主要ＭＲＣＰ表现为：圆形或卵圆形信号缺失（充盈缺损）;倒杯口征;靶征;铸型样结石。ＭＲＣＰ结合原始图像对胆管系统结石诊断总检出率为９０％,而ＭＲＣＰ对胆管系统结石诊断部检出率为８２％两者比较（Ｐ〈０．０５）。结论：ＭＲＣＰ结合原始图像对胆管系统结石的诊断有较高的准     

MRI心功能参数对陈旧性心肌梗死左心室重塑的评估价值

目的：观察陈旧性心肌梗死后心室形态和心功能参数的变化,探讨MRI测量心功能参数对心室重塑的评估价值。方法：纳入33例陈旧性心肌梗死患者为病变组,12例健康志愿者为对照组。病变组及对照组成员均行MRI检查。MRI测量参数包括：舒张末期客积（EDV）、收缩末期容积（ESV）、每搏输出量（SV）、左心室射血分数（LVEF）、射血率峰值（PER）、充盈率峰值（PFR）。同时测量梗死心肌面积所占的百分比,以24％为分界值,分为无重塑组（≤24％）和重塑组（〉24％）,分析各组间的心功能参数的差异,进行受试者操作特征（ROC）曲线分析,筛选能独立评估心室重塑的心功能指标。结果：病变组的EDV、ESV、SV均高于对照组,病变组的LVEF、PER和PFR低于对照组。ESV随EDV的增加而增加（P〈0．001）,PER、PFR及LVEF均随EDV的增加而下降（P〈0．05）,而SV与各参数均无相关性。PFR、EDV和ESV的ROC分析曲线下面积分别为0．725、0．741、0．764,分界值分别为2．27EDV／sec、140．23ml和79．12ml（P值分别为0．036、0．021和0．032）。结论：MRI可以从收缩和舒张功能的不同角度全面地评估心功能变化。MRI心功能指标对评估心室重塑有重要作用。PFR、EDV、ESV可以作为独立因子评估心室重塑,其中以PFR的评估效能更高。     

Can diffusion tensor imaging predict motor power affection after moderate traumatic brain injury?

Objective

To determine whether commissural and projection fibers fractional anisotropy (FA) abnormalities can help in the prediction of long-term outcome of motor power affection after moderately severe traumatic brain injury (TBI).

Methods

MRI protocol included diffusion tensor imaging (DTI) and was performed for 32 patients with moderate TBI and 32 matched control subjects. Regions of interests were applied in the FA maps in the corpus callosum, internal capsules posterior limb, and cerebral peduncles. Results were compared in patients with motor power affection and patients without motor power affection to the control group.

Results

All patients had FA values lower than the control group with significance differences in the corpus callosum. Patient group with weakness had FA values lower than the control groups with significance differences in the posterior limb of the left internal capsules (p = 0.001) and left cerebral peduncles (p < 0.001). Significant differences were found when comparing the posterior limb of the left internal capsule (p = 0.002) and left cerebral peduncle (p = 0.022) to the right side in the weakness group.

Conclusion

FA values measured in the acute stage provided information about associated and projectional fibers disruptions, which have a prognostic value about motor power affection.