Proton nuclear magnetic resonance studies on brain edema

The water in normal and edematous brain tissues of rats was studied by the pulse nuclear magnetic resonance (NMR) technique, measuring the longitudinal relaxation time (T1) and the transverse relaxation time (T2). In the normal brain, T1 and T2 were single components, both shorter than in pure water. Prolongation and separation of T2 into two components, one fast and one slow, were the characteristic findings in brain edema induced by both cold injury and triethyl tin (TET), although some differences between the two types of edema existed in the content of the lesion and in the degree of changes in T1 and T2 values. Quantitative analysis of T1 and T2 values in their time course relating to water content demonstrated that prolongation of T1 referred to the volume of increased water in tissues examined, and that two phases of T2 reflected the distribution and the content of the edema fluid. From the analysis of the slow component of T2 versus water content during edema formation, it was demonstrated that the increase in edema fluid was steady, and its content was constant during formation of TET-induced edema. On the contrary, during the formation of cold-injury edema, water-rich edema fluid increased during the initial few hours, and protein-rich edema fluid increased thereafter. It was concluded that proton NMR relaxation time measurements may provide new understanding in the field of brain edema research.     

1H-MRS在正常脑组织发育的应用

磁共振波谱成像(MRS)是一种可在活体上无创性测定脑内代谢物质的技术,能在分子水平上反映脑内代谢物浓度的变化,能从细胞水平上反映脑发育过程.本文就MRS在正常脑组织发育的研究应用作一综述.     

Proton magnetic resonance spectroscopic imaging in brain tumor diagnosis

The current state of standard tumor diagnostics using contrast-enhanced MRI and biopsy is assessed in this review, and the progress of proton magnetic resonance spectroscopy (MRS) over the last 15 years is discussed. We summarize MRS basics and describe a typical magnetic resonance session for noninvasive routine tumor diagnostics at 1.5 T, including two-dimensional magnetic resonance spectroscopic imaging (MRSI). The results that can be obtained from such procedures are illustrated with clinical examples. Attention is turned to cutting-edge methodologic and clinical research at 3 T, with examples using high-resolution or very short echo-time three-dimensional MRSI. The current status and limitations in proton MRSI are discussed, and we look to the potential of faster data collection and even higher field strength.     

Proton magnetic resonance spectroscopy of pediatric brain tumors.

1H magnetic resonance spectroscopy allows the regional quantitation of a number of metabolites from the brain in a noninvasive fashion. Spectra were obtained from 5 normal children and 25 children with brain tumors. Choline (Cho), N-acetylaspartate (NAA), creatine and phosphocreatine, and lactate were quantitated in the form of ratios. The brains of normal children showed relatively high concentrations of Cho and NAA and virtually no lactate, as has been shown in adults. Benign astrocytomas and ependymomas were characterized by an elevation of the Cho:NAA ratio and an abnormal accumulation of lactate. Intrinsic malignant tumors were remarkable for an even higher Cho:NAA ratio but had no more lactate than was found in the benign tumors. Proton magnetic resonance spectroscopy may prove useful in characterizing neoplastic tissue in conjunction with more conventional imaging modalities.     

Proton magnetic resonance spectroscopy

Proton magnetic resonance spectroscopy (MRS) permits in vivo determination of biochemical parameters within brain tissue, utilizing the same magnetic resonance (MR) scanner and head coil that are utilized for conventional MR imaging. This technology has been evolving and improving over the past decade, with most of the current published work based on the measurement of rather large single voxels, utilizing variable echo times, aimed at characterizing changes in brain tumors, demyelinating diseases, abscesses, and metabolic diseases. Future work will utilize multiplevoxel techniques so that volumes of tissue can be examined with smaller voxels in reasonable acquisition times, providing a greater understanding of the metabolite composition of the brain, especially as more and more metabolites are identified within the spectra.     

Nuclear magnetic resonance imaging and spectroscopy in experimental brain edema in a rat model

Many aspects of the use of high-resolution nuclear magnetic resonance (NMR) imaging in the examination of brain edema have not been fully explored. These include the quantitation of edema fluid, the ability to distinguish between various types of edema, and the extent to which tissue changes other than a change in water content can affect NMR relaxation times. The authors have compared NMR relaxation times obtained by both in vivo magnetic resonance imaging (MRI) and in vitro NMR spectroscopy of brain-tissue samples from young adult rats with cold lesions, fluid-percussion injury, hypoxic-ischemic injury, bacterial cerebritis, and cerebral tumor. Changes in relaxation times were compared with changes in brain water content, cerebral blood volume, and the results of histological examination. In general, both in vivo and in vitro longitudinal relaxation times (T1) and transverse relaxation times (T2) were prolonged in the injured hemispheres of all experimental groups. Water content of tissue from the injured hemispheres was increased in all groups. A linear correlation between T2 (but not T1) and water content was found. Changes in the values of T1 and T2 could be used to distinguish tumor from cold-injured tissue. Cerebral blood volume was reduced in the injured hemispheres and correlated inversely with prolongation of T1 and T2. The results of this study suggest that, in a clinical setting, prolongation of T2 is a better indicator of increased water content than prolongation of T1, yet quantitation of cerebral edema based solely upon prolongation of in vivo or in vitro T1 and T2 should be undertaken with caution.     

烫伤早期脑水肿家兔脑组织水通道蛋白4表达与磁共振成像结果相关性研究

目的 观察水通道蛋白4(AQP4)在严重烫伤早期合并脑水肿家兔脑组织中的表达规律以及与磁共振成像(MRI)信号变化的联系,探讨严重烫伤早期脑水肿水的跨膜转运特征. 方法 将35只健康新西兰大白兔按照随机数字表法分为正常对照组(5只)及烫伤组(30只),其中烫伤组家兔均造成50％TBSAⅢ度烫伤(经病理切片证实存在脑水肿).伤后1、2 3、4、5、6h,烫伤组家兔(每时相点5只)行MRI颅脑检查并动态检测表观弥散系数(ADC)值;烫伤组家兔取额叶、顳叶及顶叶皮质,基底节区及小脑组织,采用免疫组织化学法及RT-PCR分别检测AQP4蛋白和AQP4 mRNA的表达.正常对照组家兔同上进行检测.对数据进行单因素方差分析,对AQP4蛋白与ADC值进行一元线性相关分析和Pearson线性相关分析. 结果 与正常对照组比较,伤后6h内烫伤组家兔MRI图像(T1加权像、T2加权像、扩散加权成像)未见明显改变,伤后4～6 h烫伤组家兔脑组织各部位中ADC值均明显降低(F值为0.492～2 271,P值均小于0.05).烫伤组家兔伤后2～6 h脑组织各部位中AQP4蛋白表达趋势大体一致,均明显高于正常对照组(0.164±0.022 -0.247±0.018),其中伤后3 h或4 h达高峰(0.237±0.042-0.306±0.026),F值为2.420～11.439,P值均小于0.05.AQP4蛋白在脑组织各部位的表达均与相应ADC值变化呈显著负相关,其r值为-0.489 - -0.337P ＜0.05或P ＜0.01.烫伤组家兔伤后各时相点脑组织各部位中AQP4 mRNA表达均明显高于正常对照组(F值为39.992～238.584,P值均小于0.05),伤后2h达高峰,且在脑组织各部位表达趋势大体一致. 结论 家兔严重烫伤后早期脑水肿(伤后6h以内)以细胞毒性脑水肿为主,AQP4可能在其形成过程中发挥重要作用.ADC值对于反映AQP4变化,进而无创、便捷评估脑水肿发展状况可能具有重要参考价值.     

Traumatic brain edema induced by ventricular puncture. A study by magnetic resonance imaging

Magnetic resonance imaging demonstrates after ventricular catheterization a focal brain hypersignal corresponding to a parenchymal edema along the drain track. In the course of our daily clinical activity, this hypersignal extention seemed more pronounced when catheterizing the frontal area than the junctional parieto-tempro-occipital parenchyma (or trigonal area). In order to confirm this impression, we prospectively studied ten consecutive patients with normal pressure hydrocephalus in whom both of these brain regions were successively catheterized first by a frontal puncture for intracranial pressure monitoring and then by a trigonal one for a ventricular shunt. Each patient was evaluated by serial magnetic resonance imaging. The extention of the hypersignal induced by both catheterizations was estimated on a scale of five grades (0 to 4) of hypersignal extension. A statistically significant more important hypersignal extension was demonstrated at the level of frontal area when compared to the trigonal one. We discuss the likely underlying mechanisms of this phenomenon.     

Magnetic resonance imaging of experimental brain edema in cats

The authors observed the natural course of experimental brain edema in vivo using magnetic resonance (MR) imaging. To detect and qualify the edematous lesion, they obtained images by the spin echo technique (repetition time, 2100 ms; echo time, 80 ms). These showed the maximal brain edema on the 1st to 3rd days after the operation, as evidenced by a pixel density study and a finding of mass effect. On MR images enhanced with manganese, the inversion recovery technique (repetition time, 2100 ms; inversion time, 500 ms) demonstrated the edematous lesion as a high signal intensity area with good spatial resolution. Moreover, the follow-up inversion recovery images with manganese suggested that there was a system for absorption of edema fluid between blood vessels and the edematous lesion. The authors think that MR imaging is an important technique for observation of the dynamics of experimental brain edema.     

Peritumoral brain edema in meningiomas: correlations between magnetic resonance imaging, angiography, and pathology

BACKGROUND: The purpose of this study was to evaluate the radiologic characteristics and pathology related to the formation of peritumoral edema in meningiomas. METHODS: Seventy-nine patients with meningioma were examined by MRI and cerebral angiography. The predictive factors possibly related to peritumoral edema, such as patient age, sex, tumor location, tumor size, peritumoral rim (CSF cleft), shape of tumor margin, signal intensity of tumor in T2WI, pial blood supply, and pathology, were evaluated. We defined the edema-tumor volume ratio as EI and used this index to evaluate peritumoral edema. RESULTS: Male sex (P = .009), tumor size (P = .026), signal intensity of tumor in T2WI (P = .016), atypical and malignant tumor (P = .004), and pial blood supply (P = .001) correlated with peritumoral edema on univariate analyses. However, in multivariate analyses, pial blood supply was statistically significant as a factor for peritumoral edema in meningioma (P = .029). Male sex (P = .067, P < .1) and hyperintensity in T2WI (P = .075, P < .1) might have statistical probability in peritumoral edema. CONCLUSIONS: In our results, male sex, hyperintensity on T2WI, and pial blood supply were associated with peritumoral edema in meningioma that influence the clinical prognosis of patients.     

Proton magnetic resonance spectroscopy in pituitary macroadenomas: preliminary results

OBJECT: The aim of this study was to correlate proton MR (1H-MR) spectroscopy data with histopathological and surgical findings of proliferation and hemorrhage in pituitary macroadenomas. METHODS: Quantitative 1H-MR spectroscopy was performed on a 1.5-T unit in 37 patients with pituitary macroadenomas. A point-resolved spectroscopy sequence (TR 2000 msec, TE 135 msec) with 128 averages and chemical shift selective pulses for water suppression was used. Voxel dimensions were adapted to ensure that the volume of interest was fully located within the lesion and to obtain optimal homogeneity of the magnetic field. In addition, water-unsuppressed spectra (16 averages) were acquired from the same volume of interest for eddy current correction, absolute quantification of metabolite signals, and determination of full width at half maximum of the unsuppressed water peak (FWHM water). Metabolite concentrations of choline-containing compounds (Cho) were computed using the LCModel program and correlated with MIB-1 as a proliferative cell index from a tissue specimen. RESULTS: In 16 patients harboring macroadenomas without hemorrhage, there was a strong positive linear correlation between metabolite concentrations of Cho and the MIB-1 proliferative cell index (R = 0.819, p < 0.001). The metabolite concentrations of Cho ranged from 1.8 to 5.2 mM, and the FWHM water was 4.4-11.7 Hz. Eleven patients had a hemorrhagic adenoma and showed no assignable metabolite concentration of Cho, and the FWHM water was 13.4-24.4 Hz. In 10 patients the size of the lesion was too small (< 20 mm in 2 directions) for the acquisition of MR spectroscopy data. CONCLUSIONS: Quantitative 1H-MR spectroscopy provided important information on the proliferative potential and hemorrhaging of pituitary macroadenomas. These data may be useful for noninvasive structural monitoring of pituitary macroadenomas. Differences in the FWHM water could be explained by iron ions of hemosiderin, which lead to worsened homogeneity of the magnetic field.     

Experimental studies of brain edema by infusion edema model-- biophysical changes of edema fluid in white matter of the brain

The important changes in the area of brain edema are the accumulation and the spreading of edema fluid through the extracellular space in white matter of the brain. In this study, we described the changes of tissue resistance and compliance as the increment of accumulated volume of fluid produced by the slow infusion of normal saline or plasma into white matter of the cat brain. Adult cats (22) were tracheotomized, paralyzed with Galamine (2 mg/kg) and maintained normocapnic, normotensive under nitrous oxide anesthesia. Normal saline or plasma of their own was infused slowly through 25 gauge needle implanted into left frontal white matter by stereotaxic technique. A low compliance pressure gauge transducer was connected to the line for the measurement of inflow pressure. Tissue resistance and compliance for the movement of infused fluid into white matter were delivered from the changes of inflow pressure by adding the 3 microlitter per minutes on top of the resting steady state pressure. Values of tissue resistance in normal white matter, determined at the accumulated volume of 0.05 ml was very high (normal saline infusion: 6.42 +/- 0.61 X 10(3) mmHg/ml/min, plasma infusion: 5.47 +/- 1.43 X 10(3) mmHg/ml/min). But it decreased rapidly followed by more gradual decrease of tissue resistance became more edematous, reaching a plateau of one sixth of initial value at an infused volume of 0.5 ml. Tissue compliance changed by an opposite pattern of rapid increase and plateau to the changes of tissue resistance.     

Proton magnetic resonance in experimental acute and chronic renal failure in rats

Kidney cortical and medullary "spin-lattice" (T1) and "spin-spin" (T2) relaxation times were measured by spectroscopy in several types of experimental renal failure in rats. The T1 and the measured tissue water content were used to calculate the fraction bound (FB) and hydration fraction (HF) according to a fast proton diffusion model. The present study demonstrated the possibility to differentiate between normal and pathological renal tissue resulting from renal artery clamping (RAC), renal pedicle clamping (RPC) with or without reflow, glycerol-induced acute renal failure with or without previous dehydration, and chronic hypertensive renal failure induced by 5/6 nephrectomy and saline loading, with low (6%) or normal (21%) protein diet. Shortened T1 and prolonged T2 found in both cortex and medulla of the glycerol-induced ARF in dehydrated rats seem to represent a MR ischemic pattern. The prolongation of T1 and T2 and the increase in water content in the other groups seem to relate to different amounts of tubular obstruction and renal congestion. In summary, characteristic MR properties of different types of renal failure may provide etiological and pathogenetic diagnostic possibilities.     

不同部位伤害性刺激下大鼠脑功能性磁共振成像的变化

目的 观察不同部位伤害性刺激下大鼠脑功能性磁共振成像的变化.方法 健康清洁级SD大鼠,体重300～450 g,雌雄不拘,采用Y型迷宫筛选出对电刺激反应较敏感的48只大鼠,采用随机数定表法,将其随机分为2组(n=24):刺激鼠尾组(T组)和刺激左前爪组(LF组).T组于鼠尾给予伤害性电刺激,LF组于左前爪给予伤害性电刺激,刺激期间行脑功能磁共振成像扫描,采用统计参数图2软件行图像分析.结果 T组中枢主要的激活脑区包括:初级感觉皮层、次级感觉皮质、后扣带回皮质、杏仁核和腹后外侧丘脑核;LF组中枢主要的激活脑区包括:右侧伏膈核、右侧初级感觉皮层、右侧腹后外侧丘脑核和右侧后扣带回皮质.结论 不同部位伤害性刺激下大鼠脑功能性磁共振成像在中枢激活的脑区不同.     

Pathogenetic role of circulatory factors in brain edema development

Sufficient experimental evidence has been accumulated at present, proving that changes in cerebral blood circulation are largely involved in brain edema development. On the one hand, they might be an immediate cause of edema, e.g., a significant rise of the systemic arterial pressure surpassing the limits of cerebral blood flow autoregulation, or cerebral ischemia damaging brain tissue and the bloodbrain barrier. On the other hand, circulatory changes, e.g., systemic arterial and venous pressure variations, as well as changes in cerebrovascular resistance or in the microcirculation of cerebral tissue, might be the factors which affect in different ways the development of edema of various etiologies. The effects of these circulatory changes may have dual implications, being either malignant, i.e., aggravating edema development, or compensatory, i.e., restricting or in some cases even eliminating brain edema. Knowledge of the circulatory changes is an essential tool in neurosurgical practice, providing for effective treatment of this severe pathological process in the brain.     

Proton magnetic resonance spectroscopy (1H-MRS) for the diagnosis of brain tumors and the evaluation of treatment

MR spectroscopy (MRS) is a technique used to study a few metabolites in the brain or tumors in situ. This technique can provide information on tumor histological type and grade, and is helpful to identify tumor-like lesions, particularly abscesses. MRS can be used for treatment monitoring.     

Thresholding magnetic resonance images of human brain

In this paper, methods are proposed and validated to determine low and high thresholds to segment out gray matter and white matter for MR images of different pulse sequences of human brain. First, a two-dimensional reference image is determined to represent the intensity characteristics of the original three-dimensional data. Then a region of interest of the reference image is determined where brain tissues are present. The non-supervised fuzzy c-means clustering is employed to determine： the threshold for obtaining head mask, the low threshold for T2-weighted and PD-weighted images, and the high threshold for Tl-weighted, SPGR and FLAIR images. Supervised range-constrained thresholding is employed to determine the low threshold for Tl-weighted, SPGR and FLAIR images. Thresholding based on pairs of boundary pixels is proposed to determine the high threshold for T2- and PD-weighted images. Quantification against public data sets with various noise and inhomogeneity levels shows that the proposed methods can yield segmentation robust to noise and intensity inhomogeneity. Qualitatively the proposed methods work well with real clinical data.