Trace apparent diffusion coefficients of metabolites in human brain using diffusion weighted magnetic resonance spectroscopy.

The rotationally invariant trace/3 apparent diffusion coefficients (ADC) of N-acetyl aspartate (NAA), creatine and phosphocreatine (tCr), and choline (Cho) were determined using a diffusion-weighted stimulated echo acquisition mode sequence at 3 T in three separate human brain regions, namely the subcortical white matter, occipital gray matter, and frontal gray matter. The measurement of the mean diffusivity eliminates the dependence of the measured ADC on the direction of the diffusion gradient relative to the tissue microstructure (i.e., anisotropy). Macroscopic brain motions induce phase errors that were compensated for by phasing (zero and first order) on the single average spectrum (zero order on the NAA peak) prior to summing the individual spectra. This method yielded reproducible trace/3 ADC values in the expected range without the use of cardiac gating. The mean diffusivity of NAA (0.14 +/- 0.03 x 10(-3) mm(2)/s) appears to be less than that of tCr (0.17 +/- 0.04 x 10(-3) mm(2)/s) and Cho (0.18 +/- 0.05 x 10(-3) mm(2)/s) in human brain.     

Usefulness of apparent diffusion coefficient value and proton magnetic resonance spectroscopy as a noninvasive techniques in recurrent cerebral gliomas

Objective

Conventional MRI does not provide sufficient information to differentiate post-radiotherapy necrosis from brain tumor recurrence, recent studies have investigated the use of more advanced imaging modalities that are able to differentiate between the two entities.

Proton magnetic resonance spectroscopy in patients with symptomatic unilateral internal carotid artery / middle cerebral artery stenosis or occlusion

Purpose:

To explore the value of proton magnetic resonance spectroscopy imaging (¹H‐MRSI) in patients with stenosis or occlusion of the internal carotid artery (ICA) / middle cerebral artery (MCA).

Materials and Methods:

Fifty noninfarcted patients with stenosis or occlusion of unilateral ICA/MCA were included in our study. In the meantime, 25 patients with cerebral infarction and 25 healthy control subjects were enrolled. All patients and healthy control subjects underwent ¹H‐MRSI. Cerebral metabolic changes were studied in the noninfarcted patients and compared with the infarcted patients as well as healthy control subjects.

Results:

In 50 noninfarcted patients N‐acetylaspartate (NAA) decreased and choline increased in the ischemic hemisphere compared with the contralateral side and control subjects. Lactate peaks were observed in 12 patients. The metabolic changes were relatively slight but were associated with metabolic disruption in infarcted patients. There were relationships between metabolic abnormalities and neurological status of the noninfarcted patients.

Conclusion:

¹H‐MRSI can demonstrate abnormal metabolic changes in cerebral tissues with no infarction, while with ICA/MCA may show stenosis or occlusion at an early stage, which may help guide treatment decisions and preoperative evaluation. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Discrepancy between blood flow and muscarinic receptor distribution in rat brain after middle cerebral artery occlusion

To clarify whether muscarinic acetylcholine receptor (mAChR) binding can be a viable muscarinic neuronal marker which provides therapeutic information different from perfusional information in global brain, we evaluated the discrepancy between the distribution of cerebral blood flow (CBF), mAChR and its live subtypes of messenger ribonucleic acid (mRNA) in the acute (n=9) and chronic (n=8) phases of a middle cerebral artery (MCA) occlusion model and in sham-operated controls (n=6). In the acute phase, regional CBF was markedly reduced in the MCA territory, whereas mAChR was not reduced and the mRNA was reduced only slightly. In the chronic phase, mAChR was reduced markedly in the infarcted lesion and the mRNA was also reduced. The mAChR was slightly reduced in the ipsilateral substantia nigra and pouline nucleus because of remote effects; however, regional CBF in the substantia nigra was slightly increased and did not change in the pontine nucleus. The discrepancy between CBF and mAChR was clarified, and the tendency toward a reduction in mRNA in the acute ischaemic region without a reduction in mAChR suggested the presence of cholinergic neurons which were viable but hypometabolic. It is concluded that mAChR imaging may be of value for the assessment of the viable cholinergic neuron density in vivo.     

Differences in apparent diffusion coefficients of brain metabolites between grey and white matter in the human brain measured at 7 T

Diffusion weighted spectroscopy can provide microstructural information that is specific to compartmental geometry. So far, in human brain, apparent diffusion coefficients (ADCs) of only the metabolites N-acetyl aspartate, creatine (tCr) and choline (tCho) have been assessed. High field MR at 7 T allows the collection and analysis of diffusion weighted spectroscopy data of additional metabolites of interest such as glutamate (Glu), N-acetyl aspartyl glutamate, and glutamine (Gln), which are of interest due to their different compartmentalization and role in brain physiology. In this study, we performed (1)H diffusion weighted spectroscopy at 7 T using a diffusion-weighted PRESS sequence in parietal white matter (n = 6) and occipital grey matter (n = 7). Data were analyzed using the LCmodel. ADCs could reliably be obtained of N-acetyl aspartate, tCr, tCho, Glu, Gln in grey and white matter, and N-acetyl aspartyl glutamate in white matter. Significant differences in ADC values were observed between grey and white matter for all metabolites. ADCs in grey matter were consistently lower than in white matter. These differences can probably be attributed to different compartmentalization as well as to the differential impact of diffusion time on ADC of different molecules under conditions of restricted diffusion.     

大鼠脑缺血再灌注后血脑屏障通透性的改变

 目的探讨大鼠脑缺血再灌注后血脑屏障(BBB)通透性的改变.方法采用线栓法制备大鼠局灶性脑缺血再灌注模型,通过测定脑组织中伊文蓝(EB)含量及免疫组化法来观察血脑屏障通透性的改变.结果缺血2 h再灌注3 h,BBB通透性开始增加,24 h达高峰,72 h后明显减弱.结论缺血再灌注后BBB的通透性在24 h内逐渐增加,提示脑梗死超早期给予溶栓是可行的.     

Time evolution of cerebral perfusion and apparent diffusion coefficient measured by magnetic resonance imaging in a porcine stroke model

PURPOSE: To demonstrate the feasibility of sequential diffusion-weighted (DW) and perfusion-weighted (PW) magnetic resonance imaging (MRI) of a recently developed porcine stroke model and to evaluate the evolution of cerebral perfusion and the apparent diffusion coefficient (ADC) over time. Materials and Methods In five pigs, DW imaging (DWI) and PW imaging (PWI) was carried out for 7 hours after stroke onset, starting 1 hour after middle cerebral artery occlusion (MCAO). RESULTS: The DWI lesion volume increased significantly with time, and final DWI lesion volume correlated well with lesion area on histological sections (r = 0.910). T2 changes could be recognized 3 hours after stroke onset. At 1 hour the ADC ratio (ischemic lesion/contralateral side) was reduced to 0.81 in the caudate-putamen and to 0.87 in the cortex, and the cerebral blood flow ratio was reduced to 0.40 in the caudate-putamen and 0.51 in the cortex. CONCLUSION: The level of flow reduction in the caudate-putamen and the cortex after 1 hour is in good correlation with human thresholds of irreversible and reversible ischemic damage, and accordingly, this model might be a model for mechanisms of infarct evolution and therapeutic intervention.     

Diagnostic interplay of proton magnetic resonance spectroscopy and diffusion weighted images with apparent diffusion coefficient values in suspicious breast lesions

Aim of the work

To study the diagnostic performance of combined single voxel 1H-MRS and DW-MRI with ADC values as a non-contrast diagnostic tool, compared to the DCE-MRI, in suspicious breast lesions.

Asymptomatic middle cerebral artery stenosis diagnosed by magnetic resonance angiography

We reviewed 1440 MRA studies to identify patients with middle cerebral artery stenosis (MCAS). We identified 99 cases, and after reviewing the clinical records, classified 28 as asymptomatic MCAS (AMCAS), a prevalence of 2%. Suspected stroke was the most frequent indication for MRA. Follow-up was available for 21, mean 46.7 months (range 2.4–75.6 months). One stroke occurred in the AMCAS territory (5%), other strokes in five patients (24%). There were five deaths in patients with MCAS; age >69 ( P =0.045) was the only associated risk factor. This study suggests that patients in whom MRA is performed and shows AMCAS may be at increased risk of strokes in any vascular distribution or of death.Presented in part as an abstract at the 27 ^th International Stroke Meeting, San Antonio, Texas, February 2002 and the 54 ^th American Academy of Neurology Meeting, Denver, Colorado, April, 2002     

Role of diffusion weighted imaging and proton magnetic resonance spectroscopy in ring enhancing brain lesions

Aim of the work

To assess and compare the usefulness and efficacy of both diffusion weighted imaging (DWI) and proton magnetic resonance spectroscopy (¹HMRS) in brain lesions with ring enhancement in post contrast T1WI and to determine which method is more effective.

Subjects and methods

Thirty patients with ring-enhanced brain lesions were classified into 2 groups, abscess group (11 patients) and tumor group (19 patients), were examined using diffusion-weighted imaging (DWI) and H-proton magnetic resonance spectroscopy (¹HMRS).

Results

Restricted diffusion and low ADC value were seen in 9 (81%) patients of brain abscesses, however, free diffusion and high ADC value were found in 18 (94%) patients with necrotic brain tumor. The abscess group showed aminoacids, acetate and lactate in 9 patients and extra peak of succinate was found in 1 patient; however in the tumor group lactate alone was found in 12 patients, lactate and choline were seen in 5 patients, none of the patients showed amino acids, succinate or acetate.

Conclusion

Both DWI and ¹HMRS are useful and efficient imaging techniques in ring enhancing brain lesions and differentiate between pyogenic brain abscesses and necrotic tumors, but DWI is accurate, has less imaging time than ¹HMRS, also is available in many imaging centers.     

Assessment of normal fetal brain maturation in utero by proton magnetic resonance spectroscopy.

Cerebral maturation in the normal human fetal brain was investigated by in utero localized proton MR spectroscopy ((1)H MRS). Fifty-eight subjects at 22-39 weeks of gestational age (GA) were explored. A combination of anterior body phased-array coils (four elements) and posterior spinal coils (two to three elements) was used. Four sequences were performed (point-resolved spectroscopy (PRESS) sequence with short and long TEs (30 and 135 ms), with and without water saturation). A significant reduction in myo-inositol (myo-Ins) and choline (Cho) levels, and an increase in N-acetylaspartate (NAA) and creatine (Cr) content were observed with progressing age. A new finding is the detection of NAA as early as 22 weeks of GA. This result is probably related to the fact that oligodendrocytes (whether mature or not) express NAA, as demonstrated by in vitro studies. Cho and myo-inositol were the predominant resonances from 22 to 30 weeks and decreased gradually, probably reflecting the variations in substrate needed for membrane synthesis and myelination. The normal MRS data for the second trimester of gestation (when fetal MRI is usually performed) reported here can help determine whether brain metabolism is altered or not, especially when subtle anatomic changes are observed on conventional images.     

DWI联合~1H-MRS诊断脑单发转移瘤

脑转移瘤（brain metastasis,BM）是指原发于身体其它部位的肿瘤转移至颅内。其发病率约占颅内肿瘤的20％。脑转移瘤多发于皮髓交界区,常以多发形式出现,脑内单发转移瘤与胶质瘤等较难鉴别。     

Extracellular apparent diffusion in rat brain.

The apparent diffusion coefficients (ADCs) of a series of markers concentrated in the extracellular space of normal rat brain were measured to evaluate, by inference, the ADC of water in the extracellular space. The markers (mannitol, phenylphosphonate, and polyethylene glycols) are defined as "compartment selective" because tissue culture experiments demonstrate some leakage into the intracellular space, making them less "compartment specific" than commonly believed. These primarily extracellular markers have ADCs similar to those of intracellular metabolites of comparable hydrodynamic radius, suggesting that water ADC values in the intra- and extracellular spaces are similar. If this is the case, then it is unlikely that a net shift of water from the extra- to the intracellular space contributes significantly to the reduction in water ADC detected following brain injury. Rather, this reduction is more likely due primarily to a reduction of the ADC of intracellular water associated with injury.     

MRS定量分析鼻咽癌放疗后靶区颞叶代谢的研究

目的 探讨氢质子磁共振波谱技术(1HMRS)对鼻咽癌(NPC)放射性脑损伤的诊断价值,通过线性拟合模型(LCModel)绝对值定量鼻咽癌放疗后颞叶细胞代谢变化规律,推测细胞代谢变化的可能机制.方法 1HMRS扫描59例NPC放疗患者颞叶照射野和24例对照组健康志愿者颢叶,获取波谱图像并计算N-乙酰天冬门氨酸(NAA)/胆碱(Cho)、Cho/肌酸(Cr)值,LCModel定量NAA、Cho和Cr值,并进行统计学分析.按放疗后行1 HMRS检查的时间将患者和对照组健康志愿者分为4组:组1(放疗结束1周内,n=16),组2(放疗后1周～6个月,n=22),组3(放疗后6～1 2个月,n=21),组4(对照组,n=24).所有试验组及对照组成员常规磁共振图像均无异常影像学改变.结果 放疗结束1周内(组1)3项绝对值均最低并低于对照组,其中NAA绝对值、Cho绝对值和其余2组试验组分别具有统计学意义,Cr绝对值和对照组之间无统计学意义(0.05＜P＜0.10);放疗结束后1周～6个月的Cho绝对值最高,与对照组P值＜0.05.放疗结束后1周内NAA/Cr值最低,与对照组之间无统计学意义;放疗结束后1周～6个月Cho/Cr值最高且和其余3组均有统计学意义.结论 1HMRS能监测NPC放射性脑损伤的细胞代谢物浓度变化,LCModel定量的绝对值较传统比值更早发现NPC放射性脑损伤细胞代谢变化,提供放射性脑损伤的影像学诊断依据.     

Tyrosinemia: computed tomography, magnetic resonance imaging, diffusion magnetic resonance imaging, and proton spectroscopy findings in the brain

In a 5-month-old boy with tyrosinemia, computed tomography revealed diffuse hypodensity in the centrum semiovale. Magnetic resonance (MR) imaging revealed partial signal differences in the white matter and perirolandic regions, and the posterior limbs of the internal capsules revealed higher signal compared with the remainder of the white matter. There were high-signal changes (restricted water diffusion) in the corresponding regions on images of diffusion-weighted MR imaging (b = 1000 s/mm). This likely represented the presence of intramyelinic edema attributable to status spongiosus. Proton MR spectroscopy (repetition time = 1500 milliseconds, echo time = 40 milliseconds) from the lesion sites revealed 2 separate prominent peaks spread between 3.4 and 3.9 ppm. These peaks could represent the CH and CH2 aliphatic protons of the tyrosine molecule.     

Serial proton magnetic resonance spectroscopy of ischemic brain injury in humans

Four patients were observed serially with 1H magnetic resonance spectroscopy (MRS) at times ranging from 3 days to 10 weeks after a documented ischemic event. Spectra were obtained from 8 cc volumes in infarcted regions and contralateral matched normal regions. Reproducible variations in n-acetyl aspartate (NAA), creatine + phosphocreatine (Cr + PCr), and the sequential changes in lactate and lipid resonances are related to the pathophysiology of stroke. A conspicuous lack of significant change in the choline (Cho) resonance with concomitant decrease in NAA and Cr + PCr is reported as a possible marker of ischemic injury.     

Lipid/water ratio of bone marrow measured by phase-encoded proton nuclear magnetic resonance spectroscopy

Proton NMR spectroscopy (spatially resolved) at 0.7 Tesla with a whole body superconducting magnet was performed on bone marrow from human lumbar spine to measure the lipid/water ratio. Phase-encoded proton spectroscopy was performed by using (1) a spin-echo sequence with selective 90 degrees and 180 degrees rf pulses on the Z and X axes; (2) 64 different phase encodes along the Y axis; and (3) echo acquisition with no gradient. The lipid/water ratios also were measured by the Folch chemical extraction technique. The set of phase-encoded spectra obtained from the spine demonstrates the chemical difference between the vertebral disk (large water peak and no lipid peak) and the marrow (smaller water peak and detectable lipids). Lipid/water ratios were lower than the chemically measured ratios. The phase-encoded proton spectroscopic technique presented in this study allowed rapid acquisition of localized spectra from the bone marrow in each of three vertebral bodies of the intact human spine. This technique provided a measure of the mobile lipid/water ratio weighted by relaxation times.     

The clinical value of proton magnetic resonance spectroscopy in adult brain tumours

Proton magnetic resonance spectroscopy (1H MRS) non-invasively provides information on the biochemical profile (typically including up to nine metabolites and mobile lipids) of brain tissue, which varies according to the underlying disease process. A number of studies have assessed its accuracy in the diagnosis of adult brain tumours. This article describes the basic principles of 1H MRS, the metabolic profiles of different brain tumours, and practical points to aid interpretation of spectra. The literature is reviewed regarding the role of 1H MRS in the diagnosis of brain tumours and more specifically where it has proven to be of additional benefit over conventional magnetic resonance imaging.     

Correlation of early reduction in the apparent diffusion coefficient of water with blood flow reduction during middle cerebral artery occlusion in rats

To determine the relationship between reductions in the apparent diffusion coefficient of water (ADC) and in cerebral blood flow (CBF) during focal ischemia, we used diffusion-weighted magnetic resonance (D-MR) imaging and autoradiographic CBF analysis to examine rats subjected to 30 or 90 min of permanent middle cerebral artery (MCA) occlusion. In the 30-min occlusion group (n = 10), the area with substantially reduced ADC (15% or more below the contralateral level [ADC₁₅]) corresponded best to the area with CBF below 25 ml/100 g/min and was significantly smaller than the area with CBF below 50 ml/100 g/min (CBF₅₀), a level associated with reduced protein synthesis and delayed necrosis (40 ± 13% versus 74 ± 8% of the ischemic hemisphere; P < 0.0001). In the 90-min occlusion group (n = 6), the ADC₁₅ area corresponded best to the CBF₃₀ to CBF₃₅ area and was again significantly smaller than the CBF₅₀ area (54 ± 13% versus 73 ± 20%, P < 0.05). Thus, the area of substantially reduced ADC at 30 and 90 min represents only 53% and 74%, respectively, of the tissue at risk for infarction. These findings indicate a potential limitation in using early D-MR imaging to predict stroke outcome.