Age-related changes in proton T1 values of normal human brain

To determine whether there were age-related changes In the brain tissue of 55 healthy adult volunteers (29 men, 26 women; 18-72 years old) without known brain abnormalities, a standard inversion-recovery technique was optimized for precise and accurate T1 measurement within the constraints of a 15-minute examination. Measurements of water proton T1 were obtained in eight brain regions. T1 increased with age in the genu (P < 0.001) (analysis of variance), frontal white matter (P < 0.05), occipital white matter (P < 0.05), putamen (P < 0.001), and thalamus (P << 0.001). A significant decrease in T1 with age was found in cortical gray matter (P < 0.05). Thus, age-related changes in T1 are present in a healthy population, even if extremes of age are excluded, suggesting that T1 values generally increase with age. However, increases in T1 were also observed in the genu, putamen, and thalamus of a substantial fraction of volunteers less than 35 years old. Aging healthy persons can show subtle, nonsymp- tomatic brain changes, suggesting that brain aging is associated with occult processes that can begin at a relatively early age.     

Quantitative MR imaging of children with sickle cell disease: Striking T1 elevation in the thalamus

Nineteen patients with sickle cell disease (SCD) were examined with conventional MR imaging (cMRI), including T1- and T2-weighted sequences and MR angiography (MRA). qMRI mapping of T1 was also done using a precise and accurate inversion-recovery (PAIR) technique optimized and validated previously. In addition, 21 healthy African-American control subjects had the qMRI examination. Nonparametric Kruskal-Wallis analysis of variance of control subjects, of SCD patients without stroke, and of SCD patients with stroke showed that T1 increased with disease severity in the thalamus, frontal white matter, genu, and occipital white matter. T1 was significantly longer in SCD patients without stroke (n=13) than in control subjects (n=21) in the thalamus and frontal white matter. In addition, T1 values were significantly longer in SCD patients with stroke than in patients without stroke in the genu and frontal white matter. Abnormality of the thalamus was identified by qMRI in a substantial fraction of patients read as normal by both cMRI and MRA, suggesting that it may be possible to use T1 elevation to identify a subset of patients with SCD who are at elevated risk for stroke.     

Reproducibility of nonparametric feature map segmentation for determination of normal human intracranial volumes with MR imaging data

Semiautomated segmentation of dual-contrast magnetic resonance images was used to determine volumes of total brain, gray matter, white matter, and cerebrospinal fluid (CSF) in healthy volunteers. Reproducibility of the technique was evaluated in terms of intraobserver, interobserver, and study-to-study variations. Intraobserver coefficients of variation ranged from 0.4% to 6.0%, while interobserver values ranged from 0.8% to 9.9%. In both cases, the maximum variations were obtained in volume measurements of tissues with maximum complexity (ie, CSF), and the minimum variation was obtained in determining total brain volume. This was also true in the case of study-to-study variations in volume measurements, for which the coefficients of variation ranged from 0.5% to 8.7%. The use of appropriate preprocessing techniques, which are crucial to the accuracy and reproducibility of the segmentation technique, are described in detail.     

Volumetric assessment of tumor infiltration of adjacent white matter based on anatomic MRI and diffusion tensor tractography

RATIONALE AND OBJECTIVES: To perform a retrospective, quantitative assessment of the anatomic relationship between intra-axial, supratentorial, primary brain tumors, and adjacent white matter fiber tracts based on anatomic and diffusion tensor magnetic resonance imaging (MRI). We hypothesized that white matter infiltration may be common among different types of tumor. MATERIAL AND METHODS: Preoperative, anatomic (T1- and T2-weighted), and LINESCAN diffusion tensor MRI were obtained in 12 patients harboring supratentorial gliomas (World Health Organization [WHO] Grades II and III). The two imaging modalities were rigidly registered. The tumors were manually segmented from the T1- and T2-weighted MRI, and their volume calculated. A three-dimensional tractography was performed in each case. A second segmentation and volume measurement was performed on the tumor regions intersecting adjacent white matter fiber tracts. Statistical methods included summary statistics to examine the fraction of tumor volume infiltrating adjacent white matter. RESULTS: There were five patients with low-grade oligodendroglioma (WHO Grade II), one with low-grade mixed oligoastrocytoma (WHO Grade II), one with ganglioglioma, two with low-grade astrocytoma (WHO Grade II), and three with anaplastic astrocytoma (WHO Grade III). We identified white matter tracts infiltrated by tumor in all 12 cases. The median tumor volume (+/- standard deviation) in our patient population was 42.5 +/- 28.9 mL. The median tumor volume (+/- standard deviation) infiltrating white matter fiber tracts was 5.2 +/- 9.9 mL. The median percentage of tumor volume infiltrating white matter fiber tracts was 21.4% +/- 9.7%. CONCLUSIONS: The information provided by diffusion tensor imaging combined with anatomic MRI might be useful for neurosurgical planning and intraoperative guidance. Our results confirm previous reports that extensive white matter infiltration by primary brain tumors is a common occurrence. However, prospective, large population studies are required to definitively clarify this issue, and how infiltration relates to histologic tumor type, tumor size, and location.     

Increased self-diffusion of brain water in normal aging

With magnetic resonance (MR) imaging, brain water self-diffusion was measured in 17 healthy volunteers 22–76 (mean, 44.6) years old. The calculated values for the apparent diffusion coefficients (ADCs) ranged from 0.58 × 10^?9 to 1.23 × 10^?9 m²/sec in cerebral white matter. A significant correlation was found between the ADC in white matter and age (r =.7069, P <.01). The calculated values for ADC in cortical gray matter ranged from 1.06 × 10^?9 to 1.72 × 10^?9 m²/sec no correlation was found between ADCs in gray matter and age. The increased ADC in white matter may be caused by an increase in the extracellular volume due to age-dependent neuronal degeneration or to changes in myelination. These findings have implications for future clinical investigations with diffusion MR imaging techniques in patients with neurologic diseases, and stress the importance of having an agematched group of healthy volunteers for comparison.     

Brain MRI Findings of Carbon Disulfide Poisoning

Objective

To evaluate the findings of brain MRI in patients with carbon disulfide poisoning.

Materials and Methods

Ninety-one patients who had suffered carbon disulfide poisoning [male:female=87:4; age, 32-74 (mean 53.3) years] were included in this study. To determine the extent of white matter hyperintensity (Grade 0-V) and lacunar infarction, T2-weighted MR imaging of the brain was performed.

Results

T2-weighted images depicted white matter hyperintensity in 70 patients (76.9%) and lacunar infarcts in 27 (29.7%).

Conclusion

In these patients, the prevalent findings at T2-weighted MR imaging of the brain were white matter hyperintensity and lacunar infarcts. Disturbance of the cardiovascular system by carbon disulfide might account for these results.     

MR imaging of the central nervous system in divers.

A group of 70 professional divers and 47 healthy control subjects who had never dived were examined with magnetic resonance (MR) imaging to determine the prevalence of focal white matter changes in the brain. Spots of high signal intensity in white matter on proton density- and/or T2-weighted spin-echo images were detected in 42% of the control subjects and in 34% of the divers. In the control subjects, the prevalence of more than three changes was related to smoking, use of alcohol, head trauma, age of more than 35 years, and a combination of several cerebrovascular risk factors. This relationship was not present in the divers. The prevalence of changes in divers was inversely related to diving depth, amount of diving, participation in "unsafe diving," and decompression sickness. The reasons for these results could not be ascertained. The results are compared with those of MR imaging studies of white matter changes recently presented by other research groups.     

Thin-section MR imaging of rat brain at 4.7 T.

The brains of anesthetized 7-month-old male hooded rats were imaged in coronal, sagittal, and horizontal planes at 4.7 T. Images were obtained with a section thickness of 0.6 mm and in-plane pixel size of 0.18-0.20 mm, resulting in finer combined spatial and contrast resolution than in most previously published reports. This allowed detailed anatomic assignment of many brain structures on the basis of comparison with a histologic brain atlas. T1, apparent T2, and water proton density values of gray matter, white matter, and cerebrospinal fluid (CSF) were derived from saturation-recovery and multi-echo measurements. These values were used to calculate expected contrast-to-noise ratios as a function of TR and TE in spin-echo imaging sequences. The optimal simultaneous contrast between gray and white matter and between CSF and gray matter was obtained on images with moderate T2 weighing, with a TR of 3.6 seconds and a TE of 45 msec. The use of thin sections was found to be essential for resolving many fine structures, and the improved sensitivity provided by the high magnetic field strength was crucial for imaging such thin sections at adequate signal-to-noise ratios.     

Selective enhancement of experimental rat brain tumors with Gd-TPPS

The synthetic metalloporphyrin gadolinium (III)-tetraphenylporphine sulfonate (TPPS) was successfully used as a contrast agent for in vivo magnetic resonance (MR) imaging of rat brain glioma. After injection of Gd-TPPS, the signal intensity of experimental rat brain glioma distinctly increased on T1-weighted MR images, an effect similar to that produced by the clinically applied MR imaging contrast agent gadolinium diethylenetriaminepentaacetic acid (DTPA). In contrast to other contrast agents studied (Gd-DTPA, manganese [III]-TPPS), Gd-TPPS produced hypointensity in glioma on T2-weighted images. The tumor-selective accumulation of paramagnetic Gd-TPPS in glioma shortened T1 by 53%, from 1,315 msec ± 199 to 628 msec ± 106, and T2 by 34%, from 86 msec ± 4 to 57 msec ± 5 (2 days after injection of 0.25 mmol/kg Gd-TPPS). The relaxation times of normal cortex, striaturn, corpus callosum, and temporal muscle were not significantly affected. As a result, gliomas appeared hyperintense on T1-weighted images and hypointense on T2-weighted images. Owing to the strong effect of Gd-TPPS on the T2 of glioma, normal brain tissue, tumor, and peritumorous edema could be distinguished on T2-weighted images alone.     

Discrimination between different types of white matter edema with diffusion-weighted MR imaging

Brain edema can be classified into three categories: vasogenic, cytotoxic, and interstitial. The mechanism of edema is thought to be different in each type. The authors studied the movement of water molecules in each type of white matter edema in a rat model by using diffusion-weighted magnetic resonance imaging. Conventional T2-weighted imaging did not allow distinction between the three types of white matter edema; the three types of edema were, however, distinguished by using diffusion-weighted imaging. The apparent diffusion coefficient (ADC) of water was different in each type of edema. Water molecules in cytotoxic edema induced by triethyl-tin intoxication showed a smaller and less anisotropic ADC than in normal white matter. In contrast, water in vasogenic edema induced by cold injury had a larger and more anisotropic ADC than in normal white matter. Water in interstitial edema due to kaolin-induced hydrocephalus had an anisotropic and very large ADC.     

Quantitative proton MR spectroscopic imaging of the human brain

Multislice proton MR spectroscopic images (SI) of the brain were quantitated, using the phantom replacement technique. In 16 normal volunteers, ranging in age from 5 to 74 years, average “whole brain” concentrations of choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) were found to be 2.4 ± 0.4, 7.9 ± 1.3, and 11.8 ± 1.0 (mM, mean ± SD), respectively. These values are in good general agreement with those previously determined by single-voxel localization techniques. Cortical gray matter was found to have lower Cho and NAA levels, compared to those of white matter, corpus callosum, and basal ganglia. Cho was also found to increase significantly with age in several locations. Quantitative multislice proton SI is feasible in the clinical environment, and regional and age-dependent variations occur that must be accounted for when evaluating spectra from pathological conditions.     

A novel fast T1-mapping method

The authors present a novel fast T1-mapping technique that allows a T1 map to be reconstructed from data acquired in less than 3 seconds. Data were acquired by using two modified TurboFLASH (fast low-angle shot) sequences and were processed with a combination of one-dimensional Fourier transforms and a parameter-fitting routine, instead of a standard two-dimensional Fourier transform. Apparent T1 (T1*) maps were obtained, from which T1 maps were calculated. Comparisons of T1 values obtained in phantoms and the human brain by using this technique with those obtained with multipoint inversion-recovery T1 mapping showed that the new method yielded accurate T1 values. Optimization of the method will further improve speed and accuracy. The general approach of this T1-mapping technique is believed to be also applicable to other problems, such as T2 and T2* mapping.     

T2 detection of tumor invasion within segmented components of glioblastoma multiforme

Purpose

To use T2‐weighted images to detect tumor invasion when comparing normal individuals to groups of gliomablastoma multiforme (GBM) patients with varying levels of CXCR4, a chemokine receptor that promotes tumor migration.

Materials and Methods

T2‐weighted images were acquired preoperatively in 22 treatment‐naïve GBM patients. Two groups were formed based on the expression levels of CXCR4. A third group of normal volunteers was used for comparison. Each image was segmented to obtain four different clusters for tissue types identified as white matter, basal ganglia, gray matter/edema and cerebrospinal fluid (CSF)/tumor. Signal intensity histograms were formed for each cluster and compared between groups.

Results

In every cluster the GBM groups displayed significantly higher standard deviations of intensity distributions when compared to normal subjects. Significant differences in skewness were found between normal subjects and GBM patients in the white matter, basal ganglia, and CSF/tumor. Further, when the two groups of GBM patients were compared the CXCR4‐high group was found to have a significant shift in the median intensity values in the cluster containing gray matter and peritumoral edema.

Conclusion

T2 signal intensity histograms in normal subjects differ significantly from those obtained from GBM groups, suggesting widespread dissemination of disease. J. Magn. Reson. Imaging 2009;29:251–257. © 2009 Wiley‐Liss, Inc.     

Role of diffusion tensor imaging in characterization and preoperative planning of brain neoplasms

Background and purpose

DTI is an MR imaging measure of brain tissue integrity. It gives precise information about the involvement and integrity of the white matter tracts in the immediate region surrounding tumors. The purpose of our study is to evaluate the role of DTI in characterization and preoperative assessment of brain neoplasm.

Materials and methods

32 patients with intracranial neoplasm were included in this study which was conducted during a 2 year period. Conventional MRI before and after IV Gadolinium administration was done followed by DTI and diffusion tensor tractography, with FA and ADC value measurements of different white matter tracts in direct relation to the tumor. The values obtained were compared to the normal unaffected tract in the contralateral side.

Results

White matter involvement by a tumor was classified according to the criteria of displacement, infiltration, disruption or edema. Patients were classified into two main groups according to the tumor type: benign and malignant groups. Prevalence of tract displacement was higher among benign group in comparison to the malignant group with significant difference in between by using chi-square test (P value <0.05). While prevalence of disruption was higher among the malignant group, in comparison to the benign group significant difference was noted in between by using chi-square test. (P value <0.05).

Conclusion

The information provided by DT imaging further defined precise relationships between the sub cortical white matter structures and the cerebral neoplasm. This potentially has a role in tumor characterization, and more importantly in surgical planning.     

Peritumoral brain edema in intracranial meningiomas evaluated by dynamic perfusion-weighted MR imaging: a preliminary study

Our objective was to semi-quantitatively evaluate the cerebral perfusion in the peritumoral brain edema of meningiomas using dynamic perfusion-weighted MR imaging. Six patients with intracranial meningiomas accompanied by peritumoral brain edema were prospectively examined by perfusion-weighted MR imaging. One patient was examined twice, once before and once 5 months after the surgical resection. The relative regional cerebral blood volume (rrCBV), the relative regional cerebral blood flow (rrCBF), and the relative regional mean transit time (rrMTT) were calculated for peritumoral brain edema and the contralateral white matter. These parameters were compared between peritumoral brain edema and the contralateral white matter. The time–concentration curve of the peritumoral brain edema was less prominent than that of the contralateral white matter, resulting in a significantly lower rrCBV (mean 46%) and rrCBF (mean 45%) in peritumoral brain edema than those of contralateral white matter. The serial perfusion-weighted MR imaging also demonstrated the recovery of these parameters after the removal of meningioma by means of surgical resection. Perfusion-weighted MR imaging can demonstrate significantly decreased rrCBV and rrCBF in peritumoral brain edema compared with those in normal white matter. Electronic Publication     

Registration of images from sequential MR studies of the brain

For sequential studies of patients with brain tumors, the authors have designed an automated registration procedure for intra- and interexamination alignment of magnetic resonance images. This was evaluated with artificially misregistered data and data from repeat studies of six healthy volunteers and six brain tumor patients. In a subset of cases, a manual procedure based on matching of neuroanatomic landmarks was also applied for comparison. The results showed that the technique is robust and reproducible, giving an accuracy in the range of 1–2 mm, which corresponded to the spatial resolution of the images. Subject motion between imaging sequences within the same study was negligible, although adjustments (one to two section thicknesses) were required in the z direction to correlate multisection and volume images and to allow accurate image segmentation. For alignment between sequential volunteer and patient examinations, translations of up to 22 mm and rotations in the x, y, and z axes of up to 9° were required. This alignment procedure may be valuable in numerous aspects of treatment planning and patient follow-up.     

1H chemical shift imaging characterization of human brain tumor and edema

Longitudinal (T1) and transverse (T2) relaxation times of metabolites in human brain tumor, peritumoral edema, and unaffected brain tissue were assessed from point resolved spectroscopy (PRESS) (1)H chemical shift imaging results at different repetition times (TR=1500 and 5000 ms; T1: n=19) and echo times (TE=135 and 270 ms; T2: n=7). Metabolite T1 and T2 relaxation times in unaffected brain tissue corresponded with those published for healthy volunteers. T2 relaxation times were reduced in tumor (choline, N-acetyl aspartate) and edema (choline, creatine) compared with unaffected brain tissue ( p<0.02, each), whereas T1 relaxation times did not change significantly. Choline peak area was increased in tumor, creatine and N-acetyl aspartate were decreased in edema and tumor compared with unaffected brain tissue. Metabolite line widths were increased in tumor. It is concluded that under standard measurement conditions the metabolite profiles are not affected by differential T1 saturation. The short T2 of choline in tumor and edema implies that short-echo-time 1H chemical shift imaging is most suited in the use of choline elevation as tumor marker.     

Time after excision and temperature alter ex vivo tissue relaxation time measurements

Previously unreported effects of tissue storage were recently observed in the authors' experimental magnetic resonance (MR) studies. To evaluate the effect of elapsed time after excision and storage temperature on tissue relaxation time measurements, tissue samples from the liver, pancreas, kidney, testis, spleen, and brain were obtained in rats. T1 and T2 were first measured within 5 minutes of excision, and between subsequent measurements, tubes were kept in a water bath at 40°C, at room temperature (28°C), or in an ice bath (4°C). Cellular and organellar integrity was assessed with electron microscopy and correlated with the MR findings. At 40°C (20-MHz spectrometer), the T1 of liver decreased from 280 msec ± 8 to 212 msec ± 10 during the first 60 minutes; the T1 of pancreas decreased from 276 msec ± 3 to 208 msec ± 2. Other tissues showed less than a 5% decrease in T1. T2 changes were smaller than T1 changes in all tissues. Electron microscopy of pancreatic acinar cells showed postmortem changes in mitochondria evolving over the first 60 minutes after death. Manganese loading experiments implicated mitochondrial manganese stores in the observed enhanced postmortem decrease in T1. This study calls into question reported relaxation time data for liver and pancreas. MR studies of excised tissues must account for time and temperature to prevent systematic experimental errors.     

Quantitative magnetization transfer characteristics of the human cervical spinal cord in vivo: Application to Adrenomyeloneuropathy

Magnetization transfer (MT) imaging has assessed myelin integrity in the brain and spinal cord; however, quantitative MT (qMT) has been confined to the brain or excised tissue. We characterized spinal cord tissue with qMT in vivo, and as a first application, qMT‐derived metrics were examined in adults with the genetic disorder Adrenomyeloneuropathy (AMN). AMN is a progressive disease marked by demyelination of the white matter tracts of the cervical spinal cord, and a disease in which conventional MRI has been limited. MT data were acquired at 1.5 Tesla using 10 radiofrequency offsets at one power in the cervical cord at C2 in 6 healthy volunteers and 9 AMN patients. The data were fit to a two‐pool MT model and the macromolecular fraction (M_ob), macromolecular transverse relaxation time (T_2b) and the rate of MT exchange (R) for lateral and dorsal column white matter and gray matter were calculated. M_ob for healthy volunteers was: WM = 13.9 ± 2.3%, GM = 7.9 ± 1.5%. In AMN, dorsal column M_ob was significantly decreased (P < 0.03). T_2b for volunteers was: 9 ± 2 μs and the rate of MT exchange (R) was: WM = 56 ± 11 Hz, GM = 67 ± 12 Hz. Neither T_2b nor R showed significant differences between healthy and diseased cords. Comparisons are made between qMT, and conventional MT acquisitions. Magn Reson Med 61:22–27, 2009. © 2008 Wiley‐Liss, Inc.     

Brain MR Imaging in dietarily treated phenylketonuria

Magnetic resonance imaging is the most efficient imaging modality to evaluate brain gray and white matter of patients with metabolic diseases [1, 2, 3]. The main purpose of out study was to investigate the relation between brain MRI abnormalities and the phenylalanine (phe) and tyrosine (tyr) blood levels in 38 phenylketonuria (PKU) patients. Increased periventricular white matter intensity on T2-weighted brain images was the only pahtologic finding in 24 patients. Brain MRI abnormalities were scored (4) and correlated with the individual mean phe and phe/ tyr levels during 1 year preceding MR examination and with phe tolerance. The appearance of MRI abnormalities on brain T2-weighted images correlates with a threshold mean phe level (averaged over the year preceding the examination).