Assessment of Human Brain Water Content by Cerebral Bioelectrical Impedance Analysis: A New Technique and Its Application to Cerebral Pathological Conditions (original) (raw)
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Physiological Research
Brain edema is a fatal pathological state in which brain volume increases as a result of abnormal accumulation of fluid within the brain parenchyma. A key attribute of experimentally induced brain edema – increased brain water content (BWC) – needs to be verified. Various methods are used for this purpose: specific gravimetric technique, electron microscopic examination, magnetic resonance imaging (MRI) and dry/wet weight measurement. In this study, the cohort of 40 rats was divided into one control group (CG) and four experimental groups with 8 rats in each group. The procedure for determining BWC using dry/wet weight measurement was initiated 24 h after the completion of edema induction by the water intoxication method (WI group); after the intraperitoneal administration of Methylprednisolone (MP) together with distilled water during edema induction (WI+MP group); 30 min after osmotic blood brain barrier disruption (BBBd group); after injection of MP via the internal carotid arter...
Frontiers in Neurology
Water concentration is tightly regulated in the healthy human brain and changes only slightly with age and gender in healthy subjects. Consequently, changes in water content are important for the characterization of disease. MRI can be used to measure changes in brain water content, but as these changes are usually in the low percentage range, highly accurate and precise methods are required for detection. The method proposed here is based on a long-TR (10 s) multiple-echo gradient-echo measurement with an acquisition time of 7:21 min. Using such a long TR ensures that there is no T 1 weighting, meaning that the image intensity at zero echo time is only proportional to the water content, the transmit field, and to the receive field. The receive and transmit corrections, which are increasingly large at higher field strengths and for highly segmented coil arrays, are multiplicative and can be approached heuristically using a bias field correction. The method was tested on 21 healthy volunteers at 3T field strength. Calibration using cerebral-spinal fluid values (∼100% water content) resulted in mean values and standard deviations of the water content distribution in white matter and gray matter of 69.1% (1.7%) and 83.7% (1.2%), respectively. Measured distributions were coil-independent, as seen by using either a 12-channel receiver coil or a 32-channel receiver coil. In a test-retest investigation using 12 scans on one volunteer, the variation in the mean value of water content for different tissue types was ∼0.3% and the mean voxel variability was ∼1%. Robustness against reduced SNR was assessed by comparing results for 5 additional volunteers at 1.5T and 3T. Furthermore, water content distribution in gray matter is investigated and regional contrast reported for the first time. Clinical applicability is illustrated with data from one stroke patient and one brain tumor patient. It is anticipated that this fast, stable, easyto-use, high-quality mapping method will facilitate routine quantitative MR imaging of water content.
Acta Neurochirurgica, 2002
Background. In vivo water content determination based on magnetic resonance (MR) method is of importance in clinical practice as well as in animal studies to follow up the treatment given in order to reduce brain oedema. The methods proposed in the literature so far are largely time consuming. The aim of this study was to find a fast in vivo water quantification method having real advantage for patients su¤ering from critical conditions. Method. Cold injury was applied to provoke brain oedema in fourteen rats. T 1 values of both the oedematous area and the contralateral normal cortex were determined by two independent methods 24 hours after the cold impact. First, from a series of images recorded by inversion recovery spin echo (IRSE) sequence and then by progressive saturation experiment performed by localised MR spectroscopy using stimulated echo acquisition mode (STEAM). To reduce the acquisition time, a two-element repetition time array was optimised for the STEAM experiment, whereas four inversion times were used for T 1 mapping. Both methods were validated against gel phantoms with known T 1 values. After the MR measurements the animals were sacrificed and the water contents of the regions of interest were determined by gravimetric wet-dry method. Findings. The reciprocals of the in vivo measured T 1 values were correlated with the reciprocals of the brain water contents. STEAM experiment showed stronger correlation ðr ¼ 0:96Þ than IRSE ðr ¼ 0:93Þ. In addition, STEAM provided more accurate T 1 values in the phantom study. Determination of brain water content based on T1 measurement does work also at high magnetic field. Determination of brain water content by Magnetic Resonance Spectroscopy is feasible within 2 minutes. Interpretation. Using the presented fast method, water content can be determined within a couple of minutes in animal experiments as well as in the daily clinical practice.
Magnetic Resonance in Medicine, 1997
Therapeutic approaches to cerebral edema require an understanding of both the magnitude and location of changes in brain water content. It is desirable to have a sensitive, accurate means of measuring brain water noninvasively so that effective therapies for cerebral edema in stroke, head trauma, and other conditions can be investigated. In this work, a three-dimensional magnetic resonance imaging technique that is able to provide both spin density and Tl simultaneously is described. This method was used to quantitate regional changes in brain water content in a rat model of focal cerebral ischemia. Brain water contents estimated from both relative spin density and relative T, measurements made in vivo were compared with ex vivo measurements of relative tissue water content based on the wet-dry technique. Correlation coefficients of 0.95 and 0.98 were obtained between the wet-dry measurements and magnetic resonance measurements of T1 and spin density, respectively. Notably, the slope of the relationship between Tl and tissue water content changed dramatically after the injection of a paramagnetic contrast agent while precontrast and postcontrast spin density measurements remained essentially invariant. In addition, a plot of absolute spin density (obtained by normalizing spin density from agar gelatin phantoms of different water contents to the spin density of a sample of 100% water) was linearly related to wet-dry measurements with a slope of 0.99 (R2 = 0.99).
Inverse correlation of fluctuations of cerebral blood and water concentrations in humans
European Physical Journal Plus, 2021
Near-infrared spectroscopy (fNIRS) measures concentrations of oxygenated (HbO) and deoxygenated (HbR) hemoglobin in the brain. Recently, we demonstrated its potential also for measuring concentrations of cerebral water ( \hbox {cH}_{2}\hbox {O}).WeperformedfNIRSmeasurementsduringresttostudyfluctuationsinconcentrationsof). We performed fNIRS measurements during rest to study fluctuations in concentrations of).WeperformedfNIRSmeasurementsduringresttostudyfluctuationsinconcentrationsof\hbox {cH}_{2}\hbox {O},HbOandHbRin33well−restedhealthycontrolsubjects(HC)and18acutelysleep−deprivedHC.Resting−statefNIRSsignalwasfilteredinfull−band,cardiac,respiratory,low−,andvery−low−frequencybands.ThesumofHbOandHbRconstitutestheregionalcerebralbloodvolume(CBV).CBVand, HbO and HbR in 33 well-rested healthy control subjects (HC) and 18 acutely sleep-deprived HC. Resting-state fNIRS signal was filtered in full-band, cardiac, respiratory, low-, and very-low-frequency bands. The sum of HbO and HbR constitutes the regional cerebral blood volume (CBV). CBV and,HbOandHbRin33well−restedhealthycontrolsubjects(HC)and18acutelysleep−deprivedHC.Resting−statefNIRSsignalwasfilteredinfull−band,cardiac,respiratory,low−,andvery−low−frequencybands.ThesumofHbOandHbRconstitutestheregionalcerebralbloodvolume(CBV).CBVand\hbox {cH}_{2}\hbox {O}concentrationswereanalyzedviatemporalcorrelationandphasesynchrony.Fluctuationinconcentrationsofconcentrations were analyzed via temporal correlation and phase synchrony. Fluctuation in concentrations ofconcentrationswereanalyzedviatemporalcorrelationandphasesynchrony.Fluctuationinconcentrationsof\hbox {cH}_{2}\hbox {O}andCBVwasstronglyanti−correlatedacrossallfrequencybandsinbothfrontalandparietalcortices.Fluctuationinconcentrationsofand CBV was strongly anti-correlated across all frequency bands in both frontal and parietal cortices. Fluctuation in concentrations ofandCBVwasstronglyanti−correlatedacrossallfrequencybandsinbothfrontalandparietalcortices.Fluctuationinconcentrationsof{\hbox {cH}}_{2}{\hbox {O}}$$ and C...
In vivo water quantification in mouse brain at 9.4 Tesla in a vasogenic edema model
Magnetic Resonance in Medicine, 2001
The aim of our study was to establish a simple in vivo method for water quantification in vasogenic edema, and provide data on imaging of mouse brain at 9.4 Tesla. Apparent T 1 and spin density values determined by MRI were found to strongly correlate with the gravimetric water content of mouse brain undergoing cold injury. Using a two-point calibration line between the spin density values for pure water and cortex of mouse brain, as well as the corresponding water contents in vivo, water could be quantified with satisfactory accuracy. Magn Reson Med 46: 1246 -1249, 2001.
Magnetic Resonance Imaging, 2013
An efficient method for obtaining longitudinal relaxation time (T1) maps is based on acquiring two spoiled gradient recalled echo (SPGR) images in steady states with different flip angles, which has also been extended, with additional acquisitions, to obtain a tissue water content (M0) map. Several factors, including inhomogeneities of the radio-frequency (RF) fields and low signalto-noise ratios may negatively affect the accuracy of this method and produce systematic errors in T1 and M0 estimations. Thus far, these limitations have been addressed by using additional measurements and applying suitable corrections; however, the concomitant increase in scan time is undesirable for clinical studies. In this note, a modified dual-acquisition SPGR method based on an optimization of the sequence formulism is presented for good and reliable M0 mapping with an isotropic spatial resolution of 1×1×1 mm 3 that covers the entire human brain in 6:30 min. A combined RF transmit/receive map is estimated from one of the SPGR scans and the optimal flip angles for M0 map are found analytically. The method was successfully evaluated in eight healthy subjects producing mean M0 values of 69.8% (in white matter) and 80.1% (in gray matter) that are in good agreement with those found in the literature and with high reproducibility. The mean value of the resultant voxel-based coefficients-of-variation was 3.6%.
Measuring the local electrical conductivity of human brain tissue
Journal of Applied Physics
The electrical conductivities of freshly excised brain tissues from 24 patients were measured. The diffusion-MRI of the hydrogen nuclei of water molecules from regions that were subsequently excised was also measured. Analysis of these measurements indicates that differences between samples' conductivities are primarily due to differences of their densities of solvated sodium cations. Concomitantly, the sample-to-sample variations of their diffusion constants are relatively small. This finding suggests that non-invasive in-vivo measurements of brain tissues' local sodium-cation density can be utilized to estimate its local electrical conductivity. V
MR-visible water content in human brain: A proton MRS study
Magnetic Resonance Imaging, 1994
In vivo measurement of metabolite concentrations in the human brain by means of proton-MRS contributes significantly to the clinical evaluation of patients with diseases of the brain. The fully relaxed water signal has been proposed as an internal standard for calibration of the MRS measurements. The major drawbacks are the necessity to make the assumptions that the water concentration in the brain and that all tissue water is MR-visible. A number of in vivo measurements were carried out to estimate the concentration of MR-visible water in the brain of healthy volunteers divided into four age groups: newborn (O-23 days), adolescents (10-W yr), adults (22-28 yr), and elderly people (60-74 yr). The examinations were carried out using a Siemens Helicon SP 63/84 MR-scanner operating at 1.5 T. Except for the newborn, four regions were studied in each subject using stimulated echo (STEAM) sequences without water suppression. In vitro measurements on a standard phantom were used for calibration. The calculated water concentrations ranged between 35.8 and 39.6 (mean 36.9) mol-[kg wet weight]-' in the three groups, whereas it was 51.5 mol.[kg wet weight]-' in the newborn, p < .Ol. The observed water concentration of neither the four regions nor of the three oldest age groups were significantly different. Comparisons between the water concentrations measured and those expected based on estimation of the content of grey and white matter in the region of interest from Tt-weighted images and biochemical data published, suggest that only a small fraction (<5%) of the tissue water may be MR-invisible. The study of healthy volunteers thus shows that errors introduced by using the unsaturated water signal for calibration are less than lo%, which is comparable to expected errors when other calibration procedures are used under similar measurement conditions.
Brain electrical impedance at various frequencies: the effect of hypoxia
The 26th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2004
Non-invasive multi-frequency measurements of transcephalic impedance, both reactance and resistance, can efficiently detect cell swelling of brain tissue and can be used for early detection of threatening brain damage. We have performed experiments on piglets to monitor transcephalic impedance during hypoxia. The obtained results have confirmed the hypothesis that changes in the size of cells modify the tissue impedance. During tissue inflammation after induced hypoxia, cerebral tissue exhibits changes in both reactance and resistance. Those changes are remarkably high, up to 71% over the baseline, and easy to measure especially at certain frequencies. A better understanding of the electrical behaviour of cerebral tissue during cell swelling would lead us to develop effective non-invasive clinical tools and methods for early diagnosis of cerebral edema and brain damage prevention.