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PubMed1983

Aspects of blood-brain barrier in clinical brain imaging.

The blood-brain barrier (BBB) is selectively permeable and shows a wide range of permeability to various substances in health and becomes generally permeable to all small molecules in almost all disease states. The capillary bed in brain (the BBB) is uniquely impermeable to many polar substances. The mechanism by which the capillary bed is maintained in this state is unknown, but may be an astrocytic function. In most major neuropathology, the BBB is lost because these unique structural features creating the BBB come to resemble the permeable capillaries in other tissues. Early isotopic brain scans using polar isotopes such as 99m-TcO4 depend upon this increased permeability to demonstrate focal lesions. Positron emission tomography has made it possible to label interesting biochemical substrates allowing the tracing of certain aspects of regional brain metabolic activity. The equipment required is very expensive, but single photon tomography using lipophilic tracers is much less expensive and provides tomographic representation of regional blood flow. To penetrate a healthy BBB requires that radiotracers either be lipid soluble or have an affinity for one of the selective BBB transport systems.

Astrocytes↗

PubMed1999

Functional brain imaging during anesthesia in humans: effects of halothane on global and regional cerebral glucose metabolism.

BACKGROUND: Propofol and isoflurane anesthesia were studied previously with functional brain imaging in humans to begin identifying key brain areas involved with mediating anesthetic-induced unconsciousness. The authors describe an additional positron emission tomography study of halothane's in vivo cerebral metabolic effects. METHODS: Five male volunteers each underwent two positron emission tomography scans. One scan assessed awake-baseline metabolism, and the other scan assessed metabolism during halothane anesthesia titrated to the point of unresponsiveness (mean +/- SD, expired = 0.7+/-0.2%). Scans were obtained using a GE2048 scanner and the F-18 fluorodeoxyglucose technique. Regions of interest were analyzed for changes in both absolute and relative glucose metabolism. In addition, relative changes in metabolism were evaluated using statistical parametric mapping. RESULTS: Awake whole-brain metabolism averaged 6.3+/-1.2 mg x 100 g(-1) x min(-1) (mean +/- SD). Halothane reduced metabolism 40+/-9% to 3.7+/-0.6 mg x 100 g(-1) x min(-1) (P< or =0.005). Regional metabolism did not increase in any brain areas for any volunteer. The statistical parametric mapping analysis revealed significantly less relative metabolism in the basal forebrain, thalamus, limbic system, cerebellum, and occiput during halothane anesthesia. CONCLUSIONS: Halothane caused a global whole-brain metabolic reduction with significant shifts in regional metabolism. Comparisons with previous studies reveal similar absolute and relative metabolic effects for halothane and isoflurane. Propofol, however, was associated with larger absolute metabolic reductions, suppression of relative cortical metabolism more than either inhalational agent, and significantly less suppression of relative basal ganglia and midbrain metabolism.

Anesthesia, General↗

PubMedDate not supplied

[Brain imaging in schizophrenia -- especially by Computed Tomography].

The evaluation of the contribution of structural and functional brain imaging to the contemporary understanding of schizophrenia is presented. The studies of schizophrenia using, especially, Computed Tomography (CT) and also Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET), are reviewed and their contribution to current theories of the pathogenesis of schizophrenia are discussed. This literature is reviewed for clinical, biochemical and environmental correlates of structural brain abnormalities in schizophrenia. The results are summarized and the critical questions raised by these studies are outlined. Future studies in this field are needed to yield current insight into the pathophysiology of schizophrenia.

Biogenic Monoamines↗

PubMed1992

SPECT brain imaging in Alzheimer's disease during treatment with oral tetrahydroaminoacridine and lecithin.

Quantitative SPECT brain imaging was performed in five normal subjects and in six ambulatory patients with Alzheimer's disease before the initiation of treatment with tetrahydroaminoacridine (THA) and lecithin. Imaging data were acquired with a single-head SPECT camera and a high-resolution collimator after the intravenous injection of 5 mCi of (p,5n) I-123 IMP. Uptake per pixel in 28 regions of interest in the transverse projection of each study was normalized to uptake per pixel in the cerebellum. Perfusion in the patients with Alzheimer's disease was decreased compared with that of the subjects. Perfusion was decreased greater than 2 SD below the mean in the posterior parietal cortex of 5/6 patients, in the temporal cortex of 3/6 patients, and in the frontal cortex of 2/6 patients with Alzheimer's disease. SPECT imaging was repeated in the six patients after initial titration to peak therapy with oral THA (75 to 200mg per day). The same abnormalities were again seen in the same patients. No dramatic clinical or behavioral change in cerebral perfusion was observed from initial treatment of Alzheimer's disease with THA and lecithin.

Administration, Oral↗

PubMed1990

Automatic detection of white matter lesions in magnetic resonance brain images.

A new approach to automating radiologic diagnosis is described and tested in a system that locates multiple sclerosis lesions in magnetic resonance human brain images. This approach uses a step-by-step procedure, where the most obvious features in the images are identified first, and used to calibrate the application of the next step, until the desired features are identified. The approach stresses testing on a large number of images of the same type, and exploiting the special characteristics of this type of images. The system was designed with the variations of the various image parameters in mind, to ensure its reliability. New low-level methods of high reliability have been developed for segmenting images. A new geometric modeling method which tolerates the variability of biological structures is used to encode anatomic knowledge. The system and its components have been tested on 1132 images from 17 patients, with very good results.

Brain↗

PubMed2005

Optimized RF excitation for anatomical brain imaging of the occipital lobe using the 3D MDEFT sequence and a surface transmit coil.

An RF excitation scheme is presented for anatomical imaging of occipital brain areas at 3T using the 3D modified driven equilibrium Fourier transform (MDEFT) sequence and a transmit-receive surface coil. Surface coils operated in the transmit mode usually display a high B(1) inhomogeneity. This causes variations of the flip angle and impairs fat saturation, resulting in blurring, signal losses, and artifacts due to high scalp intensities. A composite binomial pulse with one spectral component for water selective excitation and one spatial component for B(1) inhomogeneity compensation is presented. It is shown experimentally that the pulse prevents image blurring and reduces the scalp signal considerably. The total pulse duration of only 2.4 ms is compatible with the relatively short repetition times (TRs) required for MDEFT imaging. The method is particularly useful for certain applications in neuroimaging that require technical equipment that is too large for standard coils or should not be exposed to RF fields.

Algorithms↗

PubMed1992

Geometry driven multimodality matching of brain images.

Clinical diagnosis, as well as therapy planning and evaluation, are increasingly supported by multimodal images. There are many instances desiring integration of the information obtained by various imaging devices. This paper describes a new approach to match images of different modalities. Differential operators are used in combination with Gaussian blurring to extract geometric features from the images that correspond to similar structures. The resulting 'feature' images may be used with existing matching techniques that minimize the distance between the features in the images to be matched. Our first application of this new approach concerns matching of MRI and CT brain images. The so-called L upsilon upsilon operator produces a ridge-like feature image from which in CT and MRI the center curve of the cranium is easily extracted. First results of this operator's performance in matching tasks are shown. Another promising operator is the 'umbilicity' operator, which is presented in combination with SPECT images.

Brain↗

PubMed2001

Automated PET attenuation correction model for functional brain imaging.

UNLABELLED: The failure to compensate for subject motion between attenuation correction scans and emission scans precludes the optimization of functional brain imaging techniques. We have developed an automated method for attenuation correction that compensates for subject motion by deriving each set of correction factors from the corresponding emission study. METHODS: The technique consists of generation of an estimated skull image by filtered backprojection of the reciprocal of an emission sinogram; estimation of the thickness and radius of the skull on profiles extracted from the image; scaling the radius and thickness values to generate a model of the brain, skull, and scalp; and assignment of attenuation coefficients to the head model for generation of attenuation correction factors. Values for scale factors and tissue attenuation coefficients were determined empirically by fitting the emission-derived head model to measured transmission data in five subjects using nonlinear regression (group A). The average model parameters, across five datasets (group A), were then used to generate attenuation maps for five independent emission studies (group B). Mean-squared-error values were calculated between the measured transmission data and the two model groups. For comparison, mean squared error values were calculated between the measured transmission data and homogeneous ellipses that were manually fitted to emission images. RESULTS: The difference between the mean squared error for groups A and B was not significant (P>0.8), indicating that model parameters from a small group can be used for other subjects without further fitting. The mean squared error for the automated method was significantly lower than that of the ellipse method (P<0.001). The method reduced emission image variance, resulting in a higher peak Z value in activation images. The elimination of measured transmission scans resulted in a reduction in scan time ( approximately 15 min) and radiation exposure ( approximately 0.5-1.6 mrem). CONCLUSION: We have developed an automated attenuation correction method that compensates for subject motion between scans, accurately reproduces the characteristics of the head, and eliminates the use of measured transmission data to reduce scan duration, statistical noise propagation, and radiation dose.

Acoustic Stimulation↗

PubMed1993

Functional brain imaging in late-life depression and dementia.

Studies utilizing advanced scanning technologies suggest that brain imaging may have a role in the differential diagnosis of some common neuropsychiatric disorders. In subjects with dementia of the Alzheimer type (DAT), widespread cortical reductions in glucose metabolism and blood flow have been described, with predominant involvement of the temporal and parietal lobes. The primary sensory areas and subcortical regions are relatively spared. When a "patchy" pattern of reductions in cerebral blood flow and metabolism is associated with clinical dementia, a vascular etiology should be suspected. Major depression in the elderly is associated with reductions in whole brain glucose metabolic rates comparable in magnitude with those described in DAT. Relatively distinctive patterns of flow and metabolism also are seen in frontal-temporal dementia and Parkinson's disease with dementia.

Age Factors↗

PubMed2001

Evaluation of cognitive performance in the heat by functional brain imaging and psychometric testing.

Military operations in tropical environments have imposed a significant challenge to the Australian Defence Forces (ADF). The hot and humid conditions are known to cause debilitating effects on soldiers deployed to northern regions of Australia, with the consequence that the effectiveness and efficiency of operations are severely compromised. While the adverse effects of thermal stress on soldiers' physiological capability are well established, this has not been confirmed for cognitive performance. A select range of psychometric tests were administered and functional brain electrical activity imaging was performed to investigate the impact of thermal stress on cognitive performance. The brain electrical activity of subjects was measured while undertaking a range of cognitive tasks. Steady State Probe Topography (SSPT), a novel brain imaging technology, was employed to monitor the changes in regional brain activity and neural processing speed of subjects under thermal stress. The psychometric test batteries included the following tasks; Rey Auditory Verbal Learning Test; Inspection Time; Digit Span test; a spatial working memory task; and the AX-continuous performance task. These tasks measure a range of cognitive processes including attention, memory, verbal learning, information processing and concentration. The functional brain imaging provided topographical information, which showed changes in electrical activity in response to thermal stress during cognitive performance. These changes in brain electrical activity and neural speed induced by thermal stress may help to identify the type of cognitive functions that are likely to be impaired under operational conditions. Results indicated that subjects experienced increasing cardiovascular strain through thermally neutral to thermally straining conditions. The results from the psychometric test battery showed some promising effects given the small sample size including deficits in working memory, in information retention and in information processing. There was also marked differences in the electrical responses of the brain when subjects were thermally strained. The Steady-State Visual Evoked Potential recordings showed an increase in amplitude and a decrease in latency, suggesting an increase in the utilisation of neural resources or effort by subjects to maintain the same level of performance as under thermally neutral conditions. The data are suggestive of the high sensitivity of brain imaging techniques with high temporal resolution to identify important decrements in cognitive performance in hostile environments.

Adult↗

PubMed2005

Anatomical and functional brain imaging using high-resolution echo-planar spectroscopic imaging at 1.5 Tesla.

High-resolution echo-planar spectroscopic imaging (EPSI) of water resonance (i.e. without water suppression) is proposed for anatomic and functional imaging of the human brain at 1.5 T. Water spectra with a resolution of 2.6 Hz and a bandwidth of 333 Hz were obtained in small voxels (1.7 x 1.7 x 3 mm3) across a single slice. Although water spectra appeared Lorentzian in most of the voxels in the brain, non-Lorentzian broadening of the water resonance was observed in voxels containing blood vessels. In functional experiments with a motor task, robust activation in motor cortices was observed in high-resolution T2* maps generated from the EPSI data. Shift of the water resonance frequency occurred during neuronal activation in motor cortices. The activation areas appeared to be more localized after excluding the voxels in which the lineshape of the water resonance had elevated T2* and became more non-Lorentzian during the motor task. These preliminary results suggest that high-resolution EPSI is a promising tool to study susceptibility-related effects, such as BOLD contrast, for improved anatomical and functional imaging of the brain.

Adult↗

PubMed2006

[Non-linear registration of MR brain images integrated with machine learning].

This paper presents a machine learning method to select best geometric features for deformable brain registration for each brain location. By incorporating those learned best attribute vector into the framework of HAMMER registration algorithm, The accuracy has increased by about 10% in estimating the simulated deformation fields. At the same time, on real MR brain images, we have found a great deal of improvement of registration in cortical regions.

Algorithms↗

PubMed2005

Imaging brain activity with voltage- and calcium-sensitive dyes.

This paper presents three examples of imaging brain activity with voltage- or calcium-sensitive dyes and then discusses the methodological aspects of the measurements that are needed to achieve an optimal signal-to-noise ratio. Internally injected voltage-sensitive dye can be used to monitor membrane potential in the dendrites of invertebrate and vertebrate neurons in in vitro preparations. Both invertebrate and vertebrate ganglia can be bathed in voltage-sensitive dyes to stain all of the cell bodies in the preparation. These dyes can then be used to follow the spike activity of many neurons simultaneously while the preparations are generating behaviors. Calcium-sensitive dyes that are internalized into olfactory receptor neurons in the nose will, after several days, be transported to the nerve terminals of these cells in the olfactory bulb. There they can be used to measure the input from the nose to the bulb. Three kinds of noise are discussed. a. Shot noise from the random emission of photons from the preparation. b. Vibrational noise from external sources. c. Noise that occurs in the absence of light, the dark noise. Three different parts of the light measuring apparatus are discussed: the light sources, the optics, and the cameras. The major effort presently underway to improve the usefulness of optical recordings of brain activity are to find methods for staining individual cell types in the brain. Most of these efforts center around fluorescent protein sensors of activity.

Action Potentials↗

PubMed1996

Spatial pattern analysis of functional brain images using partial least squares.

This paper introduces a new tool for functional neuroimage analysis: partial least squares (PLS). It is unique as a multivariate method in its choice of emphasis for analysis, that being the covariance between brain images and exogenous blocks representing either the experiment design or some behavioral measure. What emerges are spatial patterns of brain activity that represent the optimal association between the images and either of the blocks. This process differs substantially from other multivariate methods in that rather than attempting to predict the individual values of the image pixels, PLS attempts to explain the relation between image pixels and task or behavior. Data from a face encoding and recognition PET rCBF study are used to illustrate two types of PLS analysis: an activation analysis of task with images and a brain-behavior analysis. The commonalities across the two analyses are suggestive of a general face memory network differentially engaged during encoding and recognition. PLS thus serves as an important extension by extracting new information from imaging data that is not accessible through other currently used univariate and multivariate image analysis tools.

Algorithms↗

PubMed2000

A new nitroxyl-probe with high retention in the brain and its application for brain imaging.

In order to estimate free radical reactions and image them in the brain of living animals, a nitroxyl spin-probe, carboxy-PROXYL acetoxymethyl ester (CxP-AM) was newly synthesized. CxP-AM was designed to be hydrolyzed by esterase, but not by lipase, so that it would pass through the blood-brain barrier and be retained in the cytosolic phase of parenchymal cells in the brain after intravenous injection. The pharmacokinetics of CxP-AM was compared with those of carboxy-PROXYL (CxP) and its methyl ester (CxP-M). Carboxyl esterase almost completely hydrolyzed CxP-AM within 3 min. After intravenous injection, the brain retained 1.8 times more CxP-AM than CxP-M, and retained it for more than 30 min. Electron spin resonance computed tomographic (ESR-CT) imaging of CxP-AM in the heads of mice produced marked contrast in the encephalon region, while CxP was distributed only in the extracranial region and CxP-M was distributed in both regions, confirming the pharmacokinetics of CxP-AM. The decay rate of CxP-AM determined with time-resolved ESR-CT imaging was different in the two brain regions, suggesting regional differences in the total reducing capability. CxP-AM should become a powerful probe for the investigation and diagnosis of free radical reactions and their imaging in the brain.

Animals↗

PubMed2002

Design and performance of the UCLH mark 1b 64 channel electrical impedance tomography (EIT) system, optimized for imaging brain function.

The UCLH Mark 1b is a portable EIT system that can address up to 64 electrodes, which has been designed for imaging brain function with scalp electrodes. It employs a single impedance-measuring circuit and multiplexer so that electrode combinations may be addressed flexibly using software. It operates in the relatively low frequency band between 225 Hz and 77 kHz, as lower frequencies produce larger changes during brain activity, and has a videocassette-sized headbox on a lead 10 m long, connected to a base box the size of a video recorder, and notebook PC, so that recordings may be made in ambulant subjects. Its performance was assessed using a resistor-capacitor network, and two saline-filled tanks-a cylindrical Perspex one and a latex one which contained a human skull. System signal-to-noise ratio was better than 50 dB and the maximum reciprocity error less than 10% for most frequencies. The CMMR was better than 80 dB at 38 kHz and a sponge, 20 mm across, which caused a local 12% impedance increase, was correctly localized in images. This suggests that the system has adequate performance to image impedance changes of 5-50% known to occur in the brain during normal activity, epilepsy or stroke; clinical trials to image these conditions are in progress.

Brain↗

PubMed1996

Comparison of the BOLD- and EPISTAR-technique for functional brain imaging by using signal detection theory.

Two magnetic resonance imaging techniques, BOLD (blood oxygenation level dependent) and EPISTAR (echo-planar imaging and signal targeting with alternating radio-frequency), were compared for functional brain imaging. Ten volunteers were imaged performing a sequential finger to thumb opposition task alternating with no movement conditions. Techniques were compared using variance maps and signal detection theory (ROC analysis). True positive activation in regions of interest with expected task-dependent signal changes were computed versus false activation rates in regions in which no activation was expected. D-prime coefficients were calculated for each comparison and statistically compared using a paired t test. Activation in the perirolandic region was seen in all volunteers with both techniques. There was no significant difference for the d-prime between BOLD and EPISTAR. These results indicate that based on a different physiologic principle, EPISTAR is an alternative to BOLD to perform fMRI with similar results.

Adult↗

PubMed1997

Magnetic resonance brain imaging in women with obsessive-compulsive disorder and trichotillomania.

Magnetic resonance imaging of the brain was undertaken in women with obsessive-compulsive disorder (n = 13), trichotillomania (n = 17), and healthy controls (n = 12). Caudate volume and ventricular-brain ratio (VBR) (variables that have previously been highlighted as abnormal in studies of OCD) were compared in the three subject groups and were correlated with neuropsychological and neurological soft sign findings. No significant differences were found between women with OCD, trichotillomania and normal controls on caudate volume or VBR. Decreased left caudate volume was significantly correlated with impairment on neuropsychological testing and with increased neurological soft signs. The negative findings here may indicate that in women with OCD and related disorders structural brain abnormalities are less obvious or less common than in men with these conditions, or they may reflect inadequate sensitivity of the brain measures employed.

Adult↗