Biomedical subjects

V A Magnotta

Publications and source records attributed to V A Magnotta.

At least 19 recordsLinked to original sources

PubMed2001

Effects of olanzapine on cerebellar functional connectivity in schizophrenia measured by fMRI during a simple motor task.

BACKGROUND: According to current theories, schizophrenia results from altered connectivity in brain circuits for fundamental cognitive operations. Consequently, the poorly understood mechanisms of neuroleptic treatment may be explainable by altered functional interactions within such networks. The 'cognitive dysmetria' model hypothesizes that one key structure in these circuits is the cerebellum. To investigate the effects of olanzapine on cerebellar functional connectivity (CFC), a seed-voxel correlation analysis (SVCA) was used in a functional magnetic resonance imaging (fMRI) study of a simple finger-tapping task. METHODS: fMRI scans were obtained from six schizophrenic patients under both drug-free and olanzapine-treated conditions and from a matched control group of six healthy subjects at corresponding time points. SVCAs were performed for anatomically and functionally standardized seed voxels in the anterior cerebellum. SVCA results were then processed by three different randomization analyses. RESULTS: The analyses revealed that olanzapine caused widespread changes of CFC, including prominent changes in prefrontal cortex and mediodorsal thalamus. Significant changes in motor structures were found after subtractions within both groups and may thus indicate repetition effects rather than drug effects. Olanzapine 'normalized' the patients' CFC patterns for the right, but not for the left cerebellum. CONCLUSION: Even for a simple motor task, olanzapine affects functional interactions between the cerebellum and many non-motor brain regions, including elements of the 'cognitive dysmetria' circuit. Altogether, our findings suggest that olanzapine has a stronger differential effect on neural activity in prefrontal cortex and thalamus than in motor structures.

Adult↗

PubMed2000

Cerebral cortex: a topographic segmentation method using magnetic resonance imaging.

Remarkable developments in magnetic resonance imaging (MRI) technology provide a broad range of potential applications to explore in vivo morphological characteristics of the human cerebral cortex. MR-based parcellation methods of the cerebral cortex may clarify the structural anomalies in specific brain subregions that reflect underlying neuropathological processes in brain illnesses. The present study describes detailed guidelines for the parcellation of the cerebral cortex into 41 subregions. Our method conserves the topographic uniqueness of individual brains and is based on our ability to visualize the three orthogonal planes, the triangulated gray matter isosurface and the three-dimensional (3D) rendered brain simultaneously. Based upon topographic landmarks of individual sulci, every subregion was manually segmented on a set of serial coronal or transaxial slices consecutively. The reliability study indicated that the cerebral cortex could be parcelled reliably; intraclass correlation coefficients for each subregion ranged from 0.60 to 0.99. The validity of the method is supported by the fact that gyral subdivisions are similar to regions delineated in functional imaging studies conducted in our center. Ultimately, this method will permit us to detect subtle morphometric impairments or to find abnormal patterns of functional activation in circumscribed cortical subregions. The description of a thorough map of regional structural and functional cortical abnormalities will provide further insight into the role that different subregions play in the pathophysiology of brain illnesses.

Cerebral Cortex↗

PubMed2000

A new method for the in vivo volumetric measurement of the human hippocampus with high neuroanatomical accuracy.

Accurate and reproducible in vivo measurement of hippocampal volumes using magnetic resonance (MR) imaging is complicated by the morphological complexity of the structure. Additionally, separation of certain parts of the hippocampus from the adjacent brain structures on MR images is sometimes very difficult. These difficulties have led most investigators to either use arbitrary landmarks or to exclude certain parts of the structure from their measurements. Based on three-dimensional MR data, we have developed a reliable in vivo volumetric measurement of the human hippocampus. In contrast to most of the previously described volumetric MR-based methods, we aimed to sample the entire hippocampal formation using its true anatomical definition. This was accomplished by relying on the capacity of the BRAINS software to simultaneously visualize in multiple planes, to "telegraph" tracings or cursor position from one plane to another, and to simultaneously rely on multispectral data from three different image sets (T1, T2, and tissue classified). The methods for identifying boundaries and measuring the hippocampal volume are described. The method has excellent reliability, sensitivity, and specificity. The method may be of use in studies of structure-function relationships in neuropsychiatric disorders such as schizophrenia, temporal lobe epilepsy, and Alzheimer's disease. Future work will use these measurements as training data for a neural net-based technique to identify the anatomical boundaries automatically.

Adolescent↗

PubMed2000

Pixel analysis of MR perfusion imaging in predicting radiation therapy outcome in cervical cancer.

The purpose of this study was to assess heterogeneity of tumor microcirculation determined by dynamic contrast-enhanced magnetic resonance (MR) imaging and its prognostic value for tumor radiosensitivity and long-term tumor control using pixel-by-pixel analysis of the dynamic contrast enhancement. Sixteen patients with advanced cervical cancer were examined with dynamic contrast-enhanced MR imaging at the time of radiation therapy. Pixel-by-pixel statistical analysis of the ratio of post- to precontrast relative signal intensity (RSI) values in the tumor region was performed to generate pixel RSI distributions of dynamic enhancement patterns. Histogram parameters were correlated with subsequent tumor control based on long-term cancer follow-up (median follow-up 4.6 years; range 3.8-5.2 years). The RSI distribution histograms showed a wide spectrum of heterogeneity in the dynamic enhancement pattern within the tumor. The quantity of low-enhancement regions (10th percentile RSI < 2.5) significantly predicted subsequent tumor recurrence (88% vs. 0%, P = 0.0004). Discriminant analysis based on both 10th percentile RSI and pixel number (reflective of tumor size) further improved the prediction rate (100% correct prediction of subsequent tumor control vs. recurrence). These preliminary results suggest that quantification of the extent of poor vascularity regions within the tumor may be useful in predicting long-term tumor control and treatment outcome in cervical cancer. J. Magn. Reson. Imaging 2000;12:1027-1033.

Aged↗

PubMed2000

An MRI-based parcellation method for the temporal lobe.

The temporal lobe has long been a focus of attention with regard to the underlying pathology of several major psychiatric illnesses. Previous postmortem and imaging studies describing regional volume reductions or perfusion defects in temporal subregions have shown inconsistent findings, which are in part due to differences in the definition of the subregions and the methodology of measurement. The development of precise reproducible parcellation systems on magnetic resonance images may help improve uniformity of results in volumetric MR studies and unravel the complex activation patterns seen in functional neuroimaging studies. The present study describes detailed guidelines for the parcellation of the temporal neocortex. It parcels the entire temporal neocortex into 16 subregions: temporal pole, heschl's gyrus, planum temporale, planum polare, superior temporal gyrus (rostral and caudal), middle temporal gyrus (rostral, intermediate, and caudal), inferior temporal gyrus (rostral, intermediate, and caudal), occipitotemporal gyrus (rostral and caudal), and parahippocampal gyrus (rostral and caudal). Based upon topographic landmarks of individual sulci, every subregion was consecutively traced on a set of serial coronal slices. In spite of the huge variability of sulcal topography, the sulcal landmarks could be identified reliably due to the simultaneous display of three orthogonal (transaxial, coronal, and sagittal) planes, triangulated gray matter isosurface, and a 3-D-rendered image. The reliability study showed that the temporal neocortex could be parceled successfully and reliably; intraclass correlation coefficient for each subregion ranged from 0.62 to 0.99. Ultimately, this method will permit us to detect subtle morphometric impairments or to find abnormal patterns of functional activation in the temporal subregions that might reflect underlying neuropathological processes in psychiatric illnesses such as schizophrenia.

Adolescent↗

PubMed2000

Visualization of subthalamic nuclei with cortex attenuated inversion recovery MR imaging.

There is a significant amount of interest in studying the thalamus because of its central location in the brain and its role as a gatekeeper to higher centers of cognition. Imaging and measuring of the individual subnuclei of the thalamus has proven extremely difficult in MR because of the contrast-to-noise (CNR) of the MR sequences used. This report describes a novel MR pulse sequence known as cortex attenuated inversion recovery (CAIR), which increases the CNR in images and allows the individual subnuclei of the thalamus to be visualized by selectively nulling the gray matter in the brain using an inversion recovery sequence with an inversion time of 700 ms at 1.5 T.

Adult↗

PubMed1999

MR microcirculation assessment in cervical cancer: correlations with histomorphological tumor markers and clinical outcome.

This article reviews the experience available to date on microcirculation assessment in cancer of the cervix including correlation studies of magnetic resonance (MR) microcirculatory parameters with histo-morphometric predictors and direct correlation with patient outcome. The data suggest that MR microcirculation parameters do not always correlate with histo-morphometric parameters, while there is evidence that MR parameters predict patients' treatment outcome. These observations raise the issue that perhaps the histo-morphometric parameters, accepted gold standards for tumor angiogenesis and prognostic factors, reflect anatomical information at a "static" single time point and may not always provide sufficient information on the "dynamic" microcirculation function of the tumor. MR microcirculation assessment reflects both anatomical and functional information and may provide this additional information on the "dynamic" angiogenic and metabolic status of a tumor. Therefore, assessment of tumor microcirculation may augment the individual risk profile in cervical cancer patients and has the potential to impact on therapy selection and treatment outcome.

Contrast Media↗

PubMed1999

Human frontal cortex: an MRI-based parcellation method.

The frontal lobe is not a single anatomical and functional brain region. Several lines of research have demonstrated that particular subregions within the frontal lobe are associated with specific motor and cognitive functions in the human being. Our main purpose is to develop a magnetic resonance image (MRI)-based parcellation method of the frontal lobe that permits us to explore plausible abnormalities in functionally relevant frontal subregions in brain illnesses. We describe a procedure using MRI for subdividing the entire frontal cortex into 11 subregions: supplementary motor area (SMA), rostral anterior cingulate gyrus (r-ACiG), caudal anterior cingulate gyrus (c-ACiG), superior cingulate gyrus (SCiG), medial frontal cortex (MFC), straight gyrus (SG), orbitofrontal cortex (OFC), precentral gyrus (PCG), superior frontal gyrus (SFG), inferior frontal gyrus (IFG), and middle frontal gyrus (MFG). Our method posits to conserve the topographic uniqueness of individual brains and is based on our ability to visualize both the three-dimensional (3D) rendered brain and the three orthogonal planes simultaneously. The reliability study for gray matter volume and surface area of each subregion was performed on a set of 10 MR scans by two raters. The intraclass R coefficients for gray matter volume of each subregion ranged between 0.86 and 0.99. We describe here a reproducible and reliable topography-based parcellation method of the frontal lobe that will allow us to use new approaches to understand the role of particular frontal cortical subregions in schizophrenia and other brain illnesses.

Brain Diseases↗

PubMed1999

Quantitative in vivo measurement of gyrification in the human brain: changes associated with aging.

Clinical observation suggests that the aging process affects gyrification, with the brain appearing more 'atrophic' with increasing age. Empirical studies of tissue type indicate that gray matter volume decreases with age while cerebrospinal fluid increases. Quantitative changes in cortical surface characteristics such as sulcal and gyral shape have not been measured, however, due to difficulties in developing a method that separates abutting gyral crowns and opens up the sulci -- the 'problem of buried cortex'. We describe a quantitative method for measuring brain surface characteristics that is reliable and valid. This method is used to define the gyral and sulcal characteristics of atrophic and non-atrophic brains and to examine changes that occur with aging in a sample of 148 normal individuals from a broad age range. The shape of gyri and sulci change significantly over time, with the gyri becoming more sharply and steeply curved, while the sulci become more flattened and less curved. Cortical thickness also decreases over time. Cortical thinning progresses more rapidly in males than in females. The progression of these changes appears to be relatively stable during midlife and to begin to progress some time during the fourth decade. Measurements of sulcal and gyral shape may be useful in studying the mechanisms of both neurodevelopmental and neurodegenerative changes that occur during brain maturation and aging.

Adolescent↗

PubMed1999

Measurement of brain structures with artificial neural networks: two- and three-dimensional applications.

PURPOSE: To evaluate the ability of an artificial neural network (ANN) to identify brain structures. This ANN was applied to postprocessed magnetic resonance (MR) images to segment various brain structures in both two- and three-dimensional applications. MATERIALS AND METHODS: An ANN was designed that learned from experience to define the corpus callosum, whole brain, caudate, and putamen. Manual segmentation was used as a training set for the ANN. The ANN was trained on two-thirds of the manually segmented images and was tested on the remaining one-third. The reliability of the ANN was compared against manual segmentations by two technicians. RESULTS: The ANN was able to identify the brain structures as readily and as well as did the two technicians. Reliability of the ANN compared with the technicians was 0.96 for the corpus callosum, 0.95 for the whole brain, 0.86 (right) and 0.93 (left) for the caudate, and 0.71 (right) and 0.88 (left) for the putamen. CONCLUSION: The ANN was able to identify the structures used in this study as well as did the two technicians. The ANN could do this much more rapidly and without rater drift. Several other cortical and subcortical structures could also be readily identified with this method.

Adult↗

PubMed1999

Severe occlusive carotid artery disease: hemodynamic assessment by MR perfusion imaging in symptomatic patients.

BACKGROUND AND PURPOSE: Cerebral hemodynamic status has been reported to influence the occurrence and outcome of acute stroke. The purpose of this study was to assess hemodynamic compromise in symptomatic patients with severe occlusive disease of the carotid artery by the use of echo-planar perfusion imaging. METHODS: Spin-echo echo-planar perfusion imaging was performed in 11 patients (two had bilateral disease) with severe stenosis or occlusion of the carotid artery who had experienced either a recent transient ischemic attack or minor stroke. Relative cerebral blood volume (rCBV) maps and relative mean transit time (rMTT) maps were generated from the time-concentration curve. Findings on T2-weighted images, angiograms, rCBV maps, and rMTT maps were compared and assessed qualitatively and quantitatively. RESULTS: Although the abnormalities on T2-weighted images were absent, minimal, and/or unrelated to the degree of stenosis or collateral circulation, rMTT maps showed much larger and more distinct perfusion abnormalities along the vascular distribution of the affected vessels in all 13 vascular territories of the 11 patients. Despite obvious abnormalities on rMTT maps, none of the patients had evidence of decreased rCBV in the affected brain tissue (increased in three, normal in eight). A statistically significant difference in rMTT values was found between the affected and unaffected brain tissue, whereas no significant difference was seen in rCBV values. CONCLUSION: Echo-planar perfusion imaging is a noninvasive and rapid method for evaluating the hemodynamics in severe occlusive carotid artery disease and the compensatory vascular changes, and it may be useful in patient management.

Adult↗

PubMed1998

Prediction of tumor control in patients with cervical cancer: analysis of combined volume and dynamic enhancement pattern by MR imaging.

OBJECTIVE: Quantitative analysis of either tumor volume or dynamic enhancement pattern using MR imaging has been reported as useful in the prediction of response to radiation therapy in cancer of the cervix. Because data for both analyses can be obtained in a single MR examination, the purpose of this study was to evaluate whether combining both analyses can further improve the efficacy of using MR imaging to predict tumor control after radiation therapy. MATERIALS AND METHODS: Twenty patients with bulky carcinomas of the cervix, stages bulky IB (n = 2), IIB (n = 6), IIIA (n = 1), IIIB (n = 9), IVA (n = 1), and recurrent (n = 1), were studied. Initial tumor volumes were calculated by outlining the area of tumor in each slice on T2-weighted images and multiplying by the slice profile. Two dynamic contrast-enhanced MR studies were obtained in each patient immediately before the start of radiation therapy and after 20-22 Gy in 2 weeks of radiation therapy. Dynamic enhancement imaging was performed at 3-sec intervals in the sagittal plane for 120 sec after rapid (9 ml/sec) i.v. injection of MR contrast agent (0.1 mmol/kg of gadoteridol) using a power injector. Time and signal intensity curves reflecting the relative signal intensity of contrast enhancement in the tumor region were generated, and the relative signal intensity of the tumor region during the early plateau phase was calculated. Median follow-up was 25 months (range, 11-35 months). RESULTS: The combined analysis did not improve the prediction rate of local recurrence in small-sized tumors, which responded well to radiation therapy regardless of their dynamic enhancement pattern. However, the combined analysis did improve the prediction rate of local recurrence in intermediate- and large-sized tumors (75% and 80%, respectively) over assessment by either volume analysis (33% and 60%, respectively) or dynamic enhancement pattern analysis (64% and 64%, respectively). The combined analysis was most useful in intermediate-sized tumors (40-99 cm3; 33% recurrence), significantly improving differentiation between high-risk (80% recurrence) and low-risk 10% recurrence) patients (p = .010). CONCLUSION: Our preliminary results suggest that the combined data of both tumor morphologic (volume) and microcirculatory (dynamic enhancement pattern) parameters allow more accurate prediction of local failure in patients with advanced cervical cancer than does each individual parameter alone. Combined data appear to have the greatest potential in patients with intermediate-sized tumors, who constitute most patients (60%) and remain a challenge for outcome prediction and management.

Adenocarcinoma↗

PubMed1997

Tumor size evaluated by pelvic examination compared with 3-D quantitative analysis in the prediction of outcome for cervical cancer.

PURPOSE: Tumor size estimated by pelvic examination (PE) is an important prognostic factor in cervical cancer treated with radiation therapy (RT). Recent histologic correlation studies also showed that magnetic resonance (MR) imaging provides highly accurate measurements of the actual tumor volume. The purpose of this study was to: (a) compare the accuracy of PE and MR in predicting outcome, and (b) correlate tumor measurements by PE versus MR. METHODS AND MATERIALS: Tumor measurements were performed prospectively in 43 patients with advanced cervical cancer. MR and PE were performed at the same time intervals: (a) at the start of RT, (b) after 20-24 Gy/2-2.5 weeks, (c) after 40-50 Gy/4-5 weeks, and (d) at follow-up (1-2 months after RT completion). PE measured tumor diameters in anteroposterior, lateral, and craniocaudal direction, and PE-derived tumor size was computed as maximum diameter, average diameter, and ellipsoid volume. MR-derived tumor size was calculated by summation of the tumor areas in each section and multiplication by the section thickness. Tumor regression during RT was calculated for each method as percentage of initial volume. The measurements were correlated with local failure and disease-free survival. Median follow-up was 29 months (range: 9-56 months). RESULTS: Prediction of local control: Overall, tumor regression rate (rapid versus slow) was more precise than the initial tumor size in the prediction of outcome. MR provided a more accurate and earlier prediction of local control (at 2-2.5 weeks, and at 4-5 weeks of RT) than PE (only at follow-up). Based on the initial tumor size, MR was also better than PE in predicting disease-free survival and local control, particularly in large (> or = 100 cm3) tumors. Size correlation: Tumor size (maximum diameter, average diameter, volume) by PE and MR did not correlate well (r = 0.51, 0.61, and 0.58, respectively). When using MR measurements as a reference, PE tended to overestimate intermediate-size (40-99 cm3) tumors. CONCLUSION: This preliminary study suggests that increased precision of tumor volume measurement leads to more accurate and earlier prediction of outcome in cervical cancer. MR tumor volumetry may be useful as an adjunct to PE in selected cases, and holds the potential to impact therapeutic decision-making.

Adenocarcinoma↗

PubMed1996

Tumor perfusion studies using fast magnetic resonance imaging technique in advanced cervical cancer: a new noninvasive predictive assay.

PURPOSE: This study investigated sequential changes in tumor blood supply using magnetic resonance (MR) perfusion imaging and assessed their significance in the prediction of outcome of patients with advanced cervical cancer. The purpose of this project was to devise a simple, noninvasive method to predict early signs of treatment failure in advanced cervical cancer treated with conventional radiation therapy. METHODS AND MATERIALS: Sixty-eight MR perfusion studies were performed prospectively in 17 patients with squamous carcinomas (14) and adenocarcinomas (3) of the cervix, Stages bulky IB (1), IIB (5), IIIA (1), IIIB (8), and IVA (1), and recurrent (1). Four sequential studies were obtained in each patient: immediately before radiation therapy (pretherapy), after a dose of 20-22 Gy/ approximately 2 weeks (early therapy), after a dose of 40-45 Gy/ approximately 4-5 weeks (midtherapy), and 4-6 weeks after completion of therapy (follow-up). Perfusion imaging of the tumor was obtained at 3-s intervals in the sagittal plane. A bolus of 0.1 mmol/kg of MR contrast material (gadoteridol) was injected intravenously 30 s after beginning image acquisition at a rate of 9 ml/s using a power injector. Time/signal-intensity curves to reflect the onset, slope, and relative signal intensity (rSI) of contrast enhancement in the tumor region were generated. Median follow-up was 8 months (range 3-18 months). RESULTS: Tumors with a higher tissue perfusion (rSI > or = 2.8) in the pretherapy and early therapy (20-22 Gy) studies had a lower incidence of local recurrence than those with a rSI of < 2.8, but this was not statistically significant (13% vs. 67%; p = 0.05). An increase in tumor perfusion early during therapy (20-22 Gy), particularly to an rSI of > or = 2.8, was the strongest predictor of local recurrence (0% vs. 78%; p = 0.002). However, pelvic examination during early therapy (20-22 Gy) commonly showed no appreciable tumor regression. The slope of the time/signal-intensity curve obtained before and during radiation therapy also correlated with local recurrence. Follow-up perfusion studies did not provide information to predict recurrence. CONCLUSION: These preliminary results suggest that two simple MR perfusion studies before and early in therapy can offer important information on treatment outcome within the first 2 weeks of radiation therapy before response is evident by clinical examination. High tumor perfusion before therapy and increasing or persistent high perfusion early during the course of therapy appear to be favorable signs. High perfusion suggests a high blood and oxygen supply to the tumor. The increase in tumor perfusion seen in some patients early during radiation therapy suggests improved oxygenation of previously hypoxic cells following early cell kill. Radiation therapy is more effective in eradicating these tumors, resulting in improved local control. Our technique may be helpful in identifying early-while more aggressive therapy can still be implemented-those patients who respond poorly to conventional radiation therapy.

Adenocarcinoma↗

PubMed1996

Usefulness of tumor volumetry by magnetic resonance imaging in assessing response to radiation therapy in carcinoma of the uterine cervix.

PURPOSE: Clinical evaluation of tumor size in cervical cancer is often difficult, and clinical signs of radiation therapy failure may not be present until well after completion of treatment. The purpose of this study is to investigate early indicators of treatment response using magnetic resonance (MR) imaging for quantitative assessment of tumor volume and tumor regression rate before, during, and after radiation therapy. METHODS AND MATERIALS: Thirty-four patients with cervical cancer Stages IB [5], IIB [8], IIIA [1], IIIB [14], IVA [3], IVB [1], and recurrent [2] were studied prospectively with four serial MR examinations obtained at the start of radiation therapy, at 2-2.5 weeks (20-24 Gy), at 4-5 weeks (40-50 Gy), and 1-2 months after treatment completion. Tumor volume was assessed by three-dimensional volumetric measurements using T2-weighted images of each MR examination. The volume regression rate was generated based on the four sequential MR studies. These findings were correlated with local control, metastasis rate, and disease-free survival. Median follow-up was 18 months (range: 9-43 months). RESULTS: The tumor regression rate after a dose of 40-50 Gy correlated significantly with treatment outcome. The actuarial 2-year disease-free survival was 88.4% in patients with tumors regressing to < 20% of the initial volume compared with 45.4% in those with > or = 20% residual (p = 0.007). The incidence of local recurrence was 9.5% (2 out of 21) and 76.9% (10 out of 13), respectively (p < 0.001). Analysis by initial tumor volume showed that this observation was valid in patients with initial volumes between 40 and 100 cm3. Analysis by FIGO stage confirmed this observation in all patients except those with Stage IB. CONCLUSION: Sequential tumor volumetry using MR imaging appears to be a sensitive measure of the responsiveness of cervical cancer to irradiation. Treatment response can be assessed as early as during the course of radiation therapy by measurement of initial tumor volume and regression rate at 40-50 Gy. In patients with large (> 40 cm3) and advanced (Stage > or = IIIA) tumors, this technique may be helpful in supplementing the clinical examination for response assessment. The identification of patients at high risk for treatment failure may ultimately lead to improved clinical outcome.

Adult↗

PubMed1996

Echo-planar FLAIR imaging in evaluation of intracranial lesions.

Fluid-attenuated inversion-recovery (FLAIR) imaging is a magnetic resonance imaging technique that improves lesion detection in the brain. This technique suppresses signal from free water in cerebrospinal fluid and maintains the hyperintense lesion contrast of T2-weighted spin-echo imaging. Unfortunately, conventional FLAIR imaging requires a long acquisition time and provides a limited number of sections. A combination of echo-planar imaging and FLAIR imaging offers the image contrast effects of FLAIR imaging and the speed of echo-planar imaging. Clinically, the echo-planar FLAIR technique is most helpful in detecting subtle, early lesions that do not enhance, such as early infarct, demyelinating disease, early infection, and trauma. The increased magnetic susceptibility effect associated with the echo-planar technique can be clinically useful in detecting subtle hemorrhage and cavernous angioma. Echo-planar FLAIR imaging is a practical and efficient means of screening the entire brain in a short time.

Brain Diseases↗

PubMedDate not supplied

Peripheral nerve stimulation in a whole-body echo-planar imaging system.

Echo-planar techniques in MRI use a rapidly oscillating frequency-encoding gradient with the potential to produce peripheral nerve stimulation. To evaluate the incidence, type, and location of stimulation in a commercial whole-body scanner, we studied two groups: (a) 173 consecutive individuals scanned by echo-planar imaging for other purposes and (b) seven subjects who were scanned with an extensive set of 36 echo-planar sequences (with prompting after each scan to report any peripheral nerve stimulation) to test the effects of various parameters. Although only 5% of group A reported symptoms of peripheral nerve stimulation, all in group B experienced some type of stimulation, dependent primarily on direction of the oscillating gradient and location of the body within the gradient coil. Maximum stimulation typically occurred 30 to 40 cm from isocenter in the region of maximum dB/dt. Generally, y gradients produced truncal stimulation, and x gradients produced stimulation in the head. When hands were clasped over the abdomen, a tingling in the hands occasionally was felt. Patients should be instructed to keep their hands apart.

Adult↗

PubMedDate not supplied

Improving tissue classification in MRI: a three-dimensional multispectral discriminant analysis method with automated training class selection.

PURPOSE: To improve the reliability, accuracy, and computational efficiency of tissue classification with multispectral sequences [T1, T2, and proton density (PD)], we developed an automated method for identifying training classes to be used in a discriminant function analysis. We compared it with a supervised operator-dependent method, evaluating its reliability and validity. We also developed a fuzzy (continuous) classification to correct for partial voluming. METHOD: Images were obtained on a 1.5 T GE Signa MR scanner using three pulse sequences that were co-registered. Training classes for the discriminant analysis were obtained in two ways. The operator-dependent method involved defining circular ROIs containing 5-15 voxels that represented "pure" samples of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF), using a total of 150-300 voxels for each tissue type. The automated method involved selecting a large number of samples of brain tissue with sufficiently low variance and randomly placed throughout the brain ("plugs"), partitioning these samples into GM, WM, and CSF, and minimizing the amount of variance within each partition of samples to optimize its "purity." The purity of the plug was estimated by calculating the variance of 8 voxels in all modalities (T1, T2, and PD). We also compared "sharp" (discrete) measurements (which classified tissue only as GM, WM, or CSF) and "fuzzy" (continuous) measurements (which corrected for partial voluming by weighting the classification based on the mixture of tissue types in each voxel). RESULTS: Reliability was compared for the operator-dependent and automated methods as well as for the fuzzy versus sharp classification. The automated sharp classifications consistently had the highest interrater and intrarater reliability. Validity was assessed in three ways: reproducibility of measurements when the same individuals were scanned on multiple occasions, sensitivity of the method to detecting changes associated with aging, and agreement between the automated segmentation values and those produced through expert manual segmentation. The sharp automated classification emerged as slightly superior to the other three methods according to each of these validators. Its reproducibility index (intraclass r) was 0.97, 0.98, and 0.98 for total CSF, total GM, and total WM, respectively. Its correlations with age were 0.54, -0.61, and -0.53, respectively. Its percent agreement with the expert manually segmented tissue for the three tissue types was 93, 90, and 94%, respectively. CONCLUSION: Automated identification of training classes for discriminant analysis was clearly superior to a method that required operator intervention. A sharp (discrete) classification into three tissue types was also slightly superior to one that used "fuzzy" classification to produce continuous measurements to correct for partial voluming. This multispectral automated discriminant analysis method produces a computationally efficient, reliable, and valid method for classifying brain tissue into GM, WM, and CSF. It corrects some of the problems with reliability and computational inefficiency previously observed for operator-dependent approaches to segmentation.

Adult↗