Ponnada A Narayana

Publications (98)314.59 Total impact

• Article: Glatiramer acetate in primary progressive multiple sclerosis: results of a multinational, multicenter, double-blind, placebo-controlled trial.

  Jerry S Wolinsky, Ponnada A Narayana, Paul O'Connor, Patricia K Coyle, Corey Ford, Kenneth Johnson, Aaron Miller, Lillian Pardo, Shaul Kadosh, David Ladkani
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  ABSTRACT: To determine whether glatiramer acetate (GA) slows accumulation of disability in primary progressive multiple sclerosis. A total of 943 patients with primary progressive multiple sclerosis were randomized to GA or placebo (PBO) in this 3-year, double-blind trial. The primary end point was an intention-to-treat analysis of time to 1- (entry expanded disability status scale, 3.0-5.0) or 0.5-point expanded disability status scale change (entry expanded disability status scale, 5.5-6.5) sustained for 3 months. The trial was stopped after an interim analysis by an independent data safety monitoring board indicated no discernible treatment effect on the primary outcome. Intention-to-treat analyses of disability and magnetic resonance imaging end points were performed. There was a nonsignificant delay in time to sustained accumulated disability in GA- versus PBO-treated patients (hazard ratio, 0.87 [95% confidence interval, 0.71-1.07]; p = 0.1753), with significant decreases in enhancing lesions in year 1 and smaller increases in T2 lesion volumes in years 2 and 3 versus PBO. Post hoc analysis showed that survival curves for GA-treated male patients diverged early from PBO-treated male subjects (hazard ratio, 0.71 [95% confidence interval, 0.53-0.95]; p = 0.0193). The trial failed to demonstrate a treatment effect of GA on primary progressive multiple sclerosis. Both the unanticipated low event rate and premature discontinuation of study medication decreased the power to detect a treatment effect. Post hoc analysis suggests GA may have slowed clinical progression in male patients who showed more rapid progression when untreated.
  Annals of Neurology 02/2007; 61(1):14-24. · 11.09 Impact Factor
• Article: Diffusion tensor imaging in MDMA users and controls: association with decision making.

  F Gerard Moeller, Joel L Steinberg, Scott D Lane, Matthew Buzby, Alan C Swann, Khader M Hasan, Larry A Kramer, Ponnada A Narayana
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  ABSTRACT: Diffusion Tensor Imaging (DTI) may provide information regarding effects of 3,4-methylenedioxymethamphetamine (MDMA) use on brain structure. Twelve MDMA users and 20 healthy controls underwent whole brain DTI data acquisition. Fractional anisotropy (FA), mean diffusivity (D(av)), and longitudinal (lambda(1)) and transverse (lambda(T)) diffusivities were compared between MDMA users and controls in 6 regions of the corpus callosum. MDMA users also completed the Barratt Impulsiveness Scale (BIS), and a subset of subjects completed the Iowa Gambling Task (IGT). Results showed significantly smaller lambda(1) in the rostral body of the corpus callosum in MDMA users, with no differences between groups on lambda(T), FA, or D(av). MDMA users also had a significantly higher BIS nonplanning score and greater preference for disadvantageous choices on the IGT. There was a significant positive correlation between lambda(1) in the rostral body of the corpus callosum and advantageous choices on the IGT. Further research on the etiology of these findings is warranted.
  The American Journal of Drug and Alcohol Abuse 02/2007; 33(6):777-89. · 1.55 Impact Factor
• Article: Measurement of DTI metrics in hemorrhagic brain lesions: possible implication in MRI interpretation.

  Mohammad Haris, Rakesh K Gupta, Nuzhat Husain, Khader M Hasan, Mazhar Husain, Ponnada A Narayana
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  ABSTRACT: To understand the biological basis of possible mechanisms responsible for increased fractional anisotropy (FA) in different stages of hemorrhage and hemorrhagic brain lesions. A total of 19 patients with cerebral hemorrhage (CH), five patients with hemorrhagic infarct (HI), and nine patients with hemorrhagic brain tumor (HBT) were prospectively evaluated with diffusion tensor imaging (DTI) and the FA and mean diffusivity (MD) was quantified. Ex vivo DTI of blood clot and histology of the blood clot and HBT were performed to interpret the temporal changes in the DTI metrics. High FA (>0.20) with low MD in the acute and early subacute stage and low FA (<0.20) with increased MD in the late subacute and chronic stage of CH and HI were observed. HBT showed high FA with low MD at all stages. In CH and HI, a significant reduction in FA (P < 0.001) with increased MD (P < 0.001) was seen in the late subacute and chronic stages compared to the acute and early subacute stages, normal white matter (NWM), and HBT. In HBT, there was no significant statistical difference in the FA values between different stages. Histology of HBT and ex vivo blood clot showed structural organization of intact red blood cells (RBCs) with fibrin mesh where the FA values were high compared to normal tissue region that is devoid of blood. Intact RBCs entangled within fibrin mesh appear to be responsible for high FA in hemorrhagic brain lesions.
  Journal of Magnetic Resonance Imaging 01/2007; 24(6):1259-68. · 2.70 Impact Factor
• Conference Proceeding: The Correction of EPI-induced Geometric Distortions and Their Evaluation.

  Guozhi Tao, Renjie He, Aziz H. Poonawalla, Ponnada A. Narayana
  Proceedings of the International Conference on Image Processing, ICIP 2007, September 16-19, 2007, San Antonio, Texas, USA; 01/2007
• Article: Functional magnetic resonance imaging in rodents: Methodology and application to spinal cord injury.

  Jaivijay Ramu, Kurt H Bockhorst, Kishore V Mogatadakala, Ponnada A Narayana
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  ABSTRACT: Functional MRI (fMRI) on spinal cord-injured rodents at 4 and 8 weeks post injury (PI) is described. The paradigm for fMRI, based on electrical stimulation of rat paws, was automated using an in-house designed microprocessor-based controller that was interfaced to a stimulator. The MR images were spatially normalized to the Paxinos and Watson atlas using publicly available digital images of the cryosections. In normal uninjured animals, the activation was confined to the contralateral somatosensory cortex. In contrast, in injured animals, extensive activation, which included structures such as ipsilateral cortex, thalamus, hippocampus, and the caudate putamen, was observed at 4 and 8 weeks PI. Quantitative cluster analysis was carried out to calculate the volumes and centers of activation in individual brain structures. Based on this analysis, significant increase in activation between 4 and 8 weeks was observed only in the ipsilateral caudate putamen and thalamus. These studies suggest extensive and ongoing brain reorganization in spinal cord-injured animals.
  Journal of Neuroscience Research 12/2006; 84(6):1235-44. · 2.74 Impact Factor
• Article: Fast quantification of proton magnetic resonance spectroscopic imaging with artificial neural networks.

  Himanshu Bhat, Balasrinivasa Rao Sajja, Ponnada A Narayana
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  ABSTRACT: Accurate quantification of the MRSI-observed regional distribution of metabolites involves relatively long processing times. This is particularly true in dealing with large amount of data that is typically acquired in multi-center clinical studies. To significantly shorten the processing time, an artificial neural network (ANN)-based approach was explored for quantifying the phase corrected (as opposed to magnitude) spectra. Specifically, in these studies radial basis function neural network (RBFNN) was used. This method was tested on simulated and normal human brain data acquired at 3T. The N-acetyl aspartate (NAA)/creatine (Cr), choline (Cho)/Cr, glutamate+glutamine (Glx)/Cr, and myo-inositol (mI)/Cr ratios in normal subjects were compared with the line fitting (LF) technique and jMRUI-AMARES analysis, and published values. The average NAA/Cr, Cho/Cr, Glx/Cr and mI/Cr ratios in normal controls were found to be 1.58+/-0.13, 0.9+/-0.08, 0.7+/-0.17 and 0.42+/-0.07, respectively. The corresponding ratios using the LF and jMRUI-AMARES methods were 1.6+/-0.11, 0.95+/-0.08, 0.78+/-0.18, 0.49+/-0.1 and 1.61+/-0.15, 0.78+/-0.07, 0.61+/-0.18, 0.42+/-0.13, respectively. These results agree with those published in literature. Bland-Altman analysis indicated an excellent agreement and minimal bias between the results obtained with RBFNN and other methods. The computational time for the current method was 15s compared to approximately 10 min for the LF-based analysis.
  Journal of Magnetic Resonance 12/2006; 183(1):110-22. · 2.14 Impact Factor
• Article: Impulsivity and BOLD fMRI activation in MDMA users and healthy control subjects.

  Ignacio H Valdes, Joel L Steinberg, Ponnada A Narayana, Larry A Kramer, Donald M Dougherty, Alan C Swann, Ernest S Barratt, Frederick Gerard Moeller
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  ABSTRACT: The correlation between scores on the Barratt Impulsiveness Scale (BIS) and activation measured by functional magnetic resonance imaging in a dorsolateral prefrontal cortical (DLPFC) activating task was examined in 15 MDMA-using subjects and 19 controls. A significant correlation between BIS scores and DLPFC activation was found, supporting a role for the DLPFC in BIS-measured impulsivity.
  Psychiatry Research 11/2006; 147(2-3):239-42. · 2.52 Impact Factor
• Article: Focal Wallerian degeneration of the corpus callosum in large middle cerebral artery stroke: serial diffusion tensor imaging.

  Rakesh K Gupta, Sona Saksena, Khader M Hasan, Atul Agarwal, Mohammad Haris, Chandra M Pandey, Ponnada A Narayana
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  ABSTRACT: To detect lesion-related focal Wallerian degeneration (WD) changes in different segments of the corpus callosum (CC) in patients with large middle cerebral arterial (MCA) territory stroke using diffusion tensor imaging (DTI). Eight patients underwent DTI scans at three different time points: six to eight weeks, 10-12 weeks, and beyond six months of stroke onset. Eight healthy age-matched controls were also scanned using the same protocol at three different time points. Region-of-interest (ROI) analysis was performed on seven segments of the CC to determine the fractional anisotropy (FA), mean diffusivity (MD), and corresponding callosal cross-sectional areas. On repeated-measures analysis of variance (ANOVA), a significant reduction in the FA values was observed from the first to the third study compared to controls, reflecting temporal degeneration in the rostrum, genu, rostral body, anterior midbody, and splenium of the CC. However, a significant temporal elevation in MD values was observed in only the rostral body and anterior midbody of the CC. This was associated with a significant region-specific reduction in the cross-sectional areas at time points beyond six months, and appears to be consistent with the loss of callosal structural components due to interruption of the cortico-callosal fibers secondary to WD. These results indicate that cortico-callosal topographical changes exhibit a significant temporal decline in observed FA values that is suggestive of cortico-callosal WD in patients with large MCA territory stroke.
  Journal of Magnetic Resonance Imaging 10/2006; 24(3):549-55. · 2.70 Impact Factor
• Article: Retrospective measurement of the diffusion tensor eigenvalues from diffusion anisotropy and mean diffusivity in DTI.

  Khader M Hasan, Ponnada A Narayana
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  ABSTRACT: A simple theoretical framework to compute the eigenvalues of a cylindrically symmetric prolate diffusion tensor (D) from one of the rotationally-invariant diffusion anisotropy indices and average diffusivity is presented and validated. Cylindrical or axial symmetry assumes a prolate ellipsoid shape (lambdaparallel=lambda1>lambdaperpendicular=(lambda2+lambda3)/2; lambda2=lambda3). A prolate ellipsoid with such symmetry is largely satisfied in a number of white matter (WM) structures, such as the spinal cord, corpus callosum, internal capsule, and corticospinal tract. The theoretical model presented is validated using in vivo DTI measurements of rat spinal cord and human brain, where eigenvalues were calculated from both the set of diffusion coefficients and a tensor analysis. This method was used to retrospectively analyze literature data that reported tensor-derived average diffusivity, anisotropy, and eigenvalues, and similar eigenvalue measurements were obtained. The method provides a means to retrospectively reanalyze literature data that do not report eigenvalues. Other potential applications of this method are also discussed.
  Magnetic Resonance in Medicine 07/2006; 56(1):130-7. · 2.96 Impact Factor
• Article: In vivo serial diffusion tensor imaging of experimental spinal cord injury.

  Aparna A Deo, Raymond J Grill, Khader M Hasan, Ponnada A Narayana
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  ABSTRACT: In vivo longitudinal diffusion tensor imaging (DTI) of rodent spinal cord injury (SCI) was carried out over a period of eight weeks post-injury. A balanced, rotationally invariant, alternating gradient polarity icosahedral diffusion encoding scheme was used for an unbiased estimation of the DTI metrics. The fractional anisotropy (FA), diffusivities along (longitudinal), and perpendicular (transverse) to the fiber tracts, were estimated for the ventral, dorsal, and lateral white matter. In all the three regions, the DTI metrics were observed to be significantly different in injured cords relative to the uninjured controls close to the epicenter of the injury. However, these differences gradually disappeared away from the epicenter. The spatio-temporal changes in the DTI metrics showed a recovery pattern that is region specific. Although the temporal trends in the tissue recovery in rostral and caudal sections seem to be similar, overall the DTI metrics were observed to be closer to the normal tissue values in the caudal relative to the rostral sections (rostral-caudal asymmetry).
  Journal of Neuroscience Research 05/2006; 83(5):801-10. · 2.74 Impact Factor
• Article: Demonstration of interstitial cerebral edema with diffusion tensor MR imaging in type C hepatic encephalopathy.

  Ravindra A Kale, Rakesh K Gupta, Vivek A Saraswat, Khader M Hasan, Richa Trivedi, Asht M Mishra, Piyush Ranjan, Chandra M Pandey, Ponnada A Narayana
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  ABSTRACT: Brain water may increase in hepatic encephalopathy (HE). Diffusion tensor imaging was performed in patients with cirrhosis with or without HE to quantify the changes in brain water diffusivity and to correlate it with neuropsychological (NP) tests. Thirty-nine patients with cirrhosis, with minimal (MHE) or overt HE, were studied and compared to 18 controls. Mean diffusivity (MD) and fractional anisotropy (FA) were calculated in corpus callosum, internal capsule, deep gray matter nuclei, periventricular frontal, and occipital white matter regions in both cerebral hemispheres. The MD and FA values from different regions in different groups were compared using analysis of variance and Spearman's rank correlation test. In 10 patients with MHE, repeat studies were performed after 3 weeks of lactulose therapy to look for any change in MD, FA, and NP scores. Significantly increased MD was found with insignificant changes in FA in various regions of brain in patients with MHE or HE compared with controls, indicating an increase in interstitial water in the brain parenchyma without any microstructural changes. A significant correlation was found between MD values from corpus callosum, internal capsule, and NP test scores. After therapy, MD values decreased significantly and there was a corresponding improvement in NP test scores. Further analysis showed that MD values were different for different grades of minimal or overt HE. In conclusion, the increase in MD with no concomitant changes in FA in cirrhosis with minimal or early HE indicates the presence of reversible interstitial brain edema.
  Hepatology 05/2006; 43(4):698-706. · 11.66 Impact Factor
• Source

  Available from: Jerry S Wolinsky

  Article: Unified approach for multiple sclerosis lesion segmentation on brain MRI.

  Balasrinivasa Rao Sajja, Sushmita Datta, Renjie He, Meghana Mehta, Rakesh K Gupta, Jerry S Wolinsky, Ponnada A Narayana
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  ABSTRACT: The presence of large number of false lesion classification on segmented brain MR images is a major problem in the accurate determination of lesion volumes in multiple sclerosis (MS) brains. In order to minimize the false lesion classifications, a strategy that combines parametric and nonparametric techniques is developed and implemented. This approach uses the information from the proton density (PD)- and T2-weighted and fluid attenuation inversion recovery (FLAIR) images. This strategy involves CSF and lesion classification using the Parzen window classifier. Image processing, morphological operations, and ratio maps of PD- and T2-weighted images are used for minimizing false positives. Contextual information is exploited for minimizing the false negative lesion classifications using hidden Markov random field-expectation maximization (HMRF-EM) algorithm. Lesions are delineated using fuzzy connectivity. The performance of this algorithm is quantitatively evaluated on 23 MS patients. Similarity index, percentages of over, under, and correct estimations of lesions are computed by spatially comparing the results of present procedure with expert manual segmentation. The automated processing scheme detected 80% of the manually segmented lesions in the case of low lesion load and 93% of the lesions in those cases with high lesion load.
  Annals of Biomedical Engineering 02/2006; 34(1):142-51. · 2.37 Impact Factor
• Article: Segmentation and quantification of black holes in multiple sclerosis.

  Sushmita Datta, Balasrinivasa Rao Sajja, Renjie He, Jerry S Wolinsky, Rakesh K Gupta, Ponnada A Narayana
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  ABSTRACT: A technique that involves minimal operator intervention was developed and implemented for identification and quantification of black holes on T1-weighted magnetic resonance images (T1 images) in multiple sclerosis (MS). Black holes were segmented on T1 images based on grayscale morphological operations. False classification of black holes was minimized by masking the segmented images with images obtained from the orthogonalization of T2-weighted and T1 images. Enhancing lesion voxels on postcontrast images were automatically identified and eliminated from being included in the black hole volume. Fuzzy connectivity was used for the delineation of black holes. The performance of this algorithm was quantitatively evaluated on 14 MS patients.
  NeuroImage 02/2006; 29(2):467-74. · 5.89 Impact Factor
• Article: Diffusion tensor imaging in late posttraumatic epilepsy.

  Rakesh K Gupta, Sona Saksena, Atul Agarwal, Khader M Hasan, Mazhar Husain, Vikas Gupta, Ponnada A Narayana
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  ABSTRACT: The main objective of this study was to use diffusion tensor imaging (DTI) to search and quantify the extent of abnormality beyond the obvious lesions seen on the T2 and fluid-attenuation inversion recovery (FLAIR) magnetic resonance images in patients with chronic traumatic brain injury (TBI) with and without epilepsy. DTI was performed on 23 chronic TBI patients (with late posttraumatic epilepsy, n=14; without epilepsy, n=9) and 11 age-matched controls. The ratios of fractional anisotropy (FA) and mean diffusivity (MD) between the regions of interest beyond the T2/FLAIR-visualized abnormality and the corresponding contralateral normal-appearing region were calculated. FA and MD ratios were compared for relative changes in these parameters among the TBI subjects with and without epilepsy and controls. Tissue volumes exhibiting abnormalities on DTI also were measured in these patients. The mean regional FA ratio was significantly lower, whereas the mean regional MD value was higher in patients with TBI compared with controls. The mean regional FA ratio was significantly lower in TBI patients with epilepsy (0.57+/-0.059) than in those without epilepsy (0.68+/-0.039). Although the regional MD ratio was higher in TBI patients with epilepsy (1.15+/-0.140) relative to those without epilepsy (1.09+/-0.141), the difference did not reach statistical significance. The tissue volume with low FA value also was found to be higher in TBI patients with epilepsy than without. Severity of injury as predicted by the DTI-derived increased volume of microstructure damage is associated with delayed posttraumatic epilepsy in TBI patients. These findings could be valuable in predicting epileptogenesis in patients with chronic TBI.
  Epilepsia 10/2005; 46(9):1465-71. · 3.96 Impact Factor
• Source

  Available from: ncbi.nlm.nih.gov

  Article: Implementation of high-dimensional feature map for segmentation of MR images.

  Renjie He, Balasrinivasa Rao Sajja, Ponnada A Narayana
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  ABSTRACT: A method that considerably reduces the computational and memory complexities associated with the generation of high-dimensional (> or =3) feature maps for image segmentation is described. The method is based on the K-nearest neighbor (KNN) classification and consists of two parts: preprocessing of feature space and fast KNN. This technique is implemented on a PC and applied for generating 3D and 4D feature maps for segmenting MR brain images of multiple sclerosis patients.
  Annals of Biomedical Engineering 10/2005; 33(10):1439-48. · 2.37 Impact Factor
• Source

  Available from: ismrm.org

  Article: Diffusion tensor imaging of the developing human cerebrum.

  Rakesh K Gupta, Khader M Hasan, Richa Trivedi, Mandakini Pradhan, Vinita Das, Nehal A Parikh, Ponnada A Narayana
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  ABSTRACT: Diffusion tensor imaging (DTI) was performed on 15 fresh spontaneously or therapeutically aborted normal fetuses and five term infants at different gestational ages. Regional cortical fractional anisotropy (FA) values were observed to increase with gestational age (GA) from 15 to 28 weeks, followed by a decrease through 36 weeks. The early increase in the cortical FA value, which has never been reported before, is consistent with neuronal migration from the germinal matrix. A statistically significant inverse correlation between GA and the FA values in the germinal matrix was observed (r = -0.81, P = 0.004). In addition, there was a significant difference in the FA values in the right and left frontal cortices (P = 0.007, sign test), suggesting cortical lateralization during the early stage of development. Our studies suggest that the DTI-estimated anisotropy could be useful in following neuronal migration, cortical maturation, and associated changes in the germinal matrix during early brain development.
  Journal of Neuroscience Research 08/2005; 81(2):172-8. · 2.74 Impact Factor
• Article: Diffusion tensor fractional anisotropy of the normal-appearing seven segments of the corpus callosum in healthy adults and relapsing-remitting multiple sclerosis patients.

  Khader M Hasan, Rakesh K Gupta, Rafael M Santos, Jerry S Wolinsky, Ponnada A Narayana
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  ABSTRACT: To investigate the utility of whole-brain diffusion tensor imaging (DTI) in elucidating the pathogenesis of multiple sclerosis (MS) using the normal-appearing white matter (NAWM) of the corpus callosum (CC) as a marker of occult disease activity. A high signal-to-noise ratio (SNR) and optimized entire brain DTI data were acquired in 26 clinically-definite relapsing and remitting multiple sclerosis (RRMS) patients and 32 age-matched healthy adult controls. The fractional anisotropy (FA) values of seven functionally distinct regions in the normal-appearing CC were compared between patients and controls. This study indicates that 1) there was a gender-independent FA heterogeneity of the functionally specialized CC segments in normal volunteers; 2) FA in the MS group was significantly decreased in the anterior (P=0.0039) and posterior (P=0.0018) midbody subdivisions of the CC, possibly due to a reduction of small-caliber axons; and 3) the FA of the genu of the CC was relatively intact in the MS patients compared to the healthy age-matched controls (P=0.644), while the splenium showed an insignificant trend of reduced FA values (P=0.248). The decrease in FA in any of the CC subdivisions did not correlate with disease duration (DD) or the expanded disability status scale (EDSS) score. The preliminary results are consistent with published histopathology and clinical studies on MS, but not with some published DTI reports. This study provides insights into the pathogenesis of MS, and the role played by compromised axonal integrity in this disease.
  Journal of Magnetic Resonance Imaging 07/2005; 21(6):735-43. · 2.70 Impact Factor
• Article: High fractional anisotropy in brain abscesses versus other cystic intracranial lesions.

  Rakesh K Gupta, Khader M Hasan, Asht M Mishra, Deepak Jha, Mazhar Husain, Kashi N Prasad, Ponnada A Narayana
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  ABSTRACT: It is known that intracranial mass lesions are relatively isotropic on diffusion-weighted imaging. The purpose of this study is to report an unusually high fractional anisotropy (FA) and mean diffusivity (D(av)) in the cavity of the brain abscess compared with other cystic lesions. We performed diffusion tensor imaging (DTI) in 12 patients with cystic intracranial lesions (pyogenic abscess, n = 5; cysticercus cysts, n = 2; and low-grade astrocytoma, n = 5). Mean FA, D(av) from the lesion core, perifocal edema, and corresponding contralateral normal-appearing regions were measured and compared for relative changes in these parameters. In the abscess cases, we placed regions of interest on areas with FA >0.2 and FA <0.2 to get FA and D(av) values. There were two patterns of FA values in the abscess cavity in all five patients. Part of the abscess showed mean FA = 0.440 +/- 0.135, with D(av) = (0.993 +/- 0.185) x 10(-3) mm(2)/s, whereas other parts had FA = 0.131 +/- 0.039 with D(av) = (0.824 +/- 0.183) x 10(-3) mm(2)/s. The cystic tumors and neurocysticercosis showed very high D(av) = (2.806 +/- 0.25, 2.654 +/- 0.35)x 10(-3) mm(2)/s, with low FA = (0.108 +/- 0.037, 0.08 +/- 0.01), respectively. Brain abscess cavity shows regions of increased FA values with restricted mean diffusivity compared with other cystic intracranial lesions. This information may prevent misinterpretation of the DTI information as white matter fiber bundle abnormalities associated with mass lesions.
  American Journal of Neuroradiology 06/2005; 26(5):1107-14. · 2.93 Impact Factor
• Source

  Available from: Alan C Swann

  Article: Reduced anterior corpus callosum white matter integrity is related to increased impulsivity and reduced discriminability in cocaine-dependent subjects: diffusion tensor imaging.

  Frederick Gerard Moeller, Khader M Hasan, Joel L Steinberg, Larry A Kramer, Donald M Dougherty, Rafael M Santos, Ignacio Valdes, Alan C Swann, Ernest S Barratt, Ponnada A Narayana
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  ABSTRACT: Brain imaging studies find evidence of prefrontal cortical dysfunction in cocaine-dependent subjects. Similarly, cocaine-dependent subjects have problems with behaviors related to executive function and impulsivity. Since prefrontal cortical axonal tracts cross between hemispheres in the corpus callosum, it is possible that white matter integrity in the corpus callosum could also be diminished in cocaine-dependent subjects. The purpose of this study was to compare corpus callosum white matter integrity as measured by the fractional anisotropy (FA) on diffusion tensor imaging (DTI) between 18 cocaine-dependent subjects and 18 healthy controls. The Barratt Impulsiveness Scale (BIS-11) and a continuous performance test: the Immediate and Delayed Memory Task (IMT/DMT) were also collected. Results of the DTI showed significantly reduced FA in the genu and rostral body of the anterior corpus callosum in cocaine-dependent subjects compared to controls. Cocaine-dependent subjects also had significantly higher BIS-11 scores, greater impulsive (commission) errors, and reduced ability to discriminate target from catch stimuli (discriminability) on the IMT/DMT. Within cocaine dependent subjects there was a significant negative correlation between FA in the anterior corpus callosum and behavioral laboratory measured impulsivity, and there was a positive correlation between FA and discriminability. The finding that reduced integrity of anterior corpus callosum white matter in cocaine users is related to impaired impulse control and reduced ability to discriminate between target and catch stimuli is consistent with prior theories regarding frontal cortical involvement in impaired inhibitory control in cocaine-dependent subjects.
  Neuropsychopharmacology 04/2005; 30(3):610-7. · 7.99 Impact Factor
• Article: Magnetic resonance spectroscopy in the monitoring of multiple sclerosis.

  Ponnada A Narayana
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  ABSTRACT: In addition to providing information on tissue structure, magnetic resonance (MR) technology offers the potential to investigate tissue metabolism and function. MR spectroscopy (MRS) offers a wealth of data on the biochemistry of a selected brain tissue volume, which represent potential surrogate markers for the pathology underlying multiple sclerosis (MS). In particular, the N-acetylaspartate peak in an MR spectrum is a putative marker of neuronal and axonal integrity, and the choline peak appears to reflect cell-membrane metabolism. On this basis, a diminished N-acetylaspartate peak is interpreted to represent neuronal/axonal dysfunction or loss, and an elevated choline peak represents heightened cell-membrane turnover, as seen in demyelination, remyelination, inflammation, or gliosis. Therefore, MRS may provide a unique tool to evaluate the severity of MS, establish a prognosis, follow disease evolution, understand its pathogenesis, and evaluate the efficacy of therapeutic interventions, which complements the information obtained from the various forms of assessment made by conventional MR imaging.
  Journal of Neuroimaging 02/2005; 15(4 Suppl):46S-57S. · 1.51 Impact Factor