Andrew Poliakov

Seattle Children's Hospital, Seattle, Washington, United States

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Publications (51)153.43 Total impact

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    ABSTRACT: Background: In this observational study, white matter structure, functional magnetic resonance imaging (fMRI) task-based responses, and functional connectivity were assessed in four subjects with high functioning pyridoxine-dependent epilepsy and age-matched control subjects. Methods: Four male subjects with pyridoxine-dependent epilepsy (mean age 31 years 8 months, standard deviation 12 years 3 months) and age-matched control subjects (32 years 4 months, standard deviation 13 years) were recruited to participate in the study. Diffusion tensor data were collected and postprocessed in Functional Magnetic Resonance Imaging of the Brain Software Library to quantify corpus callosum tracts as a means to assess white matter structure. Task-based fMRI data were collected and Functional Magnetic Resonance Imaging of the Brain Software Library used to assess task response. The fMRI resting-state data were analyzed with the functional connectivity toolbox Conn to determine functional connectivity. Results: Subjects with high functioning pyridoxine-dependent epilepsy retained structural white matter connectivity compared with control subjects, despite morphologic differences in the posterior corpus callosum. fMRI task-based results did not differ between subjects with pyridoxine-dependent epilepsy and control subjects; functional connectivity as measured with resting-state fMRI was lower in subjects with pyridoxine-dependent epilepsy for several systems (memory, somatosensory, auditory). Conclusion: Although corpus callosum morphology is diminished in the posterior portions, structural connectivity was retained in subjects with pyridoxine-dependent epilepsy, while functional connectivity was diminished for memory, somatosensory, and auditory systems.
    No preview · Article · Sep 2015 · Pediatric Neurology

  • No preview · Conference Paper · Jun 2015
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    ABSTRACT: Aim: While there have been isolated reports of callosal morphology differences in pyridoxine-dependent epilepsy (PDE), a rare autosomal disorder caused by ALDH7A1 gene mutations, no study has systematically evaluated callosal features in a large sample of patients. This study sought to overcome this knowledge gap. Method: Spanning a wide age range from birth to 48 years, corpus callosum morphology and cross-sectional cerebral area were measured in 30 individuals with PDE (12 males, 18 females, median age 3.92y; 25th centile 0.27, 75th centile 15.25) compared to 30 age-matched comparison individuals (11 males, 19 females, median age 3.85y; 25th centile 0.26, 75th centile 16.00). Individuals with PDE were also divided into age groups to evaluate findings across development. As delay to treatment may modulate clinical severity, groups were stratified by treatment delay (less than or greater than 2wks from birth). Results: Markedly reduced callosal area expressed as a ratio of mid-sagittal cerebral area was observed for the entire group with PDE (p<0.001). Stratifying by age (<1y, 1-10y, >10y) demonstrated posterior abnormalities to be a consistent feature, with anterior regions increasingly involved across the developmental trajectory. Splitting the PDE group by treatment lag did not reveal overall or sub-region callosal differences. Interpretation: Callosal abnormalities are a common feature of PDE not explained by treatment lag. Future work utilizing tract-based approaches to understand inter- and intra-hemispheric connectivity patterns will help in the better understanding the structural aspects of this disease.
    No preview · Article · Jun 2014 · Developmental Medicine & Child Neurology
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    ABSTRACT: Background: The pathophysiology resulting in cerebral edema in pediatric diabetic ketoacidosis (DKA) is unknown. To investigate the changes in white matter microstructure in this disease, we measured diffusion tensor imaging (DTI) parameters, including apparent diffusion coefficient (ADC), fractional anisotropy (FA), and radial and axial diffusivity in children with DKA at two time points during treatment. Methods: A prospective observational study was conducted at Seattle Children's Hospital, Seattle, WA. Thirty-two children admitted with DKA (pH < 7.3, bicarbonate < 15 mEq/l, glucose > 300 mg/dl, and ketosis; 11.9 ± 3.2 y; and 47% male) were enrolled and underwent two serial paired diffusion magnetic resonance imaging (MRI) scans following hospital admission. Seventeen of the 32 participants had diffusion tensor images of adequate quality for tract-based spatial statistics (TBSS) analysis. Results: TBSS mapping demonstrated main white matter tract areas with a significant increase in FA and areas with a significant decrease in ADC, from the first to the second MRI. Both radial and axial diffusivity terms showed change, with a diffuse pattern of involvement. Conclusion: Consistent DTI changes occurred during DKA treatment over a short time frame. These findings describe widespread water diffusion abnormalities in DKA, supporting an association between clinical illness and DTI markers of microstructural change in white matter.
    No preview · Article · Oct 2013 · Pediatric Research
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    ABSTRACT: Posterior fossa tumors are the most common brain tumor of children. Aggressive resection correlates with long-term survival. A high incidence of posterior fossa syndrome (PFS), impairing the quality of life in many survivors, has been attributed to damage to bilateral dentate nucleus or to cerebellar output pathways. Using diffusion tensor imaging (DTI), we examined the involvement of the dentothalamic tracts, specifically the superior cerebellar peduncle (SCP), in patients with posterior fossa tumors and the association with PFS. DTI studies were performed postoperatively in patients with midline (n = 12), lateral cerebellar tumors (n = 4), and controls. The location and visibility of the SCP were determined. The postoperative course was recorded, especially with regard to PFS, cranial nerve deficits, and oculomotor function. The SCP travels immediately adjacent to the lateral wall of the fourth ventricle and just medial to the middle cerebellar peduncle. Patients with midline tumors that still had observable SCP did not develop posterior fossa syndrome (N = 7). SCPs were absent, on either preoperative (N = 1, no postoperative study available) or postoperative studies (N = 4), in the five patients who developed PFS. Oculomotor deficits of tracking were observed in patients independent of PFS or SCP involvement. PFS can occur with bilateral injury to the outflow from dentate nuclei. In children with PFS, this may occur due to bilateral injury to the superior cerebellar peduncle. These tracts sit immediately adjacent to the wall of the ventricle and are highly vulnerable when an aggressive resection for these tumors is performed.
    No preview · Article · Jul 2013 · Child s Nervous System
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    ABSTRACT: Object: Imaging-guided surgery (IGS) systems are widely used in neurosurgical practice. During epilepsy surgery, the authors routinely use IGS landmarks to localize intracranial electrodes and/or specific brain regions. The authors have developed a technique to coregister these landmarks with pre- and postoperative scans and the Montreal Neurological Institute (MNI) standard space brain MRI to allow 1) localization and identification of tissue anatomy; and 2) identification of Brodmann areas (BAs) of the tissue resected during epilepsy surgery. Tracking tissue in this fashion allows for better correlation of patient outcome to clinical factors, functional neuroimaging findings, and pathological characteristics and molecular studies of resected tissue. Methods: Tissue samples were collected in 21 patients. Coordinates from intraoperative tissue localization were downloaded from the IGS system and transformed into patient space, as defined by preoperative high-resolution T1-weighted MRI volume. Tissue landmarks in patient space were then transformed into MNI standard space for identification of the BAs of the tissue samples. Results: Anatomical locations of resected tissue were identified from the intraoperative resection landmarks. The BAs were identified for 17 of the 21 patients. The remaining patients had abnormal brain anatomy that could not be meaningfully coregistered with the MNI standard brain without causing extensive distortion. Conclusions: This coregistration and landmark tracking technique allows localization of tissue that is resected from patients with epilepsy and identification of the BAs for each resected region. The ability to perform tissue localization allows investigators to relate preoperative, intraoperative, and postoperative functional and anatomical brain imaging to better understand patient outcomes, improve patient safety, and aid in research.
    No preview · Article · Jun 2013 · Neurosurgical FOCUS
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    ABSTRACT: The cerebellum, classically viewed as a motor structure of the brain, may play a role in respiration. Brainstem dysfunction has been implicated in sleep disordered breathing (SDB), but apnea after surgery of brain tumors in the posterior fossa, not involving the brainstem has been reported. We report four cases with posterior fossa tumors without brainstem invasion who suffered SDB after surgery diagnosed by polysomnography (PSG). Advanced MRI techniques with DTI were used to find correlations with SDB. Abnormal signals in the superior, middle and inferior cerebellar peduncles were seen in these patients with the most severe changes in the inferior peduncle. SDB may be under diagnosed in the setting of posterior fossa tumors without brainstem involvement. Damage to the cerebellar peduncles, especially the inferior cerebellar peduncle, without brainstem involvement, can cause significant disruption of respiration.
    No preview · Article · May 2013 · Respiratory Physiology & Neurobiology
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    ABSTRACT: Successful resection of cortical tissue engendering seizure activity is efficacious for the treatment of refractory, focal epilepsy. The pre-operative localization of the seizure focus is therefore critical to yielding positive, post-operative outcomes. In a small proportion of focal epilepsy patients presenting with normal MRI, identification of the seizure focus is significantly more challenging. We examined the capacity of resting state functional MRI (rsfMRI) to identify the seizure focus in a group of 4 non-lesion, focal (NLF) epilepsy individuals. We predicted that computing patterns of local functional connectivity (fc) in and around the epileptogenic zone combined with a specific reference to the corresponding region within the contralateral hemisphere would reliably predict the location of the seizure focus. We first averaged voxel-wise regional homogeneity (ReHo) across regions of interest (ROIs) from a standardized, probabilistic atlas for each NLF subject as well as 16 age and gender matched controls. To examine contralateral effects, we computed a ratio of the mean pair-wise correlations of all voxels within a ROI with the corresponding contralateral region (InterRegional Connectivity - IRC). For each subject, ROIs were ranked (from lowest to highest) on ReHo, IRC and the mean of the two values. At the group level, we observed a significant decrease in the rank for ROI harboring the seizure focus for the ReHo rankings as well as for the mean rank. At the individual level, the seizure focus ReHo rank was within bottom 10% lowest ranked ROIs for all 4 NLF epilepsy patients and 3 out of the 4 for the IRC rankings. However, when the two ranks were combined (averaging across ReHo and IRC ranks and scalars), the seizure focus ROI was either the lowest or second lowest ranked ROI for 3 out of the 4 epilepsy subjects. This suggests that rsfMRI may serve as an adjunct pre-surgical tool, facilitating the identification of the seizure focus in focal epilepsy.
    Full-text · Article · May 2013 · Frontiers in Neurology
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    ABSTRACT: : The compression of the cerebellum is of unclear significance in posterior fossa compression (Chiari I). We studied the diffusion tensor imaging changes (Fractional Anisotropy - FA and Apparent Diffusion Coefficient - ADC) before and after Chiari surgery and correlated findings with clinical and radiological presentation. : We evaluated MR studies, obtained as part of clinical scans, in 10 patients before and after posterior fossa decompression of Chiari I malformations. Studies included both conventional (structural) MRI and diffusion tensor imaging (DTI). The average DTI parameters of established regions of interest were calculated. Resolution of clinical symptoms was also noted. : Nine of 10 patients showed changes from preoperative DTI parameters after decompression. Cerebellar white matter (middle cerebellar peduncle) demonstrated a significant decrease in ADC (pre = 0.77 ± 0.07 (standard deviation), post = 0.72 ± 0.04; T = 3.93, P = 0.003) and trend increase in FA (pre = 0.497 ± 0.079, post = 0.542 ± 0.096 T = -2.18, P = 0.057). All of these patients presented with both radiological and clinical improvement including resolution of syringomyelia, improvement of headaches and other neurological symptoms. All of the patients were able to resume their daily activities. : Both ADC and FA measurements returned closer to normal expected values in the middle cerebellar peduncle. The increase in FA suggests a normalization of white matter integrity not apparent in conventional imaging. The pre and postoperative diffusion tensor imaging evaluation is a readily available additional tool in the neuroradiological arsenal. It may become a valuable asset in medical decision making and successful management of Chiari I malformation patients. Nevertheless more studies are needed to assess properly its value, correlation with symptoms and outcome, reliability of repeat measurements in non-surgical patients, and any possible clinical application.
    No preview · Article · Aug 2012 · Neurosurgery
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    ABSTRACT: The gold-standard method for determining cortical functional organization in the context of neurosurgical intervention is electrical cortical stimulation (ECS), which disrupts normal cortical function to evoke movement. This technique is imprecise, however, as motor responses are not limited to the precentral gyrus. Electrical cortical stimulation also can trigger seizures, is not always tolerated, and is often unsuccessful, especially in children. Alternatively, endogenous motor and sensory signals can be mapped by somatosensory evoked potentials (SSEPs), functional MRI (fMRI), and electrocorticography of high gamma (70-150 Hz) signal power, which reflect normal cortical function. The authors evaluated whether these 4 modalities of mapping sensorimotor function in children produce concurrent results. The authors retrospectively examined the charts of all patients who underwent epilepsy surgery at Seattle Children's Hospital between July 20, 1999, and July 1, 2011, and they included all patients in whom the primary motor or somatosensory cortex was localized via 2 or more of the following tests: ECS, SSEP, fMRI, or high gamma electrocorticography (hgECoG). Inclusion criteria were met by 50 patients, whose mean age at operation was 10.6 years. The youngest patient who underwent hgECoG mapping was 2 years and 10 months old, which is younger than any patient reported on in the literature. The authors localized the putative sensorimotor cortex most often with hgECoG, followed by SSEP and fMRI; ECS was most likely to fail to localize the sensorimotor cortex. Electrical cortical stimulation, SSEP, fMRI, and hgECoG generally produced concordant localization of motor and sensory function in children. When attempting to localize the sensorimotor cortex in children, hgECoG was more likely to produce results, was faster, safer, and did not require cooperation. The hgECoG maps in pediatric patients are similar to those in adult patients published in the literature. The sensorimotor cortex can be mapped by hgECoG and fMRI in children younger than 3 years old to localize cortical function.
    No preview · Article · Jun 2012 · Journal of Neurosurgery Pediatrics
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    ABSTRACT: Often diagnosed at birth or in early childhood, mitochondrial disease presents with a variety of clinical symptoms, particularly in organs and tissues that require high energetic demand such as brain, heart, liver, and skeletal muscles. In a group of pediatric patients identified as having complex I or I/III deficits on muscle biopsy but with white matter tissue appearing qualitatively normal for age, we hypothesized that quantitative DTI analyses might unmask disturbance in microstructural integrity. In a retrospective study, DTI and structural MR brain imaging data from 10 pediatric patients with confirmed mitochondrial disease and 10 clinical control subjects were matched for age, sex, scanning parameters, and date of examination. Paired TBSS was performed to evaluate differences in FA, MD, and the separate diffusion direction terms (λr and λa). In patients with mitochondrial disease, significant widespread reductions in FA values were shown in white matter tracts. Mean diffusivity values were significantly increased in patients, having a sparser distribution of affected regions compared with FA. Separate diffusion maps showed significant increase in λr and no significant changes in λa. Despite qualitatively normal-appearing white matter tissues, patients with complex I or I/III deficiency have widespread microstructural changes measurable with quantitative DTI.
    No preview · Article · Apr 2012 · American Journal of Neuroradiology
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    ABSTRACT: The presurgical evaluation of patients with epilepsy often requires an intracranial study in which both subdural grid electrodes and depth electrodes are needed. Performing a craniotomy for grid placement with a stereotactic frame in place can be problematic, especially in young children, leading some surgeons to consider frameless stereotaxy for such surgery. The authors report on the use of a system that uses electromagnetic impulses to track the tip of the depth electrode. Ten pediatric patients with medically refractory focal lobar epilepsy required placement of both subdural grid and intraparenchymal depth electrodes to map seizure onset. Presurgical frameless stereotaxic targeting was performed using a commercially available electromagnetic image-guided system. Freehand depth electrode placement was then performed with intraoperative guidance using an electromagnetic system that provided imaging of the tip of the electrode, something that has not been possible using visually or sonically based systems. Accuracy of placement of depth electrodes within the deep structures of interest was confirmed postoperatively using CT and CT/MR imaging fusion. Depth electrodes were appropriately placed in all patients. Electromagnetic-tracking-based stereotactic targeting improves the accuracy of freehand placement of depth electrodes in patients with medically refractory epilepsy. The ability to track the electrode tip, rather than the electrode tail, is a major feature that enhances accuracy. Additional advantages of electromagnetic frameless guidance are discussed.
    No preview · Article · Nov 2011 · Journal of Neurosurgery Pediatrics
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    ABSTRACT: The study of human brain electrophysiology has extended beyond traditional frequency ranges identified by the classical EEG rhythms, encompassing both higher and lower frequencies. Changes in high-gamma-band (>70 Hz) power have been identified as markers of local cortical activity. Fluctuations at infra-slow (<0.1 Hz) frequencies have been associated with functionally significant cortical networks elucidated using fMRI studies. In this study, we examined infra-slow changes in band-limited power across a range of frequencies (1-120 Hz) in the default mode network (DMN). Measuring the coherence in band-limited power fluctuations between spatially separated electrodes makes it possible to detect small, spatially extended, and temporally coherent fluctuating components in the presence of much larger incoherent fluctuations. We show that the default network is characterized by significant high-gamma-band (65-110 Hz) coherence at infra-slow (<0.1 Hz) frequencies. This coherence occurs over a narrow frequency range, centered at 0.015 Hz, commensurate with the frequency of BOLD signal fluctuations seen by fMRI, suggesting that quasi-periodic, infra-slow changes in local cortical activity form the neurophysiological basis for this network.
    No preview · Article · Aug 2011 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience

  • No preview · Article · May 2011 · Neuroradiology
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    ABSTRACT: The authors describe their experience with functional MR (fMR) imaging in children as young as 5 years of age, or even younger in developmental age equivalent. Functional MR imaging can be useful for identifying eloquent cortex prior to surgical intervention. Most fMR imaging clinical work has been done in adults, and although children as young as 8 years of age have been included in larger clinical series, cases in younger children are rarely reported. The authors reviewed presurgical fMR images in eight patients who were 8 years of age or younger, six of whom were 5 or 6 years of age. Each patient had undergone neuropsychological testing. Three patients functioned at a below-average level, with adaptive functioning age scores of 3 to 4 years. Self-paced finger tapping (with passive movement in one patient) and silent language tasks were used as activation tasks. The language task was modified for younger children, for whom the same (not novel) stimuli were used for extensive practice ahead of time and in the MR imaging unit. Patient preparation involved techniques such as having experienced staff present to work with patients and providing external management during imaging. Six of eight patients had extensive training and practice prior to the procedure. In the two youngest patients, this training included use of a mock MR unit. All cases yielded successful imaging. Finger tapping in all seven of the patients who could perform it demonstrated focal motor activation in the frontal-parietal region, with expected activation elsewhere, including in the cerebellum. Three of four patients had the expected verb generation task activations, with left-hemisphere dominance, including a 6-year-old child who functioned at the 3-year, 9-month level. The only child (an 8-year-old) who was not prepared prior to the imaging session for the verb generation task failed this task due to movement artifact. Despite the challenges of successfully using fMR imaging in very young and clinically involved patients, these studies can be performed successfully in children with a chronological age of 5 or 6 years and a developmental age as young as 3 or 4 years.
    No preview · Article · May 2010 · Journal of Neurosurgery Pediatrics
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    ABSTRACT: Intrinsic diffuse brainstem tumors and demyelinating diseases primarily affecting the brainstem can share common clinical and radiological features, sometimes making the diagnosis difficult especially at the time of first clinical presentation. To explore the potential usefulness of new MRI sequences in particular diffusion tensor imaging fiber tracking in differentiating these two pathological entities, we review a series of brainstem tumors and demyelinating diseases treated at our institution. The clinical history including signs and symptoms and MRI findings of three consecutive demyelinating diseases involving the brainstem that presented with diagnostic uncertainty and three diffuse intrinsic brainstem tumors were reviewed, along with a child with a supratentorial tumor for comparison. Fiber tracking of the pyramidal tracts was performed for each patient using a DTI study at the time of presentation. Additionally Fractional Anisotropy values were calculated for each patient in the pons and the medulla oblongata. Routine MR imaging was unhelpful in differentiating between intrinsic tumor and demyelination. In contrast, retrospective DTI fiber tracking clearly differentiated the pathology showing deflection of the pyramidal tracts posteriorly and laterally in the case of intrinsic brainstem tumors and, in the case of demyelinating disease, poorly represented and truncated fibers. Regionalized FA values were variable and of themselves were not predictive either pathology. DTI fiber tracking of the pyramid tracts in patients with suspected intrinsic brainstem tumor or demyelinating disease presents two clearly different patterns that may help in differentiating between these two pathologies when conventional MRI and clinical data are inconclusive.
    Full-text · Article · Apr 2010 · NeuroImage
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    ABSTRACT: The relationship between changes in functional magnetic resonance imaging and neuronal activity remains controversial. Data collected during awake neurosurgical procedures for the treatment of epilepsy provided a rare opportunity to examine this relationship in human temporal association cortex. We obtained functional magnetic resonance imaging blood oxygen dependent signals, single neuronal activity and local field potentials from 8 to 300 Hz at 13 temporal cortical sites, from nine subjects, during paired associate learning and control measures. The relation between the functional magnetic resonance imaging signal and the electrophysiologic parameters was assessed in two ways: colocalization between significant changes in these signals on the same paired associate-control comparisons and multiple linear regressions of the electrophysiologic measures on the functional magnetic resonance imaging signal, across all tasks. Significant colocalization was present between increased functional magnetic resonance imaging signals and increased local field potentials power in the 50-250 Hz range. Local field potentials power greater than 100 Hz was also a significant regressor for the functional magnetic resonance imaging signal, establishing this local field potentials frequency range as a neuronal correlate of the functional magnetic resonance imaging signal. There was a trend for a relation between power in some low frequency local field potentials frequencies and the functional magnetic resonance imaging signal, for 8-15 Hz increases in the colocalization analysis and 16-23 Hz in the multiple linear regression analysis. Neither analysis provided evidence for an independent relation to frequency of single neuron activity.
    Full-text · Article · Sep 2009 · Brain
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    ABSTRACT: Brain activity patterns during face processing have been extensively explored with functional magnetic resonance imaging (fMRI) and event-related potentials (ERPs). ERP source localization adds a spatial dimension to the ERP time series recordings, which allows for a more direct comparison and integration with fMRI findings. The goals for this study were (1) to compare the spatial descriptions of neuronal activity during face processing obtained with fMRI and ERP source localization using low-resolution electromagnetic tomography (LORETA), and (2) to use the combined information from source localization and fMRI to explore how the temporal sequence of brain activity during face processing is summarized in fMRI activation maps. fMRI and high-density ERP data were acquired in separate sessions for 17 healthy adult males for a face and object processing task. LORETA statistical maps for the comparison of viewing faces and viewing houses were coregistered and compared to fMRI statistical maps for the same conditions. The spatial locations of face processing-sensitive activity measured by fMRI and LORETA were found to overlap in a number of areas including the bilateral fusiform gyri, the right superior, middle and inferior temporal gyri, and the bilateral precuneus. Both the fMRI and LORETA solutions additionally demonstrated activity in regions that did not overlap. fMRI and LORETA statistical maps of face processing-sensitive brain activity were found to converge spatially primarily at LORETA solution latencies that were within 18ms of the N170 latency. The combination of data from these techniques suggested that electrical brain activity at the latency of the N170 is highly represented in fMRI statistical maps.
    Full-text · Article · Sep 2009 · Brain Topography
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    Adam O Hebb · Andrew V Poliakov
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    ABSTRACT: Deep brain stimulation (DBS) has become a routine therapy for Parkinson's disease. Standard CT imaging, often used to evaluate DBS electrodes in patients with limited benefit or significant side effects, has limitations including inability to distinguish different metallic components of the DBS lead. CT imaging with an extended Hounsfield unit (EHU) scale allows advanced image processing techniques to detect individual electrodes. EHU-CT may be co-registered to MRI volumes to provide accurate anatomical visualization of DBS lead contacts.
    Full-text · Article · Apr 2009 · Stereotactic and Functional Neurosurgery
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    ABSTRACT: We propose a method for retrieving similar fMRI statistical images given a query fMRI statistical image. Our method thresholds the voxels within those images and extracts spatially distinct regions from the voxels that remain. Each region is defined by a feature vector that contains the region centroid, the region area, the average activation value for all the voxels within that region, the variance of those activation values, the average distance of each voxel within that region to the region's centroid, and the variance of the voxel's distance to the region's centroid. The similarity between two images is obtained by the summed minimum distance of their constituent feature vectors. Results on a dataset of fMRI statistical images from experiments involving distinct cognitive tasks are shown.
    Full-text · Article · Feb 2009 · Proceedings of SPIE - The International Society for Optical Engineering

Publication Stats

935 Citations
153.43 Total Impact Points


  • 2009-2015
    • Seattle Children's Hospital
      • Department of Radiology
      Seattle, Washington, United States
  • 1996-2013
    • University of Washington Seattle
      • • Department of Neurological Surgery
      • • Department of Biological Structure
      • • Department of Physiology and Biophysics
      Seattle, Washington, United States
  • 1999
    • University Center Rochester
      • Department of Neurology
      Rochester, Minnesota, United States
  • 1998
    • St. Mary's Hospital (WI, USA)
      Madison, Wisconsin, United States
  • 1992-1995
    • University of Adelaide
      • Department of Physiology
      Tarndarnya, South Australia, Australia