Individual MR Images Research Articles

MRI-Guided Region-of-Interest Delineation Is Comparable to Manual Delineation in Dopamine Transporter SPECT Quantification in Patients: A Reproducibility Study

A particularly sensitive step in the quantification of SPECT images of the dopamine transporter (DAT) is a correct delineation of the region of interest (ROI). In this study, we primarily compared the reproducibility of the following different approaches for ROI delineation in SPECT images of the DAT: the use of manual delineation (MD) on high-count striatal slides directly on the SPECT image, ROI delineation based on individual MR images (MRD), and oversized striatal ROIs-that is, the striatal volume of interest (SVI), as described previously. We also assessed the ability of the different approaches to identify striatal pathology in patients with parkinsonism. Eight patients with highly variable reductions in cerebral DAT availability were SPECT-scanned twice with (123)I-labeled N-(3-iodoprop-(2E)-enyl)-2beta-carboxymethoxy-3beta-(4'-methylphenyl) nortropane bolus infusion setup and once with an MRI scanner. For SPECT/MRI coregistration, we used external fiducial markers visible on both MRI and SPECT. With the MD and MRD methods, the outcome parameters for DAT availability were the binding potentials and the ratio at equilibrium of specifically bound radioligand to nondisplaceable radioligand in tissue (BP(ND)). For the SVI method, the outcome parameter was the specific binding ratio (SBR). No statistically significant difference in striatal BP(ND) intraobserver reproducibility was seen among any of the 3 methods. The intraobserver reproducibility average +/- SD for MD was 7.0% +/- 4.1%; for MRD, 5.7% +/- 5.4%; and for SVI, 6.7% +/- 6.0%. Mean intrasubject variability, as determined from the test-retest scans, did not differ with the 3 delineation methods used. The average (+/-SD) intrasubject variability of striatal BP(ND) was 11.9% +/- 10.0% with MD and 14.6% +/- 15.3% with MRD. With the SVI method, the intrasubject variability of striatal specific binding ratio was 10.0% +/- 10.2%. BP(ND) values obtained with the MD and MRD methods were similar (paired t test, P > 0.4). In patients with reduced striatal DAT binding, the reproducibility of the outcome from ROI MD is comparable to both that obtained by delineation of ROI on individual MR images, followed by coregistration to the SPECT image, and that obtained with the SVI-based approach.

The SPECT tracer [123I]ADAM binds selectively to serotonin transporters: a double-blind, placebo-controlled study in healthy young men

PurposeThe tracer 123I-2-([2-({dimethylamino}methyl)phenyl]thio)-5-iodophenylamine ([123I]ADAM) has been developed to image serotonin transporters (SERTs) with SPECT. Preclinical studies have shown that [123I]ADAM binds selectively to SERTs. Moreover, initial human studies have shown that [123I]ADAM binding could be blocked by selective serotonin reuptake inhibitors (SSRIs). However, in humans it has not been proven that [123I]ADAM binds selectively to SERTs.MethodsWe examined the in vivo availability of SERTs in 12 healthy young volunteers 5 h after bolus injection of [123I]ADAM. To evaluate the selectivity of binding, four participants were pretreated (double-blinded design) with placebo, four with paroxetine (20 mg) and four with the dopamine/norepinephrine blocker methylphenidate (20 mg). SPECT studies were performed on a brain-dedicated system (Neurofocus), and the SPECT images were coregistered with individual MR scans of the brain. ADAM binding in SERT-rich brain areas and cerebellar cortex (representing non-specific binding) was assessed by drawing regions of interest (ROIs) on the individual MR images. Specific to non-specific ratios were used as the outcome measure.ResultsWe found that specific to non-specific ratios were statistically significantly lower in paroxetine-pretreated participants than in placebo- or methylphenidate-pretreated participants. No such difference was found between groups pretreated with placebo or methylphenidate.ConclusionOur preliminary findings suggest that [123I]ADAM binds selectively to SERTs in human brain.

A histology-based atlas of the C57BL/6J mouse brain deformably registered to in vivo MRI for localized radiation and surgical targeting

The C57BL/6J laboratory mouse is commonly used in neurobiological research. Digital atlases of the C57BL/6J brain have been used for visualization, genetic phenotyping and morphometry, but currently lack the ability to accurately calculate deviations between individual mice. We developed a fully three-dimensional digital atlas of the C57BL/6J brain based on the histology atlas of Paxinos and Franklin (2001 The Mouse Brain in Stereotaxic Coordinates 2nd edn (San Diego, CA: Academic)). The atlas uses triangular meshes to represent the various structures. The atlas structures can be overlaid and deformed to individual mouse MR images. For this study, we selected 18 structures from the histological atlas. Average atlases can be created for any group of mice of interest by calculating the mean three-dimensional positions of corresponding individual mesh vertices. As a validation of the atlas' accuracy, we performed deformable registration of the lateral ventricles to 13 MR brain scans of mice in three age groups: 5, 8 and 9 weeks old. Lateral ventricle structures from individual mice were compared to the corresponding average structures and the original histology structures. We found that the average structures created using our method more accurately represent individual anatomy than histology-based atlases alone, with mean vertex deviations of 0.044 mm versus 0.082 mm for the left lateral ventricle and 0.045 mm versus 0.068 mm for the right lateral ventricle. Our atlas representation gives direct spatial deviations for structures of interest. Our results indicate that MR-deformable histology-based atlases represent an accurate method to obtain accurate morphometric measurements of a population of mice, and that this method may be applied to phenotyping experiments in the future as well as precision targeting of surgical procedures or radiation treatment.

In-vivo animation of midazolam-induced electrocorticographic changes in humans

Previous human studies have demonstrated that midazolam-induced signal changes on scalp EEG recording include widespread augmentation of sigma-oscillations and that the amplitude of such oscillations is correlated to the severity of midazolam-induced amnesia. Still unanswered questions include whether midazolam-induced sigma-augmentation also involves the medial temporal region, which plays a role in memory encoding. Taking advantage of rare and unique opportunities to monitor neuronal activities using intracranial electrocorticography (ECoG) recording, we determined how intravenous administration of midazolam elicited spectral frequency changes in the human cerebral cortex, including the medial temporal region. We studied three children with focal epilepsy who underwent subdural electrode placement and extraoperative ECoG recording for subsequent resection of the seizure focus; an intravenous bolus of midazolam was given to abort an ongoing simple partial seizure or to provide sedation prior to induction of general anesthesia. ‘Midazolam-induced ECoG frequency alteration’ in sites distant from the seizure focus was sequentially animated on their individual three-dimensional MR images. The common ECoG changes induced by midazolam included gradual augmentation of sigma-oscillations (12–16 Hz) in the widespread non-epileptic regions, including the medial temporal region. The spatial and temporal alteration of ECoG spectral frequency pattern can be appreciated via animation movies. Midazolam-induced sigma-augmentation was observed in the medial temporal region in our relatively small cohort of human subjects. In-vivo animation of ECoG spectral measures provided a unique situation to study the effect of midazolam on neuronal processing in the deep brain regions.

Kinetic Modeling of 11C-SB207145 Binding to 5-HT4 Receptors in the Human Brain In Vivo

The serotonin 4 receptor (5-HT(4) receptor) is known to be involved in learning and memory. We evaluated for the first time the quantification of a novel 5-HT(4) receptor radioligand, (11)C-SB207145, for in vivo brain imaging with PET in humans. For evaluation of reproducibility, 6 subjects were scanned twice with (11)C-SB207145 on the same day. A further 2 subjects were scanned before and after blocking with the selective 5-HT(4) receptor inverse agonist piboserod (SB207266). Arterial blood samples were drawn for the calculation of metabolite-corrected arterial input functions. Regions of interest were delineated automatically on the individual's MR images coregistered to the PET images, and regional time-activity curves were extracted. Quantitative tracer kinetic modeling was investigated with 1- and 2-tissue-compartment models using plasma input functions and the simplified reference tissue model (SRTM). (11)C-SB207145 readily entered the brain and showed a distribution consistent with the known localization of the 5-HT(4) receptor. Using plasma input models, the time-activity data were well described by the 2-tissue-compartment model in all regions and allowed for the estimate of binding potentials relative to the reference region (BP(ND): striatum, 3.38 +/- 0.72; hippocampus, 0.82 +/- 0.19; parietal cortex, 0.30 +/- 0.08). Quantification with the 1-tissue-compartment model, 2-tissue-compartment model, and SRTM were associated with good test-retest reproducibility and time stability. However, the SRTM-generated BP(ND) values in the striatum were underestimated by 20%-43% in comparison to the 2-tissue-compartment model. The blocking study with piboserod confirmed that the radioligand was selective for the 5-HT(4) receptor, that the cerebellum was a suitable reference region devoid of specific binding, and that nonspecific binding was constant across brain regions. In vivo imaging of cerebral 5-HT(4) receptors can be determined reliably using (11)C-207145 PET with arterial input in humans. SRTM showed high reproducibility and reliability but bias in the striatum, and therefore, the use of SRTM should be considered carefully for individual applications.

Attention impairment in temporal lobe epilepsy: A neurophysiological approach via analysis of the P300 wave

Attention is often impaired in temporal lobe epilepsy (TLE). The P300 wave (an endogenous, event-related potential) is a correlate of attention which is usually recorded during an "oddball paradigm," where the subject is instructed to detect an infrequent target stimulus presented amongst frequent, standard stimuli. Modifications of the P300 wave's latency and amplitude in TLE have been suggested, but it is still not known whether the source regions also differ. Our hypothesis was that temporal lobe dysfunction would modify the P3 source regions in TLE patients. A comparative, high density, 128-channel electroencephalographic analysis of the characteristics of P300 (P3b latency and amplitude) was performed in 10 TLE patients and 10 healthy controls during auditory and visual oddball paradigms. The P3b sources were localized on individual 3D MR images using the LORETA method and intergroup statistical comparisons were performed using SPM2(R) software. Our main results (in both individual analyses and intergroup comparisons) revealed a reduction in temporal (and more particularly mesiotemporal) sources and, to a lesser extent, frontal sources in TLE patients, compared with controls. This reduction may reflect direct, local cortical dysfunction caused by the epileptic focus or more complex interference between epileptic networks and normal attentional pathways.

Comparison of navigated and non-navigated transcranial magnetic stimulation for motor cortex mapping, motor threshold and motor evoked potentials

Transcranial magnetic stimulation (TMS) can be used for non-invasive assessment of cortical physiology and descending motor pathways. However, the focus/exact site of cortical activation is considerably widespread in traditional TMS. When combined with MRI-based navigation, it allows specific anatomical areas of the cortex to be stimulated. The peripheral muscle responses to TMS are commonly measured as motor evoked potentials (MEPs). We compared the accuracy of cortical mapping, as well as the congruity of the motor thresholds (MT) and MEPs between navigated and non-navigated TMS procedures. Eight volunteers were studied in two sessions. In each session both hemispheres were stimulated with and without navigation. Non-navigated TMS: Both hemispheres were mapped without navigation to find the representation area of the thenar muscles based on induced MEP amplitudes. MT was then determined at the optimum coil location. Navigated TMS: Individual MR-images were used for the on-line navigation procedure. The cortical representation area of the thenar musculature was mapped at the “hand knob”. The optimum stimulus target was used for MT determination. The order of these two procedures was randomized. Following the MT determination, MEPs were recorded from 20 consecutive stimuli. The MTs were similar from session-to-session with no inter-hemispheric differences, and with and without navigation. The stimulus location was more spatially discrete in navigated TMS producing more stable MEPs with significantly higher amplitudes and shorter latencies. In summary, MEPs exhibit significant differences depending on whether navigation is used. However, the MTs are not significantly dependent on the discrete stimulation site.

Navigated transcranial magnetic stimulation and computed electric field strength reduce stimulator-dependent differences in the motor threshold

The motor threshold (MT) is a fundamental parameter for evaluating cortical excitability in transcranial magnetic stimulation (TMS) despite remarkable variation, both within, and between subjects. We intended to test whether the variation could be reduced by targeting the stimulation on-line and modeling the TMS-induced electric field on individual MR images. Navigated TMS was used to map the primary motor cortex for the representation area of the thenar muscles (abductor pollicis brevis) and to determine the MT. Thirteen healthy subjects participated in the study. To determine the between-subject variation, the MTs of nine subjects were measured with two different stimulators (comparison study). To study the individual variation, the MT measurement was repeated 20 times in four subjects always using the same stimulator (longitudinal study). In the comparison study, the MTs differed significantly between the two stimulators over all subjects (p<0.001), whereas the electric field strengths did not exhibit significant difference between the stimulators. Both, the MTs, and the electric field strengths showed similar variations, which were greater between subjects (comparison study) than within subjects (longitudinal study). In the comparison study, the distance between the locations of the two different coils on the scalp was significantly greater than the distance between the induced electric field maxima in the brain (p<0.001). We conclude that on-line navigation can be used to reduce the variation caused by different stimulator types and individual subject anatomy. In addition, cortical excitability can be evaluated by using computed electric field strength as well as stimulator-dependent MT.

IC-P2-114: Meta-analysis ROIs and minimal deformation templates improve PET-FDG as a candidate biomarker in Alzheimer's disease

Background: Research consistently finds hypometabolism of [18F]Fluorodeoxyglucose (FDG-PET) in patients diagnosed with Alzheimer’s Disease (AD). Identifying abnormalities in metabolism requires precise delineation of affected areas in order to maximize differences between groups, detect change over time and minimize variance. We generated meta-analysis ROIs (MetaROIs) from frequently cited coordinates in existing studies, and compared these regions with standard anatomical ROIs across three image preprocessing streams in order to identify potential bio-marker regions using data from the Alzheimer’s Disease Neuroimaging Initiative (AD 13), (Normal 12). Methods: Six terms relating to FDG-PET, AD, and Mild Cognitive Impairment (MCI) were used to search PubMed, resulting in 18 cross-sectional studies. Study coordinates were used to generate MetaROIs. A minimal deformation template (MDT) was generated for each group (AD, MCI, Normal), using high-resolution MR images, based on the method by Kochonuv et al. (2001). Preprocessing was done with three methods: (1) individual FDG-PET images were spatially normalized to the MNI FDG template, (2) individual MR images were spatially normalized to a group-specific template, then this transformation was applied to individual coregistered FDG-PET images, (3) same as (2) but additionally the FDG-PET image was masked with an individual gray-matter mask. Effect size and percent annual change delineated the most effective processing stream. Results: MetaROIs included frequently cited regions in bilateral posterior cingulate, bilateral angular gyri, and primarily left-sided frontal and temporal regions. MetaROIs exhibited larger mean group difference between AD and Normals compared to corresponding AAL MNI regions (effect size in posterior cingulate increased from 0.48 to 1.82). Normalization to MDT template further improved effect size by 7-15%. MetaROIs also increased twelve month percent change in AD patients (posterior cingulate increased from 8% to 11%). The same region in normals showed little change (MNI ROI 0.4% vs MetaROI 0.3%). Conclusions: The use of research-defined MetaROIs, along with a processing stream that reduced deformation and used individual gray matter masks, greatly improved the viability of FDG-PET as a candidate biomarker in AD.

Normative data of paired pulse paradigm in hand muscles - navigated TMS study

The motor cortex excitation-inhibition balance is traditionally studied using TMS paired-pulse (pp) technique [1]. We characterized the normal behavior of human primary motor cortex using pp paradigm with TMS, which was targeted using individual MR images.

Factors influencing cortical silent period: Optimized stimulus location, intensity and muscle contraction

Inhibitory silent period (SP) is a transient suppression of voluntary muscle activity after depolarization of representative motor neuronal populations following transcranial magnetic stimulation (TMS). Our aim was to evaluate and present an optimal protocol for the measurement of SP by (1) determining the impact of muscle activation level and stimulus intensity (SI) on the duration of SP, and, (2) studying the relationship between motor evoked potential (MEP) and SP, using targeted stimulus delivery. Single magnetic pulses were focused on the optimal representation area of the thenar musculature on primary motor cortex. We utilized real-time 3D-positioning of TMS-evoked electric field on anatomical structures derived from individual MR-images. The SI varied from 80% to 120% of individual resting motor threshold (MT). Muscle activation levels varied from 20% to 80% of the maximal voluntary contraction (MVC). Contralateral SP lengthened significantly with increasing SI independent of target muscle activation. The peak amplitude of the MEP was affected by SI and force. Latency and duration of the MEP were practically unaffected by SI or force. Focal stimulation at 110–120% MT and approximately 50% MVC (with only negligible need for control) provides most stable and informative SP. MEP should be included in SP as the error from marking the onset diminishes. This study provides a guideline for the consistent measurement of SP, which is applicable when using navigated or traditional TMS.

From ECoG near fields to EEG and MEG far fields

ECoG source reconstruction is a relatively new field as compared to the well-established surface EEG or MEG source reconstruction techniques. The exact determination of the ECoG electrode positions requires post-implantation CT images. The cortical structures, which are needed for volume conductor modeling, source space constraints, and visualization purposes, are derived from pre-implantation MR images. Since there is increasing interest in mapping and source reconstruction from ECoG grid data and comparison to EEG and MEG evaluations of epileptic patients, we computed potential and field distributions and performed source reconstructions from measured and simulated ECoG, EEG, and MEG data. We used realistically shaped BEM volume conductor models derived from individual MR images with dipolar as well as cortically constrained current density source models.

High opiate receptor binding potential in the human lateral pain system

To determine how opiate receptor distribution is co-localized with the distribution of nociceptive areas in the human brain, eleven male healthy volunteers underwent one PET scan with the subtype-nonselective opioidergic radioligand [ 18F]fluoroethyl-diprenorphine under resting conditions. The binding potential (BP), a parameter for the regional cerebral opioid receptor availability, was computed using the occipital cortex as reference region. The following regions of interest (ROIs) were defined on individual MR images: thalamus, sensory motor strip (SI/MI area), frontal operculum, parietal operculum, anterior insular cortex, posterior insular cortex, anterior cingulate cortex (ACC; peri- and subgenual part of “classical ACC” only), midcingulate cortex (MCC, posterior part of “classical ACC”), putamen, caudate nucleus and the amygdala. BP for [ 18F]fluoroethyl-diprenorphine was lowest in the sensory motor strip (0.30). Highest BP was found in thalamus (1.36), basal ganglia (putamen 1.22, caudate 1.16) and amygdala (1.21). In the cingulate cortex, ACC (1.11) had higher BP than MCC (0.86). In the operculo-insular region, we found high BPs in all ROIs: anterior insula (1.16), posterior insula (1.05), frontal operculum (0.99) and parietal operculum (0.77). Factor analysis of interindividual variability of opiate receptor BP revealed four factors (95% explained variance): (1) operculo-insular areas, ACC, MCC and putamen, (2) amygdala and thalamus, (3) caudate and thalamus, (4) SI/MI and MCC. Nociceptive areas of the lateral pain system (frontoparietal operculum and insula) have opiate receptor BPs significantly higher than SI/MI, comparable to anterior and midcingulate areas of the medial pain system. These findings suggest that the cortical anti-nociceptive effects of opiates are not only mediated by ACC and MCC, but also by the operculo-insular cortex, if it can be assumed that opioid binding mediates anti-nociception in those structures.

Standard atlas space for C57BL/6J neonatal mouse brain

A standard atlas space with stereotaxic co-ordinates for the postnatal day 0 (P0) C57BL/6J mouse brain was constructed from the average of eight individual co-registered MR image volumes. Accuracy of registration and morphometric variations in structures between subjects were analyzed statistically. We also applied this atlas coordinate system to data acquired using different imaging protocols as well as to a high-resolution histological atlas obtained from separate animals. Mapping accuracy in the atlas space was examined to determine the applicability of this atlas framework. The results show that the atlas space defined here provides a stable framework for image registration for P0 normal mouse brains. With an appropriate feature-based co-registration strategy, the probability atlas can also provide an accurate anatomical map for images acquired using invasive imaging methods. The atlas templates and the probability map of the anatomical labels are available at http://www.loni.ucla.edu/MAP/ .

Degree of Cerebellar Ataxia Correlates with Three-Dimensional MRI-Based Cerebellar Volume in Pure Cerebellar Degeneration

The aim of the present study was to compare the severity of cerebellar ataxia as measured by the International Cooperative Ataxia Rating Scale (ICARS) by Trouillas et al. [ J Neurol Sci 1997;145:205–211] with the cerebellar volume in chronic cerebellar disease. Fifteen patients with pure cerebellar degeneration were investigated. Seven patients suffered from spinocerebellar ataxia type 6, 5 from idiopathic late-onset cerebellar ataxia, 2 from autosomal dominant cerebellar ataxia type III and 1 from episodic ataxia type 2. Volumetric analysis was based on individual three-dimensional MR images. Total ICARS score significantly inversely correlated with the cerebellar volume (r = –0.805, p < 0.0001), correlations between ICARS subscores and cerebellar volume were significant for upper and lower limb ataxia, ataxia of posture and gait, and dysarthria, but not for the oculomotor subscore. The results suggest that the degree of cerebellar atrophy in pure cerebellar degenerative disorders is accompanied by comparable functional impairment (i.e. degree of cerebellar ataxia).

Ventilation imaging of the lung: Comparison of hyperpolarized helium-3 MR imaging with Xe-133 scintigraphy 1

Rationale and objectives To compare hyperpolarized helium-3 (HHe) magnetic resonance imaging (MRI) of the lung with standard Xe-133 lung ventilation scintigraphy. Materials and methods We performed a retrospective review of 15 subjects who underwent HHe MRI and Xe-133 lung ventilation imaging. Coronal MRI sections were acquired after a single inhalation of HHe gas, and standard posterior planar lung ventilation scintigraphy was performed during continuous breathing of Xe-133 gas. The first breath scintigram of each patient was compared with a composite MR image composed of the sum of the individual MR images and with the individual helium-3 MR images. Ventilation defects on the two imaging modalities were compared for size, conspicuity, and concordance in presence and location. Assessment was done separately for each of four lung quadrants. Results Comparing the composite HHe MR images with Xe-133 scintigraphy, ventilation defect size, conspicuity and concordance were the same in 67% (40/60), 63% (38/60), and 62% (37/60) quadrants, respectively. Comparing the individual HHe MR image sections with the Xe-133 ventilation scan, there was concordance between the ventilation defects in 27% (16/60) of quadrants. More defects were identified on the individual HHe MR images in 62% (37/60) of quadrants. Conclusion There was good agreement between composite HHe MR image and first breath Xe-133 scintigraphic images, supporting the widely held assumption that HHe MRI likely depicts first breath lung ventilation.

Reconstruction of extended cortical sources for EEG and MEG based on a Monte-Carlo-Markov-chain estimator.

A new procedure to model extended cortical sources from EEG and MEG recordings based on a probabilistic approach is presented. The method (SPMECS) was implemented within the framework of maximum likelihood estimators. Neuronal activity generating EEG or MEG signals was characterized by the number of sources and their location and extension. Based on the noise distribution of the measured data, source configurations were associated with the according value of the likelihood function. To find the most likely source, i.e., the maximum likelihood estimator, and its level of confidence, a stochastic solver (Metropolis algorithm) was applied. The method presented supports the incorporation of virtually any constraint, e.g., based on physiological and anatomical a priori knowledge. Thus, ambiguity of the ill-posed inverse problem was reduced considerably by confining sources to the cortical surface extracted from individual MR images. The influence of different levels and types of noise on the outcome was investigated by means of simulations. Somatosensory evoked magnetic fields analyzed by the method presented suggest that larger extended cortical areas are involved in the processing of combined finger stimulation as compared to single finger stimulation.

Functional MRI in Epilepsy

*Department of Neurology, Medical College of Wisconsin, Milwaukee, Wisconsin, U.S.A.; †University Hospital Gent, Gent, Belgium; ‡Departments of Diagnostic Radiology and Neurosurgery, Yale University, New Haven, Connecticut; §Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania; Clinical Epilepsy Section, National Institutes of Health, Bethesda, Maryland; ¶Department of Radiology, Mayo Clinic, Rochester, Minnesota; and **Department of Neurology, Medical College of Georgia, Augusta, Georgia, U.S.A.

Template Images for Nonhuman Primate Neuroimaging: 1. Baboon

Coregistration of functional brain images across many subjects offers several experimental advantages and is widely used for studies in humans. Voxel-based coregistration methods require a high-quality 3-D template image, preferably one that corresponds to a published atlas. Template images are available for human, but we could not find an appropriate template for neuroimaging studies in baboon. Here we describe the formation of a T1-weighted structural MR template image and a PET blood flow template, derived from 9 and 7 baboons, respectively. Custom software aligns individual MR images to the MRI template; human supervision is needed only to initially estimate any gross rotational misalignment. In these aligned individual images, internal subcortical fiducial points correspond closely to a photomicrographic baboon atlas with an average error of 1.53 mm. Cortical test points showed a mean error of 1.99 mm compared to the mean location for each point. Alignment of individual PET blood flow images directly to the PET template was compared to a two-step alignment process via each subject's MR image. The two transformations were identical within 0.41 mm, 0.54°, and 1.0% (translation, rotation, and linear stretch; mean). These quantities provide a check on the validity of the alignment software as well as of the template images. The baboon structural MR and blood flow PET templates are available on the Internet (purl.org/net/kbmd/b2k) and can be used as targets for any image registration software.

Cortical motor reorganization after paraplegia: an EEG study.

To determine whether a previously identified posterior reorganization of the cortical motor network after spinal cord injury (SCI) is correlated with prognosis and outcome. We applied the techniques of high-resolution EEG and dipole source analysis to record and map the motor potentials (MPs) of the movement-related cortical potentials in 44 patients after SCI. Twenty normal controls were also tested. Results were analyzed using a distance metric to compare MP locations. EEG was coregistered with individual specific MR images and a boundary element model created for dipole source analysis. MPs with finger movements were mapped to a posterior location in 20 of 24 tetraplegics compared with normal controls. Two patients, one studied 4 and one 6 weeks after injury, initially had posterior MPs that, on serial testing, moved to an anterior position with recovery. Dipole source localization of the MP generators confirmed these results. Nine of 20 paraplegics had a posterior MP location with actual or attempted toe movements. All 5 patients who could move their toes had posterior MPs. The MP was posterior in 4 of the 15 paralyzed patients. This is a significant difference in proportions. The only patient with paraparesis whose testing was repeated had an MP that moved to an anterior position with recovery. Posterior reorganization has a significant relationship to prognosis in paraplegia and is reversed in some SCI patients who recover function. Posterior reorganization may result from a preferential survival of axons that originate in somatosensory cortex and contribute to the corticospinal tract. These preliminary results should be verified by a larger prospective study.