Andreas J Bartsch

Publications of Andreas J Bartsch

• Ulnar neuropathy at the elbow: MR neurography--nerve T2 signal increase and caliber.

  Authors: Philipp Bäumer, Thomas Dombert, Frank Staub, Thorsten Kaestel, Andreas J Bartsch, Sabine Heiland, Martin Bendszus, Mirko Pham

  Radiology. 07/2011; 260(1):199-206.

  To assess nerve T2 signal and caliber as diagnostic signs at magnetic resonance (MR) neurography in ulnar neuropathy at the elbow (UNE). This prospective study was approved by the institutionalTo assess nerve T2 signal and caliber as diagnostic signs at magnetic resonance (MR) neurography in ulnar neuropathy at the elbow (UNE). This prospective study was approved by the institutional review board, and written informed consent was obtained from all participants. Twenty patients with UNE were graded by using clinical criteria and nerve conduction studies as mild (n = 12) and severe (n = 8) and were compared with 20 healthy control subjects. All subjects underwent ulnar nerve MR neurography (in-plane resolution of 0.4 × 0.4 mm) covering the elbow region, including T2-weighted imaging with fat suppression (turbo inversion-recovery magnitude sequence: repetition time msec/echo time msec/inversion time msec, 6, 120/66/180) and T1-weighted turbo spin-echo imaging (843/16). Nerve T2 signal increase, measured by using T2-weighted contrast-to-noise ratios across the cubital tunnel, and nerve caliber, determined by using T1-weighted pixelwise measurement of cross-sectional nerve area, were evaluated as diagnostic signs. Qualitative assessment by using visual grading was performed additionally. Diagnostic performance, as determined with area under the receiver operating characteristic curve (AUC), was excellent for nerve T2 signal to discriminate UNE from a normal finding (AUC = 0.94; 95% confidence interval [CI]: 0.87, 1.00) and was excellent for nerve caliber to discriminate severe from mild UNE (AUC = 0.95; 95% CI: 0.85, 1.00). Qualitative assessment demonstrated sensitivity of 83% and specificity of 85% for MR neurography of UNE. Nerve T2 signal increase seems to be an accurate sign to determine the presence of UNE. Nerve caliber enlargement discriminates severe from mild UNE. UNE may be diagnosed with high accuracy by means of quantitative or qualitative evaluation of these signs.

• Sustained reperfusion after blockade of glycoprotein-receptor-Ib in focal cerebral ischemia: an MRI study at 17.6 Tesla.

  Authors: Mirko Pham, Xavier Helluy, Christoph Kleinschnitz, Peter Kraft, Andreas J Bartsch, Peter Jakob, Bernhard Nieswandt, Martin Bendszus, Guido Stoll

  PloS one. 01/2011; 6(4):e18386.

  Inhibition of early platelet adhesion by blockade of glycoprotein-IB (GPIb) protects mice from ischemic stroke. To elucidate underlying mechanisms in-vivo, infarct development was followed byInhibition of early platelet adhesion by blockade of glycoprotein-IB (GPIb) protects mice from ischemic stroke. To elucidate underlying mechanisms in-vivo, infarct development was followed by ultra-high field MRI at 17.6 Tesla. Cerebral infarction was induced by transient-middle-cerebral-artery-occlusion (tMCAO) for 1 hour in C57/BL6 control mice (N = 10) and mice treated with 100 µg Fab-fragments of the GPIb blocking antibody p0p/B 1 h after tMCAO (N = 10). To control for the effect of reperfusion, additional mice underwent permanent occlusion and received anti-GPIb treatment (N = 6; pMCAO) or remained without treatment (N = 3; pMCAO). MRI 2 h and 24 h after MCAO measured cerebral-blood-flow (CBF) by continuous arterial-spin labelling, the apparent-diffusion-coefficient (ADC), quantitative-T2 and T2-weighted imaging. All images were registered to a standard mouse brain MRI atlas and statistically analysed voxel-wise, and by cortico-subcortical ROI analysis. Anti-GPIb treatment led to a relative increase of postischemic CBF vs. controls in the cortical territory of the MCA (2 h: 44.2±6.9 ml/100 g/min versus 24 h: 60.5±8.4; p = 0.0012, F((1,18)) = 14.63) after tMCAO. Subcortical CBF 2 h after tMCAO was higher in anti-GPIb treated animals (45.3±5.9 vs. controls: 33.6±4.3; p = 0.04). In both regions, CBF findings were clearly related to a lower probability of infarction (Cortex/Subcortex of treated group: 35%/65% vs. controls: 95%/100%) and improved quantitative-T2 and ADC. After pMCAO, anti-GPIb treated mice developed similar infarcts preceded by severe irreversible hypoperfusion as controls after tMCAO indicating dependency of stroke protection on reperfusion. Blockade of platelet adhesion by anti-GPIb-Fab-fragments results in substantially improved CBF early during reperfusion. This finding was in exact spatial correspondence with the prevention of cerebral infarction and indicates in-vivo an increased patency of the microcirculation. Thus, progression of infarction during early ischemia and reperfusion can be mitigated by anti-platelet treatment.

• Background MR gradient noise and non-auditory BOLD activations: A data-driven perspective.

  Authors: Sven Haller, György A Homola, Klaus Scheffler, Christian F Beckmann, Andreas J Bartsch

  Brain research. 07/2009;

  The effect of echoplanar imaging (EPI) acoustic background noise on blood oxygenation level dependent (BOLD) activations was investigated. Two EPI pulse sequences were compared: (i) conventional EPIThe effect of echoplanar imaging (EPI) acoustic background noise on blood oxygenation level dependent (BOLD) activations was investigated. Two EPI pulse sequences were compared: (i) conventional EPI with a pulsating sound component of typically 8-10 Hz, which is a potent physiological stimulus, and (ii) the more recently developed continuous-sound EPI, which is perceived as less distractive despite equivalent peak sound pressure levels. Sixteen healthy subjects performed an established demanding visual n-back working memory task. Using an exploratory data analysis technique (tensorial probabilistic independent component analysis; tensor-PICA), we studied the inter-session/within-subject response variability introduced by continuous-sound versus conventional EPI acoustic background noise in addition to temporal and spatial signal characteristics. The analysis revealed a task-related component associated with the established higher-level working memory and motor feedback response network, which exhibited a significant 19% increase in its average effect size for the continuous-sound as opposed to conventional EPI. Stimulus-related lower-level activations, such as primary visual areas, were not modified. EPI acoustic background noise influences much more than the auditory system per se. This analysis provides additional evidence for an enhancement of task-related, extra-auditory BOLD activations by continuous-sound EPI due to less distractive acoustic background gradient noise.

• The effect of ethanol on human brain metabolites longitudinally characterized by proton MR spectroscopy.

  Authors: Armin Biller, Andreas J Bartsch, György Homola, László Solymosi, Martin Bendszus

  Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism. 03/2009;

  The effect ethanol exerts on the human brain has not yet been addressed by longitudinal magnetic resonance (MR) spectroscopic experiments. Therefore, we longitudinally characterized cerebralThe effect ethanol exerts on the human brain has not yet been addressed by longitudinal magnetic resonance (MR) spectroscopic experiments. Therefore, we longitudinally characterized cerebral metabolite changes in 15 healthy individuals by proton magnetic resonance spectroscopy ((1)H-MRS) subsequent to the ingestion of a standard beverage (mean peak blood alcohol concentration (BAC): 51.43+/-10.27 mg/dL). Each participant was examined before, over 93.71+/-11.17 mins immediately after and 726.36+/-94.96 mins (12.11+/-1.58 h) past per os alcohol exposure. Fronto-mesial and cerebellar ethanol concentrations over time were similar as determined by the LCModel analysis of spectral data. Alcohol-induced changes of fronto-mesial creatine, choline, glucose, inositol and aspartate levels for 5.79+/-2.94 mins upon ingestion as well as cerebellar choline and inositol levels for 8.64+/-2.98 mins past exposure. Closely associated with ethanol concentrations, supratentorial creatine, choline, inositol and aspartate levels decreased after ethanol administration, whereas glucose levels increased. Similarly, infratentorial choline and inositol concentrations were negatively correlated with ethanol levels over time. There were no changes in N-acetyl-aspartate levels upon alcohol exposure. Furthermore, no influence of ethanol on brain water integrals was detected. Ethanol consumption may directly increase oxidative stress and the neuronal vulnerability to it. In addition, our results are compatible with ethanol-induced cell membrane modifications and alternative energy substrate usage upon alcohol exposure.Journal of Cerebral Blood Flow & Metabolism advance online publication, 25 February 2009; doi:10.1038/jcbfm.2009.12.

• The impact of balloon angioplasty on the evolution of vasospasm-related infarction after aneurysmal subarachnoid hemorrhage.

  Authors: Leonie Jestaedt, Mirko Pham, Andreas J Bartsch, Ekkehard Kunze, Klaus Roosen, László Solymosi, Martin Bendszus

  Neurosurgery. 04/2008; 62(3):610-7; discussion 610-7.

  OBJECTIVE: Vasospasm of the cerebral vessels remains a major source for morbidity and mortality after aneurysmal subarachnoid hemorrhage. The purpose of this study was to evaluate the frequency ofOBJECTIVE: Vasospasm of the cerebral vessels remains a major source for morbidity and mortality after aneurysmal subarachnoid hemorrhage. The purpose of this study was to evaluate the frequency of infarction after transluminal balloon angioplasty (TBA) in patients with severe subarachnoid hemorrhage-related vasospasm. METHODS: We studied 38 patients (median Hunt and Hess Grade II and median Fisher Grade 4) with angiographically confirmed severe vasospasm (>70% vessel narrowing). A total of 118 vessels with severe vasospasm in the anterior circulation were analyzed. Only the middle cerebral artery, including the terminal internal carotid artery, was treated with TBA (n = 57 vessel segments), whereas the anterior cerebral artery was not treated (n = 61 vessel segments). For both the treated and the untreated vessel territories, infarction on unenhanced computed tomographic scan was assessed as a marker for adverse outcome. RESULTS: Infarction after TBA occurred in four middle cerebral artery territories (four out of 57 [7%]), whereas the infarction rate was 23 out of 61 (38%) in the anterior cerebral artery territories not subjected to TBA (P < 0.001, Fisher exact test). Three procedure-related complications occurred during TBA (dissection, n = 1; temporary vessel occlusions, n = 2). One of these remained asymptomatic, whereas this may have contributed to the development of infarction on follow-up computed tomographic scans in two cases. CONCLUSION: In a population of patients with a high risk of infarction resulting from vasospasm after subarachnoid hemorrhage, the frequency of infarction in the distribution of vessels undergoing TBA amounts to 7% and is significantly lower than in vessels not undergoing TBA despite some risk inherent to the procedure.

• Endovascular occlusion of aneurysms using a new bioactive coil: a matched pair analysis with bare platinum coils.

  Authors: Martin Bendszus, Andreas J Bartsch, Laszlo Solymosi

  Stroke; a journal of cerebral circulation. 11/2007; 38(10):2855-7.

  BACKGROUND AND PURPOSE: To assess safety and efficacy data of a new bioactive coil (Cerecyte) which is loaded with polyglycolic acid on the inside of the coil. METHODS: Fifty-four patients harboringBACKGROUND AND PURPOSE: To assess safety and efficacy data of a new bioactive coil (Cerecyte) which is loaded with polyglycolic acid on the inside of the coil. METHODS: Fifty-four patients harboring 55 aneurysms were treated with Cerecyte coils. These aneurysms were matched in localization and size with aneurysms treated with bare platinum coils. RESULTS: Periprocedural complications and handling did not differ between both groups. Initial aneurysm occlusion was comparable in both treatment groups. At 6 months angiographic follow-up, the aneurysms occluded with Cerecyte coils had a higher chance for complete occlusion (P=0.045) and tended to a lower retreatment rate (P=0.056). CONCLUSIONS: Cerecyte coils are as safe as bare platinum coils in the endovascular occlusion of aneurysms. This matched pair analysis indicates a higher occlusion rate of aneurysms occluded with Cerecyte coils.

• Scanning for the scanner: FMRI of audition by read-out omissions from echo-planar imaging.

  Authors: Andreas J Bartsch, György Homola, Stefan Thesen, Peter Sahmer, Ralph Keim, Christian F Beckmann, Armin Biller, Christoph Knaus, Martin Bendszus

  NeuroImage. 04/2007; 35(1):234-43.

  Echo-planar imaging (EPI) generates considerable acoustic noise by rapidly oscillating gradients. In functional magnetic resonance imaging (FMRI), unshielded EPI sounds activate the auditory systemEcho-planar imaging (EPI) generates considerable acoustic noise by rapidly oscillating gradients. In functional magnetic resonance imaging (FMRI), unshielded EPI sounds activate the auditory system inasmuch as it is responsive. Instead of attenuating EPI noise, our goal was to utilize it for auditory FMRI by omitting read-outs from the pulse sequence's gradient train. Read-out gradient pulses are the primary noise determinant of EPI introducing its peak sound level and fundamental frequency peak which inversely relates to twice the echo spacing. Using model-driven analyses, we demonstrate that withholding read-outs from EPI is suited to reliably evoke hemodynamic blood oxygenation level-dependent (BOLD) signal modulations bilaterally in the auditory cortex of normal hearing subjects (n=60). To investigate the utility of EPI read-out omissions for auditory FMRI at an individual subject's level, we compare traditional Family-Wise-Error-Rate (FWER)-corrected maximum height thresholding to spatial mixture modeling (SMM). With the latter, appropriate bilateral auditory activations were confirmed in 95% of the individuals, whereas FWER-based voxel thresholding detected such activations in up to 72%. We illustrate the applicability of this novel EPI modification for clinical diagnostic purposes and report on a patient with bilateral large vestibular aqueducts (LVAs) and severe binaural sensorineural hearing loss (SNHL). In this particular case, read-out omissions from EPI were used to assert residual audition prior to cochlear implantation (CI). Requiring no specific task compliance or sophisticated stimulation equipment other than the scanner on its own, FMRI by read-out omissions lends itself to auditory investigations and to quickly probe audition.

• Manifestations of early brain recovery associated with abstinence from alcoholism.

  Authors: Andreas J Bartsch, György Homola, Armin Biller, Stephen M Smith, Heinz-Gerd Weijers, Gerhard A Wiesbeck, Mark Jenkinson, Nicola De Stefano, László Solymosi, Martin Bendszus

  Brain : a journal of neurology. 02/2007; 130(Pt 1):36-47.

  Chronic alcohol abuse results in morphological, metabolic, and functional brain damage which may, to some extent, be reversible with early effects upon abstinence. Although morphometric,Chronic alcohol abuse results in morphological, metabolic, and functional brain damage which may, to some extent, be reversible with early effects upon abstinence. Although morphometric, spectroscopic, and neuropsychological indicators of cerebral regeneration have been described previously, the overall amount and spatial preference of early brain recovery attained by abstinence and its associations with other indicators of regeneration are not well established. We investigated global and local brain volume changes in a longitudinal two-timepoint study with T1-weighted MRI at admission and after short-term (6-7 weeks) sobriety follow-up in 15 uncomplicated, recently detoxified alcoholics. Volumetric brain gain was related to metabolic and neuropsychological recovery. On admission and after short-term abstinence, structural image evaluation using normalization of atrophy (SIENA), its voxelwise statistical extension to multiple subjects, proton MR spectroscopy (1H-MRS), and neuropsychological tests were applied. Upon short-term sobriety, 1H-MRS levels of cerebellar choline and frontomesial N-acetylaspartate (NAA) were significantly augmented. Automatically detected global brain volume gain amounted to nearly two per cent on average and was spatially significant around the superior vermis, perimesencephalic, periventricular and frontal brain edges. It correlated positively with the percentages of cerebellar and frontomesial choline increase, as detected by 1H-MRS. Moreover, frontomesial NAA gains were associated with improved performance on the d2-test of attention. In 10 age- and gender-matched healthy control subjects, no significant brain volume or metabolite changes were observed. Although cerebral osmotic regulations may occur initially upon sobriety, significant increases of cerebellar choline and frontomesial NAA levels detected at stable brain water integrals and creatine concentrations, serum electrolytes and red blood cell indices in our patient sample suggest that early brain recovery through abstinence does not simply reflect rehydration. Instead, even the adult human brain and particularly its white matter seems to possess genuine capabilities for regrowth. Our findings emphasize metabolic as well as regionally distinct morphological capacities for partial brain recovery from toxic insults of chronic alcoholism and substantiate early measurable benefits of therapeutic sobriety. Further understanding of the precise mechanisms of this recovery may become a valuable model of brain regeneration with relevance for other disorders.

• Acquisition and voxelwise analysis of multi-subject diffusion data with tract-based spatial statistics.

  Authors: Stephen M Smith, Heidi Johansen-Berg, Mark Jenkinson, Daniel Rueckert, Thomas E Nichols, Karla L Miller, Matthew D Robson, Derek K Jones, Johannes C. Klein, Andreas J Bartsch, Timothy E J Behrens

  Nature protocols. 01/2007; 2(3):499-503.

  There is much interest in using magnetic resonance diffusion imaging to provide information on anatomical connectivity in the brain by measuring the diffusion of water in white matter tracts. AmongThere is much interest in using magnetic resonance diffusion imaging to provide information on anatomical connectivity in the brain by measuring the diffusion of water in white matter tracts. Among the measures, the most commonly derived from diffusion data is fractional anisotropy (FA), which quantifies local tract directionality and integrity. Many multi-subject imaging studies are using FA images to localize brain changes related to development, degeneration and disease. In a recent paper, we presented a new approach, tract-based spatial statistics (TBSS), which aims to solve crucial issues of cross-subject data alignment, allowing localized cross-subject statistical analysis. This works by transforming the data from the centers of the tracts that are consistent across a study's subjects into a common space. In this protocol, we describe the MRI data acquisition and analysis protocols required for TBSS studies of localized change in brain connectivity across multiple subjects.

• Effect of fMRI acoustic noise on non-auditory working memory task: comparison between continuous and pulsed sound emitting EPI.

  Authors: Sven Haller, Andreas J Bartsch, Ernst W Radue, Markus Klarhöfer, Erich Seifritz, Klaus Scheffler

  Magma (New York, N.Y.). 12/2005; 18(5):263-71.

  Conventional blood oxygenation level-dependent (BOLD) based functional magnetic resonance imaging (fMRI) is accompanied by substantial acoustic gradient noise. This noise can influence theConventional blood oxygenation level-dependent (BOLD) based functional magnetic resonance imaging (fMRI) is accompanied by substantial acoustic gradient noise. This noise can influence the performance as well as neuronal activations. Conventional fMRI typically has a pulsed noise component, which is a particularly efficient auditory stimulus. We investigated whether the elimination of this pulsed noise component in a recent modification of continuous-sound fMRI modifies neuronal activations in a cognitively demanding non-auditory working memory task. Sixteen normal subjects performed a letter variant n-back task. Brain activity and psychomotor performance was examined during fMRI with continuous-sound fMRI and conventional fMRI. We found greater BOLD responses in bilateral medial frontal gyrus, left middle frontal gyrus, left middle temporal gyrus, left hippocampus, right superior frontal gyrus, right precuneus and right cingulate gyrus with continuous-sound compared to conventional fMRI. Conversely, BOLD responses were greater in bilateral cingulate gyrus, left middle and superior frontal gyrus and right lingual gyrus with conventional compared to continuous-sound fMRI. There were no differences in psychomotor performance between both scanning protocols. Although behavioral performance was not affected, acoustic gradient noise interferes with neuronal activations in non-auditory cognitive tasks and represents a putative systematic confound.

• Heparin and air filters reduce embolic events caused by intra-arterial cerebral angiography: a prospective, randomized trial.

  Authors: Martin Bendszus, Martin Koltzenburg, Andreas J Bartsch, Roland Goldbrunner, Thomas Günthner-Lengsfeld, Franz X Weilbach, Klaus Roosen, Klaus V Toyka, László Solymosi

  Circulation. 10/2004; 110(15):2210-5.

  BACKGROUND: Intra-arterial cerebral angiography is associated with a low risk for neurological complications, but clinically silent ischemic events after angiography have been seen in a substantialBACKGROUND: Intra-arterial cerebral angiography is associated with a low risk for neurological complications, but clinically silent ischemic events after angiography have been seen in a substantial number of patients. METHODS AND RESULTS: In a prospective study, diffusion-weighted magnetic resonance imaging (DW-MRI) before and after intra-arterial cerebral angiography and transcranial Doppler sonography during angiography were used to evaluate the frequency of cerebral embolism. One hundred fifty diagnostic cerebral angiographies were randomized into 50 procedures, each using conventional angiographic technique, or systemic heparin treatment throughout the procedure, or air filters between the catheter and both the contrast medium syringe and the catheter flushing. There was no neurological complication during or after angiography. Overall, DW-MRI revealed 26 new ischemic lesions in 17 patients (11%). In the control group, 11 patients showed a total of 18 lesions. In the heparin group, 3 patients showed a total of 4 lesions. In the air filter group, 3 patients exhibited a total of 4 lesions. The reduced incidence of ischemic events in the heparin and air filter groups compared with the control group was significantly different (P=0.002). Transcranial Doppler sonography demonstrated a large number of microembolic signals that was significantly lower in the air filter group compared with the heparin and control groups (P<0.01), which did not differ from each other. CONCLUSIONS: Air filters and heparin both reduce the incidence of silent ischemic events detected by DW-MRI after intra-arterial cerebral angiography and can potentially lower clinically overt ischemic complications. This may apply to any intra-arterial angiographic procedure.

• Brain electrical dysfunction of the anterior cingulate in schizophrenic patients.

  Authors: Andreas J Fallgatter, Andreas J Bartsch, Juergen Zielasek, Martin J Herrmann

  Psychiatry research. 10/2003; 124(1):37-48.

  The anterior cingulate cortex (ACC) is a key region within the human prefrontal cortex that has been shown to be dysfunctional in schizophrenic patients. Supporting evidence for this notion has beenThe anterior cingulate cortex (ACC) is a key region within the human prefrontal cortex that has been shown to be dysfunctional in schizophrenic patients. Supporting evidence for this notion has been collected with neuroimaging methods during various cognitive activation tasks. Recently, electrophysiological ACC activity has been demonstrated by means of a three-dimensional source location with low resolution electromagnetic tomography (LORETA) in the event-related potentials elicited during the NoGo condition of the Continuous Performance Test (CPT) as compared to its Go condition. Thirty-one schizophrenic patients and 31 age- and gender-matched healthy volunteers were investigated with this newly developed electrophysiological method. LORETA analysis revealed a significantly diminished brain electrical activity in the ACC of schizophrenic patients as compared to controls during the NoGo condition of the CPT. This result supports the assumption of a functional deficit of the ACC during this cognitive task as a central feature in schizophrenias and, thereby, specifies the general concept of hypofrontality. Moreover, this investigation underscores the value of sophisticated electrophysiological methods in combination with unambiguously designed mental tasks for the evaluation of the pathophysiological processes underlying schizophrenic diseases.

• MR imaging in the differential diagnosis of neurogenic foot drop.

  Authors: Martin Bendszus, Carsten Wessig, Karlheinz Reiners, Andreas J Bartsch, Laszlo Solymosi, Martin Koltzenberg

  AJNR. American journal of neuroradiology. 09/2003; 24(7):1283-9.

  BACKGROUND AND PURPOSE: Prolonged T2 relaxation time of denervated muscle has been described in several clinical and experimental studies. The purpose of this study was to evaluate the utility of MRBACKGROUND AND PURPOSE: Prolonged T2 relaxation time of denervated muscle has been described in several clinical and experimental studies. The purpose of this study was to evaluate the utility of MR imaging in the diagnosis of neurogenic muscle disorders compared with that of clinical and electrophysiologic examination. METHODS: In a prospective study, 40 consecutive patients clinically presenting with a foot drop were included. MR imaging of the lower leg included axial T1-weighted and axial turbo inversion recovery magnitude (TIRM) sequences. Two readers blinded to clinical data evaluated T1-weighted images for anatomic localization of affected muscles and TIRM images for patterns of signal intensity increase. After MR imaging, a detailed neurophysiologic examination was performed. Cause of foot drop was independently determined on the basis of MR and electrophysiologic data. RESULTS: Clinical examination and electromyography (EMG) disclosed 20 peroneal nerve lesions, nine cases of L5 radiculopathy, and 11 nerve lesions extending beyond neural structures. MR imaging revealed three distinct patterns of signal intensity increase on TIRM images: peroneal nerve pattern, L5 pattern, and unspecific pattern. MR imaging and EMG findings were in agreement in 37 (92%) of 40 patients. In three patients, MR imaging revealed a more widespread involvement than did EMG. In one of these patients, denervation in the corresponding muscle was validated by follow-up EMG. No false-negative diagnoses were made by use of MR imaging as compared with use of EMG. CONCLUSION: MR imaging improves accuracy in the differential diagnosis of peripheral nerve lesions compared with that of EMG and can supplement EMG in the diagnosis of denervated muscles.