Biomedical subjects

Reto A Meuli

Publications and source records attributed to Reto A Meuli.

5 recordsLinked to original sources

PubMed2006

Multisensory interactions within human primary cortices revealed by BOLD dynamics.

Whether signals from different sensory modalities converge and interact within primary cortices in humans is unresolved, despite emerging evidence in animals. This is partially because of debates concerning the appropriate analyses of functional magnetic resonance imaging (fMRI) data in response to multisensory phenomena. Using event-related fMRI, we observed that simple auditory stimuli (noise bursts) activated primary visual cortices and that simple visual stimuli (checkerboards) activated primary auditory cortices, indicative of multisensory convergence. Moreover, analyses of blood oxygen level-dependent response dynamics revealed facilitation of hemodynamic response peak latencies and slopes for multisensory auditory-visual stimuli versus either unisensory condition, indicative of multisensory interactions within primary sensory cortices. Neural processing at the lowest cortical levels can be modulated by interactions between the senses. Temporal information in fMRI data can reveal these modulations and overcome analytic and interpretational challenges of more traditional procedures. In addition to providing an essential translational link with animal models, these results suggest that longstanding notions of cortical organization need to be revised to include multisensory interactions as an inherent component of functional brain organization.

Acoustic Stimulation↗

PubMed2005

Visuo-motor pathways in humans revealed by event-related fMRI.

Whether different brain networks are involved in generating unimanual responses to a simple visual stimulus presented in the ipsilateral versus contralateral hemifield remains a controversial issue. Visuo-motor routing was investigated with event-related functional magnetic resonance imaging (fMRI) using the Poffenberger reaction time task. A 2 hemifield x 2 response hand design generated the "crossed" and "uncrossed" conditions, describing the spatial relation between these factors. Both conditions, with responses executed by the left or right hand, showed a similar spatial pattern of activated areas, including striate and extrastriate areas bilaterally, SMA, and M1 contralateral to the responding hand. These results demonstrated that visual information is processed bilaterally in striate and extrastriate visual areas, even in the "uncrossed" condition. Additional analyses based on sorting data according to subjects' reaction times revealed differential crossed versus uncrossed activity only for the slowest trials, with response strength in infero-temporal cortices significantly correlating with crossed-uncrossed differences (CUD) in reaction times. Collectively, the data favor a parallel, distributed model of brain activation. The presence of interhemispheric interactions and its consequent bilateral activity is not determined by the crossed anatomic projections of the primary visual and motor pathways. Distinct visuo-motor networks need not be engaged to mediate behavioral responses for the crossed visual field/response hand condition. While anatomical connectivity heavily influences the spatial pattern of activated visuo-motor pathways, behavioral and functional parameters appear to also affect the strength and dynamics of responses within these pathways.

Adult↗

PubMed2005

Perfusion and diffusion MRI of glioblastoma progression in a four-year prospective temozolomide clinical trial.

PURPOSE: This study was performed to determine the impact of perfusion and diffusion magnetic resonance imaging (MRI) sequences on patients during treatment of newly diagnosed glioblastoma. Special emphasis has been given to these imaging technologies as tools to potentially anticipate disease progression, as progression-free survival is frequently used as a surrogate endpoint. METHODS AND MATERIALS: Forty-one patients from a phase II temolozomide clinical trial were included. During follow-up, images were integrated 21 to 28 days after radiochemotherapy and every 2 months thereafter. Assessment of scans included measurement of size of lesion on T1 contrast-enhanced, T2, diffusion, and perfusion images, as well as mass effect. Classical criteria on tumor size variation and clinical parameters were used to set disease progression date. RESULTS: A total of 311 MRI examinations were reviewed. At disease progression (32 patients), a multivariate Cox regression determined 2 significant survival parameters: T1 largest diameter (p < 0.02) and T2 size variation (p < 0.05), whereas perfusion and diffusion were not significant. CONCLUSION: Perfusion and diffusion techniques cannot be used to anticipate tumor progression. Decision making at disease progression is critical, and classical T1 and T2 imaging remain the gold standard. Specifically, a T1 contrast enhancement over 3 cm in largest diameter together with an increased T2 hypersignal is a marker of inferior prognosis.

Analysis of Variance↗

PubMed2004

Imaging viable brain tissue with CT scan during acute stroke.

Viability of the cerebral parenchyma is dependent on cerebral blood flow (CBF). The assessment of cerebral perfusion in patients with acute stroke, in a clinically relevant time frame, could be of utmost importance for patient selection before thrombolytic therapy. In individual patients, quantitative mapping of CBF to indicate the severity and potential reversibility of neuronal damage can be used to predict which brain tissue will be salvaged with reperfusion or die without it (penumbra), as well as which brain tissue is already infarcted. Recent investigations of perfusion CT have shown major advances in the assessment of acute stroke patients. Perfusion CT offers a number of practical advantages over other cerebral perfusion imaging methods as it can be performed immediately after unenhanced CT, and used, in general, to exclude cerebral haemorrhage. It is fast (typical procedure time <5 min) and does not require specialized computer hardware. The accuracy of cerebral perfusion maps has been demonstrated for normal and decreased CBF value by comparison with xenon CT used as a gold standard. Perfusion CT infarct and penumbra maps provide a potential recuperation ratio (PRR) (or Lausanne Stroke Index), defined as PRR = penumbra/ (penumbra + infarct). This index is correlated with the improvement of the National Institutes of Health Stroke Scale (NIHSS) in case of arterial recanalization. Also, the size of the ischaemic area (infarct + penumbra) is correlated with the NIHSS score on hospital admission. Further studies may demonstrate the use of perfusion CT for the assessment of penumbra dynamics in function-specific brain areas. Perfusion CT is now ready to be used in clinical trials as a decision-making tool to tailor more precisely the thrombolytic therapy to the individual patient.

Brain↗

PubMed2002

Detection of low-contrast objects: experimental comparison of single- and multi-detector row CT with a phantom.

PURPOSE: To compare single-detector row computed tomography (CT) and multi-detector row CT by using an experimental phantom containing a contrast-detail modulus for detection of low-contrast structures to optimize acquisition protocols. MATERIALS AND METHODS: The parameters milliampere seconds, reconstructed section thickness, and elementary collimation for multi-detector CT were varied for two pitches with single- and multi-detector CT. For objective assessment of image quality, contrast-to-noise ratio (CNR) was calculated for an 8-HU low-contrast 15-mm-diameter object. Subjective assessment of image quality was performed by means of visual detection of low-contrast objects of various sizes by four independent observers. For each acquisition protocol, the effective doses required to obtain the CNR thresholds allowing 100% detection of 5-, 7-, and 9-mm-diameter objects were compared at single- and multi-detector CT at comparable section sensitivity profile with analysis of variance. RESULTS: Significant correlation was found between CNR measurements and subjective object detection (r = 0.95, P <.05). CNRs of 1.0, 0.8, and 0.6 were required to detect 100% of the 5-, 7-, and 9-mm-diameter objects, respectively. For reconstructed section thickness of 5-10 mm, comparable x-ray doses were required with single- and multi-detector CT to detect objects. For reconstructed sections thinner than 5 mm, single- and multi-detector CT allowed detection of only the 7- and 9-mm-thick objects, but a higher x-ray dose was required for multi- than for single-detector CT (P <.05). CONCLUSION: Multi-detector CT is less effective than single-detector CT in detection of small low-contrast objects if sections thinner than 5 mm are used. Results for single- and multi-detector CT were similar for sections 5 mm or thicker.

Analysis of Variance↗