Johannes Bernarding

Non-invasive functional mapping of the human motor cortex using near-infrared spectroscopy

We applied non-invasive multisite near-infrared spectroscopy (NIRS) to assess oxygenation changes during performance of a sequential finger opposition task in five healthy human adults. Oxygenation response was localized anatomically using three-dimensional high-resolution magnetic resonance imaging (3D MRI). NIRS measurements showed a localized increase in [oxy-Hb] and a decrease in [deoxy-Hb] in all subjects. The largest response was obtained when the measurement position was over the primary motor and sensory cortex hand area. Interestingly, changes in [deoxy-Hb] seemed to be more localized than changes in [oxy-Hb]. We conclude that this simple, non-invasive and flexible optical bedside method may be used for functional brain mapping.

Quantitation of simulated short echo time 1H human brain spectra by LCModel and AMARES.

LCModel and AMARES, two widely used quantitation tools for magnetic resonance spectroscopy (MRS) data, were employed to analyze simulated spectra similar to those typically obtained at short echo times (TEs) in the human brain at 1.5 T. The study focused mainly on the influence of signal‐to‐noise ratios (SNRs) and different linewidths on the accuracy and precision of the quantification results, and their effectiveness in accounting for the broad signal contribution of macromolecules and lipids (often called the baseline in in vivo MRS). When applied in their standard configuration (i.e., fitting a spline as a baseline for LCModel, and weighting the first data points for AMARES), both methods performed comparably but with their own characteristics. LCModel and AMARES quantitation benefited considerably from the incorporation of baseline information into the prior knowledge. However, the more accurate quantitation of the sum of glutamate and glutamine (Glx) favored the use of LCModel. Metabolite‐to‐creatine ratios estimated by LCModel with extended prior knowledge are more accurate than absolute concentrations, and are nearly independent of SNR and line broadening. Magn Reson Med 51:904–912, 2004.

Cerebral blood oxygenation changes induced by visual stimulation in humans

We examined local changes of cerebral oxygenation in response to visual stimuli by means of near infrared spectroscopy. A sharply outlined colored moving stimulus which is expected to evoke a broad activation of the striate and prestriate cortex was presented to sixteen healthy subjects. Six of these subjects were also exposed to a colored stationary and a gray stationary stimulus. In two subjects the colored moving stimulus was tested against the colored stationary with an optode position presumably over area V5/MT. As a control condition, subjects performed a simple finger opposition task. Since the calcarine fissure varies greatly with respect to bony landmarks, optodes were positioned individually according to 3-D reconstructed magnetic resonance imaging (MRI). Concentration changes in oxyhemoglobin ([oxy-Hb]) and deoxyhemoglobin ([deoxy-Hb]) were continuously monitored with a temporal resolution of 1 s, using an NIRO 500 (Hamamatsu Photonics, KK, Japan). In response to the visual stimulus, the grand average across all sixteen subjects resulted in a significant increase in [oxy-Hb] of 0.3360.09 arbitrary units (mean6S.E.M.) mirrored by a significant decrease in [deoxy-Hb] of −0.1860.02 arbitrary units, while the motor control condition elicited no significant changes in any parameters. When the near infrared spectroscopy probes were positioned over area V5/MT, the drop of [deoxy-Hb] associated with the moving stimulus was significantly more pronounced than with the stationary stimulus in both subjects examined. No significant differences between the visual stimuli were observed at the optode position close to the calcarine fissure. The oxygenation changes observed in this study are consistent with the pattern we have reported for motor activation. They are in line with physiological considerations and functional MRI studies relying on blood oxygenation level-dependent contrast.

Histogram-based characterization of healthy and ischemic brain tissues using multiparametric MR imaging including apparent diffusion coefficient maps and relaxometry

Decreased, renormalized, or increased values of the calculated apparent diffusion coefficient (ADC) are observed in stroke models. A quantitative description of corresponding tissue states using ADC values may be extended to include true relaxation times. A histogram‐based segmentation is well suited for characterizing tissues according to specific parameter combinations irrespective of the heterogeneity found for human healthy and ischemic brain tissues. In a new approach, navigated diffusion‐weighted images and ADC maps were incorporated into voxel‐based parameter sets of relaxation times (T1, T2), and T1‐ or T2‐weighted images, followed by a supervised histogram‐based analysis. Healthy tissues were segmented by incorporating T1 relaxation into the data set, ischemic regions by combining T2‐ or diffusion‐weighted images with ADC maps. Mean values of healthy and pathologic tissues were determined, spatial distributions of the parameter vectors were visualized using color‐encoded overlays. One to six days after stroke, ischemic regions exhibited reduced relative mean ADC values. Magn Reson Med 43:52–61, 2000.

Haemoglobin Oxygenation Changes During Visual Stimulation in the Occipital Cortex

It has been shown that near-infrared spectroscopy (NIRS) permits the assessment of functional brain activation.8,9,14,21 Four studies were dedicated to the visual system which partly yielded conflicting results.10,11,13,21 Though all studies showed an increase in [oxy-Hb] during visual stimulation using different stimulation paradigms, the changes observed in [deoxy-Hb] were not uniform. Meek et al.13 reported on a decrease in [deoxy-Hb] in 4 of 10 subjects but an increase in the other 6 subjects, while Kato et al.11 and Hoshi et al.10 using photic stimulation of 8 Hz and 10 Hz found an increase in [deoxy-Hb] in their studies. On the other hand, Villringer et al.21 observed a decrease in [deoxy-Hb] during photic stimulation and picture observation, but this included only 3 subjects lacking therefore statistical evaluation. All NIRS-investigators10,11,13,21 localised the optical probes only with respect to external bony landmarks without knowledge of the exact spatial relation of these landmarks to the anatomy of the brain. This could have led to inaccurate positions of the optical probes over the visual cortex as there is a great variability of the calcarine fissure concerning these external landmarks.18 Localising the optical probes individually according to previously acquired 3D MRI, the aim of the current study was to investigate whether there is a consistent, statistically evident pattern of changes in [oxy-Hb] and [deoxy-Hb] during visual stimulation. Furthermore, we investigated if NIRS is able to detect oxygenation changes due to activation of a secondary or prestriate visual area known from studies both in monkeys and humans as area V5 or MT to be sensitive to the submodality “visual motion”.12,19,22,24

A JAVA-based DICOM server with integration of clinical findings and DICOM-conform data encryption

The transfer of large amounts of medical data within heterogeneous hard and software infrastructures and the exploitation of distributed resources require a fast, secure, and platform-independent data exchange. To avoid costly vendor-specific solutions, a DICOM server was implemented in JAVA. Data access was enabled via internet browser technology. Relevant patient and image acquisition information was extracted from the DICOM images and stored into a relational database. Patient information such as radiological findings were transferred from the Radiological Information System into the database. Image data were accessed either by a fast preview tool or using a JAVA-based DICOM viewer. Since data security mechanisms are not yet part of the DICOM standard, a DICOM-conform encryption of sensitive patient data was implemented. The method allowed a dynamic selection of the data to be encrypted. Integrating this module into the image server enabled the fast and secure transfer of image data across insecure networks as well as long-term storage on CD-Recordables.

Towards near-infrared brain mapping

Neuronal activation is coupled to localised changes in regional cerebral blood flow, blood oxygenation and metabolism (Leninger-Follert et al. 1979, Frostig et al. 1990). On this basis it is possible to detect and localise activated brain areas by the use of functional imaging methods like PET and fMRI (Phelps et al. 1985, Fox et al. 1986, Belliveau et al. 1991). The high spatial resolution of these imaging methods allows to characterise and localise hemodynamic and metabolic changes of activated brain areas on an anatomical basis. Near infrared spectroscopy noninvasively detects changes in the concentration of oxy-Hb, deoxy-Hb and Cyt-O2 by measuring changes in absorption at specific wavelength of light in the near infrared region. The technique in the first instance was used to detect global changes in cerebral hemodynamics (Jobsis 1977, Elwell 1994) and was recently introduced to assess hemodynamic response induced by functional brain activation (Hoshi et al. 1993, Villringer et al. 1993, Obrig et al. 1995, Kato et al. 1993, Meek et al. 1995), The high temporal resolution and the ability to assess several oxygenation parameters simultaneously provides information about temporal dynamics of oxygenation changes in response to functional stimulation. Reasons for using this technique to investigate functional brain activation lie in some advantages compared to traditionally used functional imaging methods. Near infrared spectroscopy is completely non-invasive low expensive and can be used with high flexibility. NIRS allows repeated measures and administration of exogenous tracers is not required. The technique is therefore suited for assessment of brain function in clinical settings as a bedside technique.

Distributed medical services within the ATM-based Berlin regional test bed

The ATM-based Metropolitan Area Network (MAN) of Berlin connects two university hospitals (Benjamin Franklin University Hospital and Charite) with the computer resources of the Technical University of Berlin (TUB). Distributed new medical services have been implemented and will be evaluated within the highspeed MAN of Berlin. The network with its data transmission rates of up to 155 Mbit/s renders these medical services externally available to practicing physicians. Resource and application sharing is demonstrated by the use of two software systems. The first software system is an interactive 3D reconstruction tool (3D- Medbild), based on a client-server mechanism. This structure allows the use of high- performance computers at the TUB from the low-level workstations in the hospitals. A second software system, RAMSES, utilizes a tissue database of Magnetic Resonance Images. For the remote control of the software, the developed applications use standards such as DICOM 3.0 and features of the World Wide Web. Data security concepts are being tested and integrated for the needs of the sensitive medical data. The highspeed network is the necessary prerequisite for the clinical evaluation of data in a joint teleconference. The transmission of digitized real-time sequences such as video and ultrasound and the interactive manipulation of data are made possible by Multi Media tools.

Feature-based, Automated Segmentation of Cerebral Infarct Patterns Using T 2- and Diffusion-weighted Imaging

Diffusion-weighted imaging enables the diagnosis of cerebral ischemias very early, thus supporting therapies such as thrombolysis. However, morphology and tissue-characterizing parameters (e.g. relaxation times or water diffusion) may vary strongly in ischemic regions, indicating different underlying pathologic processes. As the determination of the parameters by a supervised segmentation is very time consuming, we evaluated whether different infarct patterns may be segmented by an automated, multidimensional feature-based method using a unified segmentation procedure. Ischemias were classified into 5 characteristic patterns. For each class, a 3D histogram based on T 2 - and diffusion-weighted images as well as calculated apparent diffusion coefficients (ADC) was generated from a representative data set. Healthy and pathologic tissue classes were segmented in the histogram as separate, local density maxima with freely shaped borders. Segmentation control parameters were optimized in a 3-step procedure. The method was evaluated using synthetic images as well as results of a supervised segmentation. For the analysis of cerebral ischemias, the optimal control parameter set led to sensitivities and specificities between 1.0 and 0.9.

Standardized access, display, and retrieval of medical video

The system presented here enhances documentation and data- secured, second-opinion facilities by integrating video sequences into DICOM 3.0. We present an implementation for a medical video server extended by a DICOM interface. Security mechanisms conforming with DICOM are integrated to enable secure internet access. Digital video documents of diagnostic and therapeutic procedures should be examined regarding the clip length and size necessary for second opinion and manageable with todays hardware. Image sources relevant for this paper include 3D laparoscope, 3D surgical microscope, 3D open surgery camera, synthetic video, and monoscopic endoscopes, etc. The global DICOM video concept and three special workplaces of distinct applications are described. Additionally, an approach is presented to analyze the motion of the endoscopic camera for future automatic video-cutting. Digital stereoscopic video sequences are especially in demand for surgery . Therefore DSVS are also integrated into the DICOM video concept. Results are presented describing the suitability of stereoscopic display techniques for the operating room.