Biomedical subjects

Jürgen R Reichenbach

Publications and source records attributed to Jürgen R Reichenbach.

At least 19 recordsLinked to original sources

PubMed2006

White matter abnormalities and brain activation in schizophrenia: a combined DTI and fMRI study.

Diffusion tensor imaging (DTI) studies of schizophrenia have revealed white matter abnormalities in several areas of the brain. The functional impact on either psychopathology or cognition remains, however, poorly understood. Here we analysed both functional MRI (during a working memory task) and DTI data sets in 18 patients with schizophrenia and 18 controls. Firstly, DTI analyses revealed reductions of fractional anisotropy (FA) in the right medial temporal lobe adjacent to the right parahippocampal gyrus, likely to contain fibres of the inferior cingulum bundle, and in the right frontal lobe. Secondly, functional MRI revealed prefrontal, superior parietal and occipital relative hypoactivation in patients with the main effect of task. This was accounted for by reduced prefrontal activation during the encoding phase of the task, but not during maintenance or retrieval phases. Thirdly, we found a direct correlation in patients between the frontal FA reduction (but not medial temporal reductions) and fMRI activation in regions in the prefrontal and occipital cortex. Our study combining fMRI and DTI thus demonstrates altered structure-function relationships in schizophrenia. It highlights a potential relationship between anatomical changes in a frontal-temporal anatomical circuit and functional alterations in the prefrontal cortex.

Adult↗

PubMed2006

The special involvement of the rostrolateral prefrontal cortex in planning abilities: an event-related fMRI study with the Tower of London paradigm.

Planning abilities are essential for the successful management of everyday life activities. Although several neuroimaging studies provide evidence that the prefrontal cortex is crucially involved in planning, the differential roles of its subregions are still a matter of debate. The aim of this study was to investigate the neural correlates of planning by focusing on the functional differentiation between the dorsolateral and rostrolateral prefrontal cortex using the Tower of London (ToL) task and a parametric event-related functional MRI design. In order to control for activations unspecific to planning, two control conditions were presented, which were matched for the length of single events in the ToL task. Seventeen right-handed healthy subjects participated in this study. All statistics were reported with corrections for multiple comparisons (p < 0.05). Compared to control conditions, activations in the ToL task were observed in the dorsolateral prefrontal cortex bilaterally, the right ventrolateral and left rostrolateral prefrontal cortex along with the thalamus, as well as in the parietal and premotor cortex bilaterally. Task complexity dependent analyses revealed that only the left rostrolateral prefrontal cortex showed a BOLD signal increase over the four planning levels, which could not be observed in the control conditions. Hence, current findings suggest that planning involves an extensive fronto-parieto-thalamic network. Within this network, the rostrolateral prefrontal cortex seems to be the only region that is exclusively reactive to planning specific processes, which we described in terms of simultaneous monitoring of internally generated and externally presented information.

Adult↗

PubMed2006

Susceptibility-weighted imaging to visualize blood products and improve tumor contrast in the study of brain masses.

PURPOSE: To evaluate the diagnostic value of susceptibility-weighted imaging (SWI) for studying brain masses. MATERIALS AND METHODS: SWI is a high-resolution, three-dimensional, fully velocity-compensated gradient-echo sequence that uses both magnitude and phase data. Custom postprocessing is applied to enhance the contrast in the magnitude images between tissues with different susceptibilities. This sequence was applied to 44 patients (24 males and 20 females, 15-89 years old, mean age = 50.3 years) with brain masses, pre- and/or postcontrast, and compared with conventional sequences (T1, T1 postcontrast, T2, proton density (PD), fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted imaging (DWI) at 1.5T). Correlation with pathology was obtained in 12 cases. All images were reviewed independently by three radiologists. RESULTS: In the evaluation of tumor visibility, boundary definition, blood products, venous vasculature, architecture, and edema, SWI gave better information than the standard T1-weighted postcontrast images in 11%, 14%, 71%, 73%, 63%, and 75% of the data, respectively, in a subgroup of 38 patients. This demonstrates that the information presented by SWI is complementary in nature to that available from conventional methods. On the whole, SWI was much more sensitive for showing blood products and venous vasculature. SWI showed a useful FLAIR-like contrast and complemented the information obtained by conventional T1 postcontrast sequences regarding the internal architecture of the lesions. Good pathologic correlations were found for blood products as predicted by SWI. CONCLUSION: SWI should prove useful for tumor characterization because of its ability to better highlight blood products and venous vasculature and reveal new internal architecture.

Adolescent↗

PubMed2006

Susceptibility weighted imaging: data acquisition, image reconstruction and clinical applications.

Susceptibility-weighted imaging (SWI) is a novel method, that combines magnitude and phase information from a high-resolution, fully velocity compensated 3D T2-weighted gradient echo sequence. Phase images are unwrapped and high pass filtered to highlight phase changes associated with venous vessels and converted into a mask that is multiplied with the corresponding phase image. This technique has been applied thus far to the imaging of tumors, vascular malformations, trauma, stroke, micro-hemorrhages, and as a functional imaging method. The purpose of this paper is to present an overview of the current status of the technique and to illustrate its potential.

Brain↗

PubMed2006

Demonstration of paramagnetic and diamagnetic cerebral lesions by using susceptibility weighted phase imaging (SWI).

Susceptibility-weighted MR imaging (SWI) has become a non-invasive diagnostic modality for functional MR imaging (fMRI) of the brain and also for the imaging of tumors, injuries, malformations or microhemorrhages. SWI often enables detection of otherwise subtle abnormalities or provides additional relevant information when combined with routine MR imaging. The purpose of this article is to illustrate the potential of SWI in the discrimination of paramagnetic and diamagnetic brain lesions in neuroradiological applications.

Adult↗

PubMed2006

Contrast-enhanced, high-resolution, susceptibility-weighted magnetic resonance imaging of the brain: dose-dependent optimization at 3 tesla and 1.5 tesla in healthy volunteers.

OBJECTIVES: We sought to determine the optimal dose of a contrast agent with known high relaxivity on 1.5 and 3 Tesla scanners that would achieve the best compromise between image quality and scan time for the clinical application of contrast-enhanced susceptibility-weighted imaging (CE-SWI). METHODS: Pre- and postcontrast SWI was performed with different contrast agent doses (0.05, 0.1, and 0.2 mmol/kg gadobenate dimeglumine) at both 1.5 and 3 T in 6 healthy volunteers, resulting in 72 examinations. Venograms were created from minimum intensity projection reconstructions over specified deep white matter volumes to enhance the visual appearance of connected venous structures. Three independent radiologists blindly rated the visibility of the veins on a continuous scale of 1 to 10. A general linear model was used for statistical evaluation, with fixed effects of the contrast agent dose, the field strength, the rater and the patients as a random effect. RESULTS: With CE-SWI, we found significant differences in the visibility of the deep veins dependent on the contrast media dose (P=0.02). At 3 T, the visibility of deep venous vessels, with regard to susceptibility effect, image quality, and scan time reduction after a standard contrast agent dose 0.1 mmol/kg was significantly better than that achieved with 0.05 mmol/kg. The visibility was considered equal with 0.1 mmol/kg of the contrast agent to the precontrast images and a dose of 0.2 mmol/kg. At 1.5 T, no significant difference was found between the 4 contrast agent doses. We found no difference in the visibility of the veins with the shorter sequences at 3 T compared with the sequences at 1.5 T. CONCLUSIONS: Only a standard dose (0.1 mmol/kg) of gadobenate dimeglumine is required to achieve the optimum susceptibility effect and image quality at 3 T, together with a reduced scan time. This result can be attributed to the higher relaxivity of gadobenate dimeglumine, compared with conventional gadolinium chelates.

Adult↗

PubMed2006

Influence of anisotropic conductivity on EEG source reconstruction: investigations in a rabbit model.

The aim of our work was to quantify the influence of white matter anisotropic conductivity information on electroencephalography (EEG) source reconstruction. We performed this quantification in a rabbit head using both simulations and source localization based on invasive measurements. In vivo anisotropic (tensorial) conductivity information was obtained from magnetic resonance diffusion tensor imaging and included into a high-resolution finite-element model. When neglecting anisotropy in the simulations, we found a shift in source location of up to 1.3 mm with a mean value of 0.3 mm. The averaged orientational deviation was 10 degree and the mean magnitude error of the dipole was 29%. Source localization of the first cortical components after median and tibial nerve stimulation resulted in anatomically verified dipole positions with no significant anisotropy effect. Our results indicate that the expected average source localization error due to anisotropic white matter conductivity is within the principal accuracy limits of current inverse procedures. However, larger localization errors might occur in certain cases. In contrast, dipole orientation and dipole strength are influenced significantly by the anisotropy. We conclude that the inclusion of tissue anisotropy information improves source estimation procedures.

Algorithms↗

PubMed2006

Application of generalized dynamic neural networks to biomedical data.

This paper reviews the application of continuous recurrent neural networks with time-varying weights to pattern recognition tasks in medicine. A general learning algorithm based on Pontryagin's maximum principle is recapitulated, and possibilities of improving the generalization capabilities of these networks are given. The effectiveness of the methods is demonstrated by three different real-world examples taken from the fields of anesthesiology, orthopedics, and radiology.

Algorithms↗

PubMed2006

Three-dimensional nonlinear invisible boundary detection.

The human vision system can discriminate regions which differ up to the second-order statistics only. We present an algorithm designed to reveal "hidden" boundaries in gray level images, by computing gradients in higher order statistics of the data. We demonstrate it by applying it to the identification of possible "hidden" boundaries of glioblastomas as manifest themselves in three-dimensional (3-D) MRI scans, using a model driven approach. We also demonstrate the method using a nonmodel driven approach where we have no prior information about the location of possible boundaries. In this case, we use 3-D MRI data concerning schizophrenic patients and normal controls.

Algorithms↗

PubMed2006

Investigations of back muscle fatigue by simultaneous 31P MRS and surface EMG measurements.

Investigations of back muscle fatigue are important for understanding the role of muscle strain in the development of low back pain. The aim of this contribution is to review the two main techniques used for in vivo investigations of metabolic and electrophysiological changes, namely magnetic resonance phosphorous spectroscopy ((31)P MRS) and surface electromyography (SEMG), and to report some of our recent results on simultaneous measurements using these techniques during isometric back-muscle contraction in volunteers. Since it appears that electrophysiological and metabolic factors are simultaneously involved in the processes of fatigue and muscle recovery during load application, simultaneous acquisition of complete information is quite promising for obtaining new insights into the metabolic origin of electrophysiological changes or vice versa. Performing these measurements simultaneously, however, is more intricate owing to the occurrence of signal artifacts caused by mutual signal interferences of both techniques. Besides these mutual disturbances, further experimental difficulties are related to spatial limitations within the bore of clinical whole-body high-field magnetic resonance (MR) systems (1.5 T) and the sensitivity of MR measurements to motion-induced artifacts. Our own experimental results are presented, and problems that occur using both techniques simultaneously, as well as possibilities to resolve them, are discussed. The results shed light on the interrelation of electrophysiological and metabolic changes during fatigue of the back muscle while performing an exercise.

Adenosine Triphosphate↗

PubMed2005

Diffusion tensor imaging in children and adolescents with tuberous sclerosis.

BACKGROUND: Tuberous sclerosis (TS) is characterised by benign hamartomatous lesions in many organs. Diffusion tensor imaging (DTI) can detect microstructural changes in pathological processes. OBJECTIVE: To determine apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps in children with TS and to investigate the diffusion properties in cortical tubers, white-matter lesions, perilesional white matter, and contralateral normal-appearing white matter, and to compare the results with ADC and FA maps of normal age- and sex-matched volunteers. MATERIALS AND METHODS: Seven children and adolescents (age range 2-20 years) suffering from TS were included. MRI was performed on a 1.5-T scanner using a transmit/receive coil with T1-W and T2-W spin-echo and FLAIR sequences. DT images were acquired by using a single-shot echo-planar pulse sequence. Diffusion gradients were applied in six different directions with a b value of 1,000 s/mm(2). RESULTS: ADC was higher in cortical tubers than in the corresponding cortical location of controls. ADC values were higher and FA values were lower in white-matter lesions and perilesional white matter than in both the contralateral normal-appearing white matter of patients and in controls. There were no significant differences for both ADC and FA values in the normal-appearing white matter of patients with TS compared to controls. CONCLUSIONS: DTI provides important information about cortical tubers, white-matter abnormalities, and perilesional white matter in patients with TS.

Adolescent↗

PubMed2005

Subtraction of in-phase and opposed-phase images in dynamic MR mammography.

PURPOSE: To develop and to evaluate an advanced image acquisition and analysis method for collecting T(1)-weighted dynamic 3D MR mammography data sets by using a combined in-phase (IP) and opposed-phase (OP) imaging procedure. MATERIALS AND METHODS: 3D MR mammography data sets were acquired by applying an interleaved gradient-echo OP and IP imaging sequence during administration of contrast agent. A phantom data set, two volunteer breast data sets, and six patient breast data sets were recorded. Subtraction of dynamic in-phase magnitude images was performed for clinical assessment. In addition, the magnitude subtraction (SIPOP) as well as the complex subtraction (cSIPOP) of the IP and OP magnitude and phase images were considered. RESULTS: The detection of small lesions, lesion boundaries, and tumor offshoots in fatty tissue was improved by the subtraction of IP and OP images without the risk of signal cancellation due to partial volume effects. CONCLUSION: Dynamic MR mammography acquisition of IP and OP images in combination with appropriate data processing yields important supplementary information that can support routinely applied diagnostics of breast lesions that are fully embedded in fatty tissue by only marginally increasing acquisition time.

Aged↗

PubMed2005

Clinical applications of neuroimaging with susceptibility-weighted imaging.

Susceptibility-weighted imaging (SWI) consists of using both magnitude and phase images from a high-resolution, three-dimensional, fully velocity compensated gradient-echo sequence. Postprocessing is applied to the magnitude image by means of a phase mask to increase the conspicuity of the veins and other sources of susceptibility effects. This article gives a background of the SWI technique and describes its role in clinical neuroimaging. SWI is currently being tested in a number of centers worldwide as an emerging technique to improve the diagnosis of neurological trauma, brain neoplasms, and neurovascular diseases because of its ability to reveal vascular abnormalities and microbleeds.

Brain↗

PubMed2005

Nonnvasive assessment of vascular architecture and function during modulated blood oxygenation using susceptibility weighted magnetic resonance imaging.

Susceptibility weighted imaging (SWI) is a BOLD-sensitive method for visualizing anatomical features such as small cerebral veins in high detail. The purpose of this study was to evaluate high-resolution SWI in combination with a modulation of blood oxygenation by breathing of air, carbogen, and oxygen and to directly visualize the effects of changing blood oxygenation on the magnetic field inside and around venous blood vessels. Signal changes associated with the response to carbogen and oxygen breathing were evaluated in different anatomic regions in healthy volunteers and in two patients with brain tumors. In the magnitude images inhalation of carbogen led to significant signal intensity changes ranging from +4.4 +/- 1.9% to +9.5 +/- 1.4% in gray matter and no significant changes in thalamus, putamen, and white matter. During oxygen breathing mean signal changes were smaller than during carbogen breathing. The method is capable of producing high-resolution functional maps of BOLD response to carbogen and oxygen breathing as well as high-resolution images of venous vasculature. Its sensitivity to changes in blood oxygenation was demonstrated by in vivo visualization of the BOLD effect via phase imaging.

Administration, Inhalation↗

PubMed2005

[Validation of an entropy-based algorithm for registration of serial 3D MR mammography data].

The aim of this study was to develop and implement an algorithm for the co-registration of 3D breast MRI sets acquired at two slightly different patient positions (repetitive examination). Combined translation and rotation with locally varying parameters were applied for the purpose of coordinate transformation. A phantom allowing selective changes of the volume of the glandular tissue model was developed, in order to prove the robustness of the proposed matcher against local changes. Serial 3D data sets of phantoms and volunteers were acquired to validate the routines. Co-registration was performed using mutual information (MI) as a similarity measure of the matching of the acquired images. In the phantom study, the phantom was deliberately shifted and rotated around horizontal and vertical axes. Starting the registration with global translations using a rigid matcher, the horizontal (phi) and vertical (theta) rotation angles were optimized in an iteration loop for each slice. This method was then applied to the breast data sets. Application of the algorithm on serial 3D MR data sets improved the co-registration especially in consideration of varying local tissue volumes. The algorithm represents a compromise between a pure rigid and an elastic 3D matcher.

Algorithms↗

PubMed2005

Magnetic resonance-guided large-core breast biopsy inside a 1.5-T magnetic resonance scanner using an automatic system: in vitro experiments and preliminary clinical experience in four patients.

RATIONALE AND OBJECTIVE: The aim of this study was to investigate the feasibility and the precision of magnetic resonance (MR)-guided large-core breast biopsies (LCBB) by using the second prototype of an automatic system (ROBITOM II), which is used to localize lesions while operating at the isocenter of a 1.5-T whole-body scanner. METHODS AND MATERIALS: In comparison to the first prototype, ROBITOM II is equipped with a dedicated double breast coil and a high-speed trocar setting unit. In vitro experiments (n = 25) with grapefruit phantoms, which contained multiple vitamin E capsules (12 x 7 mm in size) as artificial lesions, were performed. Four patients with MR-detectable breast lesions underwent biopsy. A trocar was positioned in front of the lesion and inserted into the breast. Specimens were harvested with a coaxial technique by using a 14-G core needle biopsy gun. RESULTS: In all 25 in vitro experiments, capsule material was detected in the specimen cylinder. In 4 patients, the coaxial needle was detected exactly at the expected position. Between 8 and 16 tissue cylinders were harvested. Histologic evaluation resulted in 1 invasive ductal carcinoma and 1 papilloma, which were confirmed after open surgery. One patient who had a proven breast cancer was biopsied for exclusion of multifocal disease. She showed fibrocystic changes, whereas open surgery revealed 3 small areas of ductal carcinoma in situ (DCIS). Another patient showed fibroadenoma after biopsy. This patient is in the follow-up period, which has lasted between 3 and 4 months up until now. CONCLUSIONS: In this pilot patient study, the feasibility of manipulator-assisted large-core breast biopsy inside a 1.5-T whole-body scanner was demonstrated by using ROBITOM II. The precision of the device was confirmed with in vitro experiments. Although these findings are preliminary and the follow-up period is rather short, they nevertheless represent a successful proof-of-principle of LCBB with ROBITOM II.

Biopsy, Needle↗

PubMed2005

Magnetic susceptibility-weighted MR phase imaging of the human brain.

BACKGROUND AND PURPOSE: MR gradient echo imaging is sensitive to the magnetic susceptibility of different tissue types. The purpose of this study was to investigate the diagnostic potential of MR phase imaging of the human brain. METHODS: High-spatial-resolution, T2*-weighted, single-echo images were acquired in five volunteers and one patient with a brain tumor on a 1.5T system by applying a 3D, first-order, velocity-compensated gradient echo sequence by using a quadrature transmit-receive head coil. Phase images were reconstructed from the raw data and unwrapped by using a region-growing phase-unwrapping algorithm. Low-spatial-frequency components originating from static background susceptibility effects were removed by high-pass filtering. RESULTS: Phase images showed excellent image contrast and revealed anatomic structures that were not visible on the corresponding magnitude images. CONCLUSION: Improved processing of susceptibility-weighted MR phase images offers a new means of contrast for neuroimaging applications.

Adult↗

PubMed2004

Early diagnosis of cerebral involvement in Sturge-Weber syndrome using high-resolution BOLD MR venography.

Sturge-Weber syndrome (SWS) is a congenital disorder characterized by a vascular birthmark and neurological abnormalities. Typical imaging findings using MRI or CT are superficial cerebral calcification, atrophy and leptomeningeal enhancement. We present a neonate diagnosed with SWS because of a port-wine stain. In the absence of neurological symptoms the first MRI was performed when he was 4 months old, and follow-up MRI studies were performed after his first seizure at the age of 12 months. MRI was performed using standard sequences before and after administration of IV gadolinium. A high-resolution T2*-weighted, rf-spoiled 3D gradient-echo sequence with first-order flow compensation in all three directions was used for additional venographic imaging [blood-oxygen-level-dependent (BOLD) venography]. The initial conventional MRI sequences did not demonstrate any abnormality, but BOLD venography identified leptomeningeal internal veins. Follow-up MRI after the first onset of seizures demonstrated strong leptomeningeal enhancement, while BOLD venography revealed pathological medullary and subependymal veins as well as deep venous structures. At this time there were the first signs of atrophy and CT showed marginal calcifications. This report demonstrates that high-resolution BOLD MR venography allows early diagnosis of venous anomalies in SWS, making early therapeutic intervention possible.

Brain Diseases↗