Stefan Vollmar

Stefan Vollmar
Max Planck Institute for Metabolism Research | NF · IT Group

Dr.

About

75
Publications
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2,152
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Publications

Publications (75)
Article
Full-text available
Pro-opiomelanocortin (POMC)-expressing neurons in the arcuate nucleus of the hypothalamus represent key regulators of metabolic homeostasis. Electrophysiological and single-cell sequencing experiments have revealed a remarkable degree of heterogeneity of these neurons. However, the exact molecular basis and functional consequences of this heterogen...
Article
Full-text available
Regional cerebral blood flow (rCBF) is spatially and temporally adjusted to local energy needs. This coupling involves dilation of vessels both at the site of metabolite exchange and upstream of the activated region. Deficits in upstream blood supply limit the 'capacity to raise rCBF' in response to functional activation and therefore compromise br...
Article
Full-text available
The purpose of this positron emission tomography (PET) study was to compare the prognostic value of pretreatment volume of [11C]-methionine (MET) uptake and semiquantitative MET uptake ratio in patients with malignant glioma. The study population comprised 40 patients with malignant glioma. Pretreatment magnetic resonance imaging (MRI) and MET-PET...
Article
Full-text available
In patients with recurrent glioblastoma multiforme (GBM), local minimally invasive treatment modalities have gained increasing interest recently because they are associated with fewer side effects than open surgery. For example, local tumor coagulation by laser-induced interstitial thermotherapy (LITT) is such a minimally invasive technique. We mon...
Article
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In Alzheimer's disease (AD), persistent microglial activation as sign of chronic neuroinflammation contributes to disease progression. Our study aimed to in vivo visualize and quantify microglial activation in 13- to 15-month-old AD mice using [(11)C]-(R)-PK11195 and positron emission tomography (PET). We attempted to modulate neuroinflammation by...
Article
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In patients with World Health Organization (WHO) grade III glioma with a lack of or minimal (< 1 cm3) magnetic resonance imaging (MRI) contrast enhancement, the volume of the metabolically active part of the tumor was assessed by [¹¹C]-methionine positron emission tomography (MET-PET). Eleven patients with WHO grade III gliomas underwent MET-PET an...
Article
The purpose of this study was to investigate the potential of 3'-deoxy-3'-[¹⁸F]fluorothymidine ([¹⁸F]FLT) positron emission tomography (PET) to detect early treatment responses in gliomas. Human glioma cells were stably transduced with genes yielding therapeutic activity, sorted for different levels of exogenous gene expression, and implanted subcu...
Article
Full-text available
Inhibition of angiogenesis has shown clinical success in patients with cancer. Thus, imaging approaches that allow for the identification of angiogenic tumors and the detection of response to anti-angiogenic treatment are of high clinical relevance. We established an in vivo magnetic resonance imaging (MRI) approach that allows us to simultaneously...
Article
Introduction: In Alzheimer's disease (AD), activated microglia play an important role in amyloid clearance and secretion of pro-inflammatory molecules that lead to chronic neuroinflammation. The nuclear peroxisome proliferator-activated receptor γ (PPAR-g) is involved in the regulation of inflammatory processes at transcriptional level. Aim: To det...
Article
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Experimental and clinical studies indicate that waves of cortical spreading depolarization (CSD) appearing in the ischemic penumbra contribute to secondary lesion growth. We used an embolic stroke model that enabled us to investigate inverse coupling of blood flow by laser speckle imaging (CBF(LSF)) to CSD as a contributing factor to lesion growth...
Article
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How does infarction in victims of stroke and other types of acute brain injury expand to its definitive size in subsequent days? Spontaneous depolarizations that repeatedly spread across the cerebral cortex, sometimes at remarkably regular intervals, occur in patients with all types of injury. Here, we show experimentally with in vivo real-time ima...
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Although Parkinson disease with dementia (PDD) and dementia with Lewy bodies (DLB) show a wide clinical and neuropathologic overlap, they are differentiated according to the order and latency of cognitive and motor symptom appearance. Whether both are distinct disease entities is an ongoing controversy. Therefore, we directly compared patients with...
Article
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The study serves to optimise conditions for multi-pinhole SPECT small animal imaging of (123)I- and (99m)Tc-labelled radiopharmaceuticals with different distributions in murine heart and brain and to investigate detection and dose range thresholds for verification of differences in tracer uptake. A Triad 88/Trionix system with three 6-pinhole colli...
Article
One of the main problems in gene therapy of malignant gliomas is limited vector distribution within the target tissue. To serve a more widespread distribution of vector-mediated gene expression throughout the tumour glioma cells can be converted to vector producer cells onsite. Conversion of tumour cells to retrovirus packaging cells has been achie...
Article
We investigated the efficacy of combined FDG-PET/CT imaging for the diagnosis of small-size uveal melanomas and the feasibility of combining separate, high-resolution (HR) FDG-PET with MRI for its improved localization and detection. 3 patients with small-size uveal melanomas (0.2-1.5 ml) were imaged on a combined whole-body PET/CT, a HR brain-PET,...
Article
Background: Gliomas demonstrate significant heterogeneity both in terms of outcome and imaging characteristics within histological grades and particularly between histopathological and genetic sub-types. Methionine uptake as measured with positron emission tomography (PET) has been shown to correlate with histological grade but interpretation of th...
Article
Full-text available
(11)C-Methionine PET is a well-established technique for evaluating tumor extent for diagnosis and treatment planning in neurooncology. Image interpretation is typically performed using the ratio of uptake within the tumor to a reference region. The precise location of this reference region is important as local variations in methionine uptake may...
Data
Regulated eGFP expression in culture. (A) Fluorescence microscopy of eGFP-expressing cells with and without mifepristone-treatment of HSV-Switch-TG17 infected cells. (B) eGFP-positive cells (GPC) were counted per field of view (f.o.v.) in the absence and presence of mifepristone (−/+MF, 24h post induction). Columns in dark grey represent the number...
Article
Full-text available
To develop efficient and safe gene therapy approaches, the herpes simplex virus type 1 thymidine kinase gene (HSV-1-tk) has been shown to function as a marker gene for the direct noninvasive in vivo localization of thymidine kinase (TK) expression by positron emission tomography (PET) using radiolabeled nucleoside analogues as specific TK substrate...
Article
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To further develop gene therapy for patients with glioblastomas, an experimental gene therapy protocol was established comprising a series of imaging parameters for (i) noninvasive assessment of viable target tissue followed by (ii) targeted application of herpes simplex virus type 1 (HSV-1) amplicon vectors and (iii) quantification of treatment ef...
Article
Full-text available
Strategies for non-invasive and quantitative imaging of gene expression in vivo have been developed over the past decade. Non-invasive assessment of the dynamics of gene regulation is of interest for the detection of endogenous disease-specific biological alterations (e.g., signal transduction) and for monitoring the induction and regulation of the...
Chapter
There are distinct advantages of including functional data from PET into surgery planning and neuronavigation: tumor delineation and localization of functional areas. Preoperative intervention planning in brain tumours poses many additional challenges if the goal is to include functional data from PET for neuronavigation: co-registration of multimo...
Article
Background : Conventional interpretation of methionine PET (Met-PET) scans in suspected brain tumors uses the ratio of the tracer uptake within the lesion to the corresponding contralateral area. The precise location at which the region of interest used to calculate the reference value is placed is vital, because local variations in methionine upta...
Article
Because of the high glucose metabolism in normal brain tissue F-18-FDG is not the ideal tracer for the detection of gliomas. Methyl-C-11-(L)-methionine (C-11-MET) is better suited for imaging the extent of gliomas, because it is transported specifically into tumors but only insignificantly into normal brain. 3'-Deoxy-3'F-18-fluorothymidine (F-18-FL...
Article
Because of the high glucose metabolism in normal brain tissue 18F-FDG is not the ideal tracer for the detection of gliomas. Methyl-11C-l-methionine (11C-MET) is better suited for imaging the extent of gliomas, because it is transported specifically into tumors but only insignificantly into normal brain. 3'-Deoxy-3'-18F-fluorothymidine (18F-FLT) has...
Conference Paper
The high resolution research tomograph (HRRT) is the first PET scanner with depth of interaction (DOI) capability. Presently three different versions have been developed: one equipped with two 7.5 mm thick crystal layers (HRRT-DC), the second with only a single 7.5 mm crystal layer (HRRT-S) and the latest HRRT with two 10 mm thick crystal layers (H...
Conference Paper
Full-text available
The High Resolution Research Tomograph (HRRT) with its improved spatial resolution (<2.5 mm), extended axial FOV (25 cm) and high sensitivity offers the possibility to obtain an image derived input function for quantitative PET studies. From the carotid artery in the region of the neck and the petrous bone, the time course of the blood activity can...
Article
The authors report a 43-year-old patient with histopathologically proven cerebral Whipple's disease. Magnetic resonance imaging (MRI) revealed a multilayered left frontal lesion without mass effect, no perifocal brain edema, no contrast enhancement, and a thin shell of fluid signal that presented as an incomplete, open ring. An [11C]methionine posi...
Article
In recent years, mutual information has proved to be an excellent criterion for registration of intra-individual images from different modalities. Multi-resolution coarse-to-fine optimization was proposed for speeding-up of the registration process. The aim of our work was to further improve registration speed without compromising robustness or acc...
Article
Full-text available
Background: The combination of transgenes encoding prodrug-activating enzymes serves synergistic anti-tumor activity (e.g. E. coli cytosine deaminase (cd) and HSV-1 thymidine kinase (tk); Aghi et al.J Nat Cancer Inst 1998). We used positron emission tomography (PET) and magnetic resonance imaging (MRI) for imaging-guided targeted application of uni...
Article
Background: The combination of transgenes encoding prodrug-activating enzymes serves synergistic anti-tumor activity (e.g. E. coli cytosine deaminase (cd) and HSV-1 thymidine kinase (tk)). We used positron emission tomography (PET) and magnetic resonance imaging (MRI) for imaging-guided targeted application of universal HSV-1 amplicon vectors and a...
Article
Positron emission tomography (PET) allows non-invasive assessment of physiological, metabolic and molecular processes in humans and animals in vivo. Advances in detector technology have led to a considerable improvement in the spatial resolution of PET (1-2 mm), enabling for the first time investigations in small experimental animals such as mice....
Article
For the development of efficient and safe gene therapy protocols for clinical application it is desirable to determine the tissue dose of vector-mediated therapeutic gene expression noninvasively in vivo. The herpes simplex virus type 1 thymidine kinase gene (HSV-1-tk) has been shown to function as a marker gene for the direct noninvasive in vivo l...
Article
A phase I/II clinical trial of gene therapy for recurrent glioblastoma has been initiated in which non-invasive monitoring of the critical steps is performed by a combination of standard clinical positron-emission tomography (PET) for metabolic identification/evaluation of malignant lesions with pioneering PET imaging of HSV-1-tk transgene expressi...
Conference Paper
The High Resolution Research Tomograph (HRRT) is the first clinical LSO scanner with depth of interaction (DOI) capability. At the moment two HRRT's exist: one is located at the Max-Planck-Institute in Cologne and is equipped with two 7.5 mm thick crystal layers and DOI (HRRT-D); the second HRRT is located at the VUme in Amsterdam with a single cry...
Conference Paper
In vivo studies on animals are required for the development of new drugs and radioactive tracers, the monitoring of gene therapy and the development of new medical treatments. Two high resolution positron emission tomographs (PET) were compared in the scope of this work with regard to their suitability for high resolution animal PET scans. The ECAT...
Article
A daily quality check plays an important role for clinical medical systems like a positron emission tomograph (PET). To guarantee image quality a constant monitoring of the scanner integrity is essential. On present PET scanners, the built-in transmission sources are being used for the measurement of a uniform blank scan and the computation of dete...
Article
Full-text available
Using iterative three-dimensional (3D) reconstruction techniques for reconstruction of positron emission tomography (PET) is not feasible on most single-processor machines due to the excessive computing time needed, especially so for the large sinogram sizes of our high-resolution research tomograph (HRRT). In our first approach to speed up reconst...
Article
Gliomas are the most common types of brain tumors, which invariably lead to death over months or years. Before new and potentially more effective treatment strategies, such as gene therapy, can be effectively introduced into clinical application the following goals must be reached: (1) the determination of localization, extent and metabolic activit...
Article
The first and second generation of the Exact and Exact HR family of scanners has been evaluated in terms of noise equivalent count rate (NEC) and count-rate capabilities. The new National Electrical Manufacturers Association standard was used for the evaluation. In spite of improved electronics and improved count-rate capabilities, the peak NEC was...
Article
Full-text available
The ECAT HRRT is a three-dimensional (3-D) only dedicated brain tomograph employing the new scintillator lutetium-oxy- orthosilicate (LSO) and using depth of interaction (DOI) information to achieve uniform isotropic resolution across a 20-cm diameter volume. With its unique technological innovations it represents the prototype of a new generation...
Conference Paper
Full-text available
We have investigated two strategies to speedup reconstruction of data from our high resolution PET scanner (HRRT) on a dedicated cluster (7 nodes with 4 PIII Xeon@700 MHz, switched Fast Ethernet and Myrinet networking, Windows NT). With the first strategy, FORE/FOREJ and a fast 2D reconstruction method, we were able to reduce the 2D reconstruction...
Conference Paper
The first and second generation of Exact and Exact HR family of scanners has been evaluated in terms of NEC and count rate capabilities. The new NEMA standard was used for the evaluation. In spite of improved electronics and improved count rate capabilities, the peak NEC was found to be fairly constant between the generations. The results are discu...
Conference Paper
Various strategies were investigated to reconstruct 3D data from the HRRT, the LSO brain PET installed at the MPI. In this octagonal geometry, the sampling is not complete due to the gaps between flat panel detectors. The standard reconstruction scheme uses a gap-filling step followed by Fourier rebinning (FORE) and attenuation-weighted (AW) OSEM....
Conference Paper
Iterative reconstruction techniques are usually too time consuming on most single processor machines that are affordable. This is especially true for the HRRT (High Resolution Research Tomograph) which produces huge sinogram data in order to take full advantage of its enhanced resolution. The use of Fourier Rebinning (FORE) in a preprocessing step...
Article
S. 25) ECAT-Format, Multiframedatei i TABLE OF CONTENTS 1. Overview ..................................................... 1 2. First Steps ................................................... 2 2.1 Starting MPITool ..................................... 2 2.2 Loading images ...................................... 2 2.3 Adjusting color table and contra...
Conference Paper
In order to improve the capability for investigating the living human brain using positron emission tomography with regard to blood flow, metabolism and receptor characteristics for small structures such as cortical sublayers and nuclei, the spatial resolution has to be improved relative to what is available today. A spatial resolution of 2 mm or l...
Conference Paper
The authors' aim was to enhance resolution and signal to noise ratio of PET reconstructions by incorporating information of other image modalities into the reconstruction process. Usually, the reconstruction with a-priori-information is based on two complementary data sets: functional data from PET or SPECT on the one hand and morphological data fr...
Article
We implemented a hydrodynamic lattice gas cellular automation with rest particles on bonds to study the behaviour of granular media in a two-dimensional closed container under the influence of dissipation, static friction and gravity. The problems posed by rest particles on bonds are described and our solutions (rules and algorithm) are discussed....
Article
We show that a simple model that incorporates a balance of helpful and deleterious mutations inherited by future generations, leads to an `explanation' of biological ageing. We also investigate the stability limit beyond which the populations decay to zero.
Article
We introduce a ``Kawasaki-type'' spin-exchange dynamics for Widom's model of microemulsions, where the numbers of the molecules of oil, water and surfactants are conserved. We investigate the relaxation of concentration fluctuations in two dimensions, using this dynamics, and find diffusion for small-amplitude deviations from equilibrium. In additi...
Article
The flow through permeable walls is studied for a variety of hole dimensions, spacings, and boundary conditions by the method of hydrodynamic cellular automata. The flux measured on the contact section of two adjacent channels is found to scale for all studied hole sizes from 1 to 128, regardless of whether the flow is forced by an imposed pressure...
Article
Full-text available
Evaluation of FOREJ (exact rebinning based on John,s equations) on HRRT, a brain scanner with large gaps. We examine ,using clinical data simulated data,, if the rebinning improvement from FOREJ is not offset by the noise introduced by the gap filling, which affects the estimation of the axial curvatureof the fully corrected projections.The interes...
Article
VINCI ("Volume Imaging in Neurological Research, Co-Registration and ROIs included") was designed for the visualization and analysis of volume data generated by medical tomographical systems with special emphasis on the needs for brain imaging with Positron Emission Tomography (PET). VINCI is highly modular, extensible, compact and runs well on cur...