Biomedical subjects

Michael Bock

Publications and source records attributed to Michael Bock.

At least 19 recordsLinked to original sources

PubMed2007

3D radial projection technique with ultrashort echo times for sodium MRI: clinical applications in human brain and skeletal muscle.

(23)Na MRI has the potential to noninvasively detect sodium (Na) content changes in vivo. The goal of this study was to implement (23)Na MRI in a clinical setting for neurooncological and muscular imaging. Due to the biexponential T(2) decay of the tissue Na signal with a short component, which ranges between 0.5-8 ms, the measurement of total Na content requires imaging techniques with echo times (TEs) below 0.5 ms. A 3D radial pulse sequence with a TE of 0.2 ms at a spatial resolution of 4 x 4 x 4 mm(3) was developed that allows the acquisition and presentation of Na images on the scanner. This sequence was evaluated in patients with low- and high-grade gliomas, and higher (23)Na MR signals corresponding to an increased Na content were found in the tumor regions. The contrast-to-noise ratio (CNR) between tumor and white matter increased from 0.8 +/- 0.2 to 1.3 +/- 0.3 with tumor grade. In patients with an identified muscular (23)Na channelopathy (Paramyotonia congenita (PC)), induced muscle weakness led to a signal increase of approximately 18% in the (23)Na MR images, which was attributed to intracellular Na(+) accumulation in this region.

Adult↗

PubMed2006

B1 field-insensitive transformers for RF-safe transmission lines.

OBJECTIVE: Integration of transformers into transmission lines suppresses radiofrequency (RF)-induced heating. New figure-of-eight-shaped transformer coils are compared to conventional loop transformer coils to assess their signal transmission properties and safety profile. MATERIALS AND METHODS: The transmission properties of figure-of-eight-shaped transformers were measured and compared to transformers with loop coils. Experiments to quantify the effect of decoupling from the B1 field of the MR system were conducted. Temperature measurements were performed to demonstrate the effective reduction of RF-induced heating. The transformers were investigated during active tracking experiments. RESULTS: Coupling to the B1 field was reduced by 18 dB over conventional loop-shaped transformer coils. MR images showed a significantly reduced artifact for the figure-of-eight- shaped coils generated by local flip-angle amplification. Comparable transmission properties were seen for both transformer types. Temperature measurements showed a maximal temperature increase of 30 K/3.5 K for an unsegmented/segmented cable. With a segmented transmission line a robotic assistance system could be successfully localized using active tracking. CONCLUSION: The figure-of-eight-shaped transformer design reduces both RF field coupling with the MR system and artifact sizes. Anatomical structure close to the figure-of-eight-shaped transformer may be less obscured as with loop-shaped transformers if these transformers are integrated into e.g. intravascular catheters.

Equipment Design↗

PubMed2006

Secondary individual prevention of occupational skin diseases in health care workers, cleaners and kitchen employees: aims, experiences and descriptive results.

OBJECTIVES: Due to increased occupational dermatoses in certain professions such as health care workers (HCW), cleaning and kitchen employees (CKE), measures of prevention and skin protection are of high significance. Skin protection courses focus on educational aims (e.g. improving skin care habits, influencing the participants' attitudes towards health) and medical aims (e.g. optimising diagnostic procedures, complementing individual therapy). METHODS: Participants are patients who have been suspected to suffer from an occupational skin disease and are insured with the German Accident Prevention & Insurance Association (BGW). Teaching units of the skin protection courses focus on basics of skin functioning and important aspects of occupational skin diseases. Practical parts include information and instructions about the correct implementation of skin protection, skin care and skin cleansing. Every participant is seen by a dermatologist obtaining a precise patient's history and performing a skin examination. All this results in working out individually adapted and professional skin protection strategies. RESULTS: In total, 791 participants (93 men and 698 women) completed the skin protections courses. Six hundred and sixty-seven patients (mean age: 36.9 years, SD = 11.6) were HCW and 124 patients (mean age: 40.4 years, SD = 10.8) were CKE. In HCW 82.5% (n = 550) and in CKE 86.3% (n = 107) suffered from hand eczema of the atopic, irritant or allergic type. Irritant contact dermatitis as a single diagnosis was the most frequent one in both groups (HCW: 34.5.%, n = 230; CKE: 49.2% n = 61). According to regularly performed evaluations, the participants rated the course as good to excellent. Nearly 80% of the participants had skin lesions while attending the course, in 27% the dermatosis was severe. CONCLUSIONS: There is a high need for health education, advisory services, diagnostics and additional therapy in occupational dermatology. Prevention of occupational skin diseases and maintenance of health through educational programmes are important complementary measures for dermatological care but still missing in endangered professions.

Adult↗

PubMed2006

Age related changes of human aortic distensibility: evaluation with ECG-gated CT.

Aortic distensibility is a parameter to grade vascular diseases and age-related effects because it is related to the elastic properties of the vessel wall. In this study vascular cross-sectional area changes have been determined using ECG-gated CT to analyse the age dependency of aortic distensibility. Distensibility measurements of the aorta were performed in 31 subjects (28 to 85 years). Time-resolved images were acquired either with a 4- or 16-detector row CT system using a modified CT angiography protocol. Cross-sectional area changes of the aorta were calculated by semiautomatic segmentation, and distensibility values were obtained using additional systemic blood pressure measurements. The aorta could be segmented successfully in all subjects. A decrease of aortic distensibility with age was found (r=0.50). Below (above) the renal arteries, the annual decrease was Delta D ( infrarenal ) =(-2.1+/-0.7).10(-7 )Pa(-1)a(-1), (D ( suprarenal ) Delta=(-3.5+/-1.1).10(-7 )Pa(-1)a(-1)). Differences between the ages, the youngest third and oldest third studied, were found to be significant (P( suprarenal )=0.003; P( infrarenal )=0.025). An age-dependent decrease of aortic wall elasticity can be determined in a modified routine CT angiography study.

Adult↗

PubMed2006

Manganese-enhanced magnetic resonance imaging for in vivo assessment of damage and functional improvement following spinal cord injury in mice.

In past decades, much effort has been invested in developing therapies for spinal injuries. Lack of standardization of clinical read-out measures, however, makes direct comparison of experimental therapies difficult. Damage and therapeutic effects in vivo are routinely evaluated using rather subjective behavioral tests. Here we show that manganese-enhanced magnetic resonance imaging (MEMRI) can be used to examine the extent of damage following spinal cord injury (SCI) in mice in vivo. Injection of MnCl2 solution into the cerebrospinal fluid leads to manganese uptake into the spinal cord. Furthermore, after injury MEMRI-derived quantitative measures correlate closely with clinical locomotor scores. Improved locomotion due to treating the detrimental effects of SCI with an established therapy (neutralization of CD95Ligand) is reflected in an increase of manganese uptake into the injured spinal cord. Therefore, we demonstrate that MEMRI is a sensitive and objective tool for in vivo visualization and quantification of damage and functional improvement after SCI. Thus, MEMRI can serve as a reproducible surrogate measure of the clinical status of the spinal cord in mice, potentially becoming a standard approach for evaluating experimental therapies.

Algorithms↗

PubMed2006

Active catheter tracking using parallel MRI and real-time image reconstruction.

In this work active MR catheter tracking with automatic slice alignment was combined with an autocalibrated parallel imaging technique. Using an optimized generalized autocalibrating partially parallel acquisitions (GRAPPA) algorithm with an acceleration factor of 2, we were able to reduce the acquisition time per image by 34%. To accelerate real-time GRAPPA image reconstruction, the coil sensitivities were updated only after slice reorientation. For a 2D trueFISP acquisition (160 x 256 matrix, 80% phase matrix, half Fourier acquisition, TR = 3.7 ms, GRAPPA factor = 2) real-time image reconstruction was achieved with up to six imaging coils. In a single animal experiment the method was used to steer a catheter from the vena cava through the beating heart into the pulmonary vasculature at an image update rate of about five images per second. Under all slice orientations, parallel image reconstruction was accomplished with only minor image artifacts, and the increased temporal resolution provided a sharp delineation of intracardial structures, such as the papillary muscle.

Algorithms↗

PubMed2006

Dynamic coil selection for real-time imaging in interventional MRI.

MR-guided intravascular interventions require image update rates of up to 10 images per second, which can be achieved using parallel imaging. However, parallel imaging requires many coil elements, which increases reconstruction times and thus compromises real-time image reconstruction. In this study a dynamic coil selection (DCS) algorithm is presented that selects a subset of receive coils to reduce image reconstruction times. The center-of-sensitivity coordinates and the relative signal intensities are determined for each coil in a prescan. During the intervention m coils are selected for reconstruction using a coil ranking based on the distance to the current slice or catheter position. In a phantom experiment for m = 6, an optimal signal-to-background ratio (SBR) was achieved and foldover artifacts were avoided. In three animal experiments involving catheter manipulation in the aorta and the right heart chamber, the anatomy was successfully visualized at frame rates of about 5 Hz using active catheter tracking.

Algorithms↗

PubMed2006

Educational and dermatological aspects of secondary individual prevention in healthcare workers.

Healthcare workers (HCW) have an increased risk of suffering from occupational skin diseases (OSDs). Therefore, we established special prevention and skin protection courses for HCW. Medical aims are to optimize diagnostic procedures and individual therapy, educational aims are to improve individual skin protection/skin care habits of the patient and also to influence the participants' attitudes towards health. Participants are patients that have been suspected to suffer from an OSD and are insured with the German Accident Prevention Insurance Association for Health Care Workers (BGW). Teaching units mainly focus on the texture and functioning of the skin, general aspects of OSDs, general information concerning skin protection, instructions about the correct use of skin cleansing and skin protection products. Besides, every participant is clinically examined by a dermatologist and a precise patient's history is obtained. Individually adapted skin protection strategies are developed. Patients can ask the dermatologist questions in confidence. 504 patients (mean age: 36.9 years, SD = 11.7) participated in the skin protection courses. 94.6% (n = 477) suffered from hand eczema frequently caused by a mixture of atopic, irritant and allergic contact dermatitis, but irritant contact dermatitis was the most frequent diagnosis (55.4%, n = 279). The participants rated the course as good to excellent. Health education and advisory services in occupational dermatology are still fragmentary. Prevention of OSD and maintenance of health through education are important complementary measures for dermatological care. In the future, similar educational programmes should be offered for employees of other professions with an increased risk for OSD.

Adult↗

PubMed2005

Source apportionment of organic pollutants of a highway-traffic-influenced urban area in Bayreuth (Germany) using biomarker and stable carbon isotope signatures.

Traffic- and urban-influenced areas are prone to enhanced pollution with products of incomplete combustion of fossil fuels and biomass such as black carbon or polycyclic aromatic hydrocarbons (PAHs). Black carbon is composed of aromatic and graphitic structures and may act as a carrier for pollutants such as PAHs and heavy metals. However, little is known about possible contributions of traffic-derived black carbon to the black carbon inventory in soils. Similar uncertainties exist regarding the contribution of different pollutant sources to total PAH and black carbon contents. Therefore, the objective of this study was to quantify the importance of traffic pollution to black carbon and PAH inventories in soils. PAH contamination of soils adjacent to a major German highway in the urban area of Bayreuth with about 50,000 vehicles per day was in the same order of magnitude compared to highway-close soils reported in other studies. Using molecular (black carbon and PAHs) and compound-specific stable carbon isotope evidence (PAHs) it was demonstrated that this contamination originated not only from automobile exhausts, here primarily diesel, but also from tire abrasion and tailpipe soot which significantly contributed to the traffic-caused black carbon and PAH contamination. Low molecular weight PAHs were more widely transported than their heavy molecular counterparts (local distillation), whereas highway-traffic-caused black carbon contamination was distributed to at least 30 m from the highway. On the other hand, urban fire exhausts were distributed more homogeneously among the urban area.

Air Pollutants↗

PubMed2005

Influence of different breathing maneuvers on internal and external organ motion: use of fiducial markers in dynamic MRI.

PURPOSE: To investigate, with dynamic magnetic resonance imaging (dMRI) and a fiducial marker, the influence of different breathing maneuvers on internal organ and external chest wall motion. METHODS AND MATERIALS: Lung and chest wall motion of 16 healthy subjects (13 male, 3 female) were examined with real-time trueFISP (true fast imaging with steady-state precession) dMRI and a small inductively coupled marker coil on either the abdomen or thorax. Three different breathing maneuvers were performed (predominantly "abdominal breathing," "thoracic breathing," and unspecific "normal breathing"). The craniocaudal (CC), anteroposterior (AP), and mediolateral (ML) lung distances were correlated (linear regression coefficient) with marker coil position during forced and quiet breathing. RESULTS: Differences of the CC distance between maximum forced inspiration and expiration were significant between abdominal and thoracic breathing (p < 0.05). The correlation between CC distance and coil position was best for forced abdominal breathing and a marker coil in the abdominal position (r = 0.89 +/- 0.04); for AP and ML distance, forced thoracic breathing and a coil in the thoracic position was best (r = 0.84 +/- 0.03 and 0.82 +/- 0.03, respectively). In quiet breathing, a lower correlation was found. CONCLUSION: A fiducial marker coil external to the thorax in combination with dMRI is a new technique to yield quantitative information on the correlation of internal organ and external chest wall motion. Correlations are highly dependent on the breathing maneuver.

Abdomen↗

PubMed2005

[Skin protection and skin disease prevention courses for secondary prevention in health care workers: first results after two years of implementation].

BACKGROUND: Healthcare workers have an increased risk of occupational dermatoses. In January 2002, the Department of Social Medicine, Occupational and Environmental Dermatology of the University of Heidelberg started organizing special prevention courses for this group of employees in cooperation with the Accident Prevention & Insurance Association for Health Care Workers (BGW). The major aims are to improve individual skin protection and skin care habits, as well as to optimize diagnostic procedures and therapy. PATIENTS AND METHODS: The two-day course has up to 14 participants. Teaching units mainly focus on skin structure and function, general aspects of occupational skin diseases, general information concerning skin protection and practical exercises emphasizing the correct use of skin cleansing and skin protection products. Additionally, every participant undergoes a dermatological examination including a detailed history and skin inspection. Individual skin protection strategies are developed, and the participants are provided with the opportunity to ask the dermatologist questions in confidence. RESULTS: Most of the 355 participants have been female (87.3%) with a mean age of 36.9 years. 95% had hand eczema, predominantly dyshidrotic morphology. In many cases, there was a mixture of atopic, irritant and allergic contact dermatitis but irritant contact dermatitis was most common (43%). Atopy was present in 68% of the patients. The participants rated the course as good to excellent. Other benefits are the exchange of experience between patients working in the same or similar occupations and transfer of the new knowledge to colleagues, family and friends. CONCLUSIONS: Examinations and advisory services in occupational dermatology are still fragmentary. Skin barrier creams and moisturizers are not sufficiently utilized in daily practice. In the future, similar courses should be offered for employees in other professions with an increased risk of occupational skin diseases.

Adult↗

PubMed2005

[Measurements of respiratory motion using fast magnetic resonance imaging and inductively-coupled marker coils].

The respiratory motion of the thoracic wall provides indirect information about the breathing displacement of the inner organs. To analyze the correlation between thoracic wall and lung motion for applications in radiation therapy, the breathing displacement of the lung is visualized with a fast gradient echo pulse sequence (trueFISP) at a rate of 2-3 images/sec. For quantification of the motion, a small inductively-coupled marker coil is attached to the chest wall and detected with a fast projection technique. Since the marker coil generates a flip angle amplification (factor 15) in its interior, very small nominal flip angles of 2 degrees can be used during the projection measurements which do not affect the image quality of the trueFISP images. Volunteer studies with the marker coil showed a good agreement with simultaneously acquired breathing belt data and position information extracted from the MR images. Whereas the breathing belt provided reliable data only within a certain dynamic range, the marker coil could detect also extreme breathing excursions with a precision better than 2 millimeters.

Equipment Design↗

PubMed2005

Evaluation of lung volumetry using dynamic three-dimensional magnetic resonance imaging.

RATIONALE AND OBJECTIVES: We sought to investigate lung volume and surface measurements during the breathing cycle using dynamic three-dimensional magnetic resonance imaging (3D MRI). MATERIALS AND METHODS: Breathing cycles of 20 healthy volunteers were examined using a 2D trueFISP sequence (3 images/second) in combination with a model and segmented 3D FLASH sequence (1 image/second) MR images using view sharing. Segmentation was performed semiautomatically using an interactive region growing technique. Vital capacity (VC) was calculated from MRI using the model (2D) and counting the voxels (3D) and was compared with spirometry. RESULTS: VC from spirometry was 4.9+/-0.9 L, 4.4+/-1.2 L from 2D MRI measurement, and 4.7+/-0.9 L for 3D MRI. Using the 3D technique, correlation to spirometry was higher than using the 2D technique (r>0.95 vs. r>0.83). Using the 3D technique, split lung volumes and lung surface could be calculated. There was a significant difference between the left and right lung volume in expiration (P<0.05). CONCLUSIONS: Dynamic 3D MRI is a noninvasive tool to evaluate split lung volumes and lung surfaces during the breathing cycle with a high correlation to spirometry.

Adult↗

PubMed2005

Physical and biological characterization of superparamagnetic iron oxide- and ultrasmall superparamagnetic iron oxide-labeled cells: a comparison.

RATIONALE: Superparamagnetic iron-oxide particles are used frequently for cellular magnetic resonance imaging and in vivo cell tracking. The purpose of this study was to compare the labeling characteristics and efficiency as well as toxicity of superparamagnetic iron oxide (SPIO) and ultrasmall superparamagnetic iron oxide (USPIO) for 3 cell lines. METHODS: Using human fibroblasts, immortalized rat progenitor cells and HEP-G2-hepatoma cells, dose- and time-dependence of SPIO and USPIO uptake were evaluated. The amount of intracellular (U)SPIO was monitored over 2 weeks after incubation by T2-magnetic resonance relaxometry, ICP-mass-spectrometry, and histology. Transmission-electronmicroscopy was used to specify the intracellular localization of the endocytosed iron particles. Cell death-rate and proliferation-index were assessed as indicators of cell-toxicity. RESULT: For all cell lines, SPIO showed better uptake than USPIO, which was highest in HEP-G2 cells (110 +/- 2 pg Fe/cell). Cellular iron concentrations in progenitor cells and fibroblasts were 13 +/- 1pg Fe/cell and 7.2 +/- 0.3pg Fe/cell, respectively. For all cell lines T2-relaxation times in cell pellets were below detection threshold (<3 milliseconds) after 5 hours of incubation with SPIO (3.0 micromol Fe/mL growth medium) and continued to be near the detection for the next 6 days. For both particle types and all cell lines cellular iron oxide contents decreased after recultivation and surprisingly were found lower than in unlabeled control cells after 15 days. Viability and proliferation of (U)SPIO-labeled and unlabeled cells were not significantly different. CONCLUSIONS: The hematopoetic progenitor, mesenchymal fibroblast and epithelial HEP-G2 cell lines accumulated SPIO more efficiently than USPIO indicating SPIO to be better suited for cell labeling. However, the results indicate that there may be an induction of forced cellular iron elimination after incubation with (U)SPIO.

Animals↗

PubMed2005

Capsid processing requirements for abrogation of Fv1 and Ref1 restriction.

Murine leukemia virus is restricted in mouse cells lines by a host factor known as Fv1 and in human cell lines by Ref1. Genetic evidence indicates that these restriction factors target the virus capsid (CA) protein. Restriction can be overcome by adding virus at a high multiplicity of infection, indicating that the restriction factors can be saturated. Cells preexposed to restricted virus will allow infection by a second virus which would normally be restricted. This phenomenon is known as abrogation; it provides us with a tool with which to study the interaction of virus with restriction factors. We tested the abilities of several Gag processing mutants to abrogate restriction. Our results show that CA must be cleaved from both p12 and nucleocapsid in order for the incoming virion to interact with the restriction factor. Endogenous expression of properly processed CA, however, failed to abrogate restriction. These results suggest that as well as being processed, CA must also be properly assembled in the form of a condensed viral core in order to interact with Fv1 and Ref1. This polymeric structure may contain restriction factor binding sites not present in monomeric CA.

Animals↗

PubMed2005

Time-resolved contrast-enhanced three-dimensional magnetic resonance angiography of the chest: combination of parallel imaging with view sharing (TREAT).

RATIONALE AND OBJECTIVES: In view sharing, some parts of k-space are updated more often than others, leading to an effective shortening of the total acquisition time. Undersampling of high-frequency k-space data, however, can result in artifacts at the edges of blood vessels, especially during the rapid signal intensity changes. The objective of this study was to evaluate a new time-resolved echo-shared angiographic technique (TREAT) combining parallel imaging with view sharing. First, the presence of artifacts arising from different temporal interpolation schemes was evaluated in simulations of the point spread function. Second, the image quality and presence of artifacts of time-resolved parallel three-dimensional magnetic resonance angiography (3D MRA) of the chest, acquired with and without view sharing, was assessed in a clinical study of patients with cardiovascular or pulmonary disease. MATERIALS AND METHODS: Using parameters from a time-resolved parallel 3D MRA sequence without view sharing (parallel MRA), giving a 33% increase in spatial resolution, our simulations have revealed that k-space segmentation in 3 regions provides acceptable artifacts. Thirty-six consecutive patients (mean age, 50 +/- 16 years; 15 females, 22 males) were examined in a clinical study with TREAT. The image data were compared with that of a group of 31 consecutive patients (mean age, 46 +/- 19 years; 12 females, 19 males) examined with a conventional time-resolved parallel MRA sequence without view sharing (parallel MRA). The image quality and presence of artifacts was assessed in a blind comparison by 2 radiologists in consensus using MPR and MIP reconstructions. Furthermore, the peak SNR of the pulmonary artery and aorta was compared between both MRA sequences. RESULTS: The image quality of TREAT was rated significantly higher than that of the parallel MRA sequence without view sharing: depending on the orientation of MPR and MIP reconstructions, an excellent image quality was found in 69-89% with TREAT and in 45-71% with the parallel MRA protocol without view sharing, respectively. The presence of artifacts was equal with both sequences. CONCLUSION: View sharing can be successfully combined with other acceleration techniques, such as parallel imaging. TREAT allows the assessment of the thoracic vasculature with a high temporal and spatial resolution.

Cardiovascular Diseases↗

PubMed2004

Volumetric computed tomography (VCT): a new technology for noninvasive, high-resolution monitoring of tumor angiogenesis.

Volumetric computed tomography (VCT) is a technology in which area detectors are used for imaging large volumes of a subject with isotropic imaging resolution. We are experimenting with a prototype VCT scanner that uses flat-panel X-ray detectors and is designed for high-resolution three-dimensional (3D) imaging. Using this technique, we have demonstrated microangiography of xeno-transplanted skin squamous cell carcinomas in nude mice. VCT shows the vessel architecture of tumors and animals with greater detail and plasticity than has previously been achieved, and is superior to contrast-enhanced magnetic resonance (MR) angiography. VCT and MR images correlate well for larger tumor vessels, which are tracked from their origin on 3D reconstructions of VCT images. When compared with histology, small tumor vessels with a diameter as small as 50 microm were clearly visualized. Furthermore, imaging small vessel networks inside the tumor tissue improved discrimination of vital and necrotic regions. Thus, VCT substantially improves imaging of vascularization in tumors and offers a promising tool for preclinical studies of tumor angiogenesis and antiangiogenic therapies.

Animals↗

PubMed2004

Mapping land-cover and mangrove structures with remote sensing techniques: a contribution to a synoptic GIS in support of coastal management in North Brazil.

This article deals with the development and application of a cartographic database for a synoptic Geographic Information System (GIS). Its purpose is the storage and evaluation of the heterogeneous datasets of the interdisciplinary scientific research program MADAM (Mangrove Dynamics and Management), which aims to develop recommendations for a tailored integrated coastal management scheme for the mangrove ecosystem at Braganca (North Brazil). The article describes the integration of remote sensing data, aerial photographs, as well as point data provided by fieldwork from different scientific fields. Using various innovative processing techniques and different scale-resolution levels, an assessment of temporal-spatial changes of the mangrove peninsula and the adjacent rural socioeconomic impact area, the type of mangrove structure, as well as a land-use cover analyses was undertaken. The definition of the spatial level of detail was found to be a major issue in the development of the GIS, as well as during the processing and analysis procedures. A division between strong and weak patterns in the mangrove ecosystem could be made, which implies different management measures and sets of specific interdisciplinary studies and monitoring at hierarchical scales.

Brazil↗