Biomedical subjects

G Brix

Publications and source records attributed to G Brix.

At least 19 recordsLinked to original sources

PubMed2006

Paclitaxel encapsulated in cationic lipid complexes (MBT-0206) impairs functional tumor vascular properties as detected by dynamic contrast enhanced magnetic resonance imaging.

Cationic lipid complexes have been shown to be bound and internalized selectively by angiogenic tumor endothelial cells after intravenous injection. Based on this phenomenon, the chemotherapeutic agent paclitaxel was encapsulated into these lipid complexes providing a vascular targeting agent (MBT-0206). As noninvasive imaging techniques are of critical importance for optimizing antivascular cancer treatment in the clinic, we have evaluated the antivascular effects of MBT-0206 in the A-MEL-3 solid tumor model using dynamic contrast enhanced magnetic resonance imaging (DCE-MRI). Twenty-four hours after three intravenous applications of MBT-0206, tumors of treated animals demonstrated a significant decrease of intratumoral blood volume and an increase of vascular permeability in comparison to size-matched control tumors. In contrast, animals treated with conventional paclitaxel given as Taxol at equal drug dose did not show any significant differences in vascular parameters acquired by DCE-MRI in comparison to controls. Immunohistological analysis confirmed a significant reduction of microvessel density in MBT-0206 treated tumors. Moreover, a significant increase of intratumoral microvascular occlusion following MBT-0206 treatment was observed compared to controls and paclitaxel treated animals. In conclusion, antivascular tumor therapy with MBT-0206 significantly impairs functional tumor microcirculation. DCE-MRI is a promising tool to quantify the antivascular effects of MBT-0206 during treatment.

Animals↗

PubMed2006

Diagnostic nuclear medicine procedures in Germany between 1996 and 2002: application frequencies and collective effective doses.

AIM: Man-made radiation exposure to the German population predominantly results from the medical use of ionizing radiation. It was therefore the aim of the present study, to provide public health information concerning diagnostic nuclear medicine procedures carried out in Germany between 1996 and 2002. MATERIAL AND METHODS: Application frequencies for 10 groups of procedures were estimated from official reimbursement data provided by the German health insurance companies. Mean effective doses for these examinations were estimated from data provided by 14 clinics and 10 practices concerning the radiopharmaceuticals in use and the activities administered. RESULTS: During the period 1996-2002, a total of (3.83 +/- 0.31) million nuclear medicine procedures were performed in average per year, which corresponds to a mean annual application frequency of approximately 47 examinations per 1 000 inhabitants. More than 90% of the examinations were scintigraphies of the thyroid (37%), skeleton (25%), myocardium (13%), lungs (8%) and kidneys (8%). The averaged collective effective dose was (10.2 +/- 1.4) . 10(3) mSv per year, which corresponds to a mean annual per caput effective dose of about (0.12 +/- 0.02) mSv. Three types of procedures were responsible for about 80% of the total collective effective dose: scintigraphies of the myocardium (36%), skeleton (33%) and thyroid (10%). Averaged over all procedures carried-out, the mean effective dose per examination was (2.7 +/- 0.8) mSv. CONCLUSION: The average effective dose per inhabitant and year caused by nuclear medicine examinations is markedly lower than that resulting from medical X-ray procedures (0.12 vs. 1.8 mSv). Reduction of patient exposure may be achieved, for example, by replacing (201)Tl-labeled radiopharmaceuticals by (99m)Tc-labeled compounds.

Germany↗

PubMed2005

An optimized workflow for the integration of biological information into radiotherapy planning: experiences with T1w DCE-MRI.

Planning of radiotherapy is often difficult due to restrictions on morphological images. New imaging techniques enable the integration of biological information into treatment planning and help to improve the detection of vital and aggressive tumour areas. This might improve clinical outcome. However, nowadays morphological data sets are still the gold standard in the planning of radiotherapy. In this paper, we introduce an in-house software platform enabling us to combine images from different imaging modalities yielding biological and morphological information in a workflow driven approach. This is demonstrated for the combination of morphological CT, MRI, functional DCE-MRI and PET data. Data of patients with a tumour of the prostate and with a meningioma were examined with DCE-MRI by applying pharmacokinetic two-compartment models for post-processing. The results were compared with the clinical plans for radiation therapy. Generated parameter maps give additional information about tumour spread, which can be incorporated in the definition of safety margins.

Algorithms↗

PubMed2005

[Introduction of a mammography screening program in Germany. Consideration of benefits and risks].

For women between 50 and 70 years of age, X-ray mammography presently represents the most effective method for early breast cancer detection. It is commonly accepted that quality assured mammography examinations conducted at regular intervals can reduce mortality from breast cancer. In the year 2002, the German Bundestag agreed to the implementation of a mammography screening program for Germany based on the European guidelines. The effectiveness of a mammography screening program is controversially discussed and two of the most commonly cited hazards are the occurrence of false-positive results and the so-called overdiagnosis. Another issue of criticism is the radiation risk due to the mammography examinations. However, in women aged 50-70 years the radiation risk has no substantial importance. In contrast to the present situation in Germany in which opportunistic screening is widespread, standardized quality assured screening will guarantee that false-positive rates are kept as low as possible and that further assessment diagnostics are effective and minimally invasive.

Adult↗

PubMed2005

[Radiation exposure of patients from diagnostic and interventional X-ray procedures. Facts, assessment and trends].

Man-made radiation exposure to the German population predominantly results from the medical use of ionizing radiation. According to the most recent evaluation, the mean effective dose per inhabitant and year from X-ray procedures increased from 1.6 to 1.8 mSv between 1996 and 2001. This rise is mainly caused by the expanding use of CT and reflects the growing importance of this imaging modality. Besides actual data on the frequency and dose of various types of X-ray examinations, patient-specific factors will be highlighted which have to be considered in the assessment of the associated individual and collective radiation risk. Moreover, different concepts to reduce radiation exposure of patients will be discussed as well as some current trends in health service that may affect radiation hygiene -- such as diagnosis-related groups for inpatients and CT screening.

Body Burden↗

PubMed2005

[Radiation exposure of patients undergoing nuclear medicine procedures in Germany between 1996 and 2000. Multicenter evaluation of age and gender-specific patient data].

UNLABELLED: The aim of this study was to estimate both the frequency and effective dose of nuclear medicine procedures performed in Germany between 1996 and 2000 for different subgroups of patients. METHODS: Electronically archived data from 14 hospitals and 10 private practices were restored and statistically analyzed. The effective dose per examination was calculated according to ICRP publication 80 using the tissue weighting factors given in ICRP publication 60. Based on the data collected, statistical parameters were computed to characterize the frequency and effective dose of the various nuclear medicine procedures. RESULTS: In total, 604,771 nuclear medicine procedures performed in 433,709 patients were analyzed. On average, 1.4 examinations were carried out per patient and year. The median effective dose was 1.7 [5.-95. percentile; mean: 0.4-8.5; 2.9] mSv per examination and 2.3 [0.5-11.2; 3.5] mSv per patient. Interestingly, the mean effective dose per examination, but not the number of examinations per year increased with the age of the patients. Most frequent were examinations of the thyroid (36.7%), the skeleton (27.1%) and the cardiovascular system (11.1%), which were associated with a median effective dose of 0.5 [0.5-1.1; 0.7] mSv, 3.4 [2.9-5.1; 3.6] mSv and 7.3 [3.2-21.0; 9.5] mSv, respectively. Over the five-year period examined, the total annual number of PET procedures (222.3%) as well as of examinations of thyroid (24.5%), skeleton (17.9%), and the cardiovascular system (14.9%) increased markedly, whereas a decrease was observed for brain (-39.3%), lung (-20.2%) and renal (-15.0%) scans. CONCLUSION: The age- and gender-specific data presented in this study provide detailed public health information on both the current status and recent trends in the practice of diagnostic nuclear medicine examinations.

Adolescent↗

PubMed2005

PET/CT: dose-escalated image fusion?

Clinical studies demonstrate a gain in diagnostic accuracy by employing combined PET/CT instead of separate CT and PET imaging. However, whole-body PET/CT examinations result in a comparatively high radiation burden to patients and thus require a proper justification and optimization to avoid repeated exposure or over-exposure of patients. This review article summarizes relevant data concerning radiation exposure of patients resulting from the different components of a combined PET/CT examination and presents different imaging strategies that can help to balance the diagnostic needs and the radiation protection requirements. In addition various dose reduction measures are discussed, some of which can be adopted from CT practice, while others mandate modifications to the existing hard- and software of PET/CT systems.

Environmental Exposure↗

PubMed2004

Assessment of a theoretical formalism for dose estimation in CT: an anthropomorphic phantom study.

Dose assessment in computed tomography (CT) is challenging due to the vast variety of CT scanners and imaging protocols in use. In the present study, the accurateness of a theoretical formalism implemented in the PC program CT-EXPO for dose calculation was evaluated by means of phantom measurements. Phantom measurements were performed with four 1-slice, four 4-slice and two 16-slice spiral CT scanners. Firstly, scanner-specific nCTDIw values were measured and compared with the corresponding standard values used for dose calculation. Secondly, effective doses were determined for three CT scans (head, chest and pelvis) performed at each of the ten installations from readings of thermoluminescent dosimeters distributed inside an anthropomorphic Alderson phantom and compared with the corresponding dose values computed with CT-EXPO. Differences between standard and individually measured nCTDIw values were less than 16%. Statistical analysis yielded a highly significant correlation (P < 0.001) between calculated and measured effective doses. The systematic and random uncertainty of the dose values calculated using standard nCTDIw values was about -9 and +/- 11%, respectively. The phantom measurements and model calculations were carried out for a variety of CT scanners and representative scan protocols validate the reliability of the dosimetric formalism considered-at least for patients with a standard body size and a tube voltage of 120 kV selected for the majority of CT scans performed in our study.

Head↗

PubMed2004

Perfusion CT in patients with advanced bronchial carcinomas: a novel chance for characterization and treatment monitoring?

Advanced bronchial carcinomas by means of perfusion and peak enhancement using dynamic contrast-enhanced multislice CT are characterized. Twenty-four patients with advanced bronchial carcinoma were examined. During breathhold, after injection of a contrast-medium (CM), 25 scans were performed (1 scan/s) at a fixed table position. Density-time curves were evaluated from regions of interest of the whole tumor and high- and low-enhancing tumor areas. Perfusion and peak enhancement were calculated using the maximum-slope method of Miles and compared with size, localization (central or peripheral) and histology. Perfusion of large tumors (> 50 cm3) averaged over both the whole tumor (P = 0.001) and the highest enhancing area (P = 0.003) was significantly lower than that of smaller ones. Independent of size, central carcinomas had a significantly (P = 0.04) lower perfusion (mean 27.9 ml/min/100 g) than peripheral ones (mean 66.5 ml/min/100 g). In contrast, peak enhancement of central and peripheral carcinomas was not significantly different. Between non-small-cell lung cancers and small-cell lung cancers, no significant differences were observed in both parameters. In seven tumors, density increase after CM administration started earlier than in the aorta, indicating considerable blood supply from pulmonary vessels. Tumor perfusion was dependent on tumor size and localization, but not on histology. Furthermore, perfusion CT disclosed blood supply from both pulmonary and/or bronchial vessels in some tumors.

Adult↗

PubMed2004

[5 years of "concerted action dose reduction in CT" -- what has been achieved and what remains to be done?].

In May 1998, the German "Concerted Action Dose Reduction in CT" was founded by all parties involved in CT. Its intention was to achieve a significant reduction of the radiation exposure caused by CT, a matter that has increasingly been considered a major challenge since the early nineties. As a result of a number of joint efforts, the essential preconditions have been established by now. The fifth anniversary of the Concerted Action gave rise for both retrospection and outlook on the tasks that have already been accomplished and those that still need to be done. For this purpose, a one-day symposium took place in Berlin on November 4, 2003. The contents of a total of 18 contributions will be outlined here in brief.

Adult↗

PubMed2004

[Acquisition of age- and sex-dependent patient data for the calculation of annual radiation exposure in nuclear medicine: a German pilot study].

AIM: A pilot study for estimation of radiation exposure due to diagnostic procedures in nuclear medicine using routine data of hospitals and practices in Germany. METHODS: Hospitals and practices willing to participate in the study supplied data of one year (1997), containing information on patients' identification number, age, sex, type of diagnostic procedure, radiopharmaceutical, administered activity, type of health insurance (private/public), inpatient/outpatient status, and so-called Leistungsziffer, which describes the type of medical performances in Germany. The effective dose per examination was calculated according to ICRP 80. Mean, standard deviation, median, 5th and 95th percentiles of the effective dose were calculated, stratified by type of organ system and also by sex and age, including patients of > or = 18 years. RESULTS: 82,039 examinations from patients of 9 hospitals and practices were analyzed. The median (5-95(th) percentiles) of the effective dose per examination for all patients was 2.9 mSv (0.4-8.5 mSv); 1.2 examinations per patient and year were performed on average. The three most frequent examinations were bone scans (median 3.4 mSv; 2.9-5.1), thyroid (0.9 mSv; 0.4-2.2) and cardiovascular studies (7.3 mSv; 3.8-20.2). The median effective dose for 18 to 40 years old women was 1.0 mSv (0.4-5.8), for women between 41 and 65 years 2.2 mSv (0.4-7.3) and for women older than 65 years 2.4 mSv (0.5-7.6). The corresponding values for men were 2.6 mSv (0.3-7.6); 3.3 mSv (0.4-9.1), and 3.4 mSv (0.5-8.8). CONCLUSION: It was possible to gain an accurate determination of radiation exposure of diagnostic procedures in nuclear medicine by routine data.

Adult↗

PubMed2004

[High resolution reconstruction of PET images using the iterative OSEM algorithm].

AIM: Improvement of the spatial resolution in positron emission tomography (PET) by incorporation of the image-forming characteristics of the scanner into the process of iterative image reconstruction. METHODS: All measurements were performed at the whole-body PET system ECAT EXACT HR(+) in 3D mode. The acquired 3D sinograms were sorted into 2D sinograms by means of the Fourier rebinning (FORE) algorithm, which allows the usage of 2D algorithms for image reconstruction. The scanner characteristics were described by a spatially variant line-spread function (LSF), which was determined from activated copper-64 line sources. This information was used to model the physical degradation processes in PET measurements during the course of 2D image reconstruction with the iterative OSEM algorithm. To assess the performance of the high-resolution OSEM algorithm, phantom measurements performed at a cylinder phantom, the hotspot Jaszczack phantom, and the 3D Hoffmann brain phantom as well as different patient examinations were analyzed. RESULTS: Scanner characteristics could be described by a Gaussian-shaped LSF with a full-width at half-maximum increasing from 4.8 mm at the center to 5.5 mm at a radial distance of 10.5 cm. Incorporation of the LSF into the iteration formula resulted in a markedly improved resolution of 3.0 and 3.5 mm, respectively. The evaluation of phantom and patient studies showed that the high-resolution OSEM algorithm not only lead to a better contrast resolution in the reconstructed activity distributions but also to an improved accuracy in the quantification of activity concentrations in small structures without leading to an amplification of image noise or even the occurrence of image artifacts. CONCLUSION: The spatial and contrast resolution of PET scans can markedly be improved by the presented image restauration algorithm, which is of special interest for the examination of both patients with brain disorders and small animals.

Algorithms↗

PubMed2004

[Establishment and application of diagnostic reference levels for nuclear medicine procedures in Germany].

UNLABELLED: Diagnostic reference levels (DRL) were introduced in Germany by a publication in the Bundesanzeiger Nr. 143 from August 5, 2003. Thereby a recommendation of the International Commission on Radiological Protection (ICRP) from 1996 and a demand by the EU Guideline 97/43/EURATOM from 1997 is converted into national law. AIM of this paper is to acquaint with and to justify the determined DRL as well as to provide information on the practical use of the concept of the DRL. MATERIAL AND METHOD: DRL were established by experts on the basis of a national survey conducted in hospitals and private practices as well as of national and international recommendations and published by the Federal Office for Radiation Protection. Besides the data basis the dosimetric principles are described for the estimation of the effective doses of the various examinations. RESULTS: DRL were established for 10 frequent and dose-relevant examinations constituting more than 80% of all nuclear medicine examinations currently performed in Germany. For some examinations two different DRL were given to take into account clinical conditions. For paediatric examinations fractions of the activities to be administered to adults are given dependent on the body weight. DISCUSSION: The published DRL are in agreement with the majority of national and international recommendations and with the present practice of nuclear medicine examinations in Germany. They are related to average activities for groups of patients with standard sizes and, moreover, to typical examinations with current standard equipment. It is planned to check and to reconsider the DRL about every 2-3 years.

Germany↗

PubMed2004

Morpho-functional visualization of dynamic MR-mammography.

In view of an increasing use of breast MRI supplementing X-ray mammography, the purpose of this study was the development of a method for fast and efficient analysis of dynamic MR image series of the female breast. The image data sets were acquired with a saturation-recovery-turbo-FLASH sequence facilitating the detection of the kinetics of the contrast agent concentration in the whole breast with a high temporal and spatial resolution. In addition, a morphological 3D-FLASH data set was acquired. The dynamic image data sets were analyzed by tracer kinetic modeling in order to describe the physiological processes underlying the contrast enhancement in mathematical terms and thus enable the estimation of functional tissue specific parameters, reflecting the status of microcirculation. To display morphological and functional tissue information simultaneously, a multidimensional real-time visualization system (using 3D-texture mapping) was developed, which enables a practical and intuitive human-computer interface in virtual reality. The spatially differentiated representation of the computed functional tissue parameters superimposed on the anatomical information offers several possibilities: improved discernibility of contrast enhancement, inspection of the data volume in 3D-space and localization of lesions in space and thus fast and more natural recognition of topological coherencies. In a feasibility study, it could be demonstrated that multidimensional visualization of contrast enhancement in virtual reality is practical. Especially, detection and localization of multiple breast lesions may be an important application

Breast Neoplasms↗

PubMed2003

Radiation exposure in multi-slice versus single-slice spiral CT: results of a nationwide survey.

Multi-slice (MS) technology increases the efficacy of CT procedures and offers new promising applications. The expanding use of MSCT, however, may result in an increase in both frequency of procedures and levels of patient exposure. It was, therefore, the aim of this study to gain an overview of MSCT examinations conducted in Germany in 2001. All MSCT facilities were requested to provide information about 14 standard examinations with respect to scan parameters and frequency. Based on this data, dosimetric quantities were estimated using an experimentally validated formalism. Results are compared with those of a previous survey for single-slice (SS) spiral CT scanners. According to the data provided for 39 dual- and 73 quad-slice systems, the average annual number of patients examined at MSCT is markedly higher than that examined at SSCT scanners (5500 vs 3500). The average effective dose to patients was changed from 7.4 mSv at single-slice to 5.5 mSv and 8.1 mSv at dual- and quad-slice scanners, respectively. There is a considerable potential for dose reduction at quad-slice systems by an optimisation of scan protocols and better education of the personnel. To avoid an increase in the collective effective dose from CT procedures, a clear medical justification is required in each case.

Data Collection↗

PubMed2003

Morphofunctional visualization of MR-mammography in virtual reality.

In view of an increasing use of breast MRI supplementing X-ray mammography, the purpose of this study was the development of a method for fast and efficient analysis of dynamic MR image series of the female breast. The dynamic image data sets were analyzed by tracer kinetic modeling in order to describe the physiological processes underlying the contrast enhancement in mathematical terms and thus to enable the estimation of functional tissue specific parameters, reflecting the status of microcirculation. To display morphological and functional tissue information simultaneously, a multidimensional real-time visualization system (using 3D-texture mapping) was developed, which enables a practical and intuitive human-computer interface in virtual reality.

Breast Neoplasms↗

PubMed2003

Dynamic MR-mammography in virtual reality.

In view of an increasing use of breast MRI supplementing X-ray mammography, the purpose of this study was the development of a method for fast and efficient analysis of dynamic MR image series of the female breast. The image data sets were acquired with a saturation-recovery-turbo-FLASH sequence facilitating the detection of the kinetics of the contrast agent concentration in the whole breast with. In addition, a morphological 3D-FLASH data set was acquired. The dynamic image data sets were analyzed by tracer kinetic modeling in order to describe the physiological processes underlying the contrast enhancement in mathematical terms and thus to enable the estimation of functional tissue specific parameters, reflecting the status of microcirculation. To display morphological and functional tissue information simultaneously, a multidimensional real-time visualization system (using 3D-texture mapping) was developed, which enables a practical and intuitive human-computer interface in virtual reality. The spatially differentiated representation of the computed functional tissue parameters superimposed on the anatomical information offers several possibilities: improved discernibility of contrast enhancement; inspection of the data volume in 3D-space using the features of rotation and transparency variation; localization of lesions in space and thus fast and more natural recognition of topological coherencies. In a feasibility study, it could be demonstrated that multidimensional visualization of contrast enhancement in virtual reality is a practicable idea. Especially, detection and localization of multiple breast lesions may be an important application.

Computer Simulation↗

PubMed2002

[Comparison of methods for quantifying contrast enhancement exemplified by dynamic MRI mammography].

AIM: Aim of this study was to demonstrate and compare different quantification techniques to assess contrast enhancement in dynamic MRI studies. The diagnostic potential of dynamic MRI studies is increasingly appreciated and already used in different organ systems. METHOD: A patient population of 314 histologically verified breast lesions (138 malignant, 176 benign) were evaluated using a high temporal resolved dynamic sequence. Different quantification techniques such as the use of a cutoff line, time dependent and pharmacokinetic assessment were comparatively evaluated. RESULTS: Time dependent quantification methods revealed higher diagnostic potential which was further improved by in vivo normalization of the contrast availability in the vascular system. Significant differences in the enhancement characteristics were determined between malignant and benign as well within the different histological entities. CONCLUSION: Time dependent quantification methods enable an angiogenic characterization of lesions to improve diagnostic interpretation as well as monitoring during therapy. They are also the basis for automated, color-coded visualization of dynamic studies.

Breast↗