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G Brix

Publications and source records attributed to G Brix.

At least 109 records · Page 6Linked to original sources
PubMed1996

Effect of radiation on blood volume in low-grade astrocytomas and normal brain tissue: quantification with dynamic susceptibility contrast MR imaging.

OBJECTIVE: The purpose of this study was to determine whether it is possible to measure radiation-induced changes in blood volume in low-grade astrocytomas and in normal brain tissue. SUBJECTS AND METHODS: The passage of a bolus of gadopentetate dimeglumine was monitored on a series of 55 T2*-weighted simultaneous dual fast low-angle shot MR images with a standard 1.5-T MR imaging system. Absolute blood volumes were calculated as the area under the tissue concentration-time curve in regions of interest and normalized to the arterial input function. We performed 41 examinations on 19 patients with grade II astrocytomas. For comparison, 13 patients were studied after whole-brain irradiation. RESULTS: A reduction in blood volume (mean +/- SD in milliliters per 100 g) within the tumors from 12.2 +/- 8.7 to 6.5 +/- 5.3 after fractionated conformation radiotherapy was detected, although there was no consistent pattern in different patients. An insignificant reduction was noted in normal gray (9.2 +/- 2.8 to 7.4 +/- 3.2) and white (4.4 +/- 1.9 to 4.1 +/- 2.3) matter outside the target volume. Conversely, we observed a significantly lower blood volume in gray (6.3 +/- 1.2) and white (3.1 +/- 1.0) matter after whole-brain radiotherapy. CONCLUSION: Our results show that a reduction of blood volume in astrocytomas and normal brain tissue after radiotherapy can be quantified by use of dynamic susceptibility contrast MR imaging. Thus, functional monitoring of tumor response and of normal tissue effects becomes possible.

Adolescent↗
PubMed1996

Pelvic lesions in patients with treated cervical carcinoma: efficacy of pharmacokinetic analysis of dynamic MR images in distinguishing recurrent tumors from benign conditions.

OBJECTIVES: Dynamic MR image series were analyzed with a pharmacokinetic two-compartment model. To preserve the spatial resolution of the dynamic MR images, the pharmacokinetic parameters were computed pixel by pixel, color coded, and superimposed on conventional MR images (pharmacokinetic mapping). The efficacies of pharmacokinetic mapping and conventional MR imaging in distinguishing between recurrent tumors and benign conditions in patients who have pelvic lesions after treatment of cervical carcinoma were compared. MATERIALS AND METHODS: Twenty-one women with 24 suspected pelvic lesions and a history of treated cervical carcinoma (stages IB-IIIA) were included in this study. Patients had been treated before MR imaging with surgery or irradiation alone (eight patients) or a combination of the two (13 patients). Patients were referred because of our findings from CT examinations and/or clinical examinations. Of 24 suspected lesions, 17 were histologically verified as tumor recurrences and seven were classified as benign masses (histologically diagnosed as fibrosis and granulation tissue). T1- and T2-weighted spin-echo images were interpreted by three observers. During and after constant-rate infusion of gadopentetate dimeglumine, the kinetics of lesion response were determined with a strongly T1-weighted saturation recovery turbo-fast low-angle shot sequence. The signal-time curves for the suspected lesions were analyzed within the framework of a pharmacokinetic two-compartment model and displayed as color-coded images. The calculated pharmacokinetic parameters (amplitude [A] and tissue distribution time [t21]) were evaluated retrospectively to obtain optimal threshold values for differentiating malignant lesions from benign lesions. RESULTS: Analysis of the pharmacokinetic mapping data showed significantly shorter (p < .005) and stronger (p < .001) contrast medium enhancement of malignant lesions (t21, 24 sec; A, 1.5 arbitrary units) than of benign lesions (t21, 65 sec; A, 0.7), resulting in a sensitivity of 100%, a specificity of 88%, and an accuracy of 96%. Interpretation of the lesions on conventional T2-weighted MR images resulted in a sensitivity of 90%, a specificity of 38%, and an accuracy of 74%. CONCLUSION: Analysis of color-coded pharmacokinetic maps is more effective than conventional MR imaging in distinguishing between malignant and benign conditions in patients who have pelvic lesions after treatment of cervical carcinoma.

Carcinoma, Squamous Cell↗
PubMed1996

[Blood volume changes after the radiotherapy of the central nervous system].

BACKGROUND: The pathogenesis of late delayed radiation damage in normal brain tissue is most likely due to damage to the vascular endothelium. The mitotic activity of gliomas was shown to correlate with the tumor induced angiogenesis. Dynamic susceptibility contrast MR imaging (DSC MRI) allows the measurement of the cerebral hemodynamics based on the indicator dilution theory. We describe theory and technique of the method and present our experience with blood volume measurements after irradiation of the CNS. METHODS: We established a double slice technique on a standard 1.5 T MR system without hardware modifications, which allows an absolute quantification of the blood volume in regions of interest (ROI) within the brain. Fifty-five T2* weighted double slice images were acquired before, during and after bolus injection of Gd-DTPA (0.1 mmol/kg in 5 sec.) using a SD FLASH sequence (simultaneous dual fast low angle shot, TR/TE1/TE2 31/16/25, flip angle 10 degrees). Concentration-time curves were calculated from the measured signal-time curves. Blood volume values in tissue were normalised and calculated in absolute values (ml/100 g) based on the knowledge of the arterial input function (AIF), which was measured in the brain supplying arteries. The whole procedure requires only 2 to 3 minutes, the time for post processing is about 15 to 20 minutes. RESULTS: Blood volume parameter images of representative cases demonstrate the blood volume changes after radiotherapy. A reduction in blood volume could be observed in normal brain tissue and low-grade gliomas, while recurrent tumors were accompanied by a local increase in blood volume. CONCLUSIONS: Radiation induced blood volume changes in the CNS can be measured using dynamic susceptibility contrast MR imaging. The measurements in normal brain tissue allow a functional in-vivo analysis of late delayed radiation reactions of the CNS. The definite value of intratumoral blood volume measurements for determination of the therapeutic success and for differentiation of recurrences versus radionecroses remains to be clarified in further studies.

Adult↗
PubMed1996

Monte Carlo-based analysis of PET scatter components.

UNLABELLED: This study quantifies the different scatter components in PET and examines how the different components degrade reconstructed PET images. METHODS: We simulated the measurement of various phantoms using Monte Carlo (MC) calculations and compared the MC-generated projections and images with the corresponding experimental data. The coincidences were subdivided in four classes: primaries, object scatter (scattered in the object only), gantry scatter (scattered in the scanner only) and mixed scatter (scattered both in the object and the scanner). RESULTS: In the projections of the line sources, the gantry scatter was closely located around the source position, whereas the object scatter was smeared over the whole field of view and could be parameterized well by a monoexponential function. The mixed scatter had nearly the same distribution as the object scatter, but with a smaller amplitude. The calculations and experimental data were in excellent agreement; i.e., led to the same parameterization of the scatter distribution functions and to a similar localization of the scatter components in the reconstructed images. CONCLUSION: The spatial distribution of the scatter components justifies the widely-used assumption that it is sufficient to restrict experimental scatter correction techniques to the object scatter. Furthermore, it is possible to derive the parameters for the scatter kernels, which are needed for the convolution-subtraction algorithm, by MC simulations.

Computer Simulation↗
PubMed1995

Pharmacokinetic mapping of the breast: a new method for dynamic MR mammography.

A dynamic contrast-enhanced MRI technique for whole breast examinations is presented. The fast kinetics of tissue response during and after constant-rate intravenous infusion of gadolinium diethylenetriaminopentaacetic acid was resolved using a strongly T1-weighted saturation recovery TurboFLASH sequence that makes it possible to acquire signal-time courses sequentially from 15 adjacent slices with a temporal sampling rate of 21 s. On the basis of the mathematically established and experimentally verified linear relationship between the measured saturation recovery TurboFLASH signal variation and the gadolinium diethylenetriaminopentaacetic acid concentration in the tissue, the signal-time courses were analyzed within the framework of pharmacokinetic modeling. In our study, the tissue response was parameterized adequately using an open linear two-compartment model. With this approach, the tissue specific information contained in the signal-time course can be described using only two parameters: an amplitude A, reflecting the degree of MR signal enhancement, and an exchange parameter k21, characterizing vascular permeability and perfusion of the tissue. A clearly arranged representation of the large amount of data (480 saturation recovery TurboFLASH breast images/examination) was accomplished by means of color coding of the computed parameters, resulting in one color-coded pharmacokinetic parameter map/cross-section.

Breast↗
PubMed1995

Mapping the biodistribution and catabolism of 5-fluorouracil in tumor-bearing rats by chemical-shift selective 19F MR imaging.

A chemical-shift selective (CHESS) 19F MR imaging technique was used to map selectively the antineoplastic drug 5-fluorouracil (5-FU) and its major catabolite alpha-fluoro-beta-alanine (FBAL) in tumor-bearing rats. The pulse sequence employed a CHESS RF saturation pulse to suppress either the 5-FU or the FBAL resonance before the other component in the two-line 19F MR spectra was measured. Selective 5-FU and FBAL images with a spatial resolution of 10 x 10 x 15 mm3 (1.5 ml) were obtained in 40 min from six ACl rats with implanted Morris hepatoma. Because the transmitter frequency could always be set to the Larmor frequency of the 19F resonance employed for imaging, the images were free of chemical-shift artifacts in readout and slice-selection direction. Whereas FBAL appeared only in the liver, the kidneys, and the bladder, 5-FU could also be detected in all major organs and in the muscular system. In the Morris hepatomas, a small 5-FU uptake and no FBAL accumulation were measured. The CHESS 19F MRI technique provides useful physiological and biochemical data on the biodistribution of the antineoplastic drug 5-FU and on the different catabolic activities of the tissues.

Animals↗
PubMed1995

[Neurofunctional MRI imaging of higher cognitive performance of the human brain].

Functional magnetic resonance imaging (fMRI) offers a powerful experimental tool for mapping activated cortical regions in man. Thereby, the paramagnetic deoxyhemoglobin in the red blood cells acts as an endogenous susceptibility contrast agent, which allows the noninvasive detection of stimulus-induced transient changes in regional cerebral blood flow and volume. Fifteen normal subjects were examined on a conventional 1.5-T MR system to visualize cortical activation during the performance of high-level cognitive tasks. A computer-controlled videoprojector was employed to present psychometrically optimized activation paradigms. Reaction times and error rates of the volunteers were acquired online during stimulus presentation. The time course of cortical activation was measured in a series of strongly T2*-weighted gradient-echo images from three or four adjacent slices. For anatomical correlation, picture elements showing a stimulus-related significant signal increase were color-coded and superimposed on T1-weighted spin-echo images. Analysis of the fMRI data revealed a subtle (range 2-5%), but statistically significant (P < 0.05) increase in signal intensity during the periods of induced cortical activation. Judgment of semantic relatedness of word pairs, for example, activated selectively cortical areas in left frontal and left temporal brain regions. The strength of cortex activation in the semantic task decreased significantly in the course of stimulus presentation and was paralleled by a decrease in the corresponding reaction times. With its move into the area of cognitive neuroscience, fMRI calls both for the careful design of activation schemes and for the acquisition of behavioral data. For example, brain regions involved in language processing could only be identified clearly when psychometrically matched activation paradigms were employed. The reaction time data correlated well with selective learning and thus helped to facilitate interpretation of the fMRI data sets.

Arousal↗
PubMed1995

[Diagnosis of recurrence of cervix carcinoma using dynamic MRI: correlation of pharmacokinetic analysis and histopathology].

PURPOSE: The aim of the study was to evaluate the value of dynamic magnetic resonance imaging (MRI) to classify suspect lesions into benign and malignant in patients previously treated for cancer of the cervix. MATERIALS AND METHODS: Eleven patients with 14 suspect lesions after treatment of cervical carcinoma were examined by dynamic contrast-enhanced MRI. The imaging findings were compared to the giant cross-section specimen as the reference standard. Computed tissue-specific enhancement parameters were obtained (pharmacokinetic mapping) and displayed as color-coded images. The regions of interest were retrospectively defined according to the pharmacokinetic images over the most suspect areas. Therein, the threshold values were determined that achieved the greatest overall accuracy and a low rate of false-positive results. RESULTS: Analysis of the lesions on T2-weighted images revealed sensitivity of 88%, specificity of 40%, and accuracy of 71%. Analysis of the dynamic MR data showed significantly shorter (p < 0.01) and stronger (p < 0.001) contrast media enhancement of malignant (n = 9) than benign lesions (n = 5). CONCLUSION: Pharmacokinetic mapping appears to yield important information for dividing suspect lesions into malignant and benign following treatment of cervical cancer.

Adult↗
PubMed1995

[Fast MRI contrast medium dynamics for characterization of tumors. Experiences with functional MR-mammography].

METHODS: MRI studies with high temporal resolution can be achieved with an optimized saturation recovery TurboFLASH sequence, which allows a more detailed characterization of contrast enhancement in tissue as is available with the current FLASH 3D techniques. A two compartment model allows characterization of signal time curves with three parameters, Amp (amplitude), k21 (distribution rate constant) and kel (elimination rate constant). RESULTS: In a prospective study on 314 patients with indetermined breast lesions signal-time-curves revealed differences in the k21 parameter between benign (0.56 +/- 0.46) and malignant lesions (1.25 +/- 0.80) (p < 0.0001) as well as between different histological classifications. CONCLUSION: The introduced MR-technique enables a better evaluation of the vascular permeability for the MR contrast media in lesions. Distinct differences were detected, which are influenced by elevated expression of angiogenesis factors such as the vascular endothelial growth factor.

Breast↗
PubMed1995

[Noninvasive quantification of cerebral blood volume and blood flow with dynamic MR tomography. Studies of probands and patients with cerebrovascular insufficiency].

PURPOSE: A non-invasive MR-method for the quantification of regional cerebral blood flow (rCBF) and blood volume (rCBV) is used to examine healthy volunteers and patients with cerebrovascular disorders. MATERIALS AND METHODS: 20 healthy volunteers and 10 patients with severe cerebrovascular disorders were examined. MR imaging was performed on a 1.5 T imaging system. Before, during and following brief antecubital vein bolus injection of Gd-DTPA, a series of 32 rapid T2*-weighted gradient echo images of two different slices ere simultaneously acquired in order to measure th concentration-time-curves in the brain tissue and the arterial input function in the brain feeding arteries. From these series of images the concentration-time-curves were computed. Principles of indicator dilution analysis were applied to compute rCBF and rCBV. The volunteers underwent one examination each. All patients underwent two examinations, one before and the second after azetazolamide stimulation. RESULTS: In volunteers the measured rCBF and rCBV values are in good agreement with data from positron emission tomography studies. In patients with cerebrovascular disorders in the asymptomatic hemisphere a mean increase of rCBF of 43,45 +/- 18.04% was observed after azetazolamide stimulation. In the affected areas of the symptomatic hemisphere in 8 from 10 patients the acetazolamide test reveals a significantly reduced response to azetazolamide stimulation, indicating an exhausted cerebrovascular reserve capacity. CONCLUSION: Dynamic MR-Imaging can provide quantitative information about rCBF and rCBV. In patients with cerebrovascular disorders, this method can be applied to estimate the cerebrovascular reserve capacity.

Acetazolamide↗
PubMed1994

[A pharmacokinetic analysis of Gd-DTPA enhancement in MRT in breast carcinoma].

Dynamic Gd-DTPA enhanced MR of the breast was performed in one single slice in 27 patients with suspicious nodular lesions. The results could be histologically verified in all cases. A rapid spin-echo sequence with a time resolution of 8.75 s was used for the dynamic examination. The signal changes were analysed using a pharmacokinetic model which allowed parametrization of the contrast enhancement and transformation of the data into colour coded parameter images. The parameters allowed reliable distinction of 9 benign from 18 malignant lesions (p < 0.05 for "amplitude", p < 0.001 for "k21"). One fibroadenoma could not be distinguished from the carcinomas. Lymph node metastases and the pharmacokinetic parameter amplitude correlated significantly (p < 0.05).

Adult↗
PubMed1994

Quantification of regional cerebral blood flow and volume with dynamic susceptibility contrast-enhanced MR imaging.

PURPOSE: Quantification of regional cerebral blood flow (rCBF) and volume (rCBV) with dynamic magnetic resonance (MR) imaging. MATERIALS AND METHODS: After bolus administration of a paramagnetic contrast medium, rapid T2*-weighted gradient-echo images of two sections were acquired for the simultaneous creation of concentration-time curves in the brain-feeding arteries and in brain tissue. Absolute rCBF and rCBV values were determined for gray and white brain matter in 12 subjects with use of principles of the indicator dilution theory. RESULTS: The mean rCBF value in gray matter was 69.7 mL/min +/- 29.7 per 100 g tissue and in white matter, 33.6 mL/min +/- 11.5 per 100 g tissue; the average rCBV was 8.0 mL +/- 3.1 per 100 g tissue and 4.2 mL +/- 1.0 per 100 g tissue, respectively. An age-related decrease in rCBF and rCBV for gray and white matter was observed. CONCLUSION: Preliminary data demonstrate that the proposed technique allows the quantification of rCBF and rCBV. Although the results are in good agreement with data from positron emission tomography studies, further evaluation is needed to establish the validity of method.

Brain↗
PubMed1994

MR mammography with pharmacokinetic mapping for monitoring of breast cancer treatment during neoadjuvant therapy.

The increased clinical understanding of neovascularization and its changes during therapy are the basis for therapy-response monitoring with MR mammography of breast cancer treatment. With dynamic MR imaging, objective quantification of neovascularization can be achieved using pharmacokinetic analysis of contrast media enhancement. This technique likely will be of major clinical importance for the noninvasive evaluation of neoadjuvant therapy with a favorable cost-benefit ratio.

Adult↗
PubMed1994

[Nuclear magnetic resonance tomography as a functional diagnostic method. New approaches to non-invasive quantification of cerebral blood volume and blood flow].

This paper presents a brief introduction to the current status of cerebral blood volume and blood flow imaging with magnetic resonance imaging (MRI) techniques. A new method for the quantitative assessment of regional cerebral blood volume (rCBV) and regional cerebral blood flow (rCBF) on the basis of the indicator dilution theory is described and preliminary quantitative results from healthy volunteers are presented. The mean values for the rCBV are 8.27 +/- 1.85 ml/100 g for grey matter and 3.78 +/- 1.34 ml/100 g for white matter. The mean values for the rCBF are 44.8 +/- 11.29 ml/min/100 g for the grey matter and 20.88 +/- 8.42 ml/min/100 g for the white matter. These results are in good agreement with PET results from the literature.

Adolescent↗
PubMed1994

Functional MR mapping of activated cortical areas.

Magnetic resonance imaging (MRI) has recently been demonstrated to be sensitive to changes in neuronal activity of cortical areas. We report our initial experiences with functional MR brain mapping at high spatial resolution using a conventional whole-body MR system. A total of 10 visual and motor cortex activation studies were carried out on 8 healthy volunteers. In each examination, a time course series of 15 strongly T2*-weighted FLASH images was measured from three adjacent slices. The image analysis revealed a subtle but highly significant signal increase in cortical layers of gray matter in primary and associative visual as well as sensorimotoric cortex regions during periods of excessive brain activity provoked by photic stimuli or motoric tasks, respectively. To correlate brain structure and brain function, the computed MR brain activation maps were directly superimposed on T1-weighted anatomic spin-echo images. With this advance into the area of functional neuroimaging, MRI is moving into an established domain of positron emission tomography (PET). We, therefore, discuss the advantages and limitations of the MR method in comparison to PET as far as this can be done at present.

Adult↗
PubMed1993

Bone marrow after autologous blood stem cell transplantation and total body irradiation: magnetic resonance and chemical shift imaging.

Magnetic resonance studies of the lumbar, pelvic, and femoral bone marrow were performed in 10 patients after autologous blood stem cell transplantation, including total body irradiation and myeloablative chemotherapy. The posttreatment interval varied between 2 and 6 yr. The appearance on T1-weighted images and the quantitative data obtained from chemical shift imaging (relative fat signal) were compared to 10 age-matched healthy volunteers. The classification of the T1-weighted images yielded no significant differences between the two groups. Chemical shift imaging by determination of the relative fat signal was able to detect a significant fatty replacement of the patients' lumbar (p < .002) and pelvic marrow (p < .01), showing the clinically inapparent decreased cellularity of the bone marrow. This difference did not change within the interval of 2-6 yr after transplantation.

Acute Disease↗
PubMed1993

MR imaging of fat-containing tissues: valuation of two quantitative imaging techniques in comparison with localized proton spectroscopy.

Since lipid protons, consisting mainly of triacylglycerols (TAG), are rather mobile, magnetic resonance imaging (MRI) is ideally suited for the examination of fat-containing tissues such as bone marrow. In contrast to water protons, however, lipid protons are chemically distinct and give rise to at least eight resonance peaks with different T1 and T2 relaxation times in the 1H spectrum. This is why the characterization of fat-containing tissues by quantitative MRI is much more difficult than that of most other tissues. In our study we wanted to examine the accuracy and the potential of a 1H chemical shift imaging (CSI) technique and a multiple spin-echo imaging (MSEI) technique. A stimulated-echo (STEAM) sequence for spatially localized proton spectroscopy was used as the reference method. In the first part of this paper, we describe quantitative imaging experiments which were performed to assess the accuracy of the fat-water separation according to the Dixon method and the bi-exponential decomposition of the MSEI data. For that purpose, we used a two-compartment phantom filled with either an aqueous Gd-DTPA solution and vegetable oil or with two different aqueous Gd-DTPA solutions, respectively. The analysis of the 1H CSI data revealed that the presence of non-methylen protons in neutral fats leads to a slight under-estimation (of about 15%) of the relative fat fraction. The error is described theoretically and verified quantitatively by STEAM measurements. The bi-exponential analysis of the transverse relaxation data, on the other hand, yields reliable T2 values if the relative proton density of both components is higher than 15%. IN the second part of our investigation, the same techniques were applied to acquire data from the subcutaneous fatty tissue, the femoral head, and the lumbar vertebrae of three healthy volunteers. In the bone marrow spectra, only two broad resonances could be resolved; they were superpositions of diverse molecular groups with different T1 and T2 relaxation times. In these cases, localized proton spectroscopy does not provide additional information with respect to 1H CSI. The MSEI data of the three examined fat containing tissue regions were adequately fitted by a bi-exponential function despite the fact that there were much more chemically distinct protons present in fatty tissues.

Adipose Tissue↗