Biomedical subjects

G Brix

Publications and source records attributed to G Brix.

At least 109 records · Page 6Linked to original sources

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↗

PubMed1993

Selective 19F MR imaging of 5-fluorouracil and alpha-fluoro-beta-alanine.

A 19F MR chemical shift imaging (CSI) technique is presented which enables selective imaging of the antineoplastic drug 5-fluorouracil (5-FU) and its major catabolite alpha-fluoro-beta-alanine (FBAL). The CSI sequence employs a chemical shift selective (CHESS) saturation pulse to suppress either the 5-FU or the FBAL resonance before the other component of the two-line 19F MR spectrum is measured. Because the transmitter frequency can always be set to the Larmor frequency of the 19F resonance to be imaged, this approach yields 5-FU and FBAL MR images free of chemical shift artifacts in read-out and slice-selection direction. In phantom experiments, selective 5-FU and FBAL images with a spatial resolution of 15 x 15 x 20 mm3 (4.5 ml) were obtained in 30 min from a model solution, whose drug and catabolite concentrations were similar to those estimated in the liver of tumor patients undergoing IV chemotherapy with 5-FU. The drug-specific MR imaging technique developed is, therefore, well-suited for the direct and noninvasive monitoring of the up-take and trapping of 5-FU in liver tumors in vivo.

Artifacts↗

PubMed1993

[Bone marrow involvement in Hodgkin's disease: MR tomography and chemical-shift imaging].

The ranking of magnetic resonance imaging (MRI) and chemical shift imaging (CSI) of the bone marrow was assessed in 30 patients in the initial staging of Hodgkin's disease or in the restaging after relapse. The results were compared with other staging procedures, especially trephine biopsies. Pathologic findings were divided into diffuse and focal lesions resulting in a better differentiation between malignant infiltrations and unspecific marrow reactions that are common in Hodgkin's disease. Diffuse changes were unspecific, a diffuse marrow infiltration could not be established in 7 patients. Focal lesions proved to be infiltrations in 6 of 7 patients; only in one case an unspecific marrow reaction was found on histology. CSI showed a pathological increase of the relative water signal in focal and diffuse marrow changes, and made no individual diagnostic contribution.

Adolescent↗

PubMed1993

Recurrent rectal cancer: diagnosis with dynamic MR imaging.

PURPOSE: To evaluate whether dynamic magnetic resonance (MR) imaging can increase the diagnostic accuracy in suspected local recurrence of rectal carcinoma. MATERIALS AND METHODS: Eighteen patients (seven men, 11 women, aged 26-78 years) with 19 suspect lesions were examined. T1-weighted (pre- and postcontrast) and T2-weighted spin-echo images were read by three observers. Computed tissue-specific enhancement parameters were obtained and displayed on gray-scale images (pharmacokinetic mapping). RESULTS: Reading of the spin-echo images yielded a sensitivity of 91%-100% (confidence interval, 67%, 100%), a specificity of 29%-43% (12%, 67%), and an accuracy of 71%-75% (48%, 91%). Analysis of the MR data showed greater (P = .0038) and faster (P = .0018) enhancement of malignant lesions (n = 12) compared with benign lesions (n = 7). CONCLUSION: Pharmacokinetic mapping of dynamic MR imaging data allows in vivo insight into tissue physiopathology, helping differentiate benign from malignant pelvic lesions in rectal cancer.

Adult↗

PubMed1992

Correction of spatial distortion in magnetic resonance angiography for radiosurgical treatment planning of cerebral arteriovenous malformations.

A treatment planning system based on magnetic resonance (MR) angiographic imaging data for the radiosurgery of inoperable cerebral arteriovenous malformations is reported. MR angiography was performed using a three-dimensional (3D) velocity-compensated fast imaging with steady-state precession (FISP) sequence. Depending on the individual MR system, inhomogeneities and nonlinearities induced by eddy currents during the pulse sequence can distort the images and produce spurious displacements of the stereotactic coordinates in both the x-y plane and the z axis. If necessary, these errors in position can be assessed by means of two phantoms placed within the stereotactic guidance system--a "2D-phantom" displaying "pincushion" distortion in the image, and a "3D-phantom" displaying displacement, warp, and tilt of the image plane itself. The pincushion distortion can be "corrected" (reducing displacements from 2-3 mm to 1 mm) by calculations based on modeling the distortion as a fourth order 2D polynomial. Displacement, warp, and tilt of the image plane may be corrected by adjustment of the gradient shimming currents. After correction, the accuracy of the geometric information is limited only by the pixel resolution of the image (= 1 mm). Precise definition of the target volume could be performed by the therapist either directly in the MR images or in calculated projection MR angiograms obtained by a maximum intensity projection algorithm. MR angiography provides a sensitive, noninvasive 3D method for defining target volume and critical structures, and for calculating precise dose distributions for radiosurgery of cerebral arteriovenous malformations.

Humans↗

PubMed1992

[MR tomographic studies of the cerebral circulation: the methodological principles and initial clinical experiences with T2*-weighted gradient-echo sequences and CM administration as a bolus].

Paramagnetic contrast agents produce local magnetic field inhomogeneity when they pass through the cerebrovascular system. This effect can be monitored with T2*-weighted gradient echo images, which show transient signal loss, while a bolus of GdDTPA is passing through the brain tissue. This signal loss is correlated to the local cerebral tissue perfusion and the local cerebral blood volume. In a prospective study 10 volunteers and 14 patients with cerebral infarcts and brain tumours were examined. After bolus application of GdDTPA a dynamic series of rapid T2*-weighted gradient echo images were recorded, and the local dynamics of contrast flow in brain tissue was examined. From the series of images, local changes in signal intensity were calculated pixel by pixel and presented as parameter images. By this method, infarcted areas and brain tumours can be distinguished from normal tissue by their contrast flow dynamics. The abnormal contrast dynamics depend on changes in local tissue perfusion and alterations in local blood volume. The separation of the influence of both parameters however is still an unsolved problem.

Adolescent↗

PubMed1992

[MR tomography of the bone marrow in malignant systemic diseases. Diagnosis and therapeutic follow-up control].

This paper presents a short survey of the current status of bone marrow diagnosis in systemic neoplastic disease by means of MR imaging. The different patterns of bone marrow infiltration from lymphomas and leukaemias are presented and the differential diagnoses are discussed. Apart from the primary diagnosis the relevance of conventional MRI and chemical shift imaging for therapy follow up and after-care is discussed.

Bone Marrow↗

PubMed1992

[Bone marrow changes following radiotherapy. Results of MR tomography].

Magnetic resonance imaging (MRI) offers a new approach in the morphologic evaluation of the bone marrow. Physiologic and pathologic changes can be assessed with very high sensitivity. Radiotherapy induces acute depletion of the hematopoietic bone marrow, resulting in fatty degeneration. With MRI it is possible to evaluate the changes during irradiation and it also discloses the long-term fatty degeneration after radiotherapy. The irradiated bone marrow mostly exhibits a homogeneous hyperintense pattern on T1-weighted images. This allows clear recognition of the former target volumes. Our quantitative studies based on chemical shift imaging data reveal a lack of recovery of hematopoiesis after radiotherapy with 30 Gy or more. These results are independent of patients' age and of the interval after radiotherapy.

Adipose Tissue↗

PubMed1992

[MR tomography and MR angiography--a new method for the planning of the irradiation of large abdominal fields].

Subdiaphragmatic radiation therapy in malignant lymphoma requires complete irradiation of retroperitoneal lymph nodes, spleen and splenic pedicle and optimal shielding of radiosensitive structures. The aim of our study was to develop a new method for individual field definition by using MR tomography and MR angiography. In 38 patients with malignant lymphoma coronal MR tomograms and MR angiograms of the abdominal vessels were obtained and superimposed by a specially created computer program. By using a Subtraskop the MRT/MRA superposition was geometrically projected onto the simulation film in correct scale. The target volume could individually be defined and was compared to standard treatment planning according to the definition by Abbatucci. In all patients an exact irradiation of the spleen, the splenic pedicle and prominent lymphatic masses was possible. Furthermore, this resulted in a 32% reduction of treated kidney volume in the average of patients. Noninvasiveness, acceptable costs and high accuracy support the application of this new method in clinical routine.

Abdomen↗

PubMed1990

Fast and precise T1 imaging using a TOMROP sequence.

Proton spin-lattice (T1) relaxation time images were computed from a data set of 32 gradient-echo images acquired with a fast TOMROP (T One by Multiple Read Out Pulses) sequence using a standard whole-body MR imager operating at 64 MHz. The data acquisition and analysis method which permits accurate pixel-by-pixel estimation of T1 relaxation times is described. As an example, the T1 parameter image of a human brain is shown demonstrating an excellent image quality. For white and gray brain matter, the measured longitudinal relaxation processes are adequately described by a single-component least-squares fit, while more than one proton component has to be considered for fatty tissue. A quantitative analysis yielded T1 values of 547 +/- 36 msec and 944 +/- 73 msec for white and gray matter, respectively.

Brain↗

PubMed1990

[MR-tomographic quantification of infiltrative bone marrow changes and therapeutic follow-up of patients with hairy cell leukemia].

The effect of treatment on bone marrow infiltration in hairy cell leukaemia was followed by means of MRT in five patients. A semi-quantitative method has been developed in order to judge the effect of treatment. The results correlate well with the findings on iliac crest biopsies. The method could partly replace the invasive iliac crest biopsies, which are used for therapy monitoring.

Bone Marrow↗