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Biomedical subjects

L Schad

Publications and source records attributed to L Schad.

11 recordsLinked to original sources
PubMed2007

Diffusion tensor imaging of cingulum fibers in mild cognitive impairment and Alzheimer disease.

BACKGROUND: Neuroimaging in mild cognitive impairment (MCI) and Alzheimer disease (AD) generally shows medial temporal lobe atrophy and diminished glucose metabolism and cerebral blood flow in the posterior cingulate gyrus. However, it is unclear whether these abnormalities also impact the cingulum fibers, which connect the medial temporal lobe and the posterior cingulate regions. OBJECTIVE: To use diffusion tensor imaging (DTI), by measuring fractional anisotropy (FA), to test 1) if MCI and AD are associated with DTI abnormalities in the parahippocampal and posterior cingulate regions of the cingulum fibers; 2) if white matter abnormalities extend to the neocortical fiber connections in the corpus callosum (CC); 3) if DTI improves accuracy to separate AD and MCI from healthy aging vs structural MRI. METHODS: DTI and structural MRI were preformed on 17 patients with AD, 17 with MCI, and 18 cognitively normal (CN) subjects. RESULTS: FA of the cingulum fibers was significantly reduced in MCI, and even more in AD. FA was also significantly reduced in the splenium of the CC in AD, but not in MCI. Adding DTI to hippocampal volume significantly improved the accuracy to separate MCI and AD from CN. CONCLUSION: Assessment of the cingulum fibers using diffusion tensor imaging may aid early diagnosis of Alzheimer disease.

Aged↗
PubMed2001

[High resolution MR-venography of cerebral arteriovenous malformations].

PURPOSE: The purpose of this study was to evaluate the diagnostic potential of a high resolution MR venography technique in patients with cerebral arteriovenous malformations (AVM). A high-resolution 3D gradient echo sequence was used with a long echo time TE to obtain venous information down to sub-pixel sized vessel diameters of several hundred microns. The method is based on the paramagnetic property of deoxyhemoglobin and the resulting developing phase difference between veins and brain parenchyma at long echo times which leads to signal cancellation. The reconstructed venograms were compared with TOF-MR angiography using qualitative and quantitative criteria with the conventional DSA serving as the reference gold standard. METHODS: In 17 patients with angiographically proven cerebral AVM the method indicates its potential in clinical applications. Venography was able to detect all AVM whereas TOF-MRA failed in three patients. In the delineation of venous drainage patterns MR venography was superior to TOF-MRA, however, as expected the method detected only about half of the main feeding arteries. Due to susceptibility artifacts at air/tissue boundaries or interference with paramagnetic hemosiderin, MR venography was limited with respect to the delineation of the exact nidus sizes and shapes in ten patients with AVM located close to the skull base or in patients having suffered from previous bleeding. RESULTS: Although the visualization of draining veins represents an important prerequisite in the surgical and radiosurgical treatment planning of cerebral AVM, there exist limitations of the technique in regions where strong induced static field inhomogeneities are present. CONCLUSIONS: Due to its high sensitivity the method may be of special importance in the early detection and assessment of small AVM which are difficult to diagnose with other MR methods.

Adolescent↗
PubMed2000

Stereotactic fractionated radiotherapy for chordomas and chondrosarcomas of the skull base.

PURPOSE: To investigate the treatment outcome of patients suffering from skull base chordoma or chondrosarcoma after fractionated stereotactic radiotherapy. METHODS AND MATERIALS: We report 45 patients treated for chordoma or chondrosarcoma with postoperative fractionated stereotactic radiotherapy between 1990 and 1997. Patients had CT and MRI for 3D treatment planning performed under stereotactic guidance. Median dose at isocenter was 66.6 Gy for chordomas and 64.9 Gy for chondrosarcomas. MRI imaging was obtained in intervals after therapy to evaluate local relapse. Survival was calculated according to the Kaplan-Meier method. RESULTS: All chondrosarcomas had achieved and maintained local control and recurrence-free status at follow-up of 5 years. Local control rate of chordomas was 82% at 2 years and 50% at 5 years. Survival was 97% at 2 years and 82% at 5 years. At maximum follow-up of 8 years local control and survival rate of chordomas was 40% (82%). Clinically significant late toxicity developed in one patient. CONCLUSIONS: Our results demonstrate the feasibility of fractionated photon beam therapy and its success in the treatment of skull base tumors. Modern 3D treatment techniques provide superior results compared to conventional techniques. The role of high-precision radiotherapy compared to particle beam therapy in the treatment of these tumors is not yet fully clear and further research is needed.

Adolescent↗
PubMed1997

[Classification of hemodynamic changes in renal artery stenosis using cine magnetic resonance phase contrast flow measurements].

PURPOSE: To evaluate the use of high-temporal resolution cine MR phase-contrast flow measurements for assessment of flow dynamics in renal artery stenosis (RAS). MATERIAL AND METHODS: In a dog model, cine MR flow measurements were validated by comparing the MR flow data to an invasive transit-time ultrasound reference technique for different degrees of RAS. Cardiac-gated MR flow curves were recorded in 56 renal arteries of 28 patients with a temporal resolution of at least 32 ms. In all cases RAS was confirmed by digital subtraction angiography (DSA). Abnormalities of flow dynamics were assessed in the calculated flow curves using the MR parameters mean flow, maximum velocity, and time to systolic maximum. RESULTS: By means of the MR blood flow parameters high-grade stenoses (> 50%, n = 23) were detected with sensitivity of 100% and specificity of 94% with reference to DSA. The overall differentiation between stenoses (n = 37) and non-stenosed vessels (n = 19) revealed a sensitivity of 87% and a specificity of 100%. CONCLUSION: Analysis of cardiac-gated MR flow curves provides a non-invasive method to assess the hemodynamic significance of RAS and thus allows a functional evaluation in relation to the morphologic characteristics of the stenosis.

Adolescent↗
PubMed1997

[Magnetic resonance urography. First clinical results].

We report our preliminary results using a new magnetic resonance imaging technique for visualization of the urinary tract. Using the paramagnetic contrast medium gadolinium diethylene triamine penta-acetic acid (DTPA), we were able to obtain images of the urinary tract comparable to those obtained by conventional excretory urography. The major advantage of our technique is that besides good morphologic visualization, the excretion of gadolinium-DTPA can be studied simultaneously. We demonstrate our preliminary results in selected cases.

Adult↗
PubMed1997

Renal artery stenosis: grading of hemodynamic changes with cine phase-contrast MR blood flow measurements.

PURPOSE: To analyze the blood flow dynamics in renal artery stenosis with high-temporal-resolution cine phase-contrast magnetic resonance (MR) flow measurements. MATERIALS AND METHODS: Cine phase-contrast MR flow measurements were invasively validated with real-time intraoperative transit-time ultrasound (US). In 23 patients, 48 renal artery stenoses were confirmed at digital subtraction angiography. Cardiac-gated cine phase-contrast MR flow measurements were obtained in 32-msec intervals, and flow curves were calculated for the whole cardiac cycle. Hemodynamic parameters evaluated included the decrease in mean flow and the delay and reduction in the systolic velocity maximum due to decrease in or absence of the early systolic peak. RESULTS: Overall differentiation between renal artery stenosis (n = 31) and nonstenosed vessels (n = 17) with cine phase-contrast MR revealed a sensitivity of 90% and specificity of 94% compared with findings at digital subtraction angiography. High-grade stenoses (>50%, n = 19) were detected with cine phase-contrast MR with sensitivity of 100% and specificity of 93%. CONCLUSION: Quantitative and qualitative analysis of cardiac-gated cine phase-contrast MR flow velocity curves provided a highly accurate method to detect hemodynamic abnormalities in patients with suspected renal artery stenosis.

Adolescent↗
PubMed1995

Elimination of gadolinium-DTPA by peritoneal dialysis.

Magnetic resonance urography (MRU) after i.v. injection of gadolinium-DTPA (0.1 mmol/kg bodyweight) was performed in a patient with transplant dysfunction after renal allograft transplantation. Renal replacement therapy was accomplished by means of peritoneal dialysis. Gadolinium-DTPA concentrations in urine and dialysate were measured repeatedly during a 48-h period with inductively coupled plasma atomic emission spectrometry. The total 24-h creatinine clearance was 10.8 ml/min on day 1 and 13.7 ml/min on day 2. The corresponding total gadolinium clearance was 12.8 ml/min and 15.8 ml/min respectively. Gadolinium-DTPA was removed from the body through peritoneal dialysis at a mean clearance rate of 5.13 ml/min. Plasma half-life of gadolinium-DTPA was prolonged to 9 h. No side-effects due to gadolinium-DTPA were noted. MRU provided a better visualization of the morphology of the urinary tract than scintigraphic studies. By measuring the changes of signal intensity, the gadolinium excretion could be calculated.

Adult↗
PubMed1993

Fractionated stereotactically guided radiotherapy of head and neck tumors: a report on clinical use of a new system in 195 cases.

Between November 1988 and December 1992, 195 patients with tumors of the head and neck (low grade gliomas, meningiomas, neurinomas, chordomas and miscellaneous) were treated with a newly developed stereotactical system for fractionated, conformal, high-precision radiotherapy. The overall preparation time, including head mask production for fixation, CT, MRI, 3-D treatment planning and stereotactical localisation could be reduced to 4-5 h per patient. The use of MR in the target definition was increased to a mean of about 60%. The medial follow-up time is 22 months. Three different patient groups were selected according to pretreatment. Patients with full high-precision radiotherapy survived in 95% of cases, patients with boost treatment in 86% and patients with preirradiated recurrent disease in 64%. Meningiomas as the largest histology group (n = 62) showed partial response in 27% and complete response in 10% of cases. Progression occurred in two patients. All patients are alive. Acute side-effects were minimal and of the order of 10%, no late complications occurred despite tumor doses ranging up to 72 Gy. High-precision radiotherapy as it is performed in Heidelberg can be regarded as an effective, reliable and tolerable system for selected tumors of the head and neck.

Adolescent↗
PubMed1992

Computer systems and mechanical tools for stereotactically guided conformation therapy with linear accelerators.

An integrated system for fractionated, stereotactically guided conformation radiotherapy has been developed. The system components are a stereotactic fixation system that can be used each treatment day, a localization, and positioning unit that can be used during x-ray computer tomography, magnetic resonance imaging, positron emission tomography, and radiographical examinations as well as for treatment. Conformal precision radiotherapy is planned with a new three-dimensional treatment planning system (Voxel-Plan-Heidelberg) which comprises, among others options, a three-dimensional image correlation procedure as well as routines for the calculation of coplanar and non-coplanar irradiations with irregularly shaped fields. Two different multi-leaf collimators have been designed for precision radiotherapy in the head and neck region. A manual multi-leaf collimator is used for irradiations with stationary beams or for moving beam treatments with invariable irregularly shaped fields. This collimator system is now being used for patient treatments. The design of a computer controlled multi-leaf collimator unit for multiple fixed field irradiation techniques is discussed. All system components are aimed at conforming dose distributions for fractionated radiotherapy treatments to the target to improve sparing of adjacent normal tissues, and at achieving a sufficient geometrical accuracy in the dose application.

Computer Systems↗
PubMedDate not supplied

Correction of spatial distortion in MR imaging: a prerequisite for accurate stereotaxy.

With magnetic resonance (MR) imaging, accurate spatial information--critical for effective stereotaxy--demands a homogeneous static field and linear gradients. Inhomogeneities and nonlinearities induced by eddy currents during the pulse sequences distort the images and produce spurious displacements of the stereotactic coordinates in both the x-y plane and the z axis. These errors in position can be assessed by means of two phantoms placed within the stereotactic guidance system--a "two-dimensional phantom" displaying "pincushion" distortion in the image (i.e., x, y) plane, and the "three-dimensional phantom" displaying displacement, warp, and tilt of the image plane itself. The pincushion distortion can be "corrected" (reducing displacements from 5 to 1-2 mm) by calculations based on modeling the distortion as a fourth order two-dimensional polynomial. Based on these corrected images, errors in the z coordinate and tilt of image planes may be corrected by adjustment of the gradient shimming currents. Such correction not only implements stereotaxy under MR guidance but also provides for the accurate transfer of anatomic/pathologic information between MR and CT images.

Humans↗