Biomedical subjects

O Dietrich

Publications and source records attributed to O Dietrich.

16 recordsLinked to original sources

PubMed2006

Quantitative and qualitative characterization of vascularization and hemodynamics in head and neck tumors with a 3D magnetic resonance time-resolved echo-shared angiographic technique (TREAT)--initial results.

The purpose of this paper is to characterize and quantify the vascularization and hemodynamic characteristics of head and neck tumors (HNT) with a dynamic 3D time-resolved echo-shared angiographic technique (TREAT) using the regular contrast agent (CA) bolus. Sixteen patients with HNT underwent 3D-TREAT during the CA administration on a 1.5-T magnetic resonance (MR) scanner. Using a parallel imaging acceleration factor of 2, 20 3D data sets at a temporal resolution of 2.3 s/frame were acquired. The quality of tumor delineation, vascularization type, and enhancement pattern were evaluated. Quantitative assessment included measurement of the contrast-to-noise ratio (CNR), determination of signal-intensity-over-time (SIT) curves, time-to-peak enhancement within the carotid arteries and the tumor, and the delay between both. TREAT was compared to conventional digital subtraction angiography (DSA) in six patients. Tumor delineation with TREAT was very good or good in 11/16 patients, and better with TREAT than with DSA in 3/6 cases. The CNR was significantly different for glomus tumors versus hypovascularized malignant tumors with TREAT (p=0.0001), but not on T1-weighted gradient echo (T1w GE) images. Qualitative assessment of tumor vascularization on dynamic TREAT shows good correlation (r=0.75) to quantitative SIT curves. We conclude that TREAT imaging permits the characterization of tumor vascularity and holds promise as a supplementary diagnostic tool in the differential diagnosis of HNT.

Adolescent↗

PubMed2006

[Reliability of multicenter magnetic resonance imaging. Results of a phantom test and in vivo measurements by the German Dementia Competence Network].

BACKGROUND: Whereas a large body of evidence suggests the usefulness of volumetric measurement of cerebral atrophy for diagnosing Alzheimer's disease (AD), the clinical applicability of cerebral volumetry for early detection of AD across multiple clinical sites is not well known. In the current study, we assessed the precision of volumetric measurement of the brain based on magnetic resonance imaging (MRI) in a multicenter setting. METHODS: The reliability of MRI was assessed by a phantom test of the American College of Radiology and voxel-based morphometry applied to the images obtained from a single subject tested at 11 centers of the German Dementia Competence Network. RESULT: Nine of the 11 centers tested met the reliability criteria of the phantom test. Across all centers, a bias was found in the measurements of slice thickness and length. For voxel-based morphometry, the coefficient of variation yielded 5.02% for gray matter volume and 12.81% (SD 9.06%) for gray matter signal intensity in voxels. Power analysis showed that a sample size of 150 subjects is sufficient for statistically valid detection of reduced gray matter volume in patients with mild cognitive impairment. CONCLUSION: The reliability of measurements from multiple centers is sufficient to allow statistically valid analysis of MRI data.

Adult↗

PubMed2006

[Oxygen-enhanced MRI of the lung: optimized calculation of difference images].

BACKGROUND: In oxygen-enhanced lung MRI, difference maps of acquisitions during inhalation of room air and pure oxygen are calculated to assess lung function. The purpose of this study was to analyze how the calculation of these difference maps depends on the delayed signal change after switching the gas supply. METHODS: Ten healthy volunteers were examined with an ECG and respiratory-triggered T1-weighting inversion recovery HASTE sequence with parallel imaging. Four blocks with 20 repetitions of up to 6 coronal slices were continuously acquired; in blocks 1 and 3 room air was supplied, in blocks 2 and 4 oxygen. Data were postprocessed, discarding between 0 and 19 repetitions after each change of gas supply before calculating the relative signal difference. RESULTS: The averaged relative signal difference increases from 9.4 to 17.4% when the number of discarded acquisitions increases; the ratio of signal difference and spatial standard deviation reaches a maximum at 5-8 discarded acquisitions. CONCLUSIONS: An optimized ratio of signal difference and statistical error is found if about 5-8 of 20 respiratory-triggered repetitions are discarded after each change of gas supply for the calculation of difference maps.

Adult↗

PubMed2006

[Magnetic resonance imaging in the evaluation of pneumonia].

Magnetic resonance imaging (MRI) of the lung is challenging because of substantial drawbacks. However, lung pathologies that are associated with increased attenuation values in CT enhance visualization in MRI: proton density is increased and tissue-air interfaces, resulting in susceptibility artifacts, are reduced in pneumonia, pneumonitis, edema, and carcinoma. On the other hand, many lung diseases result in shortness of breath, so that patients cannot hold their breath for long periods. Therefore, fast imaging techniques are required which should also allow for high spatial resolution so that small lesions can be detected. Calcifications and air pockets within lesions are not readily recognized with MRI. Thin section CT is standard for the diagnosis of pneumonia. With parallel imaging techniques, MRI examination of the lungs can be performed with short periods of breath holding, which allow for sub-centimeter resolution in the z-axis. Especially for follow-up examinations in immunocompromised patients and, in some instances, for the staging of malignant diseases (malignant pleural mesothelioma, lung cancer, respectively), MRI is very promising and may contribute to a decrease in the radiation exposure of the patients.

Humans↗

PubMed2005

Multicenter assessment of reliability of cranial MRI.

Clinical utility of magnetic resonance imaging (MRI) for the diagnosis and assessment of neurodegenerative diseases may depend upon the reliability of MRI measurements, especially when applied within a multicenter context. In the present study, we assessed the reliability of MRI through a phantom test at a total of eleven clinics. Performance and entry criteria were defined liberally in order to support generalizability of the results. For manual hippocampal volumetry, automatic segmentation of brain compartments and voxel-based morphometry, multicenter variability was assessed on the basis of MRIs of a single subject scanned at ten of the eleven sites. In addition, cranial MRI scans obtained from 73 patients with Alzheimer's disease (AD) and 76 patients with mild cognitive impairment were collected at subset of six centers to assess differences in grey matter volume. Results show that nine out of eleven centers tested met the reliability criteria of the phantom test, where two centers showed aberrations in spatial resolution, slice thickness and slice position. The coefficient of variation was 3.55% for hippocampus volumetry, 5.02% for grey matter, 4.87% for white matter and 4.66% for cerebrospinal fluid (CSF). The coefficient of variation was 12.81% (S.D.=9.06) for the voxel intensities within grey matter and 8.19% (S.D.=6.9) within white matter. Power analysis for the detection of a difference in the volumes of grey matter between AD and MCI patients across centers (d=0.42) showed that the total sample size needed is N=180. In conclusion, despite minimal inclusion criteria, the reliability of MRI across centers was relatively good.

Adult↗

PubMed2005

High-resolution diffusion tensor imaging of human patellar cartilage: feasibility and preliminary findings.

MR diffusion tensor imaging (DTI) was used to analyze the microstructural properties of articular cartilage. Human patellar cartilage-on-bone samples were imaged at 9.4T using a diffusion-weighted SE sequence (12 gradient directions, resolution = 39 x 78 x 1500 microm(3)). Voxel-based maps of the mean diffusivity, fractional anisotropy (FA), and eigenvectors were calculated. The mean diffusivity decreased from the surface (1.45 x 10(-3) mm(2)/s) to the tide mark (0.68 x 10(-3) mm(2)/s). The FA was low (0.04-0.28) and had local maxima near the surface and in the portion of the cartilage corresponding to the radial layer. The eigenvector corresponding to the largest eigenvalue showed a distinct zonal pattern, being oriented tangentially and radially in the upper and lower portions of the cartilage, respectively. The findings correspond to current scanning electron microscopy (SEM) data on the zonal architecture of cartilage. The eigenvector maps appear to reflect the alignment of the collagenous fibers in cartilage. In view of current efforts to develop and evaluate structure-modifying therapeutic approaches in osteoarthritis (OA), DTI may offer a tool to assess the structural properties of cartilage.

Anisotropy↗

PubMed2005

Techniques for diffusion-weighted imaging of bone marrow.

Diffusion-weighted magnetic resonance imaging (DWI) is an imaging technique which is sensitive to random water movements in spatial scales far below those typically accessible by magnetic resonance imaging (MRI). This property makes DWI a powerful tool for diagnosis of diseases which involve alterations in water mobility, such as acute stroke. In bone marrow, DWI has been proven to be a highly useful method for the differential diagnosis of benign and malignant compression fractures. Unfortunately, the application of DWI sequences to the bone marrow frequently suffers from artifacts, which in some cases seriously restrict the diagnostic utility of the image. This requires the introduction of additional correction techniques, or even the development of new sequences. Thus, the selection of an adequate imaging technique for DWI of the bone marrow is a very important issue. In this article the most important sequences for DWI of the bone marrow are reviewed. Special attention is paid to the problems associated with these sequences, as well as their possible solutions.

Artifacts↗

PubMed2004

[Determining global heart function with real time TrueFISP in one respiratory cycle].

Real-time multislice cine techniques lead to inaccurate results in ventricular volumes based on limited temporal resolution. The purpose of the study is to evaluate a real-time cine technique with parallel imaging algorithms in comparison to standard segmented techniques. Twelve patients underwent cardiac cine MRI using real-time multislice cine trueFISP. Temporal resolution was improved using parallel acquisition techniques (iPAT) and data acquisition was performed in a single breath-hold along the patients' short axis. Evaluation of EDV, ESV, EF and myocardial mass was performed and results compared to a standard segmented single-slice cine trueFISP. Combination of real-time cine trueFISP and iPAT provided a temporal resolution of 48 ms. Results of the multislice approach showed an excellent correlation to standard single-slice trueFISP for EDV (0.94, p <0.001), ESV (0.97, p <0.001) EF (0.99, p <0.001) and myocardial mass (0.93, p <0.001). No significant differences could be found. The use of parallel acquisition techniques (PAT) allow for a substantial improvement of temporal resolution in real-time cine MRI (<50 ms). Therefore these techniques enable an accurate and exact quantification of global ventricular function.

Algorithms↗

PubMed2004

[Cardiovascular whole body MRI with parallel imaging].

PURPOSE: To create a whole-body cardiovascular MRI protocol with parallel imaging (iPAT). MATERIAL AND METHODS: Twenty two persons participated in the whole body scan. Due to iPAT high resolution imaging of the heart could be performed. 3D contrast enhanced MR angiography (3D-CE-MRA) took only 62 s to cover the whole body at a spatial resolution of less than 1.4x1.0x1.5mm(3). Scan time for HASTE lung imaging could be reduced by the factor of 2 while maintaining the signal to noise ratio (SNR). Image quality was rated by 2 radiologists blinded to each other. RESULTS: Mean scan time was 104 min on the standard system and less than 80 min on the new system. 75% of all MRA segments were rated good in terms of vessel conspicuity, more than 80% had no venous overlay. One case of distal occlusion of the anterior tibial artery and two cases of myocardial infarction were detected. CONCLUSION: Parallel imaging offers the possibility of fast whole body imaging. A combination of morphologic and functional imaging can be performed within less than 80 min.

Adult↗

PubMed2004

[Modern visualization of the liver with MRT. Current trends and future perspectives].

This contribution provides an overview and imparts basic knowledge on pertinent technical developments in magnetic resonance imaging (MRI) of the liver: 3D sequences, respiratory triggering, parallel imaging, and 3 Tesla (3T). 3D sequences can be used as T1-weighted (T1w) sequences for analyzing dynamics of contrast enhancement or as T2w sequences for MR cholangiography. Consistent improvements in respiratory triggering make it possible to obtain good image quality on T2w scans even in patients unable to hold their breath. Parallel imaging as a universal technique to accelerate image acquisition is particularly appropriate for MRI of the liver, and it has been shown that the reduced acquisition time is not achieved at the expense of image quality. Further progress in MRI of the liver can be expected with use of the 3T systems, but hitherto irrelevant problems must still be solved. Overall the innovations presented here, applied alone or in combination, facilitate rapid, robust, and high-quality MRI diagnostic assessment of the liver.

Algorithms↗

PubMed2003

[Assessment of axonal degeneration on Alzheimer's disease with diffusion tensor MRI].

PURPOSE: Alzheimer disease (AD) causes cortical degeneration with subsequent degenerative changes of the white matter. The aim of this study was to investigate the extent of white matter tissue damage of patients with Alzheimer's disease in comparison with healthy subjects using diffusion tensor MRI (DTI). The value of integrated parallel imaging techniques (iPAT) for reduction of image distortion was assessed. MATERIAL AND METHODS: We studied 9 patients with mild AD and 10 age and gender matched healthy controls. DTI brain scans were obtained on a 1.5 tesla system (Siemens Magnetom Sonata) using parallel imaging (iPAT) and an EPI diffusion sequence with TE/TR 71 ms/6000 ms. We used an 8-element head coil and a GRAPPA reconstruction algorithm with an acceleration factor of 2. From the tensor, the mean diffusivity (D), the fractional anisotropy (FA), and the relative anisotropy (RA) of several white matter regions were determined. RESULTS: FA was significantly lower (p <0,05) in the white matter of the genu of corpus callosum from patients with AD than in the corresponding regions from healthy controls. There was a trend observed for slightly higher ADC values in the AD group (p=0,06). No significant changes were observed in the regions of the splenium, internal capsule, pericallosal areas, frontal, temporal, parietal, and occipital lobe. The images obtained with iPAT contained substantially less susceptibility artefacts and were less distorted than images acquired with non-parallel imaging technique. CONCLUSIONS: DTI is a method with potential to assess early stages of white matter damage in vivo. The altered FA and ADC values in the genu of corpus callosum of patients with AD presumably reflect the microscopic white matter degeneration. Acquisition time can be reduced by iPAT methods with less image distortion from susceptibility artefacts resulting in a more accurate calculation of the diffusion tensor.

Adult↗

PubMed2001

Noise correction for the exact determination of apparent diffusion coefficients at low SNR.

Noise in MR image data increases the mean signal intensity of image regions due to the usually performed magnitude reconstruction. Diffusion-weighted imaging (DWI) is especially affected by high noise levels for several reasons, and a decreasing SNR at increasing diffusion weighting causes systematic errors when calculating apparent diffusion coefficients (ADCs). Two different methods are presented to correct biased signal intensities due to the presence of complex noise: 1) with Gaussian intensity distribution, and 2) with arbitrary intensity distribution. The performance of the correction schemes is demonstrated by numerical simulations and DWI measurements on two different MR systems with different noise characteristics. These experiments show that noise significantly influences the determination of ADCs. Applying the proposed correction schemes reduced the bias of the determined ADC to less than 10% of the bias without correction. Magn Reson Med 45:448-453, 2001.

Artifacts↗

PubMed2001

Diffusion-weighted imaging of the spine using radial k-space trajectories.

INTRODUCTION: Diffusion-weighted MR imaging (DWI) of the spine requires robust imaging methods, that are insensitive to susceptibility effects caused by the transition from bone to soft tissue and motion artifacts due to breathing, swallowing, and cardiac motion. The purpose of this study was to develop a robust imaging method suitable for DWI of the spine. METHODS AND SUBJECTS: A radial k-space spin echo sequence has been implemented, which is self-navigating because each acquisition line passes through the origin of k-space. Influence of cardiac motion and associated flow of cerebrospinal fluid is minimized by cardiac gating with a finger photoplethysmograph. The sequence has been tested on a 1.5T system. Diffusion-weighted images of six normal volunteers were acquired in the sagittal plane with 4 b values between 50 and 500 s mm(-2). Because of the symmetries of the cord, diffusion measurements in the head-foot (HF) or left-right (LR) directions were sufficient to measure the dominant effects of anisotropy. RESULTS: The apparent diffusion coefficients (ADCs) measured, respectively, in the LR and HF directions were (0.699+/-0.050)x10(-3) and (1.805+/-0.086)x10(-3) mm(2) s(-1) in the spinal cord, (1.588+/-0.082)x10(-3) and (1.528+/-0.052)x10(-3) mm(2) s(-1) in the intervertebral disks, and (0.346+/-0.047)x10(-3) and (0.306+/-0.035)x10(-3) mm(2) s(-1) in the vertebrae of the cervicothoracic spine. CONCLUSION: Diffusion-weighted spin echo sequences with radial trajectories in k-space provide a means of achieving robust, high quality diffusion-weighted imaging and measuring ADCs in the spine. The application of the diffusion-weighting gradients in different directions allows diffusion anisotropy to be measured.

Humans↗

PubMed2001

Diffusion-weighted imaging of the brain: comparison of stimulated- and spin-echo echo-planar sequences.

We used a rat model of focal cerebral ischaemia to compare stimulated-echo (STE) and spin-echo (SE) echo planar (EPI) diffusion-weighted sequences as regards image quality and accuracy of calculation of apparent diffusion coefficients (ADC). Focal cerebral ischaemia was induced by endovascular occlusion of the middle cerebral artery in five rats. MRI was performed on a 2.35 tesla imager. For diffusion-weighted imaging (DWI) we used STE-EPI and SE-EPI with different diffusion times (delta) of 15, 30, 45, 60, 75 and 90 ms using values of b of 200, 300, 400, 500, 600 and 700 s/mm2. We assessed image quality, the signal-to-noise-ratio (SNR) and the accuracy of the ADC calculated from both sequences. Infarcts were delineated in all cases, independent of sequence type and delta. The image quality and SNR of the SE-EPI images were significantly better, with a higher SNR than STE-EPI images for short and intermediate values of delta. However, when delta reached 75 ms STE-EPI became superior to SE-EPI. ADC calculated from STE-EPI images were smaller than those from SE-EPI images for short and intermediate diffusion times, possibly because of the lower SNR of the former. We suggest that SE-EPI sequences be used for DWI of the brain, particularly on experimental systems and whole-body imagers with enhanced gradient hardware, where it is possible to run highly diffusion-weighted sequences (b > 500 s/mm2) with delta less than 50 ms. However, when using very long values of delta because of hardware restrictions or for measurement of restricted diffusion, STE sequences give better results.

Animals↗

PubMed2000

Reducing motion artefacts in diffusion-weighted MRI of the brain: efficacy of navigator echo correction and pulse triggering.

Diffusion-weighted MRI (DWI) is extremely sensitive to motion of the object being examined. Pulse triggering and navigator echo correction are methods for reducing motion artefacts which can be combined with conventional DWI sequences. Implementation of these methods in imaging sequences with a readout of one, three, or five echoes is presented and imaging results compared in a study of five healthy volunteers. As an objective measure for motion-induced image artefacts, the "artefacticity" of an image is defined. Pulse triggering and navigator echo correction significantly improve image quality and provide a technique for high-quality DWI on standard imagers without improved gradient hardware.

Adult↗

PubMed1995

Elevated levels of activities of beta-hexosaminidase and alpha-mannosidase in human immunodeficiency virus-infected patients.

To determine their value as markers of the clinical stage of human immunodeficiency virus (HIV) disease, plasma activities of lysosomal glycosidases were determined in the plasma of 97 HIV-infected patients: molecular forms of cathepsin D were characterized by Western blot to examine the mode of enzyme release. In patients with Centers for Disease Control and Prevention stage II and III of HIV disease, plasma activity of beta-hexosaminidase was significantly increased. In patients with stage III infection, alpha-mannosidase activity was also significantly increased and cathepsin D was elevated and present only in its premature form. Thus, determination of plasma activities of beta-hexosaminidase and alpha-mannosidase in HIV-positive persons may be useful for distinguishing the clinical stage of disease. The elevation of precursors of cathepsin D in patients with stage III HIV disease indicates that secretion of lysosomal enzymes rather than leakage of enzymes from damaged cells is markedly elevated.

Cathepsin D↗