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Olaf Dietrich

Publications and source records attributed to Olaf Dietrich.

26 records · Page 2Linked to original sources
PubMed2004

A comparative evaluation of a RARE-based single-shot pulse sequence for diffusion-weighted MRI of musculoskeletal soft-tissue tumors.

The purpose of this study was to evaluate the feasibility of a centric-reordered modified rapid acquisition with relaxation enhancement (mRARE) sequence for single-shot diffusion-weighted magnetic resonance imaging (DWI) of soft-tissue tumors in the musculoskeletal system. In the evaluation of this sequence, DWI was performed in a liquid phantom, in excised human tumor samples embedded in bovine muscle, and in nine patients suffering from different types of soft-tissue tumors. The measurements were compared to DWI using a spin-echo sequence and a single-shot echo planar imaging (EPI) sequence. The phantom measurements in water and dimethyl sulfoxide showed a difference of less than 5% when comparing the apparent diffusion coefficients (ADCs) determined by the mRARE sequence and the two other techniques. Comparing mRARE and EPI, the differences in the ADCs were about 10% in the excised tumor tissue and, typically, about 15% in vivo. ADCs between 0.8 x 10(-3) mm2/s and 1.4 x 10(-3) mm2/s, depending on the tumor type, were found in solid tumor tissue; in cystic tumor areas, ADCs greater than 2.0 x 10(-3) mm2/s were determined with the mRARE and the EPI sequences. Diffusion-weighted images of the mRARE sequence were less distorted than those acquired with the single-shot EPI sequence, and provided more anatomic information, since the muscle and fat signals were considerably higher.

Aged↗
PubMed2004

High-resolution MR-imaging of the liver with T2-weighted sequences using integrated parallel imaging: comparison of prospective motion correction and respiratory triggering.

PURPOSE: To compare high-resolution T2-weighted images of the liver with and without integrated parallel acquisition techniques (iPAT) using either breath-hold sequences in combination with prospective acquisition motion correction (PACE) or respiratory triggering. MATERIALS AND METHODS: Ten volunteers and 10 patients underwent each four different high-resolution fast spin echo (FSE) T2-weighted sequences with 5 mm slice thickness and a full 320 matrix: a multi-breath-hold FSE sequence with and without iPAT and PACE and a respiratory-triggered FSE sequence with and without iPAT. Image quality was rated with a five-point scale by two independent readers. Signal intensity measurements were performed on a water phantom. RESULTS: The sequences with iPAT required a substantially shorter acquisition time without loss of image quality. Overall image quality was rated equal for all sequences by both readers. Image time for nine slices with iPAT was 13 seconds (19 seconds without iPAT) with multi-breath-hold and on average 4:00 minutes (7:02 minutes without iPAT) with respiratory triggering. Imaging with the PACE technique resulted in more correct positioning of the image stacks. CONCLUSION: T2-weighted fast imaging with iPAT is feasible and results in high-quality images within a short acquisition time. Overall image quality is not negatively affected by iPAT.

Adult↗
PubMed2004

Quantification of pulmonary blood flow and volume in healthy volunteers by dynamic contrast-enhanced magnetic resonance imaging using a parallel imaging technique.

RATIONALE AND OBJECTIVES: We sought to optimize the dosage of a paramagnetic contrast medium (CM) for the quantification of pulmonary blood flow and volume by contrast-enhanced dynamic magnetic resonance imaging (MRI) using a parallel imaging technique and to prove the feasibility of the approach in healthy volunteers. METHODS: In a phantom study, the dependency of signal increase on different concentrations of the CM gadodiamide was evaluated by means of an ultra-fast MRI sequence with a generalized autocalibrating partially parallel acquisition technique (acceleration factor = 2). Using the same sequence, measurements were performed in a healthy volunteer after administration of different CM dosages for contrast dosage optimization in vivo. Finally, perfusion measurements were performed in 16 healthy volunteers after the administration of the optimal CM dose. Signal-time curves were evaluated from the pulmonary artery and from predefined regions of the lung. Pulmonary regional blood volume (RBV) and flow (RBF) were estimated using an open 1-compartment model. RESULTS: Phantom studies yielded a linear signal increase up to a concentration of 5.0 mmol/L gadodiamide. Results of contrast dosage optimization in vivo showed that the maximum CM dose providing a linear relationship between signal increase and CM concentration in the pulmonary artery of a healthy volunteer was approximately 0.05 mmol/kg-bw. Quantification of pulmonary blood volume and flow was reproducible in healthy volunteers, yielding mean values for the upper lung zones of 7.1 +/- 2.3 mL/100 mL for RBV and 197 +/- 97 mL/min/100 mL for RBF and for lower lung zones, 12.5 +/- 3.9 mL/100 mL for RBV and 382 +/- 111 mL/min/100 mL for RBF. CONCLUSIONS: If an adequate amount of gadodiamide and fast MR sequences are used, quantification of pulmonary blood flow and volume is feasible.

Adult↗
PubMed2003

Single breath-hold real-time cine MR imaging: improved temporal resolution using generalized autocalibrating partially parallel acquisition (GRAPPA) algorithm.

The purpose of this study was to test parallel imaging techniques for improvement of temporal resolution in multislice single breath-hold real-time cine steady-state free precession (SSFP) in comparison with standard segmented single-slice SSFP techniques. Eighteen subjects were examined on a 1.5-T scanner using a multislice real-time cine SSFP technique using the GRAPPA algorithm. Global left ventricular parameters (EDV, ESV, SV, EF) were evaluated and results compared with a standard segmented single-slice SSFP technique. Results for EDV ( r=0.93), ESV ( r=0.99), SV ( r=0.83), and EF ( r=0.99) of real-time multislice SSFP imaging showed a high correlation with results of segmented SSFP acquisitions. Systematic differences between both techniques were statistically non-significant. Single breath-hold multislice techniques using GRAPPA allow for improvement of temporal resolution and for accurate assessment of global left ventricular functional parameters.

Algorithms↗
PubMed2003

Diffusion-weighted imaging of bone marrow: current status.

Diffusion-weighted imaging allows for measurement of tissue microstructure and reflects the random motion of water protons. It provides a new method to study bone marrow and bone marrow alterations on the basis of altered water-proton mobility in various diseases. Different diffusion-weighted methods have proved to be capable of differentiating between benign edema and tumorous involvement of bone marrow. It is especially useful for the distinction of acute benign osteoporotic and malignant vertebral compression fractures. Diagnosis is based on the contrast to normal bone marrow. Hypo- or isointensity reflects acute benign collapse, whereas hyperintensity is indicative of the tumorous nature of a fracture. Apparent diffusion coefficients (ADC) are significantly lower in metastatic disease than in bone marrow edema. Furthermore, bone marrow cellularity can be estimated by ADC measurements. Diffusion-weighted imaging might be helpful for monitoring response to therapy in metastatic disease.

Bone Marrow↗
PubMed2003

Renal MR angiography: current debates and developments in imaging of renal artery stenosis.

Because of its safety and robustness with reproducible image quality, three-dimensional gadolinium-enhanced magnetic resonance angiography (3D-Gd-MRA) has been widely established as a diagnostic tool for screening and grading of renal artery stenosis. Accuracy and superiority over other noninvasive imaging procedures was again demonstrated in two recent meta-analyses. However, ambiguous results on the accuracy of this technique have been reported recently, again questioning the sole role of this modality for diagnostic assessment of the renal arteries. The main deficiencies of the technique are limited spatial resolution, high interobserver variability, limited anatomic coverage, as well as inability to assess the stenosis site after stent placement. In addition, a high level of competition has been introduced by techniques such as 16 detector multislice computed tomography, which generates superb image quality, with broad anatomic coverage and high spatial resolution, with minimal technical complexity. Lastly, aggressive search for renal artery stenosis by angiographic techniques in patients with hypertension is of debate, since only a limited percentage of these patients benefit from interventions. In this article, a comprehensive approach to high-resolution 3D-Gd-MRA, using parallel imaging in combination with cardiac-gated, phase-contrast flow measurements, is reviewed. This review is based on various studies and articles that address many of the problems of 3D-Gd-MRA. By making use of maximum spatial resolution and additional functional data, MRI permits accurate detection and grading of renal artery stenosis in most cases, with acceptable interobserver variability.

Contrast Media↗
PubMed2002

Diffusion-weighted imaging of the spinal column.

Diffusion-weighted imaging of the musculoskeletal system including the spine is a new MR imaging method. Several studies have shown significantly different diffusivities for various pathologic conditions such as edema and tumor. The specificity of diagnosis may be increased and therapeutic effects may be monitored. Diffusion-weighted sequences especially have been shown to be an additional tool for differentiating vertebral fractures caused by osteoporotic collapse with bone marrow edema and metastatic collapse. Inclusion criteria should include: (1) unknown reason for the vertebral collapse, (2) lack of sclerosis, and (3) no prior therapy. Patients with trauma or treated metastases may exhibit different signal intensities. In general, those patients do not pose problems in differential diagnosis. New sequence developments and higher magnetic field gradients should be able to increase spatial resolution and decrease problems from motion artifacts. Studies with larger patient groups and sequences that quantify the results with ADCs are the necessary next steps.

Aged↗