Biomedical subjects

Matthias F Mueller

Publications and source records attributed to Matthias F Mueller.

4 recordsLinked to original sources

PubMed2006

Accelerated volumetric MRI with a SENSE/GRAPPA combination.

PURPOSE: To combine the specific advantages of the generalized autocalibrating partially parallel acquisitions (GRAPPA) technique and sensitivity encoding (SENSE) with two-dimensional (2D) undersampling. MATERIALS AND METHODS: By splitting the 2D reconstruction process into multiple one-dimensional (1D) reconstructions, the normal 1D GRAPPA method can be used for image reconstruction. Due to this data-handling process, a GRAPPA reconstruction is performed along the phase-encoding (PE) direction and effectively a SENSE reconstruction is performed along the partition-encoding (PAE) direction. RESULTS: In vivo experiments demonstrate the successful implementation of the SENSE/GRAPPA combination. Experimental results with up to 9.6-fold acceleration using a prototype 32-channel receiver head coil array are presented. CONCLUSION: The proposed SENSE/GRAPPA combination for 3D imaging allows the GRAPPA method to be applied in combination with 2D undersampling. Because the SENSE/GRAPPA combination is not based on knowledge of spatial coil sensitivities, it should be the method of choice whenever it is difficult to extract the sensitivity information.

Algorithms↗

PubMed2006

Controlled aliasing in volumetric parallel imaging (2D CAIPIRINHA).

The CAIPIRINHA (Controlled Aliasing In Parallel Imaging Results IN Higher Acceleration) concept in parallel imaging has recently been introduced, which modifies the appearance of aliasing artifacts during data acquisition in order to improve the subsequent parallel imaging reconstruction procedure. This concept has been successfully applied to simultaneous multi-slice imaging (MS CAIPIRINHA). In this work, we demonstrate that the concept of CAIPIRINHA can also be transferred to 3D imaging, where data reduction can be performed in two spatial dimensions simultaneously. In MS CAIPIRINHA, aliasing is controlled by providing individual slices with different phase cycles by means of alternating multi-band radio frequency (RF) pulses. In contrast to MS CAIPIRINHA, 2D CAIPIRINHA does not require special RF pulses. Instead, aliasing in 2D parallel imaging can be controlled by modifying the phase encoding sampling strategy. This is done by shifting sampling positions from their normal positions in the under-sampled 2D phase encoding scheme. Using this modified sampling strategy, coil sensitivity variations can be exploited more efficiently in multiple dimensions, resulting in a more robust parallel imaging reconstruction.

Humans↗

PubMed2005

Controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) for multi-slice imaging.

In all current parallel imaging techniques, aliasing artifacts resulting from an undersampled acquisition are removed by means of a specialized image reconstruction algorithm. In this study a new approach termed "controlled aliasing in parallel imaging results in higher acceleration" (CAIPIRINHA) is presented. This technique modifies the appearance of aliasing artifacts during the acquisition to improve the subsequent parallel image reconstruction procedure. This new parallel multi-slice technique is more efficient compared to other multi-slice parallel imaging concepts that use only a pure postprocessing approach. In this new approach, multiple slices of arbitrary thickness and distance are excited simultaneously with the use of multi-band radiofrequency (RF) pulses similar to Hadamard pulses. These data are then undersampled, yielding superimposed slices that appear shifted with respect to each other. The shift of the aliased slices is controlled by modulating the phase of the individual slices in the multi-band excitation pulse from echo to echo. We show that the reconstruction quality of the aliased slices is better using this shift. This may potentially allow one to use higher acceleration factors than are used in techniques without this excitation scheme. Additionally, slices that have essentially the same coil sensitivity profiles can be separated with this technique.

Abdomen↗

PubMed2002

Visual function and perfusion of the optic nerve head after application of centrally acting calcium-channel blockers.

BACKGROUND: In a previous study it was shown that nimodipine 30 mg twice daily leads to an improvement in the visual field in a subgroup of normal-pressure glaucoma patients. To understand the mechanism of action of nimodipine on the visual system, the aim of this study was to examine the influence of nimodipine on different hemodynamic parameters and contrast sensitivity in healthy subjects. METHODS: Thirty-two healthy subjects (21-49 years old, mean age 28 years, 10 male, 22 female) received either nimodipine 30 mg twice a day or a placebo according to the same dosage regimen in a double-blind cross-over study design. The ocular blood flow was measured by means of the ocular blood flow system, the optic nerve head blood flow with the continuous laser Doppler flowmeter (Riva), and contrast sensitivity using the MCT 8000 Multivision Contrast Tester. Measurements were taken at baseline (1T0), 120 min after initial dose (1T3) and after 3 days (3T3) of therapy with 150 mg nimodipine or placebo in total. RESULTS: Contrast sensitivity improved significantly throughout almost all spatial frequencies in the nimodipine-treated subjects ( P=0.01), whereas there was no change in the placebo group. Ocular blood flow and optic nerve head blood flow increased slightly but not significantly in the nimodipine group (1T0: 706.6 microl/min, 9.33 AU; 3T3: 854.3 microl/min, 9.39 AU) and remained unchanged or were even lower in the placebo group ( P>0.05). CONCLUSION: The results showed a significant increase in contrast sensitivity during treatment with nimodipine in healthy subjects. This increase in visual function, however, was not correlated with an increase in ocular or optic nerve head blood flow. Therefore, another mechanism, e.g., a direct effect on the visual system, might be responsible for the improvement in visual function in healthy volunteers under nimodipine therapy.

Adult↗