Biomedical subjects

Hans-Peter Fautz

Publications and source records attributed to Hans-Peter Fautz.

6 recordsLinked to original sources

PubMed2006

2D axial moving table acquisitions with dynamic slice adaptation.

A method for axial multi-slice imaging during continuous table motion has been developed and implemented on a clinical scanner. Multiple axial slice packages are acquired consecutively and combined to cover an extended longitudinal FOV. To account for the table motion during the acquisition, the RF pulse frequencies are continuously updated according to the actual table velocity and slice position. Different strategies for the spatial-temporal acquisition sequence with extended FOV are proposed. They cover different regimes of scan requirements regarding table velocity, used scan range, and slice resolution. The method is easy to implement and compatible with most kinds of sequences. The robustness of the proposed approach has been tested in phantom studies and healthy volunteers using T1-, T2-, and STIR-weighted multi-slice techniques that are based on gradient and turbo spin echo sequences and compared to a stationary approach usually used in clinical routine. The method provides artifact free gradient echo based images during continuous table motion, while for turbo spin echo sequences limitations in choosing table translations occur due to gradient non-linearity effects.

Algorithms↗

PubMed2006

Multicontrast sequences with continuous table motion: a novel acquisition technique for extended field of view imaging.

A novel acquisition technique called multicontrast imaging is presented that provides multiple datasets of different image contrasts covering an extended field of view within one measurement procedure. The technique uses a continuously moving table and is based on the repetitive acquisition of axial volume sections while the patient moves through the scanner once. To compensate for the table motion during the measurement, adaptive slice shifting is applied. Multicontrast imaging is designed to combine the comfort of a moving table examination with the high time efficiency of a multitask protocol and can be used for generating differences in both contrast and spatial parameters of the acquired data. The technique and its properties are demonstrated on healthy human volunteers.

Humans↗

PubMed2006

T2-weighted balanced SSFP imaging (T2-TIDE) using variable flip angles.

A new technique for acquiring T2-weighted, balanced steady-state free precession (b-SSFP) images is presented. Based on the recently proposed transition into driven equilibrium (TIDE) method, T2-TIDE uses a special flip angle scheme to achieve T2-weighted signal decay during the transient phase. In combination with half-Fourier image acquisition, T2-weighted images can be obtained using T2-TIDE. Numerical simulations were performed to analyze the signal behavior of T2-TIDE in comparison with TSE and b-SSFP. The results indicate identical signal evolution of T2-TIDE and TSE during the transient phase. T2-TIDE was used in phantom experiments, and quantitative ROI analysis shows a linear relationship between TSE and T2-TIDE SNR values. T2-TIDE was also applied to abdominal and head imaging on healthy volunteers. The resulting images were analyzed quantitatively and compared with standard T2-weighted and standard b-SSFP methods. T2-TIDE images clearly revealed T2 contrast and less blurring compared to T2-HASTE images. In combination with a magnetization preparation technique, STIR-weighted images were obtained. T2-TIDE is a robust technique for acquiring T2-weighted images while exploiting the advantages of b-SSFP imaging, such as high signal-to-noise ratio (SNR) and short TRs.

Brain↗

PubMed2004

TRIM: TR independent multislice imaging.

This article introduces a novel concept to overcome the dependence of image contrast on spatial positioning parameters such as the number of slices and slice separation in multislice measurements: TR-independent multislice (TRIM) acquisition allows the number of slices in a single measurement to remain independent of the repetition time TR. Ramped TRIM (rTRIM) allows the distance between the sections excited in each repetition to remain independent of the distance between the reconstructed slices. Even images from overlapping slices can be acquired without crosstalk between the images of adjacent slices due to spatially overlapping excitation profiles. This concept is based on a special reordering scheme: Within a single TR acquisition, steps are only taken from a fraction of all slices. This necessitates attribution of different phase-encoding steps to different slices within each repetition cycle. The reordering scheme can be derived by the use of a design matrix. The imaging properties of the technique are discussed theoretically and illustrated by a point spread function analysis based on simulations and phantom measurements. Potential sources of artifacts are identified and methods for their prevention are developed. Optimized implementations with different T(1)-weighted sequences such as spin echo (SE), turbo spin echo (TSE), and spoiled gradient echo acquisitions are shown on normal volunteers with imaging parameters used in routine diagnosis.

Humans↗

PubMed2002

Homogeneous preparation encoding (HoPE) in multislice imaging.

Fast magnetization preparation techniques acquire a series of echoes after a single magnetization preparation. If these echoes are acquired from different slices using a multislice technique the change in the preparation state of the echoes due to relaxation effects leads to different contrast modification for each slice. Encoding different preparation states along the phase-encoding direction of each slice instead of acquiring each slice in a different preparation state is introduced as a general concept to obtain images of identical contrast and point-spread function. This can be realized either by cycling the slice excitation order several times over the total number of repetitions or by moving the point of time at which the preparation is applied within each repetition. One possible application of this method is chemical shift selective fat saturation imaging. A homogeneous fat suppression across a multislice volume could be achieved using a FLASH sequence at a repetition time of TR = 145 ms, including a single fat saturation preparation. Conventional fat saturated spin-echo imaging at any TR can be accelerated significantly by reducing the number of applied preparations per repetition. A further application of the homogeneous preparation encoding (HoPE) method is described that encodes the spatial self-saturation of the multislice excitation order homogeneously in all slices. Only a reduced number of slices of the total volume are excited in each repetition and the slice excitation order is continuously moved along the imaging volume. This method is applied for time of flight (TOF) imaging. Using a TONE-like series of flip angles for the slice excitations of each repetition homogeneous TOF images can be obtained on the basis of a multislice acquisition.

Abdomen↗

PubMed2002

Signal behavior in continuously ramped 2D TrueFISP for whole-body imaging.

A fast and robust imaging technique was developed based on a single-slice TrueFISP acquisition using a slice excitation frequency that is incremented, or spatially "ramped," with each repetition. The short acquisition time of single slices allows artifact-free imaging during free breathing, which demonstrates the potential use of this technique for whole-body screening. Overlapping positioning of consecutively acquired slices was used to provide gapless volume coverage in free-breathing measurements. The image contrast of ramped TrueFISP was analyzed in detail using simulations and experiments. A high ramp speed results in an increased overall signal intensity and in a modification of the known T(2)/T(1) contrast towards a proton density-weighted contrast. A further increase in imaging speed is achieved with z-interleaved phase-encoding trajectories based on weighted transitions between adjacent views.

Contrast Media↗