Tobias Wichmann

Publications of Tobias Wichmann

• Comparison of intravascular and extracellular contrast media for absolute quantification of myocardial rest-perfusion using high-resolution MRI.

  Authors: Christian O Ritter, Aline Wilke, Tobias Wichmann, Meinrad Beer, Dietbert Hahn, Herbert Köstler

  Journal of magnetic resonance imaging : JMRI. 05/2011; 33(5):1047-51.

  To use the contrast agent gadofosveset for absolute quantification of myocardial perfusion and compare it with gadobenate dimeglumine (Gd-BOPTA) using a high-resolution generalized autocalibratingTo use the contrast agent gadofosveset for absolute quantification of myocardial perfusion and compare it with gadobenate dimeglumine (Gd-BOPTA) using a high-resolution generalized autocalibrating partially parallel acquisition (GRAPPA) sequence. Ten healthy volunteers were examined twice at two different dates with a first-pass perfusion examination at rest using prebolus technique. We used a 1.5 T scanner and a 32 channel heart-array coil with a steady-state free precession (SSFP) true fast imaging with steady state precession (trueFISP) GRAPPA sequence (acceleration-factor 3). Manual delineation of the myocardial contours was performed and absolute quantification was performed after baseline and contamination correction. At the first appointment, 1cc/4cc of the extracellular contrast agent Gd-BOPTA were administered, on the second date, 1cc/4cc of the blood pool contrast agent (CA) gadofosveset. At each date the examination was repeated after a 15-minute time interval. Using gadofosveset perfusion the value (in cc/g/min) at rest was 0.66 ± 0.25 (mean ± standard deviation) for the first, and 0.55 ± 0.24 for the second CA application; for Gd-BOPTA it was 0.62 ± 0.25 and 0.45 ± 0.23. No significant difference was found between the acquired perfusion values. The apparent mean residence time in the myocardium was 23 seconds for gadofosveset and 19.5 seconds for Gd-BOPTA. Neither signal-to-noise ratio (SNR) nor subjectively rated image contrast showed a significant difference. The application of gadofosveset for an absolute quantification of myocardial perfusion is possible. Yet the acquired perfusion values show no significant differences to those determined with Gd-BOPTA, maintained the same SNR and comparable perfusion values, and did not picture the expected concentration time-course for an intravasal CA in the first pass.

• Half-fourier-acquisition single-shot turbo spin-echo (HASTE) MRI of the lung at 3 Tesla using parallel imaging with 32-receiver channel technology.

  Authors: Thomas Henzler, Olaf Dietrich, Radko Krissak, Tobias Wichmann, Titus Lanz, Maximilian F Reiser, Stefan O Schoenberg, Christian Fink

  Journal of magnetic resonance imaging : JMRI. 09/2009; 30(3):541-546.

  PURPOSE: To assess the feasibility of half-Fourier-acquisition single-shot turbo spin-echo (HASTE) of the lung at 3 Tesla (T) using parallel imaging with a prototype of a 32-channel torso array coil,PURPOSE: To assess the feasibility of half-Fourier-acquisition single-shot turbo spin-echo (HASTE) of the lung at 3 Tesla (T) using parallel imaging with a prototype of a 32-channel torso array coil, and to determine the optimum acceleration factor for the delineation of intrapulmonary anatomy. MATERIALS AND METHODS: Nine volunteers were examined on a 32-channel 3T MRI system using a prototype 32-channel-torso-array-coil. HASTE-MRI of the lung was acquired at both, end-inspiratory and end-expiratory breathhold with parallel imaging (Generalized autocalibrating partially parallel acquisitions = GRAPPA) using acceleration factors ranging between R = 1 (TE = 42 ms) and R = 6 (TE = 16 ms). The image quality of intrapulmonary anatomy and subjectively perceived noise level was analyzed by two radiologists in consensus. In addition quantitative measurements of the signal-to-noise ratio (SNR) of HASTE with different acceleration factors were assessed in phantom measurements. RESULTS: Using an acceleration factor of R = 4 image blurring was substantially reduced compared with lower acceleration factors resulting in sharp delineation of intrapulmonary structures in expiratory scans. For inspiratory scans an acceleration factor of 2 provided the best image quality. Expiratory scans had a higher subjectively perceived SNR than inspiratory scans. CONCLUSION: Using optimized multi-element coil geometry HASTE-MRI of the lung is feasible at 3T with acceleration factors up to 4. Compared with nonaccelerated acquisitions, shorter echo times and reduced image blurring are achieved. Expiratory scanning may be favorable to compensate for susceptibility associated signal loss at 3T. J. Magn. Reson. Imaging 2009;30:541-546. (c) 2009 Wiley-Liss, Inc.

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• Mouse MRI using phased-array coils.

  Authors: Daniel Gareis, Tobias Wichmann, Titus Lanz, Gerd Melkus, Michael Horn, Peter M Jakob

  NMR in biomedicine. 06/2007; 20(3):326-34.

  The advantages of array coil imaging in human whole-body MR systems are well known and have gained relevance in many applications and MR techniques. In the field of small-animal studies, this conceptThe advantages of array coil imaging in human whole-body MR systems are well known and have gained relevance in many applications and MR techniques. In the field of small-animal studies, this concept has become increasingly important. In this work, three different phased-array coils for performing MRI on mice are presented. For imaging at 300 MHz, a four-channel receive-only phased-array coil is introduced. One two-channel and a four-channel transmit/receive setup operating at 750 MHz show the feasibility of array coil imaging at 17.6 T. All of these coils show excellent performance and deliver high-quality MR images of mice.