Thomas Kampf

Publications of Thomas Kampf

• Signal evolution in the local magnetic field of a capillary - analogy to the damped driven harmonic oscillator.

  Authors: Christian H Ziener, Thomas Kampf, Gerd Melkus, Peter M Jakob, Heinz-Peter Schlemmer, Wolfgang R Bauer

  Magnetic resonance imaging. 02/2012;

  The temporal behavior of the magnetization decay caused by the local inhomogeneous magnetic field of a capillary is analyzed. Respecting the diffusion of the spins surrounding the capillary and theThe temporal behavior of the magnetization decay caused by the local inhomogeneous magnetic field of a capillary is analyzed. Respecting the diffusion of the spins surrounding the capillary and the strength of the susceptibility difference between the capillary and the surrounding medium, it is possible to distinguish different dephasing regimes. Each dephasing regime can be related to a certain characteristic form of the magnetization decay. If the influence of the diffusion dominates, the magnetization exhibits a monotonic decay. In the opposite case of dominating influence of the susceptibility effects, the magnetization shows an oscillating behavior. It can be shown that the dephasing process is closely related to the behavior of a damped driven harmonic oscillator.

• SAR-reduced spin-echo-based Bloch-Siegert B(1) (+) mapping: BS-SE-BURST.

  Authors: Thomas Christian Basse-Lüsebrink, Thomas Kampf, André Fischer, Volker Jörg Friedrich Sturm, Daniel Neumann, Herbert Köstler, Dietbert Hahn, Guido Stoll, Peter Michael Jakob

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 11/2011;

  Fast and accurate B(1) (+) mapping is possible using phase-based Bloch-Siegert (BS) methods. Importantly, the off-resonant pulses needed for BS B(1) (+) mapping methods can easily be implemented inFast and accurate B(1) (+) mapping is possible using phase-based Bloch-Siegert (BS) methods. Importantly, the off-resonant pulses needed for BS B(1) (+) mapping methods can easily be implemented in multiple MR sequences. BS-based B(1) (+) mapping has thus been introduced for gradient echo (BS-FLASH), spin-echo (BS-SE), and Carr, Purcell, Meiboom, Gill (CPMG)-based multi-SE and turbo-SE sequences. When using SE and multi-SE/turbo-SE-based BS sequences, however, the high intrinsic specific absorption rates must be considered in clinical situations. This study introduces a fast BS B(1) (+) mapping method based on a SE-BURST sequence (BS-SE-BURST). With SE-BURST sequences, multiple low-magnitude excitation pulses are applied prior to the refocusing pulse. Thus, multiple and different phase-encoded echoes can be acquired per excitation cycle. Compared with a SE sequence, this excitation strategy results in a similar signal-to-noise ratio (SNR) per unit time but with reduced specific absorption rate. The proposed BS-SE-BURST sequence was implemented on a conventional 3 T whole body MRI scanner and applied successfully. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

• In vivo imaging of stepwise vessel occlusion in cerebral photothrombosis of mice by 19F MRI.

  Authors: Gesa Weise, Thomas C Basse-Lüsebrink, Christoph Kleinschnitz, Thomas Kampf, Peter M Jakob, Guido Stoll

  PloS one. 01/2011; 6(12):e28143.

  (19)F magnetic resonance imaging (MRI) was recently introduced as a promising technique for in vivo cell tracking. In the present study we compared (19)F MRI with iron-enhanced MRI in mice with(19)F magnetic resonance imaging (MRI) was recently introduced as a promising technique for in vivo cell tracking. In the present study we compared (19)F MRI with iron-enhanced MRI in mice with photothrombosis (PT) at 7 Tesla. PT represents a model of focal cerebral ischemia exhibiting acute vessel occlusion and delayed neuroinflammation. Perfluorocarbons (PFC) or superparamagnetic iron oxide particles (SPIO) were injected intravenously at different time points after photothrombotic infarction. While administration of PFC directly after PT induction led to a strong (19)F signal throughout the entire lesion, two hours delayed application resulted in a rim-like (19)F signal at the outer edge of the lesion. These findings closely resembled the distribution of signal loss on T2-weighted MRI seen after SPIO injection reflecting intravascular accumulation of iron particles trapped in vessel thrombi as confirmed histologically. By sequential administration of two chemically shifted PFC compounds 0 and 2 hours after illumination the different spatial distribution of the (19)F markers (infarct core/rim) could be visualized in the same animal. When PFC were applied at day 6 the fluorine marker was only detected after long acquisition times ex vivo. SPIO-enhanced MRI showed slight signal loss in vivo which was much more prominent ex vivo indicative for neuroinflammation at this late lesion stage. Our study shows that vessel occlusion can be followed in vivo by (19)F and SPIO-enhanced high-field MRI while in vivo imaging of neuroinflammation remains challenging. The timing of contrast agent application was the major determinant of the underlying processes depicted by both imaging techniques. Importantly, sequential application of different PFC compounds allowed depiction of ongoing vessel occlusion from the core to the margin of the ischemic lesions in a single MRI measurement.

• Intracellular and extracellular T1 and T2 relaxivities of magneto-optical nanoparticles at experimental high fields.

  Authors: Gert Klug, Thomas Kampf, Steffen Bloemer, Johannes Bremicker, Christian H Ziener, Andrea Heymer, Uwe Gbureck, Eberhard Rommel, Ulrich Nöth, Wolfdieter A Schenk, Peter M Jakob, Wolfgang R Bauer

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 12/2010; 64(6):1607-15.

  This study reports the T(1) and T(2) relaxation rates of rhodamine-labeled anionic magnetic nanoparticles determined at 7, 11.7, and 17.6 T both in solution and after cellular internalization.This study reports the T(1) and T(2) relaxation rates of rhodamine-labeled anionic magnetic nanoparticles determined at 7, 11.7, and 17.6 T both in solution and after cellular internalization. Therefore cells were incubated with rhodamine-labeled anionic magnetic nanoparticles and were prepared at decreasing concentrations. Additionally, rhodamine-labeled anionic magnetic nanoparticles in solution were used for extracellular measurements. T(1) and T(2) were determined at 7, 11.7, and 17.6 T. T(1) times were determined with an inversion-recovery snapshot-flash sequence. T(2) times were obtained from a multispin-echo sequence. Inductively coupled plasma-mass spectrometry was used to determine the iron content in all samples, and r(1) and r(2) were subsequently calculated. The results were then compared with cells labeled with AMI-25 and VSOP C-200. In solution, the r(1) and r(2) of rhodamine-labeled anionic magnetic nanoparticles were 4.78/379 (7 T), 3.28/389 (11.7 T), and 2.00/354 (17.6 T). In cells, the r(1) and r(2) were 0.21/56 (7 T), 0.19/37 (11.7 T), and 0.1/23 (17.6 T). This corresponded to an 11- to 23-fold decrease in r(1) and an 8- to 15-fold decrease in r(2) . A decrease in r(1) was observed for AMI-25 and VSOP C-200. AMI-25 and VSOP exhibited a 2- to 8-fold decrease in r(2) . In conclusion, cellular internalization of iron oxide nanoparticles strongly decreased their T(1) and T(2) potency.

• Flow-enhanced off-resonance saturation for remote detection of iron-based contrast agents.

  Authors: Philipp Krämer, Xavier Helluy, Thomas Kampf, Esra Lang, Peter M Jakob

  Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. 06/2010; 63(6):1708-15.

  A switchable contrast mechanism, flow enhanced off-resonance saturation, is presented. This technique combines the effects of flow and off-resonance saturation for remote detection of iron oxideA switchable contrast mechanism, flow enhanced off-resonance saturation, is presented. This technique combines the effects of flow and off-resonance saturation for remote detection of iron oxide contrast agents incorporated into a vessel wall. Initial results from phantom experiments are presented and show the feasibility of this method. A specific saturation contrast could be observed. This contrast mechanism is highly dependent on field homogeneity and spectral selectivity of the off-resonance saturation pulses. The contrast scales directly with the pulse offset of the used saturation pulses, the flow velocity in the vessel, and the duration of the off-resonance saturation module prior to the imaging sequence. This technique has the potential to detect iron-loaded atherosclerotic plaques in future in vivo applications.