A major research topic of the Medical Physics Group is the development and implementation of MR imaging sequences that can acquire images with ultra-short echo-times (UTE) down to 40 µs. One possibility to achieve this is the usage of a 3D radial spatial encoding in combination with non-selective very short excitation pulse (see Figure 1). Current research projects focus on the implementation of the actual MR imaging sequences and the image reconstruction required for processing of the UTE data.
Ultra-short echo-time MRI (UTE)
With conventional MR imaging sequences compact tissues with very short T2*-relaxation times typically can't be imaged directly because their measurable MR signal decays before the first data can be acquired. The major limitation for classical Cartesian MR imaging sequences is the spatial encoding of the signal in k-space which requires more time than the very short T2*-relaxation of compact tissues. For clinical MR systems the shortest possible echo time (the time between excitation of an MR signal and the data acquisition) is between 1 and 2 ms. All tissues which have a faster signal decay will not be visible in the acquired MR images. The most prominent examples of such tissues are compact bones, tendons and ligaments.
Research Topics
The UTE research topics of the Medical Physics Group are the direct imaging of tendons and ligaments in a static position as well as during movement, the segmentation and visualization of the human skull bone and cardiac imaging off small animals. Another research topic is the quantification and mapping of relaxation parameters such as T1 and T2* by using the UTE imaging technique.
One current research project of the group is aimed at the direct imaging of ligaments and tendons by using UTE MRI. Besides the pure imaging of such structures the aim of the project is the quantification of a wide range of parameters within the tendon and the question if those parameters are changed by diseases or during stress/loading. One part of this particular project is to perform all these analysis steps during motion. For this purpose various in-house developed ergometers are used for allow for a precise and guided movement of extremities within the MR scanner. This project is currently funded by the German Research Foundation (DFG) with the project:
"Entwicklung MRT-basierter Verfahren und Technologie zur nicht-invasiven-Erfassung von mechanischen Beansprungen in Geweben: Bewegung und Dehnung von Weichgewebestrukturen am Beispiel des Kniegelenkes"
Another research topic is the UTE imaging of the human skull. The inner and outer layers of the skull are very compact and can due to their very short T2* relaxation time typically not be imaged without the UTE technique.
As part of this research project new image processing algorithms are developed in order to not only display the skull but also to separate and segment it from the surrounding tissue. For this purpose the UTE imaging is extended to acquire images at multiple echo times from which the T2* relaxation time can be quantified and mapped for the entire skull.
These obtained T2* skull maps can then be used to investigate if changes in the structure or composition of the skull bone can be visualized and recognized. One possible applications is for pediatric MR imaging where current projects research the aging and ossification of the skull in children.
Another advantage of using UTE imaging with ultra-short echo times is an increase robustness towards susceptibility artifacts. Those artifacts can arise on borders between tissue and or when there is very fast motion. Especially when performing cardiac imaging in small animals this can lead to significant artifacts due to a very fast blood flow compared to humans.
To improve cardiac imaging in mice the UTE imaging technique was extended by adding a flow encoding in cooperation with the Institute of Medical Microbiology. This allows to perform free breathing and ECG free Cardiac imaging of mice at our 9.4T Small animal MRI. In additional due to the added flow encoding gradients it is possibly to quantify the direction and speed of the blood flow in the Murine heart.
Contact
Applications for research internships and thesis positions are always welcome! We are looking for talented students who are driven to push the boundaries of biomedical imaging technology. Candidates must be self-motivated team-players who thrive in a fast-paced environment and love contributing to cutting-edge research in a multidisciplinary team of ambitious young scientists.
The ultra-short echo-time (UTE) research in the Medical Physics Group directed by:
Publikationen
Fachzeitschriften
M Krämer, B Herzau, JR Reichenbach (2019). Segmentation and visualization of the human cranial bone by T2* approximation using ultra-short echo time (UTE) magnetic resonance imaging. Zeitschrift Fur Medizinische Physik
M Krämer, MB Maggioni, NM Brisson, S Zachow, U Teichgräber, GN Duda, JR Reichenbach (2019). T1 and T2* mapping of the human quadriceps and patellar tendons using ultra-short echo-time (UTE) imaging and bivariate relaxation parameter-based volumetric visualization. Magnetic Resonance Imaging (63), 29-36
M Krämer, A Motaal, K-H Herrmann, B Löffler, J R Reichenbach, G Strijkers, V Hoerr (2017). Cardiac 4D phase-contrast CMR at 9.4 T using self-gated ultra-short echo time (UTE) imaging. Journal of Cardiovascular Magnetic Resonance (19),39
K Herrmann, M Krämer, J R Reichenbach (2016). Time Efficient 3D Radial UTE Sampling with Fully Automatic Delay Compensation on a Clinical 3T MR Scanner. PLOS ONE (11),e0150371
Konferenzbände
M Krämer, A G Motaal, K-H Herrmann, B Löffler, J R Reichenbach, G J Strijkers, V Hoerr (2017). Cardiac 4D phase-contrast MRI at 9.4 T using self-gated ultra-short echo time (UTE) imaging. Proceedings of the International Society for Magnetic Resonance in Medicine (25), 3214
M Krämer, K-H Herrmann, A G Motaal, J R Reichenbach, G J Strijkers, V Hoerr (2016). Self-Gated 4D Phase Contrast in Mice using Ultra-Short Echo Time Imaging. Proceedings of the European Society of Magnetic Resonance in Medicine and Biology (33), 179
K-H Herrmann, A Mheryan, M Stenzel, H J Mentzel, U Teichgräber, Richenbach J R (2015). Ultra short echotime MRI to locate foreign objects: Initial phantom results. Proceedings of the International Society for Magnetic Resonance in Medicine (23)
M Krämer, K-H Herrmann, H Boeth, C Tycowicz, C König, S Zachow, R M Ehrig, H-C Hege, GN Duda, J R Reichenbach (2015). Measuring 3D knee dynamics using center out radial ultra-short echo time trajectories with a low cost experimental setup. Proceedings of the International Society for Magnetic Resonance in Medicine (23)
K-H Herrmann, M Krämer, J R Reichenbach (2014). Scantime optimized 3D radial Ultra-short Echo Time imaging for breathhold examinations. Proceedings of the International Society for Magnetic Resonance in Medicine (22)
K-H Herrmann, M Krämer, M Stenzel, H-J Mentzel, J R Reichenbach (2014). First promising results using Ultra-short Echo time MR imaging for bone tumor diagnosis. Proceedings of the International Society for Magnetic Resonance in Medicine (22)
K-H Herrmann, M Krämer, J R Reichenbach (2013). High resolution radial 3D ultra-short Echo time imaging in vivo. Proceedings of the International Society for Magnetic Resonance in Medicine (21)
L Huang, F Schweser, K-H Herrmann, M Krämer, A Deistung, J R Reichenbach (2013). Conductivity Imaging Using An Ultra-short Echo Time Sequence. Proceedings of the German Chapter of the International Society for Magnetic Resonance in Medicine (16)
F Schweser, L Huang, K-H Herrmann, M Krämer, A Deistung, J R Reichenbach (2013). Evidence of tissue conductivity as a source of signal inhomogeneities in Ultrashort Echo Time (UTE) imaging. Proceedings of the International Society for Magnetic Resonance in Medicine (21)
F Schweser, L Huang, K-H Herrmann, M Krämer, A Deistung, J R Reichenbach (2013). Conductivity mapping using Ultrashort Echo Time (UTE) imaging. Proceedings of the International Society for Magnetic Resonance in Medicine (21)
F Schweser, L Huang, K-H Herrmann, M Krämer, A Deistung, J R Reichenbach (2013). Tissue conductivity can introduce signal inhomogeneities in Ultrashort Echo Time (UTE) imaging (MRT). Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (44)