Division of Medical Physics in Radiology
Prof. Dr. sc. techn. Mark E. Ladd
MR images and parametric maps for a 65-year-old patient with prostate cancer (arrows). (a) Conventional T2-weighted image, where the lesion can be identified as a slightly hypointense area. (b) Diffusion-weighted image that exploits the thermal motion of water molecules in biological tissue to probe the microstructure. Water diffusivity is reduced in the tumor area due to increased presence of diffusion barriers such as cell membranes. This yields a pronounced signal increase, which is more specific compared to the hypointensity in T2. (c) and (d) show the possibility to give the molecules different time intervals for their diffusive motion, thus probing the tissue barriers at different length scales using a spin echo sequence (TE = 70 ms) and stimulated echoes with a mixing time of 250 ms (middle) and 500 ms (right). (c) Maps showing the apparent diffusion coefficient Dapp for the three diffusion times. Dapp, which is related to the mean particle displacement, is reduced in the tumor and exhibits a slight reduction with increasing diffusion time (left to right). (d) Maps depicting the apparent diffusional kurtosis Kapp, which is related to non-Gaussian diffusion and thus to the presence of cell membranes causing restrictions. Kapp also decreases with increasing diffusion time. The time-dependence may yield additional information about tissue structure. (Modified from Kuder T.A., Laun F.B., Bonekamp D., Röthke M.C., Influence of diffusion time on parameters measured by diffusion kurtosis imaging in patients with prostate cancer, Proceedings of the German Section of the ISMRM, 2016)
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The Division of Medical Physics in Radiology plays a pivotal role in developing new and optimizing existing methods for all imaging-based diagnostic and therapeutic procedures. To improve and individualize cancer patient treatment, the acquisition of quantitative biomedical information about tumors and metastases is essential. For example, we are expanding the diagnostic value of magnetic resonance imaging (MRI) by using a very powerful magnetic field (7 Tesla) to depict the distribution of sodium, oxygen, and even potassium and chlorine in vivo. By optimizing MRI diffusion techniques, we have been able to greatly improve the diagnostic accuracy of breast cancer screening. We are also developing Computed Tomography (CT) techniques that allow dramatic reductions in radiation dose; it may become feasible in the future to utilize the three-dimensional information of CT to guide minimally-invasive interventions. Furthermore, new targeted contrast agent designs are being pursued to which different imaging tags can be attached; this approach permits the use of multiple imaging techniques (MRI, CT, Positron Emission Tomography (PET), optical imaging) to monitor molecular processes and detect metastases in vivo, even at the micromorphologic level. FUTURE OUTLOOK The Division is working to expand its role as a center of excellence in oncologic imaging methodology. In collaboration with clinical divisions, novel acquisition and reconstruction strategies for multiple imaging modalities are being translated into standard patient use. This includes state-of-the-art imaging protocols at our new MR imagers located at the National Center for Tumor Diseases (NCT). Emerging MR imaging contrasts include sodium and Chemical Exchange Saturation Transfer (CEST) imaging, as well as Quantitative Susceptibility Imaging. At 7 Tesla MRI, we have begun a concerted program focused on improving the characterization of prostate cancer. Construction of the new Radiological Research and Development Center (REZ) is proceeding apace, and we look forward to the new research possibilities that this facility will provide to us.
