Combining the advantages of two or more imaging modalities offers unique possibilities in research and diagnosis. In combined PET/MR imaging the high sensitivity of PET and its huge variety of tracers is combined with the spatial resolution and anatomical as well as functional imaging capabilities provided by MR. Therefore PET/MR is more than the sum of its parts and allows to follow in vivo processes on multiple stages such as at the receptor level and hemodynamic function.

Courtesy of Bruker BioSpin MRI GmbH, Ettlingen, Germany

PET/MRI

The combination of MRI with PET is currently entering into the preclinical and clinical field. The advantages of combining PET and MRI are the high sensitivity of PET and the multiple soft tissue and functional imaging capabilities of MRI. Combining MRI with PET bears also technical challenges which stem from mutual interference of the both modalities. This leads to different realizations of combined MRI-PET systems. The main applications of MRI-PET can be found in the fields of Neurology, Oncology and Cardiology. Finally other emerging techniques that deliver in some respect information similar to PET, like 17O NMR, hyperpolarized MR and whole body diffusion are compared to MRI-PET. In conclusion MRI-PET has the potential to pave new ways in diagnostic imaging.

Image derived from Griessinger et al. 2015, PNAS

PET/CT

The combined PET/CT completely integrates the functional sensitivity of a microPET with the rich anatomical detail of diagnostic multi-slice CT.

One application of this highly advanced combined imaging modality is shown on the left. Recently, cell migration visualization has gained increasing interest with regard to cellular immunotherapy and stem cell transplantation.  So, one of our protocols provides consequent advancements in the detection of small accumulations of these immune cells in single LNs and specific homing to the sites of inflammation by PET and an anatomical CT. A study published 2015 by our group member Dr. Grießinger in PNAS.

The WSIC Siemens small animal SPECT/CT scanner on the left and a CT scan of a mouse and of a mouse bone on the right side.

SPECT/CT

The combination of Single Photon Emission Computed Tomography (SPECT) with Computed Tomography (CT) can give an insight into the body of animals and humans. In CT, X-rays are used to generate cross-sectional images of all parts of the body with a very high resolution. Unfortunately, the CT does not provide functional information. With SPECT, the gamma radiation emitted from certain radioactive isotopes can be measured, and their exact localization can be determined. When these isotopes are bound to specific biologically active molecules, and injected in a patients or animal, SPECT can provide information about functional processes in vivo.

One of our highly specific SPECT tracers is mainly taken up by the liver, as well as the spleen.

Combining the two modalities has great advantages: CT, based on imaging with X-rays is able to visualize the anatomy of the organs, whereas SPECT shows the biological processes. When both modalities are combined in one system, their respective image data can be overlaid. This produces 3D images that offer a wide range of information, and the exact anatomical localization of functional processes can be observed.