Applications for Preclinical PET/MRI Martin S. Judenhofer, PhD, Simon R. Cherry, PhD  Seminars in Nuclear Medicine  Volume 43, Issue 1, Pages 19-29 (January 2013) DOI: 10.1053/j.semnuclmed.2012.08.004 Copyright © 2013 Elsevier Inc. Terms and Conditions

Figure 1 The performance of positron emission tomography/magnetic resonance imaging (PET/MRI) systems (diamond) and selected stand-alone PET systems (circle) plotted according to their volumetric spatial resolution and detection sensitivity. See Table 1 for more information. Seminars in Nuclear Medicine 2013 43, 19-29DOI: (10.1053/j.semnuclmed.2012.08.004) Copyright © 2013 Elsevier Inc. Terms and Conditions

Figure 2 Schematic examples of workflows for combined PET/MRI acquisitions. Because PET and MRI can both acquire dynamic data, there are, in essence, four basic workflows combining static–static (A) dynamic–static (B and C), or dynamic–dynamic acquisitions (D). One can see that all workflows benefit from the simultaneous acquisition of PET and MRI, resulting in a reduced total examination time compared with what would be necessary for sequential acquisitions with independent devices. (Color version of figure is available online.) Seminars in Nuclear Medicine 2013 43, 19-29DOI: (10.1053/j.semnuclmed.2012.08.004) Copyright © 2013 Elsevier Inc. Terms and Conditions

Figure 3 Simultaneous PET/MRI acquisition in a tumor-bearing mouse. This is an example of a combined PET/MRI acquisition based on the workflow shown in Figure 2C. The top row shows T2-weighted MRI and 18F-fluorodeoxyglucose (FDG) PET data as well as the fused images. The PET and MRI data have good spatial alignment based on the default registration of the 2 systems suing a predefined transformation matrix. The center row shows images of the dynamic contrast agent (CA) enhancement MRI (late images) as well as parametric maps derived from the CA slope and the fusion with the PET data. The images and the plot of the dynamic MRI data show that areas of high slope (Tumor 1 and Tumor 2) are more correlated to areas of high PET uptake, whereas areas of low PET uptake indicating necrosis are correlated with low slope values (Necrosis). Image courtesy of the University of Tübingen. Seminars in Nuclear Medicine 2013 43, 19-29DOI: (10.1053/j.semnuclmed.2012.08.004) Copyright © 2013 Elsevier Inc. Terms and Conditions

Figure 4 Multimodal images of radiotracer uptake in tumors, acquired with the PET insert built at UC Davis. Mice bearing MC38.CEA tumors were injected either with 18F-FDG (A) or anti-CEA [64Cu] DOTA-NHSM5A antibody (B) and sacrificed after uptake period. Tumor regions were then imaged using the PET/MRI scanner, frozen, reimaged using PET/MRI, imaged in frozen state using small-animal PET and small-animal CT, cryosectioned, and imaged using autoradiography. Matched tumor slices show qualitatively similar uptake patterns. PET/MRI scanner images of 18F-FDG show hot spot (circle) not observed with other modalities. Comparison with MRI showed hot spot to be on animal's surface, indicating that it was caused by urine residue, which was removed before subsequent imaging (scale bar = 10 mm). (Reprinted by permission of the Society of Nuclear Medicine from Ng et al.57 Figure 2.) Seminars in Nuclear Medicine 2013 43, 19-29DOI: (10.1053/j.semnuclmed.2012.08.004) Copyright © 2013 Elsevier Inc. Terms and Conditions

Figure 5 PET and MRI provide complementary information on extent and biologic activity of tumors in an angiogenic phenotypic model of glioblastoma. (A) Axial brain slices show that 18F-FDG uptake is decreased in the ipsilateral hemisphere. However, focal increase of 18F-FDG uptake could be observed (black arrow), and also the maximum of 18F-FDG uptake was not always correlated with maximum of 18F-FLT and 11C-MET uptake. (B) Low 18F-FDG and 18F-FLT uptake correlated with high T2-weighted signal intensity and increased apparent diffusion coefficient (ADC) values (black arrow), indicating cyst or ventricular enlargement. (C) Other tumor regions are characterized by low 18F-FDG and 18F-FLT uptake correlating with low T2-weighted signal intensity and reduced ADC values (black arrow), indicating necrotic areas inside the tumor. Gd, gadolinium; T1w, T1-weighted; T2w, T2-weighted. (Reprinted by permission of the Society of Nuclear Medicine from Viel et al.59 Figure 4.) Seminars in Nuclear Medicine 2013 43, 19-29DOI: (10.1053/j.semnuclmed.2012.08.004) Copyright © 2013 Elsevier Inc. Terms and Conditions

Figure 6 The principle of a dual-gated PET/MRI acquisition. Electrocardiogram (ECG) and respiratory (RESP) motion information are derived from the subject and converted into corresponding logic signals (trigger). The trigger signals are split and fed into the PET acquisition data stream to enable postacquisition sorting of the list mode into sinograms that are arranged according to an average cardiac cycle. The other part of the trigger signal is used to prospectively gate the MRI sequence acquisition. To further increase MRI image quality, the respiratory gate can be used to prevent acquisition during peak respiratory motion intervals. (Color version of figure is available online.) Seminars in Nuclear Medicine 2013 43, 19-29DOI: (10.1053/j.semnuclmed.2012.08.004) Copyright © 2013 Elsevier Inc. Terms and Conditions