In the March 2011 number of European Radiology, Boss and co-authors describe their first experiences with the feasibility of simultaneous PET-MR imaging in the head and upper neck area [1]. They found that simultaneous PETMRI of head and neck cancer was feasible with a new hybrid PET-MRI prototype, using a removable brain PETdetector that can be placed within the MR gantry. They report that MRI datasets acquired during simultaneous PET data acquisition exhibited excellent image quality without any recognisable artefacts or distortions caused by the PET insert. PET datasets showed slight streak artefacts, which did not lead to degradation of tumour visualization. Images obtained with the PET-MRI system exhibited better detailed resolution and greater image contrast in comparison to those from the PET-CT system. The authors also report that full quantification of regional radiotracer activity is not yet possible. This precludes the calculation of standardized uptake values as a semi-quantitative measure of radiotracer accumulation and local uptake needs to be scaled towards a reference tissue. The authors state that this current deficit is expected to be amended soon by implementing a calibration workflow. A clear disadvantage of this PET-MRI system mainly designed for brain imaging is the small field-ofview of the PET component of approximately 19 cm. Therefore the axial field of view of the PET insert typically reached to structures located cranially of the angle of the mandible, leaving the larynx and hypopharyx outside the fieldof-view. Actually the authors only report on nasopharyngeal and not even on oral and oropharyngeal carcinomas. Magnetic resonance imaging provides unmatched soft tissue detail along with a reasonable array of functional information through techniques as MRI diffusion and MRI perfusion. However it will take a long time before MRI can provide the molecular detail that PET does and PET provides the anatomical information that MRI does, so a combination of the two technologies is the most reasonable option. Combining the two advanced imaging technologies without degrading the original optimum performance of either is challenging [2]. At present, three solutions are considered by manufacturers: a sequential, insert and integrated approach. In the sequential construct, the PET and MRI systems are placed in a sequence. This approach is used in PET-CT and most currently available PET-MRI. However, multimodality imaging performed with separate imaging devices requires patients repositioning, which results in a greater risk of voluntary or involuntary patient movements between procedures. There are some physiologic processes such as tissue perfusion, which may change rapidly over time that consecutive data acquisition of PET and MRI may yield inaccurate results and a fully integrated system for simultaneous data acquisition is necessary. In the long term it remains to be determined if PET-MRI set-ups with sequential data acquisition capacity have a future because, especially in the mobile head and neck, there will be problems regarding reposition. In addition the options for optimizing workflow are restricted. The insert construct system involves building a removable PET-detector that can be placed within the MR gantry. The study in the article under discussion made use of this combination: a brain PET in a slightly modified clinical 3.0 J. A. Castelijns (*) Department of Radiology, VU University Medical Center, De Boelelaan 1117, 1081 HVAmsterdam, The Netherlands e-mail: j.castelijns@vumc.nl