[12][13] Fully integrated systems are the most technically challenging to achieve, but provide greatest benefits in terms of the ability to make simultaneous, exactly aligned, acquisitions.

[14][15] The first two clinical whole body PET-MRI systems were installed by Philips at Mount Sinai Medical Centre in the United States and at Geneva University Hospital in Switzerland, in 2010.

[21][22][23] Several companies offer MR-compatible preclinical PET scanner inserts for use in the bore of an existing MRI, enabling simultaneous PET/MR image acquisition.

With both PET-CT and PET-MR the intended advantage is to combine functional imaging provided by PET, with structural (anatomical) information from CT or MRI.

Combining imaging modalities in one single scanning session also has the advantage of reducing the number of appointments and therefore improving patient comfort.

[28][29] The same clinical decisions that would influence the choice between stand-alone CT or MR imaging would also determine areas where PET-CT or PET-MR would be preferred.

[34] The Dixon method can be combined with ultrashort echo time (UTE) sequences to better identify bone and increase the possible classes of tissue for segmentation.

[37] In areas of the body with predictable structures (e.g. the head), segmentation (where tissue is categorised using the MRI image data), or "atlas" methods can be used.

In atlas methods a standard MR image, with associated CT attenuation data, can be warped to fit the actual patient anatomy.