Attenuation Correction for MR-PET
Present hybrid MR-PET scanners, which allow simultaneous imaging of both modalities, do not offer transmission scans for a PET-based measured attenuation correction. Nevertheless, to achieve qualitatively and quantitatively acceptable PET images data on tissue absorption must be available as a prerequisite of attenuation correction. Such data may be derived from anatomical MR images segmented into different tissue types, attenuation coefficients are assigned to the different tissue types. An alternative approach called template-based attenuation correction (TBA) developed by our group uses templates of attenuation maps which have been obtained from conventional PET-based attenuation images. The TBA is the correction procedure routinely in our present MR-PET studies. Although this approach works quite satisfactorily in general, it may fail if the patient shows unusual or abnormal bone structures, e.g. after surgery. Therefore, we further investigate the use of ultrashort MR sequences (UTE), which are able to image bone, and more sophisticated and advanced segmentation methods, which are based not only on anatomical MR images, but also on a priori knowledge about the head anatomy (link to work of Gudrun Wagenknecht (ZEL)).