The quest for the ideal anato-molecular imaging fusion tool

The past decade has witnessed major scientific and technological advancements, and one among them was molecular imaging. Today, molecular imaging constitutes a major trend in biomedical research and seems to have the potential to revolutionise life sciences. Molecular imaging plays a valuable role in the assessment of cellular targets and the response to therapy, differential diagnosis, prediction or selection of patients who will benefit from treatment, and in dosimetry for targeted therapy. The field of preclinical and clinical molecular imaging has developed simultaneously with molecular medicine, which holds great promise to provide significant healthcare benefits in the future. The advent of dual-modality PET/CT units is a prominent example of advance in molecular imaging technology. It offers the opportunity to modernise the practice of clinical oncology by improving lesion localisation and facilitating treatment planning for radiation therapy. Although dual-modality imaging systems designed specifically for clinical practice are a recent feature, the potential advantages of combining anatomical and functional imaging has been recognised for several decades by radiological scientists and physicians [1]. Many of the pioneers of nuclear medicine recognised that a radionuclide imaging system could be augmented by adding an external radioisotope source. This would acquire transmission data for anatomical correlation of the emission image. The conceptual designs were, however, never introduced in practice or implemented in either an experimental or a clinical setting until Hasegawa and colleagues (University of California, San Francisco) pioneered in the 1990s the development of dedicated SPECT/CT [2,3]. Later, Townsend and co-workers (University of Pittsburgh) pioneered in 1998, the development of combined PET/CT imaging systems. These have the capability to record both PET emission and x-ray CT data for correlated functional/structural imaging [4,5]. Thereafter, PET/CT dual-modality imaging systems were introduced by the major scanner manufacturers for routine clinical use. According to market reports, over 90% of today's PET sales are combined PET/CT units. This led almost all scanner manufacturers to opt for replacing entirely PET-only scanners by PET/CT. While all clinical and commercial dual-modality systems have been configured in the form of PET/CT or SPECT/CT scanners, several investigators proposed, implemented, and tested prototype combined PET/MRI imaging systems [6]. PET/MRI is a more challenging technology compared with PET/CT. The importance of this development will only be understood and manifest when this and other forms of dual-modality imaging become available in the ensuing years and are utilised for clinical studies of humans as well as biological investigations involving …