The idea of combining functional and anatomical images for better localization and characterization of the lesion started long time ago, using side-by-side
comparison of hard copy films. To overcome the limitation of such comparison, induced by variation in geometric factors governing a functional study, like a nuclear medicine PET scan, and an anatomical one, such as a CT scan, the idea of image fusion emerged. This employed computer software programs that allow electronic fusion of images produced by two different machines, for example a radionuclide scan and a CT scan. Obviously the aim was to improve superimposition of images towards better localization, characterization and assessing the metabolic status of lesions. SPECT and PET are nuclear medicine techniques that provide molecular functional images, while CT scan or MRI produces the cross sectional anatomical images. Image overlay and software
fusion programs included any combination of SPECT or PET on one hand and CT or MRI on the other hand, representing the overlay of functional and structural (anatomical) images respectively. Several problems emerged and hampered the precision and practicality of such electronic image fusion technology. One important difficulty was the need for repositioning the patient in a more or less the same exact way for the two studies, the gamma camera (SPECT) and the CT scanning, for example. This was more of a problem for body imaging, of the thorax, abdomen and pelvis, than it is for the brain(1). The other major problem encountered was the signal attenuation for nuclear medicine emissions, which was not corrected. Such problems degraded prompt localization and characterization of lesions and resulted in unavoidable misleading or imprecise fused images. Medical imaging has entered a revolutionized era since the introduction of
hybrid imaging, utilizing a single “two in one" machine, like SPECT/CT or PET/CT, where functional data and structural information are acquired in a fast sequential mode, at the same clinical imaging setting, without having to change the position of the patient, thus alleviating the need for accurate repositioning of the patient, as was the case prior to integrating the two machines into one. The introduction of SPECT/CT in 1998 was the first clinical expression of hybrid imaging. PET/CT then creeped into clinical practice in the year 2000 with increasing spread since then. This means that PET/CT has been clinical lyon board since more than a decade(1).