ABSTRACT
Technology that integrates computed tomography (CT) and positron emission tomography (PET) within a single imaging device is a relatively recent development in imaging. Nevertheless, such systems are fast becoming the standard for delivery of clinical PET services. The CT component of these combined examinations has generally comprised an examination for attenuation correction and anatomical assignment of abnormalities identified on PET, and is therefore performed without contrast medium. However, there is a growing interest in the use of intravenous contrast media during PET-CT.1 Extending these applications for contrast media to include CT perfusion would enable anatomical information about tumors to be co-registered with perfusion data and metabolic information, such as glucose metabolism, in a single examination. This combined approach would allow simultaneous assessment of multiple endothelial-related (i.e. blood flow, blood volume, vascular permeability) and tumor cell-related (i.e. metabolism) aspects of tumor biology (Figure 13.1). The use of CT to assess perfusion as opposed to administration of a second PET tracer such as [O15]- water circumvents the need for an on-site cyclotron. Furthermore, because CT depicts perfusion data with higher spatial resolution, some of the limitations of PET perfusion studies can be avoided, including the underestimation of perfusion values in small tumors due to the partial volume effect, and the spill over of counts from adjacent structures with high blood flow (e.g. heart, aorta, liver).2 To date, there have been few reports describing the implementation of CT perfusion and PET on a
single imaging device. However, there have been a number of studies in which patients have been examined by both techniques on separate systems. These studies, combined with data in which other methods of perfusion imaging have been correlated against PET, have shown that tumor vascularity and metabolism are not consistently coupled, and a combined assessment using CT perfusion and PET in a single examination could provide a more detailed picture of the biological behavior of tumors.
