Radiology 2002; 225:575-581.
Hany TF, Steinert HC, Goerres GW, Buck A, von Schulthess GK.
The authors describe the initial application for tumor staging with an inline system with a positron emission tomographic (PET) scanner and a multi-detector row helical computed tomographic (CT) scanner combined in one machine. Fifty-three patients underwent imaging with four CT tube currents and PET emission and transmission data acquisition. Stepwise analysis of coreg-istered images revealed a significant (P < .05, McNemar test) improvement in lesion classification between PET images alone and coregistered images from the PET-CT examination.
In the past 2 decades, computed tomography (CT) has been the main diagnostic tool in initial staging of disease and therapy follow-up in patients with cancer. Morphologic changes depicted at CT have been equated to disease manifestations. CT has proved to be an accurate imaging modality for various cancers and has been used in the treatment decision-making process (1,2). CT has the ability to depict abnormal anatomy and abnormal contrast enhancement due to pathologic changes. However, CT has limitations in depiction of pathologic changes in normal-sized structures, such as lymph nodes, and of a lesion that does not have good contrast with the surrounding tissues, which results in a reduced sensitivity of lesion detection (3).
In recent years, imaging with fluorodeoxyglucose (FDG) positron emission tomography (PET) for tumor staging and therapy control has been introduced.
Rather than anatomic information, FDG PET provides physiologic information on glucose uptake and metabolism. FDG PET has been used successfully for detection of primary tumors, metastases, and early tumor recurrence, while the indications for PET in cardiology and neurology have existed for a longer time (4-8). The main drawback of PET in tumor imaging is the virtually complete absence of anatomic landmarks, which impedes precise localization of lesions with pathologic FDG uptake (9). Furthermore, there are some issues regarding specificity because FDG is not only taken up by many malignant tumors but also by sites of active inflammation (10).
During the early years of clinical tumor imaging with PET, the potential of mul-timodality image fusion was recognized since CT and magnetic resonance imaging on one hand and PET on the other yield complementary information in many diagnostic settings (9). Findings in several studies have shown that a combination of PET and CT by means of coreg-istration with software is more accurate than CT alone, especially in the staging of non-small cell lung cancer and detection of mediastinal lymph node metastases (9,11).
Recently, Townsend (12) introduced as proof of concept a prototype of a combined PET-CT scanner, with a single-detector row helical CT scanner and a partial-ring rotating PET scanner, that permits the acquisition of PET and CT images coregistered by means of the hardware in the same imaging session. Analysis of the results showed an improvement in lesion localization and classification, even though only restricted anatomic regions were coregistered, and spatial resolutions of both imagers used in the prototype system were suboptimal (13-15).