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Optimized Contrast-Enhanced CT Protocols for Diagnostic Whole-Body ¹⁸F-FDG PET/CT: Technical Aspects of Single-Phase Versus Multiphase CT Imaging

¹ Department of Diagnostic Radiology, University of Tuebingen, Tuebingen, Germany; ² Department of Nuclear Medicine, University of Tuebingen, Tuebingen, Germany; and ³ Department of Nuclear Medicine, University Hospital Essen, Essen, Germany

View larger version (36K): [in a new window]   FIGURE 1.  PET/CT protocols for single-phase (A) and multiphase (B) examinations. For protocol A, purple spiral represents whole body in portal-venous contrast enhancement. Scan range included base of skull to proximal thigh, as in PET (blue cylinder). For protocol B, 2 examination protocols had to be implemented because of technical standards of scanner. After injection and bolus tracking of contrast medium, first CT scan covered base of skull to lower borders of kidneys (red spiral). At 90 s after injection, CT ranging from base of lungs to proximal thighs was performed in portal-venous contrast enhancement phase (purple spiral). After short reconstruction interval, attenuation LD-CT (gray spiral) and PET were performed. Thickness of spiral lines indicates dose (thick line: 160 mAs; thin line: 30 mAs); width of spirals indicates collimation (narrow: 0.75; wide: 1.5).

View larger version (10K): [in a new window]   FIGURE 2.  Comparison of misalignment of contrast-enhanced CT examinations for protocols A, B, C, and D. Protocol B (NormExp; single phase) had significantly lowest values for all abdominal organs. Significant differences between multiphase protocols (C and D) could not be assessed. art = arterial; p-v = portal-venous. • = individual values; + = mean values. Error bars indicate SDs.

View larger version (32K): [in a new window]   FIGURE 3.  Occurrence of image artifacts caused by breathing and severe mismatching caused by movements of patient in between CT and PET scans. Mismatching was distributed equally among protocols, whereas image quality correlated strongly with breathing protocols. NormExp protocols (B and D) had significantly lower occurrences of artifacts and, therefore, superior image quality. art = arterial; p-v = portal-venous.

View larger version (10K): [in a new window]   FIGURE 4.  Multiphase PET/CT. Comparison of misalignment in protocol C (A) and protocol D (B). LD-CT attenuation scans were performed during shallow breathing. However, with regard to misalignment in liver, values for LD-CT were significantly lower. For protocol D, contrast-enhanced CT scan during NormExp did not show superiority over LD-CT scan during shallow breathing. Instead, values for LD-CT were significantly lower than those for arterial phase for liver. LD = low dose; ART = arterial; P-V = portal-venous. • = individual values; + = mean values. Error bars indicate SDs.

View larger version (7K): [in a new window]   FIGURE 5.  Comparison of CT attenuation scans. Protocol B showed lowest values for misalignment in all organs. Attenuation scans with protocol C (C LD) and protocol D (D LD) showed values similar to those with protocol A, as expected. • = individual values; + = mean values. Error bars indicate SDs.