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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

Correspondence: For correspondence contact: Klaus Brechtel, MD, Department of Diagnostic Radiology, University of Tuebingen, Hoppe-Seyler-Strasse 3, 72076 Tuebingen, Germany. E-mail: brechtkla{at}yahoo.com

The purpose of this study was to compare various PET/CT examination protocols that use contrast-enhanced single-phase or contrast-enhanced multiphase CT scans under different breathing conditions. Methods: Sixty patients with different malignant tumors were randomized into 4 different PET/CT protocols. Single-phase protocols included an intravenous contrast–enhanced (Ultravist 370; iodine at 370 mg/mL) single-phase whole-body CT scan (90 mL at 1.8 mL/min; delay, 90 s) during shallow breathing (protocol A) or during normal expiration (NormExp; protocol B). Multiphase protocols included 2 separate CT scans in the arterial contrast enhancement phase (90 mL at 2.5–2.8 mL/min; bolus tracking; scan range, base of the skull to the kidneys) and the portal-venous contrast enhancement phase (delay, 90 s; scan range, base of the lungs to the proximal thighs) during shallow breathing (protocol C) or during NormExp (protocol D) followed by a low-dose CT scan during shallow breathing for attenuation correction and whole-body PET. Feasibility was assessed by comparing the misalignment of the upper abdominal organs quantitatively by means of the craniocaudal, lateral, and anterior–posterior differences on coregistered PET/CT images. For image quality, the occurrence of CT artifacts and mismatching of rigid body points were evaluated qualitatively. Results: Misalignment was significantly lower for protocol B in almost all organs and represented the best coregistration quality. Surprisingly, protocol A showed significantly better alignment than the multiphase CT scans during NormExp. Misalignment values between the multiphase protocols were not significantly different, with a trend toward lower values for protocol D. The best CT image quality, with a significantly lower occurrence of artifacts, was found for protocols B and D (NormExp). The levels of mismatching of rigid body points because of patient movement in between the transmission and emission scans were similar for all protocols. Conclusion: Multiphase CT protocols presented a technical disadvantage represented by suboptimal image coregistration compared with single-phase protocols. Nevertheless, multiphase protocols are technically feasible and should be considered for patients who will benefit from a contrast-enhanced multiphase CT examination for diagnosis.

Key Words: contrast enhancement • multiphase CT • PET/CT • misalignment • coregistration

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