Computed Tomography-based Attenuation Correction in Neurological Positron Emission Tomography: Evaluation of the Effect of the X-ray Tube Voltage on Quantitative Analysis

Background: The advent of dual-modality positron emission tomography/computed tomography (PET/CT) imaging has revolutionized the practice of clinical oncology by improving lesion localization and facilitating treatment planning for radiation therapy. In addition, the use of CT images for CT-based attenuation correction (CTAC) allows the overall scanning time to be decreased and a noise-free attenuation map (micromap) to be created. The most common procedure requires a piecewise linear calibration curve acquired under standard imaging conditions to convert the patient's CT image from low effective CT energy into an attenuation map at 511 keV.

Aim: To evaluate the effect of the tube voltage on the accuracy of CTAC.

Methods: As different tube voltages are employed in current PET/CT scanning protocols, depending on the size of the patient and the region under study, the impact of using a single calibration curve on the accuracy of CTAC for images acquired at different tube voltages was investigated through quantitative analysis of the created micromaps, generated attenuation correction factors and reconstructed neurological PET data using anthropomorphic experimental phantom and clinical studies.

Results: For CT images acquired at 80 and 140 kVp, average relative differences of -2.9% and 0.7%, respectively, from the images acquired at 120 kVp were observed for the absolute activity concentrations in five regions of the anthropomorphic striatal phantom when CT images were converted using a single calibration curve derived at 120 kVp. Likewise, average relative differences of 1.9% and -0.6% were observed when CT images were acquired at 120 kVp and CTAC used calibration curves derived at 80 and 140 kVp, respectively.

Conclusion: The use of a single calibration curve acquired under standard imaging conditions does not affect, to a visible or measurable extent, neurological PET images reconstructed using CTAC when CT images are acquired in different conditions.