Quantitative positron emission tomography imaging in the presence of iodinated contrast media using electron density quantifications from dual‐energy computed tomography

Abstract

Purpose As preparation for future positron emission tomography (PET)/dual‐energy computed tomography (DECT)T imaging modality and new possible clinical applications, the study aimed to evaluate the utility of clinically available spectral results from a DECT system for improving attenuation corrections of PET acquisitions in the presence of iodinated contrast media. The dependence of the accuracy of PET quantification values, reconstructed with conventional and spectral‐based attenuation corrections, was examined as a function of the amount of iodine content and x‐ray radiation exposure. Methods Measurements were performed on commercial PET/CT and DECT systems, using a semi‐anthropomorphic phantom with seven centrifuge tubes in its bore. Five different configurations of tube contents were scanned by both PET/CT and DECT. With the aim of mimicking clinically observed concentrations, in all phantom configurations the center tube contained a high concentration of radionuclide while the peripheral tubes contained a lower concentration of radionuclide. Iodine content was incrementally increased between phantom configurations by replacing iodine‐free tubes with tubes that contained the original radionuclide concentration within a 10 mg/ml iodine dilution. DECT‐based attenuation correction maps were generated by scaling electron density spectral results into corresponding 511 keV photon linear attenuation coefficients. Results Mean SUV values obtained from the nominal PET reconstruction, using conventional CT images as input for the attenuation correction, demonstrate a monotonic increase of 8.6% when the water and radionuclide mixtures were replaced by iodine, water, and radionuclide (same level of activity) mixture. Mean SUV values obtained from the DECT‐based reconstruction, in which the attenuation correction utilizes electron density values as input, demonstrate different, more stable behavior across all iodine insert configurations, with a standard deviation to mean ratio of less than 1%. This observed behavior was independent of the area size used for measurement. A minor radiation dose dependency of the electron density values (below 0.5%) was observed. This resulted in consistent (iodine independent) PET quantification behavior, which persisted even at the lowest radiation dose levels tested in our experiment, that is, 25% of the radiation dose utilized for CT acquisition in the clinical PET/CT protocol. Conclusions Utilization of DECT‐generated electron density estimations for attenuation correction benefit PET quantification consistency in the presence of iodine and at nominal and low DECT radiation exposure levels. The ability to correctly account for iodinated contrast media in PET acquisitions will allow the development of new clinical applications that rely on the quantitative capabilities of spectral CT technologies and modern PET systems.

Gadolinium‐based contrast agent attenuation does not impact PET quantification in simultaneous dynamic contrast enhanced breast PET/MR

“…31 However, changes in Hounsfield units due to iodinated contrast in PET/CT leads to an overestimation of attenuation by the CT attenuation correction leading to elevated SUV. [31][32][33] The results of this study demonstrated that SUV mean and SUV max were not affected by the injection of a GBCA during simultaneous breast PET/MR imaging. The attenuation of annihilation photons caused by the presence of the GBCA is likely not substantial enough to cause a significant difference in detected signal.…”

“…There does not appear to be significant attenuation of annihilation photons by iodine contrast agents at 511 keV in general use cases 31 . However, changes in Hounsfield units due to iodinated contrast in PET/CT leads to an overestimation of attenuation by the CT attenuation correction leading to elevated SUV 31–33 …”

Spectral performance evaluation of a second‐generation spectral detector CT

“…An in‐house software tool 28 , 30 , 31 , 32 was used to automatically place the regions of interest (ROI) on each insert (covering 60% of the insert diameter, that is 17 mm) for MonoE 70 keV images of both insert configurations and phantom size combinations obtained with a DRI of 23. These ROI placements were then copied to corresponding locations on other spectral results to measure the mean and standard deviation of voxel values.…”

“…An in-house software tool 28,[30][31][32] Values that fell within the expected range of values was considered accurate. These results were illustrated by plotting the CT number for each insert versus keV with an envelope that represents the range of expected values.…”