Evaluation of two respiratory gating technologies on motion artifacts correction and quantitative analysis in Solitary Pulmonary Nodules

Objectives: We aim to compare the effects of ungated imaging (UG) acquisition and two respiratory-gated acquisition technologies, namely Q.Static (Q.Static respiratory gated imaging, QSRG) and Q.Freeze (Q.Freeze respiratory gated imaging, QFRG) on image quality and quantification of respiratory motion in pulmonary lesions, and to evaluate the clinical application value of gating technology.

Methods: A total of 49 patients (32 males and 17 females with an average age of 55.63±10.80 years old) with pulmonary nodules (73 isolated hypermetabolic lesions) previously underwent QSRG and QFRG on PET/CT in our hospital from March 2020 to November 2020 were retrospectively analyzed. The maximum standardized uptake value (SUV_max), tumor metabolic volume (MTV), %ΔSUV_max ((SUV_max-gated -SUV_max-ungated) / SUV_max-ungated) and %ΔMTV ((MTV_gated - MTV_ungated) / MTV_ungated) were measured and calculated. All isolated hypermetabolic pulmonary nodules were grouped according to the maximum diameter of nodules on CT and metabolic uptake on PET, and the differences of image quality and quantification between QSRG and QFRG respiratory gating technologies were compared. Results: The SUV_max of UG, QSRG, and QFRG were 4.88±3.09, 5.23±3.28, and 5.48±3.49, and corresponding MTV were 1.42±1.66, 1.31±1.60, and 1.28±1.51, respectively (P <0.05). Firstly, the nodules were divided into two groups based on their maximum diameter: diameter≤1cm (n=33) and 1<diameter≤3cm (n=40). For the nodules with a diameter ≤1cm, the SUV_max of UG, QSRG, and QFRG were 3.39±2.39, 3.64±2.58 and 3.74±2.55 (P >0.05), and the corresponding MTV were 0.47±0.34, 0.39±0.24, and 0.38±0.22 (P >0.05), respectively. The %ΔSUV_max of QSRG (vs.UG) and QFRG (vs.UG) were 10.76%±28.56% and 20.62%±46.19% (P>0.05), and corresponding %ΔMTV were 0.97%±53.68% and 10.78%±81.28% (P>0.05), respectively. In the group of 1<diameter≤3cm, the SUV_max of UG, QSRG, and QFRG were 6.11±3.10, 6.53±3.24 and 6.91±3.54 (P <0.05), the corresponding MTV was 2.20±1.89, 2.07±1.85 and 2.02±1.71 (P > 0.05), respectively. The %ΔSUV_max of QSRG (vs.UG) and QFRG (vs.UG) were 8.22%±18.23% and 16.11%±28.02% (P <0.05), and corresponding %ΔMTV were -7.03%±24.52 and -20.07%±34.07 (P>0.05), respectively. Secondly, taking SUV_max=2.5 as the threshold, the nodules were divided into two groups. For nodules with SUV_max<2.5, the %ΔSUV_max of QSRG (vs.UG) and QFRG (vs.UG) were16.12%±28.96% and 33.17%±42.25% (P <0.05). For nodules with SUV_max≥2.5, The %SUV_max of QSRG (vs.UG) and QFRG (vs.UG) were 6.64%±20.12% and 12.08%±33.11% (P >0.05). In the group of SUV<2.5, compared with UG, the increased uptakes of more than 2.5 in lung nodules on QSRG and QFRG were found in 6/21 and 11/21 cases, respectively. The detection rates of UG, QSRG, and QFRG for isolated hypermetabolic lesions were 83.51% (76/91), 87.91% (80/91), and 96.70% (88/91), respectively. Conclusion: Compared with UG, isolated hypermetabolic pulmonary nodules had a significantly higher SUVmax and lower MTV on QSRG and QFRG. QFRG can better detect and quantify solitary lung nodules in cases with SUVmax<2.5. Keywords: lung nodules; respiratory gating; tomography; deoxyglucose