title: Parametric Net Influx Rate Images of68Ga-DOTATOC and68Ga-DOTATATE: Quantitative Accuracy and Improved Image Contrast.
abstract: 68Ga-DOTATOC and68Ga-DOTATATE are radiolabeled somatostatin analogs used for the diagnosis of somatostatin receptor-expressing neuroendocrine tumors (NETs), and SUV measurements are suggested for treatment monitoring. However, changes in net influx rate (Ki) may better reflect treatment effects than those of the SUV, and accordingly there is a need to compute parametric images showingKiat the voxel level. The aim of this study was to evaluate parametric methods for computation of parametricKiimages by comparison to volume of interest (VOI)-based methods and to assess image contrast in terms of tumor-to-liver ratio.Methods:Ten patients with metastatic NETs underwent a 45-min dynamic PET examination followed by whole-body PET/CT at 1 h after injection of68Ga-DOTATOC and68Ga-DOTATATE on consecutive days. ParametricKiimages were computed using a basis function method (BFM) implementation of the 2-tissue-irreversible-compartment model and the Patlak method using a descending aorta image-derived input function, and mean tumorKivalues were determined for 50% isocontour VOIs and compared withKivalues based on nonlinear regression (NLR) of the whole-VOI time-activity curve. A subsample of healthy liver was delineated in the whole-body andKiimages, and tumor-to-liver ratios were calculated to evaluate image contrast. Correlation (R2) and agreement between VOI-based and parametricKivalues were assessed using regression and Bland-Altman analysis.Results:TheR2between NLR-based and parametric image-based (BFM) tumorKivalues was 0.98 (slope, 0.81) and 0.97 (slope, 0.88) for68Ga-DOTATOC and68Ga-DOTATATE, respectively. For Patlak analysis, theR2between NLR-based and parametric-based (Patlak) tumorKiwas 0.95 (slope, 0.71) and 0.92 (slope, 0.74) for68Ga-DOTATOC and68Ga-DOTATATE, respectively. There was no bias between NLR and parametric-basedKivalues. Tumor-to-liver contrast was 1.6 and 2.0 times higher in the parametric BFMKiimages and 2.3 and 3.0 times in the Patlak images than in the whole-body images for68Ga-DOTATOC and68Ga-DOTATATE, respectively.Conclusion:A highR2and agreement between NLR- and parametric-basedKivalues was found, showing thatKiimages are quantitatively accurate. In addition, tumor-to-liver contrast was superior in the parametricKiimages compared with whole-body images for both68Ga-DOTATOC and68Ga DOTATATE.
authors: Section of Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden ezgi.ilan@akademiska.se.|Medical Physics, Uppsala University Hospital, Uppsala, Sweden.
authors: Ezgi
authors: E
authors: Ilan
authors: Section of Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.|Medical Physics, Uppsala University Hospital, Uppsala, Sweden.
authors: Mattias
authors: M
authors: Sandström
authors: Section of Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.|PET-Centre, Medical Imaging Centre, Uppsala University Hospital, Uppsala, Sweden; and.
authors: Irina
authors: I
authors: Velikyan
authors: Section of Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.|PET-Centre, Medical Imaging Centre, Uppsala University Hospital, Uppsala, Sweden; and.
authors: Anders
authors: A
authors: Sundin
authors: Section of Endocrine Oncology, Department of Medical Science, Uppsala University Hospital, Uppsala, Sweden.
authors: Barbro
authors: B
authors: Eriksson
authors: Section of Nuclear Medicine and PET, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden.|Medical Physics, Uppsala University Hospital, Uppsala, Sweden.
authors: Mark
authors: M
authors: Lubberink
mesh_terms: D000368:Aged; D003198:Computer Simulation; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008297:Male; D008657:Metabolic Clearance Rate; D008954:Models, Biological; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging* / Q000378:metabolism*; D015282:Octreotide / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D009942:Organometallic Compounds / Q000493:pharmacokinetics*; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D051598:Whole Body Imaging / Q000379:methods
chemical_list: C499142:Ga(III)-DOTATOC; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; C513399:gallium Ga 68 dotatate; D015282:Octreotide
keywords: 68Ga-DOTATATE; 68Ga-DOTATOC; net influx rate; neuroendocrine tumors; parametric images