Parametric Net Influx Rate Images of ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE: Quantitative Accuracy and Improved Image Contrast

Abstract

Ga-DOTATOC and Ga-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 () may better reflect treatment effects than those of the SUV, and accordingly there is a need to compute parametric images showing at the voxel level. The aim of this study was to evaluate parametric methods for computation of parametric images by comparison to volume of interest (VOI)-based methods and to assess image contrast in terms of tumor-to-liver ratio. Ten patients with metastatic NETs underwent a 45-min dynamic PET examination followed by whole-body PET/CT at 1 h after injection ofGa-DOTATOC and Ga-DOTATATE on consecutive days. Parametric images 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 tumor values were determined for 50% isocontour VOIs and compared with values based on nonlinear regression (NLR) of the whole-VOI time-activity curve. A subsample of healthy liver was delineated in the whole-body and images, and tumor-to-liver ratios were calculated to evaluate image contrast. Correlation () and agreement between VOI-based and parametric values were assessed using regression and Bland-Altman analysis. The between NLR-based and parametric image-based (BFM) tumor values was 0.98 (slope, 0.81) and 0.97 (slope, 0.88) for Ga-DOTATOC andGa-DOTATATE, respectively. For Patlak analysis, the between NLR-based and parametric-based (Patlak) tumor was 0.95 (slope, 0.71) and 0.92 (slope, 0.74) for Ga-DOTATOC andGa-DOTATATE, respectively. There was no bias between NLR and parametric-based values. Tumor-to-liver contrast was 1.6 and 2.0 times higher in the parametric BFM images and 2.3 and 3.0 times in the Patlak images than in the whole-body images for Ga-DOTATOC andGa-DOTATATE, respectively. A high and agreement between NLR- and parametric-based values was found, showing that images are quantitatively accurate. In addition, tumor-to-liver contrast was superior in the parametric images compared with whole-body images for bothGa-DOTATOC and Ga DOTATATE.

Quantitative Analysis of Heterogeneous [18F]FDG Static (SUV) vs. Patlak (Ki) Whole-body PET Imaging Using Different Segmentation Methods: a Simulation Study

“…In particular, Chen et al [35] reported that gradient-based tumor delineation method may be more accurate on Patlak Ki parametric maps compared to conventional static SUV images using magnetic resonance imaging as the GT. Furthermore, Llan et al [36] found that Ki images present better tumor-to-liver contrast compared with SUV images. Finally, Wangerin et al [37] assessed the variations during the PET imaging process using a series of linked simulations and found that Ki images were associated with superior receiver operating characteristic performance compared to SUV images.…”

PET performance evaluation of the small-animal Hyperion II D PET/MRI insert based on the NEMA NU-4 standard

“…We reconstructed the measurement data with a listmode-based three-dimensional maximum likelihood expectation maximization algorithm including self-normalization and resolution recovery (MLEM-RM) (Salomon et al 2012). The reconstruction algorithm grouped the data into 16 ordered subsets with 5 sub-iterations each, regularized with a relative difference prior with dynamic edge preservation parameters (Andreyev et al 2017, Nuyts et al 2002), and used a voxel pitch of 0.25 mm. Additionally, the reconstruction employs a likelihood-based rejection of inter-crystal detector scatter (Gross-Weege et al 2016) and applied corrections for attenuation, scatter and randoms.…”

Evaluation of block-sequential regularized expectation maximization reconstruction of 68Ga-DOTATOC, 18F-fluoride, and 11C-acetate whole-body examinations acquired on a digital time-of-flight PET/CT scanner

“…In the present study, we investigated the behaviour of BSREM in relation to OSEM regarding image quality in terms of noise, SNR, and SBR, with three non-18 F-FDG PET tracers regularly used in the clinical practice; gallium-68-DOTA-D-Phe 1 -Tyr 3 -octreotide ( 68 Ga-DOTATOC), carbon-11-acetate ( 11 C-acetate), and 18 F-fluoride. 68 Ga-DOTA-TOC is a radiolabelled somatostatin analogue used for imaging of neuroendocrine tumours [13][14][15]. 11 C-acetate, similarly to 11 C-and 18 F-choline, can be used for imaging of the cell membrane lipid metabolism that is typically increased in prostate cancer cells [16][17][18][19][20], and 18 F-fluoride is used for bone imaging, especially for the detection and monitoring of bone metastases in prostate cancer [21,22].…”