Is the Hénon map able to predict the interaction dynamics between the knee and hip joints emerged during sit-to-stand movement?

In this study, the performance of a two-dimensional Hénon map in predicting the interactive dynamics of the knee and hip joints emerging during a normative sit-to-stand movement was evaluated. The instantaneous values of the knee and hip joints were the model inputs, and the next values of the knee and hip joints were predicted by the Hénon map. The map predicted the desired relative behavior of the joints, showing synergetic coordination between the joints. The experimental data were recorded from four healthy participants and used to identify the Hénon map via a genetic algorithm. Model performance was quantitatively assessed by computing the calculated prediction error and analyzing the behavioral dynamics of the state spaces reconstructed via the captured kinematic data. According to the results, there was an obvious similarity between the dynamics of the state space trajectories of the identified model and those of the recorded data, not only in terms of stretching and folding dynamics, but also concerning generalized synchrony. The acceptable performance of the proposed modeling solution can also be demonstrated through these results.

Heterogeneity of SSTR2 Expression Assessed by 68Ga-DOTATOC PET/CT Using Coefficient of Variation in Patients with Neuroendocrine Tumors.

High levels of somatostatin receptor subtype 2 (SSTR2) are a prerequisite for therapy with unlabeled or labeled somatostatin analogs. However, it is still unclear how the heterogeneity of SSTR2 expression may affect tumor response to therapy. The aim of our study was to test the ability of an imaging parameter such as coefficient of variation (CoV) derived from PET/CT with 68Ga-peptides in the evaluation and quantification of the heterogeneity of SSTR2 expression within primary and metastatic lesions of patients with neuroendocrine tumors. Methods: Thirty-eight patients with pathologically proven neuroendocrine tumors who underwent 68Ga-DOTATOC PET/CT were studied. Primary tumors were localized in the gastroenteropancreatic, bronchopulmonary, and other anatomic districts in 25, 7, and 6 patients, respectively. Malignant lesions were segmented using an automated contouring program and an SUV threshold of more than 2.5 or, in the case of liver lesions, a threshold of 30% of the SUVmax The imaging parameters SUVmean, CoV, SUVmax, receptor-expressing tumor volume, and total lesion receptor expression were obtained for each lesion. SUVmean, CoV, and SUVmax were also obtained for representative volumes of normal liver and spleen, as well as for the whole pituitary gland. Results: In total, 107 lesions were analyzed, including 35 primary tumors, 32 metastatic lymph nodes, and 40 distant metastases. Average CoVs were 0.49 ± 0.20 for primary tumors, 0.57 ± 0.26 for lymph node metastases, and 0.44 ± 0.20 for distant metastases. The CoVs of malignant lesions were up to 4-fold higher than those of normal tissues (P ≤ 0.0001). Among malignant lesions, the highest CoV was found for bone metastases (0.68 ± 0.20), and it was significantly greater than that of primary lesions (P = 0.01) and liver metastases (P < 0.0001). On the other hand, the lowest CoV was found for liver lesions (0.32 ± 0.07), probably because of the high background uptake. Conclusion: Our findings indicate that the heterogeneity of uptake, reflecting that of SSTR2, varies with the type and site of malignant lesions as assessed by CoVs obtained from 68Ga-DOTATOC PET/CT scans. These observations may be related to different biologic characteristics of tumor lesions in the same patient-differences that may affect their response to treatment with both labeled and unlabeled somatostatin analogs.