Gradient-based geometry learning for fan-beam CT reconstruction.

Objective.Incorporating computed tomography (CT) reconstruction operators into differentiable pipelines has proven beneficial in many applications. Such approaches usually focus on the projection data and keep the acquisition geometry fixed. However, precise knowledge of the acquisition geometry is essential for high quality reconstruction results. In this paper, the differentiable formulation of fan-beam CT reconstruction is extended to the acquisition geometry.Approach.The CT fan-beam reconstruction is analytically derived with respect to the acquisition geometry. This allows to propagate gradient information from a loss function on the reconstructed image into the geometry parameters. As a proof-of-concept experiment, this idea is applied to rigid motion compensation. The cost function is parameterized by a trained neural network which regresses an image quality metric from the motion-affected reconstruction alone.Main results.The algorithm improves the structural similarity index measure (SSIM) from 0.848 for the initial motion-affected reconstruction to 0.946 after compensation. It also generalizes to real fan-beam sinograms which are rebinned from a helical trajectory where the SSIM increases from 0.639 to 0.742.Significance.Using the proposed method, we are the first to optimize an autofocus-inspired algorithm based on analytical gradients. Next to motion compensation, we see further use cases of our differentiable method for scanner calibration or hybrid techniques employing deep models.

[Gender and developmental effects on perceived stress, coping, somatic symptoms and psychological disorders among children and adolescents]. / Geschlechtseffekte und Entwicklungsverlauf im Stresserleben, der Stressverarbeitung, der körperlichen Beanspruchung und den psychischen Störungen bei Kindern und Jugendlichen.

The aim of this one-year longitudinal study was to investigate gender and developmental effects on perceived stress related to interpersonal stressors, coping strategies, somatic symptoms and psychological disorders. Additionally, associations of perceived stress and coping styles at the first assessment with psychological problems at the second measurement were examined. In total, N = 169 Austrian children and adolescents (ages 10 to 13 years) participated in this self-report study. Compared to male children and adolescents, female counterparts scored higher on perceived stress related to interpersonal stressors and on social support but evaluated a lower amount of distraction. Moreover, girls reported higher levels of somatic symptoms and anxiety/depression. Boys showed a developmental increase in anger control problems and both genders showed developmental increases in antisocial behavior. Low levels of the emotion-focused coping strategies distraction and minimization were related longitudinally to emotional and behavioral disorders. The results support gender-adjusted stress management programs applied in the primary and secondary prevention.