Task-based transferable deep-learning scatter correction in cone beam computed tomography: a simulation study.

Purpose: X-ray scatter significantly affects the image quality of cone beam computed tomography (CBCT). Although convolutional neural networks (CNNs) have shown promise in correcting x-ray scatter, their effectiveness is hindered by two main challenges: the necessity for extensive datasets and the uncertainty regarding model generalizability. This study introduces a task-based paradigm to overcome these obstacles, enhancing the application of CNNs in scatter correction. Approach: Using a CNN with U-net architecture, the proposed methodology employs a two-stage training process for scatter correction in CBCT scans. Initially, the CNN is pre-trained on approximately 4000 image pairs from geometric phantom projections, then fine-tuned using transfer learning (TL) on 250 image pairs of anthropomorphic projections, enabling task-specific adaptations with minimal data. 2D scatter ratio (SR) maps from projection data were considered as CNN targets, and such maps were used to perform the scatter prediction. The fine-tuning process for specific imaging tasks, like head and neck imaging, involved simulating scans of an anthropomorphic phantom and pre-processing the data for CNN retraining. Results: For the pre-training stage, it was observed that SR predictions were quite accurate (SSIM≥0.9). The accuracy of SR predictions was further improved after TL, with a relatively short retraining time (≈70 times faster than pre-training) and using considerably fewer samples compared to the pre-training dataset (≈12 times smaller). Conclusions: A fast and low-cost methodology to generate task-specific CNN for scatter correction in CBCT was developed. CNN models trained with the proposed methodology were successful to correct x-ray scatter in anthropomorphic structures, unknown to the network, for simulated data.

Ventana aortopulmonar: reporte de 4 casos / Aortopulmonary window: report of four cases

La ventana aortopulmonar es una malformación congénita rara en la cual la aorta y la arteria pulmonar están comunicados por un orificio de diámetro variable. En forma retrospectiva revisamos el cuadro clínico , diagnóstico, lesiones asociadas y tratamiento en cuatro casos con esta malformación, manejados en nuestro servicio en el período comprendido entre 1980 y 1990. Dos pacientes tenían una ventana aortopulmonar de tipo distal, y dos de las del tipo proximal. Existió lesión asociada en tres pacientes: interrupción del arco aórtico tipo A, estenosis subvalcular aórtica, persistencia del conducto arteriosos y comunicación interventricular. Todos los pacientes fueron tratados quirúrgicamente encontrándose un orificio de comunicación con un diámetro entre 12 y 15 mm. Se presentó una sola reapertura que se cerró en forma satisfactoria en un segundo tiempo. Se discuten los problemas de diagnóstico y tratamiento que planea esta malformación