Landmark tracking in 4D ultrasound using generalized representation learning.

PURPOSE: In this study, we present and validate a novel concept for target tracking in 4D ultrasound. The key idea is to replace image patch similarity metrics by distances in a latent representation. For this, 3D ultrasound patches are mapped into a representation space using sliced-Wasserstein autoencoders. METHODS: A novel target tracking method for 4D ultrasound is presented that performs tracking in a representation space instead of in images space. Sliced-Wasserstein autoencoders are trained in an unsupervised manner which are used to map 3D ultrasound patches into a representation space. The tracking procedure is based on a greedy algorithm approach and measuring distances between representation vectors to relocate the target . The proposed algorithm is validated on an in vivo data set of liver images. Furthermore, three different concepts for training the autoencoder are presented to provide cross-patient generalizability, aiming at minimal training time on data of the individual patient. RESULTS: Eight annotated 4D ultrasound sequences are used to test the tracking method. Tracking could be performed in all sequences using all autoencoder training approaches. A mean tracking error of 3.23 mm could be achieved using generalized fine-tuned autoencoders. It is shown that using generalized autoencoders and fine-tuning them achieves better tracking results than training subject individual autoencoders. CONCLUSION: It could be shown that distances between encoded image patches in a representation space can serve as a meaningful measure of the image patch similarity, even under realistic deformations of the anatomical structure. Based on that, we could validate the proposed tracking algorithm in an in vivo setting. Furthermore, our results indicate that using generalized autoencoders, fine-tuning on only a small number of patches from the individual patient provides promising results.

Towards automated ultrasound imaging-robotic image acquisition in liver and prostate for long-term motion monitoring.

Real-time volumetric (4D) ultrasound has shown high potential for diagnostic and therapy guidance tasks. One of the main drawbacks of ultrasound imaging to date is the reliance on manual probe positioning and the resulting user dependence. Robotic assistance could help overcome this issue and facilitate the acquisition of long-term image data to observe dynamic processesin vivoover time. The aim of this study is to assess the feasibility of robotic probe manipulation and organ motion quantification during extended imaging sessions. The system consists of a collaborative robot and a 4D ultrasound system providing real-time data access. Five healthy volunteers received liver and prostate scans during free breathing over 30 min. Initial probe placement was performed with real-time remote control with a predefined contact force of 10 N. During scan acquisition, the probe position was continuously adjusted to the body surface motion using impedance control. Ultrasound volumes, the pose of the end-effector and the estimated contact forces were recorded. For motion analysis, one anatomical landmark was manually annotated in a subset of ultrasound frames for each experiment. Probe contact was uninterrupted over the entire scan duration in all ten sessions. Organ drift and imaging artefacts were successfully compensated using remote control. The median contact force along the probe's longitudinal axis was 10.0 N with maximum values of 13.2 and 21.3 N for liver and prostate, respectively. Forces exceeding 11 N only occurred in 0.3% of the time. Probe and landmark motion were more pronounced in the liver, with median interquartile ranges of 1.5 and 9.6 mm, compared to 0.6 and 2.7 mm in the prostate. The results show that robotic ultrasound imaging with dynamic force control can be used for stable, long-term imaging of anatomical regions affected by motion. The system facilitates the acquisition of 4D image datain vivoover extended scanning periods for the first time and holds the potential to be used for motion monitoring for therapy guidance as well as diagnostic tasks.

Patients with Schizophrenia Do Not Demonstrate Worse Outcome After Sleeve Gastrectomy: a Short-Term Cohort Study.

PURPOSE: The aim of this study was to compare surgical and psychiatric outcome and weight loss in schizophrenia patients with mentally healthy patients after sleeve gastrectomy. MATERIALS AND METHODS: A cohort study design was selected, comprising patients with schizophrenia with mentally healthy patients who underwent sleeve gastrectomy and were adherent to a follow-up at least 12 months after surgery. RESULTS: Seven schizophrenia (5 male, 2 female) and 59 (12 male, 47 female) mentally healthy patients were included in this study. A laparoscopic sleeve gastrectomy was performed safely in all 66 patients. The calculated excess weight loss (%EWL) showed no significant differences in both groups and reached 51.68 ± 15.84% for schizophrenia group and 60.68 ± 19.95% for mentally healthy group at 24-month follow-up (p = 0.33). The decrease in the HbA1c levels within 2 years after sleeve gastrectomy was similar in both groups (p = 0.79, 0.88, 0.82, 0.73 for surgery time, time of 6-, 12-, and 24-month follow-up respectively). The psychiatric status of the patients of the schizophrenia group was stable in all cases and no exacerbation of psychiatric symptoms was observed during time of follow-up. Furthermore, an overall significant improvement of the self-estimated mood and satisfaction was observed in both groups (Manova: f = 1.26, p < 0.0001). CONCLUSIONS: The results 2 years after sleeve gastrectomy in stable patients with schizophrenia and after an adequate psychological evaluation were encouraging and comparable to the outcome in mentally healthy patients.