Caliper placement is an integral part of ultrasound clinical workflow, e.g., kidney volume measurement. Automated approaches utilize anatomical segmentation followed by application-specific caliper placement. Robust clinical outcomes require confidence/uncertainty associated with such predictions be indicated. Conventional methods estimating uncertainty (MC Dropout, Deep Ensembles) with high computational load are impractical for deployment. We exploit the existence of uncertainty only on boundary pixels for any predicted segmentation. We utilize disagreement between independent predictions – region segmentation edge and direct boundary prediction, to identify uncertainty on anatomical boundary. We demonstrate our Boundary-Aware Segmentation Uncertainty (BASU) on cross-sections of kidney, correlating with ground-truth and clinician’s intuitions.
Images produced by CT systems with larger detector pixels often suffer from lower z resolution due to their wider slice sensitivity profile (SSP). Reducing the effect of SSP blur will result in resolution of finer structures and enables better clinical diagnosis. Hardware solutions such as dicing the detector cells smaller or dynami- cally deflecting the X-ray focal spot do exist to improve the resolution, but they are expensive. In the past, algorithmic solutions like deconvolution techniques also have been used to reduce the SSP blur. These model- based approaches are iterative in nature and are time consuming. Recently, supervised data-driven deep learning methods have become popular in computer vision for deblurring/deconvolution applications. Though most of these methods need corresponding pairs of blurred (LR) and sharp (HR) images, they are non-iterative during inference and hence are computationally efficient. However, unlike the model-based approaches, these methods do not explicitly model the physics of degradation. In this work, we propose Resolution Amelioration using Machine Adaptive Network (RAMAN), a self-supervised deep learning framework, that explicitly uses best of both learning and model based approaches. The framework explicitly accounts for the physics of degradation and appropriately regularizes the learning process. Also, in contrary to supervised deblurring methods that need paired LR and HR images, the RAMAN framework requires only LR images and SSP information for training, making it self-supervised. Validation of proposed framework with images obtained from larger detector systems shows marked improvement in image sharpness while maintaining HU integrity.
CT systems with large detector size suffer from lower z-resolution leading to pixelated images and inability to detect small structures thus adversely impacting the diagnosis and screening. Overlap reconstruction can partially reduce the stair-step artifacts but does not improve the effect of wider slice sensitivity profile (SSP) and thus continues to have reduced visibility of smaller structures. In this work, we propose a supervised deep learning method for z-resolution enhancement such that (a) the effective SSP of resulting image is reduced, (b) quantitative values of tissue (CT numbers) and tissue-contrast are preserved; (c) very limited noise enhancement and (d) improved tissue interface in bone/soft tissue. The proposed method devises a super resolution (SURE) network which is trained to map the low resolution (LR) slices to the corresponding high resolution (HR) slices. A 2D network is trained with sagittal and coronal slices with the LR-HR pair sets. The training is performed using ground truth HR slices obtained from high end systems, and the corresponding LR slices are synthesized by either using retro reconstruction with higher slice thickness and spacing or through averaging of slices in z-direction from HR images. The network is trained with both these types of images with helical acquisition volumes from a range of scanners. Qualitative and quantitative analysis is done on the predicted HR images and compared with the original HR images. FWHM for SSP of the predicted HR images reduced from ~0.98 to ~0.73, when the target was 0.64, thus improving the real z-resolution. HU distribution of different tissue types also showed stability in terms of mean value. Noise measured through standard deviation was slightly higher than the LR image but lower than that of original HR images. PSNR also showed consistent improvement on all the cases across 3 different systems.
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