Self-supervised Physics-based Denoising for Computed Tomography

Computed Tomography (CT) imposes risk on the patients due to its inherent X-ray radiation, stimulating the development of low-dose CT (LDCT) imaging methods. Lowering the radiation dose reduces the health risks but leads to noisier measurements, which decreases the tissue contrast and causes artifacts in CT images. Ultimately, these issues could affect the perception of medical personnel and could cause misdiagnosis. Modern deep learning noise suppression methods alleviate the challenge but require low-noise-high-noise CT image pairs for training, rarely collected in regular clinical workflows. In this work, we introduce a new self-supervised approach for CT denoising Noise2NoiseTD-ANM that can be trained without the high-dose CT projection ground truth images. Unlike previously proposed self-supervised techniques, the introduced method exploits the connections between the adjacent projections and the actual model of CT noise distribution. Such a combination allows for interpretable no-reference denoising using nothing but the original noisy LDCT projections. Our experiments with LDCT data demonstrate that the proposed method reaches the level of the fully supervised models, sometimes superseding them, easily generalizes to various noise levels, and outperforms state-of-the-art self-supervised denoising algorithms.Comment: 13 pages, 12 figures. Under revie

Transmiocardial laser revascularization in combination with bone marrow cells implantation in the ischemic heart disease surgery: long-term results

Background ― The problem of incomplete myocardial revascularization for diffuse and distal lesions of the myocardium is still relevant. We assessed the clinical and instrumental long-term results of autologous bone marrow cell (BMC) implantation in laser channels in ischemic heart disease with diffuse and distal coronary disease. Material and Methods ― In 2007 and 2008, 35 ischemic heart disease (IHD) patients with diffuse and distal coronary disease during coronary artery bypass grafting (CABG) underwent BMC implantation in laser channels in the clinic of National Medical Research Center n.a. E.N. Meshalkin (Novosibirsk, Russia). This group was named as “BMC group”. The Control group consisted of 29 patients who underwent only CABG. Clinical and instrumental assessment of the method's effect was carried out at two weeks, six months, and six years after surgery. Long-term follow-up was performed only in 30 patients from the BMC group. Results ― After six months postoperatively, the severity of angina and heart failure based on Canadian Cardiovascular Society functional class (CCS FC) and the New York Heart Association functional class (NYHA FC) was significantly less in the BMC group than in the Control group (p=0.03 for CCS FC and p=0.04 for NYHA FC). Six years after surgery angina and heart insufficiency were at the same level. According to perfusion scintigraphy, there was a slight decrease of stable perfusion defects (SPD) in the immediate postoperative period and a more pronounced SPD reduction at six months after surgery. In BMC group, the SPD value before surgery was 18.4 (12.8, 22.4) %, 16.1 (11.6, 19.3) % at two weeks after the operation, and 13.2 (8.5, 17.3) % after six months. In the long-term period (six years), SPD was 11.9 (8.7, 14.2) % (p=0.047). A similar pattern was observed in the analysis of transient perfusion defects: baseline was 29.3 (22.1, 34.1) %, 13.1 (11.2, 16.5) % at six months, and 17.0 (14.3, 20.5) % in the long term (p=0.047). Left ventricular ejection fraction before surgery was 51 (49, 57) %, 54 (49, 57) % at two weeks after the operation, 54 (49, 58) % at six months, and 52 (49, 58) % after six years. The dynamics are not statistically significant (p=0.068). Conclusion ― Autologous BMC implantation in laser channels is an effective method of IHD surgical treatment if it is impossible to perform direct myocardial revascularization. The indirect revascularization effect is formed in the first six months after surgery and remains at the same level for six years

Brain Activations and Functional Connectivity Patterns Associated with Insight-Based and Analytical Anagram Solving

Insight is one of the most mysterious problem-solving phenomena involving the sudden emergence of a solution, often preceded by long unproductive attempts to find it. This seemingly unexplainable generation of the answer, together with the role attributed to insight in the advancement of science, technology and culture, stimulate active research interest in discovering its neuronal underpinnings. The present study employs functional Magnetic resonance imaging (fMRI) to probe and compare the brain activations occurring in the course of solving anagrams by insight or analytically, as judged by the subjects. A number of regions were activated in both strategies, including the left premotor cortex, left claustrum, and bilateral clusters in the precuneus and middle temporal gyrus. The activated areas span the majority of the clusters reported in a recent meta-analysis of insight-related fMRI studies. At the same time, the activation patterns were very similar between the insight and analytical solutions, with the only difference in the right sensorimotor region probably explainable by subject motion related to the study design. Additionally, we applied resting-state fMRI to study functional connectivity patterns correlated with the individual frequency of insight anagram solutions. Significant correlations were found for the seed-based connectivity of areas in the left premotor cortex, left claustrum, and left frontal eye field. The results stress the need for optimizing insight paradigms with respect to the accuracy and reliability of the subjective insight/analytical solution classification. Furthermore, the short-lived nature of the insight phenomenon makes it difficult to capture the associated neural events with the current experimental techniques and motivates complementing such studies by the investigation of the structural and functional brain features related to the individual differences in the frequency of insight-based decisions

Muon Radiography Method for Non-Invasive Probing an Archaeological Site in the Naryn-Kala Citadel

The paper presents the test experiment to investigate one of UNESCO’s (United Nations Educational, Scientific and Cultural Organization) world heritage objects, an archaeological site in the Naryn-Kala citadel (Derbent, Republic of Dagestan, Russian Federation) hidden under the ground’s surface. The function of the site could be revealed by the muon radiography studies. Several nuclear emulsion detectors were exposed for two months inside the site at a depth about 10 m from the modern surface. The use of nuclear emulsions as probing radiation detectors combined with the potential of modern image analysis methods provides for a uniquely high resolution capacity of recording instrumentation and 3D reconstruction of the internal structure of the investigated object. Here we present the experiment and data analysis details and the first results