Adaptive iterative dose reduction (AIDR) 3D in low dose CT abdomen-pelvis: effects on image quality and radiation exposure

The widespread use of computed tomography (CT) has increased the medical radiation exposure and cancer risk. We aimed to evaluate the impact of AIDR 3D in CT abdomen-pelvic examinations based on image quality and radiation dose in low dose (LD) setting compared to standard dose (STD) with filtered back projection (FBP) reconstruction. We retrospectively reviewed the images of 40 patients who underwent CT abdomen-pelvic using a 80 slice CT scanner. Group 1 patients (n=20, mean age 41 ± 17 years) were performed at LD with AIDR 3D reconstruction and Group 2 patients (n=20, mean age 52 ± 21 years) were scanned with STD using FBP reconstruction. Objective image noise was assessed by region of interest (ROI) measurements in the liver and aorta as standard deviation (SD) of the attenuation value (Hounsfield Unit, HU) while subjective image quality was evaluated by two radiologists. Statistical analysis was used to compare the scan length, CT dose index volume (CTDIvol) and image quality of both patient groups. Although both groups have similar mean scan length, the CTDIvol significantly decreased by 38% in LD CT compared to STD CT (p<0.05). Objective and subjective image quality were statistically improved with AIDR 3D (p<0.05). In conclusion, AIDR 3D enables significant dose reduction of 38% with superior image quality in LD CT abdomen-pelvis

An Unsupervised Learning Model for Deformable Medical Image Registration

We present a fast learning-based algorithm for deformable, pairwise 3D medical image registration. Current registration methods optimize an objective function independently for each pair of images, which can be time-consuming for large data. We define registration as a parametric function, and optimize its parameters given a set of images from a collection of interest. Given a new pair of scans, we can quickly compute a registration field by directly evaluating the function using the learned parameters. We model this function using a convolutional neural network (CNN), and use a spatial transform layer to reconstruct one image from another while imposing smoothness constraints on the registration field. The proposed method does not require supervised information such as ground truth registration fields or anatomical landmarks. We demonstrate registration accuracy comparable to state-of-the-art 3D image registration, while operating orders of magnitude faster in practice. Our method promises to significantly speed up medical image analysis and processing pipelines, while facilitating novel directions in learning-based registration and its applications. Our code is available at https://github.com/balakg/voxelmorph .Comment: 9 pages, in CVPR 201

Passively mode-locked laser using an entirely centred erbium-doped fiber

This paper describes the setup and experimental results for an entirely centred erbium-doped fiber laser with passively mode-locked output. The gain medium of the ring laser cavity configuration comprises a 3 m length of two-core optical fiber, wherein an undoped outer core region of 9.38 μm diameter surrounds a 4.00 μm diameter central core region doped with erbium ions at 400 ppm concentration. The generated stable soliton mode-locking output has a central wavelength of 1533 nm and pulses that yield an average output power of 0.33 mW with a pulse energy of 31.8 pJ. The pulse duration is 0.7 ps and the measured output repetition rate of 10.37 MHz corresponds to a 96.4 ns pulse spacing in the pulse train

변형률 수명 방법과 파괴역학 접근 에 의한 적층 제조 된 AlSi10Mg 의 피로수명 평가

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 항공우주공학과, 2021. 2. 윤군진.The alloy manufactured by the selective laser melting method, which is widely known in 3D printing technology / Additive manufacturing (AM), has advantages in design flexibility and production efficiency compared to the conventional process. Titanium and aluminum (Al) alloys processed by AM are commonly used in aviation and medical fields. However, in this process, heat treatment is performed to remove internal defects such as pores in the alloy, although complete removal is inevitable. For this reason, the fatigue life of AM alloy should be evaluated in consideration of the effect of pores. In this thesis, the fatigue life was analyzed by generating a representative volume element (RVE) with pores as computed tomography (CT) image of an Al alloy processed by AM. For fatigue life analysis, the strain-life method was applied to the crack initiation cycle and Fracture Mechanical approach was applied to the crack propagation cycle. RVE was generated by increasing the image's quality and separating the pores of the CT image through an image processing algorithm. Stress and strain were obtained through 3D finite element (FE) analysis by applying periodic boundary conditions to multiple RVEs for statistical analysis. The value required for fatigue life analysis and FE analysis was calculated using commercial software ABAQUS, and FE-SAFE and the total fatigue life was calculated through post-processing and numerical integration by Python script and MATLAB code. As a result of analyzing the relationship between the pore information of the RVE and the fatigue life, the volume of pores was a critical factor, and compared with the experimental results of reference. It was good agreement that the fatigue life values of multiple RVEs had a somewhat similar range3D 프린팅 기술 / 적층제조 에서 널리 알려져 있는 선택적 레이저 용융방식으로 제조된 합금은 기존의 공정방식에 비해 설계의 유연성과 생산 효율성의 장점을 가진다. 특히 적층제조로 공정된 티타늄과 알루미늄 합금은 항공 및 의료분야에서 많이 이용된다. 하지만 이 공정과정에서 합금에 생기는 기공과 같은 내부적 결함을 제거하기 위해 열처리 과정을 진행하나 완벽한 제거는 불가피하다. 따라서 적층제조의 합금의 피로수명은 기공의 영향을 고려해서 평가되어야 한다. 본 논문에서 적층제조 방식으로 공정된 알루미늄 합금의 단층촬영(CT) 이미지로 기공이 포함된 대표체적요소(RVE)를 만들어 이에 대해 피로수명을 해석하였다. 피로수명 해석을 위해 균열 시작주기는 변형률-수명 방법을, 균열 성장주기는 파괴역학 접근을 적용하였다. RVE는 CT 이미지를 이미지 처리 알고리즘을 통해 이미지의 품질을 증가시키고, 기공의 입자를 분리시켜 만들었다. 통계적 해석을 위해 다수의 RVE에 주기적 경계조건을 적용하여 3차원 유한요소 해석을 통해 응력과 변형률을 구했다. 유한요소 해석과 피로수명 해석에 필요한 값들을 상용 소프트웨어인 ABAQUS 와 FE-SAFE를 이용하였고, Python 과 MATLAB을 통해 후처리 및 수치 적분으로 총 피로수명을 계산하였다. RVE의 기공 정보와 피로수명의 관계를 분석한 결과 기공의 부피에 가장 큰 영향을 받았으며, 문헌의 실험 결과값과 비교하여 다수의 RVE의 피로수명 값과 어느 정도 비슷한 범위를 가지는 것을 확인할 수 있었다.Abstract i Table of contents iv List of figures v List of tables vi 1. Introduction 1 1.1. Motivation 1 1.2. Objectives and Thesis Overview 6 2. Theoretical background 8 2.1. Representative volume element approach 8 2.2. Fatigue life prediction 11 2.2.1. Strain-life method 12 2.2.2. Fracture Mechanical approach 16 3. Microstructure modeling including pores 21 3.1. Material properties 21 3.2. Image processing 23 4. Fatigue Life Prediction Methods 26 4.1. Fatigue crack initiation model considering K_t 26 4.2. Fatigue crack growth model 29 5. Result and Discussion 34 5.1. Simulation result of crack initiation model 34 5.2. Simulation result of crack propagation model 43 5.2.1. Fatigue crack growth rate 43 5.2.2. Computational result of N_p 46 5.3. Estimate of Total fatigue life 47 5.3.1. Total fatigue life (N_f) 47 5.3.2. Validation of N_f with simulation results 49 5.3.3. The effect of pores on fatigue life 51 6. Conclusion and future works 52 6.1. Conclusion 52 6.2. Future works 53 국문초록 61Maste