Practical 6 – Motion simulation
Perform MRI simulations to characterise the appearance of artifacts for different motion patterns and sampling trajectories used.
Start using the Shepp-Logan phantom, later evaluate your framework using suitable MR data downloaded from open-source on the internet. 开始使用Shepp-Logan phantom，然后使用从互联网开源下载的合适MR数据评估您的框架。
In class (not assessed)
• Write code to simulate a simple translational shift of the object. Evaluate the artifact appearance as a function of translational shift amplitude and direction. 编写代码来模拟对象的简单平移。通过平移位移幅度和方向来评估伪影。
• Simulate a 2-shot cartesian acquisition by dividing the k-space acquisition along ky in two halfs. Simulate inter-view translational motion occurring between shot 1 and 2. 沿ky方向将k空间分成两半，模拟一个两次笛卡尔采样。模拟第1采集和第2采集之间的视图间平移运动。
• Simulate other 2-shot cartesian acquisitions, e.g. acquiring every 2nd shot along ky, or divide in two along kx .模拟其他2次笛卡尔采样，例如沿着ky每2行获取一次，或者将kx分成2次采集
Homework
Part 1: Simulation framework to evaluate different motion patterns and sampling trajectories in multi-shot imaging 评估多次成像中不同运动模式和采样轨迹的模拟模型
• Extend your code from 2-shot to multi-shot sequential cartesian sampling. Visualise and discuss the appearance of artifacts depending on number of shots, motion amplitude and sampling pattern (e.g. as defined in number 3 above). 将您的代码从2次连续笛卡尔采样扩展到多次连续笛卡尔采样。从采集数量，运动幅度和采样模式三个角度(如上文第3段所定义)，来讨论伪影的样子。
• Simulate different inter-view motion patterns (considering translational shifts only), e.g. bulk motion, sinusoidal motion patterns, random motion. Visualise and discuss your findings. 模拟不同的视图间运动模式(只考虑平移移动)，例如体块运动、正弦运动模式、随机运动。讨论你的发现。
• Simulate other multi-shot sampling trajectories, e.g. readout-segmented EPI, radial, spiral, PROPELLER. 模拟其他多次采样轨迹，如读出方向上的分段EPI、辐射状的、螺旋状的、PROPELLER成像序列。
• Develop suitable visualisations and quantitative metrics to evaluate and quantify the appearance of artifacts. Using these visualisations and metrics, evaluate different motion patterns and trajectories. Display and summarise your results. 开发合适的可视化和量化度量来评估和量化所产生的伪影。使用这些可视化和度量，评估不同的运动模式和轨迹、并总结结果。
Part 2: Including a low-resolution image-navigator :低分辨率图像navigator
• Design and simulate a multi-shot acquisition interleaved with a 2D-low res image navigator. 设计并模拟一个使用2d低分辨率图像navigator 的MRI多次采集序列。
• Implement a suitable algorithm to detect translational motion shifts from the navigator data. 实现一种合适的算法来检测来自导航数据的平移运动位移。
• Evaluate trade-offs in your implementation (scan time efficiency, navigator image resolution to detect motion trace). 评估上面做的算法中的优缺点(比如：扫描时间效率、用于检测运动轨迹的导航器图像分辨率)。
Marking (total 50)
Usefulness of submitted pseudo-code (appropriate framework, understandable, flexibility to incorporate all aspects of the tutorial, highlighting key aspects of the implementation framework, added useful comments)
5
Simulations using different motion patterns and different sampling trajectories, using appropriate visualisations in a structured report form (e.g. plotting multi-shot k-space sampling patterns, plotting motion traces, motion trace applied to multi-shot k-space patterns, visualising in k-space phase-corruption patterns)
20
Evaluate artefact appearance: Using appropriate visualisation and quantification metrics
5
Visualisations of final key findings and interpretation of results
10
Part 2 (same criteria as above)
10