Synthesis of Realistic Simultaneous Positron Emission Tomography and Magnetic Resonance Imaging Data

The investigation of the performance of different positron emission tomography (PET) reconstruction and motion compensation methods requires accurate and realistic representation of the anatomy and motion trajectories as observed in real subjects during acquisitions. The generation of well-controlled clinical datasets is difficult due to the many different clinical protocols, scanner specifications, patient sizes, and physiological variations. Alternatively, computational phantoms can be used to generate large data sets for different disease states, providing a ground truth. Several studies use registration of dynamic images to derive voxel deformations to create moving computational phantoms. These phantoms together with simulation software generate raw data. This paper proposes a method for the synthesis of dynamic PET data using a fast analytic method. This is achieved by incorporating realistic models of respiratory motion into a numerical phantom to generate datasets with continuous and variable motion with magnetic resonance imaging (MRI)-derived motion modeling and high resolution MRI images. In this paper, data sets for two different clinical traces are presented, ¹⁸F-FDG and ⁶⁸Ga-PSMA. This approach incorporates realistic models of respiratory motion to generate temporally and spatially correlated MRI and PET data sets, as those expected to be obtained from simultaneous PET-MRI acquisitions

Synergistic motion compensation strategies for positron emission tomography when acquired simultaneously with magnetic resonance imaging

Subject motion in positron emission tomography (PET) is a key factor that degrades image resolution and quality, limiting its potential capabilities. Correcting for it is complicated due to the lack of sufficient measured PET data from each position. This poses a significant barrier in calculating the amount of motion occurring during a scan. Motion correction can be implemented at different stages of data processing either during or after image reconstruction, and once applied accurately can substantially improve image quality and information accuracy. With the development of integrated PET-MRI (magnetic resonance imaging) scanners, internal organ motion can be measured concurrently with both PET and MRI. In this review paper, we explore the synergistic use of PET and MRI data to correct for any motion that affects the PET images. Different types of motion that can occur during PET-MRI acquisitions are presented and the associated motion detection, estimation and correction methods are reviewed. Finally, some highlights from recent literature in selected human and animal imaging applications are presented and the importance of motion correction for accurate kinetic modelling in dynamic PET-MRI is emphasized. This article is part of the theme issue ‘Synergistic tomographic image reconstruction: part 2’

Fault diagnosis for uncertain networked systems

Fault diagnosis has been at the forefront of technological developments for several decades. Recent advances in many engineering fields have led to the networked interconnection of various systems. The increased complexity of modern systems leads to a larger number of sources of uncertainty which must be taken into consideration and addressed properly in the design of monitoring and fault diagnosis architectures. This chapter reviews a model-based distributed fault diagnosis approach for uncertain nonlinear large-scale networked systems to specifically address: (a) the presence of measurement noise by devising a filtering scheme for dampening the effect of noise; (b) the modeling of uncertainty by developing an adaptive learning scheme; (c) the uncertainty issues emerging when considering networked systems such as the presence of delays and packet dropouts in the communication networks. The proposed architecture considers in an integrated way the various components of complex distributed systems such as the physical environment, the sensor level, the fault diagnosers, and the communication networks. Finally, some actions taken after the detection of a fault, such as the identification of the fault location and its magnitude or the learning of the fault function, are illustrated

Modeling Sliding Contact of Rough Surfaces with Molecularly Thin Lubricants

The sliding contact between two rough surfaces in the presence of a molecularly thin lubricant layer is investigated. Under very high shear rates, the lubricant is treated as a semi-solid layer with normal and lateral shear-dependent stiffness components obtained from experimental data. The adhesive force in the presence of lubricant is also adapted from the Sub-boundary lubrication model and improved to account for variation in surface energy with penetration into the lubricant layer. A model is then proposed, based on the Improved sub-boundary lubrication model, which accounts for lubricant contact and adhesion and its validity is discussed. The model is in good agreement with published experimental measurements of friction in the presence of molecularly thin lubricant layers and suggests that a molecularly thin lubricant bearing could be successfully used to reduce solid substrate damage at the interface.

Passive Vibration Absorption for Extremely High Density Recording

A method is proposed for passive vibration absorption in hard-disk drives during transient events such as the coming into proximity of the rotating disk within the context of thermal fly-height control nanotechnology or external shock. The method uses a nonlinear energy sink at the center of mass of the slider that can absorb energy over a wide range of excitation frequencies. Its feasibility and performance are investigated through a 4-degree-of-freedom dynamic model of the head-disk interface used to predict head-disk clearance and vibrations.

Optimization of thermal fly-height control slider geometry for Tbit/in^2 recording

Magnetic storage advances including thermal fly-height control (TFC) technology were able to reduce the clearance between the read/write elements of the slider and the disk surface to increase the recording density of hard disk drives without compromising the stability of the head–disk interface (HDI). Sliders employing TFC technology are designed for flying recording and can yield clearances of few nanometers. However, it is estimated that TFC technology alone cannot provide the even smaller clearances necessary to achieve Tbit/in^2 recording densities primarily due to the presence of instability-inducing vibrations at the HDI. In this work we perform optimization of the geometry of TFC technology sliders to achieve extremely high-density recording. We propose a flyability parameter coupled with a dynamic, contact mechanics-based friction model of the HDI that accounts for TFC geometry and its influence on the HDI dynamics. Optimization results are analyzed and an operating actuation range is identified that can yield Tbit/in^2 recording densities with Angstrom-level clearance and minimized vibrations while also accounting for manufacturing and operational tolerances. This allows for light (lubricant) contact or ‘surfing’ recording. The proposed methodology can be used to reduce wear at the interface and investigate the feasibility of contact recoding.