Numerical methods for coupled reconstruction and registration in digital breast tomosynthesis.

Digital Breast Tomosynthesis (DBT) provides an insight into the fine details of normal fibroglandular tissues and abnormal lesions by reconstructing a pseudo-3D image of the breast. In this respect, DBT overcomes a major limitation of conventional X-ray mam- mography by reducing the confounding effects caused by the superposition of breast tissue. In a breast cancer screening or diagnostic context, a radiologist is interested in detecting change, which might be indicative of malignant disease. To help automate this task image registration is required to establish spatial correspondence between time points. Typically, images, such as MRI or CT, are first reconstructed and then registered. This approach can be effective if reconstructing using a complete set of data. However, for ill-posed, limited-angle problems such as DBT, estimating the deformation is com- plicated by the significant artefacts associated with the reconstruction, leading to severe inaccuracies in the registration. This paper presents a mathematical framework, which couples the two tasks and jointly estimates both image intensities and the parameters of a transformation. Under this framework, we compare an iterative method and a simultaneous method, both of which tackle the problem of comparing DBT data by combining reconstruction of a pair of temporal volumes with their registration. We evaluate our methods using various computational digital phantoms, uncom- pressed breast MR images, and in-vivo DBT simulations. Firstly, we compare both iter- ative and simultaneous methods to the conventional, sequential method using an affine transformation model. We show that jointly estimating image intensities and parametric transformations gives superior results with respect to reconstruction fidelity and regis- tration accuracy. Also, we incorporate a non-rigid B-spline transformation model into our simultaneous method. The results demonstrate a visually plausible recovery of the deformation with preservation of the reconstruction fidelity

Performance assessment of tariff-based air source heat pump load shifting in a UK detached dwelling featuring phase change-enhanced buffering

Using a detailed building simulation model, the amount of thermal buffering, with and without phase change material (PCM), needed to time-shift an air source heat pump's operation to off-peak periods, as defined by the UK 'Economy 10' tariff, was investigated for a typical UK detached dwelling. The performance of the buffered system was compared to the case with no load shifting and with no thermal buffering. Additionally, the load shifting of a population of buffered heat pumps to off-peak periods was simulated and the resulting change in the peak demand on the electricity network was assessed. The results from this study indicate that 1000 L of hot water buffering or 500 L of PCM-enhanced hot water buffering was required to move the operation of the heat pump fully to off-peak periods, without adversely affecting the provision of space heating and hot water for the end user. The work also highlights that buffering and load shifting increased the heat pump's electrical demand by over 60% leading to increased cost to the end user and increased CO2 emissions (depending on the electricity tariff applied and time varying CO2 intensity of the electricity generation mix, respectively). The study also highlights that the load-shifting of populations of buffered heat pumps wholly to off-peak periods using crude instruments such as tariffs increased the peak loading on the electrical network by over 50% rather than reducing it and that careful consideration is needed as to how the load shifting of a group of heat pumps is orchestrated

Ray model and ray-wave correspondence in coupled optical microdisks

We introduce a ray model for coupled optical microdisks, in which we select coupling-efficient rays among the splitting rays. We investigate the resulting phase-space structure and report island structures arising from the ray-coupling between the two microdisks. We find the microdisks's refractive index to influence the phase-space structure and calculate the stability and decay rates of the islands. Turning to ray-wave correspondence, we find many resonances to be directly related to the presence of these islands. We study the relation between the (ray-picture originating) island structures and the (wave-picture originating) spectral properties of resonances, especially the leakiness of the resonances which is represented as the imaginary part of the complex wave vector.Comment: 9 pages, 8 figure

Load management of heat pumps using phase change heat storage

In the UK, heat pumps are often promoted as the means to provide low-carbon space heating and hot water for future dwellings as the electricity supply decarbonises. However, a major issue with growing heat pump use would be the additional load that this could place on the electrical network at times of peak heat and power demand. A means to alleviate potential demand problems is to stagger the operating times of heat pumps by integrating them with thermal buffering. However, focusing on the domestic sector, substantial volumes of thermal storage would be required to achieve the necessary level of operational flexibility in heat pumps and this poses a particular problem in the UK where the floor areas of urban dwellings are small. Thermal storage featuring phase change material (PCM) offers the potential of more volumetrically efficient heat buffering, which may be more suitable for integration into domestic heating systems. In this paper, the potential to shift the operating time of heat pumps integrated with phasechange- material-enhanced thermal storage is assessed and compared to conventional hot water storage, where the limits of flexible operation are determined by the comfort and hot water needs of the end-user. The results indicate that the use of PCM-enhanced thermal storage can reduce the volume of the buffering required for load shifting by up to 3 times. However, thermal buffering with load shifting can increase heat pump energy demand and (at present) in the UK results in increased emissions and cost penalties for the end user

A small-scale process for manufacturing woodwool/cement slabs in developing countries

Woodwool/cement slabs are made from a mixture of shredded timber (woodwool) and cement, shaped or formed by pressure into required thicknesses and sizes. They are a well-known product already used in many countries around the world. This bulletin outlines the work undertaken by the Natural Resources Institute (NRI) on the development of a low-cost woodwool/cement slab manufacturing process appropriate for conditions in developing countries. Typically, 500 slabs (35m3 ) can be produced per week on a single shift employing 25 people. Demonstration plants have been introduced into Malawi and Zambia. Included in the bulletin are historical background information, details and test data on assessing the suitability of timbers, a description of the process developed and the reasons for the processing techniques employed. Methods of handling and the use of the slabs in the construction industry, particularly in relation to the lower-cost housing market in Zambia, are also outlined. One of the main attractions of the NRI small-scale wood wool/ cement slab process plant is the relatively low initial capita! investment required compared with larger, less labour-intensive processes used in Europe a0d'elsewhere. The principal aim has been to develop a low capital cost, labour-intensive plant which could largely be constructed using local manufacturing and craft skills, and operated and maintained on a routine basis by trained personnel

Pulmonary Lobe Segmentation with Probabilistic Segmentation of the Fissures and a Groupwise Fissure Prior

A fully automated, unsupervised lobe segmentation algorithm is presented based on a probabilistic segmentation of the fissures and the simultaneous construction of a population model of the fissures. A two-class probabilistic segmentation segments the lung into candidate fissure voxels and the surrounding parenchyma. This was combined with anatomical information and a groupwise fissure prior to drive non-parametric surface fitting to obtain the final segmentation. The performance of our fissure segmentation was validated on 30 patients from the COPDGene cohort, achieving a high median F1-score of 0:90 and showed general insensitivity to filter parameters. We evaluated our lobe segmentation algorithm on the LOLA11 dataset, which contains 55 cases at varying levels of pathology. We achieved the highest score of 0:884 of the automated algorithms. Our method was further tested quantitatively and qualitatively on 80 patients from the COPDGene study at varying levels of functional impairment. Accurate segmentation of the lobes is shown at various degrees of fissure incompleteness for 96% of all cases. We also show the utility of including a groupwise prior in segmenting the lobes in regions of grossly incomplete fissures

Challenges in the registration of serial CT images from lung radiotherapy patients

Radiation induced lung damage is an unwanted side effect of curative radiotherapy. Radiological findings are often used as indicators of lung damage, which is identifiable as changes in the baseline imaging features (e.g., anatomy shape, intensity and texture). In this work we qualitatively investigate the challenges in registering baseline and followup CT images acquired 12 months after radiotherapy

Combined Reconstruction and Registration of Digital Breast Tomosynthesis

Digital breast tomosynthesis (DBT) has the potential to en- hance breast cancer detection by reducing the confounding e ect of su- perimposed tissue associated with conventional mammography. In addi- tion the increased volumetric information should enable temporal datasets to be more accurately compared, a task that radiologists routinely apply to conventional mammograms to detect the changes associated with ma- lignancy. In this paper we address the problem of comparing DBT data by combining reconstruction of a pair of temporal volumes with their reg- istration. Using a simple test object, and DBT simulations from in vivo breast compressions imaged using MRI, we demonstrate that this com- bined reconstruction and registration approach produces improvements in both the reconstructed volumes and the estimated transformation pa- rameters when compared to performing the tasks sequentially