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Motion Modelling and Analysis Group

School of Biomedical Engineering and Imaging Sciences,
King's College London

Motion Analysis

Using Machine Learning to Identify Noninvasive Motion-Based Biomarkers of Cardiac Function

(Funded by EPSRC grants EP/K030310/1, EP/K030523/1 and EP/L015226/1)

This project aims to apply state-of-the-art imaging, motion analysis and machine learning techniques to characterise the motion of the heart as it beats. A population-based, spatio-temporal atlas of cardiac motion has been developed that enables subtle variations in cardiac motion to be identified and quantified. This analysis forms the basis for the development of novel noninvasive biomarkers for the stratification of patients with cardiovascular disease. A notable success to date has been the development of biomarkers that can predict response to cardiac resynchronisation therapy with a success rate of 91% (Peressutti et al, Medical Image Analysis), whilst the current clinical selection criteria result in around one third of patients not responding positively to the treatment. More recent work has focused on the incorporation of multi-modal data into the atlas, in the form of MR and US imaging (Puyol-Anton et al, Medical Image Analysis) and the use of the spatio-temporal atlas to identify the characteristic spatial scales of motion signatures (Sinclair et al, Medical Image Analysis).

Tagged MR based motion tracking Tagged MR based motion tracking
Motion-based biomarkers: (left-to-right) tagged MR based motion tracking; motion fields shown on left ventricular mesh.

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Automated Quality Control of Cine MR Data From the UK Biobank Data Set

(Funded by EPSRC grant EP/P001009/1)

Recently large-scale databases of imaging and non-imaging data have started to become more widely available. Such databases have great potential for learning more about clinical risk factors and disease processes. The UK Biobank will eventually consist of data from 100,000 volunteers and contains cine and tagged cardiac MR data as well as a wide range of other personal data. However, the size of this database means that it will inevitably contain poor quality data, which could impact upon any analysis performed upon the data unless the poor quality data can be excluded. Manual exclusion is tedious, time-consuming and subject to error. In this work we investigate the use of machine learning techniques for performing automated quality control of cine MR data.

The first technique aims to detect poorly planned 4-chamber cine MR images. One common feature of such images is the presence of the left ventricular outflow tract (LVOT) in the image. We trained a deep convolutional neural network (CNN) on a training set of images featuring good/poor planning. The resulting classifier achieved an accuracy of approximately 83%.

Automated identification of the LVOT
Automated identification of the left ventricular outflow tract (LVOT).

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Subsequent work focused on the presence of motion-related artefacts in the cine MR images. Such artefacts can be caused by mistriggering due to a faulty ECG signal, or by patient breathing during the acquisition. They typically appear as blurring artefacts in the images. Again, UK Biobank data were used to train a CNN classifier to identify these artefacts. However, there is high class imbalance with this problem - there are many more good quality images than artefact images. Class imbalance in training data is known to lead to bias in the performance of the resulting classifier. To address this problem we developed a novel technique for augmenting the training data using synthetically generated artefact images. These images were generated in k-space using a similar process to that which causes the artefacts - by replacing k-space profiles for a specific frame with profiles from different frames. By augmenting the data in this way we were able to achieve 98% classification accuracy with high precision and recall.

Synthesis of motion artefacts
Synthesis of motion artefacts by replacing k-space profiles with profiles from a different cardiac phase.

Investigating Factors Influencing Cardiac Health From the UK Biobank Data Set

(Funded by EPSRC grant EP/L015226/1)

As an example application of the automated quality control techniques discussed above, we exploited the clinical information contained in the UK Biobank database to investigate factors associated with cardiac health. This involved forming a motion atlas from around 6000 subjects and statistically analysing the links between atlas-derived motion descriptors and the clinical information. Associations were found with body fat percentage, basal metabolic rate, hypertension, smoking status and alcohol intake frequency, and these associations were not identifiable by analysis of the conventional metric of ejection fraction.

Associations of clinical data with atlas-based motion descriptors
Associations of clinical information with atlas-based motion descriptors derived from the UK Biobank database.

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