SimVis Medical - SimVis Imaging and Diagnosis

Three-Dimensional Echocardiography

The Peter Bourne Scholarship provided by the East Yorkshire and Hull Hospitals NHS Trust is providing funds for a PhD project concerning research into Three-Dimensional Echocardiography techniques.

More specifically, the PhD project concerns investigating and developing new computing-based techniques for three-dimensional echocardiography. These techniques will then be used to investigate new heart diagnosis methods for problems such as heart failure and coronary artery diseases. For example, four dimensional ultrasound and advanced computing, imaging and visualization techniques will be used to identify and quantify heart wall motion, heart synchrony and flow and obstruction in arteries.

The heart specialists involved in this project namely, Professor John GF Cleland and Dr Nikolay Nikitin have identified the following two problems in cardiology where new computer-based imaging and visualization tools are required. These are indicative of the application problems for which the new 3D echocardiography techniques associated with this PhD will be developed.

Three-Dimensional Stress Echocardiography in Patients with Suspected Heart Failure

Heart failure is a common problem affecting 1-2% of the population. 30-40% of patients will die within 6 months of diagnosis; thereafter the annual mortality is 7-10%. These patients will spend about 10% of their remaining life in hospital indicating both a high morbidity and a high rate of health care utilisation. Medical treatment for heart failure secondary to left ventricular systolic dysfunction is highly effective and may reduce mortality rate by over 50%. However, a considerable burden of disease, in terms of symptoms, morbidity and mortality remains and further therapeutic interventions are required. New interventions may attempt to target this population in general, as have ACE inhibitors and beta-blockers, or may attempt to target specific problems, such as ventricular dyssynchrony or myocardial stunning and hibernation. In addition, many patients have symptoms of heart failure but do not have left ventricular systolic dysfunction. In these patients, symptoms may be due to ‘diastolic’ dysfunction, valve disease or arrhythmias or may be due to problems other than heart failure.

A major problem with current standard investigation is that cardiac function is assessed at rest when symptoms and cardiac dysfunction may not be prominent. This has lead some to begin to investigate the role of routine stress imaging for the evaluation of suspected heart failure.

Rapid, accurate, user-friendly tools are required to distinguish: -
a) Patients with and without cardiac disease
b) The underlying resting pathophysiology (i.e. systolic versus diastolic, dyssynchrony)
c) The pathophysiological response to stress (i.e. conversion of diastolic to systolic heart failure, hibernating/stunned myocardium, myocardial ischaemia, induced dyssynchrony etc)

Until now, two-dimensional echocardiography has been the standard tool for the investigation of patients with suspected heart failure. However, standard echocardiography has many limitations. Global assessment of ventricular function is often inaccurate especially if the operator is not highly experienced. Quantitative assessment of volumes and ejection fraction is cumbersome and relatively inaccurate. Standard echocardiography is usually not performed under stress conditions and obtaining serial, accurate assessment of global function is complicated. Recent additions, such as tissue Doppler velocity imaging, may improve assessment of ventricular function during stress but require further assessment.

Three-dimensional echocardiography could resolve many of these problems, especially if combined with advanced edge detection techniques, tissue Doppler and advanced computing techniques to help describe and quantify regional wall motion and synchrony.

Three-Dimensional Echocardiographic Coronary Arteriography

Coronary artery disease is a major cause of morbidity and mortality in the population that may present as angina, myocardial infarction, heart failure or sudden death; the latter often heralded by one or more of the former conditions. A simple accurate test that could identify coronary obstruction would invaluable, especially if it can quantify its severity either anatomically, or even better, pathophysiologically.

Currently, two-dimensional echocardiographic imaging can often identify proximal coronary arteries and, to some extent, flow and obstruction can be quantified using Doppler techniques. Stress imaging can identify inducible regional wall motion abnormalities, an index of ischaemia. However, such techniques have not enjoyed widespread use because of the difficulties in imaging distal vessels, a problem induced partly by the ‘tomographic’ motion of the heart. This ‘tomographic’ effect might be put to advantage with three-dimensional real-time echocardiography. If anatomical imaging can be combined with stress-imaging (anatomical and Doppler) using three-dimensional echocardiography, this could become the simplest, quickest, least expensive tool for the evaluation of patients with suspected ischaemic heart disease. It would avoid the need for radioisotopes with all their inconvenience. It could be applied in patients in whom magnetic resonance imaging is contra-indicated. It is possible that the technique may have to be used using the trans-oesophageal route in many patients and this should be considered in any development programme (also in the above programme - although less so).

Stereographic 2D X-rays

This project extends previous work on stereographic projection of 2D x-ray images and aims to overcome a number of problems, namely: confusing stereo cues and distortion between stereo pairs.  Initially all x-ray images are undistorted using an accurate distortion correction technique.  A polygonal representation of a bone is fitted to the x-ray image, to approximate the bone surface.  The polygonal representation is rendered and mixed with the x-ray image to add surface detail, without obscuring salient features.  The procedure is repeated for the second x-ray image in the stereo pair.  Various projection techniques including toed, parallel and non-symmetric viewing frustums and eye separation have also been investigated for increased stereo perception.