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Aim

This 2 year study was designed to investigate whether spectral analysis of unprocessed ultrasound data could improve the accuracy of standard intravascular ultrasound (IVUS) images to discriminate between strongly echo-reflective vessel wall components i.e. calcium (Ca), dense fibrotic tissue (DFT), microcalcification (mCa) and moderate fibrosis (MFT) and weak echo-reflective sonolucent wall components i.e. lipid, media and loose fibrotic tissue (LFT). If such a discrimination was possible it would allow the optimal evaluation of 1) the immediate and long-term results of acute interventional strategies within the coronary, pulmonary, cerebral and peripheral vessels and 2) the sequential long-term evaluation of pharmacologic attempts at atheroma and muscle hypertrophy regression.

Summary

The award of this grant has enabled an advanced high frequency ultrasound imaging, data collection and analysis system to be produced. 299 sites in coronary artery specimens, mounted in an in vitro flow phantom arrangement, were examined both ultrasonically and histologically. Advanced statistical discrimination techniques were employed to classify the tissue types. By using 4 parameters from the spectrum of the backscattered ultrasound (Maximum Power, Mean Power, Slope and Y-axis Intercept) calcium, lipid pool and mixed fibrotic tissue could be distinguished non-subjectively with clinically useful sensitivities and specificities.

The in vivo studies were postponed when it was discovered that more powerful statistical analysis techniques (than had been initially thought) were required to classify the tissues.

The results of the present study demonstrate that an increase in the amount of extracellular collagen in the fibrotic intimal thickening leads to an increase in the amount of recorded backscattered energy. Further developments are being explored in terms of the scanning technique and the data analysis to see if the mixed fibrotic tissue can be classified further in subgroups of clinical importance. The system is also being developed for the study of plaque volume and the efficacy of angioplasty and drug therapy. A related area of research into thrombus formation and therapy is also underway.

A future role of intravascular ultrasound tissue characterisation may be as a tool to facilitate decision making with regards to therapeutic strategy, when choosing fibrinolytic treatment vs mechanical recanalisation, when selecting and optimising different interventional device types and sizes, and when considering secondary prophylaxis to treat coronary atherosclerosis. Plaque characterisation might also identify those plaques prone to rupture and vessel occlusion. Serial examinations of atherosclerotic lesions would provide additional insight into the pathogenetic mechanisms of coronary disease and would also allow the long-term follow-up of changes induced by lipid-lowering drugs. Double-blind studies on the predictive accuracy of these frequency based parameters and finally in vivo studies will eventually show whether spectral analysis of unprocessed data is robust enough to for use in clinical practice.

Publications from project

Articles

Kearney P., Ramo P., Spencer T., Shaw S., Starkey I., Sutherland G. "How important are image distortion artefacts when using mechanical intravascular ultrasound transducers?" British Heart Journal 1995; 73:43.

Kearney P., Ramo M. P., Starkey I. R., Shaw T. R. D., McMurray J., Sutherland G. R. "A Comprehensive Assessment of the Short Term Reproducibility of Intravascular Ultrasound Quantitation." Submitted to the British Heart Journal.

Kearney P., Ramo M. P., Spencer T., Shaw T. R. D., Starkey I. R., Sutherland G. R. "A Study of the Quantitative and Qualitative Impact of Catheter Shaft Angulation in a Mechanical Intravascular Ultrasound System." Ultrasound in Medicine and Biology. (Accepted).

Kearney P., Ramo M. P., Spencer T., Shaw T. R. D., Starkey I. R., Sutherland G.R. "An Analysis of the Reproducibility of Reference Lumen Quantitation with Intravascular Ultrasound in Stented Coronary Arteries".Catheterisation and Cardiovascascular Diagnosis. (Accepted).

T. Spencer, M. P. Ramo, D. M. Salter, T. Anderson, P. P. Kearney, G. R. Sutherland, K. A. A. Fox, and W. N. McDicken "Characterisation of atherosclerotic plaque by spectral analysis of intravascular ultrasound: an in vitro study with histological and radiological validation."Ultrasound in Medicine and Biology (In press).

M. Pauliina Ramo, Timothy Spencer, Peter P. Kearney, George R. Sutherland, Stuart T. R. D. Shaw, lan R. Starkey, W. Norman McDicken, Keith A. A. Fox. "Characterisation of red and white thrombus by intravascular ultrasound using radio frequency and videodensitometric data based texture analysis". Ultrasound in Medicine and Biology. (In press).

M. Pauliina Moore (nee Ramo), Timothy Spencer, Donald Salter, Peter P. Kearney, George R. Sutherland, Aleksandra Lange, Stuart T. R. D. Shaw, LAN R. Starkey and Keith A. A. Fox. "Characterisation of atherosclerotic morphology by spectral analysis of radiofrequency signal: An in vitro intravasular ultrasound study with histological and radiological validation". Heart. (Accepted).

Spencer T., Ramo M. P., Salter D., Sutherland G. R., Fox K. A. A. and McDicken W. N. "Characterisation of atherosclerotic plaque by spectral analysis of 30MHz intravascular ultrasound radiofrequency data". Proc. of the IEEE Ultrasonics Symposium, 1996. (In press).

Nailon W. H., McLaughlin S., Spencer T., Ramo M.P. "Comparative study of textural analysis techniques to characterise tissue from intravascular ultrasound". Proc. Of the IEEE International Conference of Image Processing, Switzerland. IEEE Signal Processing Society:USA, 1996. (In press).

Nailon W.H., McLaughlin S., Spencer T., Ramo M. P. "Intravascular ultrasound image interpretation". Proc. Of the International Conference on Pattern Recognition, Austria. IEEE Computer Society Press:USA, 1996. (In press).

Ramo M. P., Spencer T., Kearney P. P., Shaw T. R. D., Starkey I. R., McDicken W. N., and Fox K. A. A. "The in vitro characterisation of red and white thrombus and plasma with different age and composition by spectral analysis of intravascular ultrasound radiofrequency data". European Ultrasound. (Accepted).

Lange A., Palka P., Caso P., Fenn L. N., Olszewski R., Ramo M. P., Shaw T. R. D., Nowick A., and Sutherland G. "Doppler myocardial imaging versus B-mode grey scale imaging: A comparative in vitro and in vivo study into their relative efficacy in endocardial boundary detection".Ultrasound Med Biol . (In press).

Abstracts

Ramo M. P., Kearney P., Starkey I. R., Shaw T. R. D., McMurray J., Sutherland G. R. "Assessment of the reproducibility of reference lumen quantitation with IVUS in patients undergoing coronary stenting". 7th Essen-Mayo-Mainz Symposium. May 1995. Essen, FR6.

Kearney P. P., Ramo M. P., Starkey I., Shaw T. R. D., McMurray J., Sutherland G. R. "How reproducible is reference lumen quantitation with intravascular ultrasound in patients undergoing coronary stenting". European Heart Journal, XVIIth Congress of the Eur Society of Cardiology, Amsterdam 1995, vol 16, 203.

Kearney P. P., Ramo M. P., Spencer T., Shaw T. R. D., Starkey I., Sutherland G.R. "Assessment of the reproducibility of reference lumen quantitation with intravascular ultrasound in patients undergoing coronary stenting". 68th Annual Meeting of Am Heart Association, Anaheim, California, 1996.

Kearney P. P., Ramo M. P., Spencer T., Shaw T. R. D., Starkey I., Sutherland G. R. "The reproducibility of IVUS measurements in unselected video frames assessed in sequential catheter pullbacks and in separate analysis sessions". 68th Annual Meeting of Am Heart Association, Anaheim, California, 1996.

Kearney P., Ramo P., Shaw T., Starkey I., McMurray J., Sutherland G. "The reproducibility of IVUS measurements in unselected video frames assessed in sequential catheter pullbacks and in separate analysis sessions". Circulation 1995; 92:1-78

Kearney P., Ramo P., Shaw T., Starkey I., McMurray J., Sutherland G. "Assessment of the Reproducibility of Reference Lumen Quantitation with Intravascular Ultrasound in Patients Undergoing Coronary Stenting". Circulation 1995; 92:1-601.

Roth T., Koch L., Erbel R., Kearney P., Ramo P., Spencer T., Sutherland G. "Development of a system of intracoronary ultrasound based frequency dependant tissue characterisation". In: Proceedings of "Echocardiography 1995", Rotterdam, The Netherlands. June 1995

M. Pauliina Ramo, Timothy Spencer, George R. Sutherland, Peter Kearney, Norman W. McDicken, Keith A. A. Fox. "Analysis of Unprocessed Intravascular Ultrasound radiofrequency Data can characterise Red and White Thrombus of different age". The Journal of invasive Cardiology "Transcatheter Cardiovascular Therapetics 1996", abstract, in press.

M. Pauliina Ramo, Timothy Spencer, Peter Kearney, Aleksandra Lange, Przemyslaw Palka, Keith A. A. Fox, George R. Sutherland. "Can Ultrasound Texture Analysis distinguish between Red and White Thrombi: A Comparative Study of Intravascular Videodensitometric and Radiofrequency data". American Heart Journal, American College of Cardiology 1996, abstract, in press

Nobuyaki Komiyama, Jonas Metz, Peter Presuss, Lars Gullestad, Guy Haywood, Pauliina Ramo, Yock Paul, Peter Fizgerald. "Quantitative tissue characterisation of arteriosclerotic plaques and thrombus by intravascular ultrasound radio-frequency analysis". The Journal of invasive Cardiology "Transcatheter Cardiovascular therapeutics 1996", abstract, in press.

Pauliina Ramo, Timothy Spencer, George R. Sutherland, Donald M. Salter, Peter Kearney, David Lamb, T. R. D. Stuart Shaw, Norman W. McDicken, Raimund Erbel, Peter Fitzgerald. "Can Radiofrequency Data Analysis of Intravascular Ultrasound accurately characterise Coronary Atherosclerosis?" American Heart Journal, American College of Cardiology 1996, abstract, in press

Ramo M. P., Spencer T., Sutherland G. R., Salter D. M., Kearney P., Lamb D., Shaw T. R. D., and McDicken W. N. "Can Radiofrequency Data Analysis of Intravascular Ultrasound accurately differentiate sonolucent Coronary Atherosclerotic Plaques?" ESC Meeting, Birmingham 1996.

Moore (Ramo) M. P., Spencer T., Sutherland G. R., Kearney P. P., McDicken W. N. and Fox K. A. A. "Identification of intramural lipid by spectral analysis of IVUS radiofrequency data". European Society of Cardiology, 1997. (Accepted)

Reviews and Book Chapters

Kearney P. P., Ramo M. P., Spencer T., Shaw T. R. D., Starkey I., Sutherland G.R. "Ambiguities and artefacts in intravascular ultrasound imaging: a comprehensive review" 1995. (sent for publication).

Ramo P. and Spencer T. "Tissue characterisation". R. Erbel(Ed.) in: An Atlas for Intravascular Ultrasound. Martin Ownitz Publishers: London, 1997. (In press).