Non-invasive Cardiac Imaging: 2010 and Beyond
Article Outline
In this inaugural special edition on Cardiac Imaging for the journal, Heart Lung and Circulation a panel of expert authors review the state of the art in non-invasive cardiac imaging and also take a speculative glimpse into the future in the areas of echocardiography, cardiac computed tomography (CT), cardiac magnetic resonance (CMR) imaging/spectroscopy and nuclear cardiology with SPECT and PET.
Cardiac CT is increasing in slice capacity whilst reducing radiation dose; cardiac MR is exploring higher field strength and tissue characterisation; echocardiography is advancing in quantitation of strain and strain rate as well as true three-dimensional imaging; new fast solid state SPECT cameras are in the marketplace and cardiac PET has transitioned to PET CT tomographs for hybrid imaging. Cardiac imaging has progressed beyond form, function and blood flow into the realms of molecular imaging and atherosclerosis imaging to name two examples. The role of cardiac imaging now extends beyond the important areas of diagnosis and assessing prognosis into exciting domains involving patient selection and monitoring of increasingly sophisticated therapies including gene and cell based treatments for cardiac disease.
Dr de Graaf and colleagues from the University of Leiden [1] discuss the history and evolution of multi-slice CT angiography to its current status and place this within the context of diagnostic performance and radiation dose. As well as summarising clinical outcomes data (on which there is heavy emphasis in the present health environment), they extend their discussion beyond assessment of stenosis severity into the emerging and increasingly important application of plaque assessment. Lastly, they discuss the non-coronary applications for assessment of ventricular function, myocardial perfusion and valve structure.
Drs Bohl and Schulz-Menger from Berlin and Oxford discuss the clinical utility of CMR imaging in non-coronary heart disease and the unique role of CMR in myocardial tissue characterisation [2]. They cover a range of frequently challenging diagnostic entities including arrhythmogenic right ventricular dysplasia, dilated and hypertrophic cardiomyopathies, left ventricular non-compaction, Takotsubo cardiomyopathy, amyloidosis, Fabry's disease, myocarditis, Churg Strauss syndrome, sarcoidosis, cardiac iron overload and systemic lupus erythematosus involving the heart. The existing literature is summarised together with the authors’ own opinions and speculations.
Drs Puranik and colleagues from Sydney and London review the use of imaging modalities in adult patients with congenital heart disease [3]. They begin by positioning their discussion in the clinical context of increasing numbers of adult congenital heart disease patients in the community. They go on to evaluate the relative merits and limitations of echocardiography, CT and MR imaging in the common forms of adult congenital heart disease seen in clinical practice, including atrial and ventricular septal defects, aortic diseases, coronary artery anomalies and cyanotic congenital heart disease. They offer a practical approach to clinical investigation and management as well as integrating the technical issues, including limitations, of the available imaging modalities.
Drs Cheng and Selvanayagam from Oxford and Adelaide address the salient clinical and technical issues with cardiac MR imaging at higher field strengths beyond the 1.5
T currently routine in clinical imaging [4]. The article is underpinned by discussion of the technical issues and the existing clinical literature at 1.5T supplemented by the existing clinical and research data at 3T. They extend this with a look into the future for the existing applications of cardiac dimensions, function, perfusion and scar assessment, as well as potential newer uses such as metabolism, tagging and coronary arteriography.
Drs Holloway and Clarke report on the existing status and future potential for cardiac MR spectroscopy in clinical use [5]. They furnish technical details as to how the studies are performed, then review the existing animal and clinical data. P-31 spectroscopy is discussed in relation to heart failure, cardiomyopathies, ischaemia and valvular heart disease. Potential application of H-1, Na-23 and hyperpolarisation spectroscopy are outlined. The authors conclude by outlining the technical advances necessary prior to the broader implementation of spectroscopy in clinical cardiology.
Drs Leung and Ng from Sydney review the current status of quantitative strain and strain rate measurements using tissue Doppler and speckle tracking techniques in echocardiography in clinical practice [6]. They commence with the technical basis and applications and then systematically review the literature on normal values and the use of strain/strain rate measurements in detecting early changes in LV systolic function, in valvular regurgitation, myocardial viability, transmurality of myocardial infarction, quantification of stress echo, LV dyssynchrony, RV and LA function. The authors point out some of the technical demands and potential pitfalls in the performance of these techniques also. The authors stress the potential for these techniques as a way to quantify and thus increasingly objectify observations made visually in clinical echocardiography in the past.
Dr Marwick provides a review and valuable personal perspective on the current role and future directions of echocardiography in the rapidly developing world of multimodality imaging [7]. Echocardiography has always and will remain the most readily accessible and rapid imaging tool in clinical cardiology. The modality's potential is however much greater than the way in which it is often routinely used in clinical practice. The role of contrast echocardiography, three-dimensional echo and automated myocardial tissue evaluation tools has paved the way for new clinical and research applications which guarantee a primary role of this modality in cardiac care for the foreseeable future. Integration of current developments into existing practice is explored in this review.
Dr Fukushima and colleagues from Baltimore outline the utility of imaging techniques in the expanding area of application of restorative therapies in cardiology, including the use of gene and cell based therapies to restore blood flow and contractile function [8]. Their discussion centres mostly around the use of radionuclide-labelled imaging probes, as these to date have been the most widely used in molecular and cell based imaging. They also comment on the potential utility of hybrid imaging with SPECT CT and PET CT in the future for these purposes. They cover the use of imaging to interrogate gene expression after transfer, cell tracking, visualisation of proteins and other molecules involved in healing and in angiogenesis. The existing literature is summarised and the problems and challenges clearly stated. The potential utility of other imaging modalities are also mentioned.
Dr Beller of Virginia reviews the existing state of the art in the tomographic imaging techniques of SPECT, PET, CT and CMR. He then speculates as to how these will all be utilised in 5–10 years from now [9]. This will occur within an environment of changing clinical needs, new research findings, new therapies and increased scrutiny in terms of cost, effectiveness and outcomes. He predicts an increasing use of multimodality imaging (an area where he has been active in the development of new models of training for the imaging cardiologists of the future). The increasing acceptance of the need for quantitative approaches, particularly in regards to myocardial blood flow assessment is emphasised. Dr Beller predicts this will lead to more use of cardiac PET, which will also be utilised for imaging the myocardium and atherosclerotic lesions in the coronary arteries and beyond. Both CT and MR imaging are likely to also develop/clinically refine useful ways to measure myocardial blood flow. The use of metabolic and neuronal imaging in patients with heart failure appears likely to increase with both PET and SPECT for both prognostic and clinical decision making.
The use of CT for calcium scoring and CT coronary angiography at ever increasing resolution are also discussed. These technologies are also likely to be further applied to the assessment of plaque and cellular function.
In conclusion, alongside the rapid expansion and development in all of these imaging techniques there remain many challenges. At times the hardware and software seems to advance more rapidly than investigators can respond in terms of evaluation. With increasing diversity and sophistication of techniques the question of “which test for which patient?” will be asked ever more frequently. Administrators and reimbursing bodies will demand increasingly more evidence of efficacy, cost effectiveness and now comparative effectiveness between tests as well as more outcomes based research. The bodies involved in the training of specialists in cardiac imaging, including the disciplines of cardiology, nuclear medicine, radiology and ultrasound will of necessity confront the issues of integrated training of individuals across the various techniques. This is in keeping with the emergence of the “cardiac imaging specialist” rather than the single-modality based imaging practitioner of the 20th century who would need to undergo full retraining requirements for each additional modality/specialty to be accredited and licenced for practice.
In this issue of Heart Lung and Circulation the authors present the current and possible future state for cardiac imaging in the short term. Whilst there are challenges, there are also stimulating opportunities and possibilities.
References
- . Clinical application of CT coronary angiography: state of the art. Heart, Lung and Circulation. 2010;19:107–116
- . Cardiovascular magnetic resonance imaging of non-ischaemic heart disease: established and emerging applications. Heart, Lung and Circulation. 2010;19:117–132
- . Congenital heart disease and multi-modality imaging. Heart, Lung and Circulation. 2010;19:133–144
- . High field cardiac magnetic resonance imaging—current and future perspectives. Heart, Lung and Circulation. 2010;19:145–153
- . Is MR spectroscopy of the heart ready for humans?. Heart, Lung and Circulation. 2010;19:154–160
- . Emerging clinical role of strain imaging in echocardiography. Heart, Lung and Circulation. 2010;19:161–174
- . Echocardiography in the era of multimodality imaging. Heart, Lung and Circulation. 2010;19:175–184
- . Nuclear imaging in the evaluation of restorative therapies. Heart, Lung and Circulation. 2010;19:185–192
- . Clinical cardiac imaging—what will we be doing in 5 to 10 years?. Heart, Lung and Circulation. 2010;
PII: S1443-9506(09)01111-1
doi:10.1016/j.hlc.2009.12.001
© 2010 Australasian Society of Cardiac and Thoracic Surgeons and the Cardiac Society of Australia and New Zealand. Published by Elsevier Inc. All rights reserved.
