Over the past decades, conventional coronary angiogra- phy has been the only accepted ‘gold standard’ method for clinical imaging of coronary artery disease (CAD).
However, coronary angiography is costly, causes patient discomfort, and is associated with a small but distinct procedure-related morbidity (1.5%) and mortality (0.15%). Moreover, the accuracy of coronary angiogra- phy is severely hampered by significant intraobserver as well as interobserver variability in defining the anatomic relevance of stenoses (up to 50%) [1, 2] – a problem that is underlined by the poor correlation with post-mortem coronary pathology findings [3, 4]. In addition, angio- graphic findings are unable to predict the physiologic rel- evance of a coronary stenosis [2, 5-8].
In 2002, about 2 million conventional coronary an- giography procedures were carried out in Europe [9].
Interestingly, the fact that percutaneous coronary inter- vention (PCI) was performed in only a third of these pro- cedures implies that coronary angiography was and is mostly used as purely diagnostic tool. The associated eco- nomic burden and the inconvenience to patients have prompted an intensive search for alternative, noninvasive means for coronary artery imaging [10]. Indeed, over the last 5 years there has been an impressive growth in the lit- erature on non-invasive techniques for the assessment of CAD. In particular, the introduction of multidetector computed tomographic scanners with submillimeter spa- tial resolution and subsecond gantry rotations has revolu- tionized the field of cardiac imaging by enabling ‘direct’
non-invasive imaging of the coronary arteries. As a re- sult, purely diagnostic coronary angiography may not be considered an acceptable procedure in the near future.
Coronary Angiography by Multidetector-Row Computed Tomography
The latest advances in computed tomography (CT) tech- nology using multidetector-row CT systems with 64- slices and dual source CT has led to the achievement of a non-invasive means to obtain excellent-quality images of the coronary artery tree (Fig. 1). Nevertheless, even
with 64-slice CT there is a decline in diagnostic accura- cy that is mainly associated with the presence of severe vessel-wall calcification and motion artifacts [11]. For routine clinical use, CT coronary angiography (CTA) needs to provide reliable visualization of the complete coronary artery tree. The temporal resolution of 64-slice CT sometimes is insufficient for artifact-free visualiza- tion of the coronary arteries due to their heterogeneous motion throughout the cardiac cycle, which typically af- fects distal vessel segments of the left circumflex (LCX) artery and the mid-section of the right coronary artery (RCA). As this most often occurs in patients with high and variable heart rates [12], it was considered necessary with 64-slice CT to control patient heart rate prior to scanning by administering beta-blockers and/or benzodi- azepines. The most recently developed dual-source CT scanner system further improved temporal resolution to a heart-rate-independent 83 ms by simultaneously acquir- ing data with two X-ray tubes and two detectors mount- ed onto the gantry with a 90° angular offset. A prelimi- nary study using dual-source CT reported high accuracy in the diagnosis of CAD, with a sensitivity of 96% and a specificity of 98% [13]. The authors of that study did not control heart rate with beta-blocking medication and reported a low rate of not-evaluable segments of only 1.4% – all in distal segments or side branches.
With 64-slice and dual-source CT scanners, the con- sistently high negative predictive value (approaching 100%) allows the reliable exclusion of significant CAD in a non-invasive manner. This severely challenges the role of conventional coronary angiography as a purely di- agnostic tool.
Additional benefits from cardiac CT derive from its ability to accurately evaluate ventricular function with an accuracy that is similar to that of the current standard of reference, magnetic resonance imaging [14]. In addition, cardiac valvular morphology and function can be as- sessed with results similar to those obtained with echocardiography [15, 16], and approximately 70% of the lung parenchyma [17] can be covered without the need for additional radiation or contrast media.
IDKD 2007
CT and CT Nuclear Imaging of the Heart
P.A. Kaufmann
1, H. Alkadhi
21Nuclear Medicine and Cardiology, Department of Medical Radiology, University Hospital, Zurich, Switzerland
2Institute of Diagnostic Radiology, Department of Medical Radiology, University Hospital, Zurich, Switzerland 154_157_Kaufmann 1-03-2007 15:07 Pagina 154
CT and CT Nuclear Imaging of the Heart 155
Hybrid Imaging
It has become the clinical standard to require proof of ischemia by a non-invasive test before considering revascularization procedures [18, 19]. As illustrated in Fig. 2, a purely morpho-anatomical method is insuffi- cient at predicting the functional relevance of a stenosis [6]. Thus, an accurate, non-invasive technique for the evaluation of CAD should provide complementary in- formation on coronary anatomy and the pathophysiolog- ic implications of lesion severity. Currently, the integra- tion of functional and morphological information is done by mentally combining coronary angiography findings with those from myocardial perfusion imaging (MPI).
Unfortunately, the planar nature of coronary angiogra- phy projections and the axial slice-by-slice display of cardiac MPI render a subjective integration difficult, leading to inaccurate allocation of the coronary lesion to
its subtended myocardial territory. There have been sev- eral attempts to fuse conventional coronary angiography with MPI [20-22]. However, this approach does not al- low non-invasive preplanning of the intervention, as in- formation regarding the coronary anatomy is obtained only during conventional coronary angiography. In addi- tion, the time-consuming process of fusing coronary an- giography with MPI prevents rapid decision-making dur- ing an ongoing intervention. Consequently, this ap- proach has not been adopted into daily clinical routine.
Ideally, complementary information should be obtained completely non-invasively, allowing proper planning of the elective intervention.
We have recently shown that combining MPI with multislice CTA is a feasible and interesting approach for non-invasive complementary morpho-anatomical and functional CAD assessment [23, 24], providing useful in- formation for clinical decision-making [25].
Fig. 1a-d.Dual-source computed tomography (CT) coronary angiography (mean heart rate during scanning 78 bpm) in a 49-year-old female patient with atypical chest pain and inconclusive stress testing. CT ruled-out coronary artery disease in a non-invasive means. Volume-ren- dered 3-D image (a), curved multiplanar reformations along the centerline of the right coronary artery (b), as well as curved multiplanar reformations along the centerline of the left anterior descending (c) and left circumflex (d) arteries demonstrate normal coronary arteries with no calcifications or stenoses
a b
c d
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156 P.A. Kaufmann, H. Alkadhi
The Future of Non-invasive Cardiac Imaging with CT and Nuclear Methods
Developments in non-invasive cardiac imaging using CT and nuclear methods are anticipated to proceed in two directions.
First, the most recent multidetector-row CT scanner technology appears to be robust with respect to coronary artery assessment in patients with acute chest pain, there- by optimizing the triage of those patients for further in- vasive or non-invasive workup and therapy [26]. In addi- tion, initial experience indicates that multidetector row CT allows the evaluation of acute and chronic myocardial pathologies, with results similar to those obtained with magnetic resonance imaging [27]; however, at the same time it also provides accurate information about the sta- tus of the coronary arteries.
Second, the very encouraging preliminary data sug- gest that hybrid imaging has the potential to be imple- mented into clinical practice, eventually leading to a reduction in the frequency or overuse of angioplasty and stent placement, key cost drivers in interventional cardiology practice. Occasionally, in patients whose lesions are unsuitable for angioplasty, bypass surgery may be considered directly without the need for pre- operative diagnostic coronary angiography [28].
Furthermore, new ligands are currently under investi- gation that will allow imaging of plaques in vulnerable vessels (aorta, carotids, coronaries). Optimal fusion (inherent to hybrid scanners) of molecular images with those generated by CT angiography will allow exact allocation of the vulnerability to the specific anatomic lesion.
Fig. 2a-h.64-slice CT coronary angiography (mean heart rate during scanning 69 bpm) in a 56-year-old male patient with atypical chest pain, a positive family history, and dyslipidemia. Volume-rendered 3-D images show multiple calcifications (arrows) in the left anterior descending artery (LAD) (a) and in the right coronary artery (RCA) (b). It is important to note that no diagnosis should be done on vol- ume rendered 3-D images. Curved multiplanar reformations allow calcifications involving the LAD (c), the proximal segment of the first diagonal branch (d), the left circumflex (e) and the RCA (f) to be localized.
However, even with reformations lumi- nal narrowing can sometimes be difficult to estimate. The angiographic view (g) confirms severe overall calcifications.
Myocardial perfusion scan (adenosine stress/rest Tc-99m-tetrofosmin protocol) (h) reveals slightly inhomogeneous per- fusion but neither ischemia nor scarring, indicating that none of the lesions were pathophysiologically relevant
a b
c d
e f
g h
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CT and CT Nuclear Imaging of the Heart 157
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