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16 Multislice CT in Coronary Heart Disease <strong>KCE</strong> Reports 82<br />
implemented, a high rate of false positives would result in increased downstream costs<br />
and interventions.<br />
The radiation dose associated with MSCT represents one of <strong>the</strong> major reasons to<br />
preclude its use as a screening tool for asymptomatic patients. 43 Even in <strong>the</strong> year 2008,<br />
this advice remains: “For <strong>the</strong> time being, MSCT continues not to be recommended as a<br />
screening tool, and <strong>the</strong> low radiation dose of <strong>the</strong> step-and-shoot mode in selected<br />
patients should not be taken as a justification for using this indication.” 44<br />
2.4.2.2 MSCT as an alternative for invasive coronary angiography<br />
As compared to CCA, MSCT has <strong>the</strong> advantage of avoiding some of <strong>the</strong> inconveniences<br />
and of <strong>the</strong> morbidity associated with CCA. Never<strong>the</strong>less, <strong>the</strong> exposure to ionising<br />
radiation and <strong>the</strong> need for contrast medium injection remains a matter of concern. On<br />
<strong>the</strong> o<strong>the</strong>r hand, if revascularisation is indicated, an invasive procedure with a second<br />
exposure to radiation remains necessary. MSCT seems especially useful when <strong>the</strong> result<br />
shows normal coronary arteries but <strong>the</strong>n, one might question if <strong>the</strong> same conclusion<br />
could not have been obtained by o<strong>the</strong>r noninvasive techniques in a more efficient way.<br />
Moreover, false postive examinations will lead to fur<strong>the</strong>r invasive tests and may<br />
annihilate <strong>the</strong> alleged advantages of <strong>the</strong> noninvasive angiography.<br />
2.4.2.3 MSCT as an additional noninvasive test<br />
The diagnostic accuracy of MSCT has to be compared with that of o<strong>the</strong>r tests such as<br />
ECG stress testing, MPS and DSE. The latter tests however have <strong>the</strong> advantage that<br />
<strong>the</strong>y provide information on myocardial perfusion, additional to <strong>the</strong> mere<br />
documentation of coronary stenoses. MSCT can only visualise coronary lesions without<br />
assessing <strong>the</strong> functional impact of <strong>the</strong>m. It might be possible that future generation<br />
scanners will be able to assess <strong>the</strong> nature of coronary plaques and give information that<br />
thus far is not obtainable by any o<strong>the</strong>r noninvasive test. This is a matter of current<br />
research.<br />
2.4.2.4 MSCT for <strong>the</strong> evaluation of coronary artery stents and bypass grafts<br />
Owing to <strong>the</strong> artifacts caused by metal, visualization of <strong>the</strong> coronary lumen within stents<br />
by MSCT is more challenging than evaluation of <strong>the</strong> native coronary arteries. Clinical<br />
studies published so far, show a consistently low sensitivity to identify in-stent<br />
restenosis. The limited spatial resolution of MSCT, <strong>the</strong> type of stent, and stent diameter<br />
36, 45<br />
all contribute to limited clinical results.<br />
Visualisation of bypass grafts with MSCT on <strong>the</strong> o<strong>the</strong>r hand, is generally less problematic<br />
because <strong>the</strong>y are larger than native vessels and less subject to motion artifacts. The<br />
presence of metal clips on mammary artery grafts can be problematic due to blooming<br />
artifacts. Despite <strong>the</strong> high degree of accuracy to detect lesions within grafts, MSCT has<br />
limited value after CABG, because an assessment of <strong>the</strong> native coronary arteries is also<br />
required, which tend to be more challenging because native vessels often are heavily<br />
calcified in postoperative patients. 36<br />
The role of MSCT in patients after CABG or PCI will not be fur<strong>the</strong>r discussed in this<br />
<strong>report</strong>, that focuses on native coronary arteries.