Routine functional assessment is now being offered for the first time on a CT scanner on the 64-slice CT. Though it has been possible in the research setting, clinical utility has not been forthcoming until now.
In functional assessment, the following parameters are assessed.
As with echocardiography and MRI, it is possible to reconstruct the images in multiple phases and then generate cine images to view the contractility of all the segments of the myocardium. Though the data and literature is still sparse (since this is a new technique), its use can be extrapolated to the data existing for echocardiography and MRI. We assess for the presence of reduced contractility or absent contractility in different segments of the LV. This complements the coronary artery study.
For example, if the anterior wall and septum are hypokinetic,
in a patient with a stenosis of the LAD, seen on the coronary
CT study, the systolic dysfunction makes it almost certain
that the lesion is signficant and needs to be treated. In
fact if systolic dysfunction is seen, it even obviates usually
the need for a stress-thallium or a stress-perfusion MRI examination,
since perfusion changes occur earlier in the ischemic time-line.
By the time systolic dysfunction occurs, there will always
be perfusion changes.
Fig. 1: Short axis cine of a patient
with good contractility and wall thickening of the segments.
- Wall Motion
By measuring the end-diastolic and end-systolic cavity sizes, the volumes and consequently the ejection fraction can be measured. Though again the data is sparse, a few studies done recently have shown that CT underestimates by 5-10% the ejection fraction as compared to MRI, the gold standard. This should be taken into account when interpreting the results.