Assessment of Left Ventricular Parameters Using 16-MDCT and New Software for Endocardial and Epicardial Border Delineation

Thomas Schlosser; Konstantin Pagonidis; Christoph U. Herborn; Peter Hunold; Kai-Uwe Waltering; Thomas C. Lauenstein; Jörg Barkhausen

Disclosures

Am J Roentgenol. 2005;184(3):765-773. 

In This Article

Discussion

In this study we evaluated the ability of the newest generation of CT scanners to assess left ventricular parameters. This study carries four major findings we believe are important: First, EDV and ESV values calculated on MR data sets are statistically significantly lower compared with automated and manual measurements derived from 16-MDCT examinations. Second, LVM measurements on MR data sets resulted in statistically significantly higher values compared with automated and manual measurements derived from 16-MDCT examinations. Third, EF measurements are not statistically significantly different among all techniques. Fourth, values from the automated contour detection algorithm using the new software CT Mass are not significantly different compared with manual tracing.

Cine MRI has been established as the most accurate clinical method for assessing ventricular volumes,[17,18,19] and mass.[20,21]. In particular, steady-state free-precession cine MRI is the technique of choice because of its excellent contrast between the blood-filled cavities and the surrounding myocardium. In this setting, automatic segmentation provides accurate volumetric data.[8]

In contrast to conventional angiographic volumetric analysis, the cross-sectional nature of MRI makes it independent of geometric assumptions. In addition, noninvasiveness, the lack of ionizing radiation, and the excellent soft-tissue contrast without IV contrast material injection render MRI highly attractive for patients with various cardiac diseases with compromised left ventricular function. In contrast to 3D echocardiography, MRI is operator-independent and permits a far better distinction between myocardium and the ventricular cavity. However, cardiac MRI is still limited with regard to restricted scanner availability, relatively high costs, and generally long examination times.

Several studies have shown the ability of electron beam CT and MDCT to assess left ventricular function and mass by multiplanar reformation algorithms using short-axis images.[14,15,22] Because of the retrospective gating used for cardiac MDCT, all data for the analysis of left ventricular parameters can be calculated from a standard CT coronary angiography data set without any additional radiation exposure.

Because of the introduction of the new generation of MDCT scanners that allow the reliable detection of significant coronary stenoses and calcified plaque, the number of cardiac CT investigations has increased. With regard to time constraints in clinical practice, an automatic postprocessing tool allowing fast and reliable assessment of left ventricular volumes and masses is a prerequisite for a more widespread use of left ventricular measurements based on CT data sets.

The results of our study show that automatic contour detection is feasible for CT data sets and results in fast and reliable measurements without significant differences compared with manual contour tracing. However, a drawback of CT measurements in general is the overestimation of EDV and ESV compared with MRI as the standard of reference. Regarding ESV, this overestimation might be explained by the relatively low temporal resolution, even of the latest 16-MDCT scanners, of about 210 msec compared with cine MRI (40 msec) and the inability to acquire the maximum systolic contraction. For this reason, an underestimation of the EDV might be plausible. However, in our study, CT measurements overestimated EDV in the same dimension as ESV. One reason might be that the two techniques do not display identical slices, and variations of the most basal slice thickness may result in a difference of up to 27 mL, as determined in our study.

Left ventricular EF estimated on CT with both manual and fully automated contour determination was almost identical to measurements using MRI, indicating a reliable estimation of the global left ventricular function using the former technique. Using the CT Mass software, automated analysis of left ventricular parameters was significantly quicker than manual drawing, indicating a potential improvement in workflow and data analysis.

The data provided in this study need to be interpreted critically. First, only a small group of patients were examined; the data need to be validated by larger patient cohorts. Furthermore, the influence of β-blocker administration before CT has not been assessed. For functional analysis it is crucial that no medication influencing the patient's heart rate or myocardial contractility be applied. Therefore, the administration of β-blockers in some patients before CT is not only a limitation of this study but also a general limitation of the method.

However, the major advantage of 16-MDCT regarding estimation of left ventricular parameters is the shorter examination time per patient. However, as a result of lower temporal resolution, the need of nephrotoxic contrast material, and substantial radiation doses up to 13 mSv delivered during a single CT scan,[23] CT can hardly be considered a method of choice for the determination of left ventricular parameters in clinical practice. Nevertheless these parameters are most likely to be seen as additional information in patients undergoing CT coronary angiography.

In conclusion, fully automated analysis of data acquired during CT coronary angiography using a 16-MDCT scanner allows fast and reliable assessment of left ventricular EF and a rough estimation of left ventricular volumes and mass.

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