Cardiac: Left/Right Ventricular Function

Left-ventricular volumes and myocardial mass are independent predictors of morbidity and mortality in patients with coronary heart disease, and global left-ventricular function is considered the strongest determinant of heart failure and death due to myocardial infarction. The accurate and reproducible determination of left-ventricular volumetric and functional parameters is important for clinical diagnosis and risk stratification in patients with suspected or documented coronary heart disease.

Potential and limitations of MDCT

In 1998, ECG-gated multi-detector row computed tomography (MDCT) had been introduced as a non-invasive cardiac imaging technique focusing on the detection of coronary artery stenoses and cardiac morphology. MDCT assessment of left-ventricular volumes is feasible applying different methodological approaches:

• the area-length method
• the Simpson´s method
• threshold-based direct volume measurements allowing for 3D-growing segmentation algorithms

Based on the acquired left-ventricular volumes, secondary function parameters such as left-ventricular ejection fraction, stroke volume, and cardiac output are calculated. Thus, MDCT provides quantitative information on the left-ventricular volume changes throughout the entire cardiac cycle and, consecutively, global left-ventricular function.

Regional left-ventricular function parameters can also be obtained from the identical CT datasets. However, rapid volume changes during the systolic ventricular filling and ejection phases were not adequately detected, and regional left-ventricular assessment, especially detection of diastolic dysfunction, remains limited.

DSCT assessment of left- and right ventricular function

Currently introduced Dual Source CT (DSCT) systems providing a constant temporal resolution of 83 ms and up to 40 ms applying multi-segment data reconstruction algorithms might help to overcome this limitation. Therefore, CT data post-processing for regional left-ventricular wall motion assessment should include image reconstructions of 20 phases at 5%-steps of the RR-interval from raw CT datasets to utilize the full diagnostic potential from the improved temporal resolution.

As left-ventricular function assessment is usually performed complementary to coronary CT angiography, the routine protocols used for coronary artery imaging are applied. The introduction of CT scanners with up to 64 rows and DSCT systems in combination with advanced power injectors for combined application of contrast-media and a saline bolus enabled CT data acquisition within 6 to 12 seconds. The performance of threshold-based automated 3D-growing segmentation algorithms depends on the quality of contrast opacification. If functional parameters are to be obtained, delineation of the right atrium and ventricle and the septal myocardium is improved with a modified contrast injection scheme using either a biphasic injection or application of diluted contrast after the initial bolus injection.

Clinical routine and needs for improvement

MDCT enables a combined assessment of cardiac morphology and left-ventricular function without the need for additional radiation exposure. It enables left-ventricular function assessment in patients with implantable pacemakers and cardioverter-defibrillators (ICD). Even regional left-ventricular wall motion analysis at rest is feasible from MDCT datasets in good agreement with competitive imaging modalities. Normokinetic left-ventricular segments are reliably identified with MDCT.

However, the sensitivity for detection and accurate classification of left-ventricular wall motion abnormalities has to be improved. Further improvement in temporal resolution by 64-slice MDCT and DSCT systems seems to be mandatory to match regional LV function analysis from echocardiography or Magnetic Resonance Imaging.

Authors: Kai Uwe Jürgens, Harald Seifarth, Michael Puesken, Roman Fischbach
See corresponding procotol: Protocol Left/right ventricular function
See corresponding cases: Dual Source CT preceding cardiac resynchronization therapy (CRT), Dual Source CT in left-ventricular hypertrophy [A] & in ARVCM [B]