Aortic elasticity measurement using ECG-gated multi-slice computed tomography.

Vessel elasticity is a functional parameter of the vessel wall which is correlated with cardiovascular disease. Non-invasive measurement of elasticity is difficult. The aim of this project was to develop a method to measure aortic elasticity using multi-slice computed tomography (CT). The method is based on the reconstruction of time-resolved images of the aortic cross-section from CT raw data and ECG data. It can be integrated into a standard CT angiography examination without the need for additional radiation dose. The method was validated using a phantom set-up with porcine aortic specimens. Results show a good agreement between an optical reference and the CT measurement. Patient examinations show that changes in aortic wall distension can be measured and that these changes are reduced in patients with atherosclerosis.

Estimation of aortic compliance using magnetic resonance pulse wave velocity measurement.

A method for compliance estimation employing magnetic resonance pulse wave velocity measurement is presented. Time-resolved flow waves are recorded at several positions along the vessel using a phase contrast sequence, and pulse wave velocity is calculated from the delay of the wave onsets. Using retrospective cardiac gating in combination with an optically decoupled electrocardiogram acquisition, a high temporal resolution of 3 ms can be achieved. A phantom set-up for the simulation of pulsatile flow in a compliant vessel is described. In the phantom, relative errors of pulse wave velocity estimation were found to be about 15%, whereas in a volunteer, larger errors were found that might be caused by vessel branches. Results of pulse wave velocity estimation agree with direct aortic distension measurements which rely on a peripheral estimate of aortic pressure and are therefore less accurate. Studies in 12 volunteers show values of pulse wave velocity consistent with the literature; in particular the well-known increase in pulse wave velocity with age was observed. Preliminary results show that the method can be applied to aortic aneurysms.

[Optimizing temporal resolution in CT with retrospective ECG gating]. / Optimierung der Zeitauflösung in der CT mittels retrospektivem EKG-Gating.

PURPOSE: Spiral CT of the heart using the established ways of ECG synchronization is hampered by the relatively long acquisition times of 250 to 500 ms. This only allows to acquire diastolic images in patients with moderate heart rates. In this work, algorithms for time-optimized retrospective cardiac gating are presented, and their potential to improve temporal resolution is investigated. MATERIAL AND METHODS: These algorithms use data from multiple gantry rotations for image reconstruction, which is possible for multi-scans at fixed slice positions as well as for overlapping spiral scans. Temporal resolution was quantified using computer simulations and compared to experimental data from pigs. RESULTS: Using a conventional sub-second CT scanner, considerably higher temporal resolutions are possible with spiral scanning. A temporal resolution of 170 ms already provides systolic images with little motion artifacts. Higher temporal resolutions of up to 70 ms are demonstrated for multi-scans, which allows to depict ventricle wall movement over the complete cardiac cycle. DISCUSSION: The method of time-optimized retrospective cardiac gating broadens the spectrum of conventional spiral-CT for cardiac imaging. It can be directly transferred to multi-slice scanners. Here it can be used clinically because of reduced scan time. Potential applications are the determination of functional cardiac parameters like ejection fraction and the detection of disorders of ventricle wall movement.