M.-C Herregods

Left ventricular quantification with breath-hold MR imaging: comparison with echocardiography

To evaluate the reproducibility of measurements of left ventricular (LV) dimensions, function, and myocardial mass, segmentedk-space gradient-recalled-echo (GRE) magnetic resonance (MR) imaging was performed on two occasions on 12 healthy volunteers. To compare the MR data, all volunteers underwent a two-dimensional echocardiography with determination of LV dimensions and function. The left ventricle was imaged during breath-hold by consecutive, contiguous short-axis views at end-diastole and end-systole. An average of eight short-axis views was needed to encompass the whole left ventricle. This fast MR sequence limited the total acquisition time to 12 min. LV volumes and masses were calculated after manual delineation of epicardial and endocardial surfaces by two observers in a blinded fashion.Interstudy variability varied between 4.1% and 10.3% for LV end-diastolic volume and end-systolic volume, respectively. Differences in interobserver variability were smaller and varied between 3.6% and 7.3% for LV ejection fraction and end-diastolic volume, respectively. Intraobserver variabilities ranged between 2.0% and 7.0% for LV ejection fraction and end-systolic volume, respectively. These variability percentages agree very well with other studies in literature using other MR sequences. No significant differences in LV dimensions or function were found between MR imaging and echocardiography. In conclusion, this MR sequence allows fast and reproducible LV quantification.

Hart- en vaatziekten

Techniek om met behulp van elektrodekatheters die door de bloedbaan tot in het hart worden opgevoerd ritmestoornissen te behandelen. Door wisselstroom met een frequentie van 500 tot 700 kHz (cfr. radiogolven) te sturen door een elektrodetip die tegen het myocard aanligt, ontstaat er verhitting van het onderliggende weefsel en vernietiging hiervan. De aldus aangebrachte laesies zijn enkele millimeters groot en diep.

Variability of integrated backscatter: simulations and measurements in vitro

Absolute integrated backscatter (IB) levels and other derived parameters such as cyclic variation (CV) have been used for ultrasonic tissue characterization. Ideally, such a parameter would provide information on the scattering structure and would be independent of the acquisition or the equipment used. It is well known however, that the measured reflected signal of a scattering structure depends on the precise position of the individual scatterers. In order to estimate the sensitivity of IB to this stochastical process, the authors analyzed backscattered data from structures with fixed scatterer densities but with a random distribution, Several independent measurements were made and the variability in IB was calculated. In order to produce the radio frequency (RF) data the authors firstly used computer simulations. Secondly, a real-time RF acquisition system was used to acquire RF data from a tissue mimicking phantom. Finally, an adapted imaging approach was evaluated using mathematical simulations in order to see if it can reduce the measured variability of IB.