Cine cardiac MRI using DUS was successfully demonstrated. DUS triggering is an alternative method for cardiac MRI and may be applied in a clinical setting.

Purpose:Electrocardiogram (ECG) triggering for cardiac magnetic resonance (CMR) may be influenced by electromagnetic interferences with increasing magnetic field strength. The aim of this study was to evaluate the performance of Doppler ultrasound (DUS) as an alternative trigger technique for CMR in comparison to ECG and pulse oximetry (POX) at 3T and using different sequence types.Methods:Balanced turbo field echo two-dimensional (2D) short axis cine CMR and 2D phase-contrast angiography of the ascending aorta was performed in 11 healthy volunteers at 3T using ECG, DUS, and POX for cardiac triggering. DUS and POX triggering were compared to the reference standard of ECG in terms of trigger quality (trigger detection and temporal variability), image quality [endocardial blurring (EB)], and functional measurements [left ventricular (LV) volumetry and aortic blood flow velocimetry].Results:Trigger signal detection and temporal variability did not differ significantly between ECG/DUS (I = 0.6) and ECG/POX (P = 0.4). Averaged EB was similar for ECG, DUS, and POX (pECG/DUS = 0.4, pECG/POX = 0.9). Diastolic EB was significantly decreased for DUS in comparison to ECG (P = 0.02) and POX (P = 0.04). The LV function assessment and aortic blood flow were not significantly different.Conclusion:This study demonstrated the feasibility of DUS for gating human CMR at 3T. The magnetohydrodynamic effect did not significantly disturb ECG triggering in this small healthy volunteer study. DUS showed a significant improvement in diastolic EB but could not be identified as a superior trigger method. The potential benefit of DUS has to be evaluated in a larger clinical patient population.

Previous animal experimental data had su~ested that extracorporeal shock waves acted by the interaction of shock waves witi remnant gas bubbles Iefi horn eavitational activity from previous shocks (1). ht vitro experitnenk had shown that haemolysis frotn shock waves was reduced by >95 0/0by stitic express pressures of ody 10s kPa in the exposure vessel (2). Two additional experiments confiied the interaction. ht the fret, an identical number of 100 shock waves was administered slower than us~ly to red blood cells and minimal excess pressure was applied. h the second, a single strong shock wave or two strong shock waves were applied to red blood cells. ht both haemolysis was determined, The fust experiment revealed a lower haemolysis at the slower application of the shock waves. Application of a sitt~e strong shock wave caused little haemolysis yet appliution of two shock waves caused a 5-fold increase of haemolysis, Static excess pressure abolished the increase. The only interpretation one can thii of is that the fwst shock had caused remnant gas bubbles which acted strongly at the second shock. The term shock-wave gas-bubble interaction is well known horn cavitation physics and should be used more ofien to describe the mechanism of action of extracorporeal shock waves. TRODUCTIONExtracorpord shock waves are single pressure pdses of 35-120 ma peak pressure followd by a tensile wave. They are clinically applied for lithotipsy (1,2). In tissues they can cause hemorrhages as a side effect. Previous animal experiment data had suggestd that tissue damage is generatti by cavitation, more spectilc by the interaction of shock waves with remnant gas bubbles left from cavitation activity from previous shocks (3). Shock waves can dso cause damage to cells in vitro. Hemolysis, red blood cell des~ction, is a simple means to quant@ it. In vitro experiments had shown that haemolysis from shock waves was reduced by >9570 by static express pressures of ody 105kPa in the exposure vessel (4). This was interpreted as evidence for a reduced shock wave -gas bubble interaction by a reduction of the size of the remnant gas bubbles by the excess pressure. Two simple experiments elucidated this further. One applied shock waves more slowly and the other applid just one or two shock waves, SLOW SHOCK WA~APPLICATION During slow wave application, 100 shock waves were applied to red blood cells with the normal speed of one discharge per smond. In another group 100 shock waves were applied with a slower speed of one discharge every five seconds. Red blood cell Iysis was determined photometrically. The result is shown in the figure on the Iefi.

The aim was to investigate the feasibility to perform cardiac magnetic resonance imaging (MRI) using a MR compatible Doppler-ultrasound (US) device as a new method to trigger the human heart cycle. MRI images were compared between ECG and Dopplerultrasound triggered examination in terms of image quality by an objective measure of acutance and functional assessment.

Compared with the established 3D-CRT technique, the hybrid technique allows for a decrease in dose, particularly of the mean heart and lung dose with comparable target volume acquisition and without disadvantageous low-dose load of contralateral structures. Uncomplicated implementation of the hybrid technique was demonstrated in this context. The hybrid technique combines the advantages of tangential IMRT with the superior sparing of organs at risk by VMAT.