Figure 6

Example of erroneous ECG trigger detection. Cardiac images, trigger detection tickmarks and signal waveforms obtained at 7.0 T using vector ECG (left), pulse oximetry (center) and acoustically triggered (right) 2D CINE FLASH acquisitions. All signal waveforms show the output of the scanners central physiological monitoring unit (including processing of the ECG, POX and ACT signal) as displayed at the scanners user interface. Top: Mid-ventricular, short axis views of the heart together with whole R-R interval time series of one-dimensional projections along the profile (dotted line) marked in the short axis view. Middle: Trigger detection tickmarks obtained from a single subject over 18 cardiac cycles after temporal realignment using cross correlation and reassignment. Bottom: Signal waveforms obtained from a single subject (subject 2) over 18 cardiac cycles. In this example vector ECG triggered CINE imaging was prone to severe cardiac motion artifacts due to R wave mis-registration which induced reduction in myocardium/blood contrast and image sharpness. ACT triggered 2D CINE FLASH imaging provided faultless trigger detection and hence produced images free of motion artifacts. Please note the scatter in the POX peak amplitude and peak width, causing a jitter (Δt = 72 ms) in the pulse oximetry trigger detection which constituted a synchronization problem.