Objectives:Identify the parameters required to calculate the left ventricular ejection fraction.Describe conditions associated with a depressed left ventricular ejection fraction.Recall the clinical relevance of knowing the pathophysiology of left ventricular ejection fraction.Discuss interprofessional team strategies for improving care coordination and communication to advance management of patients with a depressed LVEF and improve outcomes.Access free multiple choice questions on this topic.
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LVEF can be obtained with MRI using manual, semi-automated or automated methods. Simpson disk summation method uses the short-axis cine steady-state free precession images of the LV to obtain LVEF. During the end-systole and end-diastole phase, short-axis images are obtained. LV endocardial borders are manually traced on each short-axis image to obtain the ventricular cavity area for each slice. Multiplying the area of the tracing for each image slice by the slice interval (image gap + slice thickness) gives the volume of the slice. LV volume is then derived by the addition of the volumes of the slices. LV shape needs to be determined in this technique as the entire LV cavity is traced. A well-defined endocardial border can be obtained with the use of high contrast. Calculation of LVEF with MRI does not necessarily require the use of ionizing radiation or contrast material.
Figure 3 gives an overview of the MRXCAT cine phantom. Examples at systole and diastole are shown in inspiration and expiration states. Temporal profile plots of breathhold MRXCAT cine, free-breathing MRXCAT cine and in-vivo breathhold cine data are demonstrated (Figure 3c). Individual coil maps of a simulated 8-element cardiac coil array are displayed in Figure 3f.
MRXCAT cine phantom overview. Full field-of-view at systole and expiration (a) and at diastole and inspiration breathhold (b). (c) Profiles along dashed line in (b) for 24 heart phases for breathhold and free-breathing MRXCAT with 15 segments and the breathhold in-vivo case for comparison. (d-e) Cardiac region-of-interest at different cardiac phases for breathhold MRXCAT (d) and in-vivo scan (e). (f) Single coil images from 8 individual coils.
In Figure 4 the whole-heart myocardial perfusion MRXCAT phantom is displayed. Apical, mid-ventricular and basal slices at the time points of bolus arrival in the right and left ventricle as well as in the myocardium are shown in Figure 4a. In-plane profiles as a function of time extracted from the breathhold, free-breathing phantom and in-vivo acquisition are demonstrated in Figure 4b. A cardiac region-of-interest (ROI) is shown in Figure 4c. In addition, the effect of timing of the saturation pulse with respect to the image acquisition is shown for a long saturation to acquisition delay of 150 ms relative to a short saturation delay of 10 ms to demonstrate the non-linearity between MR signal and contrast agent concentration [41].
MRXCAT cardiac perfusion phantom overview. (a) Three slices from apex to base at maximum contrast agent enhancement in the right ventricle, left ventricle and myocardium. (b) Anterior-posterior profiles along dashed line in (a) for all heart beats for breathhold MRXCAT, free-breathing MRXCAT and in-vivo breathhold myocardial perfusion images (left-right). (c) 16 slices of the MRXCAT perfusion phantom, covering the whole left ventricle at a time frame during contrast enhancement. (d-e) Signal intensity curves extracted from the left ventricle (AIF) and the myocardium of stress and rest MRXCAT perfusion phantoms generated with saturation delays of 150 ms (d) and 10 ms (e).
Total computation times for MRXCAT generation were 38 and 124 minutes for the breathhold and free-breathing cine phantom, respectively. For the perfusion phantom, calculations took 13.6 and 10.7 minutes for breathhold and free-breathing simulations. In all cases, the vast majority of the time was spent generating the XCAT anatomy. The large difference between cine and perfusion computation times mainly stems from the fact that 360 XCAT time frames were created for cine (24 heart phases, 15 segments), while only 32 time frames were needed for perfusion. By executing only the MATLAB part of MRXCAT, calculation times spanned from 54 s (breathhold cine) to 166 s (free-breathing perfusion).
The Swaymeter recorded displacements of the body in the horizontal plane at waist level. The device consisted of an inflexible 40-cm-long rod with a vertically mounted pen at its end. The rod was mounted on a 20 cm wide metal plate which was fitted over the participant's lower back (level of the posterior superior iliac spine) by a firm belt so that the rod extended posteriorly. Fitted firmly, the Swaymeter offers 1 degree of freedom between the belt and pen as it is free to move in the pitch plane. The pen recorded participant's postural sway on a sheet of millimeter graph paper, fastened to the top of an adjustable-height table (Figure 1). The sway path length was manually determined as the number of millimetre squares traversed by the pen [14]. The anteroposterior (AP) and mediolateral (ML) peak-to-peak sway displacements were also calculated from the extremes of sway length in these two planes, as previously described [14].
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