Andersons pediatric cardiology 469

Control of the speed of the sweep enables accurate measurements of intervals in the cardiac cycle, and the high-repetition frequency of the technique allows not only excellent temporal r

methods.

M-Mode Imaging

M-mode echocardiography is derived from an M line superimposed on a cross-sectional image The M-mode trace itself shows time as the second dimension Control of the speed of the sweep enables accurate measurements of intervals in the cardiac cycle, and the high-repetition frequency of the technique allows not only excellent temporal resolution of moving structures but also precise

measurements of mural thickness and cavity size In this way, the information derived is superior to that obtained from B-mode imaging M-mode

echocardiography is still commonly used for the evaluation of left ventricular function, using short- or long-axis sections through the left ventricle, and the timing of cardiac events such as left ventricular ejection time, using a short-axis section through the aortic valve Although it is no longer recommended by the most recent pediatric quantification guidelines, M-mode is still widely used in most pediatric laboratories and has advantages in young children with high heart rates because of the excellent temporal resolution

Cross-Sectional Imaging

Although adults have the disadvantage of having poorer imaging windows often affecting penetration and signal-to-noise ratio, this rarely is a problem in

younger children Typically the imaging windows are better, resulting in higher-quality images Lower depths allow the use of higher frequencies, therefore improving spatial resolution Children have heart rates requiring a higher

temporal resolution especially for visualizing rapidly moving structures like valve leaflets Image optimization will always be a compromise between spatial and temporal resolution A few general principles can result in image

improvement:

1 Always start scanning with the highest possible transducer frequency because this optimizes spatial resolution For pediatric scanning, high-frequency probes (8 to 12 MHz) must be available and used When penetration depth is limiting image acquisition, a lower frequency probe can be used Typically, different transducers are used for different parts

of the exam For subcostal imaging, higher penetration is required and typically probes between 5 and 8 MHz are used depending on the child's age and body size For parasternal imaging, higher-frequency probes are used, typically in younger children and infants

2 In infants, scanning using fundamental frequencies generally provide good-quality images Harmonic imaging should be avoided in younger children because it reduces axial resolution If penetration and low

signal-to-noise ratio becomes problematic in older children, using

harmonic frequencies can improve image quality

3 Current machines provide good presets with automated image

optimization for different patient sizes and ages Optimal use of the presets will improve overall image quality Optimizing two-dimensional images may require manually changing gain and dynamic range settings (compression) so that the structures of interest can be seen with the highest possible definition time gain compensation is used to make the images as homogeneous as possible at different depths (particularly to reduce near field gain) Image depth and focus are always optimized to image the structures of interest

4 For optimizing temporal resolution, use the narrowest sector width where possible

5 Depth settings are minimized to include the region of interest

Blood-Pool Doppler

Optimizing the Settings for Continuous Wave

Doppler

The continuous wave image is an echocardiographic image that is influenced by all the parameters that affect a normal cross-sectional picture The gain controls, therefore, should be manipulated to produce a clean uniform profile, without any blooming Typically the Doppler gain should be increased not to miss any

information, and the gain needs to be adjusted to reduce blooming of the signal that can result in overestimating velocities and gradients The compress control assigns the varying amplitudes a certain shade of gray If this control is either very low or very high, the quality of the spectral analysis graph will be affected, and this may lead to erroneous interpretation The reject control eliminates the smaller amplitude signals that are below a certain threshold This helps to