DK2985_C000 1..28 - AlSharqia Echo Club

Principles of Ultrasound 17(A)(B)TVAoVRALARVPVCompression= 34(C)(D)ACOMPRESSION: 34BrightnessBCOMPRESSION: 84Compression= 84Aortic valveechogenicityFigure 1.19 Dynamic range compression. (A, B) Mid-esophageal short axis view of the aortic valve. The effect of varying compressionis shown. Compression ¼ 34. (C) Higher compression at 84. (D) Compression range modifies the slope of the relationshipbetween brightness and echo strength. Secondarily, it also alters the range of echo signal strength which can be displayed by the scaleof brightness. Contrast is therefore enhanced within that range. For instance, the brightness difference between blood and aortic valveis more pronounced with lower compression (slope A). Reducing compression range increases the slope such that larger difference inbrightness will occur for the same difference in echo strength. Increasing compression range reduces the perceived difference in brightnessbecause the slope is more flat (AoV, aortic valve; LA, left atrium; PV, pulmonary valve; RA, right atrium; RV, right ventricle; TV,tricuspid valve).of the overall resolution, that is the axial resolution (alongthe direction propagation of ultrasound), and the lateralresolution (perpendicular to it). For most systems, theaxial resolution, which is of the order of 1 mm, is betterthan the lateral resolution. Image resolution is largelyinfluenced by the design of the transducer, and the beamformer in both transmission and reception. Resolution isfurther discussed in Chapter 3.3. DisplayThe ultrasound image is displayed on a computer monitor,which allows for the viewing of the real-time representationof the ultrasound image. Dynamic range compressiondetermines the range of echo strength used todisplay ultrasound echo intensities and may affectoverall image contrast (Fig. 1.19). For each new frameacquired by the system, the display is refreshed with thenew image data. This is repeated many times per second,allowing for a real-time update of the image. Digital processingand storage capability are today available withmost ultrasound systems.D. Related Factors1. Pulsing CharacteristicsPulsed-waves can be characterized by the following parameters:pulse duration (PD), pulse repetition period (PRP),pulse repetition frequency (PRF), duty factor, and spatialTable 1.4Various Parameters for Pulsed UltrasoundParameters Basic units Units Determined by Common valuesPulse repetition period Time s, ms Sound source 0.1–1.0 msPulse repetition frequency 1/time 1/s, Hz Sound source 1–10 kHzPulse duration Time s, ms Sound source 0.5–3.0 msDuty factor None None Sound source 0.001–0.01Spatial pulse length Distance mm, cm Source and medium 0.1–1.0 mm