Echocardiography, or cardiac ultrasound, is the imaging of the heart, a rapidly moving and complex organ located deep within the body. For more than 30 years, engineers and doctors have collaborated to improve the imaging and analysis of the heart's function. Cardiac ultrasound relies heavily on technology to record the heart's ever-moving components – cardiac muscles, valves, and blood. This has driven the need for specialized ultrasound modes and applications for this type of analysis. nnWhile the various ultrasound Doppler approaches are common tools used to analyze valves and blood flow, there are several distinct approaches for analyzing cardiac muscle function. For instance, tissue Doppler has emerged to analyze the global left ventricular systolic and diastolic function. Tissue Doppler is additionally used in clinical studies of metabolic disease and exercise training. nnConcerning coronary artery diseases and rhythmic disorders, analysis of regional contraction is vital, with the most common approach thus far being the visual assessment of cardiac ultrasound images. This is achievable with both tissue Doppler as well as speckle tracking. The prominent technological challenge in actual imaging is to execute the frame rate/temporal resolution and spatial resolution necessary to distinguish all cardiac details.
Tissue Doppler Imaging
The 90's cardiac ultrasound scanners brought about the first commercial possibility for measuring cardiac muscle strains. Significant contributions by the ultrasound technology research group in Trondheim led to this innovation. This early technology estimated velocities using Doppler-related methods to calculate strain based on the spatial velocity gradients. A great deal of effort was given to quantify the function of the left ventricle; however, this method was limited in that it could only estimate velocities and strains based on the ultrasound beam. Unfortunately, "out-of-beam-direction" and "out-of-plane" motion were common limitations.
nSpeckle Tracking
Speckle Tracking is also known as block matching or 2D strain and serves as an alternative to Tissue Doppler. This technique focuses, frame-by-frame, on how various structures in the ultrasound image move. This is accomplished with "speckles" in the images that move together within the underlying structures. While the Doppler methods utilize a separate special acquisition and processing, speckle training relies on image analysis of gray-scale ultrasound recordings.
n3D Strain
Also known as 4D strain, 3D strain is an innovative technique explored by the ultrasound research community due to Doppler and speckle tracking limitations. Even though speckle tracking on 2D gray-scale images delivers 2D motion estimates, "out-of-plane" motion is still an obstacle. Researchers continue to explore 3D block matching and other similar approaches on 3D datasets.
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