intra-operative TEEs during surgical cases and they interpret their own studies. Anyone performing a bedside or "point of care" echocardiogram is expected to interpret their own study as it is performed. Pocket-sized TTE devices are growing in popularity. Limitations TTE is inherently limited in what it is capable of doing. Notably, it must be used through the skin, and ultrasound waves must go through skin and soft tissue before reaching the heart. This is in contrast to transesophageal echo (TEE) in which the probe is directly behind the left atrium in the esophagus and has far less tissue to penetrate, which means images from TEE are far superior in quality. Extremes in body sizes (obesity and cachexia) limit the acoustic windows and degrade the image quality of TTEs. TTE is also limited in its views of structures. Being a surface modality, the structures closest to the skin are better visualized than those deeper to the skin. A common example that demonstrates this is the visibility of the left atrial appendage. This structure is known to form clots in atrial fibrillation and the LAA is rarely seen on TTE but readily seen on TEE. Cardioversion of atrial fibrillation in someone not on anticoagulation would require TEE to best visualize the LAA to rule out a thrombus. (If a thrombus is present, there is a much higher risk of stroke if returned to a sinus rhythm.) Like all of the kinds of echocardiography, TTE is limited to structure and function. It is not, for example, able to determine perfusion of the myocardium, which would require a metabolic imaging modality such as PET or SPECT stress testing. Perfusion can be inferred based on wall motion, however. Modalities 2D echo This is the most common modality used today. A two-dimensional plane is formed by sweeping the ultrasound waves to obtain an image that varies with angle and depth. Evaluation of the structures is done in this view. M-mode This modality is obtained at a single angle and then plotted against time to obtain an image. It can be used to watch the movement of structures with time Doppler Color doppler Color doppler is a form of 2D echo in which the doppler shift of the structures is shown as color. Typically, this is shown as red and blue with red indicating movement toward the transducer and blue indicating movement away from the transducer. This