TECHNIQUE Lungs are voluminous organs, hence detection and localization of pathologies may seem challenging. These assumptions by the machine form the basis for two of the most important artifacts used in lung ultrasound–A-lines and B-lines ( Figure 1). The image formation is dependent on a few basic assumptions : the ultrasound pulse travels in a straight line, the speed of sound in tissues is constant and the depth at which echo is generated is assumed to be determined by the time delay at which the echo signal is received by the probe. The echo signal thus generated, returns to the transducer and is used for image formation. Normally, the transducer emits a short ultrasound pulse which is transmitted into the body and undergoes reflections and scatterings at various levels as it passes through the tissues. PHYSICS Basic knowledge of physics behind the generation of ultrasound artifacts is essential for image interpretation and extrapolation in various lung pathologies. Written informed consent was taken from each patient for publication of images. The following pictorial review attempts to simplify the physics, technique, interpretation, and pitfalls in performing lung ultrasound. Although the linear transducer is usually used for evaluating the pleura, lung ultrasound is widely performed with convex or micro convex transducers, the latter being preferred if available. Furthermore, lung ultrasound has a short learning curve and has been found to give reproducible results. It has the advantages of being cost-effective, feasible with bedside availability, lack of ionizing radiation, and allowing real-time imaging. Lung ultrasound is based on understanding and analyzing the existing acoustic artifacts. Today, the principles of the BLUE protocol in lung ultrasound in the critically ill (LUCI) provide a standardized and simplified technique for performing and interpreting lung ultrasound. In 1996, Lichtenstein proposed the Bedside Lung Ultrasound in Emergency (BLUE) protocol which was rejected repeatedly, before being finally accepted after 12 years. The same artifacts were used by Lichtenstein to develop the principles of lung ultrasound. Its major drawback was poor penetration of the ultrasound beam due to the overlying thoracic cage and air content within the lung which led to artifacts. INTRODUCTION Traditionally, the role of chest ultrasound in the evaluation of dyspnea was limited to the diagnosis of pleural effusion and guiding interventions like thoracocentesis. ▪ Correlation with history and clinical findings at the bedside further adds to the diagnostic value of this quick and feasible technique. ▪ Lung ultrasound is based on analyzing the ultrasound artifacts generated, and applying the principles of the Bedside Lung Ultrasound in Emergency (BLUE) protocol to arrive at a diagnosis. ▪ Lung Ultrasound is a useful tool, especially for bedside diagnosis of dyspnea in the acute and critical care setting.
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