**2. Equipment selection and patient position**

The suitable probes for chest US are these equipped with 3.5- to 10-MHz linear, convex, and sector transducers. The high-frequency linear probe can exam the detailed signs of pleura and provide assessment of superficial lesions. Commonly a 3.5–5 MHz probe is used which is suitable for imaging adequate depth of penetration of lung. In some expert's opinion, the best probe to use for chest ultrasound in the 5-MHz microconvex probe because it allows access the intercostals space and facilitates to these patients unable to cooperate by sitting. During chest US examinations, patients can be in the seated (Figure 1.1) or supine position (Figure 1.2). The probe is moved along the intercostals space to avoid interference by ribs or sternum. The transducer can be moved longitudinally or horizontally in the chest wall.

© 2013 Liao et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Liao et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

free space between the visceral and parietal pleura. The formulae to estimate the volume of pleural effusions are well documented [1-5], but the different variation of actual volume was found in individual condition. The classifications of the volume of pleural effusion known currently are minimal, small, moderate, and massive. The minimal effusion indicate the echofree space is seen within the costophrenic angle; small effusion indicates the space is greater than costphrenic angle but still within a one-probe range; moderate effusion indicates the space is greater than one-probe range but within a two-probe; and massive effusion indicates the

Ultrasound Diagnosis of Chest Diseaseses http://dx.doi.org/10.5772/55419 85

The strength of ultrasound lies in demonstrating characteristics of the pleural fluid itself. Four basic ultrasounds patterns of internal echogenicity of pleural effusion were identified and they can be subclassified as anechoic, complex nonseptated, complex septated, and homogenously echogenic (Figure 3). Anechoic effusion is defined as echo-free spaces between visceral and parietal pleura. Complex nonseptated effusion is defined as heterogenous echogenic materials inside the pleural effusions. Complex septataed effusion is defined as fibrin strands or septa floating inside the pleural effusions. Homogenously enchogenic effusion is defined as echogenic spots density evenly distributed within the effusion [2, 3]. A purely anechoic collection is found in exudates and transudates with equal frequency. However, internal echoes in the form of septations or focal areas of debris are due invariably to exudates. US presentations in transudative pleural effusions are not always in an anechoic pattern. Tran‐ sudative pleural effusions may have a complex nonseptated pattern or an anechoic pattern [4].

**Figure 2.** Sonographic images of normal pleura and chest wall using a 5-MHz convex scanner. (A) Transverse image through the intercostal space. The chest wall is visualized as multiple layers of echogenicity representing muscles and fascia. The visceral and parietal pleura appear as echogenic bright lines that glide during respiration (gliding sign). Re‐ verberation echo artifacts beneath the pleural lines imply an underlying air-filled lung. (B) Longitudinal image across the ribs. Normal ribs are seen as hyperechoic chambered surfaces (arrowheads) with prominent acoustic shadows be‐

neath the ribs. Pp, parietal pleura; Pv, visceral pleura; L, lung

space is bigger than two-probe range.

**4.2. Pleural effusion echogenicity**

**Figure 1.** During chest US examinations, patients can be in the seated or supine position (Figure 1.1 on the left; Figure 1.2 on the right).
