## 4 Acoustic Behavior of the Diseased Pleura
\begin{table}
\begin{tabular}{c|c|c} \hline
**Hydrogotologic Pattern** & **Expected Artefacts** & **Examples of Pathology** \\ \hline Alveolar filling & Combined aspect of vertical, variable, very heterogeneous artifacts, and subpleural & Organizing diffuse alveolar damage and infections \\ consolidation. & Bacterial infections & Bacterial infections \\ Many native frequencies & Pulmonary alveolar protenosis \\  & & eosinophilic lung diseases \\  & Drug toxicity \\ ARDS & \\ \hline Nodules & Nodules can be visible using a linear probes if located at pleural level. They acquire & carcinomas, sarcomas, melanoma \\  & suggestive locations depending on the disease and often appear like vertical artifacts & Lymphoma \\  & with nodular and non-point-like origin & Lymphed interstitial pneumonia \\  & & Nocardiing infections \\  & Granulomatous infections \\  & Sercoidosis & Pneumoconiosis \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._The lung artifactal pattern sometimes called White Lung (Figure 4) is characterized by a granular and mostly white texture, which starts at the pleura line and ends at the bottom of the screen. Together with the pattern characterized by very homogeneous and confluent vertical artifacts, it appears to correlate with CT ground glass attenuation [36]. The White Lung pattern suggests the presence of a relatively homogeneous scatterer distribution (many small airspaces close to each other which contribute to the formation of many small acoustic traps) which gives rise to numerous multiple reflections. A random distribution of small and close scattering air bubbles is needed to obtain such a pattern [33]. In this case, the expected histology is consistent with a diffuse pathological reduction of the air spaces which, however, would remain surrounded by enough interstitium to allow the type of interaction just described. In white lung, the distribution of the scatterers does not deny the existence of a relatively ordered porous structure. Usual Interstitial Pneumonia (UIP) is the histopathologic pattern of Idiopathic Pulmonary Fibrosis (IPF) [31], characterized by \"temporally heterogeneous\" interstitial fibrosis and honeycomb, in which zones of normal lung tissue are adjacent to zones of advanced architectural remodeling. Fibroblast foci occur at the interface between dense scar and adjacent normal lung. The abnormalities of IPF are most prominent at the periphery of the lungs (sub-pleural tissue, easily explored by ultrasound) and in the lung bases, regardless of the stage. Acute exacerbations [37] are expected in the history of patients with IPF and they show pathological pictures of diffuse alveolar damage or organizing pneumonia, superimposed on a background of peripherally accentuated lobular fibrosis with honeycomb. Therefore, the full/empty ratio in the sub-pleural tissue of patients with IPF is characterized by the presence of larger, irregular, attenuating acoustic traps with small residual airspaces (Figure 5). From a histomorphometric two-dimensional point of view, the pleural plane shows a very heterogeneous and irregular distribution of \"full\" areas (the acoustic traps). This relative disorder can be described with the use of some algorithms, which can appreciate the 2D characteristics of the traps, such as their number, thickness, perimeter, area, and connectivity [38]. Figure 4: (**A**): The picture represents a pulmonary scan of a newborn with Hyaline membrane disease, showing White lung (Image obtained with a commercially available machine, Esaote MyLab 25 equipped with a linear probe 10 MHz). On the right (**B**) the corresponding histopathological picture. Residual airspaces are small (about 50 \(\upmu\)m), separated by a mean distance in the order of 100–150 \(\upmu\)m. In this condition the small diameter of the scattering bubbles and their small relative distance are probably the prerequisites for this acoustic effect.