# Computational Modeling of Ultrasound C-Scan Imaging Using Transmitted Signal Peak Density
## 1 Introduction  
Ultrasound imaging is an effective imaging technique in the industrial and health sector as it is nondestructive, nonionizing, and relatively inexpensive [1]. It has the potential of having several centimeters of penetration depth, depending on the frequency range used [2]. Three types of scanning modes are available in ultrasound imaging, which are A-scan, B-scan, and C-scan. The A-scan mode works one-dimensionally, only providing amplitude data of the returning echoes from various reflectors situated along the wave propagation direction. On the other hand, the B-scan and C-scan modes provide a two-dimensional image of the plane parallel and perpendicular to the wave direction, respectively [3]. The image quality in the C-scan mode highly depends on the lateral resolution of the ultrasound, as the imaging plane is perpendicular to the wave direction. Therefore, the element size used in the ultrasound transducer, as well as the focusing ability of the transducer crystal, plays heavily in determining the image quality in C-scan mode. Additionally, the frequency level also plays an important role in the image resolution, as the high-frequency ultrasound beam diverges slowly, which makes the beam diameter smallerin the far zone [4]. Furthermore, during image reconstruction, parameter measurement inaccuracies can result in low image quality (e.g., poor edge detection), for which fuzzy preprocessing procedures are applied [5; 6]. Both pulse-echo and pitch-catch techniques were evaluated to produce C-scan images in ultrasonic measurements [7]. Pitch-catch methods are mostly used in industrial applications, whereas pulse-echo techniques have been adopted in medical applications [7; 8; 9; 10; 11; 12; 13; 14; 15; 16]. In the industrial sector, C-scan images can provide very high-resolution subsurface images that can evaluate defect size, delamination, and welding quality [9; 10; 15]. Although in the medical sector B-scan imaging is widely used, the imaging process only uses the RF signal envelope [1]. It fails to provide quantitative measurement related to biological and structural attributes for characterization [17; 18; 19; 20]. On the other hand, a C-scan image can utilize the quantitative ultrasound (QUS) parameters that were used for monitoring cell decay, analyzing cardiac irregularities, and characterizing tumors [1; 21]. Thus, by utilizing QUS, a C-scan image can potentially characterize various tissue properties. For example, in the ophthalmology field, by measuring the ultrasonic backscatter properties, C-scan imaging was used to evaluate eye tissue structures [13]. Various ultrasound parameters of the C-scan method have been evaluated so far. Standard parameters such as amplitude, time of flight, and quantitative parameters such as attenuation and spectral intensity have been utilized in C-scan imaging [7; 9; 22]. Some nonconventional parameters have also been investigated to improve the image quality further in terms of precise detection [22]. One of those parameters is spectral peak density. Coined by [PERSON] et al., peak density represents the total number of peaks and valleys present in a frequency spectrum. Therefore, it represents the magnitude variation of the received signal [21]. Peak density was found to be very sensitive towards the microstructural variation in soft materials [23]. This parameter was evaluated by [PERSON] et al., where it was compared against standard ultrasound parameters [22]. Peak density showed similar and, in some cases, better performance compared to the other parameters; however, the quality of the image was dependent on the application through an intuitive threshold magnitude criterion [22]. Acoustic scattering also plays an important role in evaluating ultrasound parameters during wave propagation in the forward direction [24]. Depending on the size of the structure and ultrasound wavelength, three different levels of scattering can occur. [PERSON] et al.