*3.4.2 Volume rendering*

*Artificial Intelligence - Applications in Medicine and Biology*

data and displayed to the user with 3D impression [30]. The physicians can view the 3D ultrasound reconstruction result on three orthogonal slice views, which is in terms of traverse plane, coronal plane, and sagittal plane [17]. The resliced images are presented together with texture-mapped 3D rendering. There are three approaches of display [1], which are the planar cross-sectional images, the cube view, and the orthogonal planes. The limitation of planar viewing is that there will be possibility to loss of information due to the complex shape of ROI, especially when viewing spinal curvature. Thus, the use of nonplanar volume rendering method can compensate this limitation [31]. Due to its simplicity and the fact that it does not require high computational power, the multiplanar reformatting method is favorable among researchers and practitioners alike to visualize the 3D ultrasound reconstruction. **Figure 6** shows the examples of planar cross-sectional images and the cube view, while **Figure 7** shows the difference between

*The example shows the difference of planar and nonplanar volume rendering in the assessment of scoliosis [31].*

*(a) Planar cross-sectional images of reconstructed volume data [8] and (b) cube view of reconstructed volume* 

**82**

**Figure 7.**

**Figure 6.**

*data [1].*

planar and nonplanar volume rendering.

Volume rendering technique involves ray-casting or ray-marching techniques where the change of light that went through the 3D volume data is projected as the output visualization results for the operator to view [32]. The light absorption principle [33] is implemented in the volume rendering technique where every voxel has the attributes such as brightness, transparency, and color [30]. So, there are several approaches used for the volume rendering visualization, and they are maximum intensity projection and translucency rendering [1]. The volume rendering can distinguish between tissue and fluids very well, and hence, it is suitable to view 3D ultrasound fetal image [1, 32]. However, the volume rendering is CPU-intensive and is not suitable to view the soft tissues details [1]. **Figure 8** shows the ray-casting in volume rendering technique, and **Figure 9** shows the example of volume rendering that uses maximum and minimum intensity projection.

#### **Figure 8.**

*The volume rendering technique involves several rays passing through 3D volume data. The synthesis methods can be applied to each voxel value that the ray passed to produce specific effects, such as transparency and maximum intensity projection of certain objects [32], such as tissues, blood vessels, etc.*

#### **Figure 9.**

*The different volumes rendering visualization of 3D ultrasound imaging system approaches, where (a) shows the maximum intensity projection of a fetus and (b) shows the minimum intensity projection of blood vessels in the liver [30].*
