## 2 Materials and Methods  
### Imaging System  
Multi-angle conventional ultrasound imaging is the method under evaluation within this work. MACUI uses conventional B-mode ultrasound imaging to acquire ultrasound scans that are used to reconstruct the 3D structure of breast tissue. In the method, the probe is rotated around the \(Z\)-axis of the imaging system with the probe placed radially. Breast sections are acquired in the full 360\({}^{\circ}\) range with a certain angle step selected to obtain the desired spatial resolution. Figure 1: Scanning methods for different ultrasound compound imaging (CI) configurations: (**a**) in MACUI, (**b**) in HHUS, (**c**) in FASCI. The use of B-mode ultrasound renders the method virtually probe-agnostic. There is no special need to create a specialized ultrasound transducer or to develop new preprocessing steps. All the advantages of handheld ultrasound examinations can be applied to obtain the best possible individual breast scans. In addition to the standard ultrasound frequency ranges used in HHUS, high- and even ultra-high-frequency ultrasound probes can be used. All pre-processing and even post-processing steps, such as beam steering, digital filtering, or noise reduction to improve image quality, may be applied depending on needs. Taking into account a high attenuation, high- and ultra-high-frequency ultrasound could be utilized, that is, for examination of skin and near-skin tissues [47; 48], however, the authors have not evaluated this. In theory, any standard B-mode probe and ultrasound system enabling external software control can be used in the MACUI method if the probe holder in the scanning equipment is adjusted accordingly. However, the possibility of use is not equal to the usefulness. Many B-mode ultrasound probes have a different range of frequencies, shapes, focusing, and imaging area. In this work, the linear L15-7L40H-5, the convex array C6-2R50 HI-5, and the phased P5-1L15 SI-6 transducers are evaluated. These probes represent a range of different probes available for the Telemed SmartUS ultrasound imaging system, which is a typical and widely available PC-based ultrasound system for medical evaluation. The frequencies used by each probe were 7.5 MHz, and 6 MHz, 5 MHz, accordingly. Only one of the available frequencies of each probe was used during measurement, but the probes have a range of different frequencies available and, with dedicated EchoWave II imaging software, provide tissue harmonic imaging (THI). These options have not been covered in this work. The MACUI method is intended to be used in the configuration, in which the patient lies on an examination bed that includes the water tank with the rotational mechanism below. In this configuration, the breast is submerged in water, and the ultrasound probe placed below can scan the breast at different angles, being attached to the rotational mechanism. To mimic such a system, the Universal Robots UR-3 e-Series cobot has been used to move the probe attached to the arm in the desired manner (Figure 2). The UR3 compact cobot is a six-articulated precision industrial small robot with a built-in safety system. It is force sensitive and can be set to stop immediately when it encounters resistance of as little as 50 N. It weighs only 11 kg, but has a payload of 3 kg, \(\pm\)360\({}^{\circ}\) rotation ability of 360\({}^{\circ}\) on all joints, and an unlimited rotation capability on the end joint. It operates in a range of up to 500 mm. The repeatability of the position of the arm tip is \(\pm\)0.1 mm. Maximum speeds for the wrist joints are 360\({}^{\circ}\)/s and for the other joints 180\({}^{\circ}\)/s. The maximum tool speed is 1 m/s. Figure 3 shows the UR-3 robotic arm equipped with a specially developed holder for the ultrasonic probe of a conventional B-mode ultrasound scanner, which allows it to be automatically positioned and repositioned according to arbitrarily programmed 3D trajectories. Figure 2: Photo of the UR-3 e-series cobot by Universal Robots.