# Low-Cost and Easily Fabricated Ultrasound-Guided Breast Phantom for Breast Biopsy Training
## 4 Discussion  
The learning curve for performing ultrasound-guided breast biopsy could be overcome by performing simulation training using a breast phantom. Considerable improvements were achieved in the moderately experienced and inexperienced groups through training using the developed breast phantom. Compared with the preinstructional performance, the postinstructional score revealed a 4.88-fold improvement (Figure 5), with the largest improvement achieved in the moderately experienced group. The experienced group, comprising one participant who had prior training in ultrasound-guided biopsy and frequently performed office-based ultrasound in his or her practice already had the highest percentage score in the preinstructional test and this was unchanged in the postinstructional test. The breast-phantom-based training was well received by the participants and significantly increased their confidence in performing the ultrasound-guided breast biopsy. The outcome could be seen in the improved percentage mean scores of the postinstructional test for the moderately experienced and inexperienced groups. Overall, the gelatin-based breast phantom developed in this study satisfied the participants. The Young's modulus of the phantom tissue samples measured from the indentation test fell reasonably in the reported ranges of the Young's modulus for real normal fibrog-landular tissue and normal fat tissue [9]. Simulated glandular tissue has higher Young's modulus compared to the simulated fat tissue; hence, the glandular tissue will produce a stiffer haptic feedback. However, our survey suggested that there should be a larger difference in haptic feedback between benign and malignant tumors, which can be understood as the Young's moduli in the literature having large variation. Acoustic parameters and ultrasound images for our simulated tumors have been provided as a reference for future studies. All the acoustic parameters were measured with 5 MHz single element transducer (in-house developed ultrasound system). Meanwhile, the ultrasound images were captured using the clinical available ultrasound system (8 MHz) in hospital to confirm the visual outcome. Acoustic parameters such as speed of sound are dependent on the sample's density and acoustic impedance; hence, the frequency of the transducer used will not affect the results. Moreover, our study showed that samples with a higher Young's modulus would pose a higher value in acoustic parameters (i.e., speed of sound, attenuation coefficient and relative backscatter power) and appears brighter in ultrasound imaging. The participants could differentiate between the shapes of cysts and benign and malignant tumors in ultrasound images. The multilayered gelatin-based breast phantom produced an ultrasound image similar to that produced by the fat tissue in real breasts. Artifacts caused by the boundary between the fat and glandular tissues in a real breast were successfully duplicated in our multilayered gelatin-based phantom (Figure 7e). Acoustic properties and ultrasound images for our simulated tumors have been provided as a reference for future studies. Numerous low-cost DIY breast phantoms have been proposed. Turkey/chicken breast embedded with peas and gelatin-based phantoms are the most commonly used models in ultrasound-guided breast biopsy simulation training [12, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24]. While turkey and chicken breast can be easily obtained from the supermarket, their preparation process, such as cleaning and thawing, can be troublesome and is not user friendly. Different types of ready-to-use materials have been used to simulate tumors. Aspects such as shape, brightness and contrast of the embedded simulator in ultrasound images are prioritized when selecting a material, but the haptic force produced by the embedded simulator during needle insertion may be overlooked. We were also unable to find a low-cost DIY breast phantom that contains all three types of simulators: A benign tumor, malignant tumor and cyst.