# Low-Cost and Easily Fabricated Ultrasound-Guided Breast Phantom for Breast Biopsy Training
## 2 Materials and Methods  
### Breast Phantom Manufacture  
A double-layered gelatin-based phantom consisting of malignant tumors, benign tumors and cysts was produced. Gelatin tissue samples were produced by tuning the concentration of gelatin until its Young's modulus was similar to that of fat or glandular tissues. The simulated tumors were chosen on the basis of feedback from an experienced doctor to provide a realistic haptic feedback force during core needle placement. Molds: Two hemisphere-shaped molds with different diameters, 90 mm (mold A) and 120 mm (mold B), were designed using the computer-aided design software SolidWorks (SolidWorks 2018; Dassault Systemes SolidWorks Corporation), as shown in Figure 1. The molds were manufactured through three-dimensional printing using polylactide. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Available** & **Types** &
\begin{tabular}{c} **Fabrication** \\ **Process** \\ \end{tabular} & **Cost** & \multicolumn{2}{c}{**Tissue-Mimicking Capability**} \\ \hline
[29; 30; 31] & PVC & Complex & Medium & \
\begin{tabular}{c} \(\blacklozenge\) \\ \(\blacklozenge\) \\ \(\blacklozenge\) \\ \(\blacklozenge\) \\ \end{tabular} &
\begin{tabular}{c} Can resemble acoustic and \\ mechanical properties \\ Various lesion types \\ Multilayer structure \\ \end{tabular} \\ \hline
[32] & Silicone rubber & Complex & Medium & \
\begin{tabular}{c} \(\blacklozenge\) \\ \(\blacklozenge\) \\ \(\blacklozenge\) \\ \(\blacklozenge\) \\ \end{tabular} &
\begin{tabular}{c} Can resemble acoustic and \\ mechanical properties \\ Various lesion types \\ Multilayer structure \\ \end{tabular} \\ \hline
[33; 34; 35] & Commercial & Ready to use & High & \
\begin{tabular}{c} \(\blacklozenge\) \\ \(\blacklozenge\) \\ \(\blacklozenge\) \\ \(\blacklozenge\) \\ \end{tabular} &
\begin{tabular}{c} Can resemble acoustic and \\ mechanical properties \\ Various lesion types \\ Multilayer structure \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._Simulated tumors: A rubber glove finger filled with colored solution was used to simulate cysts with a diameter of approximately 20 mm. Benign tumors were simulated using regularly shaped dried sweet potato and dried agar konjac with a diameter of 10 mm. The malignant tumor, which is the target of needle biopsy, was simulated using a pickled shallot carved into an irregular shape. Glandular tissue: Gelatin powder (40 g) was dissolved in 200 mL of 70 \({}^{\circ}\)C tap water. The solution was mixed at 60 rpm for 5 min. The air bubbles were removed. [PERSON] and blue food coloring was added to give the gel solution an opaque appearance. The gel solution was poured into mold A until it was 90% full to simulate the breast contour. The gel solution was refrigerated at 4 \({}^{\circ}\)C for 30 min until it reached a semi-molten consistency. The simulated tumors (Figure 2a) were placed shallow in the mold. The gel solution was poured into the mold again until it was fully filled to cover the simulated tumors. The semi-molten gel was then refrigerated for another 2 h. The completely solidified glandular tissue was removed from the mold and prepared for use later. Fat tissue: Gelatin powder (15 g) was dissolved in 300 mL of 70 \({}^{\circ}\)C tap water. The solution was mixed at 60 rpm for 5 min. Air bubbles were removed. [PERSON] and blue food coloring was mixed in to give the gel solution an opaque appearance. A height of 12.5 mm from the base of mold B was marked. The gel solution was poured into mold B up to the marked line (Figure 2b). The gel solution was refrigerated for 30 min at 4 \({}^{\circ}\)C. Solidified glandular tissue from mold A was placed on top of the solidified gel in mold B and it was made sure that the space between mold B and the glandular tissue was uniform (12.5 mm for spacing distance), as depicted in Figure 2b. Gel solution was poured into the mold again until the uniform space between mold B and the glandular tissue was fully filled. The gel solution was refrigerated for another 4 h until it had completely solidified.