Open Veterinary Journal, (2026), Vol. 16(4): 2288-2298

Research Article

10.5455/OVJ.2026.v16.i4.29

Development and evaluation of a gelatin-based phantom model for veterinary diagnostic imaging training

Muhammad Nico Ghossani¹, Maryani Maryani¹, Fitra Aji Pamungkas², Jakaria Jakaria³ and Mokhamad Fakhrul Ulum^4*

¹Study Program of Veterinary Medicine, School of Veterinary Medicine and Biomedical Sciences, IPB University, Bogor, Indonesia

²Research Center for Animal Husbandry, National Research and Innovation Agency (BRIN), Bogor, Indonesia

³Department of Animal Production and Technology, Faculty of Animal Science, IPB University, Bogor, Indonesia

⁴Division of Reproduction and Obstetrics, School of Veterinary Medicine and Biomedical Sciences, IPB University, Bogor, Indonesia

*Corresponding Author: Mokhamad Fakhrul Ulum. Division of Reproduction and Obstetrics, School of Veterinary Medicine and Biomedical Sciences, IPB University, Bogor, Indonesia. Email: ulum [at] apps.ipb.ac.id

Submitted: 12/11/2025 Revised: 28/02/2026 Accepted: 16/03/2026 Published: 30/04/2026

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ABSTRACT

Background: Simulation-based training enhances the competency of veterinarians and veterinary students in diagnostic imaging, with phantoms serving as ethical alternatives to the use of animal tissues. However, in many developing countries, the high cost of commercial phantoms limits their accessibility.

Aim: This study aimed to develop and evaluate a low-cost, gelatin-based phantom as an alternative model for veterinary training.

Methods: In this study, we developed and evaluated a low-cost phantom using animal-based gelatin in the form of “ballistic gel” with or without 10% buffered normal formaldehyde (BNF) preservative. Metal beads, plastic beads, and quail eggs were embedded within the phantom as foreign body models. Durability and imaging quality were assessed using ultrasonography (USG), digital radiography, and electrical impedance tomography (EIT).

Results: The non-preserved phantom exhibited extensive syneresis (90.95%), whereas the BNF-preserved phantom exhibited minimal syneresis (2.53%), thereby maintaining a better texture and durability. The addition of the BNF preservative did not affect echogenicity or visibility of embedded foreign bodies. USG provides limited differentiation among foreign body types, whereas radiography offers a clear distinction between them. EIT further identifies foreign bodies through resistivity contrast, with materials represented by distinct colors.

Conclusion: BNF-preserved gelatin phantoms offer a cost-effective and durable alternative for simulation-based imaging training.

Keywords: Ballistic gel, electrical impedance tomography, phantom, radiography, ultrasonography.

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Introduction

Rapid advances in science and technology have expanded the range of diagnostic methods available in modern medicine, particularly in the field of diagnostic imaging (Ravikanth, 2017). Various imaging modalities are now accessible, including computed tomography, magnetic resonance imaging, positron emission tomography, ultrasonography (USG), and conventional radiography (Septiyanti et al., 2020). USG plays an essential role in detecting abnormalities that may not be apparent on physical examination, thus providing real-time imaging with high clinical relevance (Earle et al., 2016). Similarly, X-ray technology has long been used to identify abnormalities or structural damage in the thoracic cavity, skeletal structures, urinary tract, and gastrointestinal system.

Another emerging modality is electrical impedance tomography (EIT), a non-invasive imaging technique that reconstructs images based on the distribution of electrical conductivity measured at the surface of an object (Endarko and Umbu, 2020). Compared with other imaging methods, EIT offers several advantages, including being radiation-free, relatively inexpensive, and simple to operate (Setiadi, 2015; Ulum et al., 2024a). Since its introduction by Barber and Brown in the early 1980s, EIT has been applied to monitor gastric emptying, lung and cardiac function, neural activity, pulmonary edema, and breast cancer (Teschner et al., 2015). Collectively, diagnostic imaging contributes to resolving approximately 70%–80% of clinical health problems in humans (Akhadi, 2020), advancing the importance of adequate training for clinicians to utilize these modalities effectively.

Simulation-based learning has proven to be more effective in accelerating trainee competency than traditional learning models while also reducing complication rates during clinical procedures (Morrow et al., 2016). Phantom-based training, particularly in USG, allows repeated practice for skill development, including foreign body detection, abscess identification, vascular access (Nolting et al., 2016), and regional anesthesia training. However, in many developing countries, limited access to adequate training remains a major barrier (Earle et al., 2016). Commercially available phantom models, which cost approximately 5–20 million IDR (300 up to 1,200 USD), pose financial constraints for many institutions (Amini et al., 2015). Alternative low-cost homemade phantoms have been explored. However, most of these products are made of perishable materials with limited durability and short shelf life (Earle et al., 2016). For example, agar-based phantoms have been developed to simulate organ imaging and vascular access in small animals, demonstrating usability for up to 4 weeks (Maulana, 2021). Strategies such as the incorporation of preservatives, coating treatments, and the use of novel materials are required to extend their shelf life to enhance their practicality.

Clear ballistic gel, originally designed for ballistic testing in military applications, has gained attention as a tissue analog owing to its superior durability and physical similarity to animal tissues (Amini et al., 2015). These properties highlight its potential as an alternative material for phantom fabrication. This study aimed to develop and evaluate ballistic gel-based phantoms as simulation tools for USG, radiography, and EIT. Ultimately, this approach seeks to provide cost-effective and durable training models to support veterinary education and strengthen the diagnostic imaging competency of veterinary students and practitioners.

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Materials and Methods

Fabrication of ballistic gel phantom

The ballistic gel was prepared following the formulation described by Fackler and Malinowski (1985). Gelatin powder (1,000 g) was dissolved in 9 l of distilled water. The gelatin powder was first mixed with cold distilled water (7°C–10°C) and refrigerated for 2 hours. Two formulations were prepared: gelatin without preservatives and gelatin with the addition of neutral buffered normal formaldehyde (BNF) preservative (Table 1). After cooling, the mixture was heated in a water bath at 40°C–45°C and stirred until homogeneous. The surface of the phantom was coated with FN Waterproof^® spray and No Drop anti-leakage^® paint (PT Avia Avian Tbk., Indonesia), ensuring complete coverage of all areas. The coated surface was allowed to dry after application, after which the effectiveness and durability of the coating were systematically evaluated.

Table 1. Formulations of ballistic gel phantoms with and without neutral BNF preservative.

Fabrication of ballistic gel phantom with embedded foreign bodies

Phantom molds were prepared using 250 ml plastic containers. The molten gel was poured into the molds in two equal layers, with an interval of 5–10 minutes to allow the first layer to partially solidify. To embed the foreign bodies, the metal bead (Ø=9.4 mm), plastic bead (Ø=10.4 mm), and quail eggs were carefully positioned at the center of the gel or between the first and second layers before pouring the remaining gelatin mixture. To ensure complete solidification, the molds were refrigerated for 36 hours. Subsequently, the phantom surface was partially coated with a waterproof spray and sealed with leak-proof paint to enhance its durability and prevent dehydration or leakage during repeated imaging procedures. The embedding of foreign bodies within the gel was intended to simulate clinical conditions, thereby enabling their evaluation using USG, digital radiography, and EIT.

Durability and consistency assessment

The durability of the phantom was evaluated over 4 weeks of storage at room temperature. Weight loss and syneresis (shrinkage) were recorded, and visible physical changes were documented. The consistency was assessed by applying pressure to the phantom using a digital scale until the rupture occurred. We measured the applied weight and penetration depth of the pressing device at the rupture point. Consistency testing was performed at weeks 1 and 4 of the study.

USG evaluation

The phantoms were evaluated using a brightness-mode ultrasound console (Chison ECO3VET) equipped with a linear transducer operating at a frequency of 6–11 MHz, a gain setting of 83 dB, and a depth of 4.4 cm. No commercial phantoms were used in this study. Scans were performed by a single trained evaluator, both longitudinally and transversely, to capture comprehensive imaging perspectives. Echogenicity was quantitatively assessed using the grayscale histogram method in ImageJ image processing software. The intensity values in the ImageJ grayscale histogram were expressed in arbitrary units (a.u.) ranging from 0 to 255 (Maulana, 2021).

For classification purposes, grayscale values were divided into three categories based on quartile segmentation: anechoic (0–85 a.u.), hypoechoic (86–170 a.u.), and hyperechoic (171–255 a.u.) (Ulum et al., 2024b). The mean grayscale value was used as a quantitative parameter for determining echogenicity. To ensure accurate measurements, regions of interest were manually delineated according to the targeted tissue-like structure or embedded foreign body within the phantom.

To monitor changes over time, echogenicity measurements were performed at weeks 0, 1, 2, 3, and 4 to evaluate the stability of the phantom and its suitability as a long-term training model.

Digital radiography evaluation

The ballistic gel phantoms were positioned under a digital radiography unit with a focus film distance of 40 in (100 cm). The exposure parameters of the radiography unit machine were adjusted to 3.2 mAs and 54 kV to optimize image clarity. Radiographic images were displayed on a monitor, annotated, and evaluated for foreign body presence and characteristics.

Radiographic interpretation was performed by assessing the opacities of the foreign objects relative to those of the surrounding phantom materials. Quantitative analysis of opacity was performed using the grayscale histogram method in ImageJ software. The intensity values in the grayscale histogram were expressed in arbitrary units (a.u.), ranging from 0 to 255 (Ulum et al., 2024b). These values were categorized into three groups based on quartile segmentation: radiolucent (0–85 a.u.), gray (86–170 a.u.), and radiopaque (171–255 a.u.).

Opacity measurements were performed at weeks 0, 1, 2, 3, and 4 to evaluate potential changes over time and to assess the durability and imaging consistency of the ballistic gel phantoms.

Electrical impedance tomography

The resistivity of the phantom was measured using an impedance meter based on the Wenner configuration principle (Fig. 1A) with an inter-electrode spacing of a=3 mm (Ulum et al., 2024b). Four electrodes were connected to the instrument and subsequently inserted into the phantoms. The measurements were displayed on a device monitor, after which the data were recorded and organized into tables using Microsoft Excel software. This procedure was repeated along three measurement paths within the phantom (Fig. 1B), with electrode spacings of 2a and 3a applied to each trajectory, respectively. The resulting data were processed in Microsoft Excel and then transferred to Notepad before being analyzed using RES2DINV software to generate the resistivity profiles of the material or foreign object embedded within the ballistic gel. The resulting images represent the material contrast, where different foreign bodies are visualized as variations in resistivity and are displayed through color mapping.

Fig. 1. EIT imaging of the phantom. (A) Wenner configuration (adapted from Utiya and Tongkukut, 2015). (B) Impedance measurement circuit along the three trajectories of the phantom. Note: trajectory a=no foreign body; trajectory b=crossing all three foreign bodies (quail egg, metal bead, and plastic bead); trajectory c=crossing only the egg.

Resistivity evaluation was performed at week 4 on the gelatin phantom with the addition of neutral BNF preservative to monitor potential changes in gel conductivity and the stability of the embedded foreign body visualization over time.

Data analysis

Qualitative findings were summarized descriptively, whereas quantitative data were tabulated and processed using Microsoft Excel software. Prior to inferential analysis, data normality was evaluated using the Shapiro–Wilk test to confirm the suitability of the parametric testing. Subsequently, a one-sample t-test was performed using an online statistical tool (GraphPad QuickCalcs: https://www.graphpad.com/), with a 95% confidence interval; a p-value <0.05 was considered statistically significant. All results are presented in tables and figures and accompanied by concise descriptive interpretations to facilitate clarity and reproducibility.

Ethical approval

This study did not involve live animals or human participants; therefore, ethical approval was not required.

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Results

Phantom fabrication and coating

Figure 2A shows the ballistic gel phantom fabricated from gelatin, measuring 11.58 × 8.32 × 3.40 cm. The phantom exhibited a bright yellow, transparent, elastic, and moist appearance. The coating was done with FN waterproof^® spray and No Drop^® anti-leakage paint (Fig. 2B and C), resulting in partial detachment of the lateral and basal surfaces. Owing to the failure of the coating treatment, further evaluations were conducted only on the uncoated phantoms.

Fig. 2. Fabrication and coating of the ballistic gel phantoms (A) Uncoated, (B) FN^® waterproof spray-coated, and (C) No-Drop^® antileakage paint-coated.

Durability of phantoms

A weight loss analysis over 4 weeks revealed substantial differences in shrinkage among the treatments. Phantoms without preservatives exhibited the highest syneresis, with 90.95% shrinkage, whereas phantoms with BNF preservative showed only 2.53% shrinkage (Table 2). Visual inspection (Fig. 3) confirmed these findings: the non-preserved phantom began to liquefy and became turbid by week 2, whereas the preserved phantom exhibited gradual reductions in rigidity but remained intact for up to 4 weeks.

Table 2. Weight loss of phantoms stored at room temperature for 4 weeks.

Fig. 3. The durability test of ballistic gel phantoms was observed through periodic physical changes over 4 weeks. (A) Phantom without preservative, (B) phantom without preservative after liquefied gel separation from the plastic packaging, and (C) phantom with BNF preservative.Note: BNF=buffered normal formalin.

Phantom consistency

Consistency tests performed on days 7 and 30 demonstrated that phantoms with the BNF preservative required a greater applied force and longer compression time before rupture (Fig. 4A). This indicates higher elasticity and resistance to breakage than non-preserved phantoms, which were more brittle. By day 30, both phantom types showed decreased resistance, indicating increased stiffness and fragility during prolonged storage.

Fig. 4. Consistency evaluation of the ballistic gel phantoms (A) Pressure weight changes over time, (B) consistency test by penetration and depth measurement, and (C) pressure weight measurement. Note: TP=without preservatives; PB=with 10% BNF preservative; 7=day 7; 30=day 30; BNF=buffered normal formalin.

Echogenicity of ballistic gel phantoms

Ultrasonographic imaging of both phantom models demonstrated low echogenicity, with the gel matrix appearing predominantly anechoic (Fig. 5). All foreign body models exhibited hyperechoic surfaces, while their interiors varied: eggs and plastic were anechoic, and metal appeared hypoechoic in non-preserved phantoms but anechoic in BNF-preserved phantoms. The quantitative grayscale histogram analysis (Table 3) confirmed these results. Notably, only the metal in the non-preserved phantom showed a temporal change in echogenicity, shifting from anechoic to hypoechoic between weeks 0 and 1.

Table 3. Echogenicity of ballistic gel phantoms and internal areas of foreign object models.

Fig. 5. Ultrasonographic imaging of the ballistic gel phantoms (A) Non-preserved and (B) BNF-preserved phantoms. Note: T=quail egg, B=metal, P=plastic, BNF=buffered normal formalin.

Radiographic imaging of ballistic gel phantoms

Both phantoms exhibited moderate opacity (gray) at weeks 0 and 1 (Fig. 6). From week 2, the non-preserved phantom displayed a reduction in opacity and became more radiolucent. Among the foreign bodies, metal consistently appeared radiopaque, eggs appeared gray, and plastic varied, appearing gray in non-preserved phantoms but radiolucent in preserved phantoms. The opacity values during the 4-week observation period are summarized in Table 4. These results demonstrate that although gel opacity varied with preservation status, the radiographic characteristics of the metal and eggs remained consistent.

Table 4. Opacity of ballistic gel phantoms and foreign object models.

Fig. 6. Comparison of radiographic imaging of ballistic gel phantoms with corresponding photographic views: (A) Phantom without preservative and (B) Phantom with BNF preservative. Note: BNF=buffered normal formalin.

EIT imaging of ballistic gel phantoms

Impedance measurements were conducted along three trajectories (Fig. 7A and B). The reconstructed resistivity maps (Fig. 7C) demonstrated homogeneous blue patterns in the trajectories without any foreign bodies, indicating uniform conductivity. In contrast, the trajectories intersecting foreign objects revealed distinct color variations representing resistivity contrasts ranging from low (blue) to high (purple). For example, in trajectory b, anomalies included a purple high-resistivity zone from 0 to 56.1 mm, transitioning to red zones (lower resistivity) at 56.1–59.4 and 69.3–75.9 mm. In trajectory c, a yellow–green medium-resistivity region was observed from 0 to 13.2 mm, followed by homogeneous blue regions. These results confirm that EIT can effectively distinguish foreign bodies based on differences in resistivity.

Fig. 7. EIT imaging of ballistic gel phantoms (A) Side view of the phantom during impedance measurement, (B) top view of the phantom showing the three measurement trajectories, and (C) resistivity maps of the EIT after image reconstruction.

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Discussion

This study successfully developed phantom models from ballistic gelatin for use as diagnostic imaging training tools. Durability testing was conducted to assess the shelf life of the phantoms by monitoring the weekly weight reduction over 4 weeks and evaluating the associated physical changes. Marked weight loss was observed in the phantoms without preservatives, which was attributed to bacterial contamination originating from the embedded foreign body models (Table 2). Gelatin liquefaction, caused by bacterial activity, has long been recognized as a fundamental property for microbial identification and differentiation (Frazier, 1926). In contrast, the addition of a neutral buffer formalin preservative effectively prevented liquefaction, thereby reducing the occurrence of syneresis. This effect can be explained by the disinfectant properties of formaldehyde, which is known to eliminate bacteria, viruses, fungi, and parasites and has been widely applied as a preservative in various industries (World Health Organization, 2002).

In addition to weight reduction, the durability of the phantom was assessed based on physical changes. The phantoms preserved with BNF displayed decreased surface rigidity (Fig. 3C), which can be attributed to syneresis. The release of water during syneresis is linked to the strengthening of the double-helix structure in the gel matrix, which leads to contraction and shrinkage (Santoso and Widjaja, 2011). Consistency, an important physical parameter in semi-solid preparations, reflects the resistance of a material to deformation under applied pressure and is closely related to its penetration ability (Nuriani et al., 2013). In ballistic gels, consistency is influenced by the amino acid composition, particularly proline and hydroxyproline, as well as the molecular weight and α/β chain ratio (Santoso and Widjaja, 2011). The addition of BNF preservatives produced a chewier and less brittle gel (Fig. 4), consistent with previous findings that low concentrations of formalin in cadaver preservation enhance tissue supply (Evelyn and Margiana, 2022). Both phantom groups exhibited reduced elasticity over time, as solvent (water) evaporation caused progressive stiffening (Liu et al., 2023).

Ultrasonographic evaluation demonstrated that both phantoms exhibited uniform anechoic echogenicity (Fig. 5). This was expected given the homogeneity of the gel matrix, which resulted in minimal reflection of the sound waves. The magnitude of the reflected echoes in USG is determined by the differences in acoustic impedance between tissues, which are influenced by tissue density and sound velocity (Thrall, 2013). The acoustic properties of ballistic gels closely resemble those of soft animal tissues, which are characterized by relatively small differences in sound velocity and acoustic impedance (Kealy et al., 2011). No differences in echogenicity were observed between the phantoms with and without the BNF preservative, indicating that the addition of the preservative did not alter the acoustic behavior (Table 3).

Foreign bodies embedded in the phantom models exhibited distinct echogenic characteristics. Eggshells appeared hyperechoic owing to their mineral-rich composition, whereas egg contents exhibited low echogenicity. Acoustic shadowing artifacts have been observed beneath highly reflective structures, reducing echogenicity in deeper regions (Thrall, 2013). Similarly, plastic fragments exhibit hyperechoic surfaces with underlying anechoic areas, often accompanied by reverberation artifacts that produce layered concave surfaces, an effect caused by repeated back-and-forth ultrasound reflections (Kealy et al., 2011). Metal objects display the highest echogenicity, with comet-tail artifacts appearing as closely spaced hyperechoic lines resulting from multiple echoes generated by air or metallic interfaces (Kealy et al., 2011). Interestingly, metal echogenicity was greater in phantoms without preservatives, likely because of partial liquefaction, which altered sound propagation by slowing wave velocity in the medium. Because sound travels fastest in solids, slowest in liquids, and slowest in gases, phase changes within a gel may amplify its hyperechogenicity (Thrall, 2013). Consistent with their higher density and atomic number, metallic foreign bodies have the highest echogenicity (Burk and Feeney, 2003).

Radiographic evaluations further supported these findings. At weeks 0 and 1, both phantoms displayed medium or gray opacities, which were consistent with the presence of partial X-ray penetration. In the phantoms without preservatives, the opacity progressively decreased from weeks 2 to 4 (Fig. 6A) owing to liquefaction, which introduced radiolucent gas pockets. Radiographic opacity is strongly determined by object density; denser objects attenuate more X-rays, resulting in greater radiographic opacity (Kealy et al., 2011). As expected, metallic foreign bodies consistently appeared radiopaque, reflecting their high density (Kealy et al., 2011), whereas eggs exhibited intermediate opacity. This phenomenon is attributed to the dense mineralized shell combined with lower egg content (Kealy et al., 2011). Plastic fragments demonstrated variable appearances, ranging from gray opacities in phantoms without preservatives to radiolucencies in preserved models. The latter is due to air gaps formed within the plastic, which, being of very low density and atomic number, consistently appear radiolucent (Burk and Feeney, 2003; Thrall, 2013).

EIT imaging revealed distinct resistivity contrasts across the phantom tracks (Fig. 7C). The homogeneous blue regions represent low-resistivity areas without embedded objects, whereas the heterogeneous red and yellow regions represent foreign materials. Eggshells, primarily composed of calcium carbonate, exhibit high resistivity owing to their insulating properties (Abd, 2014). In contrast, metallic objects exhibit low resistivity, which is consistent with their conductive nature (Bahri et al., 2017). However, their imaging is influenced by adjacent high-resistivity eggs. Similarly, plastic fragments produce high-resistivity anomalies, in line with their insulating characteristics (Ermawati, 2011). The localized red circular artifacts observed on the phantom surface were attributed to damage to the electrode pin during the measurement (Fig. 7B). These findings underscore the capacity of EIT to differentiate embedded materials based on resistivity, thereby complementing ultrasound and radiographic imaging modalities. Consistent with these results, the application of EIT in meatball phantoms has also demonstrated differences in resistivity between metallic and plastic foreign bodies (Ulum et al., 2024b). Moreover, biological tissues with varying fat contents exhibit distinct resistivity profiles (Ulum et al., 2023), and EIT has proven effective in differentiating tissue components based on resistivity variations in breast imaging models using chicken meat phantoms with soft and hard cysts (Choridah et al., 2021).

Overall, this study demonstrated that ballistic gelatin phantoms embedded with foreign bodies can serve as versatile models for multimodal diagnostic imaging, including USG, radiography, and EIT (Ulum et al., 2024a). The addition of the BNF preservative enhanced phantom durability without altering the imaging properties, thereby extending their potential usability as teaching aids. The consistent visualization of foreign bodies across modalities emphasizes the reliability of these phantoms as surrogates for soft tissue. These findings not only provide a low-cost and reproducible alternative to animal tissues but also offer significant potential for advancing training and research in veterinary and medical imaging.

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Conclusion

This study demonstrated that gelatin-based ballistic gel phantoms preserved with 10% BNF offer improved durability and consistency without altering echogenicity, making them suitable as reproducible learning media for diagnostic imaging. USG visualized foreign bodies with limited material differentiation, radiography provided a clearer distinction between metals and eggs, and EIT successfully differentiated materials based on resistivity contrasts. The novelty of this study lies in the combination of multimodal imaging approaches on a gelatin-based phantom embedded with foreign bodies, providing a low-cost, practical, and versatile platform with strong potential for future applications in veterinary and medical imaging research, as well as standardized training modules.

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Acknowledgments

The author gratefully acknowledges the Veterinary Teaching Hospital, School of Veterinary Medicine and Biomedical Sciences, IPB University, for providing access to USG and digital radiography equipment, which was instrumental in conducting this study.

Conflict of interest

The authors declare that there are no conflicts of interest.

Funding

This research was supported by the Riset Inovasi untuk Indonesia Maju (RIIM) Program of the National Research and Innovation Agency (BRIN), funded through the Indonesia Endowment Fund for Education (LPDP), Ministry of Finance of the Republic of Indonesia (Grant Nos. 18/IV/KS/06/2022, 4830/IT3.L1/PT.01.03/P/B/2022, and 3301/IT3.L1/PT.01.03/P/B/2022).

Authors' contributions

Conceptualization: M.F.U. Data curation: M.N.G., M.M., and M.F.U. Formal analysis: M.N.G. and M.M. Methodology: M.F.U. Software: M.N.G. and M.M. Validation: M.F.U., J.J., and F.A.P. Investigation: M.N.G. and M.F.U. Writing-original draft: M.N.G. and M.F.U. Writing, review, and editing: M.N.G., M.M., F.A.P., J.J., and M.F.U.

Data availability

All data are presented in this paper. Thesis data are deposited in the Bogor Agricultural University repository and can be freely accessed online at https://repository.ipb.ac.id/handle/123456789/112950

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