Lunch box and fruits as a simulator for teaching basic physics of ultrasound: A mixed research methods study

Abstract

Aim

To develop and evaluate a practical, low-cost ultrasound training simulator for teaching basic ultrasound physics and knobology, including probe orientation, tissue impedance, essential hand movements, and recognizing image artifacts while observing scanned objects.

Methods

The simulator consists of (1) one complete lemon, (2) half a lemon, (3) half a kiwi fruit, and (4) an avocado pit. These objects were secured inside a plastic box using screws, nails and double-sided foam tape, after which the box was filled with water. The estimated total cost was less than 15 US dollars. The simulator was prospectively tested to teach basic ultrasound physics during the period of 4th January 2021 till 14th October 2021 on 59 undergraduate junior surgical clerkship students, who had no prior exposure to ultrasound. Quantitative feedback was collected through a Likert-scale questionnaire evaluating educational value, skill acquisition, and user satisfaction. Qualitative data were obtained from open-ended questions. Descriptive statistics were used for quantitative responses, while inductive thematic analysis was applied to qualitative comments.

Results

58 students filled the questionnaire (response rate of 98.3%), 57 of them (98.3%) recommended the simulator to peers, and all assessed items received the highest median rating (5 out of 5), including items assessing conceptual understanding, procedural skills, and enjoyment. Thematic analysis provided three major themes: Learning Enhancement, Engagement and Motivation, and Training Limitations. Students reported improved understanding of ultrasound physics, artifact recognition, and probe handling. The simulator was described as engaging and enjoyable, promoting self-directed learning. However, students noted limitations related to session duration, realism, and the need for additional practice opportunities.

Conclusion

The proposed low-cost ultrasound simulator was highly rated for its educational value and engagement potential. Qualitative insights complemented these findings by revealing strong learner enthusiasm. Expanding session duration and increasing clinical fidelity may further enhance its utility.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13017-025-00637-z.

Introduction

Point-of-care ultrasound (POCUS) is a valuable diagnostic tool increasingly used in acute care medicine worldwide. Effective utilization of ultrasound relies heavily on the operator’s experience in selecting appropriate instrumentation, accurately scanning anatomical structures, and correctly interpreting sonographic images. Training is essential to develop competency in POCUS, and it is recommended that such training begins at the undergraduate level [1]. While experience is gained with repeated practice, it must be built on a solid understanding of basic ultrasound physics [2, 3] which is traditionally taught in theoretical POCUS courses prior to practical hands-on training [4].

There is significant disparity in the availability of medical, educational, and research resources between low-income and high-income countries [5]. Developing an affordable simulator can help make POCUS training more widely accessible particularly in low-income settings [6]. Home-made phantom models using readily available materials provide alternative low-cost training opportunities when human subjects are not available or feasible especially in interventional procedures. These models have been used to improve competency in POCUS [7, 8] in a wide range of clinical applications including diagnosis of pathological lungs, drainage of pleural effusions [9], interventional urology and radiology [8], detection of foreign bodies [10], ultrasound-guided fine needle aspiration [11, 12], venous access [13], and nerve blocks [7, 14, 15]. The highly adaptable nature of home-made models allows for easy variation in the level of complexity to suit the experience level of participants.

Computed tomography (CT) scan has been utilized to evaluate the quality of internal structures of vegetables [16], and damage from loading and storing pressures on different types of apples and pears [17, 18]. Accordingly, we thought of transferring this application to scan fruits by ultrasound. Practical hands-on training is essential for developing the required profeciency in correclty interpret ultrasound images. A thorough understanding of ultrasound physics, including tissue impedance, knobology, and common artifacts, is fundamental for accurate image interpretation and clinical decision-making [19–21]. Despite its importance, teaching these core principles remains challenging due to limited resources and the complexity of existing training equipment. Many programs face challenges to effective ultrasound education due to limited funding, which affects their ability to hire qualified instructors or acquire essential ultrasound machines and simulators [22]. Traditional teaching methods often fall short in addressing both the theoretical and practical aspects of ultrasound physics. Some advanced simulators, such as “pseudo-ultrasound,” produce images by approximating basic ultrasound physics from other imaging methods (like CT or MRI) [23]. Despite that, fully replicating all artifacts remains challenging which underscores how crucial accurate physics is for effective POCUS learning [23]. Additionally, peer-to-peer and small-group training have been found to be effective methods; however, they necessitate careful planning and execution to ensure quality education and successful skill acquisition [24]. Therefore, we aimed to develop and evaluate a practical, low-cost ultrasound training simulator to teach basic ultrasound physics and knobology including probe orientation, tissue impedance, essential hand movements, and recognizing image artifacts while observing the scanned objects.

Methods

Objectives of the model

The model objectives included learning basic physics and knobology principles. The components to be developed included: (A) Tissue impendence of fluids, soft tissues, fibrous tissues, solid tissues, and air; (B) Orientation and Knobology: orienting the probe in different sections while observing the scanned objects having different media. (C) Learning the different hand movements and developing the hand eye coordination while observing the objects being scanned. These movement were: (1) shifting, (2) tilting, and (3) fanning [6]. D) Identifying basic artifacts: The selected important artifacts were: (1) shadow artifact, (2) mirror artifact, (3) and reverberation artifact [2, 3].

Developing the model

Finding the proper container

Different containers were tested searching for a suitable design. Rounded containers were not suitable because the ultrasound probe surface will not fully contact the container wall. Air will be located between the probe and the container preventing ultrasound waves. A transparent plastic box with a cover was deemed the most suitable container for the simulator because it properly permits performing the POCUS scan while directly observing the scanned objects (Fig. 1).

Fig. 1.

Different fruits and containers were tested searching for a suitable simulator (A). Rounded containers were not suitable because air lays between the probe and the container preventing ultrasound waves (B). Flat wall containers were suitable but dark ones prevented direct vision of the studied objects (C). A transparent plastic box with a cover was deemed the most suitable container for the simulator (D)

Choosing the fruits and stabilizing them

Different types of fruits have been tested to find the most suitable ones. This included plums, clementines, tomatoes, oranges, lemon, strawberries, kiwi, apples, and avocados. It was important to cut the fruits to be able to scan the internal structures of the fruits by ultrasound. The peel of a lemon will not permit the ultrasound waves to pass through because it is waterproof to protect the lemon from mechanical damage, ultraviolet radiation and dehydration [25]. The final selected fruits were as follows: (1) one complete lemon, (2) half a lemon, (3) half a kiwi fruit, and (4) an avocado pit. Table 1 shows the final list of needed material to build up the simulator, and their estimated cost, which is less than 15 dollars, of which 5 dollars are consumables. Because fruits kept moving in the water and changing their location and direction, it was essential to fix them in specific locations to standardize the ultrasound simulator. Figure 2 demonstrates the methods of fixing the fruits in water within the plastic box.

Table 1.

The needed material to build up the simulator and their current approximate cost

Material	Approximate cost $
Reusable components
Transparent plastic box and its cover (25 × 18 × 16 cm)	3 $
Double sided foam tape	4 $
Used plastic cover of a small jar	0 $
3 Screws (3.5 cm long)	1.5 $
2 small nails	0.1 $
Consumables
Water bottle (600 ml)	0.3 $
1 full lemon	0.4 $
Half lemon (cross section)	0.2 $
Half kiwi (longitudinal section)	1.3 $
Avocado pit	1.7 $
Estimated total cost	12.5 $

Fig. 2.

Fixing the fruits in the water: Two small nails penetrated a plastic cover of a small jar then fixed by double sided foam tape to the bottom of the box (A and B). Half a kiwi was fixed by these nails (C). 3 screws were screwed through the box lid and the selected fruits so that they do not move (D)

The final model

Figure 3 shows the final design of the simulator. A small space of air was left in the top of the box. The tip of the complete lemon was directed towards the left side of the box (simulated to be proximal in the human abdomen). A space was left between the half lemon and half Kiwi to train for fanning (Fig. 3). The cut surfaces were facing each other. The final tested model fulfilled its objectives as follows: A) Tissue impendence: (1) Fluid: water in the box (2) Soft tissue half lemon and half Kiwi (3) Fibrous tissue: complete lemon (4) Solid tissue: Avocado pit, 4) Air at the top of the box (Fig. 3); B) Orientation and Knobology: the students could orient the probe by using the lemon which has different ends to appreciate the longitudinal and cross sections in relation to the probe marker (Fig. 4). C) Learning the different hand movements and developing the hand eye coordination while observing the object being scanned. These movement were: (1) shifting, (2) tilting, and (3) fanning (Figs. 4 and 5, 6, and 7). D) Identifying basic artifacts: The students could demonstrate: (1) the shadow artifact by the avocado pit (Fig. 5), (2) the mirror artifact as made by the wall of the box (Fig. 6), and (3) the reverberation artifact by scanning air by placing the probe on the lid of the box (Fig. 8).

Fig. 3.

The final design of the container shown from above (A) and from the side (B). The used fruits were complete lemon (L), half a lemon cut transversely (HL), half a kiwi fruit (HK) cut longitudinally, and an avocado pit (A). A small space of air was left in the top of the box (B). The tip of the complete lemon was directed towards the left of the box representing the proximal side of the body (black arrow). Note the space left between the half lemon and half Kiwi to train for fanning

Fig. 4.

Orientation of the probe, coronal section of the box. The marker of the small print convex array probe is directed proximally (yellow arrow) coinciding with the tip of the lemon (black arrow) (A). Sonographic image of the same section (B). The tip of the complete lemon is to the right of the screen (black arrow) corresponding to the marker of the probe (yellow arrow). Tilting the probe 90 degrees to the right (C) locates the marker of the probe up (yellow arrow) to achieve a cross section of the lemon

Fig. 5.

The probe is then shifted to the right in the coronal section (white arrow) while the probe marker is located proximally (yellow arrow) to cross through the avocado pit (A). Sonographic image of the same section (B) showing the avocado pit simulating a gall stone with shadow artifact (black arrowheads) lying between the complete lemon (white arrow) and half lemon (yellow arrowhead). Note that the probe marker to the right of the screen (yellow arrow)

Fig. 6.

The probe is then further shifted to the right in the coronal section (white arrow) to be at the distal end of the box (A). Sonographic image of the same section (B) showing the half lemon (white arrow) located near the box walls (dashed yellow line) meeting with a right angle at 16 cm depth (the width of the box). These two walls caused 3 mirror artifacts (yellow arrows)

Fig. 7.

An illustration of the fanning movement. Fanning up (dashed yellow arrow) (A) shows the half lemon on the screen (B), while fanning down (dashed yellow arrow) (C) shows the half Kiwi fruit (D)

Fig. 8.

Sagittal section of the box. The marker of the small print convex array probe is directed proximally (yellow arrow) to demonstrate the reverberation artifact of air. (A). Sonographic image of the same section using a linear probe (B) showing the classical reverberation artifact with horizontal A lines (white arrows), equal distances between them, and reduced brightness with depth

Participants

During the period of 15 November 2020 till 15th December 2020 the model was piloted on eleven fifth year undergraduate junior surgical clerkship students, who had no previous POCUS exposure, during three sessions (3 groups, 3–4 students and 4 h each) at the College of Medicine and Health Sciences, United Arab Emirates University. They gave direct feedback while using it. This feedback was used to modify and refine the model, and to design a questionnaire to be valid, simple, easy to understand clear, short, and unambiguous before using it (Appendix 1). The model was then prospectively tested during the period of 4th January 2021 till 14th October 2021 on 59 undergraduate medical junior surgical clerkship students who had no prior exposure to POCUS.

Teaching methods

Seventeen groups having a median (range) of 3 (3–5) students were taught. Each training session of a group took four complete hours (a total of 68 h). The first hour was used to theoretically discuss the basic physics of ultrasound using a white board, board markers, and a simple illustrated book chapter [3]. Our own developed Kunafa Knife and Playdough (KKP) simulator was then used for another one hour to demonstrate hand movements and to build up three-dimensional mental mapping of anatomical structures [6]. The small groups of students had then hands-on-training on the Fruit and Lunch box simulator for two hours to achieve the stated objectives. A Sonosite M-Turbo portable ultrasound machine (FUJIFILM SonoSite, Inc., WA, USA), having a small print convex array probe, and a linear probe, was used in training. All 17 sessions were taught by the first author (FMA-Z) who has more than 35 years’ experience in using and teaching POCUS.

Distribution of a questionnaire

At the end of each teaching session, a hard copy of the structured Likert type questionnaire was distributed to the students to evaluate the simulator. The questionnaire consisted of 18 items focusing on the learning experience gained while using the simulator (Appendix 1). Students anonymously and voluntarily rated items on a 5-point Likert-type scale. 17 items had the scale of (1 = strongly disagree, 2 = disagree, 3 = neutral, 4 = agree, 5 = strongly agree). One item scored the overall aspects of the simulator out of 10. Space was provided for open-ended comments to “What was good in this simulator?”, “What was bad in this simulator?” and “Would you recommend the simulator for other students”. The instructor left the room before the students started filling in the form. The students were asked to collect the forms together before handing them back to protect anonymity of the answers.

Quantitative statistical analysis

The data from anonymous hard copies of the questionnaire were entered into an Excel file and double-checked by an independent assistant. Quantitative analysis was performed utilizing the Statistical Package for the Social Sciences, version 29 (IBM-SPSS, Chicago, IL, USA). Categorical variables were presented as counts (percentages), while ordinal data were presented as medians (25th–75th percentiles IQR).

Qualitative data collection and analysis

Qualitative data were gathered through anonymous feedback forms that had no participant identifiers. The analysis process involved a combination of human oversight, specifically designed custom-GPT in ChatGPT (OpenAI) and NoteBookLM (Google), utilizing their capabilities for inductive thematic analysis and data triangulation [26, 27]. We adhered to Braun and Clarke’s six-step thematic analysis framework, providing a structured method for qualitative interpretation [28]. To accomplish this, we developed a custom-GPT [29] specifically tailored for qualitative analysis, aimed at enhancing thematic exploration. The creation of this model involved defining key objectives, configuring the thematic analysis processes based on Braun and Clarke’s framework, and conducting tests to ensure output reliability [30–32]. The anonymous qualitative data, in Excel file, was subsequently uploaded to custom-GPT, facilitating the identification and exploration of emergent themes. Triangulation was achieved among human analysts, custom-GPT, and NoteBookLM, optimizing data processing and enhancing analytical precision. This methodological approach not only streamlined the analysis process but also ensured strong and structured qualitative insights [30].

Word clouds generation

Custom-GPT uses a systematic text processing and visualization methods. First, all responses are aggregated and pre-processed to enhance analytical clarity. This involves converting text to lowercase, removing punctuation, and excluding non-informative stop words (e.g., “the”, “and”, “is”) using a predefined stop word list. Subsequently, the remaining words are listed, and their frequencies are calculated to quantify their prominence across the dataset. Each word’s relative frequency determines its visual weight, with more frequently occurring words are rendered in proportionally larger font sizes. The final word clouds are generated using the Python-based wordcloud library, which graphically represents lexical patterns to reveal salient themes and concepts within qualitative data. This technique enables a rapid and intuitive exploration of textual feedback, supporting thematic analysis and highlighting key areas of emphasis expressed by participants.

Results

Quantitative results

During the study period, 59 students completed the 8-week junior surgical clerkship including attending the workshop, 58 provided feedback (98.3% response rate), out of them 57 (98.3%) recommended the simulator to their peers. Table 2 presents the students’ responses to the questions regarding the workshop. Participants provided uniformly high ratings across all items assessing the educational value and skill acquisition facilitated by the ultrasound simulator. The median score for each item was the highest possible, indicating a strong consensus on the low-cost simulator’s effectiveness in enhancing understanding of ultrasound principles, image interpretation, and probe handling skills.

Table 2.

Participants’ ratings on educational value and skill acquisition using low-cost ultrasound simulator

Question (out of 5)	Median (25–75 Percentile)
The simulator was useful	5 (5–5)
It helped me understand the basic physics of ultrasound	5 (5–5)
The simulator helped my learning	5 (5–5)
I enjoyed using this simulator by myself	5 (5–5)
I can recognize fluid on ultrasound	5 (5–5)
I can recognize the soft tissue	5 (5–5)
I can recognize the shape of the fruits	5 (4.25-5)
I can recognise the cross section of the fruits	5 (5–5)
I can recognise the longitudinal section of the fruits	5 (5–5)
I can recognize the shadow artifact	5 (5–5)
I can recognize the mirror artifact	5 (5–5)
I can recognize the reverberation artifact	5 (5–5)
The simulator helped me to properly orient the probe	5 (5–5)
I could fan the probe properly	5 (5–5)
I could shift the probe properly	5 (5–5)
I could tilt the probe properly	5 (5–5)
It was play and fun	5 (5–5)
Overall aspects (out of 10)	10 (10–10)

Qualitative results

There were 1,177 words of comments in the feedback forms. All students responded to the question “What was good in this simulator? (100%)” while only 44 commented on the question “What was bad in this simulator? (76%)”. Six initial codes were extracted from the feedback forms: basic skills acquired, interactive and fun, real-world simulation, limited time, unrealistic elements, and the need for practice.

Three initial key themes emerged from the qualitative analysis: Learning Enhancement, Engagement and Motivation, and Training Limitations. The Learning Enhancement theme captured how the simulator contributed to a deeper understanding of ultrasound concepts, facilitated visualization of clinical scenarios and supported the development of practical skills. The Engagement and Motivation theme reflected students’ appreciation of the simulator’s interactive and enjoyable features, which promoted active participation and sustained interest. Lastly, the Training Limitations theme contained concerns regarding insufficient hands-on opportunities, a perceived lack of realism, and the expressed need for extended training duration. We retain the three main themes, as they are theoretically sound, data-driven, and reflect the participants’ priorities.

Themes

Learning enhancement

The simulator significantly contributed to students’ learning by enhancing both conceptual understanding and procedural skills. Students credited the simulator for building foundational knowledge in ultrasound and improving their ability to visualize anatomy and artifacts. Participants reported that the tool effectively supported their grasp of ultrasound fundamentals, including imaging basics and interpretation. The simulator was perceived as a valuable educational resource that helped students build foundational knowledge while simultaneously developing their hands-on abilities. As one student noted, “I’ve learned the basics of imaging. By practicing I developed my skills,” highlighting the role of practice in skill acquisition. Majority of the students specifically mentioned improved understanding of physics and scanning principles, facilitated recognition of fluid and tissue structures, helped bridge theory and clinical application.

“It was really interesting and fun. It really simplified the basic ultrasonography techniques that are usually very complicated. And I can finally say that I’ll be confident enough to try and interpret ultrasound images during my training and in my future practice.”

“It helped a lot in showing all types of artifacts, and it helped me a lot in learning how to use a probe and perform a proper US. it’s really helpful as a learning tool to see the tissue types and it’s also very fun and a good way to learn US.”

Engagement and motivation

Students expressed high levels of emotional engagement when interacting with the simulator, often describing the experience as enjoyable, interesting, and motivating. The engaging nature of the simulator fostered self-directed learning and encouraged continued participation. Such emotional responses appeared to lower the cognitive burden typically associated with technical skill development, making the learning process feel more accessible and enjoyable. One participant stated, “It was really interesting and fun. It really simplified things,” highlighting the simulator’s effectiveness in promoting a positive and immersive learning environment. Comments highlighted the activity as fun and exciting, promoted independent learning, stimulated curiosity and focus, as well as healthy teaching environment created by the instructor.

“Lucky to have the chance to learn from him!! I think I have no excuse to not be perfect on ultrasound. He didn’t teach us ultrasound only but treated us like our father.”

“It was interesting, and it kept me engaged. I was surprised to see how the fruits were used to display the difference between fibrous tissue, air/stone, fluid, or soft tissue. It was very interactive, and I really enjoyed it.”

Training limitations

Despite its strengths, several limitations of the simulator were identified. Although, majority of the students had no major criticisms, few students pointed to the lack of realism and some mentioned limited opportunities for extended practice as areas needing improvement. Constraints related to time and session availability were also cited, suggesting that while the simulator provided meaningful exposure, it may not yet replicate the depth of clinical experience required for mastery. One student reflected, “Would be better to have more sessions and get more feedback,” indicating a desire for a more comprehensive and interactive training experience. Few students described the experience as “a bit unrealistic.” Many of them requests for additional sessions and show desire for deeper exposure and complexity.

“Nothing was bad. I just feel that I need to practice direction of the probe more and how to orient it (not a problem with the simulator itself).”

“Nothing. It will just take more time. I need more practice to get used to these principles. I will try to apply what I learned in the hospital.”

“I need experience and more training to better understand and interpret the images on the US screen.”

Integration of quantitative and qualitative results

Quantitative data indicated consistently high median ratings (5 on a 5-point Likert scale) across all evaluated domains, including conceptual understanding, skill acquisition, artifact recognition, and user experience (Table 2). These findings suggest a strong consensus regarding the educational utility and experiential value of the simulator. These high numerical ratings were validated by qualitative data. The theme of Learning Enhancement aligned with top ratings for understanding basic ultrasound physics and recognizing anatomical structures and artifacts. Students explicitly mentioned improved comprehension of fundamentals of ultrasound, consistent with perfect scores in these categories. Simulator use facilitated both knowledge acquisition and procedural competence. Similarly, the simulator’s interactive nature and high enjoyment scores were mirrored in the Engagement and Motivation theme. All items related to user enjoyment and performing skill (e.g., fanning, shifting, tilting) received maximum ratings, emphasizing the simulator’s appeal and usability. Qualitative feedback further reinforced this, with students describing the activity as “fun,” “interesting,” and “motivating.” Reduced cognitive burden and enhanced willingness to engage with the learning material is also important component of this theme.

However, the Training Limitations theme revealed nuanced perspectives not captured by Likert ratings alone. While the median scores indicated universal satisfaction, some written comments highlighted constraints such as limited time for hands-on practice and the need for more realistic scenarios. For example, students expressed a desire for longer sessions and increased opportunities for feedback. While the tool was effective, its fidelity and clinical relevance could be further enhanced.

Word clouds

The word clouds generated from student survey responses highlight the overwhelmingly positive feedback on the ultrasound course. In the “What was good in this simulator?” word cloud (Fig. 9A), terms such as “ultrasound,” “fun,” “easy,” “basic,” “learning,” “helped,” and “teaching” prominently reflect that students found the simulator intuitive, engaging, and effective for grasping fundamental sonographic concepts and probe handling skills. Words like “visualize,” “understand,” “practice,” and “simple” further emphasize the simulator’s role in simplifying complex principles and promoting hands-on learning in a supportive environment. Conversely, the “What was bad in this simulator?” word cloud (Fig. 9B) shows that most students had minimal negative feedback, with “Nothing” and “None” dominating the responses, suggesting high overall satisfaction. Minor areas for improvement included the need for more “practice,” “time,” and “sessions,” indicating students desired extended opportunities to reinforce and master ultrasound skills.

Fig. 9.

The word cloud from “What was good in this simulator?” (A) and “What was bad in this simulator?” (B)

Discussion

We have developed a practical low-cost homemade POCUS training model for understanding basic ultrasound physics. The proposed model used assortment of fruits in a plastic container (lunch box) that was used for demonstrating basic concepts of tissue impedance, replicating various image artifacts, and learning essential hand movements while observing the scanned objects. The model was prospectively tested by novice 5th year medical students without POCUS experience who were for the first time exposed to the model. They found it easy, effective, and enjoyable fun for learning basic ultrasound physics and knobology. Learners also reported high levels of engagement and enjoyment, suggesting that the simulation experience was both instructive and positively received. These findings highlight the simulator’s potential as a valuable tool in ultrasound training.

The thematic analysis highlights that the low-cost ultrasound simulator is an effective tool for supporting both conceptual understanding and practical skill development. Its engaging format and interactive delivery foster student motivation and self-directed learning. However, the findings also reveal important limitations related to the simulator’s depth and realism, suggesting that its current form may not fully replicate the complexity of clinical practice. To enhance its educational value, it is recommended to increase the number of training sessions and case scenarios, integrate more realistic features into the simulation environment, and provide structured opportunities for reflective practice and individualized feedback. Furthermore, the integration of quantitative and qualitative results has illustrated a strong endorsement of the simulator as an effective and engaging learning tool, while also pointing to critical areas for enhancement to better align with the complexities of clinical training. The word clouds images supported these findings visually representing the results of the overall thematic analysis.

Homemade phantom models have been proposed as a cost-effective alternative to commercial models in training a wide range of ultrasound-guided diagnostic and interventional procedures. Innovative approaches have been proposed for simulating anatomic structures, such as the use of animal tissue [9, 13, 14], gelatine [7, 8, 12], and ballistic gel [33] for simulating human tissue. Arteries and veins have been simulated with balloons filled with water or gel [13, 14]. An assortment of berries, beans, and olives has been used to simulate thyroid nodules [11, 12]. Pasta noodles have been used to replicate the honeycomb appearance of nerves [14]. Plastic models or containers are typically used to house these models. We found that using a transparent plastic box was very useful as it permitted direct contact with the probe through the gel and observing the scanned objects. The optimal choice of material within the simulator will vary depending on the performance requirements of the model. A general requirement is an ability to replicate echogenicity of the simulated tissue so that realistic sonographic images are produced that are fit for training purposes. Some applications have very specific performance criteria such as requiring accurate tactile feedback [7, 8, 15] like fanning in our model or high levels of anatomic correctness in interventional procedures [8]. A fine balance exists between meeting performance criteria while minimising cost and complexity of construction. Our model was simple targeting novel trainers for specific educational purposes to understand the basic physics which is an important starting learning point.

The use of homemade models has consistently been reported to generate positive feedback and increased interest by course participants [8–10]. Our model was highly valued and enjoyed by medical students who had no prior ultrasound experience. This model stemmed from a build-up approach over a quarter century of POCUS educational experience following an extended period of using human [34, 35] and animal models [36], assessing the learners’ needs, and recognising the limitations of these models. In 2009, we used a knife and an apple to teach echocardiography by simulating the long parasternal, short parasternal, apical and subcostal cardiac views [37]. Ten years later, we developed a more complex Kunafa Knife and Playdough (KKP) simulator to teach ultrasound hand movements and build up three-dimensional mental mapping from two dimensional images of the convex array probe [6]. The current model has been further developed, advanced, and refined to teach tissue impedance, probe orientation, hand movements, and ultrasound artifacts. We found this simulator to be simple, light, small, portable, valid, cheap, educational, and enjoyable. It has the potential to be very useful especially for teaching POCUS in developing countries. POCUS educational methods should be tailored to match the resources of low-income countries. To achieve that, innovative tools stemming from deep understanding of learning objectives should be adopted. The current simulator is an example of this approach.

Limitations

This study has several limitations that should be considered when interpreting the findings. First, the data were collected from a single institution during an academic year, which may limit the generalizability of the results to other settings or populations. Second, the use of self-reported measures introduces the potential for response bias, including social desirability bias, as students may have rated the simulator favourably due to perceived expectations. Third, while the quantitative data showed ceiling effects, with all median scores at the maximum value, this may have obscured subtle variations in student experience. Such high uniformity may reflect either genuine satisfaction or a limitation of the Likert scale’s sensitivity. However, qualitative results were suggesting satisfaction. Fourth, qualitative feedback was voluntary, and fewer students responded to the open-ended question on simulator limitations. Additionally, the study did not include a pre-post assessment design or an objective evaluation of knowledge or skill acquisition. As such, conclusions about the simulator’s impact on actual learning outcomes are based on perceived rather than measured improvements. Finally, the relatively short duration of the simulation sessions and the absence of a comparison group or control intervention limit causal inferences regarding the low-cost simulator’s educational efficacy. Future research should incorporate longitudinal assessments, objective performance metrics, and multi-institutional sampling to strengthen the evidence base for low-cost simulation-based ultrasound training in medical education.

Conclusions

This study demonstrates that our low-cost ultrasound simulator was perceived by medical students as a highly effective and engaging educational tool during their surgery clerkship. Quantitative findings reflected uniformly high satisfaction across domains of conceptual understanding, skill development, and user engagement. These results were verified by qualitative insights, which revealed that the simulator enhanced learning, motivated participation, and fostered self-directed practice. At the same time, students identified limitations highlighting the need for further refinement.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Abbreviations

CT

Computed tomography

KKP

Kunafa Knife and Playdough

POCUS

Point-of-care ultrasound

Author contributions

FMA-Z had the idea, developed and tested the simulator, collected the data, critically read the literature, prepared the images, and wrote the manuscript. YFA-Z participated in the idea, wrote the introduction and discussion sections, and critically read the paper. AAC participated in the idea, did the quantitative and qualitative analysis, wrote the quantitative and qualitative analysis methods and their results, and critically read the paper. All authors read and approved the final manuscript.

Funding

None.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

The questionnaire did not collect any personal data or identifiable information, was anonymous, and voluntary, collected on a hard copy form and not electronically, and only evaluated the educational tool (see Appendix 1). According to the United Arab Emirates University Research Guidelines, this was an exempt from an ethical review.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.