Evaluating the effectiveness of a lower extremity venous phantom on developing ultrasound examination skills and confidence

Abstract

Introduction

The aims of this study were: (1) Determine the effect on student ultrasound scanning skills using a lower extremity venous ultrasound phantom in addition to standard teaching methods of didactic lecture and scanning live volunteers and (2) Determine the effect of using a lower extremity venous ultrasound phantom in addition to standard teaching methods of didactic lecture and scanning live volunteers on student confidence levels in performing the lower extremity venous ultrasound examination.

Methods

Participants were first year diagnostic medical sonography students with minimal scanning experience (n = 11), which were randomized into two groups. Group 1 (n = 5) received the standard didactic lecture and attended a scan lab assessment where they performed a lower extremity venous examination on a human volunteer. Group 2 (n = 6) received the standard didactic lecture, performed three scheduled scanning sessions on an anatomic lower extremity venous phantom with flow and then attended the same scan lab assessment as Group 1, where they performed a lower extremity venous examination on a human volunteer.

Results

Scan lab assessments on day 4 of the study demonstrated a significant difference in scanning performance (p = 0.019) between the two groups. Post scan lab assessment confidence scores also demonstrated a significant difference between how participants in each group scored their confidence levels (p = 0.0260), especially in the ability to image calf veins.

Conclusions

This study suggests anatomical phantoms can be used to develop scanning skills and build confidence in ultrasound imaging of the lower extremity venous structures.

Introduction

With the increase in use of bedside and point of care ultrasound imaging, more medical and allied health professionals are using this technology. This ranges from a variety of medical physician specialties, to medical students, advanced practice providers, and sonographers.^1,2 While ultrasound imaging is portable, considered safe (no ionizing radiation) and inexpensive compared to other imaging modalities, it is extremely practitioner dependent.^1,3 Image quality and the structures demonstrated are completely dependent upon the practitioner to acquire the best images possible, and recognizing when to tailor the examination to answer the clinical question.³ Thus, there is need to develop new methods of teaching scanning skills to all ultrasound practitioners prior to entry into the clinic.¹

Simulation has been shown to be a successful methodology for teaching basic skills and building confidence in learners prior to practicing on real patients.^4–11 For sonography students, simulation integrated into the curriculum allows them the opportunity to apply didactic knowledge to a clinical psychomotor skill (scanning).^12,13 Both high-fidelity and low-fidelity simulation techniques have been used to teach students scanning skills.^1,14–17 While high-fidelity simulators can provide diagnostic information (i.e. the student is not aligned in the correct plane to obtain the ideal image) and allow practitioners to practice imaging a variety of pathology states, they are not always compatible with the ultrasound systems that students would use in the clinic. An equally important skill as obtaining an on-axis view is knowing how to optimize the image based on instrumentation settings. Thus, low and medium fidelity simulators (phantoms to be used with actual ultrasound imaging systems) may offer some advantages for learning to scan and operate the ultrasound equipment.

In diagnostic medical sonography, one of the examinations taught to both physicians and sonographers is imaging of the lower extremity to evaluate for the presence of deep vein thrombosis and/or venous reflux. This requires an individual to develop scanning skills to be able to follow venous structures in the transverse and longitudinal planes and perform compression and augmentation maneuvers. Some students may require additional scan time to master these scanning skills. Hence, novel methods for teaching scanning skills, such as the use of simplified anatomical phantoms, may provide additional practice time and hands-on skill refinement to learn how to scan and build confidence.

We developed a medium fidelity anatomic phantom with continuous laminar flow that can model the lower extremity venous (LEV) structures. We tested the phantom with sonography trainees to: (1) Determine the effect on student ultrasound scanning skills and (2) determine the effect on student confidence levels.

Materials and methods

Participants

This study was reviewed by the Health Sciences Institutional Review Board and was deemed to be exempt. Participants were 11 undergraduate diagnostic medical sonography students in their first month of the professional curriculum. All participants were given information about the study and provided informed consent to participate in this four-day study.

All students were enrolled on a baccalaureate degree program in which prerequisite courses are taken prior to starting the professional curriculum (diagnostic medical sonography courses), which is two years in length. After completion of the professional curriculum, students graduate with a baccalaureate degree. All students participating in this study were in their first two weeks of the professional curriculum. The scanning experiences participants had prior to the start of the study were; observing senior (second year professional curriculum) students scan different types of examinations, basic knobology, ergonomics, scanning planes, and an introduction to the ultrasound equipment used in the scan lab at the school. Participants were stratified into two groups based on the educational tract (Echo/Vascular or General Vascular) in which they were enrolled. Three students from each tract were then selected using simple randomization¹⁸ and were randomized to one of two groups. Group 1 (n = 5) received the standard instruction for the LEV imaging learning module. Standard instruction consisted of one three-hour face-to-face didactic lecture (with live demonstration) and attendance at a scan lab assessment where they performed a LEV examination on a human volunteer. Group 2 (n = 6) received the standard didactic lecture, performed three scheduled scanning sessions on an anatomic LEV phantom with flow, and then attended the same scan lab assessment as Group 1, where they performed a LEV examination on a human volunteer. A pre-test (25-point knowledge test) was given prior to the didactic lecture on day 1 of the study followed by a post-test (25-point knowledge test) and pre-confidence measurement tool immediately following the didactic lecture (Figure 1). The confidence measurement tool listed seven scanning skills similar to what others have used¹⁹ (Table 1) for students to score their confidence in ability to perform these skills. A 10 point-scale similar to what others have used for teaching physicians needle guidance¹¹ was used to score confidence with 1 being low and 10 being high (Supplemental Appendix A). Students were also given a confidence measurement tool with the same scanning skills as the pre-confidence tool on day four of the study immediately after their scan lab assessment.

Figure 1.

Study schedule overview. Participants (N = 11) were randomly selected into two exposure groups, Group 1 (N = 5, no scan lab exposure), and Group 2 (N = 6, scan lab exposure). Both groups underwent the same pre and post knowledge test before and after the didactic lecture.

Table 1.

Scanning skills evaluated.

Scanning skills	Definition
# 1	Able to follow the venous anatomy from the simulated common femoral vein to the simulated popliteal vein in the transverse plane performing segmental compression maneuvers
# 2	Able to follow the venous anatomy from the popliteal vein to the peroneal veins, posterior tibial veins, and anterior tibial veins in the transverse plane performing segmental compression maneuvers
# 3	Able to follow the venous anatomy from the simulated common femoral vein to the simulated popliteal vein in the longitudinal plane
# 4	Able to follow the venous anatomy from the popliteal vein to the peroneal veins, posterior tibial veins, and anterior tibial veins in the longitudinal plane
# 5	Able to demonstrate how to acquire a pulsed-wave Doppler image at the common femoral vein, distal superficial femoral vein, and popliteal vein
# 6	Able to perform augmentation to show changes in Doppler flow
# 7	Able to demonstrate how to acquire a color Doppler image of the venous anatomy at the common femoral vein, distal superficial femoral vein, popliteal vein, peroneal veins, and posterior tibial veins

Didactic lecture

The didactic lecture was given on day one of the study and comprised a two-hour powerpoint lecture and live demonstration of the imaging protocol. The learning objectives for this session were: (1) identify LEV anatomy as seen on ultrasound imaging, (2) describe ultrasound findings associated with lower extremity deep venous thrombosis, and (3) describe ultrasound findings associated with venous reflux. The live demonstration provided instruction on how to perform the LEV imaging protocol to evaluate for deep vein thrombosis and reflux. The live demonstration was performed by the instructor scanning themselves in the erect and seated position. Augmentation was performed by asking a student to squeeze the calf and the instructor flexing the foot. Immediately following the didactic lecture and demonstration participants were given a posttest and a pre-confidence measurement tool to complete. The didactic lecture and live scan lab were performed by a sonography instructor with 33 years’ experience in the field and multi-credentialed (PhD, ACS, RDMS, RDCS, RVT, RT(R)).

Anatomic LEV phantom scanning sessions

Phantom scanning sessions took place on days one to three of the study using the GE LOGIQ P6 ultrasound system and L9 transducer (General Electric Medical Systems, Waukesha, WI, USA). Each student in Group 2 was assigned a 30-minute scanning session on each day. The anatomic phantom scanning session simulated scanning the saphenofemoral junction, common femoral vein, femoral and deep femoral confluence, popliteal, anterior, and posterior tibial and peroneal veins. The scanning session also provided students with the experience of following venous structures in the longitudinal plane and performing compression maneuvers in the transverse plane. Students also practiced manipulating instrumentation settings while they acquired their images. Group 2 participants also saw differences in the phantom and human calf veins with demonstrations by an instructor and scanning calf veins on the instructor in the seated position. On day four of the study, all participants attended a scan lab assessment in which they scanned a human volunteer in the reverse Trendelenburg position. The scan lab assessments were scored by a faculty member blinded to group status who evaluated the same seven scanning skills as defined in the participant confidence measurement tool on a 10 point-scale (Supplemental Appendix B). Immediately following their scan lab session study participants completed a post-confidence measurement tool.

Phantom construction

The anatomical phantom used in this study was modeled after the appearance of venous structures as they appear on ultrasound to include similar diameter and depth of venous structures (Figure 2). Venous measurements from a volunteer were used as the basis for the venous structure of the phantom. The phantom modeled venous anatomy at the common femoral vein, great saphenous vein confluence and takeoff, femoral vein and deep femoral vein confluence, femoral vein and popliteal vein, the anterior tibial vein confluence, and bifurcation of posterior tibial and peroneal veins. The phantom was developed to meet a list of specifications (Supplemental Appendix C). The synthetic tissue was created using an ultrasound elastic gel (Humimic Medical, Greenville, SC, USA) and glass microspheres (McMaster-Carr, 0.002-inch diameter, Elmhurst, IL, USA). The gel and microsphere mixture was melted and poured into 3D printed molds of both a thigh section and a calf section of a model human leg. The mold pieces were printed using a Viper Si2 Stereolithography System (3D Systems, Rock Hill, SC, USA) out of Accura60, a 3D-printing photopolymer resin (3D Systems). The venous structures in the phantom were wall-less and were molded into the gel using plastic structures that were removed after gel hardening. The channels were connected to a micropump (Uxcell, Hong Kong, China) to produce flow. The phantom allowed students to practice following the vessel in the transverse plane with compression maneuvers and follow the vessels in longitudinal using color and pulsed wave Doppler. Calf veins were modeled just at the point of confluence with smaller diameters making them difficult to follow—similar to scanning a human and the simulated posterior tibial vein demonstrated reflux (Figures 3 to 5).

Figure 2.

Phantom set up. Water in the reservoir is pumped into the LEV phantom through the micropump and out the distal end back into the reservoir.

Figure 3.

Transverse views of venous structures without and with compression. (a) The common femoral vein (CFV) and great saphenous vein (GSV). (b) Compression of the CFV and GSV. (c) Confluence of the GSV, deep femoral vein (DFV) and femoral vein (FV). (d) Compression of the GSV, FV, and DFV. (e) Transverse image of the confluence of the popliteal vein (POP V) and anterior tibial vein (ATV). (f) Compression of the POP V and ATV.

Figure 4.

Longitudinal phantom images demonstrating grayscale, color Doppler, and pulsed wave Doppler (thigh). (a) Longitudinal image of the common femoral vein (CFV) and great saphenous vein (GSV). (b) Color Doppler of the saphenofemoral junction CFV, GSV, and femoral vein (FV). (c) Pulse wave Doppler of the saphenofemoral junction. Flow rates are approximately 10 cm/s, much higher than flow rates in the human body. (d) Longitudinal image of the GSV, FV, and DFV confluence. (e) Color Doppler FV and DFV confluence in the longitudinal plane. (f) Pulse wave Doppler of the FV and DFV confluence in the longitudinal plane. Flow ranges from 0 to 10 cm/s. (g) Longitudinal image FV. (h) Color Doppler imaging of the FV. (i) Pulse wave Doppler of the FV with augmentation.

Figure 5.

Longitudinal phantom images demonstrating grayscale, color Doppler, and pulsed wave Doppler (calf). (a) Longitudinal image of popliteal vein (POP V) and anterior tibial vein (ATV). (b) Color Doppler of the POP V and ATV. (c) Pulse wave Doppler of the peroneal vein (PERO V). (d) Grayscale image of longitudinal plane of posterior tibial vein (PTV) PERO V confluence. (e) Color Doppler of the PTV–PERO V confluence. PTV modeled reflux. (f) Pulse wave Doppler of the PTV–PERO V confluence. Flow below the baseline demonstrates normal antegrade flow in the vessel color blue. Flow above the baseline demonstrates reflux in the vessel color red.

Statistical methods

Continuous variables are reported as mean (standard deviation [SD]) and the range (lowest value to highest value). Change variables were calculated as post-score–pre-score. Group differences were examined using Welch’s two-sample t-test.

Results

Participant baseline characteristics

There were no statistically significant differences in how participants in the two groups performed on the pre-test and post-test (Group 1 mean score [standard deviation] 10.8 [2.3], Group 2 mean score 11.5 [2.6]; p = 0.645), indicating that there were no significant differences in baseline didactic knowledge between the two groups. After the didactic lecture both groups improved their scores significantly (p < 0.001) on the post-test (Group 1 18.6 [5.2], Group 2 20.5 [4.4]) and there was no significant difference in performance between the two groups (p = 0.534). There was also no difference in the total score for the pre-confidence measurement tool between the two groups immediately following the didactic lecture (Group 1 36.8 [9.8], Group 2 29.0 [10.4]; p = 0.235) nor the scoring of each individual skill (all p > 0.05) (Supplemental Appendix D).

Scan lab assessments

Scan lab assessments on day four of the study demonstrated a significant difference in scanning performance (Group 1 total score mean 21.4 [6.9], Group 2 32.3 [4.2]; p = 0.019). Specifically, differences in performance were noted for scanning skill 2 (the student is able to follow the venous anatomy from the popliteal vein to the peroneal veins, posterior tibial veins, and anterior tibial veins in the transverse plane performing segmental compression maneuvers; p = 0.016) and scanning skill 4 (the student is able to follow the venous anatomy from the popliteal vein to the peroneal veins, posterior tibial veins, and anterior tibial veins in the longitudinal plane; p = .030) (Supplemental Appendix E).

Post-confidence scores

Post-confidence scores also demonstrated a significant difference between how participants in each group scored their confidence levels between the pre- and post-scoring (total difference confidence score; p = 0.026). Group 1 demonstrated a decrease in how they scored their confidence level from immediately following the didactic lecture compared to how they scored their confidence levels after the scan lab assessment (mean difference Group 1, -10.6 [10.3]). Group 2 scored their confidence levels higher after the scan lab assessment (mean difference in total confidence scoring Group 2, 6.0 [10.1]). Significant differences in how participants scored their confidence existed for scanning skill 2 (the student is able to follow the venous anatomy from the popliteal vein to the peroneal veins, posterior tibial veins, and anterior tibial veins in the transverse plane performing segmental compression maneuvers; p = 0.025), scanning skill 3 (the student is able to follow the venous anatomy from the simulated common femoral vein to the simulated popliteal vein in the longitudinal plane; p = 0.029) and scanning skill 6 (the student is able to perform augmentation to show changes in Doppler flow; p = 0.026) (Supplemental Appendix F).

Discussion

The findings from this study demonstrate that anatomical phantoms can be used to develop scanning skills and build confidence in ultrasound imaging of the LEV structures prior to practicing on live human volunteers. Participants randomized to Group 2 scored higher at the time of scan lab assessment and scored their confidence levels higher after the scan lab compared to the participants in Group 1 who did not have the opportunity to practice on a phantom. Group 2 also had opportunity to practice compression maneuvers on the phantom and gained experience seeing the simulated vein collapse. The biggest difference in performance between the two groups was the ability to image the calf veins and perform distal augmentation maneuvers. These differences were demonstrated in lab assessment score and the difference in pre- and post-confidence measurement tool scores. This may be due to exposure to both scanning the phantom and imaging a human; however, these are typically considered advanced skills for a sonographer. Also, since the phantom modeled reflux, participants in Group 2 spent more time in their scan labs imaging and performing Doppler on this structure. Hence, the observation that new students were able to feel more confident and scored higher on their scan lab assessment is still felt to be significant.

Simulation has been used to teach scanning, ultrasound guidance for medical procedures, and to improve student confidence levels.^1,11,12,20 Simulation provides practice opportunities in a nonthreatening environment and, therefore, helps students feel more comfortable with their skills when they interact with patients and studies have shown that clinical mentors also feel students are better prepared to enter the clinical environment after simulation experiences.^12,13 While independent practice on simulators has demonstrated that students feel better prepared to enter the clinic, there is also evidence that having a sonography instructor present during these practice sessions may add to the learner’s experience.^12–14 While many simulators are designed to provide feedback regarding the actual procedural imaging, they do not offer additional advice for how to manipulate the transducer to eliminate artifacts, improve the Doppler signal or have the ability take questions as they emerge in the learner’s mind. Thus, having an actual instructor present for simulation sessions may allow additional feedback for students. For this study, an instructor was present at the scan lab sessions and was able to take questions in real time as the student asked them. Questions were about the scanning technique but also were physics and instrumentation related. Having an instructor did not impede student abilities to be able to initiate the lab session.

Simulation also has the potential to assist students who need more time to learn and master their scanning skills. Many sonography programs are limited on time and clinical resources, thus if a student cannot meet the required objectives in the time frame allotted and requires additional/remedial exercises to acquire mastery of the scanning skills it is difficult to add a clinical rotation for them. In this setting, simulation (availability of a phantom), in which the student could practice as much as needed and take images to review with instructors has the potential to assist the student with mastery of these skills and further develop confidence.

For this study, we developed a medium fidelity anatomic phantom. The phantom is termed medium fidelity for patient relevance as it provides some practitioner feature interaction and is not just static. Nikitichev et al.²¹ designed a low-fidelity tissue-mimicking ultrasound phantom that utilized 3D printing to construct complex structures of wall-less vessels, such as bifurcations. It did not incorporate flow and the tissue mimicking material could not compress. Kenwright et al.²² developed a low-to-medium fidelity phantom that featured a single wall-less channel that was connected to inlets and allowed fluid to be pumped through to simulate flow. It mimicked flow but did not feature venous anatomy, such as bifurcations, and the tissue could not be compressed. The wall-less vessel molding and flow system from each respective phantom were considered in the design of the LEV phantom, but the addition of elastic synthetic gel added another level of fidelity. The LEV phantom allowed practitioners to optimize grayscale, color Doppler, and spectral Doppler parameters and to appreciate differences in image quality based on manipulation of these settings. The continuous flow feature and elastic synthetic gel of the phantom also allowed practitioners the opportunity to perform augmentation techniques and observe changes in flow associated with these maneuvers. Practice of the augmentation maneuver did appear to make a difference for Group 2 participants, as this was a skill on which they scored themselves higher in the post-confidence measurement tool. All of these capabilities of our phantom make it higher fidelity than typical low-fidelity anatomical phantoms, hence our classification as medium fidelity.

Limitations

There were limitations to our study. One limitation is the sample size (n = 11). We intentionally wanted to test this phantom with novice diagnostic medical sonography students to see how a medium fidelity phantom may contribute to developing scanning skills for vascular applications. In order to make these results generalizable, this study should be repeated with a larger sample size and could be tested at multiple clinical sites. This study was also performed prior to students entering the clinical environment and it is not known how the skills developed in the scan lab on a phantom will translate to actual patient care skills. These students were all diagnostic medical sonography students, who are motivated to learn these skills as this is their chosen profession. Results may be different if tested with other learners (i.e. medical students, advanced practice providers, and physicians). Another limitation is that the simulated blood flow was not representative of normal venous blood flow in the human. The phantom flow was spontaneous but was continuous as opposed to phasic. Also, the augmentation demonstrated an initial cessation of flow followed by an increase in flow, whereas in human we would expect just to see an increase in flow. While this was the case, students could practice the skill of holding the transducer over the vessel and using the other hand to squeeze the distal simulated calf simultaneously. The phantom described in this study was not constructed to simulate the superficial and deep fascia, which may be another limitation as these anatomic landmarks are commonly used to confirm that one is imaging the great saphenous vein. We believe this simulation did contribute to their confidence in performing this skill in that they scored their confidence higher post scan lab. Furthermore, the scan lab assessments reflected a statistically significant difference in the students’ ability to image the calf veins for the group that practiced on the phantom.

Conclusion

This study suggests anatomical phantoms can be used to develop scanning skills and build confidence in ultrasound imaging of the LEV structures prior to scanning live volunteers. Future work will include developing anatomical phantoms with longer segments of the calf veins, improved flow simulation and modeling pathology such as deep vein thrombosis and reflux and evaluating how phantoms can be effective for teaching scanning skills and developing confidence in identifying pathology. This study is not suggesting that anatomic phantoms should replace clinical competencies performed on patients. Further research is needed to see how scanning on this phantom is related to clinical scanning on patients.

Contributors

Carol Mitchell: 1, 2, 3, 4

Pazee L Xiong: 1, 2, 3, 4

Benjamin L Cox: 1, 2, 3, 4

Maame A Adoe: 1, 2, 3, 4

Michelle M Cordio: 1, 2, 3, 4

Tonya R Quade: 1, 3, 4

George Petry: 1, 3, 4

Kevin W Eliceiri: 1, 2, 3, 4

1. Substantial contributions to conception and design, data acquisition, or data analysis and interpretation; 2. Drafting the article or critically revising it for important intellectual content; 3. Final approval of the version to be published; 4. Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of the work are appropriately investigated and resolved.

All authors approved the submission of this article.