## 4 Discussion  
The results from this study indicate that EOS performs similarly to conventional radiography in both number detection and length evaluation of enchondroma-like inserts in a standardized phantom setting. The mean difference between insert length assessed with EOS and conventional radiograph, and their true length was in fact as low as 6.1 mm and 6.6 mm, respectively. However, it should be underlined that an underestimation of the insert size was expected, in view of the bidimensional imaging provided by both techniques that does not make a precise identification of the longest diameter  
Figure 4: EOS (**A**), CR (**B**), and CT (**C**) images of a phantom with six inserts (arrows). Figure 3: Radiation doses delivered by the EOS-Fast (speed 2), EOS-Medium (speed 3), and EOS-Slow (speed 4) protocols, and CR examinations. of the inserts possible. Notably, these results were obtained by testing the capability of the reviewers to detect and measure the enchondroma-like inserts on EOS fast-speed images, which should present minimal reduction of image quality when compared with the other sets of EOS images. The intermodality reliabilities of EOS imaging, conventional radiography, and CT were also excellent, which is essential when dealing with a new diagnostic test not yet used in the clinical routine [18]. Moreover, perfect agreement of measurements performed by different observers with the EOS system was observed, thus demonstrating that EOS is both accurate and reproducible. There was only a single case where the number of inserts was different between conventional radiography and EOS versus CT and the actual number of inserts placed on the phantom. In this case, two inserts were placed very close to one another. Thus, the bidimensional images of conventional radiography and EOS showed them almost superimposed on one another, making the distinction almost impossible. This study also demonstrates that, since radiation dose is inversely related to scanning speed, you can impact the radiation dose administered by the EOS system by changing the speed of the image-acquisition parameters. Indeed, doubling the speed from EOS-Slow (7.6 cm/s) to EOS-Fast (15.2 cm/s), the radiation dose decreased from 517.19 mGy cm\({}^{2}\) to 258.6 mGy cm\({}^{2}\) without affecting the capability of observers to detect and measure the inserts on the phantom. These data lead us to consider EOS as a potential imaging tool technique for detecting and following enchondromas over time, while minimizing radiation exposure. A drawback of EOS to consider is the increased risk of motion artifacts related to the fact that EOS is performed with the patient in a standing position and the acquisition time at a speed setting of 4 is about 8 s. This should be considered especially in pediatric patients who are particularly prone to movement during a scan. This limitation can be partly overcome, given that image-acquisition time can be decreased to three to four seconds (on the EOS-Fast speed setting of 2) without affecting the capability of observers to detect and measure the inserts on a phantom. In the future, we may envision a clinical setting where initial evaluation of enchondromas is performed using conventional radiography and follow-up is performed using EOS. In case of a change in the number and size of enchondromas, a standard workup should then be resumed. Clearly, one limitation of this approach is that EOS is not a widely available imaging modality. A limitation of this work is that the image quality of conventional radiography was not compared with that of EOS at different acquisition speeds. It is known that EOS is very good in assessing spine and limb orientation, but, especially at higher speeds, image quality may also decrease in favor of radiation dose reduction.