Criterios generales para la descarga de efluentes Normas generales para descarga de efluentes, tanto al sistema de alcantarillado, como a los cuerpos de agua

The training efficacy was primarily evaluated by quantitatively comparing the scan time for each task over several training image volumes. In this section, we will present the scan times of the tasks for the six image volumes, the relationship between the scan time and the scan path length, and the usage of the training videos and the help images.

Fig. 7-8 and 7-9 give the scan times for two participants, J9 and S8, for each task in the six image volumes, respectively. These two figures indicate that the scan times gradually decreased somewhat as the training progressed. The same trend was found in other participants’ scan times.

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Fig. 7-8. The scan times of image volumes 1 to 6 completed by the student J9.

Fig. 7-9. The scan times of image volumes 1 to 6 completed by the student S8.

The experimental results also show that J9 and S8 encountered difficulties in completing Task 3c of image volumes 3 and 5. For example, J9 used far more time than anticipated but could not complete the task. Thus, the scan time was set to 12 minutes, or 720 seconds, for the task she failed, as shown in Fig. 7-8. The unexpected long scan time was primarily attributed to the challenging 2D image quality for Task 3c.

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Fig. 7-10, 7-11 and 7-12 are box-whisker plots (or box plots) of the scan times of Tasks 2b, 3a and 3b in the 6 image volumes, respectively. The crosses denote outliers in terms of the scan times. The upper and lower bars denote the maximum and minimum time in each image volume, respectively. The box upper and low edges denote the 75% and 25% quantile scan time (in seconds) in each image volume, respectively. The lines inside the boxes denote the median or 50% quantile time in each image volume.

These three figures indicate that the median scan times of Tasks 2b, 3a and 3b decreased slightly with increasing amount of training and effort. We also observed similar reduction in the scan times for the other tasks. In addition, we can see that the range of the scan times of these tasks narrowed somewhat with increased training.

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Fig. 7-11. The scan times of Task 3a of image volumes 1 to 6.

Fig. 7-12. The scan times of Task 3b of image volumes 1 to 6.

Fig. 7-13 presents a 3D view of the average scan times of all 24 medical students for the six tasks, Tasks 2b to 3c, as they progressed through the six image volumes. While Fig. 7-13 shows that the average scan time was reducing with training, the trend was not

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monotonic. Such non-linear learning behavior has actually been observed in other learning situations [111]. Additionally, the quality of image volumes influenced the scan times a great deal.

In Fig. 7-14, the scan time of each image volume, averaged over all 24 medical students, also demonstrates that the training did improve ultrasound scan skills. On average, a student needed roughly 25 minutes to complete all tasks in image volume 1, but the scan time was reduced to 8-12 minutes after a student scanned three image volumes. However, we found that the scan time of image volume 5 was longer than that for image volume 4. This observation could probably be explained in two ways. First, as mentioned in Chapter 7.3.2, the medical students typically needed two sessions to complete all six image volumes. In most cases, a student was able to complete first four image volumes in the first session and the last two in the second session. The interruption of training would make the student spend some time to recall the scan skills he or she had learned before. The second reason is that the image quality of image volume 4 is better than the quality of image volume 5, and hence the student used less time to complete image volume 4.

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Fig. 7-14. The average scan times of each image volume.

As shown in Fig.7-15, the experiment results indicate that the scan path length was approximately proportion to the scan time in Task 3b. This relationship was also applicable to other tasks.

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Although we had encouraged all students to watch the training videos before the experiment, about half of them did not do that. The training videos were rarely used during the training and mostly watched during the tasks for the first image volume. According to the experimental results, the video of measuring femur length was the most watched video during the training. The videos of measuring abdominal circumference and measuring amniotic fluid were the second and third most watched videos.

In addition to the training videos, the simulator also provided the medical students with a set of help images for all image volumes except for the last one. Those help images allowed the students to glance at the 2D images containing desired anatomical structures. The experimental results show that a few students frequently used the help images to complete the training tasks whereas other students used the help images only when they had scanned a long time but had not found the correct answers. Analyzing the usage of the helps images revealed that the participants utilized the help images mostly in Task 3c, followed by Task 3b and Task 2d. Actually, the inclination of using the help images during the training was directly related with the scan time. If the participant could not find the correct answer after practicing for a certain amount of time, he or she was more likely to resort external help.