Tele-operated echograph - Discussion
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Other systems for tele-echography
Previous versions of teleoperated ultrasound examinations have been used in different settings with each presenting several limitations. For the simplest version, remote guidance consists of a trained sonographer directing a partially trained operator by the side of the patient through the ultrasound examination using a videoconference link. Using this system, only a videoconference link was required for communication between the sonographer and the patient site operator; however, this system also required significant training of patient site operator to become proficient in visualizing the organs of interest for the examination (references 15, 16, 17). Therefore, remote guidance is only effective if the operator in the isolated site has received training in ultrasound imaging. Moreover, this system has not been validated in routine practice on real patients.
To avoid the need for training operators in the isolated medical sites, a volume capture method was developed and tested in clinical settings and on the International Space Station (references 7, 8, 9). Using this method, the operator located the probe over the organ of interest then tilted the probe to scan the area containing the organ. The video from this tilt manoeuvre was used to reconstruct a virtual 3D image which a trained sonographer then used to find the appropriate view of the organ and perform the required measurements. This method was found to be useful for visualizing morphological issues, but does not allow for Doppler or time motion assessments. In addition, this is a post-processing method requiring substantial time after the initial investigation to generate a report and to deliver a diagnosis.
A robotic arm to which a standard ultrasound probe could be attached was the first generation of teleoperated ultrasound developed by our research group that was capable of real time echographic and Doppler examinations (references 11, 12, 13).
Using the robotic arm did not require the patient site operator to have any training in ultrasound imaging, but this operator was still required to operate the settings and functions on the echograph under the guidance of the expert sonographer through videoconferencing. This system has been successfully used for examinations of several hundred patients over the past 10 years with successful diagnoses in 85% of cases (references 11, 12, 13).
Currently, the most recent version of this system is still in routine clinical use and delivering successful diagnoses in 97% of cases (reference 14).
Due to the volume (40cm x 40cm x 35cm) and weight (4kg) of the robotic arm, a heavy mechanical support structure was required. The non-sonographer operator was required to move the support structure into position so that the ultrasound probe was correctly located over the appropriate acoustic window which was not easy or accurate with this support structure. Therefore, the present teleoperated integrated echograph and probe unit “TOURS” aimed to address the size and weight issue of the robotic arm and to reduce the responsibilities of the non-sonographer operator by allowing for the teleoperation of the echograph settings and functions.
Ergonomics of the current system
The motorized probes designed for the teleoperated ultrasound system were similar in size and weight to commercially available 3D ultrasound probes. The small size and light weight of both the deep organ and superficial organ probes made it easy for the non-sonographer operator to correctly position the probe on the patient and to hold it still throughout the ultrasound examination. Each probe contained motors which allowed the expert sonographer to remotely change the orientation of the transducer to optimize the image for diagnoses without requiring the assistance of the non-sonographer operator. In addition to being easy to place and hold, the small size also made it possible to locate the probe on the lateral side of the patient for visualization of the kidney or to push hard on the probe (increase hold down pressure) if requested by the expert for patients who were obese or unable to hold a breath. These motions were not possible with the robotic arm attached to a mechanical cart.
The echograph connection ends of the motorized probes were modified to allow electrical input for teleoperation. As the modifications were made on the probe connectors (Figure 1), the motorized probes could be operated in either teleoperation mode or as a standard echograph probe. In addition to using the dummy probe to teleoperated the motorized probes, the expert sonographer could activate a program in which the motorized probe performed a 90° tilt scan (2-4s) for a video volume capture of the area under the probe. This video could then be processed to produce a 3D reconstruction of the volume scanned for later analysis at the expert center. In the case of poor internet transfer rates, this tilt movement could be initiated by the non-sonographer operator at the patient site and the saved video later transferred to the expert site for analysis.
Remote control of the echograph settings and functions
The second major issue that was addressed by this teleoperated echograph and probe unit was the ability of the expert sonographer to directly control the echograph settings and functions. Software was designed that allowed the expert sonographer to control the echograph using a standard keyboard without requiring actions from the non-sonographer operator at the patient site. In addition to controlling the settings such as gain and depth, the expert was able to freeze the image or Doppler trace and access the cine loop to determine the best available image and save frozen images and video clips to the echograph and the computer at the expert site. Lastly, the expert was able to recall saved images and videos directly from the patient site echograph for additional measurements after the patient had left. The ability of the expert to control all of the echograph functions and settings greatly reduced the time required to perform the teleoperated ultrasound examination as changes and measures could be made without having to verbally direct the non-sonographer operator to make the required adjustments. This also helped to reduce the required training of the non-sonographer operator who was then only required to properly locate the ultrasound probe over the desired acoustic window which was achieved using visible landmarks (ex. xyphoid, costal border, mammary line) and direction via videoconference with the expert sonographer.
Tele-echography in practice
Teleoperation of the echograph and probe unit involved a lag time of approximately two seconds for the majority of locations tested with ground Internet. The expert sonographer was required to accommodate for this delay when moving the dummy probe and changing the echograph settings and functions. The expert was, therefore, required to move the dummy probe much slower to avoid overshooting the organ of interest or scanning though the organ too quickly. It was found that expert sonographers were able to adjust to this delay after only one hour of training with the tele-operated system.
The equipment used by the expert sonographer also presented the advantage of being portable. The system consisted of a portable computer and the dummy probe which was approximately 200cm (reference 3) in volume, weighted 150g, and connected to the computer via a USB connection. Therefore, the equipment for the expert sonographer (approximately 1kg in weight) could be transported to different locations and used for the ultrasound examinations in any location where an Internet connection was available (medical center, home, hotel, etc.). This is a definite advantage in emergency situations as the expert sonographer would not be required to travel to specialized locations thus decreasing the time required for ultrasound diagnoses.
Previous work has demonstrated the medical interest in the use of teleoperated echograph systems for examinations in isolated areas (reference 14).
Typically, a patient in an isolated medical center would be required to travel to a larger city center for the examination and wait 3-7days before getting an appointment at a radiology center and receiving the echographic report. With the teleoperated system, physicians and patients are able to get diagnoses faster leading, in many cases, to earlier treatment and improved patient outcomes.
Limitations
The lag present in the teleoperated echograph system resulted in longer durations of the ultrasound examinations. When the expert made an adjustment to the dummy probe the resulting image did not appear on the screen for 1-2s. Consequently, the expert was required to make only single movements of the dummy probe at slow speeds. This is in contrast to conventional examinations where the sonographer is able to rapidly move the probe over the patient’s skin. The expert sonographers were able to adjust to this delay with approximately one hour of training, but this still resulted in longer echography examinations.
Using Teamviewer made it easy to connect the teleoperated echograph to the expert center as it does not require a fixed IP address and can pass through several standard firewalls. Unfortunately, the flow rate and the frame rate of the transmitted video fluctuate, likely in relation to the number of customers using the Internet service at the same time. Thus, the quality of the video reaching the expert was not constant. If the quality of the image was made a priority, then the delay increased from 2s. Therefore, in some cases (not frequent) priority was set to reduce the lag initially while the sonographer found the appropriate view and then to image quality to obtain good quality images for analysis. This also served to further increase the time required for the ultrasound examination. The current expert medical center has access to an Internet flow rate of 1Mbits/s which was able to transmit good quality images at a framerate of 10fps. In the past, a bandwidth of 512 Kbits/s was used and the image quality was significantly reduced while still sufficient to evaluate the status of the organs if a frame rate above 8fps was maintained. If the frame rate dropped below 8fps the video was not transmitted correctly (image interruption, image missing, background noise and pixels on the image) preventing the delivery of a medical diagnosis. In the current study, the Internet flow rate during the tele-echography examinations was not directly measured; however, it was subjectively determined that a 1Mbit/s bandwidth and a frame rate of 10fps would consistently result in transmitted images of sufficient quality for accurate diagnoses.
The motorized probes designed for this system present a great improvement over the robotic arm and support structure. However, the motorized transducers in the probes only allow for the orientation to be adjusted in two directions. Thus, the degree of manoeuvrability of the motorized probe is restricted compared to a human hand. In some cases, is was difficult to obtain the appropriate view for diagnoses with this restricted movement resulting in longer examination time.