Table 3. Summary of evidence according to system characteristics.

Mode
Tele-mentoring+ Synchronous	Synchronous	Asynchronous
Requires: Feasibility studies determining minimum bandwidth requirements and definitive RCT. Evidence: This mode may need a high bandwidth, most effective studies had access to > 1Mbps [22, 25, 29, 42]. However, more work is needed to clarify this in order to allow researchers to assess the suitability of this technology to their setting. Good evidence of feasibility albeit from small studies of mixed quality [15, 18, 20, 27, 28, 29, 31, 34, 35, 36, 37, 42]. There is also good evidence of diagnostic accuracy from a small number of strong studies [25, 42]. There is some evidence of clinical utility from pilot studies of mixed quality [15,17, 22, 27].	Requires: Pilot studies in clinical setting with comparator groups. Evidence: Good evidence of feasibility albeit in a number of small studies [16, 32, 33, 39, 40]. Some evidence of feasibility with low bandwidth [<200kbps] [32, 33, 39, 40]. Some mixed evidence of diagnostic accuracy [26, 40]. Clinical utility has not yet been demonstrated and it is unclear what the role of this mode of transmission without the addition of tele-mentoring.	Requires: Definitive RCT Evidence: Strong evidence feasibility of this method in a large number of small studies [15, 19, 24, 27, 34, 38, 41]. Some evidence that this is possible with very low bandwidth [<200kbps] [16, 19, 34]. Good evidence of clinical utility [15, 24].
3D	Robotic	Remote task scale
Requires: Feasibility studies, with comparison with to other transmission modes. Evidence: Two small pilot studies, poor quality evaluation of method but some potential of clinical utility demonstrated [15, 34]. Wider literature suggests potential in this field.	Requires: Theoretical and feasibility work to establish superiority. Evidence: Poor quality feasibility studies [21, 23] have not established yet that robotic devices convey advantages when compared to tele-mentored telesonography in an emergency setting.	Requires: Feasibility studies. Evidence: No evidence found in this review, some evidence in the wider literature.
Setting
Rural emergency department:	Low-resource setting:	Prehospital
Requires: Definitive RCT. Evidence: Evidence in the wider literature of clinical need for such a technology. Good evidence of feasibility [17, 22, 42] and diagnostic accuracy [26, 29, 42]. A flexible approach utilising asynchronous and synchronous transmission modes dependent on local requirements and physician availability may be most appropriate.	Requires: Pilot studies and Definitive RCT. Evidence: Evidence in the wider literature of clinical need, however more assessment of the appropriateness of telesonography to the local setting is required before conducting research. Little evidence of ability to quality control and obtain usable images [15, 27]. Some evidence of clinical utility and accuracy using telementored scans [15, 27]. Also must be considered in the context of other urgent and severe healthcare needs.	Requires: Feasibility studies and pilot studies. Evidence: More work required to develop optimal transmission system, evidence of problems with reliability of transmission [17, 26, 27, 29, 30, 33, 35] particularly from moving vehicles [33, 34] clinical benefits of prehospital ultrasound have not yet been established by the wider literature.
Tele- communications available
VPN/WAN/LAN	Cellular/Wireless connection	Satellite connections
Requires: Incorporation into RCT. Evidence: Feasible to use telesonography using fixed line internet connection [42]. Feasible provided sufficient bandwidth. Shown to be clinically useful using custom VC software [17, 21, 22, 34, 37, 39, 42]. Possible using voice over phone alone [20, 28, 29]. Security may be greater with this mode of telecommunications. May be superior option is synchronous connection is required.	Requires: Incorporation into pilot studies. Evidence: Feasible using cellular [19]. Feasible using cellular connection, mixed image quality [32, 33, 39, 40]. Good evidence feasible with strong Wifi connection [15, 18, 31]. Feasible using free VOIP software [15,18, 27, 31, 35, 36].	Requires: Incorporation into pilot studies Evidence: Using a satellite connection, mixed image quality [19]. Mixed results regarding Image quality. May require substantial time for transmission [34].
Specialty/Indication
Paediatrics:	Neurological:	Trauma:
Requires: Definitive RCT. Evidence: Good quality of evidence of clinical utility, and diagnostic accuracy [25, 42].	Requires: Feasibility studies and Diagnostic accuracy studies. Evidence: Potential utility in a number of settings, some evidence feasibility and diagnostic accuracy, however the strength of evidence is currently insufficient [37, 39].	Requires: Definitive RCT. Evidence: Using synchronous transmission and tele-mentoring there is evidence of feasibility [20, 22, 32, 33, 35, 36] some evidence of clinical utility [17, 22]. Using asynchronous transmission alone there is a lack of evidence, perhaps worthwhile exploring if the transmission time is brief and there is sufficient supporting information. 3D techniques may decrease risk of inexperience resulting in inadequate visualisation.
Lung:	Musculoskeletal:	Appendix:
Requires: Diagnostic accuracy and pilot studies. Evidence: Some evidence of feasibility [17, 18, 22, 35, 36], and some evidence of clinical utility [17, 22]. Using Synchronous alone methods alone it may be feasible to transmit lung sliding data, but may require higher frame rate and therefore a higher bandwidth connection [32, 33].	Requires: Pilot studies in clinical setting. Evidence: Evidence of feasibility but not clinical utility [28].	Requires: Definitive RCT. Evidence: Strong evidence for the efficacy of telementored ultrasound with high bandwidth and good quality [25, 29].

RCT, Randomised control trial; VOIP, Voice over internet protocol; VPN, Virtual private network; WAN, Wide area network; LAN, Local area network.