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Page 8 of 12 Zhao et al. Vessel Plus 2021;5:10 I http://dx.doi.org/10.20517/2574-1209.2020.77

some cases. This may lead to difficulty in diagnosing large vessel occlusion and need for repeat in-hospital
imaging, which will delay commencement of EVT.

The final limitation is the lack of whole-brain CT-perfusion capability. Due to the low number of slices that
the CereTom scanner can perform on a 1 cm thick CT-perfusion slab, the end imaging result is adjudged not
sufficient for routine clinical use. The consequences are that firstly, the MSU is unable to provide thrombolysis
[36]
for suitable patients > 4.5 h from onset and determining potential EVT-eligible patients > 6 h [18,19] . Secondly,
CT-perfusion adds additional diagnostic information where there is uncertainty about a potential
[37]
non-stroke presentation and helps to decrease thrombolysis of stroke mimics . Lastly, the additional
information on estimated ischemic penumbra and ischemic core also help refine reperfusion decisions,
[38]
especially if the patient has risk factors for hemorrhagic transformation .

Therefore, there is a need for next generation CT scanning devices that not only deliver better imaging
quality and capabilities to better approximate in-hospital scanners, but also maintain the portability
that allows fixing into a MSU without needing a chassis that would make operation in crowded cities
impractical.

Telemedicine-based operations
Many of the US-based MSUs utilize telemedicine-based services where the medical practitioner can
view an audio-visual feed of the patient and receive transmitted CT images remotely. This has practical
advantages in allowing the medical practitioner to conduct other work in between telemedicine
consultations and provides potential for one stroke doctor to manage multiple MSUs. However, potential
downsides include slower management decisions, as the medical practitioner must rely on other personnel
to gather relevant information, as well as potential delays in transmission of imaging. In the worst-case
scenario of technical failure, the medical practitioner may be entirely unable to view the patient or not be
able to receive imaging. With no alternatives on-board the vehicle, this would force the patient to go to
hospital for definitive management, which would be delayed by the aborted MSU review.

The largest telemedicine validation study published by the Houston MSU group found a statistically
significant difference in time to thrombolysis decision making between the onboard and telemedicine
[39]
neurologist, although the absolute median time difference was 3 min (18 min vs. 21 min, P = 0.01) .
Of note, no telemedicine connection or imaging transmission failures were reported . In contrast,
[39]
telemedicine connectivity was trialed within the Berlin MSU metropolitan dispatch zone with similar
telemedicine hardware to the Melbourne MSU. This found that connectivity with 4G mobile signal failed in
[40]
17% of attempts and 3G signal in 15% of attempts . With exclusive 4G signal use on the Melbourne MSU,
this error rate would likely be unacceptable for ongoing operation should this be replicated locally.

Further considerations for telemedicine are that much of the initial assessment and decision making for
scanning occurs outside the vehicle, whereas the Melbourne MSU audio-visual equipment are fixed inside
the back cabin. Waiting for extrication and loading into the vehicle to allow telemedicine connectivity
may unduly lengthen the time that the MSU spends at each patient, making the workflow inefficient for
cases that are unlikely to be treatment eligible. Portable telemedicine equipment (such as electronic glasses
or body cameras) that can be brought away from the vehicle are preferred in this setting but maintaining
mobile signal connectivity for a good quality video signal may be challenging. Future implementation of
a telemedicine system therefore relies greatly upon technological solutions that offer very high reliability,
rapid imaging transmission, and immediate troubleshooting.