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Zhao et al. Vessel Plus 2021;5:10 I http://dx.doi.org/10.20517/2574-1209.2020.77 Page 7 of 12

subarachnoid and subdural hemorrhage. There is also evidence to suggest that hemorrhage cases have
[34]
better outcomes at neurosurgical centers, regardless of whether surgery was performed .

In addition, almost a third of all patients with parenchymal hemorrhage were recruited into a currently
running clinical trial of tranexamic acid administered within 2 h of onset (ClinicalTrials.gov Identifier:
NCT03385928). Previous hemostatic trials [28-30] in intracerebral hemorrhage have only demonstrated trends
towards benefit, with major criticisms that recruitment has occurred too late when the hematoma growth
has already slowed. Therefore, trials need to be conducted within the very early timeframe, but patients are
largely outside this window if they arrive in hospital through standard ambulance transport. As such, pre-
hospital recruitment using a MSU is critical due to the substantial time savings provided for diagnosis after
symptom onset. This also means that if future trials do show a significant benefit of hemostatic therapies
in hyperacute intracerebral hemorrhage, MSUs will be central to providing treatment within the early time
windows.

FUTURE DIRECTIONS
Although we have shown that a MSU has been successfully operationalized into the ambulance and
stroke services in Melbourne, there are research directions and challenges still to be addressed for future
operation.

CT scanner limitations
The availability of cerebral imaging is the unique feature of MSUs that enables pre-hospital stroke
treatment. The current CereTom CT scanner has been the standard hardware in almost all first-generation
MSUs due to its portability, significantly lower weight, self-mobility, and ability to run from battery power.
The trade-off for these features is that there are limitations in image quality, scanner capabilities, and
[35]
adequate coverage of the head and neck .
The overall experience in operating the CereTom scanner in the Melbourne MSU has been that whilst
standard non-contrast CT brain sequences are adequate to exclude contraindications to thrombolysis, the
substantially slower acquisition time compared to in-hospital scanners allow greater patient movement and
resultant artefact. This makes interpretation difficult and may necessitate repeat imaging in some cases,
although this rarely affected the ability to administer thrombolysis on the MSU.

The smaller bore hole where the head of the patient rests inside the scanner also presents unique challenges.
First, this does not permit imaging of most of the neck and thorax as they cannot fit in the scanner,
hence CT-angiogram covers only the intracranial vessels and not usually the common carotid bifurcation
or thoracic vessels. This missing information is useful to diagnose underlying stenosis or occlusion of
extracranial vessels and, in cases of large vessel occlusion, may help neuro-interventional services plan
the procedural approach for EVT. Second, the required head positioning for the small bore hole excludes
patients with significant upper spinal kyphosis from being scanned as they are unable to maneuvered into
the scanning position. In a similar fashion, the scanner is unable to fully scan the lower posterior fossa in
patients placed in a cervical collar or with short necks, as these require the shoulders to enter the bore hole
to fully image the brain. Thrombolysis cannot be given with incomplete images; therefore such patients
may be unable to benefit from MSU management.

Another limitation is the quality of some CT-angiogram images. The fast acquisition time of in-hospital
scanners allow tracking of a test contrast bolus to determine optimal contrast delivery individualized for
the patient. Whilst bolus tracking is possible on the CereTom scanner, the slow acquisition time makes this
impractical in routine MSU service. As a result, the Melbourne MSU uses set contrast delay timings that
are likely to be appropriate for the majority of patients but results in suboptimal CT-angiogram images in