MTT lesion volume most informative CT parameter in hyperacute stroke

8 July 2008

MedWire News: Mean transit time (MTT) is the most reliable computed tomography (CT) perfusion parameter for measuring infarct volumes in patients who present within 3 hours of stroke onset, research suggests.

Heli Silvennoinen (Helsinki University Central Hospital, Finland) and colleagues examined CT perfusion images from 44 stroke patients who underwent thrombolysis and 19 who did not. The patients presented at about 90 minutes after symptom onset.

On initial imaging, 45% of the thrombolysis group and 42% of the control group had no visible lesion on cerebral blood volume (CBV) maps, but all had CBV infarcts on follow-up imaging within the following 3 days. Also, 9% and 5%, respectively, had smaller CBV infarcts on follow-up imaging than at baseline.

"These results imply that in patients who are imaged <3 hours from stroke ictus, the CBV map does not necessarily indicate already-infarcted tissue but rather suggests that CBV lesion volumes should be included as a component of potentially salvageable tissue at risk in this patient population," comments the team.

"These findings differ from current wisdom reported elsewhere in the literature, in which investigators have concluded that lesions seen on CBV maps indicate irreversibly infarcted tissue."

Lesion volumes on MTT and cerebral blood flow (CBF) maps almost perfectly correlated, the researchers report in the American Journal of Neuroradiology.

They comment: "In practical terms, this means that in the emergency department when a patient is being triaged to a treatment, it is enough to consider only one of these maps if the visible lesion size is the parameter of interest."

Silvennoinen et al recommend using only MTT maps, saying that abnormalities are easier to identify on these than on CBF maps.

In untreated patients, initial CBV lesions provided the best indication of final infarct size. Thrombolysis treatment substantially reduced the strength of the association between initial and final CBV infarct size.

The average volume of salvaged tissue, based on initial MTT volumes and CT infarcts at follow-up, was 21.8 ml in the treated group and 13.2 ml in the untreated group.

"Our data suggest that CT perfusion techniques can be successfully used to demonstrate the quantitative efficacy of thrombolytic agents," the team concludes.

Am J Neuroradiol 2008; 29: 1118-1123