And why not thrombolysis in the ambulance (at least for some)?

The fear that alteplase may aggravate primary intracerebral hemorrhages has led to the mandatory prerequisite for prealteplase imaging in all acute stroke patients in order to exclude such hemorrhages. Consequently, in a situation in which "time is brain," administration of alteplase is delayed until the patients are transferred to a hospital where such imaging is available, at the cost of additional ischemic damage to the brain parenchyma. Yet, theoretical considerations and empirical data suggest that alteplase's effects on primary intracerebral hemorrhages may not be that detrimental. Moreover, at least some of the patients who are at a high risk of having primary cerebral bleeds, or at a high risk of developing symptomatic secondary bleeds, can be excluded from alteplase therapy on clinical grounds, and using nonimaging point-of-care devices, before their hospital arrival. We propose that clinical research should be initiated to define a population of stroke patients in whom alteplase may be administered preimaging, resulting in a greater benefit than harm and in improved functional outcome compared to deferred, postimaging, alteplase treatment.