By Charles Strother
Solid data accumulated over the last two decades shows the critical impact of time from the onset of an ischaemic stroke to treatment on both the incidence of successful large artery recanalisation and good clinical outcome. In spite of significant improvements in reducing the time from patient arrival at a hospital to the onset of treatment, significant minutes, and thus millions of neurons, are still lost as the result of the need to transport patients to and from imaging suites where studies used for diagnosis and patient selection are performed eg CT, CT angiography, CT perfusion or MR, MR angiography, MR perfusion. Over the last two years we have attempted to develop and evaluate imaging techniques that would enable diagnosis, patient selection and revascularisation all to be performed using a single modality—X-ray
Flat detector angiographic equipment provides the greatest spatial and temporal resolution of any other imaging modality. These attributes combined with the capability to now also obtain high quality CT-like images of the brain parenchyma opens the potential to perform truly comprehensive imaging evaluations of acute ischaemic stroke patients in the angiography suite.
When faced with a patient suffering an acute stroke, several bits of information are required in order to optimise treatment. After initial clinical evaluation, patients may be divided into ones that are not considered to be candidates for any attempt at revascularisation and, ones who, depending on the results of imaging studies, may be candidates for revascularisation. Patients shown to be ideal candidates for revascularisation include those with large artery occlusions and significant differences between the volume of parenchyma that is no longer salvageable (ischaemic core), and that which while non-functional, is still potentially salvageable (penumbra). Individuals falling into this category have the greatest chance of a good outcome with, all else considered, the lowest risk of adverse events.
Working in conjunction with scientists and engineers from Siemens HealthCare’s Angiography division, we have developed and tested a protocol that allows, from a single 3D-DSA rotational acquisition done in conjunction with an intravenous injection of contrast medium (60–80cc), us to obtain: 1) a 3D volume of the intracranial vasculature; 2) a non-contrast CT and: 3) a cerebral blood volume (CBV) map. The results of our pre-clinical experience with this technique have been published in the American Journal of Neuroradiology; Dörfler, Struffert and colleagues in Erlangen, Germany have recently published their experience using a similar protocol in patients with ischaemic stroke in the same journal and in the European Journal of Radiology. Based on these preliminary results, as well as on more recent developments not yet published, we are optimistic that it soon will be feasible to diagnose, triage and perform revascularisation procedures on patients with an acute ischaemic stroke in the angiography suite.
While cerebral blood volume (CBV) is perhaps the most helpful parameter in distinguishing ischaemic core from penumbra, more experience and validation is required before we can be certain about its reliability in these patients. Also, when fully tested and made available, algorithms that allow measurement of other vital perfusion parameters eg cerebral blood flow (CBF), mean transit time (MTT) and time to peak (TTP) using flat detector angiography systems will, in my opinion, enhance the ability to identify those patients most appropriate for attempts at revascularisation. Currently, the C-arm CT images of the parenchyma are not sufficient to exclude small amounts of blood or the early but important signs of acute ischaemic injury. Ongoing efforts in both reconstruction algorithms and detector technology will likely soon eliminate this deficiency. Finally, newly developed methods for adding temporal information to 3D-DSA reconstructions so that they may be viewed in the same way as a 2D acquisition along with techniques to embed fluoroscopic roadmap views in a reconstructed 3D volume should further enhance the environment of the angiographic suite.
In my opinion, current and soon to be available technologies make it feasible to consider the angiography suite the stroke unit of the future.
Charles Strother is professor emeritus, Department of Radiology, University of Wisconsin, USA. He receives research support from Siemens Healthcare AX, and is also an unpaid advisor to the company.