Intracranial vascular transfer function in acute stroke patients

Vascular transfer function (VTF) could potentially provide highly relevant physiological information, particularly in patients with cerebrovascular diseases. In this study, we aim to investigate potential alterations of intracranial VTF in patients with acute stroke. The widely employed dynamic susceptibility contrast (DSC) MR approach was employed to acquire images and spatial independent component analysis (ICA) was used to determine local arterial function (LAF) 1, reflecting MR signal changes resulted in the passage of the injected contrast. Subsequently, pixel-by-pixel VTF was derived through the deconvolution of the LAFs with a global artery function (GAF) obtained from the middle cerebral artery (MCA) using singular value decomposition (SVD). The ability to non-invasively depict VTF may offer new insights into blood flow related alterations in acute stroke patients. Perfusion images (PWI) were acquired using DSC from three healthy volunteers at 3 T and five acute stroke patients within 3-6 hrs from symptom onset at 1.5 T using a single shot T2*-weighted EPI sequence. In addition, diffusion-weighted (DWI) images were also acquired. GAF, Cga(t), was obtained through averaging contrast induced signal changes in the contralateral MCA with recirculation effects removed. The susceptibility related signal changes were converted to concentration curves. ICA analysis (ISP group, DTU, http://isp.imm.dtu.dk/toolbox) was applied to the concentration time curves throughout the entire brain 1. LAFs, Cla(x,t), were constructed based on both the spatial mappings and the temporal characteristics of the components, similar to that proposed in reference 1. Finally, VTF (T(x,t)) was obtained through SVD by deconvolving LAFs with GAF. In order to characterize how VTF differs between brain regions, DWI and PWI images were employed to define two region-of-interests (ROIs), namely, DWI-defined lesions and PWI/DWI mismatched regions while a normal ROI was defined in the contralateral hemisphere. In contrast, two ROIs were placed in the two hemispheres for the normal volunteers. Finally, the full-width-half-maximum (FWHM) and the power (EVTF) of the first harmonic of VTF were used to quantitatively determine the discrepancies between different ROIs. For comparison purposes, the ETVF obtained in stroke patients was normalized to that obtained from the normal volunteers. The FWHM obtained from normal volunteers is 5.8+/-0.2 s and 6.0+/-0.02 s, respectively, in the two ROIs. In contrast, for the stroke patients the DWI-defined lesions exhibit a much larger FWHM (9.0+/-8.8 s) while a similar FWHM was obtained for both the PWI/DWI mismatched regions (5.5+/-1.7 s) and the contralateral hemisphere (4.9+/-1.4 s) when compared with that obtained in normal subjects. In addition, the normalized power of the first harmonic of the VTF demonstrates that the DWI-defined lesion, PWI/DWI mismatched regions, and the contralateral hemisphere is 24.1+/-31.1%, 43.5+/-35.4%, and 153.5+/-103.8% with respect to that obtained in normal subjects, respectively. These findings suggest that the DWI-defined lesions exhibit the largest bolus dispersion and smallest power when compared with that obtained in the normal subjects as well as other brain regions in stroke patients. Although our study has a limited sample size, we have demonstrated a novel tool for obtaining VTF in acute stroke patients.