High Resolution Bold Venography (HRBV) MR Imaging of Acute Stroke
With PET, elevated OEF in ischemic tissue is normally observed immediately after the onset of ischemia, followed by decreased OEF when ischemic tissue becomes irreversible damaged. This temporal alteration of OEF can potentially be reflected in the small cerebral veins within and/or adjacent to the ischemic tissue as an alteration in the level of blood oxygen saturation. A MR imaging method, referred to as HRBV, was employed to elucidate the temporal alteration of small cerebral veins adjacent to the ischemic tissue. Ten patients with hemispheric strokes were prospectively imaged using a high resolution 3D T2*-weighted sequence (TE=47ms). Both magnitude and phase images were obtained. A mask which highlights pixels with the presence of local susceptibility was generated for each slice via the phase images. Finally, HRBV maps were obtained by multiplying the mask with the corresponding magnitude image. In addition, conventional MR techniques including DWI and PWI were obtained. All patients were studied within 6 hrs after onset of stroke (4.2 +1.4 hrs, t1). Follow-up MR images were obtained at 48 hrs (t2) and 3 months (t3). Diffusion-Perfusion mismatch (DPMM) was expressed as a percentage with DPMM=(PWI-DWI)/PWI. The prominence of enlarged veins in the ischemic territory on HRBV images was rated from 0 (absence of prominent veins) to 3 (numerous prominent veins). At t1, 8 patients with marked DPMM (78.6 +4.5 %) had numerous prominent (grade 3) veins in the ischemic region on HRBV images. At t2, a substantial decrease in DPMM (26.3 +10%) was associated with far fewer prominent veins (grade 0–1). One patient with persistent DPMM (69% at t1 and 62% at t2) had grade 3 veins on HRBV at both time points. Another patient with very little DPMM (5%) had very few prominent veins (grade 1) at t1 and absence of veins (grade 0) with no DPMM at t2. At t3, all patients either had an absence or decreased number of veins in the regions of infarction. Our results are in good agreement with the postulated hypothesis that DPMM may indicate the presence of salvageable tissue where HRBV exhibited numerous prominent veins with low blood oxygen saturation while these veins deminished when no DPMM and/or irreversible tissue damage occurred.