Abstract
Impaired oxygen and cellular metabolism is a hallmark of ischaemic injury in acute stroke. Magnetic resonance spectroscopic imaging (MRSI) has long been recognized as a potentially powerful tool for non-invasive metabolic imaging. Nonetheless, long acquisition time, poor spatial resolution, and narrow coverage have limited its clinical application. Here we investigated the feasibility and potential clinical utility of rapid, high spatial resolution, near whole-brain 3D metabolic imaging based on a novel MRSI technology. In an 8-min scan, we simultaneously obtained 3D maps of N-acetylaspartate and lactate at a nominal spatial resolution of 2.0 × 3.0 × 3.0 mm3 with near whole-brain coverage from a cohort of 18 patients with acute ischaemic stroke. Serial structural and perfusion MRI was used to define detailed spatial maps of tissue-level outcomes against which high-resolution metabolic changes were evaluated. Within hypoperfused tissue, the lactate signal was higher in areas that ultimately infarcted compared with those that recovered (P < 0.0001). Both lactate (P < 0.0001) and N-acetylaspartate (P < 0.001) differed between infarcted and other regions. Within the areas of diffusion-weighted abnormality, lactate was lower where recovery was observed compared with elsewhere (P < 0.001). This feasibility study supports further investigation of fast high-resolution MRSI in acute stroke.
Highlights
High-resolution mapping of brain tissue viability is key to optimal therapeutic selection and outcome prediction in acute stroke
Representative triplanar high-resolution 3D Magnetic resonance spectroscopic imaging (MRSI) maps of lactate and NAA are shown in Fig. 1A and B, respectively
Multimodal images including apparent diffusion coefficient (ADC), DWI, ASL-PWI, MRSI and FLAIR maps from six representative patients are shown in Fig. 2 and Supplementary Fig. 2
Summary
High-resolution mapping of brain tissue viability is key to optimal therapeutic selection and outcome prediction in acute stroke (van Leyen et al, 2019). Though viability is a functional characteristic, most closely assayed by cellular metabolism (Astrup et al, 1981), current clinical practice relies on structural and vascular characteristics as a surrogate for it. MRI with diffusion- and perfusion-weighting (DWI and PWI) have been used to map ischaemic brain tissue damage, with the mismatch between DWI lesion and PWI-identified region of hypoperfusion considered as the salvageable penumbra (Schlaug et al, 1999). An important suggestive finding from these studies was that the preservation of NAA coupled with an increase in lactate may be a surrogate biomarker of the ischaemic penumbra (Gillard et al, 1996; Dani and Warach, 2014). The long data acquisition time (over 5 min for a single slice), low spatial resolution (over 20 mm for single voxel and over 10 mm for 2D imaging), and narrow tissue coverage have significantly obstructed the translation of the technique into real-world clinical practice
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