Mismatch between lactate and the apparent diffusion coefficient of water in progressive focal ischemia

Imaging of cerebral perfusion in acute stroke

Rapid imaging of cerebral perfusion in acute stroke is needed for timely triage of patients for thrombolytic therapy. Accurate quantitative perfusion imaging is required for proper assessment of penumbral brain parenchyma truly at risk for extension of infarction from the irreversible core infarction. CT and MRI techniques offer rapidity and availability for acute stroke imaging, including that of cerebral perfusion. CT perfusion techniques are readily available, but suffer from limited brain coverage of present multislice scanners. MRI offers whole brain coverage, but suffers from less availability and higher cost than CT. Presently, development is directed towards increasing the quantitative accuracy of cerebral perfusion imaging and validation of surrogate parameters, such as time to peak (TTP). In the future, the need for rapid and frequent assessment of cerebral perfusion and its metabolic correlates, with minimal or no radiation, will probably be met by MRI.

Multiple spin-echo spectroscopic imaging for rapid quantitative assessment of N-acetylaspartate and lactate in acute stroke

Monitoring the signal levels of lactate (Lac) and N-acetylaspartate (NAA) by chemical shift imaging can provide additional knowledge about tissue damage in acute stroke. Despite the need for this metabolic information, spectroscopic imaging (SI) has not been used routinely for acute stroke patients, mainly due to the long acquisition time required. The presented data demonstrate that the application of a fast multiple spin-echo (MSE) SI sequence can reduce the measurement time to 6 min (four spin echoes per echo train, 32 x 32 matrix). Quantification of Lac and NAA in terms of absolute concentrations (i.e., mmol/l) can be achieved by means of the phantom replacement approach, with correction terms for the longitudinal and transversal relaxation adapted to the multiple spin-echo sequence. In this pilot study of 10 stroke patients (symptom onset < 24 hr), metabolite concentrations obtained from MSE-SI add important information regarding tissue viability that is not provided by other sequences (e.g., diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI)). Metabolic changes extended beyond the borders of the apparent diffusion coefficient (ADC) lesion in nine of the 10 patients, showing a rise in Lac concentrations up to 18 mmol/l, while NAA levels sometimes dropped below the detection level. Considerable differences among the patients in terms of the Lac concentrations and the size of the SI-ADC mismatch were observed.

Current awareness

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