One-Step-Stroke CT Imaging - Part I: Optimization of Interleaved Acquisition of Cerebral CT Perfusion and Neck CT Angiography

PURPOSE: One-Step-Stroke imaging is a CTP acquisition in which one volumetric scan is substituted by volumetric neck CTA, using a toggling table technique and a single dose of contrast agent (see figure). It is not clear how missing one time point of the CTP acquisition to obtain the neck CTA will affect the perfusion maps and which time point is best suited for neck CTA. We determined the optimum timing of neck CTA with the least effect on cerebral perfusion maps. METHOD AND MATERIALS: 20 consecutive patients with suspicion of ischemic stroke were scanned with a clinical CTP head protocol using a 320-row CT scanner. A neck CTA takes maximal 4s, therefore omitting one time point of the CTP with 2s scan interval is sufficient. The One-Step-Stroke protocol was simulated from the original protocol by eliminating one acquisition at various time points. The elimination of one acquisition of CTP simulates the acquisition of the neck CTA. For every patient one volumetric acquisition was deleted, starting from the bolus arrival time up to the fifth time point after the arterial peak determined from the middle cerebral artery (MCA). Corresponding perfusion maps were calculated. Percentage errors were calculated for all perfusion parameters (CBF, CBV, MTT) in basal ganglia and white matter per time point and per patient. Bolus tracking is simulated by using the enhancement curves in the MCA to derive relative thresholds (40-100HU). The relative thresholds were used to determine the time point resulting in the smallest error across all patients. RESULTS: A volumetric CTP scan deleted 2s after reaching a threshold of 40AC/a,!aEURoe70HU kept the absolute percentage errors of all perfusion parameters below 10% in all patients. A relative threshold of 70HU for bolus tracking of the CTA gave the lowest absolute percentage errors for CTP parameters (mean <3.0%, maximum always <7.5%) for acquiring the neck CTA. Estimated average enhancement at CTA, measured in the MCA, was 302HU (range 198AC/a,!aEURoe408HU). CONCLUSION: Our simulations suggest that the One-Step-Stroke protocol does not significantly alter absolute perfusion values and creates high enhancement in the carotids, if the neck CTA is acquired 2s after a threshold of 70HU in the MCA. CLINICAL RELEVANCE/APPLICATION: One-step stroke imaging is a single exam sequence where the neck CTA is part of the CTP. One-Step-Stroke imaging has the potential to replace CTA and CTP which saves radiation dose and contrast agent dose.