The initial methods in the paper states that collateral scoring were calculated after reconstructing the arterial vasculature from the CTP scans This is incorrect and collateral scoring were calculated from CT-angiogram images. The correct protocol is stated below:
Multimodal CT Protocol
All Stroke examinations are performed on a 64-multidetector
CT scanner (Discovery CT750HD, GE Healthcare, Waukesha, WI, USA ). The imaging protocol includes NECT, mCTA, and CTP. Whole brain NECT is performed with axial 5-mm slice thickness from the skull base to the vertex, using parameters of 120 kVp, smart AutomAs 200 – 300 (NI 7.6), 0.5 sec rotation, 32*0.625 mm slice (collimation 20 mm) and SFOV 32 cm with DFOV 21 cm, bowtiefilter for “Head”. MPR with 5 mm in axial, coronal and sagittal plane.
mCTA is obtained with dynamic bolus tracking technique (Smart Prep) to optimize imaging acquisition at peak contrast arrival, and it is performed with a delay of at least 5–7 sec using manual triggering. Our intravenous contrast agent is Visipaque (GE Healthcare) and we use a bolus of 85 ml Visipaque 320 mg l/ml and flush with 80 ml saline at a rate of 5 ml/sec. Scanning parameters are 80 kVp, smartmA and AutomAs with mA range 80 to 560 (NI 21.10), 0.625-mm slice thickness, pitch/velocity (mm/rot) 0.98:1 to 39.37, detector coverage 40 mm, and coverage speed 98.43 mm/s. The first phase is from the aortic arch up to the vertex. Phase 2 after 5 sec and phase 3 after 5 sec after phase 2 from skull base up to the vertex. For CTA-maximum intensity projection images, axial CTA-SI are reformatted as 25-mm thick slabs of all three phases in the MIP axial planes and the first phase in MIP 4 mm in axial, coronal and sagittal planes including a MPR 5 mm axial CTA-SI in average.
CTP is performed covering an 8-cm slab in 16 adjacent 5-mm slices. Patient centering is performed using NECT anatomic references, including always basal ganglia and supraganglionar levels. The scan begins after some seconds after the administration of 65 mL of contrast agent at a rate of 5 mL/sec followed by 80 mL saline flush. The parameters used are 80 kVp, 175 mA, 16 images of 5 mm thickness in 2 sets of 8 images of 5 mm thickness (using axial shuttle technique, 8 images of 5 mm per rotation), rotation time 0.4 s, detector coverage 40 mm, and 22 acquisitions, with a total exposure time of 17.6 sec. These protocols are what is done generally although they may be subject to change based on the age of the patient as well as the required area of scanning (supplementary file 1.) The Data set is transferred to an image processing workstation for postprocessing after scanning. We then performed analysis of the circle of Willis and leptomeningeal collaterals from these CT-angiogram images.