Multiphase CT angiography perfusion maps for predicting target mismatch and ischemic lesion volumes

Abstract

The complexity of CT perfusion (CTP) acquisition protocols may limit the availability of target mismatch assessment at resource-limited hospitals. We compared CTP mismatch with a mismatch surrogate generated from a simplified dynamic imaging sequence comprising widely available non-contrast CT (NCCT) and multiphase CT angiography (mCTA). Consecutive patients with anterior circulation acute ischemic stroke who received NCCT, mCTA, and CTP were retrospectively included in this study. An mCTA-perfusion (mCTA-P) dynamic series was formed by co-registering NCCT and mCTA. We simulated an ideal mCTA-P study by down-sampling CTP (dCTP) dynamic images according to mCTA timing. Ischemic core and penumbra volumes were estimated by cerebral blood flow and Tmax thresholding, respectively, on perfusion maps calculated independently for CTP, dCTP, and mCTA-P by deconvolution. Concordance in target mismatch (core < 70 ml, penumbra ≥ 15 ml, mismatch ratio ≥ 1.8) determination by dCTP and mCTA-P versus CTP was assessed. Of sixty-one included patients, forty-six had a CTP target mismatch. Concordance with CTP profiles was 90% and 82% for dCTP and mCTA-P, respectively. Lower mCTA-P concordance was likely from differences in collimation width between NCCT and mCTA, which worsened perfusion map quality due to a CT number shift at mCTA. Moderate diagnostic agreement between CTP and mCTA-P was found and may improve with optimal mCTA scan parameter selection as simulated by dCTP. mCTA-P may be a pragmatic alternative where CTP is unavailable or the risks of additional radiation dose, contrast injections, and treatment delays outweigh the potential benefit of a separate CTP scan.

Figure 1

Flow chart of included patients in the study period.

Figure 2

Region of interest (ROI) segmentations overlaid on a CT scan of an anthropomorphic head phantom (top left). In each plot, the line colour corresponds to the colour of the ROI in the segmentation. A substantial 3–5 HU increase in CT number is seen between the standard non-contrast CT (NCCT, 20 mm beam collimation width) and standard multiphase CT angiography (mCTA, 40 mm) protocols at all ROIs (top right). The effect of beam collimation width was isolated by scanning with the NCCT protocol at 20 mm and 40 mm beam collimation, which showed a similar increase in CT number at 40 mm (bottom left). A modified mCTA-perfusion protocol was tested in which mCTA beam collimation width was decreased to 20 mm to match that of NCCT, which substantially improved CT number consistency between NCCT and mCTA images (bottom right).

Figure 3

Patient presenting with unknown time from stroke symptom onset, a bilateral occlusion of the right M2 middle cerebral artery (MCA) and left distal posterior cerebral artery (PCA), and an NIHSS of 10. This patient received endovascular thrombectomy for the right M2 occlusion within 53 min of admission CT (mTICI = 3), but the posterior occlusion could not be treated. (A.i) Admission non-contrast CT; (A.ii) maximum intensity projections of CT angiography with the red circle indicating the occlusion site; (A.iii) follow-up diffusion-weighted imaging showing regions of infarction in the right M2 territory (red arrows) and the left posterior brain (red outline). (B.i) CT perfusion ischemic core (red, 19.4 ml) and penumbra (green, 45.5 ml; mismatch ratio of 2.3) derived from cerebral blood flow (B.ii) and Tmax maps (B.iii) indicated a favourable DEFUSE-3 mismatch profile. (C) Similarly, down-sampled CT perfusion (dCTP) indicated a favourable mismatch profile with an ischemic core and penumbral volumes of 4.8 ml and 26.9 ml, respectively (mismatch ratio 5.6). (D) Multiphase CT angiography-perfusion (mCTA-P) agreed with the favourable CTP mismatch profile with ischemic core and penumbral volumes of 1.2 ml and 51.2 ml, respectively (mismatch ratio 44.3). Of note, the indicated lesion volumes were only of the right MCA territory so that the left PCA lesion volumes did not affect the estimation of mismatch.

Figure 4

Patient presenting 5 h after stroke symptom onset with an occlusion of the right internal carotid to M1 middle cerebral artery and an NIHSS of 22. This patient did not receive reperfusion treatment. (A.i) Admission non-contrast CT shows early ischemic changes in the right MCA territory; (A.ii) maximum intensity projections of CT angiography with the red arrow indicating the occlusion site; (A.iii) follow-up non-contrast CT showing infarction and hemorrhage outlined in red. (B.i) CT perfusion ischemic core (red, 84.0 ml) and penumbra (green, 236.8 ml; mismatch ratio of 2.8) derived from cerebral blood flow (B.ii) and Tmax maps (B.iii). DEFUSE-3 mismatch was unfavourable by CT perfusion due to the large core volume. (C) Similarly, down-sampled CT perfusion (dCTP) indicated an unfavourable mismatch profile with an ischemic core and penumbral volumes of 71.7 ml and 205.3 ml, respectively (mismatch ratio 2.9). (D) Multiphase CT angiography-perfusion (mCTA-P) showed a similar ischemic lesion, but underestimated ischemic core and penumbra at 58.0 ml and 202.5 ml, respectively (mismatch ratio 3.5), leading to a favourable DEFUSE-3 mismatch profile and disagreement with CTP.

Figure 5

Correlation (top row) and Bland–Altman plots (bottom row) of CT perfusion (CTP) versus (left) down-sampled CTP (dCTP) and (right) multiphase CT angiography-perfusion (mCTA-P) ischemic core volume. R indicates the Pearson correlation coefficient; MD, mean difference; ± 1.96SD, standard deviation, indicate the 95% limits of agreement.

Figure 6

Correlation (top row) and Bland–Altman plots (bottom row) of CT perfusion (CTP) versus (left) down-sampled CTP (dCTP) and (right) multiphase CT angiography-perfusion (mCTA-P) ischemic penumbra volume. R indicates the Pearson correlation coefficient; MD, mean difference; ± 1.96SD, standard deviation, indicate the 95% limits of agreement.