Purpose: To directly measure enhancement in acute thrombi using thin-reconstructed perfusion CT images for prediction thrombolytic efficacy.
Materials and Methods: Prior to administration of tissue plasminogen activator (tPA), noncontrast CT (NCCT), 60-second 70-kVp adaptive 4D spiral CT (CTP), and CT angiography (CTA) were prospectively obtained and reconstructed at 1-mm thickness. Length and Hounsfield unit ratio (HUr) of thrombus were measured using 1-mm NCCT. Collateral circulation was assessed on dynamic CTA that were reconstructed from 1-mm CTP images. Good collateral circulation was defined as the criteria that were used for ESCAPE trial. After spatial motion correction of 1-mm CTP images, circular regions of interest were drawn in the central portion and each end of thrombus to measure the level of HU increase from baseline on time-attenuation curves (TAC). Recanalization was assessed on follow-up vascular imaging studies that were obtained within 24 hours after tPA. Modified TICI 2b or 3 was considered successful recanalization. Thrombus length, HUr, collaterals, and minimum increase of HU on TAC (HUmin) were compared between the recanalized and non-recanalized groups.
Results: Of 57 patients who received tPA therapy, 31 patients (female, 13; mean age, 66.5 years) with occlusions in ICA (n=7), M1 (n=8), M1-M2 (n=6), and M2 (n=10) were only assessed. Thrombus length ranged 3-45 mm (median, 12 mm; IQR, 7). HUr was measured from 1.03 to 1.69 (median, 1.26; IQR, 0.19). Good collaterals were noted in 27 patients. HUmin ranged 3-70 HU (median, 15; IQR, 12), and showed negative correlation with thrombus length (rho=-0.410, P=0.022), but not with HUr. HUmin was significantly higher in the recanalized group (n=19) than the non-recanalized group (mean HUmin 23.79 vs 7.83; P<0.0001) independent of thrombus location. Thrombus length, HUr, or collateral status was not significantly different between the two groups. HUmin > 13 was determined with sensitivity of 89.5%, specificity of 91.7%, and AUC of 0.961 for prediction of recanalization.
Conclusion: HUmin of thrombus was significantly higher in patients with successful recanalization after tPA therapy.