Clinically Relevant Reperfusion in Acute Ischemic Stroke: MTT Performs Better than Tmax and TTP
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ORIGINAL ARTICLE
Clinically Relevant Reperfusion in Acute Ischemic Stroke: MTT Performs Better than Tmax and TTP Andria L. Ford & Hongyu An & Linglong Kong & Hongtu Zhu & Katie D. Vo & William J. Powers & Weili Lin & Jin-Moo Lee
Received: 15 July 2013 / Revised: 11 December 2013 / Accepted: 5 January 2014 # Springer Science+Business Media New York 2014
Abstract While several MRI parameters are used to assess tissue perfusion during hyperacute stroke, it is unclear which is optimal for measuring clinically relevant reperfusion. We directly compared mean transit time (MTT) prolongation (MTTp), time-to-peak (TTP), and time-to-maximum (Tmax) to determine which best predicted neurological improvement and tissue salvage following early reperfusion. Acute ischemic stroke patients underwent three MRIs: 6 s, while there was no correlation with any TTP threshold. Among all parameters, reperfusion defined by MTTp was most strongly associated with ΔNIHSS (MTTp >3 s, P=0.0002) and tissue salvage (MTTp >3 s and 4 s, P3 s longer than the median MTT of the contralateral hemisphere (MTTp >3 s threshold). The blue mask delineates the tp2 perfusion deficit at MTTp >3 s. At tp2, the perfusion deficit shrinks and the non-overlapped region (yellow arrow) indicates the region of reperfusion
Transl. Stroke Res. Table 1 Baseline characteristics N=50 Femalea Age, yearsb Admission NIHSSb African-Americana tPA treatmenta Admission mean arterial pressure, mmHgb Admission glucose, mg/dlb Time to tp1, hourb Time to tp2, hourb Medical history Hypertensiona Diabetesa Congestive heart failurea Tobacco usea Coronary artery diseasea Stroke or TIAa a
n (%)
b
Median [interquartile range]
18 (35 %) 65 [57,74] 16 [8, 20] 19 (37 %) 38 (74 %) 113 [104,129] 124 [106,148] 2.7 [2.1,3.5] 6.2 [6.1,6.5] 38 (74 %) 17 (33 %) 6 (12 %) 12 (24 %) 14 (28 %) 8 (16 %)
variables were entered into all 12 regression models. Regression diagnostics evaluated distributional assumptions of the residuals and functional form of the covariates. To measure the effect of reperfusion on tissue fate, Vreperf for each parameter/threshold was correlated with tissue salvage using Spearman rank correlation (ρ). Differences in Vreperf, Vnon-reperf, and %Reperf between MTTp vs. Tmax and MTTp vs. TTP were compared using Wilcoxon matched-pairs signed-rank test. The overlap (similarity index (SI)) between two parameters was assessed using the Dice coefficient, computed as 2×|A∩B|/(|A|+|B|), where A and B are regions of tp1 perfusion deficit, reperfusion, or non-reperfusion from the two MR parameters being compared. SI ranged from 0 and 1 corresponding to no and perfect overlap, respectively.
Results A total of 63 acute ischemic stroke patients were prospectively scanned. Five patients did not go on to receive tp2 due to intolerance of tp1 scan including claustrophobia, poor contrast delivery on the perfusion weighted imaging, or medical instability, leaving 58 patients who received the tp2 scan. An additional eight patients who received both tp1 and tp2 scans were excluded from the
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