Recent Administration of Iodinated Contrast Renders Core Infarct Estimation Inaccurate Using RAPID Software

Abstract

Background and purpose: Automated CTP software is increasingly used for extended window emergent large-vessel occlusion to quantify core infarct. We aimed to assess whether RAPID software underestimates core infarct in patients with an extended window recently receiving IV iodinated contrast.

Materials and methods: We reviewed a prospective, single-center data base of 271 consecutive patients who underwent CTA ± CTP for acute ischemic stroke from May 2018 through January 2019. Patients with emergent large-vessel occlusion confirmed by CTA in the extended window (>6 hours since last known well) and CTP with RAPID postprocessing were included. Two blinded raters independently assessed CT ASPECTS on NCCT performed at the time of CTP. RAPID software used relative cerebral blood flow of <30% as a surrogate for irreversible core infarct. Patients were dichotomized on the basis of receiving recent IV iodinated contrast (<8 hours before CTP) for a separate imaging study.

Results: The recent IV contrast and contrast-naïve cohorts comprised 23 and 15 patients, respectively. Multivariate linear regression analysis demonstrated that recent IV contrast administration was independently associated with a decrease in the RAPID core infarct estimate (proportional increase = 0.34; 95% CI, 0.12-0.96; P = .04).

Conclusions: Patients who received IV iodinated contrast in proximity (<8 hours) to CTA/CTP as part of a separate imaging study had a much higher likelihood of core infarct underestimation with RAPID compared with contrast-naïve patients. Over-reliance on RAPID postprocessing for treatment disposition of patients with extended window emergent large-vessel occlusion should be avoided, particularly with recent IV contrast administration.

FIG 1.

Scatterplot of CT-ASPECTS versus log-transformed CTP-estimated core infarct for the recent IV contrast group (red) and the contrast-naïve group (blue) with lines of best fit. For the same CT-ASPECTS, the CTP-estimated core infarct is consistently less in the recent IV contrast group with divergence of the lines of best fit toward the lower ASPECTS indicative of more substantial differences between the 2 cohorts and more significant underestimation of estimated core infarct for lower CT-ASPECTS.

FIG 2.

Scatterplot of CTP-measured core infarct volume versus postoperative core infarct volume as measured by MR imaging or CT for the recent IV contrast group (red) and the contrast-naïve group (blue) with lines of best fit. For the same preoperative CTP-measured core, the postoperative core infarct is greater in the recent IV contrast group, suggesting that recent IV contrast underestimates CTP-measured core infarct volume at presentation.

FIG 3.

A 56-year-old man who presented to an outside hospital with a right MCA syndrome and ELVO confirmed on CTA. Last known well was approximately 11 hours before imaging at our institution. A, NCCT demonstrates loss of gray-white matter differentiation, in keeping with acute infarct, involving the right insula as well as the frontal and temporal opercula. B, CTA confirms a right M1 segment (yellow circle) occlusion. C, DWI reveals an extensive area of acute infarct correlating with the areas of hypoattenuation on the NCCT. TICI 3 reperfusion was achieved within 60 minutes of the CTP study, and the MR imaging was obtained later in the day.

FIG 4.

CTP with RAPID postprocessing from the same patient as in Fig 3 suggests no core infarct (lack of pink color-coding and an rCBF of <30% volume of 0 mL) with a large area of ischemic penumbra (green color-coding with time-to-maximum [Tmax] of >6 seconds of 129 mL).

FIG 5.

A 67-year-old man who presented directly to our institution (no recent IV contrast) with a left MCA syndrome and last known well approximately 8 hours before imaging. A and B, NCCT demonstrates hypoattenuation involving a large volume of the left MCA and anterior cerebral artery territories. C, CTA demonstrates a internal carotid terminus occlusion with involvement of the carotid terminus and A1 and M1 segments.

FIG 6.

CTP imaging with RAPID postprocessing from the same patient as in Fig 5 suggests an extensive area of core infarct (pink color-coding and an rCBF of <30% volume of 234 mL) corresponding to the large volume of hypoattenuation on NCCT. Tmax indicates time-to-maximum.

FIG 7.

The same 56-year-old man with right M1 segment occlusion as presented in Fig 3. A, rCBF map from the RAPID postprocessing of CTP data demonstrates subtle decreased blood flow to the right MCA territory corresponding to the suggested core infarct volume of 0 mL. B, rCBF map from GE Healthcare processing of the CTP data demonstrates much more conspicuous decreased blood flow within the right MCA territory (scale bar = 0–100 mL/g/min).