Magnetic resonance imaging quantitative T2* mapping to predict the red blood cell content of in vivo thrombi retrieved from patients with large vessel occlusions in acute ischemic stroke

Abstract

Background and purpose: Magnetic resonance imaging quantitative T2* mapping has shown reliable identification of thrombus red blood cell content in vitro. The thrombus composition has been in vivo, associated with outcomes after endovascular therapy for acute ischemic stroke. We aim to analyze the red blood cell content of thrombi retrieved from patients with large vessel occlusions in relation to the thrombus-T2* relaxation time in magnetic resonance imaging.

Material and methods: Consecutive acute ischemic stroke patients treated by endovascular therapy were scanned with an magnetic resonance imaging quantitative T2* mapping sequence. Quantitative histologic evaluations of red blood cell content were performed. A linear regression assessed the association between vascular risk factors, comorbidities, antithrombotic drugs intake, baseline National Institutes of Health Stroke Scale (NIHSS), intravenous thrombolysis before endovascular therapy, time between onset and groin puncture, patient's outcome at 3 months, magnetic resonance imaging quantitative T2* mapping results, and the red blood cell content of thrombi. The correlation between the mean thrombus-T2* relaxation time and red blood cell content was assessed by calculating the Pearson correlation coefficient.

Results: Among 31 thrombi, 16 were "Fibrin rich" and 15 "red blood cell dominant." The median red blood cell content was 39 (range, 0-90; interquartile range, 37). The median (interquartile range) thrombus-T2* relaxation time was shorter in "red blood cell dominant" thrombi (21, interquartile range 6) than in "Fibrin rich" thrombi (24, interquartile range 7), without significant difference (p = 0.15), as shown in the Box plot. An inverse correlation between thrombus-T2* relaxation time and red blood cell content was found, with a correlation coefficient of -0.41 (95% CI, -0.67 to -0.08, p = 0.02).

Conclusion: Our study shows that a shorter thrombus-T2* relaxation time is related to a higher red blood cell content within in vivo thrombi.

Keywords: Magnetic resonance imaging; stroke; thrombectomy; thrombus.

Figure 1.

MRI showing left MCA occlusion. The mean Thrombus T2* relaxation time (TT2*RT) is measured at 30 ms. Histological analysis has found a Fibrin rich thrombus. (a) TOF sequence shows an MCA occlusion (white arrow). (b) Thrombus-T2* sequence shows the thrombus (black arrow). (c) Thrombus-T2* sequence with maximal zoom and manual contouring for thrombus-T2* relaxation time (TT2*RT). (d) Histological analysis of this Fibrin rich thrombus. This thrombus consists of fibrin/platelets aggregations and very rare white blood cells. (hematoxylin and eosin (G × 20; G × 400).

Figure 2.

MRI showing left MCA SVS+ occlusion. The mean Thrombus T2* relaxation time (TT2*RT) is measured at 19 ms. Histological analysis has found a RBC dominant thrombus. (a) GRE sequence shows a SVS+ occlusion (white arrow). (b) TOF sequence shows an MCA occlusion (discontinued white arrow). (c) Thrombus-T2* sequence with maximal zoom and manual contouring for thrombus-T2* relaxation time (TT2*RT). (d) Histological analysis of the RBC dominant thrombus. This thrombus is composed mainly of erythrocytes (red blood cells—high magnification image) and very rare fibrin/platelets aggregations. (hematoxylin and eosin (G × 20; G × 400).

Figure 3.

Box plot for the thrombus-T2* relaxation time measured in each group, “fibrin rich” thrombi and “RBC dominant” thrombi. RBC: red blood cells. Minimum (Q0 or 0th percentile): The lowest data point maximum (Q4 or 100th percentile): The largest data point median (Q2 or 50th percentile): The middle value of the dataset. First quartile (Q1 or 25th percentile): also known as the lower quartile qn(0.25), is the median of the lower half of the dataset. Third quartile (Q3 or 75th percentile): also known as the upper quartile qn(0.75), is the median of the upper half of the dataset. Interquartile range (IQR) is the distance between the upper and lower quartiles.

Figure 4.

Pearson's correlation between the thrombus-T2* relaxation time (y-axis) and the red blood cells (RBC) content (x-axis) in each thrombus.