Work

Time-dependent effects of formalin fixation on magnetic resonance imaging relaxation times in ex vivo human thrombus tissue

Year: 2025

Type: article

Abstract: Background: Magnetic resonance imaging (MRI)-based ex vivo thrombus imaging is an emerging modality for evaluating clot composition and guiding therapy. However, when it comes to sample handling, the effect of formalin fixation on MRI relaxation times (T1, T2, and T2*) of thrombus tissue remains poorly characterized. Formalin fixation is widely used in studies investigating the MRI properties of thrombus tissue; however, fixation alters tissue biochemistry and water dynamics. Understanding these effects is essential for accurately interpreting existing literature and for developing reliable ex vivo imaging biomarkers. This study aims to assess the impact of formalin fixation on human thrombus MRI properties using an ultra-high-resolution ex vivo 9.4 T MRI scanner. Methods: A total of 19 clot samples from 13 patients undergoing mechanical thrombectomy were evaluated. The samples were imaged fresh, after <6 hours of formalin fixation, and after >24 hours of formalin fixation. T1, T2, and T2* relaxation time maps were created and evaluated over the fixation stages. Linear mixed-effects models were used to assess the effect of fixation stage and biological covariates, including clot age, patient age, and body mass index (BMI). Results: Formalin fixation induced significant reductions in T1 and T2 relaxation times. T1 decreased from 1,801.6±236.3 ms (fresh) to 1,205.0±491.6 ms (>24 h formalin, P<0.001). T2 declined from 77.6±16.5 ms (fresh) to 44.3±13.8 ms (>24 h formalin). Most T2 reduction occurred within the first 6 hours of fixation. T2* values showed minimal changes across fixation stages. Higher BMI and older clot age were significantly associated with shorter T1 values, while no covariates influenced T2 or T2*. Conclusions: Formalin fixation substantially alters T1 and T2 relaxation times in thrombus tissue, while T2* remains relatively stable. These findings highlight the necessity of accounting for fixation effects and patient-specific biological factors when designing and interpreting ex vivo thrombus MRI data and developing imaging biomarkers.

Source: Annals of Translational Medicine

DOI: 10.21037/atm-25-108

Authors: Eniko Pomozi, Caroline Jordan, Alexander B. Crichton, Judit Csore, Christof Karmonik, Trisha Roy

Institutions: Semmelweis University, Houston Methodist, Texas A&M University, University of Birmingham

Language: English

Topic: Advanced MRI Techniques and Applications

Subfield: Radiology, Nuclear Medicine and Imaging

Field: Medicine

Domain: Health Sciences

SDG: Good health and well-being

Open Access status: diamond

Funder: National Heart, Lung, and Blood Institute