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Updated: Jul 5, 2026
A Comprehensive Approach to Analyze the Cell Components of Cerebral Blood Clots
Published on: July 21, 2023
Discrimination between red blood cell and platelet components of blood clots by MR microscopy
Jernej Vidmar1, Igor Sersa, Eduard Kralj
1Jozef Stefan Institute, Jamova 39, Ljubljana, 1000, Slovenia. jernej.vidmar@ijs.si
Abstract:
Magnetic resonance imaging (MRI) of pulmonary emboli obtained ex vivo, verified by immunohistochemistry, showed that platelet layers display brighter signal intensity than areas containing predominantly red blood cells (RBC) in T1-weighted MRI. These results were surprising since platelets do not contain paramagnetic haemoglobin that would enhance magnetic relaxation. Our assumption was that the fibrin meshwork areas with entrapped RBC retain abundant extracellular space filled with serum, whereas platelets regroup into tight aggregates lacking serum, essentially mimicking solid tissue structure, rich with cellular proteins that enhance T1-relaxation. Our hypothesis was examined by MRI and NMR relaxometry of in vitro RBC suspensions and sedimented platelets, as well as by MRI of model clots and pulmonary emboli obtained ex vivo. Pure sedimented platelets exhibited shorter proton spin lattice relaxation times (T1 = 874 +/- 310 ms) than those of venous blood of a healthy male with 40% haematocrit (T1 = 1277 +/- 66 ms). T1-values of RBC samples containing high haematocrit (> or = 80%) resembled T1 of platelet samples. In T1-weighted spin-echo MRI echo time and repetition time (TE/TR = 10/120 ms) the ratio of signal intensities between a non-retracted whole blood clot (with a haematocrit of 35%) and a pure platelet clot was 3.0, and the ratio between a retracted whole blood clot with an estimated haematocrit of about 58% and a pure platelet clot was 2.6. We conclude that T1-weighted MRI can discriminate between platelet layers of thrombi and RBC-rich areas of thrombi that are not compacted to a haematocrit level of > or = 80%.
Insights
T1-weighted magnetic resonance imaging (MRI) reveals that platelet-rich thrombi appear brighter than red blood cell (RBC)-rich areas. This finding helps differentiate clot components using MRI, aiding in pulmonary embolism diagnosis.
Area of Science:
- Biomedical Imaging
- Hematology
- Cardiovascular Research
Background:
- Pulmonary emboli (PE) diagnosis relies on imaging, but differentiating clot composition can be challenging.
- Magnetic resonance imaging (MRI) signal intensity in thrombi is influenced by cellular components and their packing.
- Platelets, unlike red blood cells (RBCs), lack hemoglobin but their aggregation may affect MRI signal.
Purpose of the Study:
- To investigate the T1-weighted MRI signal characteristics of platelet-rich versus RBC-rich areas within pulmonary emboli.
- To determine if MRI can distinguish between platelet aggregates and RBC-rich regions in thrombi.
- To explore the underlying biophysical mechanisms for observed signal differences.
Main Methods:
- Ex vivo MRI of pulmonary emboli and model clots.
- Nuclear Magnetic Resonance (NMR) relaxometry of in vitro RBC suspensions and platelet samples.
- Immunohistochemistry for ex vivo clot verification.
Main Results:
- Platelet-rich layers showed significantly brighter signal intensity than RBC-rich areas in T1-weighted MRI.
- Pure sedimented platelets exhibited shorter T1 relaxation times compared to venous blood with normal hematocrit.
- High hematocrit RBC samples (>80%) showed T1 values similar to those of platelets.
- T1-weighted MRI demonstrated signal intensity ratios differentiating pure platelet clots from whole blood clots with varying retraction and hematocrit.
Conclusions:
- T1-weighted MRI can differentiate platelet-rich thrombus components from RBC-rich areas.
- The observed signal intensity differences are related to the packing density and composition of thrombus elements, not solely hemoglobin content.
- This imaging approach may improve the characterization of pulmonary emboli and other thrombi.
