Quantifying Erythrocyte Concentration in Thrombi

Erythrocytes, a primary component of thrombi, can cause significant alterations of the magnetic susceptibility of a sample. Quantitative susceptibility mapping (QSM) is an MRI sequence that maps the sample magnetization. Paramagnetic tissues appear hyperintense in QSM images, and diamagnetic tissues appear hypointense^{73 (link)}. A clinical 3 Tesla (3T) MR system (Ingenia dStream, Philips Healthcare, Best, The Netherlands) with a body transmit coil and a 16-channel head-and-neck receive coil was used to collect QSM images of the agarose embedded samples. A three-dimensional gradient echo recall sequence was employed to acquire multiple echoes. Utilizing the real and imaginary portions of the received signals, magnetic susceptibility was computed via the morphology enabled dipole inversion (MEDI) pipeline^{86 (link),87} . Thrombi were contoured manually to exclude background QSM values. Positive QSM values (i.e. parts per billion, ppb > 0) were tabulated to gauge the concentration of erythrocytes in VTE samples⁴⁶ . This technique exploits the paramagnetic nature of hemoglobin while excluding highly diamagnetic tissues.