Estimating Thrombus Elasticity by Shear Wave Elastography to Evaluate Ultrasound Thrombolysis for Thrombus With Different Stiffness

Abstract

Objective: There is uncertainty about deep vein thrombosis standard treatment as thrombus stiffness alters each case. Here, we investigated thrombus' stiffness of different compositions and ages using shear wave elastography (SWE). We then studied the effectiveness of ultrasound-thrombolysis on different thrombus compositions.

Methods: Shear waves generated through mechanical shaker and traveled along thrombus of different hematocrit (HCT) levels, whereas 18-MHz ultrasound array used to detect wave propagation. Thrombus' stiffness was identified by the shear wave speed (SWS). In thrombolysis, a 3.2 MHz focused transducer was applied to different thrombus compositions using different powers. The thrombolysis rate was defined as the percentage of weight loss.

Results: The estimated average SWS of 20%, 40%, and 60% HCT thrombus were 0.75 m/s, 0.44 m/s, and 0.32 m/s, respectively. For Thrombolysis, the percentage weight loss at 8 MPa Negative pressure for the same HCT groups were 23.1%, 35.29%, and 39.66% respectively.

Conclusion: SWS is inversely related to HCT level and positively related to thrombus age. High HCT thrombus had higher weight loss compared to low HCT. However, the difference between 20% and 40% HCT was more significant than between 40% and 60% HCT in both studies. Our results suggest that thrombus with higher SWS require more power to achieve the same thrombolysis rate as thrombus with lower SWS.

Significance: Characterizing thrombus elastic property undergoing thrombolysis enables evaluation of ultrasound efficacy for fractionating thrombus and reveals the appropriate ultrasound parameters selection to achieve a certain thrombolysis rate in the case of a specific thrombus stiffness.

Fig. 1.

(a) schematic diagram of SWE in-vitro experimental setup (b) thrombus sample (40% HCT, five days age) and different sizes of tube holder used in the study.

Fig. 2.

(a) Schematic diagram of ultrasound thrombolysis experimental setup (b) Vessel phantom (L:70 mm, OD: 11 mm, ID: 10 mm) with center hole covered by a plastic thin layer (~ 100 um thickness) (c) front side of the focused transducer (aperture diameter: 20 m𝑚).

Fig. 3.

Schematic diagram of PCD experimental setup.

Fig. 4.

(a, b, c) B-mode images and (d, e, f) spatiotemporal maps of different HCT levels thrombus. (a, d) 20% HCT, (b, e) 40% HCT, and (e, f) 60% HCT. The slope in the dotted line represents the estimated SWS.

Fig. 5.

Estimated shear wave speed (Mean ± SDs) of 20%, 40%, and 60% HCT thrombus (n=3). Thrombus age: 5 days.

Fig. 6.

Estimated shear wave speed (Mean ± SDs) of 20%, 40%, and 60% HCT thrombus with respect to aging (n=3).

Fig. 7.

Spatiotemporal maps of 20% HCT thrombus with different ages: (a) five days, (b) 15 days, and (25) 25 days.

Fig. 8.

(a) Detected signals at different power level (PNP: 0, 1, 2, 8 MPa), and (b) the normalization of power magnitude in dB for 1, 2, and 8 MPa: 3.17, 18.60, and 46.29 dB respectively, in the frequency Range: 4.1 MHz to 6 MHz.

Fig. 9.

Thrombolysis rate vs peak negative pressure (MPa) of different thrombus groups: 20% HCT, 40% HCT, and 60% HCT. treatment time: 10 minutes. Acoustic parameters: 1KHz PRF, 10% duty cycle (320 cycles). n=3.

Fig. 10.

Representation images of the ultrasound effect on (a,b,c) 20% HCT thrombus and (d, e, f) 40% HCT thrombus. (a,d) 0 MPa, (b,e) 2 MPa, and (e, f) 8 MPa PNP. Acoustic parameters: 1 KHz PRF and 10% duty cycle. 10 minutes exposure time. Yellow dotted circle represents the ultrasound effect on thrombus.

Fig. 11

Thrombus cycle of estimating the SWS in two different medium (a) thrombus incubated in gelatin phantom (b) SWE experimental setup of thrombus incubated in gelatin phantom (c) representation of thrombus stack to the phantom (d) removing the thrombus from the phantom (e) placing the thrombus in open window tube (f) SWE experimental setup in water-bath. Experiments were conducted five times and the average was taken.

Fig. 12.

The relation between shear wave speed (SWS) and peak negative pressure (PNP) to achieve 20 ± 5% thrombolysis rate.