Characteristics and pathological mechanism on magnetic resonance diffusion-weighted imaging after chemoembolization in rabbit liver VX-2 tumor model

Abstract

Aim: To investigate dynamic characteristics and pathological mechanism of signal in rabbit VX-2 tumor model on diffusion-weighted imaging (DWI) after chemoembolization.

Methods: Forty New Zealand rabbits were included in the study and forty-seven rabbit VX-2 tumor models were raised by implanting directly and intrahepatically after abdominal cavity opened. Forty VX-2 tumor models from them were divided into four groups. DWI was performed periodically and respectively for each group after chemoembolization. All VX-2 tumor samples of each group were studied by pathology. The distinction of VX-2 tumors on DWI was assessed by their apparent diffusion coefficient (ADC) values. The statistical significance between different time groups, different area groups or different b-value groups was calculated by using SPSS12.0 software.

Results: Under b-value of 100 s/mm(2), ADC values were lowest at 16 h after chemoembolization in area of VX-2 tumor periphery, central, and normal liver parenchyma around tumor, but turned to increase with further elongation of chemoembolization treatment. The distinction of ADC between different time groups was significant respectively (F = 7.325, P < 0.001; F = 2.496, P < 0.048; F = 6.856, P < 0.001). Cellular edema in the area of VX-2 tumor periphery or normal liver parenchyma around tumor, increased quickly in sixteen h after chemoembolization but, from the 16th h to the 48th h, cellular edema in the area of normal liver parenchyma around tumor decreased gradually and that in the area of VX-2 tumor periphery decreased lightly at, and then increased continually. After chemoembolization, Cellular necrosis in the area of VX-2 tumor periphery was more significantly high than that before chemoembolization. The areas of dead cells in VX-2 tumors manifested low signal and high ADC value, while the areas of viable cells manifested high signal and low ADC value.

Conclusion: DWI is able to detect and differentiate tumor necrotic areas from viable cellular areas before and after chemoembolization. ADC of normal liver parenchyma and VX-2 tumor are influenced by intracellular edema, tissue cellular death and microcirculation disturbance after chemoembolization.

Figure 1

A: The area of VX-2 tumor center; B: The area of VX-2 tumor periphery; C: The area of VX-2 tumor outer layer; D: The normal liver parenchyma area around tumor when the values of ADC and signals were measured on DWI and samples were investigated pathologically.

Figure 2

ADC values of different areas on DWI after chemoembolization. A: B-value was 100 s/mm²; B: B-value was 300 s/mm².

Figure 3

Signal values on DWI when area and b-value was different after chemoembolization. Areas: 1-signal of VX-2 tumor periphery area when b-value was 100 s/mm²; 2-signal of VX-2 tumor center area when b-value was 100 s/mm²; 3-signal of the normal liver parenchyma area around tumor when b-value was 100 s/mm²; 4-signal of VX-2 tumor periphery area when b-value was 300 s/mm²; 5-signal of VX-2 tumor center area when b-value was 300 s/mm²; 6-signal of the normal liver parenchyma area around tumor when b-value was 300 s/mm².

Figure 4

Image manifestations of hepatic VX-2 tumor on DWI and ADC map when b-value was 100 s/mm² at 6 h after chemoembolization A: High signal and distinct margin of VX-2 tumor on DWI; B: Low signal of it on the ADC map.

Figure 5

Image manifestations of hepatic VX-2 tumor on DWI and ADC map when b-value was 100 s/mm² at 48 h after chemoembolization A: High and uneven signal and distinct margin of VX-2 tumor on DWI; B: Low and uneven signal of it on the ADC map.

Figure 6

Cellular edema of different areas after chemoembolization.

Figure 7

A: Cell nest of VX-2 tumor and wide zone of necrosis in the tumor(x 100) and B: cellular edema in the VX-2 tumor (x 400).