Shuohui Yang1, Jiang Lin1, Fang Lu2, Yuanyuan Dai1, Zhihong Han3, and Caixia Fu4
1Radiology, Zhongshan Hospital, Shanghai Medical College, Fudan University, Shanghai, China, People's Republic of, 2Radiology, Shuguang Hosipital, Shanghai University of Traditional Chinese Medicine, Shanghai, China, People's Republic of, 3Pathology, Shuguang Hosipital, Shanghai University of Traditional Chinese Medicine, Shanghai, China, People's Republic of, 4Siemens Shenzhen Magnetic Resonance Ltd., Shenzhen, China, People's Republic of
Synopsis
Hepatocellular carcinoma (HCC) is a
hyper-vascular tumor and knowledge of the intratumoral vascularity is essential. Susceptibility weighted imaging (SWI) uses magnitude and filtered-phase
information to provide high sensitivity to susceptibility changes caused by
hemorrhage, calcium, iron, and small veins. It has been used to visualize
normal or pathologic vascular structures that are not visible on conventional
MRI. Ultrasmall superparamagnetic iron oxide (USPIO) is an intravascular
blood pool contrast medium. After intravenous administration, it can cause a
greater effect on local magnetic field inhomogeneities and results in higher
susceptibility differences between all intratumoral vessels and the tumor on
SWI. This study showed that USPIO-enhanced SWI could further enhance the
demonstration of tumor vascularity inside HCC when compared to unenhanced SWI
in an orthotopic xenograft nude mice HCC model. Purpose
To
evaluate the effectiveness of contrast-enhanced susceptibility weighted imaging
with ultrasmall superparamagnetic iron oxide (USPIO-enhanced SWI) in assessment
of intratumoural vascularity in hepatocellular carcinoma (HCC).
Methods
This experiment was approved by our institutional ethics and animal care committee. Orthotopic xenograft HCC-LM3 nude mice were first established and MRI was performed on a 1.5 Tesla MR scanner (MAGNETOM Aera; Siemens Healthcare, Erlangen, Germany) equipped with a 16-channel wrist surface coil one month later. Three groups of mice, ten in each, were imaged with SWI before and after intravascular bolus injection of a self-made USPIO at three different doses of 4, 8 and 12 mg Fe/kg
respectively in the corresponding nude mice group 1-3. SWI scan parameters were: TR/TE, 30/20 ms; field of view, 120 mm; Flip Angle, 15°; section thickness, 0.9 mm; intersection gap, 0 mm; voxel size, 0.5 ×0.5 × 0.9 mm
3; bandwidth, 150 Hz/Px; scan time, 1 min 38 s. All
SWI images were evaluated in random order by two experienced radiologists with
10 and 23 years’ experience. The degree of intratumoral susceptibility signal intensity (ITSS) was scored. ITSS-to-tumor contrast-to-noise ratio (ITSST-CNR) was measured. These measurements were compared between unenhanced and USPIO-enhanced SWI at each dose and differences in the measurements among different dose groups were estimated. The tumor specimens were removed and studied pathologically with various staining methods. Correlation of ITSS scoring on SWI with tumor micro-vessel density (MVD) was analyzed.
Results
Compared with unenhanced
SWI, significantly higher scorings of ITSS were identified on USPIO-enhanced
SWI at doses of 8 mg Fe/kg (
Z =
-2.000,
P = 0.046) (Figures 1, 2) and
12 mg Fe/kg (
Z = -2.333,
P = 0.020). Among three different dose
groups of USPIO-enhanced SWI, significant differences of ITSS scorings were
found (
χ2 = 8.011,
P = 0.018). The Mann-Whitney U
test demonstrated the difference was significant between groups with doses of
4 and 8 mg Fe/kg (
Z = -2.251,
P = 0.024). The significantly higher values of ITSST-CNR were found on USPIO-enhanced SWI at all doses than on
unenhanced SWI (P < 0.05). There
were also statistically significant
differences of ITSST-CNR on enhanced SWI among three different dose groups (
χ2 = 10.524,
P = 0.005). Significantly higher
ITSST-CNR at a dose of 8 mg Fe/kg was observed than that at 4 mg Fe/kg (
Z = -3.326,
P = 0.001). Kappa values for inter-observer agreement on ITSS
scoring on USPIO-enhanced SWI in Group 1, 2 and 3 were 0.492, 0.825 and 0.720 (
P < 0.05), while those values on
unenhanced SWI were lower. High intraclass
correlation coefficients between two radiologists were observed for
measuring ITSST-CNR in all three dose groups on USPIO-enhanced SWI images (
P
< 0.001).
Pathologically, large
amounts of iron particles were found within tumour vessels (Figure 3). Significantly positive correlation between ITSS scoring on USPIO-enhanced SWI at a dose of 8 mg Fe/kg and histological MVD was found (Spearman’s rho,
r = 0.905,
P = 0.000) (Figure 4).
Discussion
HCC is a solid tumor featured by abundant vascularity and aberrant microvasculature. In the development and progression of HCC, the tumor neovascularization plays a crucial role in providing the essential blood supply to the tumor [1, 2]. Prior studies have shown that unenhanced SWI could be used in liver imaging to improve the detection of siderotic nodules, hemorrhage and venous vasculatures in HCC [3, 4, 5]. USPIO is an intravascular blood pool contrast medium.
After intravenous administration, it can cause a greater effect on local
magnetic field inhomogeneities and results in higher susceptibility differences
between all intratumoral vessels and the tumor on SWI [6, 7]. In our tumor model, by pathologically excluding the susceptibility changes caused by hemorrhage, USPIO swallowed by macrophages and iron deposition, we reached the conclusion that the retained iron particles in tumor vessels resulted in the pronounced ITSS and higher ITSST-CNR on USPIO-enhanced SWI. Based on the significantly positive
correlation found between ITSS scoring and histological MVD and the highest
ITSST-CNR value obtained at a dose of 8 mg Fe/kg, we could conclude
that 8 mg Fe/kg might be the optimal dose for USPIO-enhanced SWI.
Conclusion
USPIO-enhanced SWI improves the detection of intratumoural vascularity in HCC. A dose of 8 mg Fe/kg may be optimal. USPIO-enhanced SWI may have the potential to noninvasively and quantitatively identify tumor angiogenesis in HCC and monitor its response to various treatments.
Acknowledgements
This work is supported by National Natural Science Foundation of China
(Nos. 81371542, 81403204 and 81272568) and Shanghai Health Committee (No. XBR2013115).References
[1] Zhu AX, Duda
DG, Sahani DV, Jain RK. HCC and angiogenesis: possible targets and future
directions. Nat Rev Clin Oncol. 2011; 8:292-301.
[2] Wu XZ, Xie GR,
Chen D. Hypoxia and hepatocellular carcinoma: the therapeutic target for
hepatocellular carcinoma. J Gastroenterol Hepatol. 2007; 22:1178-1182.
[3] Chang SX, Li GW, Chen Y, et al. Characterizing venous vasculatures of hepatocellular carcinoma using a multi-breath-hold two-dimensional susceptibility weighted imaging. PLoS One. 2013; 8:e65895.
[4] Dai Y, Zeng M, Li R, et al. Improving detection of siderotic nodules in cirrhotic liver with a multi-breath-hold susceptibility-weighted imaging technique. J Magn Reson Imaging. 2011; 34:318-325.
[5] Li RK, Zeng MS, Rao SX, et al. Using a 2D multibreath-hold susceptibility-weighted imaging to visualize intratumoral hemorrhage of hepatocellular carcinoma at 3T MRI: correlation with pathology. J Magn Reson Imaging. 2012; 36:900-906.
[6] Hamans BC, Barth M, Leenders WP, Heerschap A. Contrast enhanced susceptibility weighted imaging (CE-SWI) of the mouse brain
using ultrasmall superparamagnetic ironoxide particles (USPIO). Z Med Phys. 2006;
16:269-274.
[7] Bolan PJ,
Yacoub E, Garwood M, Ugurbil K, Harel N. In vivo micro-MRI of
intracortical neurovasculature. Neuroimage. 2006; 32:62-29.