Diffusion-weighted multiparametric MRI for monitoring longitudinal changes of parameters in rabbit VX2 liver tumors

Advanced Diffusion-Weighted MRI for Cancer Microstructure Assessment in Body Imaging, and Its Relationship With Histology

Diffusion-weighted magnetic resonance imaging (DW-MRI) aims to disentangle multiple biological signal sources in each imaging voxel, enabling the computation of innovative maps of tissue microstructure. DW-MRI model development has been dominated by brain applications. More recently, advanced methods with high fidelity to histology are gaining momentum in other contexts, for example, in oncological applications of body imaging, where new biomarkers are urgently needed. The objective of this article is to review the state-of-the-art of DW-MRI in body imaging (ie, not including the nervous system) in oncology, and to analyze its value as compared to reference colocalized histology measurements, given that demonstrating the histological validity of any new DW-MRI method is essential. In this article, we review the current landscape of DW-MRI techniques that extend standard apparent diffusion coefficient (ADC), describing their acquisition protocols, signal models, fitting settings, microstructural parameters, and relationship with histology. Preclinical, clinical, and in/ex vivo studies were included. The most used techniques were intravoxel incoherent motion (IVIM; 36.3% of used techniques), diffusion kurtosis imaging (DKI; 16.7%), vascular, extracellular, and restricted diffusion for cytometry in tumors (VERDICT; 13.3%), and imaging microstructural parameters using limited spectrally edited diffusion (IMPULSED; 11.7%). Another notable category of techniques relates to innovative b-tensor diffusion encoding or joint diffusion-relaxometry. The reviewed approaches provide histologically meaningful indices of cancer microstructure (eg, vascularization/cellularity) which, while not necessarily accurate numerically, may still provide useful sensitivity to microscopic pathological processes. Future work of the community should focus on improving the inter-/intra-scanner robustness, and on assessing histological validity in broader contexts. LEVEL OF EVIDENCE: NA TECHNICAL EFFICACY: Stage 2.

Experimental study of camptothecin combined with drug-eluting bead transarterial chemoembolization in the rabbit VX2 liver tumor model

Drug-eluting bead transarterial chemoembolization (DEB-TACE) has been widely used in the treatment of liver cancer; however, the utilization rate of chemotherapeutic drugs after embolization is low. Chemotherapy resistance mediated by high nuclear factor E2-related factor 2 (NRF2) expression limits DEB-TACE efficacy. Camptothecin (CPT), an NRF2 inhibitor, exerts chemosensitizing effects. We designed a controlled experiment to determine the efficacy and feasibility of DEB-TACE combined with CPT for the treatment of rabbit VX2 hepatoma. DEB-TACE activated NRF2 expression in the tumor region. NRF2 activation could be inhibited by the combined use of CPT. After DEB-TACE alone, the tumor necrosis was incomplete, there were still highly active tumor residues, and the apparent diffusion coefficient (ADC) value, which was negatively correlated with tumor activity observed by magnetic resonance imaging, remained low. After DEB-TACE combined with CPT, the relative necrosis of the tumor was more complete, the ADC value was higher, and the ADC change was greater. The single application of CPT did not result in evident liver function and physical burden to the rabbits. The combined use of CPT and DEB-TACE did not significantly increase DEB-TACE imaging of liver function and body. In conclusion, CPT can also inhibit high NRF2 expression after DEB-TACE treatment. Combining CPT with DEB-TACE can improve the sensitivity of DEB-TACE in the treatment of VX2 tumors, improve the therapeutic effect, and has no evident toxic and side effects. This study explored the methods for enhancing the efficacy of DEB-TACE in liver cancer from a new perspective and performed model experiments, which provided a theoretical basis for future clinical treatment.

Evaluation of the efficacy of transcatheter arterial embolization combined with apatinib on rabbit VX2 liver tumors by intravoxel incoherent motion diffusion-weighted MR imaging

Background and purpose

It is crucial to evaluate the efficacy, recurrence, and metastasis of liver tumors after clinical treatment. This study aimed to investigate the value of Introvoxel Incoherent Motion (IVIM) imaging in the evaluation of rabbit VX2 liver tumors treated with Transcatheter Arterial Embolization (TAE) combined with apatinib.

Methods

Twenty rabbit VX2 liver tumor models were established and randomly divided into either the experimental group (n=15) or the control group (n=5). The experimental group was treated with TAE combined with oral apatinib after successful tumor inoculation, while no treatment was administered following inoculation in the control group. IVIM sequence scan was performed in the experimental group before treatment, at 7 and 14 days after treatment. All rabbits were sacrificed after the last scan of the experimental group. Marginal tissues from the tumors of both groups were excised for immunohistochemical analysis to observe and compare the expression of microvessel density (MVD). The alterations of IVIM-related parameters of tumor tissues in the experimental group, including Apparent Diffusion Coefficient (ADC), True Diffusion Coefficient (D), Pseudodiffusion Coefficient (D*), and Perfusion Fraction (f) were compared at different periods, and the correlation between these parameters and MVD was analyzed.

Results

After treatment, ADC and D values significantly increased, whereas D* and f values both decreased, with statistically significant differences.(P<0.05). The average tumor MVD of the experimental group after TAE combined with apatinib ((33.750 ± 6.743) bars/high power field (HPF)) was significantly lower than that in the control group ((64.200 ± 10.164) bars/HPF)). Moreover, D and f were positively correlated with tumor MVD in the experimental group (r=0.741 for D and r=0.668 for f, P<0.05). However, there was no significant correlation between ADC and D* values of the experimental group and tumor MVD (r=0.252 for ADC and r=0.198 for D*, P>0.05).

Conclusion

IVIM imaging can be employed to evaluate the efficacy of TAE combined with apatinib in rabbit VX2 liver tumors. Alterations in D and f values were closely related to the MVD of liver tumor tissues.

Idarubicin-Loaded ONCOZENE Drug-Eluting Bead Chemoembolization in a Rabbit Liver Tumor Model: Investigating Safety, Therapeutic Efficacy, and Effects on Tumor Microenvironment

PURPOSE

To investigate toxicity, efficacy, and microenvironmental effects of idarubicin-loaded 40-μm and 100-μm drug-eluting embolic (DEE) transarterial chemoembolization in a rabbit liver tumor model.

MATERIALS AND METHODS

Twelve male New Zealand White rabbits with orthotopically implanted VX2 liver tumors were assigned to DEE chemoembolization with 40-μm (n = 5) or 100-μm (n = 4) ONCOZENE microspheres or no treatment (control; n = 3). At 24-72 hours postprocedurally, multiparametric magnetic resonance (MR) imaging including dynamic contrast-enhanced (DCE), diffusion-weighted imaging (DWI), and biosensor imaging of redundant deviation in shifts (BIRDS) was performed to assess extracellular pH (pHe), followed by immediate euthanasia. Laboratory parameters and histopathologic ex vivo analysis included fluorescence confocal microscopy and immunohistochemistry.

RESULTS

DCE MR imaging demonstrated a similar degree of devascularization of embolized tumors for both microsphere sizes (mean arterial enhancement, 8% ± 12 vs 36% ± 51 in controls; P = .07). Similarly, DWI showed postprocedural increases in diffusion across the entire lesion (apparent diffusion coefficient, 1.89 × 10^-3 mm²/s ± 0.18 vs 2.34 × 10^-3 mm²/s ± 0.18 in liver; P = .002). BIRDS demonstrated profound tumor acidosis at baseline (mean pHe, 6.79 ± 0.08 in tumor vs 7.13 ± 0.08 in liver; P = .02) and after chemoembolization (6.8 ± 0.06 in tumor vs 7.1 ± 0.04 in liver; P = .007). Laboratory and ex vivo analyses showed central tumor core penetration and greater increase in liver enzymes for 40-μm vs 100-μm microspheres. Inhibition of cell proliferation, intratumoral hypoxia, and limited idarubicin elution were equally observed with both sphere sizes.

CONCLUSIONS

Noninvasive multiparametric MR imaging visualized chemoembolic effects in tumor and tumor microenvironment following DEE chemoembolization. Devascularization, increased hypoxia, coagulative necrosis, tumor acidosis, and limited idarubicin elution suggest ischemia as the predominant therapeutic mechanism. Substantial size-dependent differences indicate greater toxicity with the smaller microsphere diameter.

Intravoxel incoherent motion diffusion-weighted imaging assessment of microvascular characteristics in the murine embryonal rhabdomyosarcoma model

Background

Intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) can distinguish the false diffusion generated by microvascular blood flow from the true water molecule diffusion.

Purpose

To investigate the correlation between IVIM-DWI parameters and angiogenic markers such as the microvessel density and vascular endothelial growth factor (VEGF) expression in the murine embryonal rhabdomyosarcoma model.

Material and Methods

The murine embryonal rhabdomyosarcoma model was produced by subcutaneously injecting 107 human embryonal rhabdomyosarcoma cells into the right back of nude mice. The apparent diffusion coefficient (ADC), pseudo-diffusion coefficient (D*), true diffusion coefficient (D), and perfusion fraction (f) were obtained from 22 mice models using IVIM-DWI with b-values of 0, 50, 100, 150, 200, 400, 600, 800, 1000, and 1200 s/mm2. The microvessel density and VEGF expression were obtained by histologic examination. We then compared the correlation between IVIM-DWI parameters and microvessel density and VEGF expression.

Results

The average ADC, D*, D, and f values were 1.05 ± 0.27 × 10−3 mm2/s, 6.19 ± 1.78 × 10−3 mm2/s, 0.69 ± 0.09 ×10−3 mm2/s, and 17.68 ± 8.41 (%), respectively. There was moderate positive correlation between D* value and microvessel density and VEGF expression (r = 0.484, P = 0.023; r = 0.511, P = 0.015). However, there was no significant correlation between ADC, D, and f values and microvessel density and VEGF expression.

Conclusion

The D* value from IVIM-DWI may be used to evaluate tumor angiogenesis in the murine embryonal rhabdomyosarcoma model.

Quantitative MRI for Assessment of Treatment Outcomes in a Rabbit VX2 Hepatic Tumor Model

Globally, primary and secondary liver cancer is one of the most common cancer types, accounting 8.2% of deaths worldwide in 2018. One of the key strategies to improve the patient's prognosis is the early diagnosis, when liver function is still preserved. In hepatocellular carcinoma (HCC), the typical wash-in/wash-out pattern in conventional magnetic resonance imaging (MRI) reaches a sensitivity of 60% and specificity of 96-100%. However, in recent years functional MRI sequences such as hepatocellular-specific gadolinium-based dynamic-contrast enhanced MRI, diffusion-weighted imaging (DWI), and magnetic resonance spectroscopy (MRS) have been demonstrated to improve the evaluation of treatment success and thus the therapeutic decision-making and the patient's outcome. In the preclinical research setting, the VX2 liver rabbit tumor, which once originated from a virus-induced anaplastic squamous cell carcinoma, has played a longstanding role in experimental interventional oncology. Especially the high tumor vascularity allows assessing the treatment response of locoregional interventions such as radiofrequency ablation (RFA) and transcatheter arterial embolization (TACE). Functional MRI has been used to monitor the tumor growth and viability following interventional treatment. Besides promising results, a comprehensive overview of functional MRI sequences used so far in different treatment setting is lacking, thus lowering the comparability of study results. This review offers a comprehensive overview of study protocols, results, and limitations of quantitative MRI sequences applied to evaluate the treatment outcome of VX2 hepatic tumor models, thus generating a unique basis for future MRI studies and potential translation into the clinical setting. Level of Evidence: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2019. J. Magn. Reson. Imaging 2020;52:668-685.

Role of intravoxel incoherent motion MRI in preoperative evaluation of DNA mismatch repair status in rectal cancers

AIM

To explore the role of intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) in evaluating DNA mismatch repair (MMR) status of rectal cancers preoperatively.

MATERIALS AND METHODS

Seventy-six patients with a diagnosis of rectal cancer confirmed at endoscopic biopsy were enrolled prospectively and underwent IVIM MRI before surgery.

RESULTS

The perfusion fraction (f) values of MMR proteins (MMRP) positive rectal cancers were significantly higher than negative cancers. The f values could differentiate MMRP positive rectal cancers from negative cancers with an area under the curve (AUC) of 0.695. The vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor 2 (VEGFR2) expression rates of positive MMRP rectal cancers were significantly higher than negative cancers.

CONCLUSION

This pilot study indicated that the f value derived from IVIM MRI differed significantly between rectal cancers with different MMRP expression levels, which might be involved with different VEGF and VEGFR2 expression rates.

Dynamics of angiogenesis and cellularity in rabbit VX2 tumors using contrast-enhanced magnetic resonance imaging and diffusion-weighted imaging

A number of studies have demonstrated that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) may be used to evaluate microvessel density (MVD), and may quantitatively reflect tumor angiogenesis. To investigate the dynamics, including angiogenesis and tumor cellularity, of rabbit VX2 tumors during the 4 weeks following tumor implantation, the present study used DCE-MRI combined with diffusion-weighted imaging (DWI) to scan the tumors at 3 days, and then at 1, 2, 3 and 4-week intervals, following tumor implantation. The dynamics, volume transfer coefficient (K^trans) and apparent diffusion coefficient (ADC) of the tumor parenchyma were analyzed. Furthermore, the associations between K^trans and MVD at 4 weeks after tumor implantation were analyzed. Tumor K^trans was positively correlated with MVD at 4 weeks (r=0.674, P<0.001). Following tumor implantation, the tumor K^trans level rose for 2 weeks and then began to decline, reaching its lowest point at 4 weeks (P<0.001). ADC values at 1 week were higher than at 3 days, but declined thereafter (P<0.001). Tumor necrosis appeared by 1 week after tumor implantation. The necrosis degree of tumor was gradually increased from the occurrence of necrosis within the 4-week time span of the present study (1 vs. 2 weeks, P=0.008; 2 vs. 3 weeks, P<0.001; 3 vs. 4 weeks, P<0.001). The present study identified that tumor angiogenesis is a dynamic process that serves a function in tumor growth, and that DCE-MRI may reflect tumor parenchymal MVD and be useful in evaluating angiogenesis.

Evaluation of antiangiogenic and antiproliferative effects of sorafenib by sequential histology and intravoxel incoherent motion diffusion-weighted imaging in an orthotopic hepatocellular carcinoma xenograft model

PURPOSE

To investigate the effectiveness of intravoxel incoherent motion (IVIM) in the assessment of the therapeutic efficacy of sorafenib in an orthotopic hepatocellular carcinoma (HCC) xenograft model.

MATERIALS AND METHODS

Thirty-five HCC nude mouse models were established. IVIM was performed on a 1.5T MR scanner at baseline (n = 5) and serially at 7, 14, and 21 days after sorafenib treatment. The apparent diffusion coefficient (ADC_total ), true diffusion coefficient (D), pseudodiffusion coefficient (D*), and perfusion fraction (f) at these timepoints were measured and compared between the treated (n = 15) and control group (n = 15). Differences in measurements among different timepoints were evaluated. Correlations between IVIM parameters and histologic features including necrotic fraction (NF) and microvessel density (MVD) were analyzed.

RESULTS

Compared to the control group, ADC_total and D were significantly higher at each timepoint (P = 0.009), while f significantly decreased at 7 days (P = 0.009) and increased at 21 days (P = 0.028) in the treated group. Serial measurements in the treated group showed that both ADC_total and D increased significantly at 7, 14, and 21 days compared to baseline (P < 0.05), while f significantly declined at 7 days (P = 0.016) and increased at 21 days (P = 0.009). Significant correlations were found between ADC_total and NF (r = 0.811, P < 0.001), D and NF (r = 0.838, P < 0.001), and between f and NF (r = 0.528, P = 0.017) in the treated group.

CONCLUSION

IVIM may provide useful biomarkers for evaluating the therapeutic effects of sorafenib on HCC.

LEVEL OF EVIDENCE

1 J. Magn. Reson. Imaging 2017;45:270-280.