Introduction

Perfusion MRI has the potential to provide pathophysiological biomarkers for the evaluating, staging and therapy monitoring of rectal cancer. Pseudo continuous arterial spin labeling (pCASL) perfusion MRI is a noninvasive, nonradioactive and non-contrast-enhanced method capable of quantitatively measuring microvascular perfusion characteristics of tissues by tagging arterial water. The objective of this study was to investigate potential correlations between the blood flow (BF) measured by pCASL and dynamic contrast-enhanced (DCE) MRI-derived pharmacokinetic parameters in rectal cancer.

Methods

Twenty-one consecutive patients with pathologically confirmed rectal cancer were recruited. A 3D pCASL and DCE MRI were performed on a clinical 3.0T Philips scanner. The acquisition of pCASL was performed by using 3D volume isotropic TSE imaging to obtain control and labeled images. The labeling plane was 80mm above the center of the image field of view. Labeling was applied for 3 seconds followed by a 1.6-second post labeling delay before image acquisition. The total scan time of one pCASL examination in one subject was 4min 7sec. DCE MRI were acquired after the bolus injection of 0.1 mmol/kg using power injector (3.0mL/s). Image acquisition was performed using a 3D-T 1fast field echo (T1-FFE) sequence. For T1 maps, precontrast 3DT1-FFE with dual flip angles (5^o and 15^o) was performed. BF on pCASL and DCE MRI-derived parameters including K^trans (forward volume transfer constant), K^ep(reverse reflux rate constant between extracellular space and plasma), Ve (the fractional volume of extracellularspace per unit volume of tissue), Vp (vascular plasma volume) and iAUC (initial area under the enhancement) within rectal cancers were calculated Spearman’s bivariate correlation was used to assess the relationship between BF and DCE MRI-derived parameters.

Results

Perfusion result from one subject was presented in Figure 1. There were significant positive correlations between BF and K^trans (p = 0.006, r = 0.579) or K^ep (p = 0.002, r = 0.644). There were no significant correlations between BF and other DCE MRI-derived parameters (Ve, Vp or iAUC) (Table 1).

Discussions

In this study, there was a significant positive correlation between BF and K^trans. Several studies have shown that K^trans is the most important pharmacokinetic parameter of DCE-MRI with regard to evaluation after CRT for rectal cancer ^1,2. A high K^trans before CRT indicates high permeability and vascularity of the tumor, which is believed to make the tumor more accessible to chemotherapy and less hypoxic, making the tumor more sensitive for radiation ³.Our result shows that BF could be useful for evaluation and response prediction after CRT for rectal cancer. There was significant positive correlation between BF and K^ep. K^ep has been shown to correlate well with micro vessel density, a marker of tumor angiogenesis and with T-stage. This could be explained by more extensive neoangiogenesis in more aggressive tumors, which causes greater accumulation of contrast in these tumors. Therefore, BF on pCASL may be proposed as an imaging biomarker for tumor aggressiveness.

Conclusion

pCASL may have the potential to be a noninvasive alternative to DCE MRI.

Acknowledgements

No acknowledgement found.

References

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2. Intven M, Reerink O, Philippens ME, et al. Dynamic contrast enhanced MR imaging for rectal cancer response assessment after neo-adjuvant chemoradiation. J Magn Reson Imaging 2015; 41: 1646-1653.
3. Tong T, Sun Y, Gollub MJ, et al. Dynamic contrast-enhanced MRI: use in predicting pathological complete response to neoadjuvant chemoradiation in locally advanced rectal cancer. J Magn Reson Imaging 2015; 42: 673-680.