Synopsis

Keywords: Tumors, Cancer

This study is to utilize the relaxometry generated by unenhanced and Gd-enhanced synthetic MRI to identify the recurrence and necrosis in patient with high grade glioma after radiotherapy. The results indicated enhanced T1 was significantly shortened in tumor and peripheral edema region for recurrent tissue in compare with necrosis and showed well ability of differentiation

Introduction

Chemoradiotherapy is usually necessary for patients with high grade glioma (HGG), but high recurrence rate can be found even with careful surgery and treatment [1,2]. The identification of postoperative recurrence and radiation induced brain injury remains a major challenge, since the enhancement in conventional weighted MRI images for recurrent lesion behave similar to that on the radiation necrotic tissue [3]. Relaxometry are considered associated with the tissue components and potentially provides quantitative and sensitive tumor characterization. Studies with T1 or T2 in tumor grading and differentiation have been reported [4,5]. Synthetic MRI is the promising technique developed recently for simultaneously generating relaxometry map in clinical tolerant time. This study aims to explore the possibility of synthetic MRI in identifying recurrence and radiation necrosis for HGG patients after radiotherapy.

Methods

36 patients (age: 51±15 years old; male/female: 19/17) confirmed HGG and went through radiotherapy were collected. . 21 patients were diagnosed as recurrent by secondary operation or MRI follow-up, and 15 patients were diagnosed as radiation necrosis. Conventional T1-weighted (T1W), T2-weighted (T2W), and synthetic MRI with magnetic resonance image compilation (MAGiC) were acquired on a 3.0T scanner (SIGNA Architect, GE Healthcare, Milwaukee, WI) for all subjects during the follow up and the parameters for MAGiC were as follows: field of view (FOV) = 240 mm×180 mm, TR/TE1/TE2 = 4000/19/95.2ms, matrix = 320×256, slice thickness/gap = 5mm/2.5mm, echo train length = 16, bandwidth = 27.78 kHz, number of slices = 20 and total imaging time = 3min 28s. Enhanced imaging of same sequences were scanned after injecting Gadopentetate dimeglumine (Gd-DTPA, Consun, Guangdong, China) with a single of 02ml/kg, at a rate of 2.0ml/s. Imaging done in 1~2 month after 3 times of radiation therapies was used for analysis. . The MAGiC data were then processed with SytheticMR (version 8.04, LinkÖping, Sweden) to obtain the parametric T1/T2 relaxometry map. Region of interests (ROIs) with size of 25-35mm² were manually delineated in unenhanced (T1) and enhanced (T1+C) relaxometry map in the area of enhancing tumor core and peripheral edema using the enhanced T1W as the reference separately by two radiologist both with 12 experience on brain tumor imaging (Figure 1 & 2). The mean of two measures in each region were used as the final quantification for comparison between radiation necrosis and recurrence group with Student-t test or Mann-Whitney U test after the normality and homogeneity test. Receiver operator characteristic (ROC) curve analysis were also done. All statistics were conducted with R language (version 4.0). P <0.05 indicated significant difference.

Results

T1 was significantly shortened in the Gd enhanced imaging in tumor region and peripheral edema for recurrence group while only in tumor region for necrosis group. T2 in tumor region for recurrence group was significantly decreased. In compare with radiation necrosis lesion, Significant lower T1+C relaxometries in HGG recurrence lesions were showed both in tumor and peripheral edema (Figure 3, Table 1), but no significant differences for other relaxometry quantifications. The AUC for T1+C in HGG recurrence and radiation necrosis lesions was respectively 0.9571 (tumor, sensitivity = 1, specificity = 0.8667) and 0.8984 (edema, sen. = 1, spe. = 0.7333) (Figure 4).

Discussion

As paramagnetic contrast, gadolinium (Gd) shortened the T1 and T2 relaxometry when perfusing into the tissue through vessels, inducing the enhanced signal in T1W images but reduced quantification in T1 mapping. In tumor region, due to more abundant vasculature, remarkable decreasing in T1 and T2 could be found in recurrent lesion. T1 was also shortened in necrosis tumor region, which might be because of the leakage of Gd resulted from the damaged blood-brain barrier. For recurrence group, reduced T1 in edema region might mean that there was tumor cell infiltration along with angiogenesis. Since T1 in recurrence group was shortened significantly greater than that of necrosis group, it could be used to well differentiate the tumor recurrence and necrosis after radiation therapy.

Summary of main finding

Enhanced T1 relaxometry in tumor and peripheral edema region of recurrent lesion was significantly shortened in compare with necrosis for patients with high grade glioma after therapy and showed well performance of differentiation of necrosis and recurrence (AUC= 0.9571, 0.8984).

Acknowledgements

No acknowledgement found.

References

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