Monitoring of extra-axial brain tumor response to radiotherapy using pseudo-continuous arterial spin labeling images: Preliminary results

Evaluation of obliteration of arteriovenous malformations after stereotactic radiosurgery with arterial spin labeling MR imaging

PURPOSE

Complete obliteration of treated arteriovenous malformations (AVMs) can be diagnosed only by confirming the disappearance of arterio-venous (A-V) shunts with invasive catheter angiography. The authors evaluated whether non-invasive arterial spin labeling (ASL) magnetic resonance (MR) imaging can be used to diagnose the obliteration of AVMs facilitate the diagnosis of AVM obliteration after treatment with stereotactic radiosurgery (SRS).

MATERIAL AND METHODS

Seven patients with a cerebral AVM treated by SRS were followed up with ASL images taken with a 3T-MR unit, and received digital subtraction angiography (DSA) after the AVM had disappeared on ASL images. Three patients among the seven received DSA also after the postradiosurgical AVM had disappeared on conventional MR images but A-V shunt was residual on ASL images. Four patients among the seven received contrast-enhanced (CE) MR imaging around the same period as DSA.

RESULTS

ASL images could visualize postradiosurgical residual A-V shunts clearly. In all seven patients, DSA after the disappearance of A-V shunts on ASL images demonstrated no evidence of A-V shunts. In all three patients, DSA after the AVM had disappeared on conventional MR images but not on ASL images demonstrated residual A-V shunt. CE MR findings of AVMs treated by SRS did not correspond with DSA findings in three out of four patients.

CONCLUSIONS

Findings of radiosurgically treated AVMs on ASL images corresponded with those on DSA. The results of this study suggest that ASL imaging can be utilized to follow up AVMs after SRS and to decide their obliteration facilitate to decide the precise timing of catheter angiography for the final diagnosis of AVM obliteration after SRS.

Diffusion and perfusion weighted magnetic resonance imaging for tumor volume definition in radiotherapy of brain tumors

Accurate target volume delineation is crucial for the radiotherapy of tumors. Diffusion and perfusion magnetic resonance imaging (MRI) can provide functional information about brain tumors, and they are able to detect tumor volume and physiological changes beyond the lesions shown on conventional MRI. This review examines recent studies that utilized diffusion and perfusion MRI for tumor volume definition in radiotherapy of brain tumors, and it presents the opportunities and challenges in the integration of multimodal functional MRI into clinical practice. The results indicate that specialized and robust post-processing algorithms and tools are needed for the precise alignment of targets on the images, and comprehensive validations with more clinical data are important for the improvement of the correlation between histopathologic results and MRI parameter images.

Assessment of glioma response to radiotherapy using 3D pulsed-continuous arterial spin labeling and 3D segmented volume

BACKGROUND

Gliomas are the most common primary brain tumors in adults, in some cases, radiotherapy may be the preferred treatment option especially for elderly people who cannot endure surgery. Therefore, it is necessary to evaluate the effects of radiotherapy on glioma. Arterial spin labeling (ASL) is an MR imaging technique that allows for a quantitative determination of cerebral blood flow (CBF) noninvasively. Tumor volume is still an important determinant for evaluating treatment response. The purpose of this study was to investigate the relationship between the tumor perfusion parameters and tumor volume and assess the effects of radiotherapy on glioma using pulsed-continuous arterial spin labeling (pcASL) technique.

METHODS

35 patients with gliomas, histologically classified as low-grade group (n=16) and high-grade group (n=19), treated with radiotherapy only or before using other therapies were included in this study. MR examinations, including T1 weighted image and pcASL, were performed before and 4, 8, 12, 16 weeks after radiotherapy. Regional CBF of normal tissue, mean tumor blood flow (TBF_mean), maximum tumor blood flow (TBF_max), and tumor volume were evaluated at each time point. Both the percentage change in CBF (CBF ratio), TBF_mean (TBF_mean ratio), TBF_max (TBF_max ratio) and the percentage change in tumor volume (volume ratio) were calculated using values obtained before and after radiotherapy. The correlation between the volume ratio and CBF ratio, TBF_mean ratio, TBF_max ratio was assessed using linear regression analysis and Pearson's correlation.

RESULTS

The TBF_mean and TBF_max of high-grade gliomas were significantly higher than that of low-grade group. In high-grade group, a strong correlation was demonstrated between the tumor volume and the TBF_max before radiotherapy (R²=0.35, r_s=0.59, p<0.05). There was also a significant correlation between the TBF_max before radiotherapy and the tumor volume ratio before and 8 weeks after radiotherapy (R²=0.56, r_s=-0.74, p<0.05).

CONCLUSION

The TBF_max measured using pcASL could assess tumoral grade and also could become a potential tool for evaluating the therapeutic effects of radiation.

Pseudo-continuous arterial spin labeling reflects vascular density and differentiates angiomatous meningiomas from non-angiomatous meningiomas

Pseudo-continuous arterial spin labeling (PCASL) can measure tumor blood flow (TBF) reliably. We investigated meningioma TBF using PCASL and assessed for any correlation with histopathological microvascular density (MVD) and the World Health Organization (WHO) classification. Conventional MRI with contrast T1-weighted images and PCASL were acquired with a 3 T scanner before surgery in 25 consecutive patients with meningiomas. Using the PCASL perfusion map, the mean and maximum TBF were calculated from regions of interest placed in the largest cross-sectional plane of each tumor. Tissue sections from 16 patients were stained with CD31 to evaluate MVD and were assigned a WHO classification. The TBFs were statistically compared with MVD and the histopathological meningioma subtypes. There were 16 meningothelial meningiomas, four angiomatous meningiomas, two fibrous meningiomas, one transitional meningioma, and two atypical meningiomas. We observed significant correlation between MVD and both mean and maximum TBF (p < 0.05). The mean and maximum TBF ((mean)TBF, (max)TBF) in angiomatous meningiomas are significantly higher than that in non-angiomatous meningiomas (p < 0.05). PCASL is useful in assessing meningioma vascularity, and in differentiating angiomatous meningiomas from non-angiomatous meningiomas.