3D T1-weighted turbo spin echo contrast-enhanced MRI at 1.5 T for frameless brain metastases radiotherapy

Abstract

Purpose: Performance of 3D-T1W-TSE has been proven superior to 3D-MP-GRE at 3 T on brain metastases (BM) contrast-enhanced (CE) MRI. However, its performance at 1.5 T is largely unknown and sparsely reported. This study aims to assess image quality, lesion detectability and conspicuity of 1.5 T 3D-T1W-TSE on planning MRI of frameless BM radiotherapy.

Methods: 94 BM patients to be treated by frameless brain radiotherapy were scanned using 3D-T1W-TSE with immobilization on multi-vendor 1.5 T MRI-simulators. BMs were jointly diagnosed by 4 reviewers. Enhanced lesion conspicuity was quantitatively assessed by calculating contrast ratio (CR) and contrast-to-noise ratio (CNR). Signal-to-noise ratio (SNR) reduction of white matter due to the use of flexible coil was assessed. Lesion detectability and conspicuity were compared between 1.5 T planning MRI and 3 T diagnostic MRI by an oncologist and a radiologist in 10 patients.

Results: 497 BMs were jointly diagnosed. The CR and CNR were 75.2 ± 39.9% and 14.2 ± 8.1, respectively. SNR reduced considerably from 31.7 ± 8.3 to 21.9 ± 5.4 with the longer distance to coils. 3 T diagnostic MRI and 1.5 T planning MRI yielded exactly the same detection of 84 BMs. Qualitatively, lesion conspicuity at 1.5 T was not inferior to that at 3 T. Quantitatively, lower brain SNR and lesion CNR were found at 1.5 T, while lesion CR at 1.5 T was highly comparable to that at 3 T.

Conclusion: 1.5 T 3D-T1W-TSE planning MRI of frameless BM radiotherapy was comprehensively assessed. Highly comparable BM detectability and conspicuity were achieved by 1.5 T planning MRI compared to 3 T diagnostic MRI. 1.5 T 3D-T1W-TSE should be valuable for frameless brain radiotherapy planning.

Keywords: 3D T1-weighted turbo spin echo; Brain metastases; Contrast enhanced MRI; MR-guided-radiotherapy; Stereotactic radiotherapy.

Fig. 1

The illustration of 3D-T1W-TSE CE-MRI of brain metastases (isotropic voxel size of 1 × 1 × 1mm³) on three 1.5 T MRI scanners by different vendors. (GE General Electric, SPACE Sampling Perfection with Application-optimized Contrasts using different flip angle Evolution, VISTA Volume ISotropic Turbo spin echo Acquisition) *CUBE is simply a sequence name of GE and not an acronym

Fig. 2

The illustration of signal-to-noise ratio reduction due to the use of flexible RF coils in two patients. As seen in the figure, the conspicuity of the brain metastases located in the central brain is compromised due to the longer distance to the coil surface compared to that of the brain metastases located in the peripheral brain

Fig. 3

The demonstration of small brain metastasis (< 5 mm in the maximum 1D size, yellow arrows) conspicuity between 3 T diagnostic MRI and 1.5 T planning MRI using 3D-T1W-TSE sequence. 3 T diagnostic MRI was acquired prior to 1.5 T planning MRI within 14 days and lesion size did not apparently change

Fig. 4

The demonstration of non-small brain metastasis (≥ 5 mm in the maximum 1D size, yellow arrows) conspicuity between 3 T diagnostic MRI and 1.5 T planning MRI using 3D-T1W-TSE sequence. 3 T diagnostic MRI was acquired prior to 1.5 T planning MRI within 14 days and lesion size did not apparently change