Technical Note: Diffusion‐weighted MRI with minimal distortion in head‐and‐neck radiotherapy using a turbo spin echo acquisition method

Abstract

Purpose: Diffusion-weighted (DW) MRI, showing high contrast between tumor and background tissue, is a promising technique in radiotherapy for tumor delineation. However, its use for head-and-neck patients is hampered by poor geometric accuracy in conventional echo planar imaging (EPI) DW-MRI. An alternative turbo spin echo sequence, DW-SPLICE, is implemented and demonstrated in patients. Methods: The DW-SPLICE sequence was implemented on a 3.0 T system and evaluated in 10 patients. The patients were scanned in treatment position, using a customized head support and immobilization mask. Image distortions were quantified at the gross tumor volume (GTV) using field map analysis. The apparent diffusion coefficient (ADC) was evaluated using an ice water phantom. Results: The DW images acquired by DW-SPLICE showed no image distortions. Field map analysis at the gross tumor volumes resulted in a median distortion of 0.2 mm for DW-SPLICE, whereas for the conventional method this was 7.2 mm. ADC values, measured using an ice water phantom were in accordance with literature values. Conclusions: The implementation of DW-SPLICE allows for diffusion-weighted imaging of patients in treatment position with excellent geometrical accuracy. The images can be used to facilitate target volume delineation in RT treatment planning.

Evaluation of diffusion weighted imaging for tumor delineation in head-and-neck radiotherapy by comparison with automatically segmented 18F-fluorodeoxyglucose positron emission tomography

“…MR imaging was performed on a 3.0T Ingenia wide bore MR system (Philips Healthcare, The Netherlands) using 2-element Flex-M surface coils. The DW-SPLICE sequence was prototyped and loaded on the system, generating geometrically accurate diffusion weighted images [21] . Diffusion weighting was applied in an isotropic fashion using three orthogonal directions with b-values of 0 and 800 s/mm 2 (b0 and b800 respectively).…”

“…Here, EPI is replaced with FSE for data acquisition, which leads to less distortions as it is relatively insensitive to magnetic field inhomogeneities introduced by the patient. The DW-SPLICE sequence has excellent geometric performance, allowing the DW-MRI images to be used for target delineation [21] .…”

Emerging role of MRI in radiation therapy

“…For this reason, turbospin echo (TSE)-based DWI has seen renewed interest. DWI with a modified fast spinecho acquisition (DW-SPLICE) 83 has been shown to be a viable, distortion-free alternative for imaging of head and neck patients at 3T, 84 but comes at the price of reduced SNR and prolonged imaging time due to the TSE readout, which hampers the transitioning to 1.5T. Apart from off-resonance-induced distortion, distortions caused by gradient nonlinearities are also an important consideration.…”

Target Volume Delineation Using Diffusion-weighted Imaging for MR-guided Radiotherapy: A Case Series of Laryngeal Cancer Validated by Pathology

“…Prior to surgery, CT imaging was performed. Various MR scans were acquired at 3.0 T (Ingenia, Philips Healthcare, The Netherlands), including a T1-weighted scan with gadolinium contrast, a T2-weighted scan, and a geometrically accurate turbo-spin-echo (TSE)-DWI sequence [ 8 ] with three b-values (s/mm 2 ): b0, b200, and b800. A corresponding apparent diffusion coefficient (ADC) map was calculated.…”

“…The conventional DWI acquisition method is prone to geometric distortions, especially near air cavities. However, using a different acquisition scheme, geometrically accurate diffusion-weighted images can be acquired in a radiotherapy simulation setup [ 8 ]. This technique might pave the way for fast semi-automatic tumor segmentation based on MRI.…”