Characterization and evaluation of a flexible MRI receive coil array for radiation therapy MR treatment planning using highly decoupled RF circuits

Abstract

The growth in the use of magnetic resonance imaging (MRI) data for radiation therapy (RT) treatment planning has been facilitated by scanner hardware and software advances that have enabled RT patients to be imaged in treatment position while providing morphologic and functional assessment of tumor volumes and surrounding normal tissues. Despite these advances, manufacturers have been slow to develop radiofrequency (RF) coils that closely follow the contour of a RT patient undergoing MR imaging. Instead, relatively large form surface coil arrays have been adapted from diagnostic imaging. These arrays can be challenging to place on, and in general do not conform to the patient's body habitus, resulting in sub optimal image quality. The purpose of this study is to report on the characterization of a new flexible and highly decoupled RF coil for use in MR imaging of RT patients. Coil performance was evaluated by performing signal-to-noise ratio (SNR) and noise correlation measurements using two coil (SNR) and four coil (noise correlation) element combinations as a function of coil overlap distance and comparing these values to those obtained using conventional coil elements. In vivo testing was performed in both normal volunteers and patients using a four and 16 element RF coil. Phantom experiments demonstrate the highly decoupled nature of the new coil elements when compared to conventional RF coils, while in vivo testing demonstrate that these coils can be integrated into extremely flexible and form fitting substrates that follow the exact contour of the patient. The new coil design addresses limitations imposed by traditional surface coil arrays and have the potential to significantly impact MR imaging for both diagnostic and RT applications.

Repetitive MRI of organs at risk in head and neck cancer patients undergoing radiotherapy

“…Comparability of the different studies is hampered by factors like the use of different MR scanners [29], [30] with 1.5 or 3.0 Tesla field strength and variable image acquisition parameters [29], [30], [31], like different b-values, slice thickness, slice gap, TR/TE (repetition time/echo time). It has also to be taken into account that different coils influence the image quality [32], [33] and only in a few cases, RT-immobilization devices, which have an effect on positional stability [34] have been used for MR imaging.

Fig. 1Variables from patient selection to data analysis, influencing imaging parameters and the correlation with toxicity measurements and radiotherapy dose.

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Task group 284 report: magnetic resonance imaging simulation in radiotherapy: considerations for clinical implementation, optimization, and quality assurance

“…This is particularly problematic for head and neck MR-SIM. Recently introduced adaptive image receive coil technology permits individual coil elements to be positioned directly on immobilized patients, permitting increased SNR, acceleration, and accommodation of RT setups 121 . However, at the time of this writing, this technology is only available under research agreements.…”

A 12-channel flexible receiver coil for accelerated tongue imaging

“…Although these hyperintensities did not affect the image quality in the sagittal images of swallowing graded by speech therapists, they were more clearly present in transverse images. These inhomogeneities were also reported in other flexible receiver coils [33]. We tested several correction methods, such as normalisation using the coil sensitivity maps, but we could not find a method that sufficiently homogenised the images.…”