Commissioning of a new wide-bore MRI scanner for radiotherapy planning of head and neck cancer

Abstract

Objective: A combination of CT and MRI is recommended for radiotherapy planning of head and neck cancers, and optimal spatial co-registration is achieved by imaging in the treatment position using the necessary immobilisation devices on both occasions, something which requires wide-bore scanners. Quality assurance experiments were carried out to commission a newly installed 1.5-T widebore MRI scanner and a dedicated, flexible six-channel phased array head and neck coil. Methods: Signal-to-noise ratio (SNR) and spatial signal uniformity were quantified using a homogeneous aqueous phantom, and geometric distortion was quantified using a phantom with water-filled fiducials in a grid pattern. Volunteer scans were also used to determine the in vivo image quality. Clinically relevant T 1 weighted and T 2 weighted fat-suppressed sequences were assessed in multiple scan planes (both sequences fast spin echo based). The performance of two online signal uniformity correction schemes, one utilising low-resolution reference scans and the other not utilising low-resolution reference scans, was compared. Results: Geometric distortions, for a 635-kHz bandwidth, were ,1 mm for locations within 10 cm of the isocentre rising to 1.8 mm at 18 cm away. SNR was above 50, and uniformity in the axial plane was 71% and 95% before and after uniformity correction, respectively. Conclusion: The combined performance of the wide-bore scanner and the dedicated coil was adjudged adequate, although superior-inferior spatial coverage was slightly limited in the lower neck. Advances in knowledge: These results will be of interest to the increasing number of oncology centres that are seeking to incorporate MRI into planning practice using dedicated equipment.

Development and validation of a novel large field of view phantom and a software module for the quality assurance of geometric distortion in magnetic resonance imaging

“…The algorithm for correcting geometric distortion used in our study, in Wang et al [11] and Liney et al [15], is provided by the vendor. The GE algorithm applied in our study involves the use of spherical harmonics expansion up to 5th degree in order to represent the magnetic field generated by the gradient coils.…”

“…However, existing protocols and phantoms do not allow for the detailed characterization of geometric distortion for large field of view (FOV) acquisitions, nor for assessment and monitoring of the performance of vendor-specific geometric distortion correction algorithms. Most studies have been performed for relatively small fields of view [15,7,9,10,6,11]. These considerations are particularly critical in image-guided radiotherapy, where large FOV acquisitions are required to provide a geometrically accurate representation of the tumor, the organs at risk as well as the entire patient body contour for the anatomical region of interest imaged.…”

Continuous table acquisition MRI for radiotherapy treatment planning: Distortion assessment with a new extended 3D volumetric phantom

“…Spatial distortion assessment is a vital part of MRI quality assurance (QA) for RTP in addition to other specific QA required for RTP (e.g. surface 80 coil intensity correction 6 , laser alignment, etc. ).…”

Quantitative analysis of image quality for acceptance and commissioning of an MRI simulator with a semiautomatic method

“…Conducting simulation sequences with the simulation head coil, the PIU is still quite low. Liney et al12 reported that the radiation head coil was less homogeneous than the GE head and neck coil and the body phase array. The intensity correction method is recommended to be chosen when using six‐channel simulation head coil.…”

“…The image acceptance and commissioning for an MRI simulator are mostly described in AAPM Report 100,10 and the accuracies of laser and table are dealt with in AAPM Report TG 66 11. Several studies12, 13 have already reported and discussed the procedures and strategies of using an MRI simulator in radiation oncology department. However, overall strategies of image quality testing for acceptance and commissioning of MRI simulation still need to be explored.…”