Image quality comparisons of coil setups in 3T MRI for brain and head and neck radiotherapy simulations

PURPOSE

MRI is increasingly used for brain and head and neck radiotherapy treatment planning due to its superior soft tissue contrast. Flexible array coils can be arranged to encompass treatment immobilization devices, which do not fit in diagnostic head/neck coils. Selecting a flexible coil arrangement to replace a diagnostic coil should rely on image quality characteristics and patient comfort. We compared image quality obtained with a custom UltraFlexLarge18 (UFL18) coil setup against a commercial FlexLarge4 (FL4) coil arrangement, relative to a diagnostic Head/Neck20 (HN20) coil at 3T.

METHODS

The large American College of Radiology (ACR) MRI phantom was scanned monthly in the UFL18, FL4, and HN20 coil setup over 2 years, using the ACR series and three clinical sequences. High-contrast spatial resolution (HCSR), image intensity uniformity (IIU), percent-signal ghosting (PSG), low-contrast object detectability (LCOD), signal-to-noise ratio (SNR), and geometric accuracy were calculated according to ACR recommendations for each series and coil arrangement. Five healthy volunteers were scanned with the clinical sequences in all three coil setups. SNR, contrast-to-noise ratio (CNR) and artifact size were extracted from regions-of-interest along the head for each sequence and coil setup. For both experiments, ratios of image quality parameters obtained with UFL18 or FL4 over those from HN20 were formed for each coil setup, grouping the ACR and clinical sequences.

RESULTS

Wilcoxon rank-sum tests revealed significantly higher (p < 0.001) LCOD, IIU and SNR, and lower PSG ratios with UFL18 than FL4 on the phantom for the clinical sequences, with opposite PSG and SNR trends for the ACR series. Similar statistical tests on volunteer data corroborated that SNR ratios with UFL18 (0.58 ± 0.19) were significantly higher (p < 0.001) than with FL4 (0.51 ± 0.18) relative to HN20.

CONCLUSIONS

The custom UFL18 coil setup was selected for clinical application in MR simulations due to the superior image quality demonstrated on a phantom and volunteers for clinical sequences and increased volunteer comfort.

Use of magnetic resonance image-guided radiotherapy for breast cancer: a scoping review

In recent years, we have seen the integration of magnetic resonance imaging (MRI) simulators into radiotherapy centres and the emergence MR linear accelerators (MR-linac). Currently, there are limited studies to demonstrate the clinical effectiveness of MRI guided radiotherapy (MRIgRT) treatment for breast cancer patients. The objective of this scoping review was to identify and map the existing evidence surrounding the clinical implementation of MRIgRT for breast cancer patients. We also identified the challenges and knowledge gaps in the literature. The scoping review was reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) extension for Scoping Reviews reporting guidelines. Titles and abstracts were screened by two independent reviewers. Quantitative and qualitative data were extracted and summarised using thematically organised tables. Results identify that accelerated partial breast irradiation (APBI) is the most common form of treatment for MRIgRT. The presence of the magnet does not affect target coverage or violate organ at risk (OAR) constraints compared to standard radiotherapy methods. Consideration is advised for skin and chest wall (CW) due to the electron return effect (ERE) and areas such as armpit and chin due to the electron stream effect (ESE). Clinically, bolus has been used to protect and prevent unwanted dose in these areas. Overall treatment for APBI on the MR-linac is feasible.

MRzero - Automated discovery of MRI sequences using supervised learning

PURPOSE

A supervised learning framework is proposed to automatically generate MR sequences and corresponding reconstruction based on the target contrast of interest. Combined with a flexible, task-driven cost function this allows for an efficient exploration of novel MR sequence strategies.

METHODS

The scanning and reconstruction process is simulated end-to-end in terms of RF events, gradient moment events in x and y, and delay times, acting on the input model spin system given in terms of proton density, T 1 and T 2 , and Δ B 0 . As a proof of concept, we use both conventional MR images and T 1 maps as targets and optimize from scratch using the loss defined by data fidelity, SAR penalty, and scan time.

RESULTS

In a first attempt, MRzero learns gradient and RF events from zero, and is able to generate a target image produced by a conventional gradient echo sequence. Using a neural network within the reconstruction module allows arbitrary targets to be learned successfully. Experiments could be translated to image acquisition at the real system (3T Siemens, PRISMA) and could be verified in the measurements of phantoms and a human brain in vivo.

CONCLUSIONS

Automated MR sequence generation is possible based on differentiable Bloch equation simulations and a supervised learning approach.

Use of magnetic resonance imaging-guided radiotherapy for breast cancer: a scoping review protocol

BACKGROUND

In recent years, we have seen the incorporation of magnetic resonance imaging (MRI) simulators into radiotherapy centres and the emergence of the new technology of MR linacs. However, the significant health care resources associated with this advanced technology impact immediate widespread use and availability. There are currently limited studies to demonstrate the clinical effectiveness and inform decision-making on the use of MRI in radiotherapy. The objective of this scoping review is to identify and map the existing evidence surrounding the clinical implementation of MRI-guided radiotherapy in patients with breast cancer. It also aims to identify challenges and knowledge gaps in the literature.

METHODS

We will perform a comprehensive search in MEDLINE and EMBASE databases from January 2010 onwards. Grey literature sources will include the WHO International Clinical Trials Registry Platform. We will include systematic reviews, randomised and non-randomised controlled studies published in English. Literature should examine the use of magnetic resonance imaging-guided radiotherapy in adults with breast cancer, regardless of cancer stage or severity. Two reviewers will independently screen all titles, abstracts and full-text reports. Data will be extracted and summarised using qualitative (e.g. content and thematic analysis) methods and presented in tables.

DISCUSSION

The results from this review will consolidate the evidence surrounding MRI-guided radiotherapy for breast cancer, contributing to the development and optimisation of patient selection, simulation, planning, treatment delivery, quality assurance and research, to help improve patient outcomes, cancer care and treatment for women with breast cancer.

SYSTEMATIC REVIEW REGISTRATION

The protocol is available on Open Science Framework at DOI https://doi.org/10.17605/OSF.IO/8TEV6.

Consensus opinion on MRI simulation for external beam radiation treatment planning

AIM

To determine the levels at which consensus could be reached regarding general and site-specific principles of MRI simulation for offline MRI-aided external beam radiation treatment planning.

METHODS

A process inspired by the Delphi method was employed to determine levels of consensus using a series of questionnaires interspersed with controlled opinion feedback.

RESULTS

In general, full consensus was reached regarding general principles of MRI simulation. However, the level of consensus decreased when site-specific principles of MRI simulation were considered.

CONCLUSIONS

These results indicate variability in MRI simulation approaches that are largely explained by the use of MRI in combination with CT.