A novel amplitude binning strategy to handle irregular breathing during 4DMRI acquisition: improved imaging for radiotherapy purposes

Z Van Kesteren,A Bel,T Alderliesten,I Bones,R Klaassen,D Tekelenburg,A Van Der Horst,H W M Van Laarhoven,G Van Tienhoven,O J Gurney-Champion

doi:10.1186/s13014-019-1279-z

Abstract

BackgroundFor radiotherapy of abdominal cancer, four-dimensional magnetic resonance imaging (4DMRI) is desirable for tumor definition and the assessment of tumor and organ motion. However, irregular breathing gives rise to image artifacts. We developed a outlier rejection strategy resulting in a 4DMRI with reduced image artifacts in the presence of irregular breathing.MethodsWe obtained 2D T2-weighted single-shot turbo spin echo images, with an interleaved 1D navigator acquisition to obtain the respiratory signal during free breathing imaging in 2 patients and 12 healthy volunteers. Prior to binning, upper and lower inclusion thresholds were chosen such that 95% of the acquired images were included, while minimizing the distance between the thresholds (inclusion range (IR)). We compared our strategy (Min95) with three commonly applied strategies: phase binning with all images included (Phase), amplitude binning with all images included (MaxIE), and amplitude binning with the thresholds set as the mean end-inhale and mean end-exhale diaphragm positions (MeanIE). We compared 4DMRI quality based on:Data included (DI); percentage of images remaining after outlier rejection.Reconstruction completeness (RC); percentage of bin-slice combinations containing at least one image after binning.Intra-bin variation (IBV); interquartile range of the diaphragm position within the bin-slice combination, averaged over three central slices and ten respiratory bins.IR.Image smoothness (S); quantified by fitting a parabola to the diaphragm profile in a sagittal plane of the reconstructed 4DMRI.A two-sided Wilcoxon’s signed-rank test was used to test for significance in differences between the Min95 strategy and the Phase, MaxIE, and MeanIE strategies.ResultsBased on the fourteen subjects, the Min95 binning strategy outperformed the other strategies with a mean RC of 95.5%, mean IBV of 1.6 mm, mean IR of 15.1 mm and a mean S of 0.90. The Phase strategy showed a poor mean IBV of 6.2 mm and the MaxIE strategy showed a poor mean RC of 85.6%, resulting in image artifacts (mean S of 0.76). The MeanIE strategy demonstrated a mean DI of 85.6%.ConclusionsOur Min95 reconstruction strategy resulted in a 4DMRI with less artifacts and more precise diaphragm position reconstruction compared to the other strategies.Trial registrationVolunteers: protocol W15_373#16.007; patients: protocol NL47713.018.14

Highlights

For radiotherapy of abdominal cancer, four-dimensional magnetic resonance imaging (4DMRI) is desirable for tumor definition and the assessment of tumor and organ motion
Based on the fourteen subjects, the Min95 binning strategy outperformed the other strategies with a mean Reconstruction completeness (RC) of 95.5%, mean Intra-bin variation (IBV) of 1.6 mm, mean Inclusion range (IR) of 15.1 mm and a mean S of 0.90
Our Min95 reconstruction strategy resulted in a Four-dimensional Magnetic resonance imaging (MRI) (4DMRI) with less artifacts and more precise diaphragm position reconstruction compared to the other strategies

Summary

Introduction

For radiotherapy of abdominal cancer, four-dimensional magnetic resonance imaging (4DMRI) is desirable for tumor definition and the assessment of tumor and organ motion. Radiotherapy for upper abdominal cancer patients, such as pancreatic, esophageal and gastric cancer, is challenging because of poor contrast between these tumors and other soft tissues on planning CT scans and because of respiratory-induced tumor and organ motion. It was shown that there is a large variation between observers when delineating upper abdominal tumors on computed tomography (CT) [1] This variation appears to decrease when adding MRI images, which offer better contrast between tumor and the surrounding tissues [1,2,3]. For pancreatic cancer it was shown that the initial 4DCT is not representative for the respiratory-induced motion during actual treatment, whilst for esophageal cancer this is the case [4, 5]. To limit X-ray dose burden, the 4DCT acquisition is typically done with a limited number of acquisitions, compromising image quality even further

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Results

Conclusion