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Gradient system characterization of a 1.5 T MR‐Linac with application to 4D UTE imaging for adaptive MR‐guided radiotherapy of lung cancer.

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Title: Gradient system characterization of a 1.5 T MR‐Linac with application to 4D UTE imaging for adaptive MR‐guided radiotherapy of lung cancer.
Authors: Goodburn, Rosie1,2 (AUTHOR) rosie.goodburn@icr.ac.uk, Bruijnen, Tom3 (AUTHOR), Lecoeur, Bastien1,4 (AUTHOR), Nair, Prashant1 (AUTHOR), Ahmed, Merina2 (AUTHOR), Barnes, Helen2 (AUTHOR), Oelfke, Uwe1 (AUTHOR), Wetscherek, Andreas1 (AUTHOR)
Source: Magnetic Resonance in Medicine. Jul2025, Vol. 94 Issue 1, p28-40. 13p.
Subjects: Image reconstruction, Lung cancer, Transfer functions, Cancer patients, Cancer radiotherapy
Abstract: Purpose: To measure the gradient system transfer function (GSTF) of an MR‐Linac (Elekta Unity, Stockholm, Sweden) using an accessible phantom‐based method and to apply trajectory corrections for UTE image reconstruction in the context of MR‐guided radiotherapy of lung cancer. Methods: The first‐order GSTF of a 1.5 T, split gradient Elekta Unity MR‐Linac was measured using a thin‐slice technique to characterize gradient system imperfections for each physical gradient axis (X, Y, Z). Repeatability measurements of the GSTF were performed 48 h apart. The GSTF was applied to trajectory correction in multi‐echo UTE image reconstruction (TEs = 0.176, 1.85, 3.52 ms) to allow for UTE‐Dixon inputs in the generation of synthetic CT. Images were acquired in an anthropomorphic phantom and in two free‐breathing lung cancer patients. For patient scans, respiratory‐correlated 4D‐MR images were reconstructed using self‐navigation and an iterative compressed‐sensing algorithm. Results: The GSTF magnitude was similar across the X/Y/Z axes up to ˜6 kHz. The GSTF phase was similar between the X/Y/Z components up to ˜3 kHz. Repeatability measurements demonstrated minimal variations corresponding to a system delay difference of 0.06 μs. Corrected UTE trajectory spokes are shifted approximately 1 m−1 compared to the nominal k‐space location. Corrected phantom and patient UTE images exhibited improved signal uniformity and contrast and reduced halo and signal loss artifacts. Trajectory correction for the later TE images did not improve overall image quality. Conclusion: The proposed GSTF measurement method using standard MR‐Linac hardware enables successful trajectory correction in UTE imaging reconstruction, with applications to lung synthetic CT generation for MR‐guided radiotherapy. [ABSTRACT FROM AUTHOR]
Copyright of Magnetic Resonance in Medicine is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Gradient system characterization of a 1.5 T MR‐Linac with application to 4D UTE imaging for adaptive MR‐guided radiotherapy of lung cancer.
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  Data: <searchLink fieldCode="AR" term="%22Goodburn%2C+Rosie%22">Goodburn, Rosie</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<i> rosie.goodburn@icr.ac.uk</i><br /><searchLink fieldCode="AR" term="%22Bruijnen%2C+Tom%22">Bruijnen, Tom</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Lecoeur%2C+Bastien%22">Lecoeur, Bastien</searchLink><relatesTo>1,4</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Nair%2C+Prashant%22">Nair, Prashant</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Ahmed%2C+Merina%22">Ahmed, Merina</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Barnes%2C+Helen%22">Barnes, Helen</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Oelfke%2C+Uwe%22">Oelfke, Uwe</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Wetscherek%2C+Andreas%22">Wetscherek, Andreas</searchLink><relatesTo>1</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Magnetic+Resonance+in+Medicine%22">Magnetic Resonance in Medicine</searchLink>. Jul2025, Vol. 94 Issue 1, p28-40. 13p.
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  Data: <searchLink fieldCode="DE" term="%22Image+reconstruction%22">Image reconstruction</searchLink><br /><searchLink fieldCode="DE" term="%22Lung+cancer%22">Lung cancer</searchLink><br /><searchLink fieldCode="DE" term="%22Transfer+functions%22">Transfer functions</searchLink><br /><searchLink fieldCode="DE" term="%22Cancer+patients%22">Cancer patients</searchLink><br /><searchLink fieldCode="DE" term="%22Cancer+radiotherapy%22">Cancer radiotherapy</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Purpose: To measure the gradient system transfer function (GSTF) of an MR‐Linac (Elekta Unity, Stockholm, Sweden) using an accessible phantom‐based method and to apply trajectory corrections for UTE image reconstruction in the context of MR‐guided radiotherapy of lung cancer. Methods: The first‐order GSTF of a 1.5 T, split gradient Elekta Unity MR‐Linac was measured using a thin‐slice technique to characterize gradient system imperfections for each physical gradient axis (X, Y, Z). Repeatability measurements of the GSTF were performed 48 h apart. The GSTF was applied to trajectory correction in multi‐echo UTE image reconstruction (TEs = 0.176, 1.85, 3.52 ms) to allow for UTE‐Dixon inputs in the generation of synthetic CT. Images were acquired in an anthropomorphic phantom and in two free‐breathing lung cancer patients. For patient scans, respiratory‐correlated 4D‐MR images were reconstructed using self‐navigation and an iterative compressed‐sensing algorithm. Results: The GSTF magnitude was similar across the X/Y/Z axes up to ˜6 kHz. The GSTF phase was similar between the X/Y/Z components up to ˜3 kHz. Repeatability measurements demonstrated minimal variations corresponding to a system delay difference of 0.06 μs. Corrected UTE trajectory spokes are shifted approximately 1 m−1 compared to the nominal k‐space location. Corrected phantom and patient UTE images exhibited improved signal uniformity and contrast and reduced halo and signal loss artifacts. Trajectory correction for the later TE images did not improve overall image quality. Conclusion: The proposed GSTF measurement method using standard MR‐Linac hardware enables successful trajectory correction in UTE imaging reconstruction, with applications to lung synthetic CT generation for MR‐guided radiotherapy. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Magnetic Resonance in Medicine is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Type: general
      – SubjectFull: Lung cancer
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      – SubjectFull: Transfer functions
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      – SubjectFull: Cancer patients
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      – SubjectFull: Cancer radiotherapy
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              M: 07
              Text: Jul2025
              Type: published
              Y: 2025
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