Susceptibility‐based positive contrast MRI of brachytherapy seeds

Dong, Ying; Chang, Zheng; Xie, Guoxi; Whitehead, Gregory; Ji, Jim

doi:10.1002/mrm.25453

Cited by 29 publications

(44 citation statements)

References 31 publications

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“…37 Other means of improving the detection accuracy of GFM could be by magnetic susceptibility mapping or by providing positive contrast in the vicinity of the marker using off-resonance signals. [29][30][31][32]47 As MEGRE is a generic and available sequence on multiple vendor platforms this should be further explored for both automatic and manual GFM identification.…”

Section: Discussionmentioning

confidence: 99%

“…27,28 The use of more exotic sequences to even enable a positive contrast of the metal has been developed. [29][30][31][32] The use of multiple dedicated MRI sequences for prostate RTP is common. The proposed MRI only workflows for EBRT of prostate present in the literature all depend on separate MRI sequences for GFM identification, target delineation, and sCT generation.…”

Section: Introductionmentioning

confidence: 99%

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Registration free automatic identification of gold fiducial markers in MRI target delineation images for prostate radiotherapy

et al. 2017

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Purpose: The superior soft tissue contrast of magnetic resonance imaging (MRI) compared to computed tomography (CT) has urged the integration of MRI and elimination of CT in radiotherapy treatment (RT) for prostate. An intraprostatic gold fiducial marker (GFM) appears hyperintense on CT. On T2-weighted (T2w) MRI target delineation images, the GFM appear as a small signal void similar to calcifications and post biopsy fibrosis. It can therefore be difficult to identify the markers without CT. Detectability of GFMs can be improved using additional MR images, which are manually registered to target delineation images. This task requires manual labor, and is associated with interoperator differences and image registration errors. The aim of this work was to develop and evaluate an automatic method for identification of GFMs directly in the target delineation images without the need for image registration. Methods: T2w images, intended for target delineation, and multiecho gradient echo (MEGRE) images intended for GFM identification, were acquired for prostate cancer patients. Signal voids in the target delineation images were identified as GFM candidates. The GFM appeared as round, symmetric, signal void with increasing area for increasing echo time in the MEGRE images. These image features were exploited for automatic identification of GFMs in a MATLAB model using a patient training dataset (n = 20). The model was validated on an independent patient dataset (n = 40). The distances between the identified GFM in the target delineation images and the GFM in CT images were measured. A human observatory study was conducted to validate the use of MEGRE images. Results: The sensitivity, specificity, and accuracy of the automatic method and the observatory study was 84%, 74%, 81% and 98%, 94%, 97%, respectively. The mean absolute difference in the GFM distances for the automatic method and observatory study was 1.28 AE 1.25 mm and 1.14 AE 1.06 mm, respectively. Conclusions: Multiecho gradient echo images were shown to be a feasible and reliable way to perform GFM identification. For clinical practice, visual inspection of the results from the automatic method is needed at the current stage.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Registration free automatic identification of gold fiducial markers in MRI target delineation images for prostate radiotherapy

et al. 2017

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“…The co‐RASOR (center‐out radial sampling with off‐resonance reception) method was proposed to shift local signal pile‐ups caused by off‐resonance back to the center of the brachytherapy seed in radial acquisitions . Dong et al applied susceptibility gradient mapping to specifically use the local dephasing around brachytherapy seeds to generate positive contrast at the location of the seed . Since these two approaches are based on local susceptibility effects, they are less sensitive to other field inhomogeneities.…”

Section: Introductionmentioning

confidence: 99%

Challenges in MR‐only seed localization for postimplant dosimetry in permanent prostate brachytherapy

et al. 2017

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Purpose: An MR-only postimplant dosimetry workflow for low dose rate (LDR) brachytherapy could reduce patient burden, improve accuracy, and improve cost efficiency. However, localization of brachytherapy seeds on MRI scans remains a major challenge for this type of workflow. In this study, we propose and validate an MR-only seed localization method and identify remaining challenges. Methods and materials: The localization method was based on template matching of simulations of complex-valued imaging artifacts around metal brachytherapy seeds. The method was applied to MRI scans of 25 prostate cancer patients who underwent LDR brachytherapy and for whom postimplant dosimetry was performed after 4 weeks. The seed locations found with the MR-only method were validated against the seed locations found on CT. The circumstances in which detection errors were made were classified to gain an insight in the nature of the errors. Results: A total of 1490 of 1557 (96%) seeds were correctly detected, while 67 false-positive errors were made. The correctly detected seed locations had a high spatial accuracy with an average error of 0.8 mm compared with CT. A majority of the false positives occurred near other seeds. Most false negatives were found in either stranded configurations without spacers or near other seeds. Conclusions: The low detection error rate and high localization accuracy obtained by the complexvalued template matching approach are promising for future clinical application of MR-only dosimetry. The most important remaining challenge is robustness with regard to configurations of multiple seeds in close vicinity, such as in strands of seeds without spacers. This issue could potentially be resolved by simulating specific configurations of multiple seeds or by constraining the treatment planning to avoid these configurations, which could make the proposed method competitive with CTbased seed localization.

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“…By taking advantage of the seeds' high magnetic susceptibility, recent efforts in seed visualization on MRI images include the use of an inversion-recovery with ONresonant water suppression (IRON) prepulse to spectrally select off-resonant protons, 20 the use of ultrashort-TE sequences to preserve signal before rapid transverse dephasing, 21 the postprocessing use of homodyne high-pass filters of various sizes, 22,23 the use of susceptibility gradient mapping using the original resolution (SUMO) by filtering in k-space, 24 the use of a kernel deconvolution algorithm with regularized L 1 minimization 25 (the dipole kernel 26 and a nominal seed kernel 27 have been explored), as well as the use of centerout radial sampling with off-resonance reception (co-RASOR) that moves the radial signal pile-up to the seed's center (using multiple acquisitions 28 and only a single acquisition 29 ). However, imaging susceptibility may be inconsistent across MRI slices, difficult to locate accurately, and more challenging in heterogeneous tissue.…”

mentioning

confidence: 99%

“…23 Ultimately, MRI-only postimplant dosimetry allows for superior soft tissue contouring, no extraneous radiation dose, image-acquisition flexibility, and possible integration of functional imaging. Regardless of whether MRI-only postimplant dosimetry is achieved using markers 6 or the other solutions [18][19][20][21][22][23][24][25][26][27][28][29] described above, the next step is to explore the impact of MRI soft tissue contrast on the accuracy and precision of anatomical contouring on patient images, so as to examine the correlation of dose deposited in the prostate and normal tissue to tumor control and normal tissue complications. Ultimately, in future patient studies comparing MRI-only to MRI-CT fusion-based postimplant dosimetry, we need to evaluate the improvements in the accuracy and precision of contouring prostate and organs at risk, the accuracy and precision of seed localization, as well as the subsequent accuracy and precision of dose volume histogram parameters, apart from accounting from fusion uncertainties.…”

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confidence: 99%

Effect of pulse sequence parameter selection on signal strength in positive‐contrast MRI markers for MRI‐based prostate postimplant assessment

et al. 2016

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Purpose: For postimplant dosimetric assessment, computed tomography (CT) is commonly used to identify prostate brachytherapy seeds, at the expense of accurate anatomical contouring. Magnetic resonance imaging (MRI) is superior to CT for anatomical delineation, but identification of the negative-contrast seeds is challenging. Positive-contrast MRI markers were proposed to replace spacers to assist seed localization on MRI images. Visualization of these markers under varying scan parameters was investigated. Methods: To simulate a clinical scenario, a prostate phantom was implanted with 66 markers and 86 seeds, and imaged on a 3.0T MRI scanner using a 3D fast radiofrequency-spoiled gradient recalled echo acquisition with various combinations of scan parameters. Scan parameters, including flip angle, number of excitations, bandwidth, field-of-view, slice thickness, and encoding steps were systematically varied to study their effects on signal, noise, scan time, image resolution, and artifacts. Results: The effects of pulse sequence parameter selection on the marker signal strength and image noise were characterized. The authors also examined the tradeoff between signal-to-noise ratio, scan time, and image artifacts, such as the wraparound artifact, susceptibility artifact, chemical shift artifact, and partial volume averaging artifact. Given reasonable scan time and managable artifacts, the authors recommended scan parameter combinations that can provide robust visualization of the MRI markers. Conclusions: The recommended MRI pulse sequence protocol allows for consistent visualization of the markers to assist seed localization, potentially enabling MRI-only prostate postimplant dosimetry.

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Susceptibility‐based positive contrast MRI of brachytherapy seeds

Abstract: The results show that the proposed method provides positive contrast for the seeds and correctly differentiates them from other structures that appear similar to the seeds on conventional magnitude images.

Cited by 29 publications

References 31 publications

Registration free automatic identification of gold fiducial markers in MRI target delineation images for prostate radiotherapy

Registration free automatic identification of gold fiducial markers in MRI target delineation images for prostate radiotherapy

Challenges in MR‐only seed localization for postimplant dosimetry in permanent prostate brachytherapy

Effect of pulse sequence parameter selection on signal strength in positive‐contrast MRI markers for MRI‐based prostate postimplant assessment

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