Feasibility of cardiac-synchronized quantitative T1 and T2 mapping on a hybrid 1.5 Tesla magnetic resonance imaging and linear accelerator system

Akdag, Osman; Mandija, Stefano; Lier, Astrid L.H.M.W. van; Borman, P.; Schäkel, T.; Alberts, Eveline; Heide, Oscar van der; Hassink, Rutger J.; Verhoeff, Joost J.C.; Hoesein, Firdaus A. A. Mohamed; Raaymakers, B W; Fast, Martin F.

doi:10.1016/j.phro.2022.02.017

Cited by 6 publications

(7 citation statements)

References 38 publications

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“…For each volunteer, 2D single‐slice cine MR images were acquired using the bSSFP imaging sequence (TR/TE = 3/1.48 ms, flip angle = 48

^{\cdot }

, SENSE = 1.5, field‐of‐view = 400

\times

207

{\rm mm}^{2}

, voxel size = 3

\times 3

\times

{\rm mm}^{3}

, partial Fourier factor = 0.65, frame rate = 13.3 Hz). The ECG‐signal was recorded during each image acquisition using the Philips MRI 4‐lead ECG device 35 . Three cine MRI acquisitions were performed per volunteer.…”

Section: Methodsmentioning

confidence: 99%

“…The ECG-signal was recorded during each image acquisition using the Philips MRI 4-lead ECG device. 35 Three cine MRI acquisitions were performed per volunteer. Cine acquisitions of 1000 frames (acquisition time (TA): 1:24 min) were performed in the coronal and sagittal plane.…”

Section: Study Group and Data Acquisitionmentioning

confidence: 99%

“…33,34 Cardiacsynchronized MRI was recently enabled in research mode on the 1.5 T Unity MR-linac (Elekta AB, Stockholm, Sweden) after installing the clinical Philips MRI ECG equipment (Philips Healthcare, Best, The Netherlands). 35 In this study, our aim was to investigate the feasibility of cardiac motion mitigation during dose delivery based on an ECG-signal as a cardiac motion surrogate. A prototype adaptive dose delivery workflow was developed in which the installed ECG-equipment was used to gate the radiation beam in the quiescent period of the cardiac cycle in real-time.…”

Section: Introductionmentioning

confidence: 99%

“…The dosimetric results were improved with respect to an ungated dose delivery and the radiation beam characteristics remained stable 33,34 . Cardiac‐synchronized MRI was recently enabled in research mode on the 1.5 T Unity MR‐linac (Elekta AB, Stockholm, Sweden) after installing the clinical Philips MRI ECG equipment (Philips Healthcare, Best, The Netherlands) 35 …”

Section: Introductionmentioning

confidence: 99%

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Experimental demonstration of real‐time cardiac physiology‐based radiotherapy gating for improved cardiac radioablation on an MR‐linac

Akdag,

Borman,

Mandija

et al. 2024

Medical Physics

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BackgroundCardiac radioablation is a noninvasive stereotactic body radiation therapy (SBRT) technique to treat patients with refractory ventricular tachycardia (VT) by delivering a single high‐dose fraction to the VT isthmus. Cardiorespiratory motion induces position uncertainties resulting in decreased dose conformality. Electocardiograms (ECG) are typically used during cardiac MRI (CMR) to acquire images in a predefined cardiac phase, thus mitigating cardiac motion during image acquisition.PurposeWe demonstrate real‐time cardiac physiology‐based radiotherapy beam gating within a preset cardiac phase on an MR‐linac.MethodsMR images were acquired in healthy volunteers (n = 5, mean age = 29.6 years, mean heart‐rate (HR) = 56.2 bpm) on the 1.5 T Unity MR‐linac (Elekta AB, Stockholm, Sweden) after obtaining written informed consent. The images were acquired using a single‐slice balance steady‐state free precession (bSSFP) sequence in the coronal or sagittal plane (TR/TE = 3/1.48 ms, flip angle = 48, SENSE = 1.5, , voxel size = , partial Fourier factor = 0.65, frame rate = 13.3 Hz). In parallel, a 4‐lead ECG‐signal was acquired using MR‐compatible equipment. The feasibility of ECG‐based beam gating was demonstrated with a prototype gating workflow using a Quasar MRI4D motion phantom (IBA Quasar, London, ON, Canada), which was deployed in the bore of the MR‐linac. Two volunteer‐derived combined ECG‐motion traces (n = 2, mean age = 26 years, mean HR = 57.4 bpm, peak‐to‐peak amplitude = 14.7 mm) were programmed into the phantom to mimic dose delivery on a cardiac target in breath‐hold. Clinical ECG‐equipment was connected to the phantom for ECG‐voltage‐streaming in real‐time using research software. Treatment beam gating was performed in the quiescent phase (end‐diastole). System latencies were compensated by delay time correction. A previously developed MRI‐based gating workflow was used as a benchmark in this study. A 15‐beam intensity‐modulated radiotherapy (IMRT) plan ( Gy) was delivered for different motion scenarios onto radiochromic films. Next, cardiac motion was then estimated at the basal anterolateral myocardial wall via normalized cross‐correlation‐based template matching. The estimated motion signal was temporally aligned with the ECG‐signal, which were then used for position‐ and ECG‐based gating simulations in the cranial–caudal (CC), anterior–posterior (AP), and right–left (RL) directions. The effect of gating was investigated by analyzing the differences in residual motion at 30, 50, and 70% treatment beam duty cycles.ResultsECG‐based (MRI‐based) beam gating was performed with effective duty cycles of 60.5% (68.8%) and 47.7% (50.4%) with residual motion reductions of 62.5% (44.7%) and 43.9% (59.3%). Local gamma analyses (1%/1 mm) returned pass rates of 97.6% (94.1%) and 90.5% (98.3%) for gated scenarios, which exceed the pass rates of 70.3% and 82.0% for nongated scenarios, respectively. In average, the gating simulations returned maximum residual motion reductions of 88%, 74%, and 81% at 30%, 50%, and 70% duty cycles, respectively, in favor of MRI‐based gating.ConclusionsReal‐time ECG‐based beam gating is a feasible alternative to MRI‐based gating, resulting in improved dose delivery in terms of high rates, decreased dose deposition outside the PTV and residual motion reduction, while by‐passing cardiac MRI challenges.

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“…For each volunteer, 2D single‐slice cine MR images were acquired using the bSSFP imaging sequence (TR/TE = 3/1.48 ms, flip angle = 48

^{\cdot }

, SENSE = 1.5, field‐of‐view = 400

\times

207

{\rm mm}^{2}

, voxel size = 3

\times 3

\times

{\rm mm}^{3}

Section: Methodsmentioning

confidence: 99%

Section: Study Group and Data Acquisitionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Experimental demonstration of real‐time cardiac physiology‐based radiotherapy gating for improved cardiac radioablation on an MR‐linac

Akdag,

Borman,

Mandija

et al. 2024

Medical Physics

Self Cite

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show abstract

“…This tip is observable on CT images and acts as a surrogate of the motion of the non-visible target tissue (Knybel et al 2021, Dvorak et al 2022. From an imaging perspective, the superior soft-tissue contrast of MR systems compared to CT systems makes hybrid MR-linac systems another good candidate for STAR treatments, as they can allow accurate visualization of the target tissue (Puntmann et al 2016, Akdag et al 2022b, and thereby fulfil the first requirement posed above. A first case study already demonstrated that MR imaging highly improved the accuracy of the target definition, allowing beam-gating for treatment guidance and delivery (Mayinger et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Real-time myocardial landmark tracking for MRI-guided cardiac radio-ablation using Gaussian Processes

et al. 2023

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The high speed of cardiorespiratory motion introduces a unique challenge for cardiac stereotactic radio-ablation (STAR) treatments with the MR-linac. Such treatments require tracking myocardial landmarks with a maximum latency of 100 ms, which includes the acquisition of the required data. The aim of this study is to present a new method that enables tracking myocardial landmarks from few readouts of MRI data, thereby achieving a latency sufficient for STAR treatments. We present a tracking framework that requires few readouts of k-space data as input, which can be acquired at least an order of magnitude faster than MR-images. Combined with the real-time tracking speed of a probabilistic machine learning framework called Gaussian Processes, this allows to track myocardial landmarks with a sufficiently low latency for cardiac STAR guidance. This includes both the acquisition of required data, and the tracking inference. The framework is demonstrated in 2D on a motion phantom, and in vivo on volunteers and a ventricular tachycardia (arrhythmia) patient. Moreover, the feasibility of an extension to 3D was demonstrated by in silico 3D experiments with a digital motion phantom. The framework was compared with template matching - a reference, image-based, method - and linear regression methods. Results indicate an order of magnitude lower total latency (<10 ms) for the proposed framework in comparison with alternative methods. The root-mean-square-distances and mean end-point-distance with the reference tracking method was less than 0.8 mm for all experiments, showing excellent (sub-voxel) agreement. The high accuracy in combination with a total latency of less than 10 ms – including data acquisition and processing - make the proposed method a suitable candidate for tracking during STAR treatments. Additionally, the probabilistic nature of the Gaussian Processes also gives access to real-time prediction uncertainties, which could prove useful for real-time quality assurance during treatments.

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Evaluation of the impact of cardiac implantable electronic devices on cine MRI for real‐time adaptive cardiac radioablation on a 1.5 T MR‐linac

Akdag,

Mandija,

Borman

et al. 2024

Medical Physics

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BackgroundStereotactic arrhythmia radioablation (STAR) is a novel treatment approach for refractory ventricular tachycardia (VT). The risk of treatment‐induced toxicity and geographic miss can be reduced with online MRI‐guidance on an MR‐linac. However, most VT patients carry cardiac implantable electronic devices (CIED), which compromise MR images.PurposeRobust MR‐linac imaging sequences are required for cardiac visualization and accurate motion monitoring in presence of a CIED during MRI‐guided STAR. We optimized two clinically available cine sequences for cardiorespiratory motion estimation in presence of a CIED on a 1.5 T MR‐linac. The image quality, motion estimation accuracy, and geometric fidelity using these cine sequences were evaluated.MethodsClinically available 2D balanced steady‐state free precession (bSSFP, voxel size = 3.0 3.0 10 mm3, Tscan = 96 ms, bandwidth (BW) = 1884 Hz/px) and ‐spoiled gradient echo (‐GRE, voxel size = 4.0 4.0 10 mm3, Tscan = 97 ms, BW = 500 Hz/px) sequences were adjusted for real‐time cardiac visualization and cardiorespiratory motion estimation on a 1.5 T Unity MR‐linac (Elekta AB, Stockholm, Sweden), while complying with safety guidelines for MRI in presence of CIEDs (specific absorption rate 2 W/kg and 80 mT/s). Cine acquisitions were performed in five healthy volunteers, with and without an implantable cardioverter– defibrillator (ICD) placed on the clavicle, and a VT patient. Generalized divergence‐curl (GDC) deformable image registration (DIR) was used for automated landmark motion estimation in the left ventricle (LV). Gaussian processes (GP), a machine‐learning technique, was trained using GDC landmarks and deployed for real‐time cardiorespiratory motion prediction. ‐mapping was performed to assess geometric image fidelity in the presence of CIEDs.ResultsCIEDs introduced banding artifacts partially obscuring cardiac structures in bSSFP acquisitions. In contrast, the ‐GRE was more robust to CIED‐induced artifacts at the expense of a lower signal‐to‐noise ratio. In presence of an ICD, image‐based cardiorespiratory motion estimation was possible for 85% (100%) of the volunteers using the bSSFP (‐GRE) sequence. The in‐plane 2D root‐mean‐squared deviation (RMSD) range between GDC‐derived landmarks and manual annotations using the bSSFP (T1‐GRE) sequence was 3.1–3.3 (3.3–4.1) mm without ICD and 4.6–4.6 (3.2–3.3) mm with ICD. Without ICD, the RMSD between the GP‐predictions and GDC‐derived landmarks ranged between 0.9 and 2.2 mm (1.3–3.0 mm) for the bSSFP (T1‐GRE) sequence. With ICD, the RMSD between the GP‐predictions and GDC‐derived landmarks ranged between 1.3 and 2.2 mm (1.2–3.2 mm) using the bSSFP (T1‐GRE) sequence resulting in an RMSD‐increase of 42%–143% (bSSFP) and −61%–142% (T1‐GRE). Lead‐induced spatial distortions ranged between −0.2 and 0.2 mm (−0.7–1.2 mm) using the bSSFP (‐GRE) sequence. The 98th percentile range of the spatial distortions in the gross target volume of the patient was between 0.0 and 0.4 mm (0.0–1.8 mm) when using bSSFP (‐GRE).ConclusionsTailored bSSFP and ‐GRE sequences can facilitate real‐time cardiorespiratory estimation using GP trained with GDC‐derived landmarks in the majority of landmark locations in the LV despite the presence of CIEDs. The need for high temporal resolution noticeably reduced achievable spatial resolution of the cine MRIs. However, the effect of the CIED‐induced artifacts is device, patient and sequence dependent and requires specific assessment per case.

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Feasibility of cardiac-synchronized quantitative T1 and T2 mapping on a hybrid 1.5 Tesla magnetic resonance imaging and linear accelerator system

Cited by 6 publications

References 38 publications

Experimental demonstration of real‐time cardiac physiology‐based radiotherapy gating for improved cardiac radioablation on an MR‐linac

Experimental demonstration of real‐time cardiac physiology‐based radiotherapy gating for improved cardiac radioablation on an MR‐linac

Real-time myocardial landmark tracking for MRI-guided cardiac radio-ablation using Gaussian Processes

Evaluation of the impact of cardiac implantable electronic devices on cine MRI for real‐time adaptive cardiac radioablation on a 1.5 T MR‐linac

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