Highly Accelerated Real-Time Free-Breathing Cine CMR for Patients With a Cardiac Implantable Electronic Device

Cardiac Function Evaluation in Healthy Volunteers and Patients with Implantable Cardioverter-Defibrillators using High-Bandwidth Spoiled Gradient-Echo Cine

BACKGROUND

Implantable cardioverter-defibrillators (ICDs) cause banding artifacts around areas of B0 inhomogeneity in conventional steady-state free precession (SSFP) cine sequences. Alternatively, high-bandwidth gradient-echo (GRE) cine sequences can be used to minimize artifacts in the myocardium. In this study, we assessed the bias and interobserver variability in cardiac volumes and ejection fractions between GRE cines in acquired in the presence of ICDS and ground-truth SSFP cines (without ICDs present) in a population of healthy volunteers. Further, a small cohort of ICD patients were recruited and scanned to demonstrate clinical feasibility.

METHODS

High-bandwidth GRE cine was performed in eleven healthy volunteers with taped ICDs mimicking clinical implants. After the ICD was removed, ground-truth SSFP cine was performed. Two observers separately assessed image quality metrics and contoured the cine images to return cardiac volumes and ejection fractions. Nine patients with an ICD were also scanned with the GRE cine protocol before contrast administration; data was contoured by two observers and analyzed for interobserver agreement.

RESULTS

In the healthy volunteer dataset, no statistically significant differences were found when comparing volumes or ejection fractions between sequences (p > 0.05). Statistically significant differences were found when comparing RVEF (p = 0.009) and RVESV (p = 0.029) between observers, with no other significant interobserver differences. The interobserver variability of patient LVEF and RVEF data was 3-4%, with lower image quality metrics for patient scans than volunteer scans.

CONCLUSION

GRE cine imaging in healthy volunteers with taped ICDs demonstrated good agreement with SSFP cine, but increased interobserver variability. In patients, reducing the breath-hold duration caused a decrease in image quality, with GRE cine imaging in patients with ICDs demonstrating poorer image quality and greater interobserver variability than in healthy volunteer studies. Future work is needed to improve GRE cine image quality in patients with ICDs to reduce interobserver variability and improve clinical confidence.

Cumulative radiation dose from medical imaging in paediatric congenital heart disease patients with epicardial cardiac implantable electronic devices

Aims

To determine whether paediatric congenital heart disease (CHD) patients with epicardial cardiac implantable electronic devices (CIEDs) receive high cumulative effective doses (CEDs) of ionizing radiation from medical imaging tests.

Methods and results

We compared 28 paediatric CHD patients with epicardial CIEDs (cases) against 40 patients with no CIED matched by age at operation, sex, surgical era, and CHD diagnosis (controls). We performed a retrospective review of radiation exposure from medical imaging exams between 2006 and 2022. Radiation dose from computed tomography (CT) and X-ray radiography was calculated using the National Cancer Institute Radiation Dosimetry Tool. We performed univariate analysis to compare the CED between the two groups. In the case subgroup, we convened experts' review to adjudicate the prevalence of CT exams that should have been performed with magnetic resonance imaging (MRI) in the absence of a CIED. Children (median age 2.5 years at implant) with CIEDs received significantly higher median CED compared with matched controls (6.90 vs. 1.72 mSv, P = 0.0018). In cases, expert adjudication showed that 80% of the CT exams would have been performed with MRI in the absence of a CIED. This resulted, on average, a five-fold increase in the effective dose (ED) from post-lead implant CTs.

Conclusion

Paediatric CHD patients with CIED received four times higher CED than matched controls. Improved access to medical imaging tests without ionizing radiation, such as MRI, could potentially reduce the ED in CIED patients by up to five times.

Fast acquisition of left and right ventricular function parameters applying cardiovascular magnetic resonance in clinical routine - validation of a 2-shot compressed sensing cine sequence

Objectives. To evaluate if cine sequences accelerated by compressed sensing (CS) are feasible in clinical routine and yield equivalent cardiac morphology in less time. Design. We evaluated 155 consecutive patients with various cardiac diseases scanned during our clinical routine. LV and RV short axis (SAX) cine images were acquired by conventional and prototype 2-shot CS sequences on a 1.5 T CMR. The 2-shot prototype captures the entire heart over a period of 3 beats making the acquisition potentially even faster. Both scans were performed with identical slice parameters and positions. We compared LV and RV morphology with Bland-Altmann plots and weighted the results in relation to pre-defined tolerance intervals. Subjective and objective image quality was evaluated using a 4-point score and adapted standardized criteria. Scan times were evaluated for each sequence. Results. In total, no acquisitions were lost due to non-diagnostic image quality in the subjective image score. Objective image quality analysis showed no statistically significant differences. The scan time of the CS cines was significantly shorter (p < .001) with mean scan times of 178 ± 36 s compared to 313 ± 65 s for the conventional cine. All cardiac function parameters showed excellent correlation (r 0.978-0.996). Both sequences were considered equivalent for the assessment of LV and RV morphology. Conclusions. The 2-shot CS SAX cines can be used in clinical routine to acquire cardiac morphology in less time compared to the conventional method, with no total loss of acquisitions due to nondiagnostic quality.

TRIAL REGISTRATION

ISRCTN12344380. Registered 20 November 2020, retrospectively registered.

First experimental exploration of real-time cardiorespiratory motion management for future stereotactic arrhythmia radioablation treatments on the MR-linac

Objective.Stereotactic arrhythmia radioablation (STAR) is a novel, non-invasive treatment for refractory ventricular tachycardia (VT). The VT isthmus is subject to both respiratory and cardiac motion. Rapid cardiac motion presents a unique challenge. In this study, we provide first experimental evidence for real-time cardiorespiratory motion-mitigated MRI-guided STAR on the 1.5 T Unity MR-linac (Elekta AB, Stockholm, Sweden) aimed at simultaneously compensating cardiac and respiratory motions.Approach.A real-time cardiorespiratory motion-mitigated radiotherapy workflow was developed on the Unity MR-linac in research mode. A 15-beam intensity-modulated radiation therapy treatment plan (1 × 25 Gy) was created in Monaco v.5.40.01 (Elekta AB) for the Quasar MRI^4Dphantom (ModusQA, London, ON). A film dosimetry insert was moved by combining either artificial (cos⁴, 70 bpm, 10 mm peak-to-peak) or subject-derived (59 average bpm, 15.3 mm peak-to-peak) cardiac motion with respiratory (sin, 12 bpm, 20 mm peak-to-peak) motion. A balanced 2D cine MRI sequence (13 Hz, field-of-view = 400 × 207 mm², resolution = 3 × 3 × 15 mm³) was developed to estimate cardiorespiratory motion. Cardiorespiratory motion was estimated by rigid registration and then deconvoluted into cardiac and respiratory components. For beam gating, the cardiac component was used, whereas the respiratory component was used for MLC-tracking. In-silico dose accumulation experiments were performed on three patient data sets to simulate the dosimetric effect of cardiac motion on VT targets.Main results.Experimentally, a duty cycle of 57% was achieved when simultaneously applying respiratory MLC-tracking and cardiac gating. Using film, excellent agreement was observed compared to a static reference delivery, resulting in a 1%/1 mm gamma pass rate of 99%. The end-to-end gating latency was 126 ms on the Unity MR-linac. Simulations showed that cardiac motion decreased the target's D98% dose between 0.1 and 1.3 Gy, with gating providing effective mitigation.Significance.Real-time MRI-guided cardiorespiratory motion management greatly reduces motion-induced dosimetric uncertainty and warrants further research and development for potential future use in STAR.

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

Background and Purpose

Materials and methods

Results

Conclusions