Ventricular Intramyocardial Navigation for Tachycardia Ablation Guided by Electrograms (VINTAGE): Deep Ablation in Inaccessible Targets.

BACKGROUND: Deep intramural ventricular tachycardia substrate targets are difficult to access, map, and ablate from endocardial and epicardial surfaces, resulting in high recurrence rates. OBJECTIVES: In this study, the authors introduce a novel approach called ventricular intramyocardial navigation for tachycardia ablation guided by electrograms (VINTAGE) to access and ablate anatomically challenging ventricular tachycardia from within the myocardium. METHODS: Guidewire/microcatheter combinations were navigated deep throughout the extravascular myocardium, accessed directly from the right ventricle cavity, in Yorkshire swine (6 naive, 1 infarcted). Devices were steered to various intramyocardial targets including the left ventricle summit, guided by fluoroscopy, unipolar electrograms, and/or electroanatomic mapping. Radiofrequency ablations were performed to characterize ablation parameters and reproducibility. Intramyocardial saline irrigation began 1 minute before ablation and continued throughout. Lesions were analyzed on cardiac magnetic resonance and necropsy. RESULTS: VINTAGE was feasible in all animals within naive and infarcted myocardium. Forty-three lesions were created, using various guidewires and power settings. Forty-one (95%) lesions were detected on cardiac magnetic resonance and 38 (88%) on necropsy; all undetected lesions resulted from intentionally subtherapeutic ablation energy (10 W). Larger-diameter guidewires yielded larger size lesions. Lesion volumes on necropsy were significantly larger at 20 W than 10 W (178 mm3 [Q1-Q3: 104-382 mm3] vs 49 mm3 [Q1-Q3: 35-93 mm3]; P = 0.02). Higher power (30 W) did not create larger lesions. Median impedance dropped with preablation irrigation by 12 Ω (Q1-Q3: 8-17 Ω), followed by a further 15-Ω (Q1-Q3: 11-19 Ω) drop during ablation. Intramyocardial navigation, ablation, and irrigation were not associated with any complications. CONCLUSIONS: VINTAGE was safe and effective at creating intramural ablation lesions in targets traditionally considered inaccessible from the endocardium and epicardium, both naive and infarcted. Intramyocardial guidewire irrigation and ablation at 20 W creates reproducibly large intramural lesions.

Reshaping the Ventricle From Within: MIRTH (Myocardial Intramural Remodeling by Transvenous Tether) Ventriculoplasty in Swine.

MIRTH (Myocardial Intramural Remodeling by Transvenous Tether) is a transcatheter ventricular remodeling procedure. A transvenous tension element is placed within the walls of the beating left ventricle and shortened to narrow chamber dimensions. MIRTH uses 2 new techniques: controlled intramyocardial guidewire navigation and EDEN (Electrocardiographic Radial Depth Navigation). MIRTH caused a sustained reduction in chamber dimensions in healthy swine. Midventricular implants approximated papillary muscles. MIRTH shortening improved myocardial contractility in cardiomyopathy in a dose-dependent manner up to a threshold beyond which additional shortening reduced performance. MIRTH may help treat dilated cardiomyopathy. Clinical investigation is warranted.

Impact of Vasodilation on Oxygen-Enhanced Functional Lung MRI at 0.55 T.

BACKGROUND: Oxygen-enhanced magnetic resonance imaging (OE-MRI) can be used to assess regional lung function without ionizing radiation. Inhaled oxygen acts as a T1-shortening contrast agent to increase signal in T1-weighted (T1w) images. However, increase in proton density from pulmonary hyperoxic vasodilation may also contribute to the measured signal enhancement. Our aim was to quantify the relative contributions of the T1-shortening and vasodilatory effects of oxygen to signal enhancement in OE-MRI in both swine and healthy volunteers. METHODS: We imaged 14 anesthetized female swine (47 ± 8 kg) using a prototype 0.55 T high-performance MRI system while experimentally manipulating oxygenation and blood volume independently through oxygen titration, partial occlusion of the vena cava for volume reduction, and infusion of colloid fluid (6% hydroxyethyl starch) for volume increase. Ten healthy volunteers were imaged before, during, and after hyperoxia. Two proton density-weighted (PDw) and 2 T1w ultrashort echo time images were acquired per experimental state. The median PDw and T1w percent signal enhancement (PSE), compared with baseline room air, was calculated after image registration and correction for lung volume changes. Differences in median PSE were compared using Wilcoxon signed rank test. RESULTS: The PSE in PDw images after 100% oxygen was similar in swine (1.66% ± 1.41%, P = 0.01) and in healthy volunteers (1.99% ± 1.79%, P = 0.02), indicating that oxygen-induced pulmonary vasodilation causes ~2% lung proton density increase. The PSE in T1w images after 100% oxygen was also similar (swine, 9.20% ± 1.68%, P < 0.001; healthy volunteers, 10.10% ± 3.05%, P < 0.001). The PSE in T1w enhancement was oxygen dose-dependent in anesthetized swine, and we measured a dose-dependent PDw image signal increase from infused fluids. CONCLUSIONS: The contribution of oxygen-induced vasodilation to T1w OE-MRI signal was measurable using PDw imaging and was found to be ~2% in both anesthetized swine and in healthy volunteers. This finding may have implications for patients with regional or global hypoxia or vascular dysfunction undergoing OE-MRI and suggest that PDw imaging may be useful to account for oxygen-induced vasodilation in OE-MRI.

Dynamic pressure-volume loop analysis by simultaneous real-time cardiovascular magnetic resonance and left heart catheterization.

BACKGROUND: Left ventricular (LV) contractility and compliance are derived from pressure-volume (PV) loops during dynamic preload reduction, but reliable simultaneous measurements of pressure and volume are challenging with current technologies. We have developed a method to quantify contractility and compliance from PV loops during a dynamic preload reduction using simultaneous measurements of volume from real-time cardiovascular magnetic resonance (CMR) and invasive LV pressures with CMR-specific signal conditioning. METHODS: Dynamic PV loops were derived in 16 swine (n = 7 naïve, n = 6 with aortic banding to increase afterload, n = 3 with ischemic cardiomyopathy) while occluding the inferior vena cava (IVC). Occlusion was performed simultaneously with the acquisition of dynamic LV volume from long-axis real-time CMR at 0.55 T, and recordings of invasive LV and aortic pressures, electrocardiogram, and CMR gradient waveforms. PV loops were derived by synchronizing pressure and volume measurements. Linear regression of end-systolic- and end-diastolic- pressure-volume relationships enabled calculation of contractility. PV loops measurements in the CMR environment were compared to conductance PV loop catheter measurements in 5 animals. Long-axis 2D LV volumes were validated with short-axis-stack images. RESULTS: Simultaneous PV acquisition during IVC-occlusion was feasible. The cardiomyopathy model measured lower contractility (0.2 ± 0.1 mmHg/ml vs 0.6 ± 0.2 mmHg/ml) and increased compliance (12.0 ± 2.1 ml/mmHg vs 4.9 ± 1.1 ml/mmHg) compared to naïve animals. The pressure gradient across the aortic band was not clinically significant (10 ± 6 mmHg). Correspondingly, no differences were found between the naïve and banded pigs. Long-axis and short-axis LV volumes agreed well (difference 8.2 ± 14.5 ml at end-diastole, -2.8 ± 6.5 ml at end-systole). Agreement in contractility and compliance derived from conductance PV loop catheters and in the CMR environment was modest (intraclass correlation coefficient 0.56 and 0.44, respectively). CONCLUSIONS: Dynamic PV loops during a real-time CMR-guided preload reduction can be used to derive quantitative metrics of contractility and compliance, and provided more reliable volumetric measurements than conductance PV loop catheters.

Imaging gravity-induced lung water redistribution with automated inline processing at 0.55 T cardiovascular magnetic resonance.

BACKGROUND: Quantitative assessment of dynamic lung water accumulation is of interest to unmask latent heart failure. We develop and validate a free-breathing 3D ultrashort echo time (UTE) sequence with automated inline image processing to image changes in lung water density (LWD) using high-performance 0.55 T cardiovascular magnetic resonance (CMR). METHODS: Quantitative lung water CMR was performed on 15 healthy subjects using free-breathing 3D stack-of-spirals proton density weighted UTE at 0.55 T. Inline image reconstruction and automated image processing was performed using the Gadgetron framework. A gravity-induced redistribution of LWD was provoked by sequentially acquiring images in the supine, prone, and again supine position. Quantitative validation was performed in a phantom array of vials containing mixtures of water and deuterium oxide. RESULTS: The phantom experiment validated the capability of the sequence in quantifying water density (bias ± SD 4.3 ± 4.8%, intraclass correlation coefficient, ICC = 0.97). The average global LWD was comparable between imaging positions (supine 24.7 ± 3.4%, prone 22.7 ± 3.1%, second supine 25.3 ± 3.6%), with small differences between imaging phases (first supine vs prone 2.0%, p < 0.001; first supine vs second supine - 0.6%, p = 0.001; prone vs second supine - 2.7%, p < 0.001). In vivo test-retest repeatability in LWD was excellent (- 0.17 ± 0.91%, ICC = 0.97). A regional LWD redistribution was observed in all subjects when repositioning, with a predominant posterior LWD accumulation when supine, and anterior accumulation when prone (difference in anterior-posterior LWD: supine - 11.6 ± 2.7%, prone 5.5 ± 2.7%, second supine - 11.4 ± 2.9%). Global LWD maps were calculated inline within 23.2 ± 0.3 s following the image reconstruction using the automated pipeline. CONCLUSIONS: Redistribution of LWD due to gravitational forces can be depicted and quantified using a validated free-breathing 3D proton density weighted UTE sequence and inline automated image processing pipeline on a high-performance 0.55 T CMR system.

Self-gated 3D stack-of-spirals UTE pulmonary imaging at 0.55T.

PURPOSE: To develop an isotropic high-resolution stack-of-spirals UTE sequence for pulmonary imaging at 0.55 Tesla by leveraging a combination of robust respiratory-binning, trajectory correction, and concomitant-field corrections. METHODS: A stack-of-spirals golden-angle UTE sequence was used to continuously acquire data for 15.5 minutes. The data was binned to a stable respiratory phase based on superoinferior readout self-navigator signals. Corrections for trajectory errors and concomitant field artifacts, along with image reconstruction with conjugate gradient SENSE, were performed inline within the Gadgetron framework. Finally, data were retrospectively reconstructed to simulate scan times of 5, 8.5, and 12 minutes. Image quality was assessed using signal-to-noise, image sharpness, and qualitative reader scores. The technique was evaluated in healthy volunteers, patients with coronavirus disease 2019 infection, and patients with lung nodules. RESULTS: The technique provided diagnostic quality images with parenchymal lung SNR of 3.18 ± 0.0.60, 4.57 ± 0.87, 5.45 ± 1.02, and 5.89 ± 1.28 for scan times of 5, 8.5, 12, and 15.5 minutes, respectively. The respiratory binning technique resulted in significantly sharper images (p < 0.001) as measured with relative maximum derivative at the diaphragm. Concomitant field corrections visibly improved sharpness of anatomical structures away from iso-center. The image quality was maintained with a slight loss in SNR for simulated scan times down to 8.5 minutes. Inline image reconstruction and artifact correction were achieved in <5 minutes. CONCLUSION: The proposed pulmonary imaging technique combined efficient stack-of-spirals imaging with robust respiratory binning, concomitant field correction, and trajectory correction to generate diagnostic quality images with 1.75 mm isotropic resolution in 8.5 minutes on a high-performance 0.55 Tesla system.

Native contrast visualization and tissue characterization of myocardial radiofrequency ablation and acetic acid chemoablation lesions at 0.55 T.

PURPOSE: Low-field (0.55 T) high-performance cardiovascular magnetic resonance (CMR) is an attractive platform for CMR-guided intervention as device heating is reduced around 7.5-fold compared to 1.5 T. This work determines the feasibility of visualizing cardiac radiofrequency (RF) ablation lesions at low field CMR and explores a novel alternative method for targeted tissue destruction: acetic acid chemoablation. METHODS: N = 10 swine underwent X-ray fluoroscopy-guided RF ablation (6-7 lesions) and acetic acid chemoablation (2-3 lesions) of the left ventricle. Animals were imaged at 0.55 T with native contrast 3D-navigator gated T1-weighted T1w) CMR for lesion visualization, gated single-shot imaging to determine potential for real-time visualization of lesion formation, and T1 mapping to measure change in T1 in response to ablation. Seven animals were euthanized on ablation day and hearts imaged ex vivo. The remaining animals were imaged again in vivo at 21 days post ablation to observe lesion evolution. RESULTS: Chemoablation lesions could be visualized and displayed much higher contrast than necrotic RF ablation lesions with T1w imaging. On the day of ablation, in vivo myocardial T1 dropped by 19 ± 7% in RF ablation lesion cores, and by 40 ± 7% in chemoablation lesion cores (p < 4e-5). In high resolution ex vivo imaging, with reduced partial volume effects, lesion core T1 dropped by 18 ± 3% and 42 ± 6% for RF and chemoablation, respectively. Mean, median, and peak lesion signal-to-noise ratio (SNR) were all at least 75% higher with chemoablation. Lesion core to myocardium contrast-to-noise (CNR) was 3.8 × higher for chemoablation. Correlation between in vivo and ex vivo CMR and histology indicated that the periphery of RF ablation lesions do not exhibit changes in T1 while the entire extent of chemoablation exhibits T1 changes. Correlation of T1w enhancing lesion volumes indicated in vivo estimates of lesion volume are accurate for chemoablation but underestimate extent of necrosis for RF ablation. CONCLUSION: The visualization of coagulation necrosis from cardiac ablation is feasible using low-field high-performance CMR. Chemoablation produced a more pronounced change in lesion T1 than RF ablation, increasing SNR and CNR and thereby making it easier to visualize in both 3D navigator-gated and real-time CMR and more suitable for low-field imaging.

A 20-gauge active needle design with thin-film printed circuitry for interventional MRI at 0.55T.

PURPOSE: This work aims to fabricate RF antenna components on metallic needle surfaces using biocompatible polyester tubing and conductive ink to develop an active interventional MRI needle for clinical use at 0.55 Tesla. METHODS: A custom computer numeric control-based conductive ink printing method was developed. Based on electromagnetic simulation results, thin-film RF antennas were printed with conductive ink and used to fabricate a medical grade, 20-gauge (0.87 mm outer diameter), 90-mm long active interventional MRI needle. The MRI visibility performance of the active needle prototype was tested in vitro in 1 gel phantom and in vivo in 1 swine. A nearly identical active needle constructed using a 44 American Wire Gauge insulated copper wire-wound RF receiver antenna was a comparator. The RF-induced heating risk was evaluated in a gel phantom per American Society for Testing and Materials (ASTM) 2182-19. RESULTS: The active needle prototype with printed RF antenna was clearly visible both in vitro and in vivo under MRI. The maximum RF-induced temperature rise of prototypes with printed RF antenna and insulated copper wire antenna after a 3.96 W/kg, 15 min. long scan were 1.64°C and 8.21°C, respectively. The increase in needle diameter was 98 µm and 264 µm for prototypes with printed RF antenna and copper wire-wound antenna, respectively. CONCLUSION: The active needle prototype with conductive ink printed antenna provides distinct device visibility under MRI. Variations on the needle surface are mitigated compared to use of a 44 American Wire Gauge copper wire. RF-induced heating tests support device RF safety under MRI. The proposed method enables fabrication of small diameter active interventional MRI devices having complex geometries, something previously difficult using conventional methods.

Evaluation of a Flexible 12-Channel Screen-printed Pediatric MRI Coil.

Background Screen-printed MRI coil technology may reduce the need for bulky and heavy housing of coil electronics and may provide a better fit to patient anatomy to improve coil performance. Purpose To assess the performance and caregiver and clinician acceptance of a pediatric-sized screen-printed flexible MRI coil array as compared with conventional coil technology. Materials and Methods A pediatric-sized 12-channel coil array was designed by using a screen-printing process. Element coupling and phantom signal-to-noise ratio (SNR) were assessed. Subjects were scanned by using the pediatric printed array between September and November 2017; results were compared with three age- and sex-matched historical control subjects by using a commercial 32-channel cardiac array at 3 T. Caregiver acceptance was assessed by asking nurses, technologists, anesthesiologists, and subjects or parents to rate their coil preference. Diagnostic quality of the images was evaluated by using a Likert scale (5 = high image quality, 1 = nondiagnostic). Image SNR was evaluated and compared. Results Twenty study participants were evaluated with the screen-printed coil (age range, 2 days to 12 years; 11 male and nine female subjects). Loaded pediatric phantom testing yielded similar noise covariance matrices and only slightly degraded SNR for the printed coil as compared with the commercial coil. The caregiver acceptance survey yielded a mean score of 4.1 ± 0.6 (scale: 1, preferred the commercial coil; 5, preferred the printed coil). Diagnostic quality score was 4.5 ± 0.6. Mean image SNR was 54 ± 49 (paraspinal muscle), 78 ± 51 (abdominal wall muscle), and 59 ± 35 (psoas) for the printed coil, as compared with 64 ± 55, 65 ± 48, and 57 ± 43, respectively, for the commercial coil; these SNR differences were not statistically significant (P = .26). Conclusion A flexible screen-printed pediatric MRI receive coil yields adequate signal-to-noise ratio in phantoms and pediatric study participants, with similar image quality but higher preference by subjects and their caregivers when compared with a conventional MRI coil. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Lamb in this issue.

Targeted rapid knee MRI exam using T2 shuffling.

BACKGROUND: MRI is commonly used to evaluate pediatric musculoskeletal pathologies, but same-day/near-term scheduling and short exams remain challenges. PURPOSE: To investigate the feasibility of a targeted rapid pediatric knee MRI exam, with the goal of reducing cost and enabling same-day MRI access. STUDY TYPE: A cost effectiveness study done prospectively. SUBJECTS: Forty-seven pediatric patients. FIELD STRENGTH/SEQUENCE: 3T. The 10-minute protocol was based on T2 Shuffling, a four-dimensional acquisition and reconstruction of images with variable T2 contrast, and a T1 2D fast spin-echo (FSE) sequence. A distributed, compressed sensing-based reconstruction was implemented on a four-node high-performance compute cluster and integrated into the clinical workflow. ASSESSMENT: In an Institutional Review Board-approved study with informed consent/assent, we implemented a targeted pediatric knee MRI exam for assessing pediatric knee pain. Pediatric patients were subselected for the exam based on insurance plan and clinical indication. Over a 2-year period, 47 subjects were recruited for the study and 49 MRIs were ordered. Date and time information was recorded for MRI referral, registration, and completion. Image quality was assessed from 0 (nondiagnostic) to 5 (outstanding) by two readers, and consensus was subsequently reached. STATISTICAL TESTS: A Wilcoxon rank-sum test assessed the null hypothesis that the targeted exam times compared with conventional knee exam times were unchanged. RESULTS: Of the 49 cases, 20 were completed on the same day as exam referral. Median time from registration to exam completion was 18.7 minutes. Median reconstruction time for T2 Shuffling was reduced from 18.9 minutes to 95 seconds using the distributed implementation. Technical fees charged for the targeted exam were one-third that of the routine clinical knee exam. No subject had to return for additional imaging. DATA CONCLUSION: The targeted knee MRI exam is feasible and reduces the imaging time, cost, and barrier to same-day MRI access for pediatric patients. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 6 J. Magn. Reson. Imaging 2019.

Radiation-free CMR diagnostic heart catheterization in children.

BACKGROUND: Children with heart disease may require repeated X-Ray cardiac catheterization procedures, are more radiosensitive, and more likely to survive to experience oncologic risks of medical radiation. Cardiovascular magnetic resonance (CMR) is radiation-free and offers information about structure, function, and perfusion but not hemodynamics. We intend to perform complete radiation-free diagnostic right heart catheterization entirely using CMR fluoroscopy guidance in an unselected cohort of pediatric patients; we report the feasibility and safety. METHODS: We performed 50 CMR fluoroscopy guided comprehensive transfemoral right heart catheterizations in 39 pediatric (12.7 ± 4.7 years) subjects referred for clinically indicated cardiac catheterization. CMR guided catheterizations were assessed by completion (success/failure), procedure time, and safety events (catheterization, anesthesia). Pre and post CMR body temperature was recorded. Concurrent invasive hemodynamic and diagnostic CMR data were collected. RESULTS: During a twenty-two month period (3/2015 - 12/2016), enrolled subjects had the following clinical indications: post-heart transplant 33%, shunt 28%, pulmonary hypertension 18%, cardiomyopathy 15%, valvular heart disease 3%, and other 3%. Radiation-free CMR guided right heart catheterization attempts were all successful using passive catheters. In two subjects with septal defects, right and left heart catheterization were performed. There were no complications. One subject had six such procedures. Most subjects (51%) had undergone multiple (5.5 ± 5) previous X-Ray cardiac catheterizations. Retained thoracic surgical or transcatheter implants (36%) did not preclude successful CMR fluoroscopy heart catheterization. During the procedure, two subjects were receiving vasopressor infusions at baseline because of poor cardiac function, and in ten procedures, multiple hemodynamic conditions were tested. CONCLUSIONS: Comprehensive CMR fluoroscopy guided right heart catheterization was feasible and safe in this small cohort of pediatric subjects. This includes subjects with previous metallic implants, those requiring continuous vasopressor medication infusions, and those requiring pharmacologic provocation. Children requiring multiple, serial X-Ray cardiac catheterizations may benefit most from radiation sparing. This is a step toward wholly CMR guided diagnostic (right and left heart) cardiac catheterization and future CMR guided cardiac intervention. TRIAL REGISTRATION: ClinicalTrials.gov NCT02739087 registered February 17, 2016.

Acute Cardiac MRI Assessment of Radiofrequency Ablation Lesions for Pediatric Ventricular Arrhythmia: Feasibility and Clinical Correlation.

BACKGROUND: Arrhythmia ablation with current techniques is not universally successful. Inadequate ablation lesion formation may be responsible for some arrhythmia recurrences. Periprocedural visualization of ablation lesions may identify inadequate lesions and gaps to guide further ablation and reduce risk of arrhythmia recurrence. METHODS: This feasibility study assessed acute postprocedure ablation lesions by MRI, and correlated these findings with clinical outcomes. Ten pediatric patients who underwent ventricular tachycardia ablation were transferred immediately postablation to a 1.5T MRI scanner and late gadolinium enhancement (LGE) imaging was performed to characterize ablation lesions. Immediate and mid-term arrhythmia recurrences were assessed. RESULTS: Patient characteristics include median age 14 years (1-18 years), median weight 52 kg (11-81 kg), normal cardiac anatomy (n = 6), d-transposition of great arteries post arterial switch repair (n = 2), anomalous coronary artery origin post repair (n = 1), and cardiac rhabdomyoma (n = 1). All patients underwent radiofrequency catheter ablation of ventricular arrhythmia with acute procedural success. LGE was identified at the reported ablation site in 9/10 patients, all arrhythmia-free at median 7 months follow-up. LGE was not visible in 1 patient who had recurrence of frequent premature ventricular contractions within 2 hours, confirmed on Holter at 1 and 21 months post procedure. CONCLUSIONS: Ventricular ablation lesion visibility by MRI in the acute post procedure setting is feasible. Lesions identifiable with MRI may correlate with clinical outcomes. Acute MRI identification of gaps or inadequate lesions may provide the unique temporal opportunity for additional ablation therapy to decrease arrhythmia recurrence.

Improved workflow for quantification of left ventricular volumes and mass using free-breathing motion corrected cine imaging.

BACKGROUND: Traditional cine imaging for cardiac functional assessment requires breath-holding, which can be problematic in some situations. Free-breathing techniques have relied on multiple averages or real-time imaging, producing images that can be spatially and/or temporally blurred. To overcome this, methods have been developed to acquire real-time images over multiple cardiac cycles, which are subsequently motion corrected and reformatted to yield a single image series displaying one cardiac cycle with high temporal and spatial resolution. Application of these algorithms has required significant additional reconstruction time. The use of distributed computing was recently proposed as a way to improve clinical workflow with such algorithms. In this study, we have deployed a distributed computing version of motion corrected re-binning reconstruction for free-breathing evaluation of cardiac function. METHODS: Twenty five patients and 25 volunteers underwent cardiovascular magnetic resonance (CMR) for evaluation of left ventricular end-systolic volume (ESV), end-diastolic volume (EDV), and end-diastolic mass. Measurements using motion corrected re-binning were compared to those using breath-held SSFP and to free-breathing SSFP with multiple averages, and were performed by two independent observers. Pearson correlation coefficients and Bland-Altman plots tested agreement across techniques. Concordance correlation coefficient and Bland-Altman analysis tested inter-observer variability. Total scan plus reconstruction times were tested for significant differences using paired t-test. RESULTS: Measured volumes and mass obtained by motion corrected re-binning and by averaged free-breathing SSFP compared favorably to those obtained by breath-held SSFP (r = 0.9863/0.9813 for EDV, 0.9550/0.9685 for ESV, 0.9952/0.9771 for mass). Inter-observer variability was good with concordance correlation coefficients between observers across all acquisition types suggesting substantial agreement. Both motion corrected re-binning and averaged free-breathing SSFP acquisition and reconstruction times were shorter than breath-held SSFP techniques (p < 0.0001). On average, motion corrected re-binning required 3 min less than breath-held SSFP imaging, a 37% reduction in acquisition and reconstruction time. CONCLUSIONS: The motion corrected re-binning image reconstruction technique provides robust cardiac imaging that can be used for quantification that compares favorably to breath-held SSFP as well as multiple average free-breathing SSFP, but can be obtained in a fraction of the time when using cloud-based distributed computing reconstruction.

Free-breathing motion-corrected late-gadolinium-enhancement imaging improves image quality in children.

BACKGROUND: The value of late-gadolinium-enhancement (LGE) imaging in the diagnosis and management of pediatric and congenital heart disease is clear; however current acquisition techniques are susceptible to error and artifacts when performed in children because of children's higher heart rates, higher prevalence of sinus arrhythmia, and inability to breath-hold. Commonly used techniques in pediatric LGE imaging include breath-held segmented FLASH (segFLASH) and steady-state free precession-based (segSSFP) imaging. More recently, single-shot SSFP techniques with respiratory motion-corrected averaging have emerged. OBJECTIVE: This study tested and compared single-shot free-breathing LGE techniques with standard segmented breath-held techniques in children undergoing LGE imaging. MATERIALS AND METHODS: Thirty-two consecutive children underwent clinically indicated late-enhancement imaging using intravenous gadobutrol 0.15 mmol/kg. Breath-held segSSFP, breath-held segFLASH, and free-breathing single-shot SSFP LGE sequences were performed in consecutive series in each child. Two blinded reviewers evaluated the quality of the images and rated them on a scale of 1-5 (1 = poor, 5 = superior) based on blood pool-myocardial definition, presence of cardiac motion, presence of respiratory motion artifacts, and image acquisition artifact. We used analysis of variance (ANOVA) to compare groups. RESULTS: Patients ranged in age from 9 months to 18 years, with a mean +/- standard deviation (SD) of 13.3 +/- 4.8 years. R-R interval at the time of acquisition ranged 366-1,265 milliseconds (ms) (47-164 beats per minute [bpm]), mean +/- SD of 843+/-231 ms (72+/-21 bpm). Mean +/- SD quality ratings for long-axis imaging for segFLASH, segSSFP and single-shot SSFP were 3.1+/-0.9, 3.4+/-0.9 and 4.0+/-0.9, respectively (P < 0.01 by ANOVA). Mean +/- SD quality ratings for short-axis imaging for segFLASH, segSSFP and single-shot SSFP were 3.4+/-1, 3.8+/-0.9 and 4.3+/-0.7, respectively (P < 0.01 by ANOVA). CONCLUSION: Single-shot late-enhancement imaging with motion-corrected averaging is feasible in children, robust at high heart rates and with variable R-R intervals, and can be performed without breath-holding with higher image quality ratings than standard breath-held techniques. Use of free-breathing single-shot motion-corrected technique does not compromise LGE image quality in children who can hold their breath, and it can significantly improve image quality in children who cannot hold their breath or who have significant arrhythmia.

Interventional-Cardiovascular MR: Role of the Interventional MR Technologist.

BACKGROUND: Interventional-cardiovascular magnetic resonance (iCMR) is a promising clinical tool for adults and children who need a comprehensive hemodynamic catheterization of the heart. Magnetic resonance (MR) imaging-guided cardiac catheterization offers radiation-free examination with increased soft tissue contrast and unconstrained imaging planes for catheter guidance. The interventional MR technologist plays an important role in the care of patients undergoing such procedures. It is therefore helpful for technologists to understand the unique iCMR preprocedural preparation, procedural and imaging workflows, and management of emergencies. The authors report their team's experience from the National Institutes of Health Clinical Center and a collaborating pediatric site.

Optimized protocols for cardiac magnetic resonance imaging in patients with thoracic metallic implants.

BACKGROUND: Cardiac magnetic resonance (MR) imaging is a valuable tool in congenital heart disease; however patients frequently have metal devices in the chest from the treatment of their disease that complicate imaging. Methods are needed to improve imaging around metal implants near the heart. Basic sequence parameter manipulations have the potential to minimize artifact while limiting effects on image resolution and quality. OBJECTIVE: Our objective was to design cine and static cardiac imaging sequences to minimize metal artifact while maintaining image quality. MATERIALS AND METHODS: Using systematic variation of standard imaging parameters on a fluid-filled phantom containing commonly used metal cardiac devices, we developed optimized sequences for steady-state free precession (SSFP), gradient recalled echo (GRE) cine imaging, and turbo spin-echo (TSE) black-blood imaging. We imaged 17 consecutive patients undergoing routine cardiac MR with 25 metal implants of various origins using both standard and optimized imaging protocols for a given slice position. We rated images for quality and metal artifact size by measuring metal artifact in two orthogonal planes within the image. RESULTS: All metal artifacts were reduced with optimized imaging. The average metal artifact reduction for the optimized SSFP cine was 1.5+/-1.8 mm, and for the optimized GRE cine the reduction was 4.6+/-4.5 mm (P < 0.05). Quality ratings favored the optimized GRE cine. Similarly, the average metal artifact reduction for the optimized TSE images was 1.6+/-1.7 mm (P < 0.05), and quality ratings favored the optimized TSE imaging. CONCLUSION: Imaging sequences tailored to minimize metal artifact are easily created by modifying basic sequence parameters, and images are superior to standard imaging sequences in both quality and artifact size. Specifically, for optimized cine imaging a GRE sequence should be used with settings that favor short echo time, i.e. flow compensation off, weak asymmetrical echo and a relatively high receiver bandwidth. For static black-blood imaging, a TSE sequence should be used with fat saturation turned off and high receiver bandwidth.

Method for calculating confidence intervals for phase contrast flow measurements.

BACKGROUND: Phase contrast (PC) measurements play an important role in several cardiovascular magnetic resonance (CMR) protocols but considerable variation is observed in such measurements. Part of this variation stems from the propagation of thermal noise from the measurement data through the image reconstruction to the region of interest analysis used in flow measurement, which limits the precision. The purpose of this study was to develop a method for direct estimation of the variation caused by thermal noise and to validate this method in phantom and in vivo data. METHODS: The estimation of confidence intervals in flow measurements is complicated by noise correlation among the image pixels and cardiac phases. This correlation is caused by sequence and reconstruction parameters. A method for the calculation of the standard deviation of region of interest measurements was adapted and expanded to accommodate typical clinical PC measurements and the region-of-interest analysis used for such measurements. This included the dependency between cardiac phases that arises due to retrospective cardiac gating used in such studies. The proposed method enables calculation of standard deviations of flow measurements without the need for repeated experiments or repeated reconstructions. The method was compared to repeated trials in phantom measurements and pseudo replica reconstructions of in vivo data. Three different flow protocols (free breathing and breath hold with various accelerations) were compared in terms of the confidence interval ranges caused by thermal noise in the measurement data. RESULTS: Using the proposed method it was possible to accurately predict confidence intervals for flow measurements. The method was in good agreement with repeated measurements in phantom experiments and there was also good agreement with confidence intervals predicted by pseudo replica reconstructions in both phantom and in vivo data. The proposed method was used to demonstrate that the variation in cardiac output caused by thermal noise is on the order of 1% in clinically used free breathing protocols, and on the order of 3-5% in breath-hold protocols with higher parallel imaging factors. CONCLUSIONS: It is possible to calculate confidence intervals for Cartesian PC contrast flow measurements directly without the need for time-consuming pseudo replica reconstructions.

Quantitative MR characterization of disease activity in the knee in children with juvenile idiopathic arthritis: a longitudinal pilot study.

BACKGROUND: The development of a quantifiable and noninvasive method of monitoring disease activity and response to therapy is vital for arthritis management. OBJECTIVE: The purpose of this study was to investigate the utility of quantitative dynamic contrast-enhanced MRI (DCE-MRI) based on pharmacokinetic (PK) modeling to evaluate disease activity in the knee and correlate the results with the clinical assessment in children with juvenile idiopathic arthritis (JIA). MATERIALS AND METHODS: A group of 17 children with JIA underwent longitudinal clinical and laboratory assessment and DCE-MRI of the knee at enrollment, 3 months, and 12 months. A PK model was employed using MRI signal enhancement data to give three parameters, K(trans') (min(-1)), k(ep) (min(-1)), and V(p) (') and to calculate synovial volume. RESULTS: The PK parameters, synovial volumes, and clinical and laboratory assessments in most children were significantly decreased (P < 0.05) at 12 months when compared to the enrollment values. There was excellent correlation between the PK and synovial volume and the clinical and laboratory assessments. Differences in MR and clinical parameter values in individual subjects illustrate persistent synovitis when in clinical remission. CONCLUSION: A decrease in PK parameter values obtained from DCE-MRI in children with JIA likely reflects diminution of disease activity. This technique may be used as an objective follow-up measure of therapeutic efficacy in patients with JIA. MR imaging can detect persistent synovitis in patients considered to be in clinical remission.