Feasibility of ferumoxytol-enhanced neonatal and young infant cardiac MRI without general anesthesia

Unveiling the next generation of MRI contrast agents: current insights and perspectives on ferumoxytol-enhanced MRI

Contrast-enhanced magnetic resonance imaging (CE-MRI) is a pivotal tool for global disease diagnosis and management. Since its clinical availability in 2009, the off-label use of ferumoxytol for ferumoxytol-enhanced MRI (FE-MRI) has significantly reshaped CE-MRI practices. Unlike MRI that is enhanced by gadolinium-based contrast agents, FE-MRI offers advantages such as reduced contrast agent dosage, extended imaging windows, no nephrotoxicity, higher MRI time efficiency and the capability for molecular imaging. As a leading superparamagnetic iron oxide contrast agent, ferumoxytol is heralded as the next generation of contrast agents. This review delineates the pivotal clinical applications and inherent technical superiority of FE-MRI, providing an avant-garde medical-engineering interdisciplinary lens, thus bridging the gap between clinical demands and engineering innovations. Concurrently, we spotlight the emerging imaging themes and new technical breakthroughs. Lastly, we share our own insights on the potential trajectory of FE-MRI, shedding light on its future within the medical imaging realm.

Cardiac Magnetic Resonance Imaging to Determine Single Ventricle Function in a Pediatric Population is Feasible in a Large Trial Setting: Experience from the Single Ventricle Reconstruction Trial Longitudinal Follow up

The Single Ventricle Reconstruction (SVR) Trial was a randomized prospective trial designed to determine survival advantage of the modified Blalock-Taussig-Thomas shunt (BTTS) vs the right ventricle to pulmonary artery conduit (RVPAS) for patients with hypoplastic left heart syndrome. The primary aim of the long-term follow-up (SVRIII) was to determine the impact of shunt type on RV function. In this work, we describe the use of CMR in a large cohort follow up from the SVR Trial as a focused study of single ventricle function. The SVRIII protocol included short axis steady-state free precession imaging to assess single ventricle systolic function and flow quantification. There were 313 eligible SVRIII participants and 237 enrolled, ages ranging from 10 to 12.5 years. 177/237 (75%) participants underwent CMR. The most common reasons for not undergoing CMR exam were requirement for anesthesia (n = 14) or ICD/pacemaker (n = 11). A total of 168/177 (94%) CMR studies were diagnostic for RVEF. Median exam time was 54 [IQR 40-74] minutes, cine function exam time 20 [IQR 14-27] minutes, and flow quantification time 18 [IQR 12-25] minutes. There were 69/177 (39%) studies noted to have intra-thoracic artifacts, most common being susceptibility artifact from intra-thoracic metal. Not all artifacts resulted in non-diagnostic exams. These data describe the use and limitations of CMR for the assessment of cardiac function in a prospective trial setting in a grade-school-aged pediatric population with congenital heart disease. Many of the limitations are expected to decrease with the continued advancement of CMR technology.

4D Flow cardiovascular magnetic resonance consensus statement: 2023 update

Hemodynamic assessment is an integral part of the diagnosis and management of cardiovascular disease. Four-dimensional cardiovascular magnetic resonance flow imaging (4D Flow CMR) allows comprehensive and accurate assessment of flow in a single acquisition. This consensus paper is an update from the 2015 '4D Flow CMR Consensus Statement'. We elaborate on 4D Flow CMR sequence options and imaging considerations. The document aims to assist centers starting out with 4D Flow CMR of the heart and great vessels with advice on acquisition parameters, post-processing workflows and integration into clinical practice. Furthermore, we define minimum quality assurance and validation standards for clinical centers. We also address the challenges faced in quality assurance and validation in the research setting. We also include a checklist for recommended publication standards, specifically for 4D Flow CMR. Finally, we discuss the current limitations and the future of 4D Flow CMR. This updated consensus paper will further facilitate widespread adoption of 4D Flow CMR in the clinical workflow across the globe and aid consistently high-quality publication standards.

Ferumoxytol-Enhanced MRI in Children and Young Adults: State of the Art

Ferumoxytol is an ultrasmall iron oxide nanoparticle that was originally approved by the FDA in 2009 for IV treatment of iron deficiency in adults with chronic kidney disease. Subsequently, its off-label use as an MRI contrast agent increased in clinical practice, particularly in pediatric patients in North America. Unlike conventional MRI contrast agents that are based on the rare earth metal gadolinium (gadolinium-based contrast agents), ferumoxytol is biodegradable and carries no potential risk of nephrogenic systemic fibrosis. At FDA-approved doses, ferumoxytol shows no long-term tissue retention in patients with intact iron metabolism. Ferumoxytol provides unique MRI properties, including long-lasting vascular retention (facilitating high-quality vascular imaging) and retention in reticuloendothelial system tissues, thereby supporting a variety of applications beyond those possible with gadolinium-based contrast agents (GBCAs). This Clinical Perspective describes clinical and early translational applications of ferumoxytol-enhanced MRI in children and young adults through off-label use in a variety of settings, including vascular, cardiac, and cancer imaging, drawing on the institutional experience of the authors. In addition, we describe current advances in pre-clinical and clinical research using ferumoxytol in cellular and molecular imaging as well as the use of ferumoxytol as a novel potential cancer therapeutic agent.

Comprehensive Neonatal Cardiac, Feed and Wrap, Non-contrast, Non-sedated, Free-breathing Compressed Sensing 4D Flow MRI Assessment

BACKGROUND

Cardiac MRI is an important imaging tool in congenital cardiac disease, but its use has been limited in the neonatal population as general anesthesia has been needed for breath-holding. Technological advances in four-dimensional (4D) flow MRI have now made nonsedated free-breathing acquisition protocols a viable clinical option, but the method requires prospective validation in neonates.

PURPOSE

To test the feasibility of compressed sensing (CS) 4D flow MRI in the neonatal population and to compare with standard previously validated two-dimensional (2D) phase-contrast (PC) flow MRI.

STUDY TYPE

Prospective, cohort, image quality.

POPULATION

A total of 14 healthy neonates (median [range] age: 2.5 [0-80] days; 8 male).

FIELD STRENGTH AND SEQUENCE

Noncontrast 2D cine gradient echo sequence with through-plane velocity encoding (PC) sequence and compressed sensing (CS) three-dimensional (3D), time-resolved, cine phase-contrast MRI with 3D velocity-encoding (4D flow MRI) at 3 T.

ASSESSMENT

Aortic 2D PC, and aortic, pulmonary trunk and superior vena cava CS 4D flow MRI were acquired using the feed and wrap technique (nonsedated) and quantified using commercially available software. Aortic flow and peak velocity were compared between methods. Internal consistency of 4D flow MRI was determined by comparing mean forward flow of the main pulmonary artery (MPA) vs. the sum of left and right pulmonary artery flows (LPA and RPA) and by comparing mean ascending aorta forward flow (AAo) vs. the sum of superior vena cava (SVC) and descending aorta flows (DAo).

STATISTICAL TESTS

Flow and peak-velocity comparisons were assessed using paired t-tests, with P < 0.05 considered significant, and Bland-Altman analysis. Interobserver and intraobserver agreement and internal consistency were analyzed by intraclass correlation co-efficient (ICC).

RESULTS

There was no statistically significant difference between ascending aortic forward flow between 2D PC and CS 4D Flow MRI (P = 0.26) with a bias of 0.11 mL (-0.59 to 0.82 mL) nor peak velocity (P = 0.11), with a bias of -5 cm/sec and (-26 to 16 cm/sec). There was excellent interobserver and intraobserver agreement for each vessel (interobserver ICC: AAo 1.00; DAo 0.94, SVC 0.90, MPA 0.99, RPA 0.98, LPA 0.96; intraobserver ICC: AAo 1.00; DAo 0.99, SVC 0.98, MPA 1.00, RPA 1.00, LPA 0.99). Internal consistency measures showed excellent agreement for both mean forward flow of main pulmonary artery vs. the sum of left and right pulmonary arteries (ICC: 0.95) and mean ascending aorta forward flow vs. the sum of superior vena cava and descending aorta flows (ICC: 1.00).

CONCLUSION

Sedation-free neonatal feed and wrap MRI is well tolerated and feasible. CS 4D flow MRI quantification is similar to validated 2D PC free-breathing imaging with excellent interobserver and intraobserver agreement.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 2.

Comparison of 2D and 4D Flow MRI in Neonates Without General Anesthesia

BACKGROUND

Neonates with critical congenital heart disease require early intervention. Four-dimensional (4D) flow may facilitate surgical planning and improve outcome, but accuracy and precision in neonates are unknown.

PURPOSE

To 1) validate two-dimensional (2D) and 4D flow MRI in a phantom and investigate the effect of spatial and temporal resolution; 2) investigate accuracy and precision of 4D flow and internal consistency of 2D and 4D flow in neonates; and 3) compare scan time of 4D flow to multiple 2D flows.

STUDY TYPE

Phantom and prospective patients.

POPULATION

A total of 17 neonates with surgically corrected aortic coarctation (age 18 days [IQR 11-20]) and a three-dimensional printed neonatal aorta phantom.

FIELD STRENGTH/SEQUENCE

1.5T, 2D flow and 4D flow.

ASSESSMENT

In the phantom, 2D and 4D flow volumes (ascending and descending aorta, and aortic arch vessels) with different resolutions were compared to high-resolution reference 2D flow. In neonates, 4D flow was compared to 2D flow volumes at each vessel. Internal consistency was computed as the flow volume in the ascending aorta minus the sum of flow volumes in the aortic arch vessels and descending aorta, divided by ascending aortic flow.

STATISTICAL TESTS

Bland-Altman plots, Pearson correlation coefficient (r), and Student's t-tests.

RESULTS

In the phantom, 2D flow differed by 0.01 ± 0.02 liter/min with 1.5 mm spatial resolution and -0.01 ± 0.02 liter/min with 0.8 mm resolution; 4D flow differed by -0.05 ± 0.02 liter/min with 2.4 mm spatial and 42 msec temporal resolution, -0.01 ± 0.02 liter/min with 1.5 mm, 42 msec resolution and -0.01 ± 0.02 liter/min with 1.5 mm, 21 msec resolution. In patients, 4D flow and 2D flow differed by -0.06 ± 0.08 liter/min. Internal consistency in patients was -11% ± 17% for 2D flow and 5% ± 13% for 4D flow. Scan time was 17.1 minutes [IQR 15.5-18.5] for 2D flow and 6.2 minutes [IQR 5.3-6.9] for 4D flow, P < 0.0001.

DATA CONCLUSION

Neonatal 4D flow MRI is time efficient and can be acquired with good internal consistency without contrast agents or general anesthesia, thus potentially expanding 4D flow use to the youngest and smallest patients.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 2.

Ferumoxytol-Enhanced Cardiac Magnetic Resonance Angiography and 4D Flow: Safety and Utility in Pediatric and Adult Congenital Heart Disease

Cardiac magnetic resonance imaging and angiography have a crucial role in the diagnostic evaluation and follow up of pediatric and adult patients with congenital heart disease. Although much of the information required of advanced imaging studies can be provided by standard gadolinium-enhanced magnetic resonance imaging, the limitations of precise bolus timing, long scan duration, complex imaging protocols, and the need to image small structures limit more widespread use of this modality. Recent experience with off-label diagnostic use of ferumoxytol has helped to mitigate some of these barriers. Approved by the U.S. FDA for intravenous treatment of anemia, ferumoxytol is an ultrasmall superparamagnetic iron oxide nanoparticle that has a long blood pool residence time and high relaxivity. Once metabolized by macrophages, the iron core is incorporated into the reticuloendothelial system. In this work, we aim to summarize the evolution of ferumoxytol-enhanced cardiovascular magnetic resonance imaging and angiography and highlight its many applications for congenital heart disease.

Impact of ferumoxytol vs gadolinium on 4D flow cardiovascular magnetic resonance measurements in small children with congenital heart disease

BACKGROUND

Cardiovascular magnetic resonance (CMR) allows for time-resolved three-dimensional phase-contrast (4D Flow) analysis of congenital heart disease (CHD). Higher spatial resolution in small infants requires thinner slices, which can degrade the signal. Particularly in infants, the choice of contrast agent (ferumoxytol vs. gadolinium) may influence 4D Flow CMR accuracy. Thus, we investigated the accuracy of 4D Flow CMR measurements compared to gold standard 2D flow phase contrast (PC) measurements in ferumoxytol vs. gadolinium-enhanced CMR of small CHD patients with shunt lesions.

METHODS

This was a retrospective study consisting of CMR studies from complex CHD patients less than 20 kg who had ferumoxytol or gadolinium-enhanced 4D Flow and standard two-dimensional phase contrast (2D-PC) flow collected. 4D Flow clinical software (Arterys) was used to measure flow in great vessels, systemic veins, and pulmonary veins. 4D Flow accuracy was defined as percent difference or correlation against conventional measurements (2D-PC) from the same vessels. Subgroup analysis was performed on two-ventricular vs single-ventricular CHD, arterial vs venous flow, as well as low flows (defined as < 1.5 L/min) in 1V CHD.

RESULTS

Twenty-one ferumoxytol-enhanced and 23 gadolinium-enhanced CMR studies were included, with no difference in age (2.1 ± 1.6 vs. 2.3 ± 1.9 years, p = 0.70), patient body surface area (0.50 ± 0.2 vs. 0.52 ± 0.2 m2, p = 0.67), or vessel diameter (11.4 ± 5.2 vs. 12.4 ± 5.6 mm, p = 0.22). Ten CMR studies with single ventricular CHD were included. Overall, ferumoxytol-enhanced 4D flow CMR measurements demonstrated less percent difference to 2D-PC when compared to gadolinium-enhanced 4D Flow CMR studies. In subgroup analyses of arterial vs. venous flows (high velocity vs. low velocity) and low flow in single ventricle CHD, ferumoxytol-enhanced 4D Flow CMR measurements had stronger correlation to 2D-PC CMR. The contrast-to-noise ratio (CNR) in ferumoxytol-enhanced studies was higher than the CNR in gadolinium-enhanced studies.

CONCLUSIONS

Ferumoxytol-enhanced 4D Flow CMR has improved accuracy when compared to gadolinium 4D Flow CMR, particularly for infants with small vessels in CHD.

Contrast-enhanced MR Angiography without Gadolinium-based Contrast Material: Clinical Applications Using Ferumoxytol

Vascular imaging can be challenging because of the wide variability of contrast dynamics in different vascular territories and potential safety concerns in patients with renal insufficiency or allergies. Off-label diagnostic use of ferumoxytol, a superparamagnetic iron nanoparticle approved for therapy, is a promising alternative to gadolinium-based contrast agents for MR angiography (MRA). Ferumoxytol has exhibited a reassuring safety profile when used within the dose range recommended for diagnostic imaging. Because of its prolonged and stable intravascular residence, ferumoxytol can be used in its steady-state distribution for a wide variety of imaging indications, including some where conventional MRA is unreliable. In this article, authors discuss some of the major vascular applications of ferumoxytol and highlight how it may be used to provide highly diagnostic images and improve the quality, workflow, and reliability of vascular imaging. Keywords: MR Angiography, MRI Contrast Agent, Cardiac, Vascular © RSNA, 2022.

Sustainable low-field cardiovascular magnetic resonance in changing healthcare systems

Cardiovascular disease continues to be a major burden facing healthcare systems worldwide. In the developed world, cardiovascular magnetic resonance (CMR) is a well-established non-invasive imaging modality in the diagnosis of cardiovascular disease. However, there is significant global inequality in availability and access to CMR due to its high cost, technical demands as well as existing disparities in healthcare and technical infrastructures across high-income and low-income countries. Recent renewed interest in low-field CMR has been spurred by the clinical need to provide sustainable imaging technology capable of yielding diagnosticquality images whilst also being tailored to the local populations and healthcare ecosystems. This review aims to evaluate the technical, practical and cost considerations of low field CMR whilst also exploring the key barriers to implementing sustainable MRI in both the developing and developed world.

How to stop using gadolinium chelates for magnetic resonance imaging: clinical-translational experiences with ferumoxytol

Gadolinium chelates have been used as standard contrast agents for clinical MRI for several decades. However, several investigators recently reported that rare Earth metals such as gadolinium are deposited in the brain for months or years. This is particularly concerning for children, whose developing brain is more vulnerable to exogenous toxins compared to adults. Therefore, a search is under way for alternative MR imaging biomarkers. The United States Food and Drug Administration (FDA)-approved iron supplement ferumoxytol can solve this unmet clinical need: ferumoxytol consists of iron oxide nanoparticles that can be detected with MRI and provide significant T1- and T2-signal enhancement of vessels and soft tissues. Several investigators including our research group have started to use ferumoxytol off-label as a new contrast agent for MRI. This article reviews the existing literature on the biodistribution of ferumoxytol in children and compares the diagnostic accuracy of ferumoxytol- and gadolinium-chelate-enhanced MRI. Iron oxide nanoparticles represent a promising new class of contrast agents for pediatric MRI that can be metabolized and are not deposited in the brain.

Increasing the Utilization of Moderate Sedation Services for Pediatric Imaging

Performing motion-free imaging is frequently challenging in children. To bridge the gap between examinations performed in children who are awake and in those under general anesthesia, a moderate sedation program was implemented at our institution but was seldom used despite substantial eligibility. In conjunction with a 5-month quality improvement (QI) course, a multidisciplinary team was assembled and, by using an A3 approach, sought to address the most important key drivers of low utilization, namely the need for clear moderate sedation eligibility criteria, reliable protocol routing order, consistent moderate sedation screening performed by registered nurses (RNs), and enhanced visibility of moderate sedation services to ordering providers. Initial steps focused on developing better-defined criteria and protocoling standard work for technologists and RNs, with coaching and audits. Modality-specific forecasting was then implemented to reroute profiles of patients who were awaiting scheduling or already scheduled for an examination with general anesthesia to the moderate sedation queue to identify more eligible patients. These manual efforts were coupled with higher reliability but more protracted electronic health record changes, facilitating automated protocol routing on the basis of moderate sedation eligibility and order entry constraints. As a result, scheduled imaging examinations requiring moderate sedation increased from a mean of 1.2 examinations per week to a sustained 6.1 examinations per week (range, 4-8) over the 5-month period, exceeding the team SMART (specific, measurable, achievable, relevant, and time bound) goal to achieve an average of five examinations per week by the QI course end. By targeting the most high-impact yet modifiable process deficiencies through a multifaceted team approach and initially investing in manual efforts to gain cultural buy-in while awaiting higher-reliability interventions, the project achieved success and may serve as a more general model for workflow change when there is organizational resistance. ^©RSNA, 2021.

Pulmonary Functional Imaging: Part 1-State-of-the-Art Technical and Physiologic Underpinnings

Over the past few decades, pulmonary imaging technologies have advanced from chest radiography and nuclear medicine methods to high-spatial-resolution or low-dose chest CT and MRI. It is currently possible to identify and measure pulmonary pathologic changes before these are obvious even to patients or depicted on conventional morphologic images. Here, key technological advances are described, including multiparametric CT image processing methods, inhaled hyperpolarized and fluorinated gas MRI, and four-dimensional free-breathing CT and MRI methods to measure regional ventilation, perfusion, gas exchange, and biomechanics. The basic anatomic and physiologic underpinnings of these pulmonary functional imaging techniques are explained. In addition, advances in image analysis and computational and artificial intelligence (machine learning) methods pertinent to functional lung imaging are discussed. The clinical applications of pulmonary functional imaging, including both the opportunities and challenges for clinical translation and deployment, will be discussed in part 2 of this review. Given the technical advances in these sophisticated imaging methods and the wealth of information they can provide, it is anticipated that pulmonary functional imaging will be increasingly used in the care of patients with lung disease. © RSNA, 2021 Online supplemental material is available for this article.

Additional value and new insights by four-dimensional flow magnetic resonance imaging in congenital heart disease: application in neonates and young children

Cardiovascular MRI has become an essential imaging modality in children with congenital heart disease (CHD) in the last 15-20 years. With use of appropriate sequences, it provides important information on cardiovascular anatomy, blood flow and function for initial diagnosis and post-surgical or -interventional monitoring in children. Although considered as more sophisticated and challenging than CT, in particular in neonates and infants, MRI is able to provide information on intra- and extracardiac haemodynamics, in contrast to CT. In recent years, four-dimensional (4-D) flow MRI has emerged as an additional MR technique for retrospective assessment and visualisation of blood flow within the heart and any vessel of interest within the acquired three-dimensional (3-D) volume. Its application in young children requires special adaptations for the smaller vessel size and faster heart rate compared to adolescents or adults. In this article, we provide an overview of 4-D flow MRI in various types of complex CHD in neonates and infants to demonstrate its potential indications and beneficial application for optimised individual cardiovascular assessment. We focus on its application in clinical routine cardiovascular workup and, in addition, show some examples with pathologies other than CHD to highlight that 4-D flow MRI yields new insights in disease understanding and therapy planning. We shortly review the essentials of 4-D flow data acquisition, pre- and post-processing techniques in neonates, infants and young children. Finally, we conclude with some details on accuracy, limitations and pitfalls of the technique.

Cardiac magnetic resonance using fused 3D cine and 4D flow sequences:Validation of ventricular and blood flow measurements

PURPOSE

Current cardiovascular magnetic resonance (CMR) examinations require expert planning, multiple breath holds, and 2D imaging. To address this, we sought to develop and validate a comprehensive free-breathing 3D cine function and flow CMR examination using a steady-state free precession (SSFP) sequence to depict anatomy fused with a spatially registered phase contrast (PC) sequence for blood flow analysis.

METHODS

In a prospective study, 25 patients underwent a CMR examination which included a 3D cine SSFP sequence and a 3D cine PC (also known as 4D flow) sequence acquired during free-breathing and after the administration of a gadolinium-based contrast agent. Both 3D sequences covered the heart and mediastinum, and used retrospective vectorcardiogram gating (20 phases/beat interpolated to 30 phases/beat) and prospective respiratory motion compensation confining data acquisition to end-expiration. Cardiovascular measurements derived from the 3D cine SSFP and PC images were then compared with those from standard 2D imaging.

RESULTS

All 3D cine SSFP and PC acquisitions were completed successfully. The mean time for the 3D cine sequences including prescription was shorter than that for the corresponding 2D sequences (21 min vs. 36 min, P-value <0.001). Left and right ventricular end-diastolic volumes and stroke volumes by 3D cine SSFP were slightly smaller than those from 2D cine SSFP (all biases ≤5%). The blood flow measurements from the 3D and 2D sequences had close agreement in the ascending aorta (bias -2.6%) but main pulmonary artery flow was lower with the 3D cine sequence (bias -11.2%).

CONCLUSION

Compared to the conventional 2D cine approach, a comprehensive 3D cine function and flow examination was faster and yielded slightly lower left and right end-diastolic volumes, stroke volumes, and main pulmonary artery blood flow. This free-breathing 3D cine approach allows flexible post-examination data analysis and has the potential to make examinations more comfortable for patients and easier to perform for the operator.

Magnetic Resonance Safety: Pregnancy and Lactation

MRI is a powerful diagnostic tool with excellent soft tissue contrast that uses nonionizing radiation. These advantages make MRI an appealing modality for imaging the pregnant patient; however, specific risks inherent to the magnetic resonance environment must be considered. MRI may be performed without and/or with intravenous contrast, which adds further fetal considerations. The risks of MRI with and without intravenous contrast are reviewed as they pertain to the pregnant or lactating patient and to the fetus and nursing infant. Relevant issues for gadolinium-based contrast agents and ultrasmall paramagnetic iron oxide particles are reviewed.

Brain iron deposition after Ferumoxytol-enhanced MRI: A study of Porcine Brains

Recent evidence of gadolinium deposition in the brain has raised safety concerns. Iron oxide nanoparticles are re-emerging as promising alternative MR contrast agents, because the iron core can be metabolized. However, long-term follow up studies of the brain after intravenous iron oxide administration have not been reported thus far. In this study, we investigated, if intravenously administered ferumoxytol nanoparticles are deposited in porcine brains.

Methods: In an animal care and use committee-approved prospective case-control study, ten Göttingen minipigs received either intravenous ferumoxytol injections at a dose of 5 mg Fe/kg (n=4) or remained untreated (n=6). Nine to twelve months later, pigs were sacrificed and the brains of all pigs underwent ex vivo MRI at 7T with T2 and T2*-weighted sequences. MRI scans were evaluated by measuring R2* values (R2*=1000/T2*) of the bilateral caudate nucleus, lentiform nucleus, thalamus, dentate nucleus, and choroid plexus. Pig brains were sectioned and stained with Prussian blue and evaluated for iron deposition using a semiquantitative scoring system. Data of ferumoxytol exposed and unexposed groups were compared with an unpaired t-test and a Mann-Whitney U test.

Results: T2 and T2* signal of the different brain regions was not visually different between ferumoxytol exposed and unexposed controls. There were no significant differences in R2* values of the different brain regions in the ferumoxytol exposed group compared to controls (p>0.05). Prussian blue stains of the same brain regions, scored according to a semiquantitative score, were not significantly different either between the ferumoxytol exposed group and unexposed controls (p>0.05).

Conclusions: Our study shows that intravenous ferumoxytol doses of 5-10 mg Fe/kg do not lead to iron deposition in the brain of pigs. We suggest iron oxide nanoparticles as a promising alternative for gadolinium-enhanced MRI.

Artifact-robust diffusion-weighted whole-body imaging with background suppression at 3 T using improved turbo spin-echo diffusion-weighted imaging

OBJECTIVE:

To compare single-shot turbo spin-echo (TSE) diffusion-weighted whole-body imaging with background suppression (DWIBS) and echo-planar imaging (EPI) DWIBS to determine the feasibility of direct-coronal TSE-DWIBS.

METHODS:

All measurements were performed using a 3.0 T MRI scanner. In the phantom study, we compared the contrast ratios (CRs) of tumor-mimicking phantom (tumor) to muscle-mimicking phantom (muscle) and water to muscle and the signal-to-noise ratio (SNR) between TSE-DWIBS and EPI-DWIBS. In the volunteer study, 10 healthy volunteers were whole-body scanned with direct-coronal TSE-DWIBS, direct-coronal EPI-DWIBS (corEPI-DWIBS), and transverse EPI-DWIBS (traEPI-DWIBS). Two radiologists assessed the image distortion, uniformity of fat suppression, overall artifacts, and overall image quality in maximum intensity projection (MIP) images from each DWIBS image using a 5-point scale.

RESULTS:

In the phantom study, the CR of tumor to muscle was found to be lower for TSE-DWIBS (10.57 ± 0.45) than for EPI-DWIBS (15.38 ± 0.27), and the CR of water to muscle was higher for TSE-DWIBS (9.61 ± 0.66) than for EPI-DWIBS (2.52 ± 0.60). The volunteer study revealed good inter observer agreement between TSE-DWIBS and EPI-DWIBS with respect to image distortion, uniformity of fat suppression, overall artifacts, and overall image quality, with weighted Cohen's κ coefficients of 0.91, 0.74, 0.87, and 0.72, respectively. Qualitative analysis scores for image distortion, uniformity of fat suppression, overall artifacts, and overall image quality were significantly higher for TSE-DWIBS than for corEPI-DWIBS or traEPI-DWIBS (p < 0.05).

CONCLUSION:

Direct-coronal TSE-DWIBS is robust against magnetic field inhomogeneity. High-quality images without distortion or fat suppression inhomogeneity were obtained.

ADVANCES IN KNOWLEDGE:

Many studies on DWIBS have been previously reported; however, these studies used EPI read-out. To the best of our knowledge, no studies using TSE read-out have been reported. In this study, we examined the feasibility of TSE-DWIBS with lesser artifacts than EPI-DWIBS.

High-resolution 3D volumetric contrast-enhanced MR angiography with a blood pool agent (ferumoxytol) for diagnostic evaluation of pediatric brain arteriovenous malformations

OBJECTIVE Patients with brain arteriovenous malformations (AVMs) often require repeat imaging with MRI or MR angiography (MRA), CT angiography (CTA), and digital subtraction angiography (DSA). The ideal imaging modality provides excellent vascular visualization without incurring added risks, such as radiation exposure. The purpose of this study is to evaluate the performance of ferumoxytol-enhanced MRA using a high-resolution 3D volumetric sequence (fe-SPGR) for visualizing and grading pediatric brain AVMs in comparison with CTA and DSA, which is the current imaging gold standard. METHODS In this retrospective cohort study, 21 patients with AVMs evaluated by fe-SPGR, CTA, and DSA between April 2014 and August 2017 were included. Two experienced raters graded AVMs using Spetzler-Martin criteria on all imaging studies. Lesion conspicuity (LC) and diagnostic confidence (DC) were assessed using a 5-point Likert scale, and interrater agreement was determined. The Kruskal-Wallis test was performed to assess the raters' grades and scores of LC and DC, with subsequent post hoc pairwise comparisons to assess for statistically significant differences between pairs of groups at p < 0.05. RESULTS Assigned Spetzler-Martin grades for AVMs on DSA, fe-SPGR, and CTA were not significantly different (p = 0.991). LC and DC scores were higher with fe-SPGR than with CTA (p < 0.05). A significant difference in LC scores was found between CTA and fe-SPGR (p < 0.001) and CTA and DSA (p < 0.001) but not between fe-SPGR and DSA (p = 0.146). A significant difference in DC scores was found among DSA, fe-SPGR, and CTA (p < 0.001) and between all pairs of the groups (p < 0.05). Interrater agreement was good to very good for all image groups (κ = 0.77-1.0, p < 0.001). CONCLUSIONS Fe-SPGR performed robustly in the diagnostic evaluation of brain AVMs, with improved visual depiction of AVMs compared with CTA and comparable Spetzler-Martin grading relative to CTA and DSA.

Use of Ultrasmall Superparamagnetic Iron Oxide Enhanced Susceptibility Weighted Imaging and Mean Vessel Density Imaging to Monitor Antiangiogenic Effects of Sorafenib on Experimental Hepatocellular Carcinoma

We investigated effectiveness of ultrasmall superparamagnetic iron oxide enhanced susceptibility weighted imaging (USPIO-enhanced SWI) and mean vessel density imaging (Q) in monitoring antiangiogenic effects of Sorafenib on orthotopic hepatocellular carcinoma (HCC). Thirty-five HCC xenografts were established. USPIO-enhanced SWI and Q were performed on a 1.5 T MR scanner at baseline, 7, 14, and 21 days after Sorafenib treatment. Intratumoral susceptibility signal intensity (ITSS) and Q were serially measured and compared between the treated (n = 15) and control groups (n = 15). Both ITSS and Q were significantly lower in the treated group at each time point (P < 0.05). Measurements in the treated group showed that ITSS persisted at 7 days (P = 0.669) and increased at 14 and 21 days (P < 0.05), while Q significantly declined at 7 days (P = 0.028) and gradually increased at 14 and 21 days. In the treated group, significant correlation was found between Q and histologic microvessel density (MVD) (r = 0.753, P < 0.001), and ITSS correlated well with MVD (r = 0.742, P = 0.002) after excluding the data from baseline. This study demonstrated that USPIO-enhanced SWI and Q could provide novel biomarkers for evaluating antiangiogenic effects of Sorafenib on HCC.

Free-breathing pediatric chest MRI: Performance of self-navigated golden-angle ordered conical ultrashort echo time acquisition

PURPOSE

To assess the feasibility and performance of conical k-space trajectory free-breathing ultrashort echo time (UTE) chest magnetic resonance imaging (MRI) versus four-dimensional (4D) flow and effects of 50% data subsampling and soft-gated motion correction.

MATERIALS AND METHODS

Thirty-two consecutive children who underwent both 4D flow and UTE ferumoxytol-enhanced chest MR (mean age: 5.4 years, range: 6 days to 15.7 years) in one 3T exam were recruited. From UTE k-space data, three image sets were reconstructed: 1) one with all data, 2) one using the first 50% of data, and 3) a final set with soft-gating motion correction, leveraging the signal magnitude immediately after each excitation. Two radiologists in blinded fashion independently scored image quality of anatomical landmarks on a 5-point scale. Ratings were compared using Wilcoxon rank-sum, Wilcoxon signed-ranks, and Kruskal-Wallis tests. Interobserver agreement was assessed with the intraclass correlation coefficient (ICC).

RESULTS

For fully sampled UTE, mean scores for all structures were ≥4 (good-excellent). Full UTE surpassed 4D flow for lungs and airways (P < 0.001), with similar pulmonary artery (PA) quality (P = 0.62). 50% subsampling only slightly degraded all landmarks (P < 0.001), as did motion correction. Subsegmental PA visualization was possible in >93% scans for all techniques (P = 0.27). Interobserver agreement was excellent for combined scores (ICC = 0.83).

CONCLUSION

High-quality free-breathing conical UTE chest MR is feasible, surpassing 4D flow for lungs and airways, with equivalent PA visualization. Data subsampling only mildly degraded images, favoring lesser scan times. Soft-gating motion correction overall did not improve image quality.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:200-209.

4D MUSIC CMR: value-based imaging of neonates and infants with congenital heart disease

BACKGROUND

4D Multiphase Steady State Imaging with Contrast (MUSIC) acquires high-resolution volumetric images of the beating heart during uninterrupted ventilation. We aim to evaluate the diagnostic performance and clinical impact of 4D MUSIC in a cohort of neonates and infants with congenital heart disease (CHD).

METHODS

Forty consecutive neonates and infants with CHD (age range 2 days to 2 years, weight 1 to 13 kg) underwent 3.0 T CMR with ferumoxytol enhancement (FE) at a single institution. Independently, two readers graded the diagnostic image quality of intra-cardiac structures and related vascular segments on FE-MUSIC and breath held FE-CMRA images using a four-point scale. Correlation of the CMR findings with surgery and other imaging modalities was performed in all patients. Clinical impact was evaluated in consensus with referring surgeons and cardiologists. One point was given for each of five key outcome measures: 1) change in overall management, 2) change in surgical approach, 3) reduction in the need for diagnostic catheterization, 4) improved assessment of risk-to-benefit for planned intervention and discussion with parents, 5) accurate pre-procedural roadmap.

RESULTS

All FE-CMR studies were completed successfully, safely and without adverse events. On a four-point scale, the average FE-MUSIC image quality scores were >3.5 for intra-cardiac structures and >3.0 for coronary arteries. Intra-cardiac morphology and vascular anatomy were well visualized with good interobserver agreement (r = 0.46). Correspondence between the findings on MUSIC, surgery, correlative imaging and autopsy was excellent. The average clinical impact score was 4.2 ± 0.9. In five patients with discordant findings on echo/MUSIC (n = 5) and catheter angiography/MUSIC (n = 1), findings on FE-MUSIC were shown to be accurate at autopsy (n = 1) and surgery (n = 4). The decision to undertake biventricular vs univentricular repair was amended in 2 patients based on FE-MUSIC findings. Plans for surgical approaches which would have involved circulatory arrest were amended in two of 28 surgical cases. In all 28 cases requiring procedural intervention, FE-MUSIC provided accurate dynamic 3D roadmaps and more confident risk-to-benefit assessments for proposed interventions.

CONCLUSIONS

FE-MUSIC CMR has high clinical impact by providing accurate, high quality, simple and safe dynamic 3D imaging of cardiac and vascular anatomy in neonates and infants with CHD. The findings influenced patient management in a positive manner.

A comprehensive literatures update of clinical researches of superparamagnetic resonance iron oxide nanoparticles for magnetic resonance imaging

This paper aims to update the clinical researches using superparamagnetic iron oxide (SPIO) nanoparticles as magnetic resonance imaging (MRI) contrast agent published during the past five years. PubMed database was used for literature search, and the search terms were (SPIO OR superparamagnetic iron oxide OR Resovist OR Ferumoxytol OR Ferumoxtran-10) AND (MRI OR magnetic resonance imaging). The literature search results show clinical research on SPIO remains robust, particularly fuelled by the approval of ferumoxytol for intravenously administration. SPIOs have been tested on MR angiography, sentinel lymph node detection, lymph node metastasis evaluation; inflammation evaluation; blood volume measurement; as well as liver imaging. Two experimental SPIOs with unique potentials are also discussed in this review. A curcumin-conjugated SPIO can penetrate brain blood barrier (BBB) and bind to amyloid plaques in Alzheime's disease transgenic mice brain, and thereafter detectable by MRI. Another SPIO was fabricated with a core of Fe3O4 nanoparticle and a shell coating of concentrated hydrophilic polymer brushes and are almost not taken by peripheral macrophages as well as by mononuclear phagocytes and reticuloendothelial system (RES) due to the suppression of non-specific protein binding caused by their stealthy ''brush-afforded'' structure. This SPIO may offer potentials for the applications such as drug targeting and tissue or organ imaging other than liver and lymph nodes.