BOOSTING SKULL-STRIPPING PERFORMANCE FOR PEDIATRIC BRAIN IMAGES

Skull-stripping is the removal of background and non-brain anatomical features from brain images. While many skull-stripping tools exist, few target pediatric populations. With the emergence of multi-institutional pediatric data acquisition efforts to broaden the understanding of perinatal brain development, it is essential to develop robust and well-tested tools ready for the relevant data processing. However, the broad range of neuroanatomical variation in the developing brain, combined with additional challenges such as high motion levels, as well as shoulder and chest signal in the images, leaves many adult-specific tools ill-suited for pediatric skull-stripping. Building on an existing framework for robust and accurate skull-stripping, we propose developmental SynthStrip (d-SynthStrip), a skull-stripping model tailored to pediatric images. This framework exposes networks to highly variable images synthesized from label maps. Our model substantially outperforms pediatric baselines across scan types and age cohorts. In addition, the <1-minute runtime of our tool compares favorably to the fastest baselines. We distribute our model at https://w3id.org/synthstrip.

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.

Developmental Factors That Predict Head Movement During Resting-State Functional Magnetic Resonance Imaging in 3-7-Year-Old Stuttering and Non-stuttering Children

Early childhood marks a period of dynamic neurocognitive development. Preschool-age coincides with the onset of many childhood disorders and is a developmental period that is frequently studied to determine markers of neurodevelopmental disorders. Magnetic resonance imaging (MRI) is often used to explore typical brain development and the neural bases of neurodevelopmental disorders. However, acquiring high-quality MRI data in young children is challenging. The enclosed space and loud sounds can trigger unease and cause excessive head movement. A better understanding of potential factors that predict successful MRI acquisition would increase chances of collecting useable data in children with and without neurodevelopmental disorders. We investigated whether age, sex, stuttering status, and childhood temperament as measured using the Child Behavioral Questionnaire, could predict movement extent during resting-state functional MRI (rs-fMRI) in 76 children aged 3–7 years, including 42 children who stutter (CWS). We found that age, sex, and temperament factors could predict motion during rs-fMRI scans. The CWS were not found to differ significantly from controls in temperament or head movement during scanning. Sex and age were significant predictors of movement. However, age was no longer a significant predictor when temperament, specifically effortful control, was considered. Controlling for age, boys with higher effortful control scores moved less during rs-fMRI procedures. Additionally, boys who showed higher negative affectivity showed a trend for greater movement. Considering temperament factors in addition to age and sex may help predict the success of acquiring useable rs-fMRI (and likely general brain MRI) data in young children in MR neuroimaging.

Numerical simulation of the radiofrequency safety of 128-channel hd-EEG nets on a 29-month-old whole-body model in a 3 Tesla MRI

This study investigates the radiofrequency (RF) induced heating in a pediatric whole-body voxel model with a high-density electroencephalogram (hd-EEG) net during magnetic resonance imaging (MRI) at 3 Tesla. A total of three cases were studied: no net (NoNet), a resistive hd-EEG (NeoNet), and a copper (CuNet) net. The maximum values of specific absorption rate averaged over 10g-mass (10gSAR) in the head were calculated with the NeoNet was 12.51 W/kg and in the case of the NoNet was 12.40 W/kg. In contrast, the CuNet case was 17.04 W/Kg. Temperature simulations were conducted to determine the RF-induced heating without and with hd-EEG nets (NeoNet and CuNet) during an MRI scan using an age-corrected and thermoregulated perfusion for the child model. The results showed that the maximum temperature estimated in the child's head was 38.38 °C for the NoNet, 38.43 °C for the NeoNet, and 43.05 °C for the CuNet. In the case of NeoNet, the maximum temperature estimated in the child's head remained compliant with IEC 60601 for the MRI RF safety limit. However, the case of CuNet estimated to exceed the RF safety limit, which may require an appropriate cooling period or a hardware design to suppress the RF-induced heating.

Predictors of Anesthetic Exposure in Pediatric MRI

BACKGROUND. Anesthetic exposure in children may impact long-term neurocognitive outcomes. Therefore, minimizing pediatric MRI scan time in children under anesthesia and the associated anesthetic exposure is necessary. OBJECTIVE. The purpose of this study was to evaluate pediatric MRI scan time as a predictor of total propofol dose, considering imaging and clinical characteristics as covariates. METHODS. Electronic health records were retrospectively searched to identify MRI examinations performed from 2016 to 2019 in patients 0-18 years old who received propofol anesthetic. Brain; brain and spine; brain and abdomen; and brain, head, and neck MRI examinations were included. Demographic, clinical, and imaging data were extracted for each examination, including anesthesia maintenance phase time, MRI scan time, and normalized propofol dose. MRI scan time and propofol dose were compared between groups using a t test. A multiple linear regression with backward selection (threshold, p < .05) was used to evaluate MRI scan time as a predictor of total propofol dose, adjusting for sex, age, time between scan and study end, body part, American Society of Anesthesiologists (ASA) classification, diagnosis, magnet strength, and IV contrast medium administration as covariates. RESULTS. A total of 501 examinations performed in 426 patients (172 girls, 254 boys; mean age, 6.55 ± 4.59 [SD] years) were included. Single body part examinations were shorter than multiple body part examinations (mean, 52.7 ± 18.4 vs 89.3 ± 26.4 minutes) and required less propofol (mean, 17.7 ± 5.7 vs 26.1 ± 7.7 mg/kg; all p < .001). Among single body part examinations, a higher ASA classification, oncologic diagnosis, 1.5-T magnet, and IV contrast medium administration were associated with longer MRI scan times (all p ≤ .009) and higher propofol exposure (all p ≤ .005). In multivariable analysis, greater propofol exposure was predicted by MRI scan time (mean dose per minute of examination, 0.178 mg/kg; 95% CI, 0.155-0.200; p < .001), multiple body part examination (p = .04), and IV contrast medium administration (p = .048); lower exposure was predicted by 3-T magnet (p = .04). CONCLUSION. Anesthetic exposure during pediatric MRI can be quantified and predicted based on imaging and clinical variables. CLINICAL IMPACT. This study serves as a valuable baseline for future efforts to reduce anesthetic doses and scan times in pediatric MRI.

Success of Nonsedated Neuroradiologic MRI in Children 1-7 Years Old

BACKGROUND. MRI use and the need for monitored anesthesia care (MAC) in children have increased. However, MAC is associated with examination delays, increased cost, and safety concerns. OBJECTIVE. The purpose of this study was to evaluate the success rate of nonsedated neuroradiologic MRI studies in children 1-7 years old and to investigate factors associated with success. METHODS. We retrospectively reviewed data from our institutional nonsedated MRI program. Inclusion criteria were outpatient nonsedated MRI referral, age 1-7 years old, and neuroradiologic indication. Exclusion criteria were MRI examinations for ventricular checks and contrast material use. Success was determined by reviewing the clinical MRI report. We recorded patient age and sex, type of MRI examination (brain, spine, craniospinal, head and neck, and brain with MRA), protocol length, presence of child life specialist, video goggle use, and MRI appointment time (routine daytime appointment or evening appointment). We used descriptive statistics to summarize patient demographics and clinical data and logistic regression models to evaluate predictors of success in the entire sample. Subset analyses were performed for children from 1 to < 3 years old and 3 to 7 years old. RESULTS. We analyzed 217 patients who underwent nonsedated MRI examinations (median age, 5.1 years). Overall success rate was 82.0% (n = 178). The success rates were 81.4% (n = 127) for brain, 90.3% (n = 28) for spine, 71.4% (n = 10) for craniospinal, 66.7% (n = 6) for head and neck, and 100% (n = 7) for brain with MRA. Age was significantly associated with success (odds ratio [OR], 1.33; p = .009). In children 1 to < 3 years old, none of the factors analyzed were significant predictors of success (all, p > .48). In children 3-7 years old, protocol duration (OR, 0.96; 95% CI, 0.93-0.99; p = .02) and video goggle use (OR, 6.38; 95% CI, 2.16-18.84; p = .001) were significantly associated with success. CONCLUSION. A multidisciplinary approach with age-appropriate resources enables a high success rate for nonsedated neuroradiologic MRI in children 1-7 years old. CLINICAL IMPACT. Using age as the primary criterion to determine the need for MAC may lead to overuse of these services. Dissemination of information regarding nonsedated MRI practice could reduce the rate of sedated MRI in young children.

The MRI Self-Efficacy Scale for Children: Development and Preliminary Psychometrics

OBJECTIVE

Magnetic resonance imaging (MRI) is a common procedure that can be distressing for children. Although not yet studied in the context of pediatric medical procedures, self-efficacy may be a good predictor of procedural stress and a clinically feasible target for behavioral intervention. The objectives of this study were to develop the MRI Self-Efficacy Scale for Children (MRI-SEC) and assess the preliminary psychometric properties.

METHODS

Development of the MRI-SEC was informed by literature searches and feedback from healthcare providers. Twenty child-parent dyads naïve to MRI and 10 child-parent dyads with MRI experience completed the MRI-SEC to assess the comprehensibility and ease of use, and to inform item and scale refinement. The final version includes four practice items and 12 items directly assessing MRI self-efficacy. To evaluate the psychometric properties, 127 children (ages 6-12) and parents naïve to MRI completed the MRI-SEC, and a series of measures to assess construct validity. To evaluate test-retest reliability 27 children completed the MRI-SEC a second time.

RESULTS

The MRI-SEC demonstrated acceptable internal consistency, test-retest reliability, and convergent validity.

CONCLUSION

Development of the MRI-SEC provides an opportunity to better understand the role of self-efficacy as a predictor of procedural stress and cooperation with MRI, informing reliable prediction of children who may benefit from additional support for MRI and the development of tailored behavioral interventions.

Retrospective correction of head motion using measurements from an electromagnetic tracker

PURPOSE

To investigate the feasibility of using an electromagnetic (EM) tracker to estimate rigid body head motion parameters, and using these measurements to retrospectively reduce motion artifacts.

THEORY AND METHODS

A clinically used MPRAGE sequence was modified to measure motion using the EM tracking system once per repetition time. A retrospective k-space based motion correction algorithm that corrects for phase ramps (translation in image domain) and rotation of 3D k-space (rotation in image domain) was developed, using the parameters recorded using an EM tracker. The accuracy of the EM tracker for the purpose of motion measurement and correction was tested in phantoms, volunteers, and pediatric patients.

RESULTS

Position localization was accurate to the order of 200 microns compared with registration localization in a phantom study. The quality of reconstructed images was assessed by computing the root mean square error, the structural similarity metric and average edge strength. Image quality improved consistently when motion correction was applied in both volunteer scans with deliberate head motion and in pediatric patient scans. In patients, the average edge strength improved significantly with retrospective motion correction, compared with images with no correction applied.

CONCLUSIONS

EM tracking was effective in measuring head motion in the MRI scanner with high accuracy, and enabled retrospective reconstruction to improve image quality by reducing motion artifacts.

3D printing with MRI in pediatric applications

3D printing (3DP) applications for clinical evaluation, preoperative planning, patient and trainee education, and simulation has increased in the past decade. Most of the applications are found in cardiovascular, head and neck, orthopedic, neurological, urological, and oncological surgical cases. This review has three parts. The first part discusses the technical pathway to realizing a physical model, 3DP considerations in pediatric MRI image acquisition, data and resolution requirements, and related structural segmentation and postprocessing steps needed to generalize both virtual and physical models. Standard practices and processing software used in these processes will be assessed. The second part discusses complementary examples in pediatric applications, including cases from cardiology, neuroradiology, neurology, and neurosurgery, head and neck, orthopedics, pelvic and urological applications, oncological applications, and fetal imaging. The third part explores other 3D printing applications and considerations such as using 3DP to develop tissue-specific phantoms and devices for testing in the MR environment, to educate patients and their families, to train clinicians and students, and facility requirements for building a 3DP program. Level of Evidence: 5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2020;51:1641-1658.

Robust kidney perfusion mapping in pediatric chronic kidney disease using single-shot 3D-GRASE ASL with optimized retrospective motion correction

PURPOSE

To develop a robust renal arterial spin labeling (ASL) acquisition and processing strategy for mapping renal blood flow (RBF) in a pediatric cohort with severe kidney disease.

METHODS

A single-shot background-suppressed 3D gradient and spin-echo (GRASE) flow-sensitive alternating inversion recovery (FAIR) ASL acquisition method was used to perform 2 studies. First, an evaluation of the feasibility of single-shot 3D-GRASE and retrospective noise reduction methods was performed in healthy volunteers. Second, a pediatric cohort with severe chronic kidney disease underwent single-shot 3D-GRASE FAIR ASL and RBF was quantified following several retrospective motion correction pipelines, including image registration and threshold-free weighted averaging. The effect of motion correction on the fit errors of saturation recovery (SR) images (required for RBF quantification) and on the perfusion-weighted image (PWI) temporal signal-to-noise ratio (tSNR) was evaluated, as well as the intra- and inter-session repeatability of renal longitudinal relaxation time (T₁ ) and RBF.

RESULTS

The mean cortical and/or functional renal parenchyma RBF in healthy volunteers and CKD patients was 295 ± 97 and 95 ± 47 mL/100 g/min, respectively. Motion-correction reduced image artefacts in both T₁ and RBF maps, significantly reduced SR fit errors, significantly increased the PWI tSNR and improved the improved the repeatability of T₁ and RBF in the pediatric patient cohort.

CONCLUSION

Single-shot 3D-GRASE ASL combined with retrospective motion correction enabled repeatable non-invasive RBF mapping in the first pediatric cohort with severe kidney disease undergoing ASL scans.

Accelerated ferumoxytol-enhanced 4D multiphase, steady-state imaging with contrast enhancement (MUSIC) cardiovascular MRI: validation in pediatric congenital heart disease

The purpose of this work was to validate a parallel imaging (PI) and compressed sensing (CS) combined reconstruction method for a recently proposed 4D non-breath-held, multiphase, steady-state imaging technique (MUSIC) cardiovascular MRI in a cohort of pediatric congenital heart disease patients. We implemented a graphics processing unit accelerated CS-PI combined reconstruction method and applied it in 13 pediatric patients who underwent cardiovascular MRI after ferumoxytol administration. Conventional breath-held contrast-enhanced magnetic resonance angiography (CE-MRA) was first performed during the first pass of ferumoxytol injection, followed by the original MUSIC and the proposed CS-PI MUSIC during the steady-state distribution phase of ferumoxytol. Qualities of acquired images were then evaluated using a four-point scale. Left ventricular volumes and ejection fractions calculated from the original MUSIC and the CS-PI MUSIC were also compared with conventional multi-slice 2D cardiac cine MRI. The proposed CS-PI MUSIC reduced the imaging time of the MUSIC acquisition to 4.6 ± 0.4 min from 8.9 ± 1.2 min. Computationally intensive image reconstruction was completed within 5 min without interruption of sequential clinical scans. The proposed method (mean 3.3-4.0) provided image quality comparable to that of the original MUSIC (3.2-4.0) (all P ≥ 0.42), and better than conventional breath-held first-pass CE-MRA (1.1-3.3) for 13 anatomical structures (all P ≤ 0.0014) with good inter-observer agreement (κ > 0.46). The calculated ventricular volumes and ejection fractions from both original MUSIC (r > 0.90) and CS-PI MUSIC (r > 0.85) correlated well with 2D cine imaging. In conclusion, PI and CS were successfully incorporated into the 4D MUSIC acquisition to further reduce scan time by approximately 50% while maintaining highly comparable image quality in a clinically practical reconstruction time.

Pediatric whole-body MRI: A review of current imaging techniques and clinical applications

There are many congenital, neoplastic, inflammatory, and infectious processes in the pediatric patient for which whole-body imaging may be of benefit diagnostically and prognostically. With recent improvements in magnetic resonance imaging (MRI) hardware and software and resultant dramatically reduced scan times, imaging of the whole body with MRI has become a much more practicable technique in children. Whole-body MRI can provide a high level of soft tissue and skeletal detail while avoiding the exposure to ionizing radiation inherent to computed tomography and nuclear medicine imaging techniques. This article reviews the more common current whole-body MRI techniques in children and the primary pathologies for which this imaging modality may be most useful to the radiologists and referring clinicians. J. MAGN. RESON. IMAGING 2016;44:783-793.

Four-dimensional, multiphase, steady-state imaging with contrast enhancement (MUSIC) in the heart: a feasibility study in children

PURPOSE

To develop a technique for high resolution, four-dimensional (4D), multiphase, steady-state imaging with contrast enhancement (MUSIC) in children with complex congenital heart disease.

METHODS

Eight pediatric patients underwent cardiovascular MRI with controlled mechanical ventilation after ferumoxytol administration. Breath-held contrast-enhanced MRA (CE-MRA) was performed during the first-pass and delayed phases of ferumoxytol, followed by a respiratory gated, 4D MUSIC acquisition during the steady state distribution phase of ferumoxytol. The subjective image quality and image sharpness were evaluated. Assessment of ventricular volumes based on 4D MUSIC was compared with those based on multislice 2D cardiac cine MRI.

RESULTS

The 4D MUSIC technique provided cardiac-phase-resolved (65-95 ms temporal resolution) and higher spatial resolution (0.6-0.9 mm isotropic) images than previously achievable using first-pass CE-MRA or 2D cardiac cine. When compared with Ferumoxytol-based first-pass CE-MRA, the 4D MUSIC provided sharper images and better definition of the coronary arteries, aortic root, myocardium, and pulmonary trunk (P < 0.05 for all). The ventricular volume measurements were in good agreement between 4D MUSIC and 2D cine (concordance correlation coefficient >0.95).

CONCLUSION

The 4D MUSIC technique may represent a new paradigm in MR evaluation of cardiovascular anatomy and function in children with complex congenital heart disease.

A semiflexible 64-channel receive-only phased array for pediatric body MRI at 3T

PURPOSE

To design, construct, and validate a semiflexible 64-channel receive-only phased array for pediatric body MRI at 3T.

METHODS

A 64-channel receive-only phased array was developed and constructed. The designed flexible coil can easily conform to different patient sizes with nonoverlapping coil elements in the transverse plane. It can cover a field of view of up to 44 × 28 cm(2) and removes the need for coil repositioning for body MRI patients with multiple clinical concerns. The 64-channel coil was compared with a 32-channel standard coil for signal-to-noise ratio and parallel imaging performances on different phantoms. With IRB approval and informed consent/assent, the designed coil was validated on 21 consecutive pediatric patients.

RESULTS

The pediatric coil provided higher signal-to-noise ratio than the standard coil on different phantoms, with the averaged signal-to-noise ratio gain at least 23% over a depth of 7 cm along the cross-section of phantoms. It also achieved better parallel imaging performance under moderate acceleration factors. Good image quality (average score 4.6 out of 5) was achieved using the developed pediatric coil in the clinical studies.

CONCLUSION

A 64-channel semiflexible receive-only phased array has been developed and validated to facilitate high quality pediatric body MRI at 3T. Magn Reson Med 76:1015-1021, 2016. © 2015 Wiley Periodicals, Inc.

Safety and efficacy of gadobutrol-enhanced MRI in patients aged under 2 years-a single-center, observational study

Gadobutrol is a 1-molar gadolinium-based contrast agent with well-characterized safety and efficacy for magnetic resonance imaging (MRI) in adults and children ≥ 2 years old. This observational study assessed gadobutrol-enhanced MRI in children < 2 years of age. Sixty infants (mean age 11.1 months) underwent MRI using gadobutrol at standard dose of 0.1 mL/kg (0.1 mmol/kg) body weight. MRI examinations included brain, spine, and neck (n = 24), subcutaneous soft tissues (n = 14), chest, abdomen, and pelvis (n = 12), musculoskeletal system (n = 7) and vascular system (n = 3). No patients experienced adverse events related to gadobutrol injection. In 57 patients with confirmed diagnoses, gadobutrol-enhanced MRI provided findings consistent with confirmed pathologies. This study indicates that gadobutrol at a standard dose for MRI is safe in patients aged < 2 years and provides diagnostic information for multiple pathologies.