Ferumoxytol-enhanced magnetic resonance imaging with volume rendering: A new approach for the depiction of internal placental structure in vivo

Longitudinal Placental Blood Volume Measurements in Zika-Infected Rhesus Macaques Using Ferumoxytol Enhanced MRI

Introduction

Measures of maternal fractional blood volume (mFBV) in the placenta holds potential to diagnose placental vasculature deficiencies. However, methods for quantitative mapping of blood volume are challenging to implement for clinical placenta evaluation. As a preliminary step towards human applications, this study assesses the feasibility of blood volume measurements using ferumoxytol enhanced variable flip angle (VFA) T1-mapping in Zika-infected rhesus macaques.

Methods

Seven pregnant rhesus macaques were imaged longitudinally at up to 3 timepoints across gestation (days 64.5±1.9, 100.8±3.9, and 145.3±1.8), corresponding to first, second, and third pregnancy trimester of the rhesus. Four animals received a Zika virus (ZIKV) injection into the amniotic fluid, while three control rhesus macaques received a saline injection. T1-weighted spoiled gradient echo sequences at four flip angles (2°, 6°, 10°, 14°) were used for quantitative mFBV assessment derived from pre- and post-contrast T1 mapping using ferumoxytol. Image quality assessment and segmentation assessment was performed on the full 3D coverage. Placental histopathology for all animals was analyzed by a professional pathologist with over 15 years of experience.

Results

All scans were successfully acquired and analyzed with no significant motion artifacts. 3D mFBV maps show regional heterogeneities within slices. FBV and total placental blood volume has an increasing trend with gestation.

Discussion

This study shows feasibilities to measure mFBV in non-human primates using ferumoxytol enhanced VFA T1-mapping.

Ferumoxytol-enhanced MRI of retroplacental clear space disruption in placenta accreta spectrum

INTRODUCTION

Placenta accreta spectrum (PAS) occurs when the placenta is pathologically adherent to the myometrium. An intact retroplacental clear space (RPCS) is a marker of normal placentation. In this study, we investigate use of the FDA-approved iron supplement ferumoxytol for contrast-enhanced MRI of the RPCS in mouse models of normal pregnancy and PAS. We then demonstrate the translational potential of this technique in human patients (n = 6) presenting with severe PAS (FIGO Grade 3C), moderate PAS (FIGO Grade 1), and no PAS.

METHODS

T1-weighted sequences were used to determine the optimal dose of ferumoxytol in pregnant mice. Pregnant Gab3-/- mice which demonstrate adherent placentation were imaged alongside wild-type (WT) pregnant mice with non-adherent placentation. Fe-MRI was also performed in 6 pregnant subjects using standard T1 and T2 weighted sequences and a 3D magnetic resonance angiography (MRA) sequence.

RESULTS

Ferumoxytol administered at 5 mg/kg led to strong placental enhancement in Fe-MRI images. Gab3-/- mice demonstrated loss of the hypointense region characteristic of the RPCS relative to WT mice. In human patients, Fe-MRI enabled high uteroplacental vasculature signal and quantification of the volume and signal profile in severe and moderate invasion of the placenta relative to non-PAS cases.

DISCUSSION

Ferumoxytol, an FDA-approved iron oxide nanoparticle formulation, enabled T1w MRI visualization of abnormal vascularization and loss of uteroplacental interface in a murine model of PAS. The potential of this non-invasive visualization technique was then further demonstrated in human subjects and suggests the possibility of PAS diagnosis using contrast enhanced MRI.

Cotyledon-Specific Flow Evaluation of Rhesus Macaque Placental Injury Using Ferumoxytol Dynamic Contrast-Enhanced MRI

BACKGROUND

Recently, dynamic contrast-enhanced (DCE) MRI with ferumoxytol as contrast agent has recently been introduced for the noninvasive assessment of placental structure and function throughout. However, it has not been demonstrated under pathological conditions.

PURPOSE

To measure cotyledon-specific rhesus macaque maternal placental blood flow using ferumoxytol DCE MRI in a novel animal model for local placental injury.

STUDY TYPE

Prospective animal model.

SUBJECTS

Placental injections of Tisseel (three with 0.5 mL and two with 1.5 mL), monocyte chemoattractant protein 1 (three with 100 μg), and three with saline as controls were performed in a total of 11 rhesus macaque pregnancies at approximate gestational day (GD 101). DCE MRI scans were performed prior (GD 100) and after (GD 115 and GD 145) the injection (term = GD 165).

FIELD STRENGTH/SEQUENCE

3 T, T1-weighted spoiled gradient echo sequence (product sequence, DISCO).

ASSESSMENT

Source images were inspected for motion artefacts from the mother or fetus. Placenta segmentation and DCE processing were performed for the dynamic image series to measure cotyledon specific volume, flow, and normalized flow. Overall placental histopathology was conducted for controls, Tisseel, and MCP-1 animals and regions of tissue infarctions and necrosis were documented. Visual inspections for potential necrotic tissue were conducted for the two Tisseelx3 animals.

STATISTICAL TESTS

Wilcoxon rank sum test, significance level P < 0.05.

RESULTS

No motion artefacts were observed. For the group treated with 1.5 mL of Tisseel, significantly lower cotyledon volume, flow, and normalized flow per cotyledon were observed for the third gestational time point of imaging (day ~145), with mean normalized flow of 0.53 minute-1. Preliminary histopathological analysis shows areas of tissue necrosis from a selected cotyledon in one Tisseel-treated (single dose) animal and both Tisseelx3 (triple dose) animals.

DATA CONCLUSION

This study demonstrates the feasibility of cotyledon-specific functional analysis at multiple gestational time points and injury detection in a placental rhesus macaque model through ferumoxytol-enhanced DCE MRI.

LEVEL OF EVIDENCE

NA TECHNICAL EFFICACY: Stage 2.

MR Imaging of Placenta Accreta Spectrum: A Comprehensive Literature Review of the Most Recent Advancements

This article delves into the latest MR imaging developments dedicated to diagnosing placenta accreta spectrum (PAS). PAS, characterized by abnormal placental adherence to the uterine wall, is of paramount concern owing to its association with maternal morbidity and mortality, particularly in high-risk pregnancies featuring placenta previa and prior cesarean sections. Although ultrasound (US) remains the primary screening modality, limitations have prompted heightened emphasis on MR imaging. This review underscores the utility of quantitative MR imaging, especially where US findings prove inconclusive or when maternal body habitus poses challenges, acknowledging, however, that interpreting placenta MR imaging demands specialized training for radiologists.