Magnetic Resonance Imaging for the Evaluation of Pulmonary Embolism

Systematic review and meta-analysis of magnetic resonance imaging in the diagnosis of pulmonary embolism

BACKGROUND

Pulmonary embolism is a significant clinical challenge with high mortality risk. Computed Tomography Pulmonary Angiography (CTPA) is the gold standard for diagnosis but involves radiation risks. Magnetic Resonance Imaging (MRI) offers a radiation-free alternative, yet its adoption is hindered by inconsistent validation of its diagnostic accuracy. This study systematically assesses MRI's efficacy in diagnosing pulmonary embolism, incorporating a broad range of literature to ensure comprehensive analysis.

METHODS

Relevant studies on the diagnostic use of MRI for pulmonary embolism were collected through computer searches of PubMed, Embase, Cochrane Library, Web of Science, China National Knowledge Infrastructure (CNKI), Wanfang Database, VIP Database, and China Biology Medicine disc (CBM) databases up to May 12, 2024. Literature was screened based on inclusion and exclusion criteria, data extracted, and study quality assessed according to Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) standards. Data analysis was performed using Stata (versions 17.0 and 14.0) and Meta-Disc 1.4 software. Stata software was used to calculate pooled sensitivity, pooled specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio, and to plot forest plots, hierarchical summary receiver operating characteristic (HSROC) curves, and summary receiver operating characteristic (SROC) curves. The area under the SROC curve (AUC) was calculated, and publication bias was assessed through Deek's funnel plot, Egger's test, and Begg's test.

RESULTS

Eighteen articles involving 1,264 participants were included. The meta-analysis showed that MRI for the diagnosis of pulmonary embolism had a pooled sensitivity of 0.89 (95% CI: 0.79-0.94) and a specificity of 0.94 (95% CI: 0.89-0.97). The pooled positive likelihood ratio was 14.6 (95% CI: 8.0-26.7) and the negative likelihood ratio was 0.12 (95% CI: 0.06-0.23). The diagnostic odds ratio was 121 (95% CI: 49-299). The AUC of the SROC was 0.97. Deek's funnel plot suggested potential publication bias in the studies included.

CONCLUSION

MRI exhibits high sensitivity and specificity in the diagnosis of pulmonary embolism, demonstrating excellent diagnostic efficacy. Despite potential publication bias, MRI continues to show strong potential for clinical application.

Gadopiclenol Enables Reduced Gadolinium Dose While Maintaining Quality of Pulmonary Arterial Enhancement for Pulmonary MRA: An Opportunity for Improved Safety and Sustainability

RATIONALE AND OBJECTIVES

Pulmonary magnetic resonance angiography (MRA) is an imaging method with proven utility for the exclusion of pulmonary embolism and avoids the need for ionizing radiation and iodinated contrast agents. High-relaxivity gadolinium-based contrast agents (GBCAs), such as gadopiclenol, can be used to reduce the required gadolinium dose for pulmonary MRA. The aim of this study was to compare the contrast enhancement performance of gadopiclenol with an established gadobenate dimeglumine-enhanced pulmonary MRA protocol.

MATERIALS AND METHODS

In this retrospective single-center study, data from 152 patients who underwent pulmonary MRA at 1.5 T were analyzed. Imaging was performed with either 0.05 mmol/kg gadopiclenol (n = 75) or 0.1 mmol/kg gadobenate dimeglumine (n = 77), using dedicated multiphasic imaging protocols with precontrast, pulmonary arterial phase, immediate delayed phase, and a low flip-angle T1-weighted spoiled gradient echo acquisition. Subjective image quality evaluation was performed blinded by 2 radiologists on a 5-point Likert scale. For the estimation of interrater reliability, Cohen weighted κ was calculated. For semiquantitative assessment, signal intensities were measured in the pulmonary arteries, and relative signal enhancement was calculated. Data from groups were compared with Mann-Whitney U tests using Bonferroni corrections.

RESULTS

Signal enhancement relative to precontrast in the first-pass pulmonary arterial phase was higher with 0.05 mmol/kg gadopiclenol compared with 0.1 mmol/kg gadobenate dimeglumine (20.0-fold ± 5.6-fold vs 17.8-fold ± 5.8-fold; P = 0.015). Readers observed no difference in subjective rating in terms of intravascular contrast, peripheral vessel depiction, and diagnostic confidence with substantial interrater reliability (Cohen κ = 0.73 [95% confidence interval: 0.57-0.89], 0.65 [0.55-0.75], and 0.74 [0.65-0.84], all P's < 0.001). No severe adverse events were recorded for any clinical MRA examination.

CONCLUSIONS

The high-relaxivity contrast agent gadopiclenol can facilitate a reduction in gadolinium dose by 50% without compromising contrast enhancement for pulmonary MRA. This approach may enhance the safety and sustainability of pulmonary MRA in the long term.

MRA as the Preferred Test for Pulmonary Embolism During the Iodinated Contrast Media Shortage of 2022: A Single-Center Experience

BACKGROUND. Closure of a GE Healthcare facility in Shanghai, China, in 2022 disrupted the iodinated contrast media supply. Technologic advances have addressed limitations associated with the use of pulmonary MRA for diagnosis of pulmonary embolism (PE). OBJECTIVE. The purpose of this study was to describe a single institution's experience in the use of pulmonary MRA as an alternative to CTA for the diagnosis of PE in the general population during the iodinated contrast media shortage in 2022. METHODS. This retrospective single-center study included all CTA and MRA examinations performed to exclude PE from April 1 through July 31 (18 weekly periods) in 2019 (before the COVID-19 pandemic and contrast media shortage), 2021 (during the pandemic but before the shortage), and 2022 (during both the pandemic and the shortage). From early May through mid-July of 2022, MRA served as the preferred test for PE diagnosis, to preserve iodinated contrast media. CTA and MRA reports were reviewed. The total savings in iodinated contrast media volume resulting from preferred use of MRA was estimated. RESULTS. The study included 4491 examinations of 4006 patients (mean age, 57 ± 18 [SD] years; 1715 men, 2291 women): 1245 examinations (1111 CTA, 134 MRA) in 2019, 1547 examinations (1403 CTA, 144 MRA) in 2021, and 1699 examinations (1282 CTA, 417 MRA) in 2022. In 2022, the number of MRA examinations was four (nine when normalized to a 7-day period) in week 1, and this number increased to a maximum of 63 in week 10 and then decreased to 10 in week 18. During weeks 8-11, more MRA examinations (range, 45-63 examinations) than CTA examinations (range, 27-46 examinations) were performed. In 2022, seven patients with negative MRA underwent subsequent CTA within 2 weeks; CTA was negative in all cases. In 2022, 13.9% of CTA examinations (vs 10.3% of MRA examinations) were reported as having limited image quality. The estimated 4-month savings resulting from preferred use of MRA in 2022, under the assumption of uniform simple linear growth in CTA utilization annually and a CTA dose of 1 mL/kg, was 27 L of iohexol (350 mg I/mL). CONCLUSION. Preferred use of pulmonary MRA for PE diagnosis in the general population helped to conserve iodinated contrast media during the 2022 shortage. CLINICAL IMPACT. This single-center experience shows pulmonary MRA to be a practical substitute for pulmonary CTA in emergency settings.

Normal placental structural anatomy: ultrasound and doppler features elucidated with US-MR image fusion and ferumoxytol-enhanced MRI

PURPOSE

To elucidate ultrasound features of normal placental anatomy through correlation of gray-scale and ultrasound Doppler with ferumoxytol-enhanced MRI features using US-MR image fusion.

METHODS

All patients referred to MR for ultrasound findings worrisome for PAS (placenta accreta spectrum) were included in this retrospective study. MR studies included a ferumoxytol-enhanced T1-weighted MRI. Ultrasound imaging included gray-scale, color Doppler, power Doppler, and spectral Doppler techniques. After the MR, US-MRI fusion was performed by co-registering a MR acquisition to real-time US, which allowed precise, point-to-point correlation of placental features.

RESULTS

Fourteen patients at risk for PAS were studied using the US-MR image fusion. At delivery, there were six cases without PAS (gestational age range: 24 weeks 3 days to 34 weeks 0 days), and these composed the study cohort. Placental features that were on high signal intensity on post-ferumoxytol acquisitions represent spaces with maternal blood flow and corresponded to hypoechoic areas on ultrasound created by a paucity of reflective interfaces (villi). Color and spectral Doppler allowed the separation of maternal and fetal circulations in individual perfusional domains and demonstrated spiral artery inflow, circulation around the villous tree, and return of blood flow to the basal plate. Recognizable histopathologic features by ultrasound included the central cavity, villous tree, and venous return channels.

CONCLUSION

Internal placental architecture can be discerned on ultrasound. This anatomy can be correlated and confirmed with ferumoxytol-MR through US-MR fusion. Understanding this structural anatomy on ultrasound could serve as a basis to identify normal and abnormal placental features.

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

INTRODUCTION

Placental function is vitally important, but placental assessment is limited by current imaging methods in vivo. The goal of this study is to determine if ferumoxytol-enhanced MR studies might be used to depict placental structure during pregnancy.

METHODS

Ten pregnant women were referred for MRI evaluation of abnormal placentation. The study group was composed five of these patients whose placentas were normal at pathology. MR studies consisted of pre-contrast SSFSE (single-shot fast spin-echo), SSFP (steady-state free procession), diffusion, and ferumoxytol-enhanced acquisitions. The post-contrast sequences were compared to pre-contrast SSFSE, SSFP, and diffusion acquisitions for features of correspondence. MR images were also compared to histopathology for anatomic landmarks including the three-ring pattern of the functional vascular exchange unit (the placentone) created by this central cavity surrounded by a ring of clustered villi, and an outer ring of dispersed villi corresponding to the maternal venous outflow channel. The measured sizes of these features on MR were compared to reported sizes.

RESULTS

Post-ferumoxytol images showed enhancement of the maternal blood within the placenta, notably the intervillous space and the myometrial vessels. The unenhanced fetal vessels were most visible on the MinIP (minimum intensity projection) images; the enhanced maternal vessels were most visible on the MIP (maximum intensity projection) images. Composite MIP/MinIP images show the relation of maternal and fetal circulations. The signal intensities replicate the relative contributions from enhanced maternal blood and unenhanced chorionic villi.

DISCUSSION

Ferumoxytol-enhanced MR imaging can depict the internal anatomy of the placenta in vivo of clarity and detail. This could represent a new diagnostic approach to placental disorders.

Pediatric Pulmonary Embolism: Imaging Guidelines and Recommendations

In contrast with the algorithms and screening criteria available for adults with suspected pulmonary embolism, there is a paucity of guidance on the diagnostic approach for children. The incidence of pulmonary embolism in the pediatric population and young adults is higher than thought, and there is an urgent need for updated guidelines for the imaging approach to diagnosis in the pediatric population. This article presents an up-to-date review of imaging techniques, characteristic radiologic findings, and an evidence-based algorithm for the detection of pediatric pulmonary embolism to improve the care of pediatric patients with suspected pulmonary embolism.

Acute pulmonary embolism multimodality imaging prior to endovascular therapy

The manuscript discusses the application of CT pulmonary angiography, ventilation–perfusion scan, and magnetic resonance angiography to detect acute pulmonary embolism and to plan endovascular therapy. CT pulmonary angiography offers high accuracy, speed of acquisition, and widespread availability when applied to acute pulmonary embolism detection. This imaging modality also aids the planning of endovascular therapy by visualizing the number and distribution of emboli, determining ideal intra-procedural catheter position for treatment, and signs of right heart strain. Ventilation–perfusion scan and magnetic resonance angiography with and without contrast enhancement can also aid in the detection and pre-procedural planning of endovascular therapy in patients who are not candidates for CT pulmonary angiography.

Magnetic resonance angiography for the primary diagnosis of pulmonary embolism: A review from the international workshop for pulmonary functional imaging

Pulmonary contrast enhanced magnetic resonance angiography (CE-MRA) is useful for the primary diagnosis of pulmonary embolism (PE). Many sites have chosen not to use CE-MRA as a first line of diagnostic tool for PE because of the speed and higher efficacy of computerized tomographic angiography (CTA). In this review, we discuss the strengths and weaknesses of CE-MRA and the appropriate imaging scenarios for the primary diagnosis of PE derived from our unique multi-institutional experience in this area. The optimal patient for this test has a low to intermediate suspicion for PE based on clinical decision rules. Patients in extremis are not candidates for this test. Younger women (< 35 years of age) and patients with iodinated contrast allergies are best served by using this modality We discuss the history of the use of this test, recent technical innovations, artifacts, direct and indirect findings for PE, ancillary findings, and the effectiveness (patient outcomes) of CE-MRA for the exclusion of PE. Current outcomes data shows that CE-MRA and NM V/Q scans are effective alternative tests to CTA for the primary diagnosis of PE.