Fetal MRI and prenatal diagnosis of congenital heart defects
Authors: Jimmy Espinoza
Journal: The Lancet (2019)

Congenital anomalies are among the leading causes of infant mortality in developed countries.1Petrini J Damus K Russell R Poschman K Davidoff MJ Mattison D Contribution of birth defects to infant mortality in the United States.Teratology. 2002; 66: S3-S6Crossref PubMed Scopus (112) Google Scholar Mortality associated with congenital heart defects is decreasing; however, it remains unacceptably high.2Gilboa SM Salemi JL Nembhard WN Fixler DE Correa A Mortality resulting from congenital heart disease among children and adults in the United States, 1999 to 2006.Circulation. 2010; 122: 2254-2263Crossref PubMed Scopus (383) Google Scholar The conventional approach for prenatal diagnosis of congenital heart defects is two-dimensional (2D) fetal echocardiography. Using this approach, one group3van Velzen CL Clur SA Rijlaarsdam ME et al.Prenatal detection of congenital heart disease—results of a national screening programme.BJOG. 2016; 123: 400-407Crossref PubMed Scopus (127) Google Scholar reported a significant increase in the detection of congenital heart defects (from 35·8% to 59·7%) after the introduction of a national screening programme. Over the past decade, the use of three-dimensional (3D) and four-dimensional (4D) fetal echocardiography has been introduced into clinical practice as a strategy to facilitate 2D fetal echocardiography, with the hope of increasing detection of congenital heart defects,4Espinoza J Contemporary clinical applications of spatio-temporal image correlation in prenatal diagnosis.Curr Opin Obstet Gynecol. 2011; 23: 94-102Crossref PubMed Scopus (23) Google Scholar particularly with the use of algorithms that are intended to reduce operator dependency.5DeVore GR Polanco B Sklansky MS Platt LD The "spin" technique: a new method for examination of the fetal outflow tracts using three-dimensional ultrasound.Ultrasound Obstet Gynecol. 2004; 24: 72-82Crossref PubMed Scopus (129) Google Scholar, 6Goncalves LF Espinoza J Romero R et al.Four-dimensional fetal echocardiography with spatiotemporal image correlation (STIC): a systematic study of standard cardiac views assessed by different observers.J Matern Fetal Neonatal Med. 2005; 17: 323-331Crossref PubMed Scopus (46) Google Scholar, 7Espinoza J Romero R Kusanovic JP et al.Standardized views of the fetal heart using four-dimensional sonographic and tomographic imaging.Ultrasound Obstet Gynecol. 2008; 31: 233-242Crossref PubMed Scopus (17) Google Scholar, 8Abuhamad A Falkensammer P Reichartseder F Zhao Y Automated retrieval of standard diagnostic fetal cardiac ultrasound planes in the second trimester of pregnancy: a prospective evaluation of software.Ultrasound Obstet Gynecol. 2008; 31: 30-36Crossref PubMed Scopus (59) Google Scholar However, all of these efforts are substantially hindered by the inherent limitations of an imaging technique that relies on acoustic windows that are frequently obscured by maternal or fetal anatomic structures or motion artifacts. Moreover, volume datasets obtained with 3D and 4D ultrasonography are non-isotropic, which limits the image resolution in sonographic planes perpendicular to the original plane of volume acquisition, thus limiting their diagnostic value. In The Lancet, David Lloyd and colleagues9Lloyd DFA Pushparajah K Simpson JM et al.Three-dimensional visualisation of the fetal heart using prenatal MRI with motion-corrected slice-volume registration: a prospective, single-centre cohort study.Lancet. 2019; (published online March 22.)http://dx.doi.org/10.1016/S0140-6736(18)32490-5Summary Full Text Full Text PDF PubMed Scopus (57) Google Scholar now show that novel computational techniques coupled with fetal MRI imaging have the potential to overcome some of the limitations of prenatal ultrasonography in the diagnosis of congenital heart defects. Lloyd and colleagues9Lloyd DFA Pushparajah K Simpson JM et al.Three-dimensional visualisation of the fetal heart using prenatal MRI with motion-corrected slice-volume registration: a prospective, single-centre cohort study.Lancet. 2019; (published online March 22.)http://dx.doi.org/10.1016/S0140-6736(18)32490-5Summary Full Text Full Text PDF PubMed Scopus (57) Google Scholar report the results of a study involving 85 fetuses, in which they used a novel reconstruction algorithm based on 2D MRI data to produce a high-resolution (0·50–0·75mm isotropic) 3D volume dataset of the fetal thorax. Notably, the algorithm used by the authors allowed for correction of fetal motion artifacts. The authors then used the 3D volume datasets obtained from MRI images to compare 2D ultrasound images in fetuses with normal and abnormal cardiovascular structures, with good inter-observer agreement across both methods (intraclass correlation coefficient 0·92, 95% CI 0·89–0·95 for echocardiography; 0·94, 0·92–0·96 for MRI). There was also good agreement when measurements of cardiovascular structures were compared between 2D ultrasonography and those obtained from reconstructed 3D datasets obtained from 2D MRI data (0·78, 0·68–0·84). The authors show that high-resolution 3D imaging of the fetal cardiovascular system can be obtained with the proposed algorithm, which could be complementary to fetal echocardiography. To support this hypothesis, the authors reported that in ten cases, MRI-reconstructed datasets allowed for the identification of anatomical features that had not been previously described using ultrasonography. In 4D fetal echocardiography, volume datasets obtained with spatiotemporal image correction can be compared with blocks of pathological specimens in which the information obtained from the tissue embedded depends on the level and orientation that the paraffin block is cut. Similarly, in 4D volume datasets of the fetal heart, all the information of the area of interest is contained in a virtual volume (provided that the volume dataset contains good image quality). When slicing a virtual volume in 4D fetal echocardiography the operator can choose to assess dynamic cine loops or to freeze the image in a specific part of the cardiac cycle for analysis. To facilitate navigation in 4D-volume datasets of the fetal heart, several algorithms have been published with optimal results in selected volume datasets.5DeVore GR Polanco B Sklansky MS Platt LD The "spin" technique: a new method for examination of the fetal outflow tracts using three-dimensional ultrasound.Ultrasound Obstet Gynecol. 2004; 24: 72-82Crossref PubMed Scopus (129) Google Scholar, 6Goncalves LF Espinoza J Romero R et al.Four-dimensional fetal echocardiography with spatiotemporal image correlation (STIC): a systematic study of standard cardiac views assessed by different observers.J Matern Fetal Neonatal Med. 2005; 17: 323-331Crossref PubMed Scopus (46) Google Scholar, 7Espinoza J Romero R Kusanovic JP et al.Standardized views of the fetal heart using four-dimensional sonographic and tomographic imaging.Ultrasound Obstet Gynecol. 2008; 31: 233-242Crossref PubMed Scopus (17) Google Scholar, 8Abuhamad A Falkensammer P Reichartseder F Zhao Y Automated retrieval of standard diagnostic fetal cardiac ultrasound planes in the second trimester of pregnancy: a prospective evaluation of software.Ultrasound Obstet Gynecol. 2008; 31: 30-36Crossref PubMed Scopus (59) Google Scholar However, maternal or fetal motion and acoustic shadowing frequently affect the image quality contained in these volume datasets, which might have contributed to the limited uptake of 4D fetal echocardiography, despite it being available for more than a decade. To the extent that fetal MRI with novel computational techniques can overcome some of the limitations of prenatal ultrasonography, including acoustic shadowing and correction of fetal or maternal motion artifacts, fetal MRI has the potential to increase the detection rates of congenital heart defects. It is also possible that algorithms used in 3D and 4D ultrasonography designed to facilitate the assessment of the fetal heart could be applied to fetal MRI imaging. The technique proposed by Lloyd and colleagues9Lloyd DFA Pushparajah K Simpson JM et al.Three-dimensional visualisation of the fetal heart using prenatal MRI with motion-corrected slice-volume registration: a prospective, single-centre cohort study.Lancet. 2019; (published online March 22.)http://dx.doi.org/10.1016/S0140-6736(18)32490-5Summary Full Text Full Text PDF PubMed Scopus (57) Google Scholar might have the biggest impact in characterising abnormal vascular connections to the fetal heart and abnormal cardiovascular spatial arrangements, such as those seen in conotruncal anomalies, which represent about 20% of all congenital heart defects.10Sivanandam S Glickstein JS Printz BF et al.Prenatal diagnosis of conotruncal malformations: diagnostic accuracy, outcome, chromosomal abnormalities, and extracardiac anomalies.Am J Perinatol. 2006; 23: 241-245Crossref PubMed Scopus (43) Google Scholar This approach could be essential when planning surgical palliation or correction of congenital heart defects. It remains unclear from the data presented if fetal MRI imaging could also help in the prenatal diagnosis of intracardiac anomalies. An important limitation of the study of Lloyd and colleagues is that the mean gestational age at MRI was 32 weeks (range 24–36 weeks), which is important because assessment of the fetal heart is typically done between 18 and 23 weeks' gestation. Additional studies are required to determine if the technique proposed by the authors can be used at earlier gestational ages. I declare no competing interests. Three-dimensional visualisation of the fetal heart using prenatal MRI with motion-corrected slice-volume registration: a prospective, single-centre cohort studyStandard fetal MRI with open-source image processing software is a reliable method of generating high-resolution 3D imaging of the fetal vasculature. The 3D volumes produced show good spatial agreement with ultrasound, and significantly improved visualisation and diagnostic quality compared with source 2D MRI data. This freely available combination requires minimal infrastructure, and provides safe, powerful, and highly complementary imaging of the fetal cardiovascular system. Full-Text PDF Open Access