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

Abstract

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.

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

“…The phantom experiment showed that improving 4D flow spatial resolution from 2.4 mm to 1.5 mm improved accuracy. This study used an acquired temporal resolution of 42 msec, similar to earlier studies and guidelines 10,30 . Since increased temporal resolution has been shown to improve accuracy of 4D flow volume assessment, 31–33 differences in temporal resolution might also contribute to the difference in flow volumes.…”

“…This means that scan duration can be extensive in patients with complex CHD and highly trained scanner operators are required 9 . Recent developments in three‐dimensional (3D) time‐resolved three‐directional phas‐contrast MRI (four‐dimensional [4D] flow) have enabled shorter scan duration as flows in all vessels of interest are acquired simultaneously and requires minimal slice planning compared to two‐dimensional (2D) flow 10,11 . This shorter scan duration increases the chance of successful study when using feed‐and‐sleep, 12 instead of sedation or general anesthesia.…”

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

“…double outlet right ventricle, interstage single ventricles at 4–6 kg) and in smaller vessels (i.e. pulmonary vein flow to measure total pulmonary blood flow in mixing lesions), it becomes important to understand what, if any, advantages contrast agents convey in the assessment of cardiothoracic blood flow using 4D Flow CMR [ 13 , 14 ]. The purpose of this study was to assess the accuracy of 4D Flow CMR (as compared with 2D-PC) in ferumoxytol-enhanced CMR studies compared to gadolinium-enhanced CMR studies in small children with CHD.…”

Editorial for “Neonatal 4D Flow Magnetic Resonance Imaging Without General Anesthesia”

“…Neonates bring challenging imaging requirements: high heart and respiratory rates, small cardiovascular structures, and a tendency to ignore instructions. To limit motion and buy additional quiescent imaging time, the use of general anesthesia or sedation are commonly used 2 . Furthermore, exogenous contrast agents are frequently employed to increase signal‐to‐noise, speed up scan time, or increase spatiotemporal resolution.…”

“…To limit motion and buy additional quiescent imaging time, the use of general anesthesia or sedation are commonly used. 2 Furthermore, exogenous contrast agents are frequently employed to increase signalto-noise, speed up scan time, or increase spatiotemporal resolution. These approaches have enabled assessment of complex congenital heart disease that is unavailable with other imaging modalities.…”