diagnostics Review Applications of Advanced Ultrasound Technology in Obstetrics Kwok-Yin Leung Obstetrics and Gynaecology, Gleneagles Hong Kong, Hong Kong, China; [email protected] Abstract: Over the years, there have been several improvements in ultrasound technologies including high-resolution ultrasonography, linear transducer, radiant flow, three-/four-dimensional (3D/4D) ultrasound, speckle tracking of the fetal heart, and artificial intelligence. The aims of this review are to evaluate the use of these advanced technologies in obstetrics in the midst of new guidelines on and new techniques of obstetric ultrasonography. In particular, whether these technologies can improve the diagnostic capability, functional analysis, workflow, and ergonomics of obstetric ultrasound examinations will be discussed. Keywords: obstetrics; ultrasound; 3D; 4D; Doppler; artificial intelligence 1. Introduction Ultrasound is widely used in obstetric practice to detect fetal abnormalities with a view to provide prenatal opportunities for further investigations including genetic testing and discussion of management options. In 2010, International Societies of Ultrasound in Obstetrics and Gynecology (ISUOG) published the practice guidelines on the minimal and optional requirements for a routine mid-trimester ultrasound scan [1]. Recently, The Citation: Leung, K.-Y. Applications American Institute of Ultrasound in Medicine (AIUM) suggests a detailed diagnostic of Advanced Ultrasound Technology second/third trimester scan for high-risk pregnancies [2], and fetal echocardiography for in Obstetrics. Diagnostics 2021, 11, at-risk pregnancies [3]. ISUOG has published recent guidelines on indications and practice 1217. https://doi.org/10.3390/ of targeted neurosonography [4,5]. Although the introduction of prenatal cell-free DNA- diagnostics11071217 based screening for Down syndrome has changed the role of the first trimester scan, the latter should still be offered to women [6]. Around 50% of major structural abnormalities Academic Editor: Ritsuko can be detected in the first trimester [7]. In addition, a recent study showed that a routine Kimata Pooh scan at around 36 weeks’ gestation can detect around 0.5% of previously undetected fetal abnormalities, as well as fetal growth restriction (FGR) [8]. Received: 7 June 2021 The detection rate of fetal abnormalities varies, depending on anatomy survey pro- Accepted: 3 July 2021 tocol, ultrasound equipment and setting, among other factors [9]. A high-resolution Published: 6 July 2021 ultrasound can facilitate a detailed diagnostic scan and a first-trimester scan and allow the detection of a small or subtle abnormality [10–12]. Although a detailed diagnostic scan is Publisher’s Note: MDPI stays neutral not required for all pregnant women, the indications include family history of congenital with regard to jurisdictional claims in malformation, maternal age 35 or above, gestational diabetes mellitus, artificial reproduc- published maps and institutional affil- tion technology, body mass index >= 30, teratogen, fetal nuchal translucency >= 3mm, and iations. many other conditions [2]. In the midst of such increasing standards of obstetric ultrasound examination, there is a demand on improving the diagnostic capability, functional anal- ysis, workflow, and ergonomics. Over the years, there have been several improvements in ultrasound technologies including high-resolution ultrasonography, linear transducer, Copyright: © 2021 by the author. radiant flow, three/four-dimensional (3D/4D) ultrasound, speckle tracking of the fetal Licensee MDPI, Basel, Switzerland. heart, and artificial intelligence. The aim of this review is to evaluate the use of these This article is an open access article advanced technologies in obstetrics. distributed under the terms and conditions of the Creative Commons 2. High-Resolution Ultrasonography Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ High-resolution ultrasonography includes the use of a high-frequency transducer, 4.0/). and the means of enhancing image and signal processing including harmonic imaging Diagnostics 2021, 11, 1217. https://doi.org/10.3390/diagnostics11071217 https://www.mdpi.com/journal/diagnostics Diagnostics 2021, 11, x FOR PEER REVIEW 2 of 18 2. High-Resolution Ultrasonography High-resolution ultrasonography includes the use of a high-frequency transducer, Diagnostics 2021, 11, 1217 and the means of enhancing image and signal processing including2 of harmonic 18 imaging (HI), spatial compound imaging (SCI), and speckle reduction imaging (SRI). Compared to a transducer with the low-frequency range (2 to 5 MHz), a transducer with the high-fre- (HI), spatialquency compound range imaging(5 to 9 MHz) (SCI), can and allow speckle for reduction improved imaging resolution (SRI). though Compared with limited tissue to a transducerpenetration. with the HI, low-frequency utilizing the rangephysics (2 toof 5non- MHz),linear a transducer propagation with of the ultrasound high- through the frequency range (5 to 9 MHz) can allow for improved resolution though with limited tissue body tissues, can produce high-resolution images with few artifacts. SCI, combining mul- penetration. HI, utilizing the physics of non-linear propagation of ultrasound through the bodytiple tissues, lines can of produce sight to high-resolution form a single images composite with fewimage artifacts. at real-time SCI, combining frame rates, can reduce multiple linesangle-dependent of sight to form artifacts. a single composite The use of image SRI atcan real-time reduce frame speckles rates, or can disturbances reduce that result angle-dependentfrom the artifacts. echo, which The use is ofprojected SRI can reducefrom an speckles ultrasound or disturbances transducer. that result from the echo, which is projected from an ultrasound transducer. 2.1. Fetal Echocardiography and Targeted Neurosonography 2.1. Fetal Echocardiography and Targeted Neurosonography ISUOG recommends the use of the highest possible transducer frequency to perform ISUOG recommends the use of the highest possible transducer frequency to perform fetal echocardiographyfetal echocardiography with a view with to improve a view the to likelihood improve of the detecting likelihood subtle of heart detecting de- subtle heart fects, albeitdefects, at the expensealbeit at of the reduced expense acoustic of reduced penetration acoustic [10] (Figure penetration1a–d and [10]Video (Figure S1). 1a–d and Video The use ofS1). HI The can improveuse of HI the can quality improve of ultrasound the quality images, of ultrasound especially when images, the maternalespecially when the ma- abdominalternal wall abdominal is thick during wall the is third thick trimester during ofthe pregnancy third trimester [11,13]. of pregnancy [11,13]. (a) (b) (c) (d) Figure 1. High-resolutionFigure 1. ultrasonographyHigh-resolution ultrasonographyof the fetal heart of at the 20 fetalweeks’ heart gestation at 20 weeks’ showing gestation (a) a four-chamber showing (a) a view show- ing right atrium (RA),four-chamber left atrium view (LA), showing righ rightt ventricle atrium (RA),(RV), left and atrium left (LA),ventricle right (LV), ventricle (b) (RV), five-chamber and left ventricle view showing as- cending aorta (AAo)(LV), arising (b) five-chamber from the left view ventricle, showing ascendingthe right aortaand left (AAo) superior arising pulmonary from the left veins ventricle, (RSPV, the right LSPV) enter the left atrium (LA), andand descending left superior aorta pulmonary (DAo) veins behind (RSPV, the LSPV)LA (c) enter Three-vessel the left atrium view (LA),showing and descendingthe PA dividing aorta into the left (LPA) and right (RPA)(DAo) PA, behind AAo, the and LA the (c) Three-vessel superior vena view cava showing (SVC), the (d PA) three-vessel dividing into and the trachea left (LPA) view and showing right PA with the ductal branch (DA)(RPA) joining PA, AAo, the and DAo, the AAo, superior SVC, vena and cava trachea (SVC), (T); (d) Thymus three-vessel is anteri and tracheaor to the view three showing vessels. PA with the ductal branch (DA) joining the DAo, AAo, SVC, and trachea (T); Thymus is anterior to the three vessels. For a targeted neurosonographic examination, ISUOG recommends the use of high- resolution transvaginal transducers whenever possible [5]. An alternative is to use high- Diagnostics 2021, 11, 1217 3 of 18 Diagnostics 2021, 11, x FOR PEER REVIEW 3 of 18 For a targeted neurosonographic examination, ISUOG recommends the use of high- resolution transvaginal transducers whenever possible [5]. An alternative is to use high- resolution transabdominal transducers with high frequency reaching 8–9 MHzMHz [[5].5]. TheThe anatomy ofof thethe fetalfetal brain brain is is examined examined in in details details on on a continuum a continuum of transverse, of transverse, sagittal sagittal and andcoronal coronal planes planes (Figure (Figure2a–d, 2a–d, Video Video S2a,b). S2a,b). (a) (b) (c) (d) Figure 2. High-resolution ultrasonography of the fetal brain at 20 weeks’ gestation: transverse views showing (a) posterior horn of the lateral ventricle (Vp), (b) cavum septi pellucidi (C.S.P.), ((cc)) cerebellumcerebellum (Cereb),(Cereb), CisternaCisterna magnamagna (CM),(CM), nuchalnuchal fold (NF),(NF), andand sagittal sagittal view view showing showing (d ()d corpus) corpus callosum callosum (CC), (CC), thalamus thalamus (TH), (TH), brain brain stem stem (BS), (BS), and cerebellarand cerebellar vermis vermis (CV). (CV). 2.2. Face and Neck 2.2.