Eva Tegnander

Prenatal detection of heart defects in a non‐selected population of 30 149 fetuses—detection rates and outcome

To evaluate the detection rate of congenital heart defects (CHD) in a non‐selected population and to follow outcome after diagnosis.

The examiner's ultrasound experience has a significant impact on the detection rate of congenital heart defects at the second‐trimester fetal examination

To determine whether training and experience in performing ultrasound examinations are factors that influence the prenatal detection of congenital heart defects (CHDs) in a non‐selected population, in order to evaluate and improve the current training program.

Tissue Doppler gated (TDOG) dynamic three-dimensional ultrasound imaging of the fetal heart

Dynamic three‐dimensional (3D) ultrasound imaging of the fetal heart is difficult due to the absence of an electrocardiogram (ECG) signal for synchronization between loops. In this study we introduce tissue Doppler gating (TDOG), a technique in which tissue Doppler data are used to calculate a gating signal. We have applied this cardiac gating method to dynamic 3D reconstructions of the heart of eight fetuses aged 20–24 weeks.

Automatic measurement of biparietal diameter with a portable ultrasound device

Knowledge of the exact gestational age and expected day of delivery is essential for providing optimal medical surveillance. Fetal biparietal diameter (BPD) computed by ultrasound has been shown to correlate well with gestational age (before week 22) or it can be used for detecting growth abnormalities, later in the pregnancy. We have been developing a portable ultrasound scanner (the Umoja scanner) that can be used by midwives in LMIC countries with limited ultrasound and technological expertise. The aim of this work was to develop a technique for automatized computation of BPD which can run on tablet devices. An ultrasound image containing a contour of a fetal head is recorded with the prototype scanner. The image is preprocessed: converted to grayscale, gain adjusted, smoothed, dilated/eroded and finally binary thresholded. The potential contour candidates and their Cartesian coordinates are identified by applying the Canny edge detector. A line connecting the two most distant edge contours across the skull is computed. The original grayscale values along this line are used to identify the top and the bottom edge points which are used for measuring the BPD value. All image processing is performed using OpenCV (Open source Computer Vision), which is optimized for tablet devices. 27 ultrasound images suitable for BPD measurement were acquired by an experienced midwife and 9 student midwives with limited or no prior ultrasound experience, on 8 different fetuses from 18 to 34 weeks. Both manual (experienced midwife) and automatic BPD measurements were computed. The correlation plot and the error versus reference plot are produced, the mean error ± 1.96*STD was 0.72±3.62 [mm], while the correlation coefficient was R=0.9932. The automatic measurement failed in 4 cases. The overall computation time on a Nexus 10 tablet was 3.47 seconds, therefore our tool is suited for a portable device with limited computation power. The agreement of the proposed algorithm with the reference measurements is comparable to the interobserver agreement for BPD (2.6 to 3.1 mm from literature study). Testing of the method on an extended dataset, including fetuses at different gestational ages is ongoing.

Fetal medicine – a reality thanks to ultrasound

The introduction of ultrasound in the field of gynaecology and obstetrics has not only changed, but has revolutionized the work of the obstetrician and created the basis for a new medical field – foetal medicine. Medical diagnosis is partly or completely based on imaging technology and our ability to document a disease process or a maldeveloped organ by producing a visible image outlining, on a macro or micro level, the anatomical consequences for the organs involved. For obvious reasons, X-rays could never be used extensively in pregnancy for the presentation of foetal and/ or maternal problems. The obstetrician was left with his senses and ability to palpate the maternal uterus and in some cases obtain indirect information about the foetus based on maternal biochemical analysis. The use of ultrasound for medical diagnosis was initiated by cardiologists, but it is not surprising that the extensive use of this technique to image the human anatomy was pioneered by obstetricians – who for many years had been in great need of information (Donald et al., 1958). Rapidly the technique gained popularity worldwide in the field of obstetrics and gynaecology and is now established a basic diagnostic tool (Campbell, 1969). The practice of obstetrics and gynaecology has changed completely over the last 30 years as a consequence of this new and exciting technique. The use of ultrasound has challenged the traditional education in this field and has become an ever-increasing part of the teaching and training. One of the driving forces for the rapid development of ultrasound has been the clinician’s need for detailed information about the intrauterine environment, together with the fact that computing technology is an essential part of a modern ultrasound machine. Consequently, our possibilities to image the foetus has been advancing in parallel with the development of the computing power (Fig. 1). The pioneer of clinical ultrasound in general and in obstetrics and gynaecology in particular was Ian Donald in Glasgow, Scotland (Donald et al., 1958). One of the first academic theses on ultrasound was defended at the University of Lund in 1964 by Bertil Sundén (Sundén, 1964). He used the ultrasound machine, Diasonograph (Nuclear Enterprises, Edinburgh, UK), which initiated the clinical era of ultrasound – a development that has expanded ever since.

Dynamic 3D ultrasound imaging of the fetal heart

Dynamic 3D ultrasound imaging of the fetal heart is difficult due to the absence of ECG signal for synchronization between loops. In this work we introduce a technique for image synchronization based on acquisition of tissue Doppler signals dedicated to compute a sync-signal. We have applied this method to dynamic 3D reconstructions of the heart of 9 fetuses aged 19 to 24 weeks. The sync-signal is generated by peak velocity detection of the TVI data. Once it is available, we can use a standard technique for reconstruction; in our case the EchoPAC3D software from GE Medical Systems. The basis for one reconstruction is a 2D sector scan, taken trans-abdominally and slowly tilted in free-hand, so that we cover the entire fetal heart over approximately 40 cardiac cycles. The total angle of the sweep is estimated by recording a separate loop through the centre of the heart, in the elevation direction of the sweep. We show an example with 1950 frames over 50 cardiac cycles, recorded with a frame rate of 96 and hence a time span of 20 seconds. The reconstruction consists of 31 volumes, each assumed to have 50 equidistantly tilted frames. Furthermore, every frame consists of 91 beams with 583 samples each. A typical good position of the heart is about 5 cm from the probe, which gives us a radial resolution of 0.15 mm, azimuthal resolution of 0.3/spl deg/ /spl sim/ 0.26 mm and elevational resolution of 0.5/spl deg/ /spl sim/ 0.44 mm.

A robust Doppler spectral envelope detection technique for automated blood flow measurements

Maximum velocity estimation in a Doppler Spectrogram is of clinical interest. Two existing approaches to maximum velocity estimation, the Geometric method (GM) and the Signal Noise Slope Intersection (SNSI) method are combined in the new approach described in this paper. Further, a data adaptive validity check is introduced that makes the proposed technique independent of user defined parameters. The method enables accurate maximum velocity point detection and obtains an automated, robust tracing of the maximum velocity envelope, which can be further used for automated blood flow measurements. In order to verify the robustness of the algorithm, Pulsatility Index measurements were compared with the observations made by a midwife trained in ultrasound. Evaluation of the steadiness of the location of identified maximum frequency point in simulated flow with varying SNR, ranging to a minimum SNR level of 6dB, also aided the verification. This technique is expected to prove useful in ultrasound machines for diagnoses by clinically inexperienced users.

Automatic detection and measurement of fetal femur length using a portable ultrasound device

A reliably estimated date of delivery (EDD) and gestational age (GA) are important to provide optimal care during pregnancy. Using ultrasound technology, the biparietal diameter (BPD) and femur length (FL) of a fetus are measured to calculate these parameters. Our research group has been developing a portable and user-friendly ultrasound scanner for the midwives inexperienced in the use of ultrasound in low- and middle-income countries (LMIC). The goal of this work was to develop an automatic method of detecting and measuring fetal femur length that can run on a tablet device to assist the health care worker during the scanning process. An ultrasound image containing a fetal femur was saved in the portable scanner. Colored UI elements were separated by selecting a threshold from HSV color space and the image was converted into grayscale. An adaptive binary threshold was selected by calculating the mean and standard deviation of the intensity of image pixels and a binary image was produced. Potential fetal femur contour candidates were computed from the edges between the black and white regions in the binary image. The fetal femur was detected by comparing its size, orientation, and position with other femur candidates. A Hough transform was applied in the location of the detected femur to find a straight line with the highest number of votes to measure the length of the fetal femur. All these steps were performed by using OpenCV image processing library. Fifty-eight different femur ultrasound images were acquired by ultrasound experienced (44 images) and inexperienced midwives (14 images). The gestational age range of the fetuses was between 18 - 32 weeks. The images had different quality, intensity, and zoom levels. The automatic method was able to detect femurs in 37 out of 44 images (84%) from experienced midwives, and 9 out of 14 images (64%) from inexperienced midwives. The automatic measurements were compared with the manual measurements from experienced midwives. The correlation plot and the error versus reference plot are presented. The correlation coefficient was R=0.95 and the mean error±1.96*STD was -2.34±6.52[mm]. Images containing curved femurs caused important FL underestimation; our method is currently being adapted to work on these cases. The average time of computation was 3.2 seconds in a Samsung P600 tablet device.

Detailed flow visualization in fetal and neonatal hearts using 2-D speckle tracking

Two-dimensional blood speckle tracking has shown promise for measuring the complex flow patterns in neonatal hearts when based on linear array and high-frame-rate plane wave imaging. For phased array pediatric imaging, additional challenges emerge due to the reduced lateral bandwidth and increased imaging depth and field-of-view. In this work, a clinically approved setup with pediatric phased array probes and unfocused pulses was used to investigate the potential of blood speckle tracking to acquire 2-D vector velocity maps for neonates, infants and children with congenital heart disease.Promising results were observed for depths <; 10 cm, where complex cardiac flow patterns could be visualized. However, due to the small aperture available, diffraction effects could be observed. Further, as the depth dependent lateral resolution and loss in signal-to-noise ratio degrades tracking results for increasing depths, a larger feasibility study is needed to establish clinical viability. Vector velocity maps were also obtained from fetal examinations with the phased array setup as well as with a diverging beam setup on a research scanner, where detailed secondary flows such as the vortex formations in the ventricles of the fetal heart could be observed.

Automatic measurement of the fetal abdominal section on a portable ultrasound machine for use in low and middle income countries

General pregnancy monitoring with ultrasound includes the measurement of the biparietal diameter (BPD), femur (FL) and the mean abdominal diameter (MAD) of the fetus. This study was aimed to develop an automatic method for localization of the presented section through the abdomen and measurement of MAD. The algorithm may be run on a conventional ultrasound machine or on a tablet-based machine designed to be used in the rural areas of low- and middle-income countries (LMIC). The open source computer vision (OpenCV) library was used to process a B-mode ultrasound image to detect the location of a fetal abdomen. A Kalman based tracker (RCTL, GE Vingmed Ultrasound) was used to converge a deformable circle model along the boundary of the detected abdomen. The mean of the models major and minor axes was considered as MAD. The method automatically localized the abdomen and measured MAD in 57 of 61 images (93%) collected from 16 - 41-week-old fetuses. The correlation and the error plots between reference and automatic MAD measurements are presented. The correlation coefficient was 0.96, mean error was -0.06 mm and the error range (95% CI) was -14.80 to 14.68 mm. The resulting errors increased with the gestational age (GA) of the fetuses due to inner shadow and lack of edge information. The method was tested to perform well both in a PC and on various mobile devices.