Table 2.

Performing 4D sonography with STIC: important points and tips

• Many factors which affect the acquisition and quality of STIC volume datasets also pertain to 2D sonography

• Success rates of volume acquisition in fetuses with normal hearts range widely (26–100%) and depend on many factors (e.g. operator skill), preset criteria/requirements for acquisition, and the purpose of study

• Four essential steps in performing 4D sonography with STIC include: volume acquisition, display, manipulation / post-processing, and storage of volumes and images

• When acquiring volumes and determining whether they are appropriate for further analysis, there are three main time points: before acquisition, acquisition, and immediately after acquisition

• Volumes may be obtained in each trimester (recommend 19–30 gestational weeks for optimal assessment of fetal cardiac anatomy)

• Ask the mother who is lying supine to turn (or roll) laterally onto her side in the same direction that you wish the fetal cardiac apex to turn

• Constantly adapt to the fetal “situation” throughout the ultrasound examination and take advantage of any proper moments to obtain volumes

• If the fetal heart is in an optimal position and conditions are appropriate, immediately acquire multiple volumes in rapid succession

• Image quality of volume datasets depends primarily on the original quality of the 2D image

• A high frame rate can be achieved by decreasing depth, sector width, and the number of focal zones

• Adjust the region of interest (ROI) box size to be as small as possible to maximize the frame rate during acquisition and improve the temporal resolution of the volume dataset

• Set the acquisition angle at least 5 degrees more than the gestational age; however, the angle should not be too wide either

• The quality of a volume acquisition is reflected by the acquisition time, and volumes should be obtained using the longest possible time (higher image resolution). Recommend an acquisition time of at least 10 seconds, with adjustment based upon presence/absence of fetal breathing or movements

• When the fetal spine location is between 5 and 7 o’clock, this reduces the possibility of acoustic shadowing from ribs or spine

• Use the technique of driving the transducer to “convert” the fetal spine to a posterior position on the monitor screen

• Fetal breathing and gross body movements during the volume acquisition can lead to motion artifact(s) within the volume dataset, with distortion of images and anatomical structures

• In most cases, the acquisition plane will be the four-chamber view

• A correct (or appropriate) four-chamber view should be obtained (i.e. true cross-section of the thorax with proper alignment in the axial plane)

• Sonologists tend to foreshorten the left (vs. right) side of the heart when imaging the apical four-chamber view

• Visualizing a fetal staircase spine indicates that a true transverse plane of the fetal chest has not been obtained, and therefore should be avoided

• In general, sonologists have more difficulty in obtaining an appropriate apical four-chamber view when the fetus is in breech presentation (vs. vertex)

• At the time a volume acquisition begins by pressing a button, the fetal anatomical plane on the monitor screen at that moment will become the acquisition plane

• It is very helpful to verbally support and encourage patients throughout the breath hold which occurs during the acquisition

• During the actual volume sweep, observe the sequential images within the ROI box on the monitor screen to evaluate for satisfactory or unsatisfactory (e.g. fetal movement) conditions

• Practicing efficiency during the sonographic examination is immediate awareness of when a volume will be uninformative and needs to be discarded (e.g. fetal heart shifts outside the ROI box during the acquisition)

• In the presence of an abnormal fetal heart rate (e.g. tachycardia, bradycardia), sudden changes in fetal heart rate, or cardiac rhythm disturbances/arrhythmias, volume acquisitions may not be feasible

• Two methods of STIC volume display (multiplanar view or STICLoop™) are useful to immediately determine whether the volume is appropriate for further analysis (e.g. to obtain fetal cardiac views)

• The multiplanar display of a volume dataset provides information on the ROI box size (A plane) and the acquisition angle (B plane)

• The A plane image (multiplanar display) has the highest resolution, best image quality, and is equivalent to a 2D image displayed during sonographic examination

• Both B and C planes (multiplanar display) are reconstructed planes, and therefore these images are characterized by lower resolution than that of the A plane

• The B plane of multiplanar display may be evaluated for motion artifact(s), such as wavy lasagna wall, water dive, or piano keys

• Fetal breathing or movement will not alter the A plane image unless it is excessive. In this case, the A plane image may appear to “jump” out of place, or one may observe a ghost image or double vision image in a specific frame(s)

• Although acoustic shadowing or dropout may seem absent in the 2D image plane during real-time scanning, this may actually be present within the volume

• STICLoop™ is a 2D cine loop tool that aids the user in determining the appropriateness of STIC volume datasets before applying the FINE method to such volumes

• STICLoop™ allows improved detection of issues (e.g. undulating movements) vs. manual navigation through the A plane

2D, two-dimensional; FINE, Fetal Intelligent Navigation Echocardiography; ROI, region of interest; STIC, spatiotemporal image correlation