Table 1.

Terms and definitions related to 4D sonography with STIC

Term	Definition
Acoustic dropout	Signal loss in the sound path without intervening structures
Acoustic shadowing	Signal loss in the sound path secondary to echogenic structures
Acquisition angle (degrees)	Determines the acquisition depth (amount of information acquired in the z-plane)
Acquisition plane	• Starting 2D plane for the volume acquisition  • Known as the A plane in the multiplanar display
Acquisition time (seconds)	• Equivalent to the duration of volume acquisition  • Determines the speed at which the transducer sweeps the region of interest  • An inverse relationship exists between acquisition time and sweep speed of transducer
Dolphin	Refers to fetal transverse aortic arch (appears like a dolphin on ultrasound)
Double vision image	• Observed in the A plane (multiplanar display) in the presence of excessive fetal breathing or movement  • When a single object looks like two images simultaneously, or when two images of the same object overlap
Drifting spine	• Fetal spine location “migrates” on the monitor screen during the automatic STICLoop™ scroll  • When sequential axial planes are parallel to each other (similar to a loaf of bread), there is no drifting spine
Driving the transducer	Sonographic technique to “convert” the fetal spine to a posterior position on the monitor screen
Four-dimensional or 4D	Volume datasets that incorporate information about the three spatial dimensions plus the temporal dimension
Ghost image	• Observed in the A plane (multiplanar display) in the presence of excessive fetal breathing or movement  • When two images are only very slightly separated and not two distinct images
Multiplanar display or view	• Display format of sonographic volumes (e.g. STIC) in which there are three orthogonal planes (transverse, sagittal, coronal)  • Allows correlation between image planes that are perpendicular to the main acquisition plane  • Can be used to determine whether a STIC volume is appropriate for further analysis
a. A plane	• Acquisition plane  • Displays the size of the region of interest box (selected height and width) of volume  • Located in upper left corner of multiplanar display
b. B plane	• Plane orthogonal to A plane, but parallel to ultrasound beam  • Demonstrates the acquisition angle of volume  • Located in upper right corner of multiplanar display
c. C plane	• Plane perpendicular to both A plane and ultrasound beam  • Commonly referred to as the coronal plane  • Located in lower left corner of multiplanar display
Piano keys artifact	• Characterized by a distinctive appearance in the B plane of multiplanar display  • Similar to a pianist sharply pressing and releasing multiple piano keys at fixed intervals apart on the keyboard  • Occurs in presence of fetal hiccups
Reference point or dot	• Intersection of three planes in the multiplanar display  • Tool can be used to manually navigate through the STIC volume and localize the same anatomic structure in all three orthogonal planes
Region of interest (ROI)	Box determines the height (y-plane) and width (x-plane) of the volume dataset
Rendered image or display	• Contains depth in the z-plane, and provides additional information not available from thin 2D image slices  • Volumes can be rendered in various display modes (e.g. surface rendering, inversion)  • Located in right lower corner of multiplanar display
Spatiotemporal Image Correlation (STIC) technology	Allows acquisition of a fetal cardiac volume dataset, and displays a cine loop of a complete single cardiac cycle in motion
Staircase (or caterpillar) spine	• Fetus in which the transverse view of fetal spine on ultrasound shows ossification centers “stacked” upon each other like a staircase or caterpillar; coronal view of curved ribs may also be seen  • Ossification centers are imaged obliquely and appear to “move” vertically on the monitor screen as the volume is being acquired
a. Upstairs spine	• Fetus is tilted upwards (feet raised higher than the head)  • Exaggerated view of ventricles will be evident in apical four-chamber view
b. Downstairs spine	• Fetus is tilted downward (head raised higher than the feet)  • Left atria may appear foreshortened in apical four-chamber view and Eustachian valve may be visible
STICLoop™	• 2D cine loop to aid the user in determining the appropriateness of STIC volume datasets before applying the FINE method to such volumes  • Facilitates detection of: 1) discontinuity or undulating movements that could modify anatomical structure representation and are due to motion artifacts or errors in STIC assembly; 2) azimuthal issues (tilted acquisitions); and 3) drifting spines  • Operator independent and runs automatically at a constant speed
Voxel	Volume of pixels
Water dive artifact	• Discrete area(s) of motion artifact seen in the B plane of multiplanar display  • Occurs when there is isolated breathing or gross body movements during volume acquisition
Wavy lasagna wall artifact	• Wall of the fetal longitudinal descending aorta (B plane of multiplanar display) appears undulated or wavy at regular intervals  • Occurs in presence of regular breathing motion (fetal or maternal)

2D, two-dimensional; 3D, three-dimensional; FINE, Fetal Intelligent Navigation Echocardiography