Fetal Three-Dimensional Echocardiography

Published on 07/06/2015 by admin

Filed under Neonatal - Perinatal Medicine

Last modified 07/06/2015

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28 Fetal Three-Dimensional Echocardiography

III. THREE-DIMENSIONAL TERMINOLOGY AND PHYSICS

The most important developments for accomplishing the transition to fetal echocardiography from 2-D to 3-D echocardiography are real-time 3-D imaging and spatiotemporal realignment motion gating. Real-time means there is no significant delay between acquisition and display.

B. Physics

1. Overview.

a. It is generally stated that the human eye and brain retain a visual impression for about 1/10 to 1/30 of a second, equivalent to a frame or volume rate of 10 to 30 Hz.

b. The exact time depends on the brightness and clarity of the image and pattern recognition.

c. When referring to real-time imaging, we are actually talking about whether an imaging system can achieve the visual continuity that will satisfy the human eye and brain.

2. Built-in, spatial, and temporal realignment of 4-D data.

a. It is hard to consistently find a stationary volume of interest in utero due to unwanted patient movements (e.g., fetal activity, maternal respiration) and/or environmental movements such as abdominal deformation from probe movement when using conventional approaches.

b. Real-time 3-D systems can acquire a volume data set without manual displacement of the transducer.

3. Sufficient temporal resolution for the time scale of interest.

a. For general analysis of dynamic anatomy of the fetal heart, a minimum volume rate of about 15 to 25 Hz is required with fetal heart rates of 150 bpm or more. This is equivalent to a maximum of 40 ms for each imaging volume sampling period.

b. Except for isovolumetric contraction and relaxation, other cardiac phases each rarely last longer than 80 ms (rounded numbers are used in this discussion for mathematical simplicity) and can be fully sampled at least once in one imaging volume per cardiac cycle.

c. To achieve 90% accuracy for the measurement, a 500-Hz volume rate may be necessary.

IV. THREE-DIMENSIONAL ECHOCARDIOGRAPHY SYSTEMS

A. Rapidly oscillating cross-sectional transducer

1. Volumetric scanning.

a. Volumetric scanning is less dependent on the angle of acquisition, and thus less dependent on fetal lie or operator expertise, than 2-D scanning.

b. The most promising aspect is the possibility of storing and compressing a volume of 4-D information for later offline evaluation by an expert.

c. Because the heart is beating, nongated acquisition produces artifacts in the reconstructed volume data.

2. Spatiotemporal image correlation (STIC).

a. Description.

b. Method.

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