Ultrasound in 3D

Over the years ultrasound has emerged as the primary imaging modality in OB/GYN practices, particularly in obstetrics as a routine and expected management of care. It is traditionally performed in two dimensions (2D), using two planes (X and Y) of an anatomic structure to display diagnostic information. This technique has been used for the last 30 years. Over the last decade sonographers have been exploring three dimension/four dimension (3D/4D) ultrasound to offer a third plane (C plane) of information to the diagnostic clinician.

3D imaging is volume scanning, and when acquired is termed a volume acquisition. When is it acquired it provides a number of different types of displayed information by individual slices and total volume displays. Some explored methods of display include multiple plane reconstruction, tomographic imaging (TUI), and surface rendering.

Here's how it works. An acquired 2D image is stored in a 3D volume. In the 3D reconstruction of that same acquisition, three images are displayed on the screen in the relationship of three right-angled orthogonal planes: Saggital plane (Long), Transverse plane, and Coronal plane. A dot representing a single point in space can be seen in all three images. The sonographer can manipulate the dot, with the right angled planes changing continuously to show the dot in all three orientations. This method of digital reconstruction enables the ultrasound practitioner to be less dependent on the method of the initial acquisition of the anatomy. Volume sonography also allows for the review of planes not obtainable by traditional 2D.

The logistical advantage to this technology is that just a few acquisitions can be made to view an entire organ or fetus, and the operator can reconstruct the diagnostic information at any time. This theory may eliminate the need for extended time to perform the ultrasound examination and perhaps change how ultrasound examinations are performed in the near future.

For gynecologic evaluations of the uterus, the three orthogonal planes are necessary to evaluate the shape of the uterine cavity. The new coronal (C) plane helps the sonographer diagnose uterine abnormalities and possibly eliminate the need for magnetic resonance imaging (MRI), particularly when the sonographic operator makes tomographic parallel cuts 1-4mm apart (similar to traditional MRI cuts). The introduction of fluid into the endometrial canal using a standard insemination catheter (sonohysterography), is beneficial to visualize polyps and can be enhanced using the 3D inverse mode (which appears similar to a contrast mode, which is used in radiological special procedures, such as cardiac catheterization). 

3D ultrasound also may eliminate the need for some patients to undergo a hysterosalingogram or HSG, a technique that involves injecting a special X-ray dye into the uterus and fallopian tubes in order to observe the image of these structures by X-ray.

For imaging the fibroid uterus, researchers have found that during the late phase of the endometrial cycle, a thick hyperechoic (contrasting) endometrium enables visualization of submucosal fibroid (between the muscle and endometrial layer) versus an intramural fibroid (within the muscle wall) when reviewed in the reconstructed coronal plane. Fibroids, also known as myomas, are nonmalignant growths within the wall of the uterus htat may grow during pregnancy or inhibit implantation. They're most common in women over age 35 and sometimes can increase the risk of preterm delivery, miscarriage, and delivery complications.

In the diagnosis of tubal disease, the coronal lane can identify hidden hydrosalpinx (a blocked, dilated, fluid-filled fallopian tube), and additionally, the inverse mode in 3D can illustrate the entire volume of the structure.

Volume scanning has been used in obstetrical applications, and studies are being performed to standardize the protocol of automated sonography of the fetus, particularly in the central nervous system and the fetal heart.

There are vast possibilities for the use of this technology. Its advantages will further standardize ultrasound imaging, reduce human error, enhance reproducibility and organization of anatomical relationships, and reduce examination time. Researchers are continuing to study the efficiency of automated sonography by using 3D and display technologies. At DVIF& G we have already placed this major breakthrough in the world of sonography to help us improve the diagnosis and management of our patients.

By Laurie Miller, BS, RDMS, DVIF& G Chief Sonographer

Date Posted: February 13, 2007