4D Ultrasound Basic Training for Obstetric “Babyface” Imaging
FEBRUARY 17, 2015 BY BRIAN GILL
How to Perform 4D Ultrasound for “Babyface” Images
The concept of 4D ultrasound can be a difficult process for experienced and inexperienced sonographers alike. The views for this blog post and video tell the story: of the hundreds of videos we have on our site, this training video is one of the top-viewed of all time.
Since 1999, I’ve trained more than 1,000 people in performing 4D obstetric ultrasound. From experienced sonographers, to physicians, to people who have never used an ultrasound before, I’ve trained every type of user.
In those years, I’ve found that neither experience, degree, nor general intelligence can predict whether 4D ultrasound will be easy for the user. The fact is that it’s not easy, and the only way to really learn it is practice, practice, practice.
But you have to start somewhere, and this guide will give you the foundation to start practicing.
This guide assumes you have basic knowledge of your ultrasound machine. We have free online ultrasound training for many ultrasound systems, and a free ultrasound image optimization guide to help you optimize your 2D ultrasound image. If you are not familiar with your ultrasound machine, it will be difficult for you to proceed with these steps.
This guide cannot replace applications training, but will help you on your way to learning this difficult task.
Step 1: Get a Good 2D Image
It all starts here. Without a good 2D image, you won’t get a good 4D image. Luckily, your machine takes the first step for you: Every machine will have settings that automatically optimize machine settings for a good 2D image. These settings are found in your application settings for the probe. First, choose the Obstetric setting. From there, you should see a “2-3 Trimester”, “Mid-Pregnancy” or something to indicate a general OB setting for 20+ weeks. Select this and you’re ready to scan.
Assuming you have some knowledge of positioning of the probe and finding the baby, you’ll want to get a good 2D image of the baby’s profile.
Most often, the best angle for the baby’s face is NOT from the middle of the belly. Most often, you’ll find the baby’s face by positioning the probe near the pelvic bone on the left or right side, with the probe head angled towards the cervix, pretend you’re aiming a flashlight towards the cervix. If you see the spine, you’ll need to angle the probe from the other side (i.e. right pelvic to left pelvic or vice versa).
What is a good 2D image for 4D? The ideal 2D image that produces a good “babyface” image has the following characteristics:
- The baby’s profile is facing the probe. This means the nose should be pointing up. A common mistake among experienced sonographers is to show the two orbits of the eyes on the 2D image… however, in 4D that will render an image of the side of the baby’s face (profile), which produces a 4D picture of the baby’s ear.
- There is fluid in front of the baby’s face. This is very important in order to isolate the face.
- There are no obstructions in front of the baby’s face. This includes hands, feet, umbilical cord, placenta, etc. When something is touching the face, it will likely become part of the 4D image and appear as though it’s part of the face.
- There aren’t hands, arms, or feet in the area. Ultrasound waves can’t penetrate bone very well, so if there is any appendage between the face and the transducer, it will create a shadow-like image on the face, or block the image of the face entirely.
If you’re struggling to meet all these criteria, don’t worry, rarely is the baby positioned so perfectly that you have a nice amount of fluid in front of the baby’s face, with no obstructions. What you’re trying to do is eliminate as many obstructions as possible.
Adjust the Gain: Getting a good 2D image includes clearing up the image with the Gain control. The Gain is essentially the brightness of the image. Too much gain will give you a “fuzzy” image, and too little gain produces a very dark image. You’re looking for an optimal mix that provides contrast between fluid and the face.
On some machines, the gain control is the 2D knob that and you twist. On other machines, it’s indicated as “2D”, “B”, or “Gain”.
Use the gain to find a nice balance of getting the fluid dark, while still retaining a bright image of the baby’s profile.
Step 2: Set the Region of Interest/Render Box Correctly
The Region of Interest is that convex box that appears when you first enter 4D. This is the mode where you’ll have a 2D image on the screen along with a convex outline over the image. You’ll be able to adjust the size and position of this overlay.
This box is the Region of Interest box. You MUST set this in a good position in order to get a good image.
Essentially, this box tells the machine what you want to see in 4D. Everything inside the box will appear in 4D, and everything outside the box will not.
Also note the horizontal line across the top of the box. The machine will also exclude anything above that line (it’s green on Voluson ultrasound machines). This line is what you’ll use to separate the face from any obstruction, such as placenta or uterus. Typically you’ll place this line just above the baby’s nose.
You’ll also have an option to change the size of the region of interest box. You’ll typically want to set the depth to the back of the head, and make sure width of the box encompasses everything that you want in the image.
Step 3: Check Your Preset!!
Before entering 4D mode, check to see if your machine has presets for particular types of 4D mode. You’re looking for something that will perform “surface” rendering. Not all machines have a specific preset, but it’s crucial to use these if your machine has them.
This preset will optimize your image for surface rendering, which will provide the best 4D babyface image possible.
Once you’ve selected the proper preset and have your ROI (Region of Interest) Box set appropriately, enter Live (4D) mode.
Step 4: Adjust your Gain (again)
The first thing to do when you enter 4D is to adjust the gain. Most often you’ll want to adjust to a lower gain, which will eliminate artifact in the image. When the gain is high (bright), the machine will display all small artifacts in the image clearly. By decreasing the gain, you’ll eliminate the weak echoes (artifacts) and the face will appear more clearly. On the same note, if the image is too dark, you’ll want to slowly increase gain to make the face appear.
Technique is very important here. Because it takes time for the machine to render the image, you MUST be sure to adjust the gain slowly. Be sure to pause after each adjustment and wait for the on-screen image to catch up to your adjustment. Turning it too quickly without waiting will result in a very dark or bright image.
Step 5: Invert the Image
If you don’t see what you’re looking for, try inverting the image because the baby’s face may be upside-down. When the baby is in the vertex position and the probe is oriented correctly, inverting the image will be necessary every time.
Whether to invert or not is completely dependent upon the baby’s position and the probe orientation. I’ve seen plenty who simply hold the probe upside-down instead, which is a big no-no in diagnostic ultrasound.
Step 6: Return to 2D
Whether your new or experienced, you’ll find that you’ll need to return to 2D often in order to reposition the probe to adjust for better angles, or to adjust to the baby’s movement. It’s a lot easier to find the baby and get a better position in 2D, rather than searching in 4D. Repositioning in 4D is less efficient because of the ROI box and the slower rendering times. 2D is simply the best place to find a better position.
Step 7: Optimize the Image
Even with perfect positioning of the baby, it’s possible that your image is still somewhat poor. It’s crucial to get proper settings to allow the machine to render the best 4D images possible… and most often the factory defaults aren’t very good. This is a technical issue that will be addressed in another article, but it’s important that you get to know your machine and learn what controls achieve the best 4D image quality.
There are a few common problems that every technician faces. In Part II of this 4D ultrasound training series, I’ll address some of the more common problems/mistakes I’ve seen over the years that are are experienced by experienced and inexperienced technicians.
This is one part of a multipart series on 4D ultrasound machines setup and usage. Here are links to the remaining articles: