Straight From the Cutter’s Mouth: A Retina Podcast, hosted by Dr. Jay Sridhar, is a wonderful weekly podcast for ophthalmologists, featuring insights from both prominent, as well as up-and-coming retina specialists, about their lives, passions, and work.
In this episode, Dr. Fisher discusses a variety of tips for learning and utilizing ultrasonography as a retinal specialist, in addition to applications of endoscopy for retinal surgery. For the link to the full episode, click here.
When teaching residents/fellows about ultrasounds, you’ve seen the good and the bad. What do you think is most important when using ultrasound in one’s practice?
Remember to include enough background.
The number one item of most importance is the ultrasound exam technique and how it is geared to using the ultrasound probe. The biggest mistakes that I see is that there isn’t enough background.
The background usually comes from some degree of information about acoustic competence and the mismatch which produces the signals that are eventually turned into images. You’re seeing across sections in B-Scan, as opposed to the linear display you see in A-Scan.
Strengthen your three-dimensional thinking.
The biggest mistakes likely are in three-dimensional thinking — learning how to reconstruct the eye from cross-sections, because we’re used to seeing enface. We look inside the pupil and we see everything in the back. Now, you’re being asked to probe in various portions of the globe to obtain cross-sections and B-Scan.
Those cross-sections are hard to put together. You’d think they’d be easy but it’s not if you want to avoid the lens, which is really important in ultrasound —to avoid a lot of the lens induced artifacts, as the lens does the same to sound that it does to light; it bends it. So you try never to examine anterior-posteriorly right through the lens, and that’s likely the biggest mistake.
You need to get off to the side to avoid the lens, and then once you’re on the side, you have to know how your images register; meaning, what does the image represent since images are copies? You have to know what you’re looking at on that screen, and how movement of the probe changes the image.
There’s a manufacturer mark on each probe, no matter which machine you’re using. That mark represents what’s going to be displayed at the top of the screen. The bottom of the image will then be the display created by the arc-like seep of the ultrasound transducer.
If you don’t realize that you’re changing the registration as you move the probe around the eye, it’s extremely confusing. Three-dimensional thinking takes a period of time. It’s not hard to do and I would suggest in order to correct those mistakes, image patients with clear media and pathologic abnormalities inside the eye, and keep asking yourself:
What is the registration of the screen? What does the image look like to the left, to the right? What does the top part of the screen represent, and what does the bottom part of the screen represent?
Since it’s a 50 degree cut, the image is going to change every time you move the probe, or rotate it, or tilt it. Grasping 3-D thinking is probably the primary problem with interpreting ultrasonography: learning the technique of a routine exam.
Start with “normal”.
You start with normal, because most of the time, we can image the vitreous, whether it’s attached or detached. Then, as you get into more complicated things, begin if you can, with simple, clear media retinal detachments and similar things, so you can see what they look like and correlate them with what you can see with an indirect or direct enface vision. In addition to any type of imaging like wide field photography, so that you can say: if the image looks like this enface, what will it look like in cross-section?
I often tell people when they first begin, to cut up fruit in various positions. The cross-section of a banana is basically a circle, and if you change the cut to longitudinal, you’ll get an arc rather than a circle. That kind of thought process is what I’m really talking about when learning three-dimensional thinking.
Keep in mind the major concepts: real-time and reflectivity/intensity.
The other two concepts for ultrasound are easy.
It’s real time, looks like a movie and that’s a big help in deciding what’s solid and what’s not. The other one is reflectivity or intensity. The stronger the echo reflection, the brighter the dots are going to be on the screen, remembering it must be perpendicular to induce the greatest reflection you can get.