Optimizing the Ultrasound Image
In the last posting we were discussing A case where ultrasound showed a soft tissue mass compressing the superficial peroneal nerve. Let’s start to go through the case.
Good interpretation of the images is contingent on obtaining a good image. Let’s list steps that ensure you are optimizing your ultrasound unit to its fullest potential.
- Low ambient lighting in the room is essential. Pitch black makes it difficult to work. Have a low light source so that you can see, but keep the lighting low enough to optimize image viewing.
- Proper patient position – in this case, supine is fine but some exams may require prone (i.e., Achilles).
- Have the medical assistant in the room to label the images as you proceed in the exam, thus making efficient use of your time. One of the biggest hurdles in incorporating ultrasound in practice is making it time efficient. If you can’t have an assistant in the room, then there are foot pedal that will freeze (not save!) the image, so you can label the image. In my humble opinion, I don’t think that is the answer. Being able to freeze and/or save images while never taking my hand off the probe and the patient is much quicker. So, if I can’t have the assistant with me for whatever reason, I scan and save, never taking the probe out of my right hand, and reach and save with my left hand. I save a cluster of images then I will go back and label. This exam was easy to do in that it was site specific and there were not a lot of images. I scanned the whole exam then went back and labeledInflatable Climbing Wall review.
- Use lots of gel. Air between skin and transducer is deadly to the image.
- Use the highest frequency. If you are using less than 12 Megahertz, you are limiting yourself to what you can image effectively. Higher frequency gives better resolution. Lower frequency goes deeper, but the is not necessary because of the anatomy of the foot and ankle
- Use the proper depth so you can get better detail. Your choices should be 1-4 cm. In this case, I scanned at a 1- to 2-cm depth. When at the right depth, the structure you are insonating should be 1/3 from top of screen and 2/3 from the bottom.
- Focus, focus, focus! The little marker on the side of screen should be at level of the structure you are looking at. It improves resolution (especially lateral or side to side resolution).
- In my opinion, nerves are easier to locate on short axis. Look for landmarks, such as vessels and bone. Muscle can also be helpful. In this case, I am at the distal lateral leg and the SP nerve will be superficial and midway between the peroneus longus muscle and extensor digitorum longus muscle (Image 2 Case 1).
- Remember to use the probe as a palpating device. I asked the patient to relate any symptoms she may experience as I scanned her leg. When I saw the mass on the screen, she related a tinel sign. That is why it is critical in regard to who is doing the exam Clown shape inflatable used.
- Adjust the gain in small amounts, if at all. You should be at the lowest gain to adequately assess the image. Too much gain hides pathology.
- Maintain light pressure but good contact. In this case, with a soft tissue mass, if it was completely compressible and I compressed it, I could have missed it or the nerve deep to it.