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Diagnostic Ultrasound

Ultrasound was first used for medical purposes in the late 1940's at the Naval Medical Research Institute in Bethesda, Maryland, and has since been adopted by many healthcare professionals to serve a variety of needs. 



Diagnostic ultrasound machines use high frequency sound waves to send energy into a bodily tissue.  The image is created by differences in how much of the energy is absorbed by tissues with differing densities, and in the time it takes for the sound wave to hit a tissue and return to the receiver.  â€‹



Tissues with different densities absorb different amounts of ultrasound waves, and are displayed as a different color on the machine.  

Bone: White

Fluid: Black

​Everything in between: Shades of Gray (more than 50...)



Transducer heads use various frequencies to reach different depths within the tissue.  The higher the frequency, the more superficial structures it will display.  The lower the frequency, the deeper the structures it will display.  These frequencies also affect the resolution of the image.  The higher frequencies cause wavelengths to decrease, creating more clear images.  Lower frequencies decrease wavelengths, which decreases the resolution of the image.  

     Translation:

High Frequency = Superficial Tissue = More Clear Picture

Low Frequency = Deep Tissue = Less Clear Picture

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​Contraindications: non-soft tissue ailments (because ultrasound "ain't got time for that!").  Also, pregnant women should limit the amount of ultrasounds they receive.  There is no danger in the regular number of scans used by your doctor, but getting ultrasound every day of your pregnancy may not be a good idea.  Ask your doctor for more information.



Procedure for visualizing TA:  Use the 7.5 MHz transducer head to visualize transversus abdominus (TA), as it is relatively superficial.  However, if the patient has a large amount of adipose tissue (obese or just has a beer belly), a lower frequency will be needed.  Put patient in supine (lying face up). Ask them to relax as the electroconductive gel is placed on the transducer (also tell them it'll be cold, because that's the nice thing to do). Palpate the iliac crest and the inferior angle of the 12th rib (of the patient), and put the transducer transversely in the middle of those two landmarks.  Look for the muscle layers on the screen; they should look like this:



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Use the caliper function on the machine to draw a line from the bottom of the TA plane up to the fascial plane between the TA and IAO.  There are no norms for muscle thickness measurements for TA, so compare bilaterally to verify if the muscle is "normal' on either side for that person.  Ask the patient to contract saying, "Draw your belly button in to your spine" or "Pretend you're squeezing into those skinny jeans".  Educate the patient on the importance of core stability and exercises can be performed (so they know why the heck you're doing this). Follow this up with exercise, including isometric contractions (which they can watch on the screen and see if they are doing them the right way!), followed by dead bug exercises and bridging in supine (after that you can get as creative as you want to progress your patient). 



Procedure for visualizing multifidus: â€‹Use the 5 MHz convex transducer to best visualize the multifidus.  Put the patient in prone, with a pillow under the stomach to minimize lumbar lordosis (otherwise you get a bad picture).  Palpate the sacrum and the spinous processes of L5 to L2. Again, tell the patient to relax as you put the cold electroconductive gel  on their low back in the area you palpated. Start with a longitudinal orientation of the transducer head, so you can visualize which segment you are seeing (count them!).  Freeze the picture, then you can take a thickness measurement of the multifidus.  For women, normal multifidus thickness AP is 2.2 cm, and lateral is 3.0 cm.  For men, norms for multifidus thickness AP is 2.6 cm, and lateral is 2.8 cm

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Next, put the transducer transversely over the vertebral segment being measured. You should be able to see both multifidi with the spinous processes in the middle (they will look black due to artifact).  Have the patient contract their multifidi by lifting their legs off the table (nerd alert: they spiral when they contract, it's pretty cool!).  After having a little fun, drop just off the spinous process to get a good picture of the multifidus, freeze the image, and use the manual setting on the caliper function to draw along the inside borders of the muscle.  For women, normal cross-sectional area of the multifidus is 6 sq cm at L4 and 7 sq cm at L5.  For men, norms are 8 sq cm at L4 and 9 sq cm at L5.  You should educate your patient on the importance of this muscle, as it pretty much affects everything in your life (for real), but especially on core stability and preventing or rehabilitating low back pain.  For exercise, have them do isometric contractions (again, looking on the screen to see if they are doing it correctly. Yay biofeedback tools!), followed by knee bending, and ending with prone leg lifts (then get creative with further progressions!). 

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In physical therapy, diagnostic ultrasound can be used for:


 

  • Biofeedback for re-education of core musculature, including transversus abdominus, multifidus, & pelvic floor



  • Viewing soft tissues to identify inflammation, tears, ruptures, lesions, fluid collection, and soft tissue masses



  • Measuring cross-sectional area and thickness of muscles to compare these to established norms

Transverse image of bilateral multifidi

Longitudinal image of multifidi & surrounding structures

​TREATMENT RATIONALES

REFERENCES

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