1. Lean Body Mass Assessment: Interpretations of Ultrasound
Christan Bury MS, RD, LD, CNSC
Clinical Dietitian – Intensive Care Unit
Cleveland Clinic
Cleveland, OH

2. Learning Objectives
Upon completion of this session, the learner will be able to:
Describe the benefits and limitations of portable ultrasound to measure body composition
Summarize the principles of measurement for ultrasound
Interpret ultrasound results

3. Ultrasound Introduced as alternative to skin calipers
Recent research has suggested that US may be as accurate as MRI in ability to quantify tissue thickness
Rectus femoris muscle thickness representative of overall muscle mass
Anatomy of the thigh

4. Ultrasound Benefits: Limitations Easily performed at bedside
Available in most ICUs
Low cost, painless
No risk to patients (no exposure to radiation)
Limitations
Affected by edema
Prone to technical errors
Unable to be used in patients with lower extremity injury or pre-existing skeletal deformity
Some technical errors include
compressibility
selection of reliable site
ability to ensure full relaxation state
hydration status

5. Ultrasound
High frequency sound waves passed from a transducer through skin
Sound waves echo back at different frequencies - differentiation among tissues
Echoes converted into signals for analysis
US allows you to quantify tissue thickness
The way the US works is via high frequency sound waves that pass from the transducer through skin
The Sound waves echo back at different frequencies, allowing for differentiation among tissues, as echoes are converted into signals for processing
Particularly looking at Skeletal Muscle, they are seen as thin bright linear bands.

6. Ultrasound Impedance Bone Muscle Air
Air < adipose tissue < muscle < bone
Difficulty differentiating between muscle-bone and adipose-bone interfaces
The strength of each image is represented by a dot, and the dot’s position represents the depth by which the echo was received
The dots are combined to form an image
High
Medium
None
It’s all about density or impedence. Air < adipose tissue < muscle < bone
Air has almost no imepedance or density whereas bone is quite dense and has a high impedence. Fat and muscle fall in between (tissue and muscle are relatively similar).
Because muscle and fat are similar in density/impedence, there is difficulty in differentiating between the muscle-bone and adipose-bone interfaces.
Strong reflections appear white (bone), weaker are grey (muscle and fat), no reflections are black (air)
The strength of each image is represented by a dot, and the dot’s position represents the depth by which the echo was received. The dots are combined to form an image.

7. Ultrasound Probe Selection Musculoskeletal structures
Long, striated and layered
High frequency, linear array
8.0 MHz and higher provide the highest resolution
Probe Selection
Musculoskeletal structures are long, striated and many times layered tissues. Due to the striated morphology of these tissues and their superficial location, high frequency, linear array transducers are best suited for this application. Ideally, 8.0 megahurtz MHz and above provide the highest resolution.

8. Ultrasound Probe Selection Musculoskeletal- long, striated and layered
High frequency, linear array MHz and provide the highest resolution
There are many types of probes, but the linear probe (image in the middle) has a higher frequency and therefore provides the highest resolution.

9. Ultrasound Quadriceps femoris
surrogate for lean body mass
Difficult to assess absolute values alone
no reference values
Repeated measures- changes in lean body mass over time
There is data to show that the Quadriceps femoris muscle is indicative of overall LBM
Added bonus that it’s relatively accessible in most ICU patients
Difficult to assess absolute values by themselves as measures of malnutrition, you don’t know what a patients baseline is. This is where a good hx is important, where did the patient come from? What’s their story?
It is more valuable to obtain repeated measures of the quadriceps femoris muscle to determine a change in LBM (likely loss) over time

10. Ultrasound Procedure lay supine with knee extended and relaxed
Locate the top of the patella and anterior superior iliac spine
Measure the midpoint between the two areas of interest
Heyland et al. Top Up Trial Manual

11. Ultrasound
Generous amount of water soluble transmission gel applied to prob
Transducer pressed against skin surface at 900 angle (perpendicular to skin)
Maximal compression applied once appropriate area visualized on screen

12. Ultrasound
Start at maximum depth to easily identify femur, then focus in as much as possible
Area of interest focused and frozen on screen, then measured using electronic calipers
As healthy muscle contains only little fibrous tissue only a few reflections occur, resulting in a relatively black picture. The acoustical impedance is very different between muscle and bone, causing a strong reflection, with hardly any sound passing through. This results in a bright bone echo with a characteristic bone shadow.

13. In this picture, there is clear definition between the different quadriceps muscles

14. Uncompressed
Ultrasound
 Resolution 2/2 edema

15. Mid-Thigh
Max Compression

16. Mid-Thigh
Calipers

17. Ultrasound: Summary
Ultrasounds are readily available at the bedside and are of no additional risk to the patient
Allow for identification of quadriceps muscle thickness
May be useful in measuring changes in muscle thickness over time

18. Learning Assessment Question
1. Which of the following is true of bedside US:
Edema has no effect on the results of quadriceps muscle layer thickness
You should minimally compress the probe when assessing the quadriceps
The curved probe is preferred over the linear probe for the assessment of the quadriceps femoris
The quadriceps measurement is best used to assess a change in LBM over time
Edema does effect results, to combat this you should maximally compress the US probe
You should maximally compress to get a better resolution
The linear probe is preferred
CORRECT ANSWER: best used as a change over time, not as individual number