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CRS56
Does Unit of Reporting, Depth and Probe Load Influence the Reliability of Muscle Shear Wave Elastography?

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Background

Several shear wave elastography (SWE) systems offer the option to report readings in shear wave velocity (m/s) and Young’s modulus (kPa). 

The difference in the reliability between the two units is unknown. 

The difference in the reliability between the two units is unknown. 

Although shear wave propagation is known to be depth dependent, there is no standardised protocol or recommendation regarding measurement depth in muscle.
SWE is less operator-dependent than strain elastography; however, it is still dependent on the pressure applied by the operator.
 

Objective

To test the effect of using different reporting units, acquisition depth and probe load on the reliability of SWE in healthy skeletal muscle. 

 

Methods

The vastus lateralis, biceps femoris, biceps brachii and abductor digiti minimi muscles were investigated in twenty healthy participants.
The SWE readings were measured in SWV (m/s) and Young’s modulus (kPa).
Three acquisitions of varying depths were acquired from vastus lateralis (fig 1).
Minimal probe load was compared with the use of a standoff gel layer (0.5 cm).
Three repeated readings were acquired to assess reliability using intraclass correlations (ICC).
 

Results

The mean elasticity varied across the muscles and ranged from 1.54 m/s to 2.55 m/s [difference= 1.01 m/s (95% CI= 0.92, 1.10)]. (table 1 and fig 2)
Reporting readings in m/s resulted in higher ICC of .83 (.65, 93) in comparison to .77 (.52, .90) for kPa for the vastus lateralis muscle only (table 1).
The standoff gel method decreased reliability to .62 (.20, .84) despite the mean velocity being similar to minimal probe load.
The variance of the repeated readings increased significantly with depth (fig.3) from 0.07 at 4cm to 0.17 at 6cm (p<0.001). SWV value was not significantly affected by depth (fig 4).
 

Conclusions

SWV proportionally increase in variability as depth increases despite no significant change in the mean value.
Placing the probe in direct contact with the skin using minimal pressure yields more reliable reading in comparison to utilising a standoff gel between the probe and skin surface.
Attention to these factors should assist in acquiring reliable readings and developing a standardised operating procedure.
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