We will stick to low frequency probes here (i.e. curvilinear and phased array - linear has its own purpose for detailed pleural assessment)
Which preset do you prefer for B line assessment?
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A tweetorial on optimal machine settings for B line image acquisition, with a focus on: focal position at pleura, harmonics off, and increased far gain.
Inspired/based on the recent article - https://t.co/vv2xBSZm6N
@cameron_baston @IsaacMatthiasM1
#POCUS #IMPOCUS
1/18
We will stick to low frequency probes here (i.e. curvilinear and phased array - linear has its own purpose for detailed pleural assessment)
Which preset do you prefer for B line assessment?
2/
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We won't discuss much about preset or probe type. But we will discuss machine settings to optimize B line quality, based on
1) Theory based on physical basis of B lines
2) In vitro study
3) Study in patients
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B lines are
1) reverberation artifacts
2) formed from the pleural interface when the interstitium is thickened
3) span the full depth of the field
See explanation in tweetorial on ABCs of lung ultrasound here
https://t.co/6GPdnK9gUP
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When the interstitium thickens, B lines form. The mechanism is not entirely understood. Either
— IM POCUS Focus (@IMPOCUSFocus) September 27, 2019
1) Tetrahedral structure created at the pleural surface continuously reflects
2) Some waves are able to pass through the lung
11/ pic.twitter.com/rrWEI2ICfX
Tissue harmonic imaging is a technology designed to minimize artifact. In theory, harmonics being "on" may reduce B line quantity. The same idea applies for cardiac presets, which tend to minimize artifact.
(Notably, there is conflicting literature here)
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Thus it would make sense to put the focus at the pleural line. The focal position is the depth at which lateral resolution is highest, so interstitial thickening is more likely to be detected w pleural at focal position.
Here, focus at 10 cm
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Often the brightness of B lines fades deeper into the image due to loss of energy with subsequent reverberations. Increasing the far gain can theoretically improve ease of visualizing B lines in the far field (as shown here).
10/
-focus at pleura
-more far-gain
-lung preset (vs abd)
Did not acheive significance for "harmonics off"
Limitations: one machine (Sparq), needs further study in pts.
https://t.co/jzJmSr0ZRZ
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This study sought to test if adjusted settings (developed based on in-vitro experiments) were associated change in perceived quality (and quantity) of B lines.
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In a retrospective study, most exams resembled the typical settings (and cardiac was most common preset).
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Adj settings were reported to have better quality in ~97% of cases
14/
Though more data is needed, it seems reasonable that for B line assessment:
1) focus set at pleural line
2) harmonics off
3) increased fair gain
Limitations: these were studied as a bundle (not individual). Study not designed to compare probes or presets.
15/
1) Consistency is important, in both clinical practice and in research.
2) The utility of B lines lies in their high sensitivity for interstitial edema. If settings are suboptimum and limit sensitivity, that reduces the power of the B line assessment.
16/
-remember to find the most perpendicular angle to the pleural line. Otherwise you may end up with a non-A non-B pattern, which is non-diagnostic.
-if ribs are obscuring view, can turn probe to remove ribs from view.
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Tagging a few #POCUS friends @kyliebaker888 @iceman_ex @msenussiMD @cameron_baston @Manoj_Wickram @DRsonosRD @NephroP @ArgaizR @ria_dancel @hraza222 @ThinkingCC @Wilkinsonjonny @katiewiskar
