A-mode and B-mode ultrasound measurement of fat thickness: a cadaver validation study

With technological advances, there has been a resurgence in ultrasound as a method to measure subcutaneous fat thickness. Despite the increased interest in this methodology, research comparing A-mode and B-mode ultrasound devices is lacking. Subcutaneous fat thickness measured by a low resolution (2.5 MHz) A-mode ultrasound and a high resolution (12 MHz) B-mode ultrasound were compared to the actual fat thickness in dissected cadavers.

Subcutaneous fat thickness of six cadavers was measured at the abdomen, thigh, triceps, and calf (plus chest for males and suprailiac for females) with both ultrasound devices before the cadavers were dissected and site-specific thickness was measured.

Correlations between both ultrasounds and the dissected measurement exceeded 0.90 at all sites with a few exceptions. At the abdomen, the relationship between the ultrasounds was 0.76, and the B-mode and dissected measurement was also 0.76. The correlation between dissection and A-mode was 0.75 for the suprailiac site, but it was not possible to discern the separation of tissue at this site when using the B-mode device. There were no significant differences (P > 0.05) between the devices and the dissected measurement at any of the six sites. The mean difference in fat thickness between A-mode and B-mode was <0.7 mm at all sites except the calf (1.2 mm) CONCLUSION: With the exception of the suprailiac site, both A-mode and B-mode ultrasound are equally capable of providing measurements of subcutaneous fat thickness with an accuracy of <1 mm at most sites.