Corrigendum: Reliability of assessing skeletal muscle architecture and tissue organization of the gastrocnemius medialis and vastus lateralis muscle using ultrasound and spatial frequency analysis

Melanie Lesinski^1*Greg Bashford²Adrian Markov¹Lucie Risch³Michael Cassel³

• ¹University of Potsdam, Potsdam, Germany
• ²University of Nebraska-Lincoln Department of Biological Systems Engineering, Lincoln, United States
• ³Universitat Potsdam Hochschulambulanz, Potsdam, Germany

Corrigendum on: Reliability of assessing skeletal muscle architecture and tissue organization of the gastrocnemius medialis and vastus lateralis muscle using ultrasound and spatial frequency analysis Error in Figure/Table In the published article, there was an error in Table 2 as published. An error was made in the description of the physiological correlate for P6. The correct wording is: 'a higher P6 value indicates more disorganization of tendon/muscle fibers'. The corrected Table 2 and its caption "Mathematical description and physiological correlate of spatial frequency parameters" appear below. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated. Table 2. Mathematical description and physiological correlate of spatial frequency parameters. Parameter Mathematical description Mathematical formulation Physiological correlates Peak Spatial Frequency Radius (PSFR) Distance from origin to peak of maximum frequency amplitude in 2-D FFT spectrum 2 2 m m u v + , where ( ) , m m u v is the location of the model spectral peak • Most dominant spacing between hyperechoic perimysium of the muscle fascicles and hypoechoic muscle fibers • Higher value primarily indicates a tighter packing of tendon/muscle fibers P6 Width Euclidian distance of the standard deviation vector of the spatial frequency peak on 2-D FFT spectrum 2 2 u v   + , from model fit • A higher P6 value indicates more disorganization of tendon/muscle fibers Q6 Factor Ratio of Peak Spatial Frequency Radius to P6 Width Q6 = PSFR P6 • Normalization factor to faciliate comparision of fiber packing with fiber alignment • Higher value primarily indicates a "purer" (parallel) alignment of tendon/muscle fibers. Amax Normalized peak value of amplitude spectrum ( ) ( ) max , numel F u v F • Strength factor of the most dominant spacing of fascicles/fibers • Higher value primarily indicates more tendon/muscle fibers per unit volume PWP Image power within dominant spacing peak ( ) ( ) 2 , numel S F u v F  , where S is the region of the dominant narrowband peak • Strength factor of fiber spacing close to most dominant spacing • Higher value primarily indicates more tendon/muscle fibers per unit volume PPP Peak power percent ( ) 2 PWP 100% 2 , F u v   • Strength factor of most dominant spacing of fascicles/fibers as compared to other tissue • Higher value primarily indicates more tissue in alignment compared to other tissue in the sample volume