Effect of scanning level and muscle condition on ultrasonographic cross-sectional measurements of the anterior masseter muscle S. BERTRAM*, G. BODNER † , A. RUDISCH † , I. BRANDLMAIER* & R. EMSHOFF* *Department of Oral and Maxillo-Facial Surgery, † Department of Radiology, University of Innsbruck, Innsbruck, Austria SUMMARY With the disadvantage of computed tomography showing cumulative biological effects and magnetic resonance imaging posing a problem in clinical availability and cost, several authors described the technique of ultrasonography to measure non-invasively local cross-sectional dimensions (LCSDs) of masseter muscle sites. However only few studies addressed the issue of ‘technique-related factors for intra- and inter- observer reliability’ to gain more consistent testing and diagnosis. The purpose of the present study was to determine (1) whether the scanning level and/or the muscle condition may affect LCSD measurements and (2) whether measurements made at identical levels may be reproducible. The study included 35 subjects with signs and symtoms of temporomandibular diorders. Bilateral ultra- sonographic investigation was performed with a linear (B-scan) 7 ® 5 Mhz small-part transducer to register LCSDs of the anterior masseter muscle on three different levels. Scans were made on the relaxed and contracted muscle. Measurements were made in two sessions with a time interval of at least 5 min. Data were analysed for repro- ducibility by using the intra-class correlation coef- ficient (ICC) and the method error (ME). Scanning level and muscle condition had a significant effect on muscle measurements (P ¼ 0 ® 000). There was no difference in LCSD between the right and left muscle (P ¼ 0 ® 531). Measurements recorded at a given site were consistent across the testing ses- sions (P ¼ 0 ® 058). The scanning level with highest reproducibility was halfway between the origin and insertion (ICC ¼ 0 ® 92; ME ¼ 6 ® 2%). The data suggest that ultrasonography is a reliable method for measuring LSCDs of the anterior masseter muscle. KEYWORDS: masseter muscle, ultrasonography Introduction Computed tomography (CT) (Weijs & Hillen, 1986; Newton al., 1987) and magnetic resonance imaging (MRI) (Hannam & Wood, 1989; Van Spronsen et al., 1989, 1991) are common diagnostic methods for the evaluation of cross-sectional areas and volumes of masticatory muscles. However, CT shows cumulative biological effects, and MRI poses a problem in terms of clinical availability and cost. Ultrasonography enables dynamic visualization of muscles of the head and neck. Several reports about the use of ultrsonography in the measurement of local cross-sectional dimensions (LCSDs) have been published (Kiliaridis & Ka ¨ lebo, 1991; Bakke et al., 1992; Raadsheer et al., 1996; Emshoff & Bertram, 1995, 1998; Emshoff, Bertram & Strobl, 1999). However, little attention has been directed at ‘tech- nique-related factors for intra- and inter-observer reliability’ to gain more consistent testing and diag- nosis. The purpose of the present study was to determine (i) whether the scanning level and ⁄ or the muscle condition may affect anterior masseter mus- cle LCSD measurements and (ii) whether measure- ments made at identical locations may be reproducible. ª 2003 Blackwell Publishing Ltd 430 Journal of Oral Rehabilitation 2003 30; 430–435