Original Contribution
Induced Transducer Orientation During Ultrasound Imaging: Effects on Abdominal Muscle Thickness and Bladder Position

https://doi.org/10.1016/j.ultrasmedbio.2009.05.018Get rights and content

Abstract

The use of ultrasound imaging (USI) by physiotherapists to assess muscle behavior in clinical settings is increasing. However, there is relatively little evidence of whether the clinical environment is conducive to valid and reliable measurements. Accurate USI measurements depend on maintaining a relatively stationary transducer position, because motion may distort the image and lead to erroneous conclusions. This would seem particularly important during dynamic studies typical of a physiotherapy assessment. What is not known is how much transducer motion can occur before error is introduced. The aim of this study is to shed some light on this question. Eight healthy volunteers (19 to 52 y) participated. USI images were taken of the lateral abdominal wall (LAW) and bladder base (midline suprapubic) at various manually induced transducer orientations (approximately –10 to 10° about 3 axes of rotation), which were quantified by a digital optical motion capture system. Measurements of transversus abdominis (TrA) thickness and bladder base position (cranial /caudal and anterior/posterior) were calculated. Repeated measures analysis of variance was performed to determine if the measurements obtained at the induced transducer orientations were statistically different (p < 0.05) from an image corresponding to a reference or starting transducer orientation. Motion analysis data corresponding to measurements that did not differ from reference image measurements were summarized to provide a range of acceptable transducer motion (relative to the pelvis) for clockwise (CW)/counter-clockwise (CCW) rotation, cranial/caudal tilting, medial/lateral tilting and inward/outward displacement. There were no significant changes in TrA thickness measurements if CW/CCW transducer motion was <9° and cranial/caudal or medial/lateral transducer tilting was <5°. Further, there were no significant changes in measurements of bladder base position if CW/CCW transducer motion was <10°, cranial/caudal or medial/lateral transducer tilting was <10° and 8°, respectively and inward/outward motion was <8 mm. These findings provide guidance on acceptable amounts of transducer motion relative to the pelvis when generating measurements of TrA thickness and bladder base position. Future sonographic studies and clinical assessment investigating these parameters could take these findings into account to improve imaging technique reliability. (E-mail: [email protected])

Section snippets

Introduction and Literature

There has been a significant increase in the clinical use of ultrasound imaging (USI) by physiotherapists to objectively measure architectural changes of muscle (e.g., thickness and cross-sectional area) and bladder position in both static and dynamic conditions. These applications fall within the scope of rehabilitative ultrasound imaging (RUSI) (Teyhen, 2006, Whittaker et al., 2007a). In the lumbopelvic region USI has been used to measure the thickness and/or cross-sectional area of the

Participants

Eight healthy volunteers (7 female and 1 male) aged 19–52 y were studied. Participants averaged 30.5 ± 10.7 y, 64.5 ± 10.3 kg and had a mean body mass index of 23.7 ± 3.1 kg/m2. Exclusion criteria included musculoskeletal or neuromuscular disorder affecting the lumbopelvic region, a history of lumbopelvic pain in the last year that required medical attention or resulted in the inability to work or perform recreational activities, a BMI >31 kg/m2, an inability to follow instructions or a skin disorder.

Results

In total, 111 transducer orientations and associated USI images of the TrA, and 143 transducer orientations and associated USI images of bladder base, from eight subjects, were used in the analysis. Vicon camera data was unavailable for 18 (7%) induced transducer orientations and the USI images associated with these missing motion analysis data were excluded from analysis.

A summary of the descriptive statistics (mean ± standard deviation, range) for transducer motion relative to the pelvis for

Discussion

This appears to be the first study that has attempted to establish guidance for acceptable (threshold) amounts of transducer motion for generating reliable measurements of TrA thickness and bladder base position (see Table 5 for a summary) during a clinical simulation. Although the absolute values of the USI parameters (i.e., TrA thickness) investigated are consistent with values published previously (Rankin et al. 2006), it may be useful to determine if the threshold amounts of acceptable

Summary

The purpose of this study was to shed light on the amount of USI transducer motion that is required before there is a significant error introduced into the measurement of TrA thickness and bladder base position, and in doing so, inform both clinicians and researchers using USI and designing future studies. We have done this by first determining if induced transducer orientation produced a significant difference in specific USI parameters compared with a reference position and then secondly by

Acknowledgements

The authors would like to thank Ion Medical Solutions, USA, and Vicon, Oxford, UK, for funding Ph.D. studentships for J.L.W. and M.B.W., respectively. Further, they express their thanks to the participants who volunteered to take part in the study, as well as physiotherapists Peter Worsley and San-Pei Chen for their assistance during data collection.

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