The assessment of spinal posture is a difficult endeavour given the lack of identifiable bony landmarks for placement of skin markers. Moreover, potentially significant soft tissue artefacts along the spine further affect the accuracy of marker-based approaches. The objective of this proof-of-concept study was to develop an experimental framework to assess spinal postures by using three-dimensional (3D) ultrasound (US) imaging. A phantom spine model immersed in water was scanned using 3D US in a neutral and two curved postures mimicking a forward flexion in the sagittal plane while the US probe was localised by three electromagnetic tracking sensors attached to the probe head. The obtained anatomical ‘coarse’ registrations were further refined using an automatic registration algorithm and validated by an experienced sonographer. Spinal landmarks were selected in the US images and validated against magnetic resonance imaging data of the same phantom through image registration. Their position was then related to the location of the tracking sensors identified in the acquired US volumes, enabling the localisation of landmarks in the global coordinate system of the tracking device. Results of this study show that localised 3D US enables US-based anatomical reconstructions comparable to clinical standards and the identification of spinal landmarks in different postures of the spine. The accuracy in sensor identification was 0.49 mm on average while the intra- and inter-observer reliability in sensor identification was strongly correlated with a maximum deviation of 0.8 mm. Mapping of landmarks had a small relative distance error of 0.21 mm (SD = ± 0.16) on average. This study implies that localised 3D US holds the potential for the assessment of full spinal posture by accurately and non-invasively localising vertebrae in space.

鉴于缺乏用于放置皮肤标记的可识别骨骼标志，脊柱姿势的评估是一项艰巨的工作。此外，沿着脊柱的潜在显着软组织伪影进一步影响基于标记的方法的准确性。这项概念验证研究的目的是开发一个实验框架，通过使用三维 (3D) 超声 (US) 成像来评估脊柱姿势。使用 3D US 扫描浸入水中的幻影脊柱模型，以中立和两个弯曲的姿势模拟在矢状面上向前弯曲，同时 US 探头由连接到探头头的三个电磁跟踪传感器定位。使用自动配准算法进一步细化获得的解剖“粗略”配准，并由经验丰富的超声医师验证。在 US 图像中选择脊柱标志，并通过图像配准对同一体模的磁共振成像数据进行验证。然后，它们的位置与在获取的 US 体积中识别的跟踪传感器的位置相关，从而能够在跟踪设备的全球坐标系中定位地标。这项研究的结果表明，局部 3D US 能够实现与临床标准相当的基于 US 的解剖重建，并能够识别不同脊柱姿势的脊柱标志。传感器识别的准确度平均为 0.49 毫米，而传感器识别的观察者内部和观察者间可靠性与 0.8 毫米的最大偏差密切相关。地标的映射平均有 0.21 毫米 (SD = ± 0.16) 的小相对距离误差。