EBCT DYNAMIC IMAGING OF THE SHOULDER RHYTHM

Abstract

The motion of the shoulder complex, the scapulo-humero-thoracic rhythm, is an equilibrium between transmission of loads and positioning of the upper limb. This rhythm, which can be described by 12 spatial variables, is either responsible for, or affected by the genesis of shoulder pathology and trauma. Thus, imaging the articulations of the shoulder through a global range of motion is essential in aiding diagnosis, management decisions and interpreting operative outcome. As such, the objective of this study was to dynamically image the scapulo-humero-thoracic rhythm.

The subjects were seated between the toroid of the scanner and maximally slewn table on a customised tripod which both protects the target rings and provides a degree of comfort. Each subject was asked to carryout 4 movements; adduction to abduction in the scapular plane, internal rotation to external rotation at 0° and 90° abduction and flexion to extension. Each movement was carried out over a period of 5 seconds, enabling the acquisition of 20 volumes per movement.

Electron Beam Computed Tomography (EBCT) enables the scanning of a number of contiguous slices, each taking 50 msec. Previously this has facilitated real-time imaging and rendering of both cardiopulmonary function and colonography. A GE Imatron EBCT C300 scanner was used with a multislice sequence imaging protocol to collect 8 transaxial slices per volume by sweeping an x-ray beam sequentially over 4 tungsten target rings and recording x-ray intensity via two fixed detector rings after the reflected beam passes through the body.

Each slice was post-processed by semi-automatic segmention using Amira software, and reconstructed to produce three-dimensional volumes of the humerus, scapula, clavicle and selected ribs. Anatomical landmarks were then identified and the normal rhythm of the shoulder was described.

In conclusion, EBCT provides a quick and efficient method for direct realtime dynamic imaging of the shoulder girdle under normal conditions, the first time this has been achieved to the best of our knowledge. Not only do these reconstructions provide further input matter for preexisting and future computational shoulder models, but estabilishes an initial baseline for further clinical experience. As such, we hypothesise the ability of this modalitiy to image pathological and traumatic disruption to shoulder rhythm. The potential clinical application of this tool would include imaging of traumatic instability and impingement, facilitated by some minor ergonomic alterations to the apparatus.