Development and evaluation of a phantom for morphometric X-ray absorptiometry

Morphometric X-ray absorptiometry (MXA) provides the potential to assess ve rtebral deformity using a technique with much lower radiation dose to the p atient than standard radiographic procedures. MXA overcomes many other limi tations such as cone beam distortion observed in conventional plane radiogr aphs. A phantom has been designed to assess the accuracy of the MXA techniq ue, to monitor long-term precision and to assess inter- and intra-operator variability. The phantom consists of two columns of 12 cylinders representi ng the vertebral bodies, one of regular components and one representing ver tebral deformities. Each column may be inserted, as required, into a Perspe x torso-mimicking block. Initial assessment on the Lunar Expert-XL demonstr ates that the phantom provides image parameters reflecting those found clin ically. Measurement of vertebral height was found to be consistently under- estimatedd by 4.9%. Operator precision ranged from 0.6% for posterior heigh t measurement to 1.0% for middle height measurement of the regular componen t column. The corresponding precision range for the column representing ver tebral deformation was 0.6% (posterior) and 1.1% (middle). Analysis of 10 s cans of each column by two independent operators demonstrated a few signifi cant differences in height assessment confined to the 'thoracic' region of the regular column. However, inter-operator variability was found to increa se with increasing complexity of vertebral shape producing several differen ces, particularly in posterior height assessment of the deformed column.