Lumbar spine radiology: analysis of the posteroanterior projection

The use of the posteroanterior (PA) technique as a means of dose reduction has been used effectively in radiology departments for chest and abdominal examinations. The aim of this investigation was to establish if the PA lumbar spine projection offers any advantages over the traditional anteroposterior (AP) view in terms of radiation dose and image quality. The contribution of tissue displacement to any dose reduction was also evaluated. The first part of the study involved the use of an anthropological phantom where entrance surface and an internal dose were measured for both the PA and AP projections. Entrance surface doses for both projections were then measured on randomly allocated female patients. Resultant image quality was assessed using CEC quality criteria. Anterior to posterior patient diameter was also recorded. The results demonstrated that with the PA compared with the AP projection, reductions of 38.6% (p = 0.016) and 38.9% (p = 0.02) in patient entrance surface dose and internal phantom dose, respectively. No significant differences in image quality were noted between the two projections. Patient diameter decreased by 1.8 cm with the PA view. The authors conclude that tissue displacement is the main factor for the patient dose reduction and recommend employment of the PA procedure for routine lumbar spine examinations.