MAGNIFICATION ERROR IN RADIOGRAPHS OF CERVICAL SPINE IN LATERAL PROJECTION
VELIKOST VRATNIH VRETENC V STRANSKI PROJEKCIJI
Keywords:source to image receptor distance (SID), object to image receptor distance (OID), lateral radiography of the cervical spine, entrance skin dose (ESD)
Purpose: The main purpose of this study was to determine how the distance between the cervical spine and the image receptor on the one hand and the distance between the source and the image receptor on the other aff ects the image size of the cervical vertebrae. Moreover, it was important to understand how the entrance skin dose varies when the distance between the object to image receptor and the distance source to image receptor changes.
Methods: The theoretical part of this study was carried out based on an analysis of the readings, the practical part was carried out on a head, neck and trunk phantom at the radiological laboratory of the Faculty of Health Sciences (University of Ljubljana).
Results: When the object to image receptor distance (OID) was increased from 24 to 39 cm, the image size of the vertebra increased by 23% at a source to image receptor distance (SID) of 115 cm. At an SID of 150 cm, it increased by 17% and by 11% at an SID of 180 cm. When SID was decreased from 150 to 115 cm at an OID of between of 24 and 29 cm, the entrance skin dose increased by 26%. As the OID was increased further, the entrance skin dose (ESD) was even higher. Similarly, the ESD decreased with an increase in SID. For example, when SID was increased from 150 to 180 cm at an OID of between 24 and 29 cm, the ESD decreases by 8.5%.
Discussion and conclusion: The results indicate that the lateral radiography of the cervical spine should be performed at a SID of 150 cm. By doing so, it is assured that a proper image size is obtained, and the entrance skin dose is not harmful to the patient.