Background: To estimate and compare the sacroiliac joint (SIJ) index in skeletal scintigraphy by four different methods of quantification employed in normal subjects of different age groups.
Material and methods: The whole-body skeletal survey of 100 subjects, who underwent skeletal scintigraphy three hours after injection of 99mTc-Methylene Diphosphonate (MDP), were selected for this analysis. The patients having previous history of low back pain, joint pain or any benign bone joint disorders (e.g. ankylosing spondylitis, metabolic bone disease, and osteoarthritis), documented bone lesions or tumors within the pelvis region were excluded from the study. All subjects had normal posterior pelvis view on visual assessment in the respective study. Sacroiliac joint index was calculated by quantitative sacroiliac scintigraphy. In each subject, four different methods of quantification were carried out: 1. irregular region of interest (ROI) method, 2. rectangular ROI method, 3. profile peak counts (PPC) method and 4. profile integrated counts (PIC) method and applied to calculate SIJ index. SIJ indices for left and right sacroiliac joints were calculated by dividing the count for each joint by the count for the sacrum. Results obtained by the four methods were compared statistically.
Results: The overall SIJ index was found to range from 1.06 to 1.36 in the study population of 100 subjects encompassing all age groups. There was no significant difference in the estimated SIJ index within each age group obtained by the four different methods employed in this study. The values of SIJ index were as follows: in patients aged 2-20 years - they ranged from 1.22 to 1.36; in patients aged 21-40 years - from 1.07 to 1.19; for patients aged 41-60 years - from 1.08 to 1.19 and in patients aged 61 years and older, SIJ values were slightly lower than in other groups and ranged from 1.06 to 1.13.
Conclusion: Methods of selecting a region of interest have no significant effect on the calculation of SIJ index and in healthy subjects its values range between 1.06 and 1.36, depending on the age of the subject. The maximum value was observed in patients aged 2-20 years and minimum values were noted in patients aged 61 and older.