Abstract
P1134
Introduction: Sacroiliitis may frequently occur in spondyloarthropathies, scoliosis, lumbar spinal fusion surgery, or trauma. Different modalities are utilized to evaluate sacroiliitis, including X-ray, Magnetic Resonance Imaging (MRI) and skeletal scintigraphy (Bone scan). Quantitative sacroiliac indices derived from various methods using skeletal scintigraphy have been utilized and can be of additional value in evaluating sacroiliitis than qualitative/visual methods alone. More recently, visual and quantitative methods have also been studied in Single Photon Emission Computed Tomography (SPECT) and hybrid SPECT/Computed Tomography (SPECT/CT) images for this purpose. This exhibit reviews and illustrates different methods described in the literature to calculate the sacroiliac joint (SIJ) index and the added value of SPECT and SPECT/CT in cases of sacroiliitis. The role of bone scintigraphy in prognostication and follow-up in sacroiliitis is also discussed.
Methods: Methods 1-4 are performed in posterior planar view. Method 1: A rectangular region of interest (ROI) is drawn over the left SIJ region and adjusted to cover the right iliac bone. This process is repeated for the right sacroiliac joint. For background, a rectangular ROI is drawn over the sacrum between the two SIJ ROIs. Average counts within each ROI are calculated as counts per pixel. Method 2: An irregular ROI is drawn over the left SIJ region. A similar mirror ROI is placed over the right sacroiliac joint region. For background calculation, irregular ROI is drawn manually over the sacrum between the two SI ROIs. Average counts within each ROI are calculated as counts per pixel. Method 3: A horizontal rectangular profile ROI is drawn to cover both the SIJs and sacrum. A profile of the counts (graph) in the profile ROI is generated to show peak counts noted over both the SIJs and sacrum. Method 4: Two similar rectangular ROIs are drawn over the left SIJ in the upper (superior ROI) and lower half (inferior ROI) adjusted for covering the entire joint region. Similarly, two ROIs are then placed over the right sacroiliac joint. A rectangular ROI is drawn over the sacrum between the SIJ ROIs. Average counts within each ROI are calculated as counts per pixel. Method 5: This involves comparison of tracer uptake in the SIJ and sacrum and visual scoring on SPECT and SPECT/CT images, and classified as uptake in the SIJ lesser, equal or greater than tracer uptake in the sacrum. Method 6: Quantitative analysis of SPECT/CT images is performed by drawing volumes of interest (VOIs) to obtain the maximum counts for each region. These ROIs are drawn in the whole and then separately in the inferior regions of the SIJs. Another ROI is drawn over the sacral promontory. The quantification of the maximum value in each ROI is noted from the counts in the VOIs of the SIJ with respect to the sacral promontory.
Results: SIJ index is calculated for each SIJ as the ratio of average counts in the ROI over the SIJ to the average counts in the ROI over sacrum (background) in planar images. In the profile ROI method (method 3), comparison of peak counts over each SIJ and sacrum is noted to assess presence of sacroiliitis. Qualitative (visual) and quantitative assessment on SPECT and SPECT/CT images is done in addition to the planar SIJ calculation. Different quantitative methods to assess sacroiliitis have been applied in various studies, but no study to date has compared all the methods in the same set of patients to determine the superiority of any of them, if present. The SIJ index may also vary depending on age and gender.
Conclusions: Different methods can be employed to evaluate SIJ for sacroiliitis. Quantitation using SPECT and SPECT/CT is a relatively newer concept, and potentially adds value to the findings of planar scintigraphy for sacroiliitis. Further studies are required to address the heterogeneity in the reporting sensitivity and specificity of these methods, variations in age groups and genders.
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