Quantification of 99mTc-MDP SPECT bone scans in the spine of Patients with Osseous metastases and normal patients using MRI guided attenuation correction

Background: Attenuation alone is the biggest destructive factor in quantifying the SPECT images. To correct this factor an attenuation map is needed. The entry of dual modality systems such as SPECT-CT to nuclear medicine, made it possible to correct attenuation in SPECT images. However, the combination of CT with SPECT results in receiving an additional dose by the patient. In this study, the MRI images of lumbar spine are used for providing an attenuation map specific of each patient for AC of 99mTC-MDP SPECT with segmentation-based attenuation correction (AC) in patients who had metastatic lesions in lumbar spine and normal patients. then the standardized uptake value (SUV) and activity concentration (ACC) values of lumbar spine were calculated.Methods: 16 patients (7 women and 9 men, mean age of 57.2±16.3) referred to perform 99m Tc- MDP bone scintigraphy of the lumbar region participated. Ten subjects lacked any bone lesion in the lumbar vertebrae and six other patients had at least one metastatic lesion in the lumbar spine. The MR images were realigned to preliminary reconstructed SPECT data using a semi manually algorithm and then segmented by means of a manually or semi manually algorithm. For generation of the attenuation map, the voxels depending to different regions were segmented into air, bone and soft tissue. attenuation coefficients of these voxels were obtained from the ICRU44 report. The attenuation map was then used for reconstruction of SPECT images by the STIR software, then ACC and Various SUVs were calculated and compared.Results: In this study, among the SUVBW values for reconstructed image by attenuation map, SUVmean had the lowest CV. The statistical comparison between ACC and SUV values of the normal and metastatic groups obtained from the reconstructed SPECT images by attenuation map and images without any AC showed a significant difference. The mean values of ACC and SUVs in two different images for metastatic vertebrae were higher than normal vertebrae. These differences for images with attenuation correction is greater than the images without attenuation correction.Conclusion: Without attenuation correction, the ACC and SUVs of spine bone were underestimated. The results of this study will be useful for understanding bias in SUV and ACC between reconstructed images with AC and reconstructed images without AC. Since the MRI images are also used to detect bone lesions along with bone scans. Therefore, Considering the additional dose associated with CT guided attenuation correction, MRI-based attenuation correction in bone SPECT would probably be as an another method especially in a nuclear medicine center that does not have SPECT-CT imaging.

کلیدواژه ها:

SPECT ، attenuation correction ، standard uptake value (SUV) ، MRI ، bone metastasis