Objective: Our aim was to design a practical and reproducible image segmentation method for calculations of total absorbed doses in organs and tumours for internally delivered radioisotopes. We have built upon our previously proposed use of two separate thresholds and employed an iterative technique for semiautomatic selection of background regions for segmenting an object of interest using thresholds that depend on the source-to-background ratio of activity concentrations.
Methods: The parameters of curves relating volume and activity thresholds to source-to-background ratio were established using phantoms with 20 different inserts. The accuracy of our technique was validated using a second phantom experiment, whereas the reproducibility of volume, activity and dose estimates of organs and tumours was investigated using 13 patient studies. The accuracy and reproducibility of segmentations achieved were assessed using images reconstructed with three different methods that ranged from a standard clinical reconstruction to an advanced quantitative reconstruction approach.
Results: In the validation phantom experiment, bottle volumes and activities measured using iterative adaptive thresholding agreed on average with the true values to within 4%, regardless of the reconstruction method used. In the patient studies, volumes and activities estimated from the single-photon emission computed tomography images reconstructed with clinical software agreed with the volumes and activities estimated using the advanced reconstruction approach to within 6%, whereas the corresponding doses agreed to within 4%.
Conclusion: The proposed iterative adaptive thresholding technique can accurately determine object volume and activity, which allows standard clinical reconstructions to generate absorbed dose estimates that are similar to those values obtained using more advanced reconstruction methods.
Departments of aPhysics and Astronomy
bRadiology, University of British Columbia, Vancouver, British Columbia, Canada
cDepartment of Nuclear Medicine, Pomeranian Medical University, Szczecin, Poland
Correspondence to Joshua Grimes, BSc, Medical Imaging Research Group, Vancouver General Hospital Research Pavilion, 366 828 West 10th Avenue, Vancouver, BC, Canada V5Z 1M9 Tel: +1 604 875 4111 x68688; fax: +1 604 875 5289; e-mail: firstname.lastname@example.org
Received April 15, 2012
Accepted August 20, 2012