An Automatic Method for Measurement of Vertebral Bone Density Based on QCT without an External Reference Phantom

摘要

Purpose:We developed an automatic method for measurement of vertebral bone density based on QCT with the use of internal references(muscle and subcutaneous fat) instead of traditional external phantom.Methods:The automatic multistep approach starts with segmentation of periosteal and endosteal surfaces of spine to define ellipse ROI in cancellous bone followed by segmentation of muscle and subcutaneous fat in the spine image and a subsequent calculation of bone mineral density in ellipse ROI and segmentation trabecular and cortical bone ROI using muscle and subcutaneous fat as internal references.The segmentation approach used a hybrid region-growing method which used local adaptive threshold and morphological operation.Results:We conducted with-phantom and without-phantom measurements by using 94 clinical cases. The doctor manually defined the ellipse ROI in the with-phantom measurement. As for the without-phantom measurement, we use our method to automatically gain the BMD. The Interaclass Correlation Coefficient (ICC) is 0.93. We removed the points whose muscle and fat values are 2 times deviated from the standard deviation. And the calibrated ICC value is 0.999.Conclusion:The without-phantom measurement method is not fit for the patients whose muscle and fat are seriously deviated from the average value. The without-phantom measurement method proposed in this paper can automatically measure the BMD of spine. By accurately segmenting cortical bone and trabecular bone, determining ROI and removing inappropriate data, it is proved that the BMD measurement result by this method is highly consistent with that by with-phantom method.