Length and angle measurements of the lower extremity in digital composite overview images.

We here introduce a digital scanning method for determining leg length and angles. The leg length and angle measurements, image quality and radiation dose were evaluated. A composite overview image was reconstructed from a series of individual images. In 45 overview images, the total leg length and the femoro-tibial angle were determined by two radiologists, and the inter- and intra-observer variability was examined in the light of the measured values as well as the subjective assessment of the image quality. A dose comparison was carried out with a series of conventional whole leg images. The mean standard deviation of the multiple measurements of leg length was 0.4 mm for researcher I and 0.5 mm for researcher II. The difference in the mean values of the measured leg lengths between the researchers was 0.3 mm. The mean standard deviation of the multiple measurements of the femoro-tibial angle was 0.1 degrees for both researchers. The difference in the mean values of the measured femoro-tibial angle between the researchers was 0.03 degrees. On average, the marks for the image quality awarded by researcher II with an average score of 2 were very significantly worse than those awarded by researcher I with an average score of 1.5. The mean entrance dose value determined was 0.16 mGy lower in the digital system (0.49 mGy) than that of the comparative conventional series (0.65 mGy). Where there is a large number of possible length and angle measurements, the proposed procedure offers the advantages of good image quality, digital image processing, measurements that are easy to perform, reproducible and accurate, and lower radiation dose, and it is superior to conventional whole leg images.