Error analysis of 4-dimensional computed tomography image reconstruction in uniform motion state

Abstract

Objective To investigate the accuracy of 4-dimensional computed tomography (4DCT) image reconstruction in uniform motion state using respiratory motion phantom. Methods The cosine wave movements of lung tumor in the craniocaudal direction were simulated on a respiratory motion phantom, and the simulations were divided into 6 groups according to the respiratory motion amplitude (A) and the breathing period (T), that is, A=0.5 cm, T=6 s; A=0.5 cm, T=3 s; A=1.0 cm, T=6 s; A=1.0 cm, T=3 s; A=1.5 cm, T=6 s; A=1.5 cm T=3 s. 4DCT scans were acquired using Philips big bore CT simulator, and the movements were scanned twice for each group, with same scanning parameters. Finally, the internal target volume (ITV) was delineated on the reconstructed 4DCT images, and the volume and length of ITVs were measured and compared with their theoretical values to analyze reconstruction errors of 4DCT. Results There were errors in all the 6 groups of ITV delineated on the reconstructed 4DCT images. The relative error range of ITV volume was from 1.13% to 27.64%, and that of ITV length was from -0.95~0.03 cm. The average ITV length error was 0.25 cm. When A=1.5 cm and T=6 s, the reconstruction error showed the maximum, and the volume errors presented 27.64% and 19.04%, while the length errors were 0.11 and 0.84 cm between the 2 scans. There were also differences between the results of 2 scans under the same respiratory motion parameters and scanning parameters. When A=0.5 cm and T=6 s, the volume errors of ITV were 14.47% and 4.43% in the 2 scans, with a difference of 10.00%. Conclusion There remain errors in 4DCT image reconstruction under uniform motion, and the size of the error is randomized and unpredictable.

Keywords

• 4-dimensional computed tomography
• image reconstruction
• delineation of gross target volume