Ventilation Series Similarity: A Study for Ventilation Calculation Using Deformable Image Registration and 4DCT to Avoid Motion Artifacts

Abstract

The major problem with ventilation distribution calculations using DIR and 4DCT is the motion artifacts in 4DCT. Quite often not all phases would exhibit mushroom motion artifacts. If the ventilation series similarity is sufficiently robust, the ventilation distribution can be calculated using only the artifact-free phases. This study investigated the ventilation similarity among the data derived from different respiration phases. Fifteen lung cancer cases were analyzed. In each case, DIR was performed between the end-expiration phase and all other phases. Ventilation distributions were then calculated using the deformation matrices. The similarity was compared between the series ventilation distributions. The correlation between the majority phases was reasonably good, with average SCC values between 0.28 and 0.70 for the original data and 0.30 and 0.75 after smoothing. The better correlation between the neighboring phases, with average SCC values between 0.55 and 0.70 for the original data, revealed the nonlinear property of the dynamic ventilation. DSC analysis showed the same trend. To reduce the errors if motion artifacts are present, the phases without serious mushroom artifacts may be used. To minimize the effect of the nonlinearity in dynamic ventilation, the calculation phase should be chosen as close to the end-inspiration as possible.

Volumetric multiphase ventilation imaging based on four‐dimensional computed tomography for functional lung avoidance radiotherapy

“…Most of the existing studies use BHCT or the EE/EI phase image pairs from 4DCT, which have moderate motion magnitudes. However, in our calculation process of the dynamic ventilation sequence, the registrations of phases pairs near the EE phase (DIR of T50/T40 and T50/T60) are faced with such a problem, especially due to the following: (a) When undergoing 4DCT scanning, patients tend to hold the breath for a short time at end‐exhalation, which makes the image of T60 phase very similar to that of T50 phase 22 . (b) Compared with common smoothness‐regularized strategy, in the TV algorithm we used, the sliding‐preserving constraint was imposed on the entire DVF, including most non‐sliding regions 39 .…”

“…However, in our calculation process of the dynamic ventilation sequence, the registrations of phases pairs near the EE phase (DIR of T50/T40 and T50/T60) are faced with such a problem, especially due to the following: (a) When undergoing 4DCT scanning, patients tend to hold the breath for a short time at end-exhalation, which makes the image of T60 phase very similar to that of T50 phase. 22 (b) Compared with common smoothnessregularized strategy, in the TV algorithm we used, the sliding-preserving constraint was imposed on the entire DVF, including most non-sliding regions. 39 This makes it necessary to consider the robustness of input DVFs when selecting the DIR-based expansion estimation metrics,whereas IJF method,as a proven robust CT ventilation algorithm, 31,32 is a suitable choice for our task.…”

“…presented normalization schemes that took into account the dynamic changes in lung volume during breathing to correct CTVI. Zhang et al 22 . observed that the usage of different 4DCT phase image pairs during calculating CTVI would lead to different ventilation distributions.…”

“…Du et al 21 presented normalization schemes that took into account the dynamic changes in lung volume during breathing to correct CTVI. Zhang et al 22 observed that the usage of different 4DCT phase image pairs during calculating CTVI would lead to different ventilation distributions. Moreover, Shao et al 23 proposed an Nphase CTVI concept to reduce the affection of lung tissue's out-of -phase behaviors.…”