Ventilation measurements using fast‐helical free‐breathing computed tomography

Abstract

To examine the use of multiple fast-helical free breathing computed tomography (FHFBCT) scans for ventilation measurement. Methods: Ten patients were scanned 25 times in alternating directions using a FHFBCT protocol. Simultaneously, an abdominal pneumatic bellows was used as a real-time breathing surrogate. Regions-of -interest (ROIs) were selected from the upper right lungs of each patient for analysis. The ROIs were first registered using a published registration technique (pTV). A subsequent followup registration employed an objective function with two terms, a ventilationadjusted Hounsfield Unit difference and a conservation-of -mass term labeled ΔΓ that denoted the difference between the deformation Jacobian and the tissue density ratio. The ventilations were calculated voxel-by-voxel as the slope of a first-order fit of the Jacobian as a function of the breathing amplitude. Results: The ventilations of the 10 patients showed different patterns and magnitudes. The average ventilation calculated from the deformation vector fields (DVFs) of the pTV and secondary registration was nearly identical, but the standard deviation of the voxel-to-voxel differences was approximately 0.1. The mean of the 90 th percentile values of ΔΓ was reduced from 0.153 to 0.079 between the pTV and secondary registration, implying first that the secondary registration improved the conservation-of -mass criterion by almost 50% and that on average the correspondence between the Jacobian and density ratios as demonstrated by ΔΓ was less than 0.1. This improvement occurred in spite of the average of the 90th percentile changes in the DVF magnitudes being only 0.58 mm. Conclusions: This work introduces the use of multiple free-breathing CT scans for free-breathing ventilation measurements. The approach has some benefits over the traditional use of 4-dimensional CT (4DCT) or breath-hold scans. The benefit over 4DCT is that FHFBCT does not have sorting artifacts. The benefits over breath-hold scans include the relatively small motion induced by quiet respiration versus deep-inspiration breath hold and the potential for characterizing dynamic breathing processes that disappear during breath hold.

Motion compensated cone-beam CT reconstruction using an a priori motion model from CT simulation: a pilot study

“…With 5DCT, any arbitrary breathing state can be reconstructed without sorting artifacts with the same dose to patients as conventional 4DCT. Additionally, many investigations have shown potential downstream applications of 5DCT, such as tissue elasticity estimation (Stiehl et al 2020), ventilation imaging (Low et al 2021), and computational fluid dynamics modeling (Lauria et al 2021a). It is for these reasons that an a priori model based on 5DCT could provide many inherent benefits to CBCT.…”

An analysis of the regional heterogeneity in tissue elasticity in lung cancer patients with COPD

“…Evidence has been shown that ventilation mapping could aid in treatment planning by highlighting areas of high and low ventilation (27). While these studies of functional tissue mapping using ventilation are promising, accurately calculating ventilation from CT is still an ongoing effort (28)(29)(30)(31). Many of the developed approaches incorporate transformation-based calculations, or calculations based on a mapping of CT images and comparison of densities, both of which rely on the accuracy of deformable image registration.…”