Comparison of low‐ and ultralow‐dose computed tomography protocols for quantitative lung and airway assessment

Abstract

Purpose Quantitative computed tomography (CT) measures are increasingly being developed and used to characterize lung disease. With recent advances in CT technologies, we sought to evaluate the quantitative accuracy of lung imaging at low and ultra-low radiation doses with the use of iterative reconstruction (IR), tube current modulation (TCM), and spectral shaping. Methods We investigated the effect of five independent CT protocols reconstructed with IR on quantitative airway measures and global lung measures using an in-vivo large animal model as a human subject surrogate. A control protocol was chosen (NIH-SPIROMICS + TCM) and five independent protocols investigating TCM, low and ultra-low radiation dose, and spectral shaping. For all scans quantitative global parenchymal measurements (mean, median and standard deviation of the parenchymal HU, along with measures of emphysema) and global airway measurements (number of segmented airways and pi10) were generated. In addition, selected individual airway measurements (minor and major inner diameter, wall thickness, inner and outer area, inner and outer perimeter, wall area fraction, and inner equivalent circle diameter) were evaluated. Comparisons were made between control and target protocols using difference and repeatability measures. Results Estimated CT volume dose index (CTDIvol) across all protocols ranged from 7.32 mGy to 0.32 mGy. Low and ultra-low dose protocols required more manual editing and resolved fewer airway branches; yet, comparable pi10 whole lung measures were observed across all protocols. Similar trends in acquired parenchymal and airway measurements were observed across all protocols, with increased measurement differences using the ultra-low dose protocols. However, for small airways (1.9 ± 0.2mm) and medium airways (5.7 ± 0.4mm) the measurement differences across all protocols were comparable to the control protocol repeatability across breath-holds. Diameters, wall thickness, wall area fraction, and equivalent diameter had smaller measurement differences, than area and perimeter measurements. Conclusions In conclusion, the use of IR with low and ultra-low dose CT protocols with CT volume dose indices down to 0.32 mGy maintains selected quantitative parenchymal and airway measurements relevant to pulmonary disease characterization.

Impact of advanced detector technology and iterative reconstruction on low‐dose quantitative assessment of lung computed tomography density in a biological lung model

“…Pigs have previously been used as surrogates for the testing and development of imaging protocols due to their similarities to humans. 31 We chose two animals for this study to acquire data prior to and following the installation of the upgraded detectors and advanced software. Data were acquired across several days to incorporate realistic variability within the context of a biological subject undergoing separate imaging studies serving as a clinically relevant translational step between phantom studies and human patients.…”

Immune-Related Adverse Events: Pneumonitis

“…Chest radiography is not sufficiently sensitive to detect subtle findings of pneumonitis; therefore, symptomatic patients should be referred for thoracic CT imaging [78]. Radiation doses associated with thoracic CT are low with modern scanners, making serial thoracic imaging a safe and effective method to evaluate progression or resolution of pneumonitis [79]. Pulmonary function testing should be performed at the time of evaluation, as early impairment in pulmonary function may herald the onset of pneumonitis [80].…”

Technical Note: Radiation dose reduction from computed tomography localizer radiographs using a tin spectral shaping filter

“…The selective photon shield represented by a tin filter mounted in front of the x‐ray tube was initially introduced for better separation of the two energy spectra in dual‐energy CT . It was recently shown that such spectral shaping can be also used for single‐energy CT resulting in more efficient x‐ray beam utilization and allowing for further dose reduction …”

“…[6][7][8] The selective photon shield represented by a tin filter mounted in front of the x-ray tube was initially introduced for better separation of the two energy spectra in dual-energy CT. 9 It was recently shown that such spectral shaping can be also used for single-energy CT resulting in more efficient x-ray beam utilization and allowing for further dose reduction. [10][11][12] As a consequence of these dose reduction opportunities leading to CT examinations being at the range of one millisievert for various indications, the contribution from localizer radiographs (LRs) to the overall dose from CT becomes more prominent. Thus, respective adaptation and optimization of LR acquisition parameters are desired.…”