Free-Breathing Three-Dimensional Computed Tomography of the Lung Using Prospective Respiratory Gating

Changes of Emphysema Parameters over the Respiratory Cycle During Free Breathing: Preliminary Results Using Respiratory Gated 4D-CT

The purpose of this research was to evaluate respiratory gated CT of the lung in patients with COPD for analysis of parenchymal characteristics who were potential candidates for volume reduction surgery. Eleven patients with clinically known emphysematous disease underwent a respiratory gated, free-breathing 64-multislice-CT (Aquilion 64, Toshiba). Retrospective image reconstruction was performed similar to cardiac CT at every 10% of the respiratory loop, resulting in 10 complete volumetric datasets at 10 equidistant time points. All images were transferred onto a PC for calculation of the total lung volume, emphysema volume, emphysema index, and mean lung density. Complete datasets could be successfully reconstructed in all patients. The mean lung volume increased from 6.9 L to 7.5 L over the respiratory cycle. Emphysema volume increased from 1.6 L to 2.0 L and emphysema index from 22.6% to 26.5% from expiration to inspiration. In conclusion, respiratory gated chest 4D-CT allows for combined morphologic and functional image analysis, which can provide new insight into functional impairment and individual treatment planning.

Combined Electrocardiography- and Respiratory-Triggered CT of the Lung to Reduce Respiratory Misregistration Artifacts between Imaging Slabs in Free-Breathing Children: Initial Experience

Objective

Cardiac and respiratory motion artifacts degrade the image quality of lung CT in free-breathing children. The aim of this study was to evaluate the effect of combined electrocardiography (ECG) and respiratory triggering on respiratory misregistration artifacts on lung CT in free-breathing children.

Materials and Methods

In total, 15 children (median age 19 months, range 6 months–8 years; 7 boys), who underwent free-breathing ECG-triggered lung CT with and without respiratory-triggering were included. A pressure-sensing belt of a respiratory gating system was used to obtain the respiratory signal. The degree of respiratory misregistration artifacts between imaging slabs was graded on a 4-point scale (1, excellent image quality) on coronal and sagittal images and compared between ECG-triggered lung CT studies with and without respiratory triggering. A p value < 0.05 was considered significant.

Results

Lung CT with combined ECG and respiratory triggering showed significantly less respiratory misregistration artifacts than lung CT with ECG triggering only (1.1 ± 0.4 vs. 2.2 ± 1.0, p = 0.003).

Conclusion

Additional respiratory-triggering reduces respiratory misregistration artifacts on ECG-triggered lung CT in free-breathing children.

Prospective respiratory-triggered 64-slice CT pulmonary angiography for detection of pulmonary embolism--a feasibility study in a porcine model

The objective of this study is to investigate the feasibility of prospectively respiratory-triggered CT pulmonary angiography (CTPA) for detection of pulmonary embolism (PE) in a porcine model. A free-breathing respiratory-triggered multislice CTPA (120 kV, 140 mAs(eff), 2.5-mm slice thickness) and two CTPA in breath-hold technique (120 kV, 140 mAs(eff.) and 250mAs(eff), 1-mm and 3-mm image reconstruction) were performed in six pigs with pulmonary embolism. Diagnostic accuracy was computed, and differences in detection rates between both techniques were assessed on a per-embolus basis with the Wilcoxon test. Thin-sliced 1-mm images, acquired with 250mAs(eff), served as the standard of reference. Respiratory-triggered CTPA reached high diagnostic accuracy in detection of lobar and segmental PE equal to the results with the breath-hold technique (p > 0.05). For detection of subsegmental emboli, standard breath-hold techniques performed significantly better than respiratory-gated CTPA (sensitivity, 68.3% versus 24.4%; p < 0.05). Free-breathing respiratory-triggered CTPA is feasible for detection of lobar and segmental PE, with diagnostic accuracy equivalent to that of a standard CTPA in breath-hold. Although this technique is not recommended for assessment of emboli in the subsegmental vasculature, prospective respiratory-triggered CTPA may be of added value in patients who cannot hold their breath appropriately for CTPA scanning.

Evaluation of a Reduced Dose Protocol for Respiratory Gated Lung Computed Tomography in an Animal Model

OBJECTIVE

We sought to evaluate and validate a low-dose protocol for respiratory-gated multislice computed tomography (CT) for volume calculations in small ventilated neonatal animals as a model for the ventilated human neonatal lung.

MATERIALS AND METHODS

Five mechanically ventilated newborn piglets were imaged in a multislice CT scanner (0.5-mm slice thickness, 4:16 pitch, 0.5 seconds rotation time, 120 kV) using a normal (100 mAs) and a reduced (10 mAs) dose protocol. All animals were scanned twice (at 100 and 10 mAs) at each of 3 different ventilator settings. Complete volume datasets were reconstructed throughout the respiratory cycle in increments of 10% using retrospective half-scan reconstruction. End-inspiratory volumes and volumes during maximal expiration (functional residual capacity) were calculated by a customized software and values for normal and reduced dose protocols were compared using Kolmogorov-Smirnov test and Bland-Altman plots.

RESULTS

Two volume datasets (one normal and one reduced dose protocol) showed artifacts on the axial images, which could not be analyzed by the software. Those values were determined after manual segmentation and excluded from final analysis. The mean (+/-SD) end-inspiratory volumes and functional residual capacity were 34.3 +/- 10.1 mL and 25.3 +/- 8.0 mL for the normal-dose protocol versus 33.1 +/- 10.0 mL and 24.7 +/- 8.1 mL for the reduced-dose protocol, respectively. There was no statistically significant difference between normal and reduced dose protocol (KS-Test: D = 0.14 < Dmax).

CONCLUSION

Lung volume calculation in ventilated newborn piglets (end-inspiratory volumes and functional residual capacity) can be performed using respiratory-gated multislice CT even at a substantially reduced dose (eg, to 10 mAs). This makes the technique a candidate for future pediatric use.