Volumetric Xenon-CT Imaging of Conventional and High-frequency Oscillatory Ventilation1

Abstract

Rationale and Objectives For mechanical ventilation of patients with pulmonary injuries it has been proposed that high-frequency oscillatory ventilation (HFOV) offers advantages over conventional ventilation (CV), however, these advantages have been difficult to quantify. We used volumetric, dynamic imaging of Xenon (Xe) washout of the canine lung during both HFOV and CV to compare regional ventilation in the two modalities. Materials and Methods Three anesthetized, mechanically ventilated animals were studied, each at three different ventilator settings. Imaging was performed on an experimental Toshiba 256-slice scanner at 80 kV, 250 mAs, and 0.5 sec scans, yielding 12.8 cm of Z-axis coverage. Repeated images were acquired at increasing intervals between 1 and 10 seconds for 90 seconds during HFOV, and using retrospective respiratory gating to end-expiration for 60 seconds during CV. Image series were analyzed to quantify regional specific ventilation (sV̇) from the regional density washout time constants. Results High quality, high-resolution regional ventilation maps were obtained during both CV and HFOV. Overall ventilation decreased at smaller tidal volume, as expected. Regional sV̇ was more uniform during HFOV compared to CV but the underlying distribution of lung aeration was similar. Conclusions High-resolution volumetric ventilation maps of the lung may be obtained with the 256-slice multidetector CT scanner. There is a marked difference in the distribution of regional ventilation between CV and HFOV, with a significant gravitational ventilation gradient in CV that was not present during HFOV. This technique may be useful in exploring the mechanisms by which HFOV improves gas exchange.

Imaging of Ventilation with Dual-Energy CT during Breath Hold after Single Vital-Capacity Inspiration of Stable Xenon

“…Section thickness can be adjusted to match particular study needs. The mean pixel values of the xenon-enhanced images were 21.3-30 HU, which seem comparable to those obtained by using the multiplewith a slight anterior-posterior gradient as in animal experiments (7)(8)(9)11 ). We conclude that the xenon-enhanced images acquired with dual-energy CT in the single-breath-hold technique and processed with 3MD can qualitatively depict pulmonary ventilation.…”

“…Scan and reconstruction parameters were as follows: tube voltage of 80 kV and 140 kV with a 0.4-mm-thick tin (Sn) fi lter (hereafter, Sn/140 kV) for the fi rst scan and of 100 kV and Sn/140 kV for the second scan with respective tube currents of 193 and 82 mAs, a rotation time of 0.33 second, collimation of 0.6 3 128 mm, pitch of 0.55, reconstructed fi eld of view of 20 cm, reconstructed section thickness of 1.5 mm, reconstruction interval of 1 mm, and medium sharp reconstruction kernel X enon-enhanced dual-energy computed tomography (CT) has been reported as a promising tool for detection of abnormal pulmonary ventilation (1)(2)(3)(4)(5). To date, xenon-enhanced CT has been used with a multiplebreath-hold technique in animal experiments (6)(7)(8)(9)(10)(11)(12) and in clinical studies (1)(2)(3)(4)(5)13 ), in which patients inhale xenon for 1-2 minutes ( 1-5 ) to reach equilibrium before scanning of the thorax and xenon washout. Xenon-enhanced images showing regional pulmonary xenon concentrations can be calculated from the dual-energy CT data by using threematerial decomposition (3MD) technique ( 14,15 ).…”

Physiological predictors of survival during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

“…This results in the protection of the recruited lung (with greater compliance) from excessive cyclic variations in alveolar pressure. In addition, if the continuous distending pressure (CDP) is optimized following a stepwise recruitment maneuver, the more compliant lung regions are less susceptible to static hyperinflation [3,5,6], thereby reducing lung strain and ventilation-induced inflammation [7,8]. …”

Redistribution of Pulmonary Blood Flow Impacts Thermodilution-based Extravascular Lung Water Measurements in a Model of Acute Lung Injury

“…Repeated perfusion studies at additional locations could reduce this sampling error, but the additional contrast load eventually affects the ability to quantitate lung density63. Another solution has recently been provided with volumetric CT scanners that provide up to 320 simultaneous slices and 16 cm axial coverage64. This would enable total lung perfusion imaging with only 2 injections per condition.…”