Determination of regional ventilation and perfusion in the lung using xenon and computed tomography

Abstract

We propose a model to measure both regional ventilation (V) and perfusion (Q) in which the regional radiodensity (RD) in the lung during xenon (Xe) washin is a function of regional V (increasing RD) and Q (decreasing RD). We studied five anesthetized, paralyzed, mechanically ventilated, supine sheep. Four 2.5-mm-thick computed tomography (CT) images were simultaneously acquired immediately cephalad to the diaphragm at end inspiration for each breath during 3 min of Xe breathing. Observed changes in RD during Xe washin were used to determine regional V and Q. For 16 mm(3), Q displayed more variance than V: the coefficient of variance of Q (CV(Q)) = 1.58 +/- 0.23, the CV of V (CV(V)) = 0.46 +/- 0.07, and the ratio of CV(Q) to CV(V) = 3.5 +/- 1.1. CV(Q) (1.21 +/- 0.37) and the ratio of CV(Q) to CV(V) (2.4 +/- 1.2) were smaller at 1,000-mm(3) scale, but CV(V) (0.53 +/- 0.09) was not. V/Q distributions also displayed scale dependence: log SD of V and log SD of Q were 0.79 +/- 0.05 and 0.85 +/- 0.10 for 16-mm(3) and 0.69 +/- 0.20 and 0.67 +/- 0.10 for 1,000-mm(3) regions of lung, respectively. V and Q measurements made with CT and Xe also demonstrate vertically oriented and isogravitational heterogeneity, which are described using other methodologies. Sequential images acquired by CT during Xe breathing can be used to determine both regional V and Q noninvasively with high spatial resolution.

3He MRI-based assessment of posture-dependent regional ventilation gradients in rats

“…Improved spatial resolution has been realized with xenon-enhanced computed tomography, where the ventilation is determined from the wash-in and wash-out rates of stable xenon (13,14,18,20). Using a MRI-based method, regional ventilation has been evaluated qualitatively from the variations in lung parenchyma signal when a volunteer was breathing air and pure oxygen, respectively (10).…”

Functional Imaging: CT and MRI

“…Little work had been done since the original description of this technique nearly twenty five years ago (97-100), although the FDA approval of Xe-MDCT for measurement of cerebral blood flow has met with moderate clinical acceptance (101). Recently, however, the application of Xe-MDCT for measurement of regional pulmonary ventilation has been updated, validated, and refined including extension of the technique to estimate regional perfusion and V/Q (28,(102)(103)(104)(105)(106)(107)(108)(109)(110)(111) In Figure 3, we demonstrate a typical Xenon wash-in wash-out attenuation curve in a sheep, along with a color coded image of regional ventilation. Scanning was accomplished through gated imaging (endexpiration) as a fixed concentration of Xenon gas was inspired during the wash-in phase and then room air was inspired during wash-out.…”

Microsphere maps of regional blood flow and regional ventilation

“…While the highest resolution where aerosol deposition can still be interpreted as a valid measure of regional ventilation remains to be determined, the results from FMS ventilation maps at the ϳ2-cm 3 level of scale can be compared with other high-resolution methods for regional ventilation measurement. Kreck et al (38) developed a regional ventilation model that utilized sequential computed tomography (CT) lung images acquired during the washin of 65% xenon to create a high-resolution a map of regional ventilation. Robertson et al (50) compared regional FMS ventilation measurements in five anesthetized sheep with measurements with the CT xenon model described by Kreck et al (38), where the CT analysis volume was adjusted to the ϳ2-cm 3 size of the cut lung pieces.…”

“…Kreck et al (38) developed a regional ventilation model that utilized sequential computed tomography (CT) lung images acquired during the washin of 65% xenon to create a high-resolution a map of regional ventilation. Robertson et al (50) compared regional FMS ventilation measurements in five anesthetized sheep with measurements with the CT xenon model described by Kreck et al (38), where the CT analysis volume was adjusted to the ϳ2-cm 3 size of the cut lung pieces. Because the CT images were acquired with sheep imaged in the supine posture, there were minor lung shape discrepancies, but the overall extent of heterogeneity described by the two methods was comparable, and large-scale gradients of ventilation were likewise comparable.…”