Effect of low-xenon and krypton supplementation on signal/noise of regional CT-based ventilation measurements

Abstract

EA. Effect of low-xenon and krypton supplementation on signal/ noise of regional CT-based ventilation measurements. J Appl Physiol 102: [1535][1536][1537][1538][1539][1540][1541][1542][1543][1544] 2007. First published November 22, 2006; doi:10.1152/japplphysiol.01235.2005.-Xenon computed tomography (Xe-CT) is used to estimate regional ventilation by measuring regional attenuation changes over multiple breaths while rebreathing a constant Xe concentration ([Xe]). Xe-CT has potential human applications, although anesthetic properties limit [Xe] to Յ35%. We investigate effects of lower [Xe], including a low [Xe]-krypton (Kr) combination, on time constant (TC) determination. Six anesthetized sheep were scanned prone and supine using multidetector row CT. Lungs were imaged by respiratory gating during washin of a 30%, 40%, 55% Xe, and a 30% Xe/30% Kr mixture. Using Kr avoids unwanted effects of Xe. Mean TCs, coefficients of variation (CV), and half confidence intervals (CI)/ mean served as indexes of sensitivity to noise. Mean supine and prone TCs of three [Xe] values were not significantly different. Average CVs of TCs increased from 57% (55% Xe), 58% (40% Xe), and 73% (30% Xe) (P Ͻ 0.05: paired t-tests; 30% Xe vs. higher [Xe]). Monte Carlo simulation indicated a CV based on inherent image noise was 8% for 55% Xe and 17% for 30% Xe (P Ͻ 0.05). Adding 30% Kr to 30% Xe gave a washin signal equivalent to 40% Xe. Half CI/mean using the 30% Xe/30% Kr mixture was not significantly different from 55 and 40% Xe. Although average TCs were not affected by changes in [Xe], the higher CV and half CI/mean suggested reduced signal-to-noise ratio at the 30% [Xe]. The 30% Xe/30% Kr mixture was comparable to that of 40% Xe, providing an important agent for CT-based assessment of regional ventilation in humans.washin; regional ventilation measurements; computed tomography; pulmonary imaging; multidetector computed tomography; Monte Carlo simulation; regional lung function SINCE XENON (XE) GAS WAS FIRST introduced by Knipping and coworkers (21) as a contrast material applicable to the assessment of pulmonary function, it has been used extensively in scintigraphy (2, 3, 26), MRI (36), single-photon emission computed tomography (CT) (1), and X-ray CT (10,25,28). Stable (nonradioactive) Xe gas has a K-edge similar to that of iodine and is a potent X-ray attenuator, providing good contrast enhancement when used in conjunction with CT scanning (42). When imaged in a conventional CT scanner, lung attenuation varies linearly with the Xe concentration ([Xe]) in the air spaces (9), and the time course of Xe accumulation in the lung periphery during breathing, measured with serial CT images, is the basis for the Xe-CT measurement of regional ventilation (4, 33).Although Xe is an inert gas, it is moderately soluble in blood and tissue (18) and has been used clinically (7) as an inhaled anesthetic, ϳ30% more potent than nitrous oxide (5, 12, 25).[Xe] values of 30 -50% have been used to measure cerebral blood flow in human studies, but with repo...

Krypton-enhanced ventilation CT with dual energy technique: Experimental study for optimal krypton concentration

“…Krypton, another radio-opaque inert gas, has a lower attenuation effect than xenon gas, but may be useful for detecting functional alterations in the lungs with DECT because krypton has fewer effects on the body than xenon. To overcome these limitations of xenon, one report showed that a krypton and xenon gas mixture was a better contrast medium than a limited concentration of xenon gas in single energy CT [17]. Another report showed that ventilation DECT with aerosol inhalation of iodinated contrast instead of xenon in animals is feasible, but that the safety of inhaling an iodine contrast medium is unknown [18].…”

Krypton Ventilation Imaging Using Dual-Energy CT in Chronic Obstructive Pulmonary Disease Patients: Initial Experience

“…At the end of each stage, the results are computed and the trial can be stopped if the effectiveness is less than a minimum success rate or greater than an expected success rate (19). The sample size was computed by using the 81m ( 81m Kr) gas used in nuclear medicine for many decades, stable krypton could be an alternative to xenon for ventilation imaging with the use of DE CT. Its clinical tolerance was successfully tested in a few human subjects in the early 1950s (16), and its potential usefulness as a ventilation CT contrast agent, first suggested by Winkler et al (17), was recently reemphasized by Chon et al (18). To our knowledge, this technique has not been used in a clinical setting.…”

State of the Art. A Structural and Functional Assessment of the Lung via Multidetector-Row Computed Tomography: Phenotyping Chronic Obstructive Pulmonary Disease

“…Average regional time constants are similar for repeat runs reducing inspired Xe gas concentrations from 55 to 30%, but the coefficient of variation at 30% Xe is significantly greater than at 40% and higher concentrations. The addition of 30% krypton gas to 30% Xe gas provides the same contrast enhancement and signal-to-noise ratio as 40% Xe (155). Krypton has none of the unwanted side effects of higher concentrations of Xe gas.…”