title: Effect of low-xenon and krypton supplementation on signal/noise of regional CT-based ventilation measurements.
abstract: 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 <or=35%. 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 < 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 < 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.
authors.affiliation: Department of Radiology, University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: Deokiee
authors.initials: D
authors.lastname: Chon
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Beck
authors.forename: Brett A
authors.initials: BA
authors.lastname: Simon
authors.forename: Hidenori
authors.initials: H
authors.lastname: Shikata
authors.forename: Osama I
authors.initials: OI
authors.lastname: Saba
authors.forename: Eric A
authors.initials: EA
authors.lastname: Hoffman
mesh_terms: D000280:Administration, Inhalation; D000818:Animals; D007726:Krypton / Q000008:administration & dosage; D008168:Lung / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D011856:Radiographic Image Enhancement / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012756:Sheep; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014978:Xenon / Q000008:administration & dosage
chemical_list: D014978:Xenon; D007726:Krypton