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

• Published in: Journal of applied physiology (1985) 2007-04, Vol.102 (4), p.1535-1544
• Main Authors: Chon, Deokiee, Beck, Kenneth C, Simon, Brett A, Shikata, Hidenori, Saba, Osama I, Hoffman, Eric A
• Format: Article
• Language: English
• Subjects: Administration, Inhalation; Animals; Biological and medical sciences; Chemical elements; Confidence intervals; Effects; Fundamental and applied biological sciences. Psychology; Krypton - administration & dosage; Lung - diagnostic imaging; Lung - physiopathology; Monte Carlo simulation; Pulmonary Gas Exchange - physiology; Pulmonary Ventilation - physiology; Radiographic Image Enhancement - methods; Reproducibility of Results; Sensitivity and Specificity; Sheep; Signal to noise ratio; Tomography; Tomography, X-Ray Computed - methods; Xenon - administration & dosage
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.01235.2005

Departments of 1 Radiology and 2 Biomedical Engineering, University of Iowa, Iowa City, Iowa; 3 Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins University, Baltimore, Maryland Submitted 28 September 2005 ; accepted in final form 13 November 2006 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 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. washin; regional ventilation measurements; computed tomography; pulmonary imaging; multidetector computed tomography; Monte Carlo simulation; regional lung function Address for reprint requests and other correspondence: E. A. Hoffman, Dept. of Radiology, Univ. of Iowa College of Medicine, 200 Hawkins Dr., Iowa City, IA 52242 (e-mail: eric-hoffman{at}uiowa.edu )