Hyperpolarized³He MR Imaging: Physiologic Monitoring Observations and Safety Considerations in 100 Consecutive Subjects

Abstract

Purpose:To evaluate the safety of hyperpolarized helium 3 ( 3 He) magnetic resonance (MR) imaging. Materials and Methods:Local institutional review board approval and informed consent were obtained. Physiologic monitoring data were obtained before, during, and after hyperpolarized 3 He MR imaging in 100 consecutive subjects (57 men, 43 women; mean age, 52 years Ϯ 14 [standard deviation]). The subjects inhaled 1-3 L of a gas mixture containing 300 -500 mL 3 He and 0 -2700 mL N 2 and held their breath for up to 15 seconds during MR imaging. Heart rate and rhythm and oxygen saturation of hemoglobin as measured by pulse oximetry (SpO 2 ) were monitored continuously throughout each study. The effects of 3 He MR imaging on vital signs and SpO 2 and the relationship between pulmonary function, number of doses, and clinical classification (healthy volunteers, patients with asthma, heavy smokers, patients undergoing lung volume reduction surgery for severe emphysema, and patients with lung cancer) and the lowest observed SpO 2 were assessed. Any subjective symptoms were noted. Results:Except for a small postimaging decrease in mean heart rate (from 78 beats per minute Ϯ 13 to 73 beats per minute Ϯ 11, P Ͻ .001), there was no effect on vital signs. A mean transient decrease in SpO 2 of 4% Ϯ 3 was observed during the first minute after gas inhalation (P Ͻ .001) in 77 subjects who inhaled a dose of 1 L for 10 seconds or less, reaching a nadir of less than 90% at least once in 20 subjects and of less than 85% in four subjects. There was no correlation between the lowest SpO 2 and pulmonary function parameters other than baseline SpO 2 (r ϭ 0.36, P ϭ .001). The lowest mean SpO 2 varied by 1% between the first and second and second and third doses (P Ͻ .001) and was unrelated to clinical classification (P ϭ .40). Minor subjective symptoms were noted by 10 subjects. No serious adverse events occurred.

In Vivo Detection of Acinar Microstructural Changes in Early Emphysema with3He Lung Morphometry

“…This technique is a safe ( 14 ) and highly sensitive method with which to characterize the severity and distribution of alveolar structural abnormalities. In this approach, the lung acini are treated-in the framework proposed by Haefeli-Bleuer and Weibel ( 15 ) He diffusion measurements are used to determine values for acinar duct radii ( R ) and airway lumen radii ( r ) and to determine the depth of the alveolar sleeve ( h ) in each image pixel with the following equation: h = R 2 r .…”

“…In contrast, in subjects with an FEV 1 /FVC ratio between 70% and 79%, there were signifi cant differences in acinar duct radii, alveolar depth, and mean chord length compared with subjects with an FEV 1 /FVC ratio of 80% or more, indicating that 3 He lung morphometry MR imaging is capable of depicting and transient (duration of P O 2 decrease, 48 seconds 6 10; range, 32-99 seconds). The safety fi ndings in these subjects were incorporated into a 100-subject safety study previously reported in this Journal ( 14 ). Figure 2 shows 3 He MR and CT images in three subjects; there are large abnormalities and heterogeneity in 3 He lung morphometry parameters in the subject with GOLD 0 disease who is a smoker and the subject with GOLD 2 disease who is a former smoker.…”

Comparison Between Multivolume CT-Based Surrogates of Regional Ventilation in Healthy Subjects

“…Computed tomography (CT) using xenon gas measures ventilation from the gas wash-in and wash-out rate but is limited by expensive equipment and anesthetic properties of xenon gas (2). Different magnetic resonance imaging (MRI) techniques have been proposed to visualize ventilation defects, but currently, they are only partially quantitative and are able to provide low anatomic detail (3,4).…”

Morphometric changes in the human pulmonary acinus during inflation

“…The results can be used to calculate the average surface area and volume of individual alveoli and alveolar duct units as well as the total number of alveoli (34). Furthermore, these experiments are safe and suitable for in vivo studies in humans (15).…”