Rationale and Objectives
To investigate immobilization-induced ventilation defects when performing hyperpolarized 3 He (H 3 He) magnetic resonance imaging (MRI) of the lung.
Methods and Materials
Twelve healthy subjects underwent MRI of the lungs after inhalation of H 3 He gas at three time points: 1) immediately after having been positioned supine on the MRI scanner table, 2) at 45 minutes while remaining supine, 3) and immediately thereafter after having turned prone. All image sets were reviewed in random order by three independent, blinded readers who recorded number, location, and size of H 3 He ventilation defects. Scores were averaged for each time point and comparisons were made to determine change in number, location, and size of ventilation defects with time and positioning of the subject in the scanner.
Results
At baseline supine, there were small numbers of defects in the dependent (posterior) and nondependent (anterior) portions of the lung ( P = .625). At 45 minutes, there was a significant increase in the mean number of ventilation defects/slice (VDS) for the dependent ( P = .005) and a decrease for the nondependent lung portions ( P = .021). After subjects turned prone, mean VDS for posterior defects decreased significantly ( P = .011), whereas those for anterior defects increased ( P = .010). Most defects were less than 3 cm in diameter.
Conclusion
It was found that immobilization of the subject for an extended period led to increased number of H 3 He ventilation defects in the dependent portions of the lung. Therefore, after a subject is positioned in the scanner, H 3 He MR imaging should be performed quickly to avoid the occurrence of the immobilization-induced ventilation defects and possible overestimation of disease.
Hyperpolarized helium-3 (H 3 He) is a gaseous magnetic resonance imaging (MRI) contrast agent that, when inhaled, can be used to evaluate the airspaces of the lung. With this technique, high spatial resolution MRIs of lung ventilation can be obtained, as has been shown in numerous studies involving normal volunteers and patients with a variety of diseases ( ). Although there is generally homogeneous distribution of the MRI signal throughout the lung in healthy subjects after inhalation of the gas, small peripheral ventilation defects in the dependent areas of the lungs can been seen and are believed to be caused by collapse of small portions of the lung ( ). The purpose of this study was to investigate the effect of patient positioning and time on the frequency, size, and location of these defects to better understand their impact and significance in the diagnosis of pulmonary disease when using H 3 He MRI. Our findings were compared with earlier work done in posture-dependence of lung function, in animal studies and patients, using a variety of other modalities ( ).
Materials and methods
Subjects
The study group consisted of 12 healthy volunteers who had never smoked (6 men and 6 women; age range, 22–43 years; median age, 34 years) and had no history of lung disease. None had undergone H 3 He MRI of the lungs previously. All volunteers had to meet the following criteria: normal physical examination, normal spirometric results (predicted forced expiratory volume in one second [FEV 1 ] of 80% or greater); ratio of FEV 1 to forced vital capacity [FEV 1 /FVC] >0.70), normal chest radiography, >95% oxygen saturation at pulse oximetry, and no known allergies. All studies were performed with approval from the Food and Drug Administration for using H 3 He as an Investigational New Drug (IND 57,866) and under a protocol approved by our institution’s investigational review board. All volunteers provided informed written consent before their studies.
3 He Polarization
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MR Imaging
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Image Analysis
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Statistical Analysis
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Results
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Table 1
Presentation of the Mean Number (± Standard Deviation) of Hyperpolarized 3 He Magnetic Resonance Imaging Ventilation Defects Per Slice for the Group of 12 Subjects Imaged at Three Time Points: Baseline Supine, 45-Minute Supine, and Immediately after Turning Prone
Baseline_P_ ⁎ 45 Minutes_P_ ⁎ Prone_P_ ⁎ Entire lung 0.87 ± 0.89 1.43 ± 0.96 1.00 ± 0.67 Anterior 0.40 ± 0.036 .625 0.24 ± 0.029 .007 0.59 ± 0.076 .058 Posterior 0.47 ± 0.072 1.19 ± 0.161 0.41 ± 0.048 Defects <3 cm 0.69 ± 0.064 .012 1.28 ± 0.154 .034 0.92 ± 0.053 .001 Defects >3 cm 0.17 ± 0.015 0.16 ± 0.016 0.08 ± 0.008 Right Lung 0.43 ± 0.044 .893 0.66 ± 0.112 .428 0.56 ± 0.076 .227 Left Lung 0.44 ± 0.067 0.78 ± 0.145 0.44 ± 0.049 Superior 0.37 ± 0.037 .307 0.66 ± 0.123 .396 0.48 ± 0.062 .500 Inferior 0.50 ± 0.071 0.77 ± 0.136 0.53 ± 0.067
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Discussion
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Conclusion
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Acknowledgments
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