69098
The distribution of specific ventilation within the lung can be inferred using Multiple Breath Washout ( MBW ) experiments or imaging techniques such as Positron Emission Tomography ( PET ) using 13N , Magnetic Resonance Imaging ( MRI ) using either hyperpolarized gas ( 3 He , 129 Xe ) or proton MRI ( oxygen enhanced imaging ) .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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