Name: quantitative mapping of specific ventilation in the human lung using proton magnetic resonance imaging and oxygen as a contrast agent
Uploaded: 2019-06-05T14:00:00
Description: Watch this Scientific Journal Video about Quantitative Mapping of Specific Ventilation in the Human Lung using Proton Magnetic Resonance Imaging and Oxygen as a Contrast Agent at JoVE.com

This work was supported by the National Heart, Lung and Blood Institute (NHLBI) (grants R01 HL-080203, R01 HL-081171, R01 HL-104118 and R01-HL119263) and the National Space Biomedical Research Institute (National Aeronautics and Space Administration grant NCC 9-58). E.T. Geier was supported by NHLBI grant F30 HL127980.

The University of California, San Diego Human Research Protection Program has approved this protocol.
1. Subject Safety and Training
<ol>
	<li>Obtain written, informed consent from the subject. Describe the potential risks presented by exposure to rapidly changing magnetic fields, and the potential discomfort of using facial mask and breathing dry gas.</li>
	<li>Ensure that the subject can safely undergo MR scanning, utilizing the locally approved MRI safety screening questionnaire.</li>
	<l...

<ol>
	<li>S&#225;, R. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vertical+distribution+of+specific+ventilation+in+normal+supine+humans+measured+by+oxygen-enhanced+proton+MRI.">Vertical distribution of specific ventilation in normal supine humans measured by oxygen-enhanced proton MRI.</a> Journal of Applied Physiology. 109 (6), 1950-1959 (2010).</li><li>Henderson, A. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+gravitational+distribution+of+ventilation-perfusion+ratio+is+more+uniform+in+prone+than+supine+posture+in+the+normal+human+lung.">The gravitational distribution of ventilation-perfusion ratio is more uniform in prone than supine posture in the normal human lung.</a> Journal of Applied Physiology. 115 (3), 313-324 (2013).</li><li>Geier, E. T., Neuhart, I., Theilmann, R. J., Prisk, G. K., S&#225;, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatial+persistence+of+reduced+specific+ventilation+following+methacholine+challenge+in+the+healthy+human+lung.">Spatial persistence of reduced specific ventilation following methacholine challenge in the healthy human lung.</a> Journal of Applied Physiology. 124 (5), 1222-1232 (2018).</li><li>Tedjasaputra, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+heterogeneity+of+regional+specific+ventilation+is+unchanged+following+heavy+exercise+in+athletes.">The heterogeneity of regional specific ventilation is unchanged following heavy exercise in athletes.</a> Journal of Applied Physiology. 115 (1), 126-135 (2013).</li><li>Fowler, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lung+Function+Studies.+III.+Uneven+Pulmonary+Ventilation+in+Normal+Subjects+and+in+Patients+with+Pulmonary+Disease.">Lung Function Studies. III. Uneven Pulmonary Ventilation in Normal Subjects and in Patients with Pulmonary Disease.</a> Journal of Applied Physiology. 2 (6), 283-299 (1949).</li><li>Robertson, J. S., Siri, W. E., Jones, H. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lung+ventilation+patterns+determined+by+analysis+of+nitrogen+elimination+rates;+use+of+mass+spectrometer+as+a+continuous+gas+analyzer.">Lung ventilation patterns determined by analysis of nitrogen elimination rates; use of mass spectrometer as a continuous gas analyzer.</a> Journal of Clinical Investigation. 29 (5), 577-590 (1950).</li><li>S&#225;, R. C., Asadi, A. K., Theilmann, R. J., Hopkins, S. R., Prisk, G. K., Darquenne, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Validating+the+distribution+of+specific+ventilation+in+healthy+humans+measured+using+proton+MR+imaging.">Validating the distribution of specific ventilation in healthy humans measured using proton MR imaging.</a> Journal of Applied Physiology. 116 (8), 1048-1056 (2014).</li><li>Musch, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Topographical+distribution+of+pulmonary+perfusion+and+ventilation,+assessed+by+PET+in+supine+and+prone+humans.">Topographical distribution of pulmonary perfusion and ventilation, assessed by PET in supine and prone humans.</a> Journal of Applied Physiology. 93 (5), 1841-1851 (2002).</li><li>Venegas, J. G., Schroeder, T., Harris, R. S., Winkler, R. T., Melo, M. F. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+distribution+of+ventilation+during+bronchoconstriction+is+patchy+and+bimodal:+a+PET+imaging+study.">The distribution of ventilation during bronchoconstriction is patchy and bimodal: a PET imaging study.</a> Respiratory Physiology &amp; Neurobiology. 148 (1-2), 57-64 (2005).</li><li>Orphanidou, D., Hughes, J. M., Myers, M. J., Al-Suhali, A. R., Henderson, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tomography+of+regional+ventilation+and+perfusion+using+krypton+81m+in+normal+subjects+and+asthmatic+patients.">Tomography of regional ventilation and perfusion using krypton 81m in normal subjects and asthmatic patients.</a> Thorax. 41 (7), 542-551 (1986).</li><li>King, G. G., Eberl, S., Salome, C. M., Meikle, S. R., Woolcock, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Airway+closure+measured+by+a+technegas+bolus+and+SPECT.">Airway closure measured by a technegas bolus and SPECT.</a> American Journal of Respiratory and Critical Care Medicine. 155 (2), 682-688 (1997).</li><li>Horn, F. C., Deppe, M. H., Marshall, H., Parra-Robles, J., Wild, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+regional+fractional+ventilation+in+human+subjects+by+measurement+of+hyperpolarized+3He+washout+with+2D+and+3D+MRI.">Quantification of regional fractional ventilation in human subjects by measurement of hyperpolarized 3He washout with 2D and 3D MRI.</a> Journal of Applied Physiology. 116 (2), 129-139 (2014).</li><li>Hamedani, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+hybrid+multibreath+wash-in+wash-out+lung+function+quantification+scheme+in+human+subjects+using+hyperpolarized+3+He+MRI+for+simultaneous+assessment+of+specific+ventilation,+alveolar+oxygen+tension,+oxygen+uptake,+and+air+trapping.">A hybrid multibreath wash-in wash-out lung function quantification scheme in human subjects using hyperpolarized 3 He MRI for simultaneous assessment of specific ventilation, alveolar oxygen tension, oxygen uptake, and air trapping.</a> Magnetic Resonance in Medicine. 78 (2), 611-624 (2017).</li><li>Hall, E. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+supine+exercise+on+the+distribution+of+regional+pulmonary+blood+flow+measured+using+proton+MRI.">The effect of supine exercise on the distribution of regional pulmonary blood flow measured using proton MRI.</a> Journal of Applied Physiology. 116 (4), 451-461 (2014).</li><li>Henderson, A. C., S&#225;, R. C., Barash, I. A., Holverda, S., Buxton, R. B., Prisk, G. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+intravenous+infusion+of+20mL/kg+saline+alters+the+distribution+of+perfusion+in+healthy+supine+humans.">Rapid intravenous infusion of 20mL/kg saline alters the distribution of perfusion in healthy supine humans.</a> Respiratory Physiology &amp; Neurobiology. 180 (2-3), 331-341 (2012).</li><li>Arai, T. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+quantitative+multiple-breath+specific+ventilation+imaging+using+colocalized+2D+oxygen-enhanced+MRI+and+hyperpolarized+3He+MRI.">Comparison of quantitative multiple-breath specific ventilation imaging using colocalized 2D oxygen-enhanced MRI and hyperpolarized 3He MRI.</a> Journal of Applied Physiology. 125 (5), 1526-1535 (2018).</li><li>Chen, Q., Jakob, P. M., Griswold, M. A., Levin, D. L., Hatabu, H., Edelman, R. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oxygen+enhanced+MR+ventilation+imaging+of+the+lung.">Oxygen enhanced MR ventilation imaging of the lung.</a> Magma: Magnetic Resonance Materials in Physics, Biology, and Medicine. 7 (3), 153-161 (1998).</li><li>. Deforminator: Projective transformation to register small scale Lung deformation Available from: <a target="_blank" href="https://github.com/UCSDPulmonaryImaging/Deforminator">https://github.com/UCSDPulmonaryImaging/Deforminator</a> (2019)</li><li>Yang, G., Stewart, C. V., Sofka, M., Tsai, C. -. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Registration+of+Challenging+Image+Pairs:+Initialization,+Estimation,+and+Decision.">Registration of Challenging Image Pairs: Initialization, Estimation, and Decision.</a> IEEE Transactions on Pattern Analysis and Machine Intelligence. 29 (11), 1973-1989 (2007).</li><li>Arai, T. J., Villongco, C. T., Villongco, M. T., Hopkins, S. R., Theilmann, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Affine+transformation+registers+small+scale+lung+deformation.">Affine transformation registers small scale lung deformation.</a> Conf Proc IEEE Eng Med Biol Soc. 2012, 5298-5301 (2012).</li><li>Theilmann, R. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+MRI+measurement+of+lung+density+must+account+for+the+change+in+T(2)+(*)+with+lung+inflation.">Quantitative MRI measurement of lung density must account for the change in T(2) (*) with lung inflation.</a> Journal of Magnetic Resonance Imaging. 30 (2), 527-534 (2009).</li><li>Arai, T. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetic+Resonance+Imaging+Quantification+of+Pulmonary+Perfusion+using+Calibrated+Arterial+Spin+Labeling.">Magnetic Resonance Imaging Quantification of Pulmonary Perfusion using Calibrated Arterial Spin Labeling.</a> Journal of Visualized Experiments. 51 (51), e2712 (2011).</li><li>Lewis, S. M., Evans, J. W., Jalowayski, A. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+Distributions+of+Specific+Ventilation+Recovered+From+Inert-Gas+Washout.">Continuous Distributions of Specific Ventilation Recovered From Inert-Gas Washout.</a> Journal of Applied Physiology. 44 (3), 416-423 (1978).</li><li>Cook, F. R., Geier, E. T., Asadi, A. K., S&#225;, R. C., Prisk, G. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+Prototyping+of+Inspired+Gas+Delivery+System+for+Pulmonary+MRI+Research.">Rapid Prototyping of Inspired Gas Delivery System for Pulmonary MRI Research.</a> 3D Printing and Additive Manufacturing. 2 (4), 196-203 (2015).</li><li>Zapol, W. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pulmonary+Delivery+of+Therapeutic+and+Diagnostic+Gases.">Pulmonary Delivery of Therapeutic and Diagnostic Gases.</a> Journal of Aerosol Medicine and Pulmonary Drug Delivery. 31 (2), 78-87 (2018).</li><li>Kang, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+silico+modeling+of+oxygen-enhanced+MRI+of+specific+ventilation.">In silico modeling of oxygen-enhanced MRI of specific ventilation.</a> Physiological Reports. 6 (7), e13659 (2018).</li></ol>

Specific ventilation imaging allows quantitative mapping of the spatial distribution of specific ventilation in the human lung. Alternatives to SVI exist but are limited in some manner: Multiple breath washout provides a measure of heterogeneity but lacks spatial information23. Alternative imaging methods expose patients to ionizing radiation (e.g., SPECT, PET, CT, gamma scintigraphy) or are not widely available (hyperpolarized gas imaging using MRI). Specific ventilation imaging provides spatial ...

The overall goal of specific ventilation imaging (SVI) &#8213; a proton magnetic resonance imaging (MRI) technique that uses oxygen as a contrast agent1 &#8213; is to quantitatively map specific ventilation in the human lung. Specific ventilation is the ratio of fresh gas delivered to a lung region in one breath divided by the end expiratory volume of the same lung region1. In conjunction with measurements of local lung density, specific ventilation can be used to compute regional ventilation2. Measurements of local ventilation and ventilation heterogeneity that are provided by SVI have the potential to enrich the understanding of how the lung functions, both normally and abnormally3,4.
Specific ventilation imaging is an extension of the classical physiology test, multiple breath washout (MBW), a technique first introduced in the 1950s5,6. Both techniques use gas washin/washout to measure heterogeneity of specific ventilation, but SVI provides spatially-localized information while MBW provides only global measures of heterogeneity. In MBW, a mass spectrometer is used to measure the mixed expired concentration of an insoluble gas (nitrogen, helium, sulfur hexafluoride, etc.) over many breaths during a washout of that gas, as depicted in Figure 1. Along with the expired volume per breath during the washout period, this information can be used to compute the overall distribution of specific ventilation in the lung. In SVI, an MRI scanner is used to measure the T1-weighted signal &#8213; which is a surrogate for the amount of oxygen in solution in lung tissue, a direct indicator of local oxygen concentration &#8213; in each lung voxel over many breaths during several washin/washouts of oxygen. In a way that is directly analogous to MBW, this information allows us to compute the specific ventilation of each lung voxel. In other words, the technique performs thousands of parallel MBW-like experiments, one for each voxel, during an SVI experiment. Indeed, the spatial maps of specific ventilation thus produced can be compiled to recover the specific ventilation heterogeneity output of MBW. A validation study7 showed that the two methodologies produced comparable results when performed in series on the same subjects.
Other imaging modalities exist that, like SVI, provide spatial measures of ventilation heterogeneity. Positron emission tomography (PET)8,9, single-photon emission computed tomography (SPECT)10,11, and hyperpolarized gas MRI12,13 techniques have been used to create a substantial body of literature regarding the spatial pattern of ventilation in healthy and abnormal subjects. In general, these techniques have at least one distinct advantage over SVI, in that their signal-to-noise ratio is characteristically higher. However, each technique also has a characteristic disadvantage: PET and SPECT involve exposure to ionizing radiation, and hyperpolarized MRI requires the use of highly specialized hyperpolarized gas and a MR scanner with non-standard multi-nuclei hardware.
SVI, a proton-MRI technique, typically uses 1.5 Tesla MR hardware with inhaled oxygen as a contrast agent (both elements are readily available in healthcare), making it potentially more generalizable to the clinical environment. SVI leverages the fact that oxygen shortens the longitudinal relaxation time (T1) of lung tissues1, which in turn translates to a change in signal intensity in a T1-weighted image. Thus, changes in the concentration of inspired oxygen induce change in signal intensity of appropriately timed MRI images. The rate of this change following an abrupt change in inspired oxygen concentration, typically air and 100% oxygen, reflects the rate at which resident gas is replaced by the inhaled gas. This replacement rate is determined by specific ventilation.
As SVI involves no ionizing radiation, it has no contraindications for longitudinal and interventional studies that follow patients over time. Thus, it is ideally suited for studying disease progression or evaluating how individual patients responds to treatment. Due to its relative ease and safe repeatability, specific ventilation imaging is, in general, an ideal technique for those who wish to study large effects and/or a large number of people over time or in several different clinical locations.
Following the original publication describing the technique1, specific ventilation imaging (SVI) has been used in studies focused on the effect of rapid saline infusion, posture, exercise, and bronchoconstriction2,3,4,14,15. The technique&#8217;s ability to estimate whole lung heterogeneity of specific ventilation has been validated using the well-established multiple breath washout test7 and more recently, a regional a cross-validation was performed, by comparing SVI and hyperpolarized gas multiple breath specific ventilation imaging16. This reliable and readily deployable technique, capable of quantitatively mapping specific ventilation in the human lung, has the potential to significantly contribute to early detection and diagnosis of respiratory disease. It also presents new opportunities to quantify regional lung abnormalities and follow changes induced by therapy. These changes in region-specific lung function, which SVI enables us to measure for the first time, have the potential to become biomarkers for assessing the impact of drugs and inhaled therapies, and could be an extremely useful tool in clinical trials.
The purpose of this article is to present the methodology of specific ventilation imaging in detail and in a visual form, thus contributing to the dissemination of the technique to more centers.

<table>
	<tbody>
		<tr>
			<td>3D-printed flow bypass system</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Face mask</td>
			<td>Hans Rudolph</td>
			<td></td>
			<td>7400 series Oro-nasal mask, different sizes</td>
		</tr>
		<tr>
			<td>Gas/oxygen regulator</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Mask head set</td>
			<td>Hans Rudolph</td>
			<td></td>
			<td>7400 compatible head set</td>
		</tr>
		<tr>
			<td>Matlab</td>
			<td>Mathworks</td>
			<td></td>
			<td>analysis software developed locally</td>
		</tr>
		<tr>
			<td>Medical oxygen</td>
			<td>Air Liquide/Linde</td>
			<td></td>
			<td>Oxygen to be delivered to the subject</td>
		</tr>
		<tr>
			<td>MRI</td>
			<td>GE healthcare</td>
			<td></td>
			<td>1.5 T GE HDx Excite twin-speed scanner</td>
		</tr>
		<tr>
			<td>Plastic tubing</td>
			<td></td>
			<td></td>
			<td>&#188;&#8221;, 3/8&#8221; and 1/2&#8221; tubing and connectors</td>
		</tr>
		<tr>
			<td>Pulse oximeter</td>
			<td>Nonin</td>
			<td></td>
			<td>7500 FO (MR compatible)</td>
		</tr>
		<tr>
			<td>Switch valve</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Torso coil</td>
			<td>GE healthcare</td>
			<td></td>
			<td>High gain torso coil for GE scanner</td>
		</tr>
	</tbody>
</table>

quantitative mapping of specific ventilation in the human lung using proton magnetic resonance imaging and oxygen as a contrast agent

Specific ventilation imaging (SVI) is a functional magnetic resonance imaging technique capable of quantifying specific ventilation &#8213; the ratio of the fresh gas entering a lung region divided by the region&#8217;s end-expiratory volume &#8213; in the human lung, using only inhaled oxygen as a contrast agent. Regional quantification of specific ventilation has the potential to help identify areas of pathologic lung function. Oxygen in solution in tissue shortens the tissue&#8217;s longitudinal relaxation time (T1), and thus a change in tissue oxygenation can be detected as a change in T1-weighted signal with an inversion recovery acquired image. Following an abrupt change between two concentrations of inspired oxygen, the rate at which lung tissue within a voxel equilibrates to a new steady-state reflects the rate at which resident gas is being replaced by inhaled gas. This rate is determined by specific ventilation. To elicit this sudden change in oxygenation, subjects alternately breathe 20-breath blocks of air (21% oxygen) and 100% oxygen while in the MRI scanner. A stepwise change in inspired oxygen fraction is achieved through use of a custom three-dimensional (3D)-printed flow bypass system with a manual switch during a short end-expiratory breath hold. To detect the corresponding change in T1, a global inversion pulse followed by a single shot fast spin echo sequence was used to acquire two-dimensional T1-weighted images in a 1.5&#160;T MRI scanner, using an eight-element torso coil. Both single slice and multi-slice imaging are possible, with slightly different imaging parameters. Quantification of specific ventilation is achieved by correlating the time-course of signal intensity for each lung voxel with a library of simulated responses to the air/oxygen stimulus. SVI estimations of specific ventilation heterogeneity have been validated against multiple breath washout and proved to accurately determine the heterogeneity of the specific ventilation distribution.

Single slice SVI in a healthy subject 
Specific ventilation imaging produces quantitative maps of specific ventilation as shown in Figure 3A, which depicts a single slice in the right lung of a 39-year-old healthy female. Note the presence of the expected vertical gradient in specific ventilation; the dependent portion of the lung presents higher specific ventilation than the non-dependent portion of the lung. A histogram of the mapped specific vent...

Watch this Scientific Journal Video about Quantitative Mapping of Specific Ventilation in the Human Lung using Proton Magnetic Resonance Imaging and Oxygen as a Contrast Agent at JoVE.com

Quantitative Mapping of Specific Ventilation in the Human Lung using Proton Magnetic Resonance Imaging and Oxygen as a Contrast Agent

Specific ventilation imaging is a functional magnetic resonance imaging technique that allows for quantification of regional specific ventilation in the human lung, using inhaled oxygen as a contrast agent. Here, we present a protocol to collect and analyze specific ventilation imaging data.

Specific ventilation imaging (SVI) is a functional magnetic resonance imaging technique capable of quantifying specific ventilation &#8213; the ratio of ...

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