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On the Potential Role of MRI Biomarkers of COPD to Guide Bronchoscopic Lung Volume Reduction

Posted Jan 31, 2018 Updated Apr 10, 2023
By Colin J. Adams MD , Dante P.I. Capaldi BSc , Robert Di Cesare , David G. McCormack MD FRCPC , Grace Parraga PhD
17 min read

Rationale and Objectives

In patients with severe emphysema and poor quality of life, bronchoscopic lung volume reduction (BLVR) may be considered and guided based on lobar emphysema severity. In particular, x-ray computed tomography (CT) emphysema measurements are used to identify the most diseased and the second–most diseased lobes as BLVR targets. Inhaled gas magnetic resonance imaging (MRI) also provides chronic obstructive pulmonary disease (COPD) biomarkers of lobar emphysema and ventilation abnormalities. Our objective was to retrospectively evaluate CT and MRI biomarkers of lobar emphysema and ventilation in patients with COPD eligible for BLVR. We hypothesized that MRI would provide complementary biomarkers of emphysema and ventilation that help determine the most appropriate lung lobar targets for BLVR in patients with COPD.

Materials and Methods

We retrospectively evaluated 22 BLVR-eligible patients from the Thoracic Imaging Network of Canada cohort (diffusing capacity of the lung for carbon monoxide = 37 ± 12% predicted , forced expiratory volume in 1 second = 34 ± 7% predicted , total lung capacity = 131 ± 17% predicted , and residual volume = 216 ± 36% predicted ). Lobar CT emphysema, measured using a relative area of <−950 Hounsfield units (RA 950 ) and MRI ventilation defect percent, was independently used to rank lung lobe disease severity.

Results

In 7 of 22 patients, there were different CT and MRI predictions of the most diseased lobe. In some patients, there were large ventilation defects in lobes not targeted by CT, indicative of a poorly ventilated lung. CT and MRI classification of the most diseased and the second–most diseased lobes showed a fair-to-moderate intermethod reliability (Cohen κ = 0.40–0.59).

Conclusions

In this proof-of-concept retrospective analysis, quantitative MRI ventilation and CT emphysema measurements provided different BLVR targets in over 30% of the patients. The presence of large MRI ventilation defects in lobes next to CT-targeted lobes might also change the decision to proceed or to guide BLVR to a different lobar target.

Introduction

Chronic obstructive pulmonary disease (COPD) is characterized by a chronic airflow limitation associated with airway inflammation due to long-term exposure to inhaled toxins and particles . In patients with COPD, emphysematous tissue destruction and narrowing of the small airways contribute to airflow limitation , lung hyperinflation, dyspnea, and worsening quality of life . Emphysema is inexorably progressive and irreversible, whereas lung hyperinflation also worsens over time and leads to worsening lung compliance, loss of exercise capacity, increased frequency of exacerbations, and a significant decline in quality of life . To improve symptoms and quality of life in patients with very severe COPD and extensive emphysema, lung volume reduction techniques were developed to selectively reduce or remove emphysematous tissue .

The overarching goal of lung volume reduction methods is to improve lung function and to decrease hyperinflation, which together result in improved patient quality of life and functional status . Such surgical approaches, however, are associated with significant morbidity and mortality . However, in a specific subgroup of patients with heterogeneous upper lobe predominant emphysema and poor functional status, there were significant benefits , including modest improvements in quality of life . Since then, a number of minimally invasive bronchoscopic lung volume reduction (BLVR) approaches have been developed with the goal of improving outcomes and diminished morbidity and mortality associated with the procedure. Several methods have been pioneered, including coils to collapse large airways , one-way endobronchial valves to promote passive collapse and deflation over time , and thermal vapor ablation to create an inflammatory response with subsequent scarring and loss of volume . Collateral ventilation is an important determinant of optimal BLVR outcomes , although recent studies showed that BLVR using vapor ablation may be successful regardless of interlobar or intralobar collateral ventilation . For all of these approaches, typically one or two severely diseased lobes are targeted with the aim of diverting blood flow and ventilation to remaining areas of healthier lung parenchymas .

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Materials and Methods

Study Subjects

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Pulmonary Function Tests

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Image Acquisition

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Image Analysis

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Statistics

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Results

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Table 1

Subject Demographic and Pulmonary Function Measurements

Mean (±SD) All ( n = 22) Age (y) 69 (9) Male, n 14 BMI (kg/m 2 ) 25 (4) Pack-year history (y) 60 (35) FEV 1 , % pred 34 (7) FVC, % pred 74 (17) FEV 1 /FVC (%) 46 (9) TLC, % pred 131 (17) RV, % pred 216 (36) RV/TLC (%) 164 (18) R AW , % pred 304 (126) DL CO , % pred 37 (12) 6MWD (min) 325 (73) RA 950 (%) 20 (10) VDP (%) 33 (9) DSC (%) 29 (12) SOC RA950 (%) 40 (14)

% pred , percent of predicted value; 6MWD, 6-minute walk test distance; BMI, body mass index; DL CO , diffusing capacity for carbon monoxide; DSC, dice similarity coefficient; FEV 1 , forced expiratory volume in 1 second; FVC, forced vital capacity; RA 950 , relative area of computed tomography density histogram with attenuation values of <−950 HU; R AW , airways resistance; RV, residual volume; SD, standard deviation; SOC, spatial overlap coefficient normalized by RA 950 ; TLC, total lung capacity; VDP, ventilation defect percent.

Table 2

Participant Listing of Demographic and Other Measurements

Subject Age (y) FEV 1 , % pred TLC, % pred RV, % pred RV/TLC (%) DL CO , % pred RA 950 (%) VDP (%) DSC (%) SOC RA950 (%) 1 71 45 127 186 63 31 21 31 38 47 2 48 43 148 189 36 41 20 22 21 23 3 78 38 123 186 58 29 23 32 29 35 4 72 40 135 210 67 54 7 21 14 28 5 51 40 114 208 54 46 12 42 28 64 6 74 30 135 236 66 39 22 37 38 52 7 60 21 102 205 65 45 9 30 16 34 8 68 23 124 214 76 — 27 29 31 33 9 76 32 125 220 64 40 16 36 27 45 10 65 39 120 156 54 63 8 26 18 36 11 78 42 161 221 67 27 19 32 28 37 12 73 34 165 289 64 37 17 40 32 53 13 75 28 141 267 71 17 29 33 38 40 14 67 37 154 265 72 21 32 41 46 53 15 61 30 128 222 71 30 24 42 40 54 16 74 34 141 225 59 24 33 57 51 69 17 63 22 116 180 64 41 23 32 29 34 18 63 38 111 183 55 40 8 26 15 31 19 85 38 124 194 63 36 18 30 24 32 20 73 32 133 230 65 35 15 14 15 14 21 72 26 155 291 68 21 52 44 55 51 22 73 41 107 172 58 54 8 23 13 24 Mean (±SD) 69 (9) 34 (7) 131 (17) 216 (36) 63 (8) 37 (12) 20 (10) 33 (9) 29 (12) 40 (14)

% pred , percent of predicted value; DL CO , diffusing capacity for carbon monoxide; DSC, dice similarity coefficient; FEV 1 , forced expiratory volume in 1 second; RA 950 , relative area of computed tomography density histogram with attenuation values of <−950 HU; RV, residual volume; SD, standard deviation; SOC, spatial overlap coefficient normalized by RA 950 ; TLC, total lung capacity; VDP, ventilation defect percent.

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Figure 1, Magnetic resonance and CT images in representative patients with severe chronic obstructive pulmonary disease that meet the inclusion criteria for bronchoscopic lung volume reduction. Top to bottom : CT images ( gray scale ) showing low-attenuating regions below −950 HU (RA 950 ) in yellow, CT images showing low-attenuation clusters and CT airway tree, and hyperpolarized MRI ventilation images ( blue ) coregistered with anatomic proton pulmonary MRI ( grayscale ) for S1 (female, age = 71 years, FEV 1 = 45% pred , FEV 1FVC = 41%), S10 (female, age = 65 years, FEV 1 = 39% pred , FEV 1FVC = 34%), S8 (female, age = 68 years, FEV 1 = 23% pred , FEV 1FVC = 38%), and S21 (male, age = 72 years, FEV 1 = 26% pred , FEV 1FVC = 28%). Color outlines indicate the segmented lobe delineations ( red = right upper lobe, purple = right middle lobe, gold = right lower lobe, green = left upper lobe, and blue = left lower lobe). CT, computed tomography; FEV 1 , forced expiratory volume in 1 second; FVC, forced vital capacity; GOLD, Global Initiative for Chronic Obstructive Lung Disease; LAC, low-attenuating cluster; MRI, magnetic resonance imaging.

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Table 3

VDP and RA 950 Classification of Most Diseased Lobes by Participant

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LLL, left lower lobe; LUL, left upper lobe; MDL, most diseased lung lobe; RA 950 , relative area of computed tomography density histogram with attenuation values of <−950 HU; RLL, right lower lobe; RML, right middle lobe; RUL, right upper lobe; VDP, ventilation defect percent.

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Table 4

VDP and RA 950 Agreement for Identifying and Ranking the Most Diseased Lobes

Most Diseased Lung Lobe VDP-RA 950 Agreement, N = 22 Cohen’s κ (Confidence Interval)P Value 1 15 (68%) 0.59 (0.35–0.83) <0.001 1 + 2 14 (64%) 0.55 (0.32–0.78) <0.001 2 12 (55%) 0.41 (0.14–0.68) <0.001 3 10 (46%) 0.30 (0.04–0.55) 0.007 4 11 (50%) 0.36 (0.23–0.48) 0.001 5 12 (55%) 0.38 (0.25–0.51) 0.001

RA 950 , relative area of computed tomography density histogram with attenuation values of <−950 HU; VDP, ventilation defect percent.

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Figure 2, MRI and CT bronchoscopic lung volume reduction targets in four participants with severe emphysema. ( a ) Subject S18 (male, age = 63 years, FEV 1 = 38% pred , DL CO = 40% pred ). The RUL was identified as the most diseased lobe using CT RA 950 = 12%, whereas MRI identified the RLL as the most diseased lobe (VDP = 65%). The lower lobes showed a relatively mild emphysema but significant MRI ventilation defects. ( b ) Subject S19 (male, age = 85 years, FEV 1 = 38% pred , DL CO = 36% pred ). The LUL was identified as the most diseased lobe using RA 950 = 23%, whereas MRI identified the LLL as the most diseased lobe using VDP = 54%. ( c ) Subject S13 (male, age = 75 years, FEV 1 = 28% pred , DL CO = 17% pred ). Both MRI (VDP = 58%) and CT (RA 950 = 38%) identified the RLL as the most diseased lobe. The second–most diseased lobe based on RA 950 identified the RUL and LLL (RUL: RA 950 = 32%, LLL: RA 950 = 30%) with VDP significantly greater in the LLL (LLL: VDP = 41%, RUL: VDP = 24%). ( d ) Subject S10 (female, age = 65 years, FEV 1 = 39% pred , DL CO = 63% pred ). RA 950 was the same in all lobes (RUL, RML, LUL, and LLL: RA 950 = 8%, RLL: RA 950 = 9%), and the lower lobes showed significant ventilation defects (RLL: VDP = 32%, LLL: VDP = 33%). Color outlines indicate the segmented lobe delineations ( red = RUL, purple = RML, gold = RLL, green = LUL, and blue = LLL). Arrows indicate spatial discordance of the ventilation defect and the emphysema regions. CT, computed tomography; FEV 1 , forced expiratory volume in 1 second; LLL, left lower lobe; LUL, left upper lobe; MRI, magnetic resonance imaging; RLL, right lower lobe; RML, right middle lobe; RUL, right upper lobe; VDP, ventilation defect percent.

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Discussion

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Figure 3, Identification of potential therapy targets using functional gas MRI coregistered to structural. Three-dimensional coregistration of 3 He MRI ventilation ( cyan ) and CT ( grayscale ) with CT airway tree ( brown ) and CT RA 950 ( yellow ). ( a ) Subject S19, described in Figure 2 , with the left upper lobe as the most diseased lobe using RA 950 = 23% and MRI VDP = 54% in LLL. ( b ) Subject S10, described in Figure 2 , with RA 950 = 8%–9% in all lobes and the lower lobes showed significant ventilation defects (VDP = 32% in LLL and VDP = 33% in the LLL). A, anterior; CT, computed tomography; I, inferior; L, left; LLL, left lower lobe; MRI, magnetic resonance imaging; P, posterior; R, right; S, superior; VDP, ventilation defect percent.

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Acknowledgments

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Supplementary Data

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Video S1

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Academic Radiology, Volume 25, Issue 2
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