Regional correlation of emphysematous changes in lung function and structure: a comparison between pulmonary function testing and hyperpolarized MRI metrics.
Regional and global relationships of lung function and structure were studied using hyperpolarized ³He MRI in a rat elastase-induced model of emphysema (n = 4) and healthy controls (n = 5). Fractional ventilation (r) and apparent diffusion coefficient (ADC) of ³He were measured at a submillimeter planar resolution in ventral, middle, and dorsal slices 6 mo after model induction. Pulmonary function testing (PFT) was performed before MRI to yield forced expiratory volume in 50 ms (FEV₅₀), airway resistance (R(I)), and dynamic compliance (C(dyn)). Cutoff threshold values of ventilation and diffusion, r* and ADC*, were computed corresponding to 80% population of pixels falling above or below each threshold value, respectively. For correlation analysis, r* was compared with FEV₅₀/functional residual capacity (FRC), R(I) and C(dyn), whereas ADC* was compared with FEV₅₀/FRC, total lung capacity (TLC), and C(dyn). Regional correlation of r and ADC was evaluated by dividing each of the three lung slices into four quadrants. C(dyn) was significantly larger in elastase rats (0.92 ± 0.16 vs. 0.61 ± 0.12 ml/cmH₂O). The difference of R(I) and FEV₅₀ was insignificant between the two groups. The r* of healthy rats was significantly larger than the elastase group (0.42 ± 0.03 vs. 0.28 ± 0.06), whereas ADC* was significantly smaller in healthy animals (0.27 ± 0.04 vs. 0.36 ± 0.01 cm²/s). No systematic difference in these quantities was observed between the three lung slices. A significant 33% increase in ADC* and a significant 31% decline in r* for elastase rats was observed compared with a significant 51% increase in C(dyn) and a nonsignificant 26% decline in FEV₅₀/FRC. Correlation of imaging and PFT metrics revealed that r and ADC divide the rats into two separate clusters in the sample space.
Emami
Kiarash
K
Department of Radiology, University of Pennsylvania, PA, USA. kiarash.emami@uphs.upenn.edu
Chia
Elaine
E
Kadlecek
Stephen
S
Macduffie-Woodburn
John P
JP
Zhu
Jianliang
J
Pickup
Stephen
S
Blum
Allison
A
Ishii
Masaru
M
Rizi
Rahim R
RR
D000818:Animals; D003287:Contrast Media; D004646:Emphysema / Q000175:diagnosis / Q000473:pathology* / Q000503:physiopathology*; D006371:Helium; D007554:Isotopes; D008168:Lung / Q000473:pathology* / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D019275:Radiopharmaceuticals; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D012129:Respiratory Function Tests / Q000379:methods*; D012680:Sensitivity and Specificity
D003287:Contrast Media; D007554:Isotopes; D019275:Radiopharmaceuticals; D006371:Helium