Table 3. Cross-correlation of T1 reduction at room air, with pure O₂ and perfusion.

COPD stage		Lung zones n	r	p
	T1 vs. Perfusion	108	0.81	<0.001
Overall	ΔT1 vs. Perfusion	108	0.80	<0.001
	ΔT1 vs. T1	120	0.80	<0.001
	T1 / Perfusion	54	0.85	<0.001
Mild (GOLD I&II)	ΔT1 / Perfusion	54	0.63	<0.001
	ΔT1 / T1	60	0.65	<0.001
	T1 / Perfusion	54	0.67	<0.001
Severe (GOLD III&IV)	ΔT1 / Perfusion	54	0.73	<0.001
	ΔT1 / T1	60	0.77	<0.001

Spearman rank order correlation coefficient r calculated for T1 abnormalities at room air (T1), abnormal T1 shortening with 100% O₂ (ΔT1) and perfusion abnormalities (Perfusion), grouped according to COPD stages in a per-zone approach.