Semi-quantitation of pulmonary perfusion heterogeneity on respiratory-gated inspiratory and expiratory perfusion SPECT in patients with pulmonary emphysema.

OBJECTIVE

Pulmonary perfusion heterogeneity (PPH) in pulmonary emphysema (PE) was semi-quantified by functional lung volume rate (FLVR) curves obtained from respiratory-gated inspiratory and expiratory single-photon emission computed tomography (SPECT).

METHODS::

Gated and ungated SPECT were obtained in 36 PE patients [25 with stage IIA and 11 with stage IIB for global initiative for chronic obstructive lung disease (GOLD) stage classification] and 12 controls, using a triple-head SPECT system and a respiratory tracking device. On gated SPECT, the voxel numbers calculated at the 10% cutoff threshold for the maximum lung radioactivity were assumed to be the functional lung volume of the lung (V). FLVR (%) was calculated as FLV divided by V at every additional 10% thresholds, yielding inspiratory and expiratory FLVR curves. The dissociations between these curves (DeltaFLVRinsp-exsp) and the total difference (D index) of these curves from the normal standard curve (averaged inspiratory and expiratory curve in controls) were calculated. D index and the extent of low attenuation area (%LAA) on CT were correlated with the transfer coefficient for carbon monoxide (KCO) in PE patients.

RESULTS:

Although gated and ungated SPECT showed fairly uniform perfusion in controls, gated SPECT-enhanced PPH compared with ungated SPECT in PE patients, with significantly higher dissociation (DeltaFLVRinsp-exsp) than that in controls (24.9%+/-9.5% vs. 4.5%+/-1.3%; P<0.0001). DeltaFLVRinsp-exsp was significantly higher even in stage IIA patients (P<0.0001). Expiratory D index was significantly higher than the inspiratory one in PE patients (P<0.01). This index was significantly higher in stage IIB patients than in stage IIA patients (44.1%+/-19.0% vs. 29.4%+/-13.7%; P<0.05), and was significantly correlated with KCO (R=0.642, P<0.0001) in all PE patients, although %LAA was not correlated with KCO.

CONCLUSIONS:

FLVR curve analysis on gated SPECT appears useful for semi-quantitation of respiratory change of PPH in PE. Expiratory D index may better reflect the lung pathophysiology of PE than morphologic CT.