Ching-Long Lin

PURPOSE
Low attenuation areas (LAAs) on CT scans have been used to evaluate emphysema and air trapping. However, the regional ventilation changes of LAAs while breathing may vary due to the various causes of emphysema or air trapping. Therefore, the purpose of this study was to investigate regional air volume change at acinar scale of the lung using mass preserving image registration technique and compare with the -950HUinsp, -856HUexp and PFTs in COPD.
METHOD AND MATERIALS
18 emphysema patients (12 centriacinar, 6 distal acinar emphysema) and 10 normal subjects were included in the study. VIDA Apollo software (Coralville, IA) and mass preserving image registration technique were used to compute relative regional air volume change (RRAVC) between inspiration and expiration CT scans. Then, low ventilation area (LVA) was defined as percent lung volume of RRAVC < 0.8. -950HUinsp, -856HUexp and LVA0.8 in total lung were correlated with FEV1, FEV1/FVC and compared between normal and emphysema patients.
RESULTS
LVA0.8 and -856HUexp showed positive correlation with FEV1 (r=-0.89 and p=0.016, r=-0.91, p=0.014) while -950HUinsp did not show a correlation with FEV1 in distal acinar emphysema patients. -950HUinsp and -856HUexp correlated well with FEV1/FVC in centriacinar emphysema (r=-0.61, p=0.036; r=-0.65, p=0.021). In the RRAVC map, LVA0.8 (colored blue) was well-matched with low attenuation (emphysema) regions, demonstrating decreased ventilation (air volume change) when compared with adjacent normal lung.
CONCLUSION
RRAVC map correlates well with FEV1 and demonstrates various ventilation patterns in the LAAs on CT in COPD and the proposed LVA0.8 may provide additional functional information at an acinar scale, supplementing LAAs in quantitative CT scans.
CLINICAL RELEVANCE/APPLICATION
Relative regional air volume change map using mass preserving registration technique may be useful for the explanation of different pathophysiology of the LAAs in COPD.

PURPOSE
Elastography has been used for the assessment of fibrosis in the liver and breast. However, ultrasonography is not easy to be applied for the fibrosis in the lung parenchyma due to the air. In this study, we applied image registration based local displacement information from expiration to inspiration to grade the degree of fibrosis in the idiopathic interstitial lung disease such as usual interstitial pneumonia and nonspecific interstitial pneumonia.
METHOD AND MATERIALS
10 normal and 18 idiopathic interstitial lung disease (13 IPF and 5 NSIP) subjects were included in our study. VIDA Apollo software (Coralville, Iowa) and mass preserving image registration technique were used to compute displacement vectors of local lung regions at an acinar scale. Three-dimensional displacements and dorsal basal displacements were normalized by the cubic root of global lung volume change from expiration to inspiration CT scans. Displacements and volume changes in the upper and lower lobes and the whole lung are compared between three groups using analysis of variance test (ANOVA).
RESULTS
IPF and NSIP were not differentiated by volume changes of the whole lung or upper and lower lobes, whereas lower lobe air volume change were smaller in both IPF and NSIP than normal subjects (p=0.02, p=0.001). In the whole lung, dorsal basal displacement was smaller in ILD and normal subjects (p=0.035), while three-dimensional displacement was not different between the groups. Three-dimensional and dorsal basal displacement was smaller in the lower lobes of IPF subjects than NSIP (p=0.044) and normal (p=0.006) subjects.
CONCLUSION
Lung motionography using image registration based dorsal basal displacement in the lower lobe may be used for the understanding of the structure-function relationships in fibrotic lung disease.
CLINICAL RELEVANCE/APPLICATION
Image registration based local displacement information may help us to assess the degree of lung fibrosis and to make a diagnosis in the fibrotic lung disease.

PURPOSE
Honeycombing cyst is a hallmark of idiopathic pulmonary fibrosis (IPF), but differentiation of paraseptal cysts on CT scans alone is at times difficult. The purpose of this study was to investigate if identification of functional differences between honeycombing cysts and paraseptal low attenuation areas (LAAs) is possible using a relative regional air volume change (RRAVC) map.
METHOD AND MATERIALS
10 normal, 19 emphysema, and 20 idiopathic interstitial lung disease (11 IPF and 9 NSIP) were included in our study. VIDA Apollo software (Coralville, IA) and mass preserving image registration technique were used to compute low ventilation area (LVA) from inspiration and expiration CT scans. LVA0.8 is defined as percent lung volume reflecting less ventilation than 80% of the whole lung mean value. LVA0.8 in the whole lung and fractional air volume change in upper and lower lobes were compared between the three groups using analysis of variance test (ANOVA). The honeycombing cysts in IPF and LAAs in emphysema were visually inspected on the RRAVC map.
RESULTS
LVA0.8 was higher in emphysema patients than IPF or normal subjects (p=0.001). (emphysema: 29.1+/-5.1%, IPF: 19.3+/-5.8%, normal: 20.6+/-5.7) in both lungs. There were significant differences between ILD and emphysema patients in both upper and lower lobe fractional air volume change, where emphysema patients had significantly higher fractional air volume change than normal patients in the upper lobe and ILD patients had lower fractional air volume change than normal patients in the lower lobe. In the RRAVC map, distal acinar emphysema cysts showed decreased air volume change between inspiration and expiration, which represents regional obstruction, characteristic of COPD. Whereas relatively higher ventilation was noted in honeycombing cysts compared to emphysema, suggesting a relatively preserved airway flow in IPF patients.
CONCLUSION
LAAs in distal acinar emphysema were demonstrated as low ventilation areas while cysts in honeycombing did not demonstrate a decreased ventilation on the RRAVC map. This could provide a method for differentiating between distal acinar emphysema and honeycombing cysts.
CLINICAL RELEVANCE/APPLICATION
Cystic lesions which can be seen in IPF and emphysema could be differentiated by the quantitation of acinar scale functional impairment assessed by image matching method, using pairs of inspiratory/expiratory CT data sets.