title: Lung structure and function relation in systemic sclerosis: application of lung densitometry.
abstract: BACKGROUND
  Interstitial lung disease occurs frequently in patients with systemic sclerosis (SSc). Quantitative computed tomography (CT) densitometry using the percentile density method may provide a sensitive assessment of lung structure for monitoring parenchymal damage. Therefore, we aimed to evaluate the optimal percentile density score in SSc by quantitative CT densitometry, against pulmonary function.
  
  
  METHODS
  We investigated 41 SSc patients by chest CT scan, spirometry and gas transfer tests. Lung volumes and the nth percentile density (between 1 and 99%) of the entire lungs were calculated from CT histograms. The nth percentile density is defined as the threshold value of densities expressed in Hounsfield units. A prerequisite for an optimal percentage was its correlation with baseline DLCO %predicted. Two patients showed distinct changes in lung function 2 years after baseline. We obtained CT scans from these patients and performed progression analysis.
  
  
  RESULTS
  Regression analysis for the relation between DLCO %predicted and the nth percentile density was optimal at 85% (Perc85). There was significant agreement between Perc85 and DLCO %predicted (R=-0.49, P=0.001) and FVC %predicted (R=-0.64, P<0.001). Two patients showed a marked change in Perc85 over a 2 year period, but the localization of change differed clearly.
  
  
  CONCLUSIONS
  We identified Perc85 as optimal lung density parameter, which correlated significantly with DLCO and FVC, confirming a lung parenchymal structure-function relation in SSc. This provides support for future studies to determine whether structural changes do precede lung function decline.
authors: Department of Pulmonology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands. Electronic address: m.k.ninaber@lumc.nl.
authors: Maarten K
authors: MK
authors: Ninaber
authors: Department of Pulmonology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands.
authors: Jan
authors: J
authors: Stolk
authors: Department of Pulmonology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands.
authors: Jasper
authors: J
authors: Smit
authors: Department of Pulmonology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands.
authors: Ernest J
authors: EJ
authors: Le Roy
authors: Department of Radiology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands.
authors: Lucia J M
authors: LJ
authors: Kroft
authors: Division of Image Processing, Radiology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands.
authors: M Els
authors: ME
authors: Bakker
authors: Department of Rheumatology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands.
authors: Jeska K
authors: JK
authors: de Vries Bouwstra
authors: Department of Rheumatology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands.
authors: Anne A
authors: AA
authors: Schouffoer
authors: Division of Image Processing, Radiology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands.
authors: Marius
authors: M
authors: Staring
authors: Division of Image Processing, Radiology, Leiden University Medical Center, Albinusdreef 2, 2333ZA Leiden, The Netherlands.
authors: Berend C
authors: BC
authors: Stoel
mesh_terms: D000328:Adult; D000368:Aged; D003720:Densitometry; D018450:Disease Progression; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology*; D017563:Lung Diseases, Interstitial / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D012595:Scleroderma, Systemic / Q000150:complications*; D014057:Tomography, X-Ray Computed
keywords: Chest CT imaging; Interstitial lung disease; Lung densitometry; Systemic sclerosis