title: Measuring diffuse metabolic activity on FDG-PET/CT: new method for evaluating Langerhans cell histiocytosis activity in pulmonary parenchyma.
abstract: BACKGROUND
  Pulmonary Langerhans cell histiocytosis (PLCH) is a rare cause of interstitial lung disease characterized by formation of nodules in the active phase of the disease that evolve into nonactive cystic lesions later on. To evaluate PLCH activity in patients, we developed a new method for measuring diffuse metabolic activity on fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) using a lung-to-liver activity ratio.
  
  
  METHODS
  We retrospectively studied a series of 4 FDG-PET and 23 FDG-PET/CT scans from 7 patients with PLCH and analyzed a sample of 100 randomly chosen FDG-PET/CT studies free from any known lung or hepatic diseases. Maximum standardized uptake value (SUVmax) in a spherical volume (6-8 cm in diameter) in the right lung was put into relation with SUVmax in a spherical volume (9-10 cm in diameter) in the reference liver parenchyma to set up the SUVmaxPULMO/SUVmaxHEPAR index. The index values were compared to the disease course in each patient.
  
  
  RESULTS
  In patients with PLCH, a close correlation between the index value and the disease course was found in all seven subjects, where the increasing index values indicated disease activity, while decreasing index values were observed after therapy administration. In the group of 100 healthy control subjects, we found index values lower than 0.3 in 80% and lower than 0.4 in 96% [range: 0.14-0.43; 0.24±0.07 (100)].
  
  
  CONCLUSIONS
  Measuring SUVmaxPULMO/SUVmaxHEPAR values and their time-trend monitoring represent simple, noninvasive screening tools allowing an early diagnosis and treatment response follow-up assessment in patients with PLCH.
authors.affiliation: Department of Internal Medicine-Hematooncology, Faculty of Medicine of Masaryk University and University Hospital Brno, Czech Republic. petr.szturz@fnbrno.cz
authors.forename: Petr
authors.initials: P
authors.lastname: Szturz
authors.forename: Zdeněk
authors.initials: Z
authors.lastname: Řehák
authors.forename: Renata
authors.initials: R
authors.lastname: Koukalová
authors.forename: Zdeněk
authors.initials: Z
authors.lastname: Adam
authors.forename: Marta
authors.initials: M
authors.lastname: Krejčí
authors.forename: Luděk
authors.initials: L
authors.lastname: Pour
authors.forename: Lenka
authors.initials: L
authors.lastname: Zahradová
authors.forename: Jiří
authors.initials: J
authors.lastname: Vaníček
authors.forename: Tomáš
authors.initials: T
authors.lastname: Nebeský
authors.forename: Roman
authors.initials: R
authors.lastname: Hájek
authors.forename: Jiří
authors.initials: J
authors.lastname: Mayer
mesh_terms: D000328:Adult; D005260:Female; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D006646:Histiocytosis, Langerhans-Cell / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000628:therapy; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography / Q000379:methods*; D011379:Prognosis; D019275:Radiopharmaceuticals; D012129:Respiratory Function Tests; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18