title: Positron emission mammography (PEM): effect of activity concentration, object size, and object contrast on phantom lesion detection.
abstract: OBJECTIVE
  To characterize the relationship between lesion detection sensitivity and injected activity as a function of lesion size and contrast on the PEM (positron emission mammography) Flex Solo II scanner using phantom experiments.
  
  
  METHODS
  Phantom lesions (spheres 4, 8, 12, 16, and 20 mm diameter) were randomly located in uniform background. Sphere activity concentrations were 3 to 21 times the background activity concentration (BGc). BGc was a surrogate for injected activity; BGc ranged from 0.44-4.1 kBq∕mL, corresponding to 46-400 MBq injections. Seven radiologists read 108 images containing zero, one, or two spheres. Readers used a 5-point confidence scale to score the presence of spheres.
  
  
  RESULTS
  Sensitivity was 100% for lesions ≥12 mm under all conditions except for one 12 mm sphere with the lowest contrast and lowest BGc (60% sensitivity). Sensitivity was 100% for 8 mm spheres when either contrast or BGc was high, and 100% for 4 mm spheres only when both contrast and BGc were highest. Sphere contrast recovery coefficients (CRC) were 49%, 34%, 26%, 14%, and 2.8% for the largest to smallest spheres. Cumulative specificity was 98%.
  
  
  CONCLUSIONS
  Phantom lesion detection sensitivity depends more on sphere size and contrast than on BGc. Detection sensitivity remained ≥90% for injected activities as low as 100 MBq, for lesions ≥8 mm. Low CRC in 4 mm objects results in moderate detection sensitivity even for 400 MBq injected activity, making it impractical to optimize injected activity for such lesions. Low CRC indicates that when lesions <8 mm are observed on PEM images they are highly tracer avid with greater potential of clinical significance. High specificity (98%) suggests that image statistical noise does not lead to false positive findings. These results apply to the 85 mm thick object used to obtain them; lesion detectability should be better (worse) for thinner (thicker) objects based on the reduced (increased) influence of photon attenuation.
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA 98195, USA. macdon@uw.edu
authors.forename: Lawrence R
authors.initials: LR
authors.lastname: Macdonald
authors.forename: Carolyn L
authors.initials: CL
authors.lastname: Wang
authors.forename: Marna
authors.initials: M
authors.lastname: Eissa
authors.forename: David
authors.initials: D
authors.lastname: Haseley
authors.forename: Mary M
authors.initials: MM
authors.lastname: Kelly
authors.forename: Franklin
authors.initials: F
authors.lastname: Liu
authors.forename: Jay R
authors.initials: JR
authors.lastname: Parikh
authors.forename: J David
authors.initials: JD
authors.lastname: Beatty
authors.forename: James V
authors.initials: JV
authors.lastname: Rogers
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging*; D006801:Humans; D008327:Mammography / Q000295:instrumentation*; D019047:Phantoms, Imaging