title: Positron Emission Mammography Image Interpretation for Reduced Image Count Levels.
abstract: We studied the effects of reduced (18)F-FDG injection activity on interpretation of positron emission mammography (PEM) images and compared image interpretation between 2 postinjection imaging times.
  
  
  METHODS
  We performed a receiver-operating-characteristic (ROC) study using PEM images reconstructed with different count levels expected from injected activities between 23 and 185 MBq. Thirty patients received 2 PEM scans at postinjection times of 60 and 120 min. Half of the patients were scanned with a standard protocol; the others received one-half of the standard activity. Images were reconstructed using 100%, 50%, and 25% of the total counts acquired. Eight radiologists used a 5-point confidence scale to score 232 PEM images for the presence of up to 3 malignant lesions. Paired images were analyzed with conditional logistic regression and ROC analysis to investigate changes in interpretation.
  
  
  RESULTS
  There was a trend for increasing lesion detection sensitivity with increased image counts: odds ratios were 2.2 (P = 0.01) and 1.9 (P = 0.04) per doubling of image counts for 60- and 120-min uptake images, respectively, without significant difference between time points (P = 0.7). The area under the ROC curve (AUC) was highest for the 100%-count, 60-min images (0.83 vs. 0.75 for 50%-counts, P = 0.02). The 120-min images had a similar trend but did not reach statistical significance (AUC = 0.79 vs. 0.73, P = 0.1). Our data did not yield significant trends between specificity and image counts. Lesion-to-background ratios increased between 60- and 120-min scans (P < 0.001).
  
  
  CONCLUSIONS
  Reducing the image counts relative to the standard protocol decreased diagnostic accuracy. The increase in lesion-to-background ratio between 60- and 120-min uptake times was not enough to improve detection sensitivity in this study, perhaps in part due to fewer counts in the later scan.
authors.affiliation: Radiology Department, University of Washington, Seattle, Washington; and macdon@uw.edu.
authors.forename: Lawrence R
authors.initials: LR
authors.lastname: MacDonald
authors.affiliation: Radiology Department, University of Washington, Seattle, Washington; and.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Hippe
authors.affiliation: Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Leila C
authors.initials: LC
authors.lastname: Bender
authors.affiliation: Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Cotter
authors.affiliation: Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Pooja R
authors.initials: PR
authors.lastname: Voria
authors.affiliation: Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Paula S
authors.initials: PS
authors.lastname: Hallam
authors.affiliation: Radiology Department, University of Washington, Seattle, Washington; and Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Carolyn L
authors.initials: CL
authors.lastname: Wang
authors.affiliation: Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: David R
authors.initials: DR
authors.lastname: Haseley
authors.affiliation: Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Mary M
authors.initials: MM
authors.lastname: Kelly
authors.affiliation: Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: Jay R
authors.initials: JR
authors.lastname: Parikh
authors.affiliation: Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: J David
authors.initials: JD
authors.lastname: Beatty
authors.affiliation: Swedish Cancer Institute, Swedish Medical Center, Seattle, Washington.
authors.forename: James V
authors.initials: JV
authors.lastname: Rogers
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001940:Breast / Q000000981:diagnostic imaging; D001943:Breast Neoplasms / Q000000981:diagnostic imaging; D015331:Cohort Studies; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008327:Mammography / Q000379:methods*; D008875:Middle Aged; D015588:Observer Variation; D049268:Positron-Emission Tomography / Q000379:methods*; D012372:ROC Curve; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000493:pharmacokinetics; D013997:Time Factors
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: free-response ROC; injected activity; low-dose PET; positron emission mammography (PEM)