Positron Emission Mammography Image Interpretation for Reduced Image Count Levels

J Nucl Med. 2016 Mar;57(3):348-54. doi: 10.2967/jnumed.115.165787. Epub 2015 Dec 3.

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).

Conclusion: 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.

Keywords: free-response ROC; injected activity; low-dose PET; positron emission mammography (PEM).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Algorithms
  • Breast / diagnostic imaging
  • Breast Neoplasms / diagnostic imaging
  • Cohort Studies
  • Female
  • Fluorodeoxyglucose F18
  • Humans
  • Image Processing, Computer-Assisted / methods*
  • Mammography / methods*
  • Middle Aged
  • Observer Variation
  • Positron-Emission Tomography / methods*
  • ROC Curve
  • Radiopharmaceuticals / administration & dosage
  • Radiopharmaceuticals / pharmacokinetics
  • Time Factors

Substances

  • Radiopharmaceuticals
  • Fluorodeoxyglucose F18