Rapid Performance Evaluation for Ideal FROC and AFROC Observers

FROC and AFROC analyses are useful in medical imaging to characterize detection performance for the case of multiple lesions. We had previously developed(1) ideal FROC and AFROC observers. Their performance is ideal in that they maximize the area or any partial area under the FROC or AFROC curve. Such observers could be useful in imaging system optimization or in assessing human observer efficiency. However, the performance evaluation of these ideal observers is impractically computationally complex. We propose 3 reasonable assumptions under which the ideal observers reduce approximately to a particular form of a scan-statistic observer. Performance for the "scan-statistic-reduced ideal observer" can be evaluated far more rapidly albeit with slight error than that of the originally proposed ideal observer. Through simulations, we confirm the accuracy of our approximate ideal observers. We also compare the performance of our approximate ideal observer with that of a conventional scan-statistic observer and show that the performance of our approximate ideal observer is significantly greater.