Corrections for the effects of accidental coincidences, Compton scatter, and object size in positron emission mammography (PEM) imaging

Positron emission mammography (PEM) has begun to show promise as an effecti ve method for the detection of breast lesions. Due to its utilization of tu mor-avid radiopharmaceuticals labeled with positron-emitting radionuclides, this technique may be especially useful in imaging of women with radiodens e or fibrocystic breasts. While the use of these radiotracers affords PEM u nique capabilities, it also introduces some limitations. Specifically, acce ptance of accidental and Compton-scattered coincidence events can decrease lesion detectability. We studied the effect of accidental coincidence event s on PEM images produced by the presence of F-18-Fluorodeoxyglucose in the organs of a subject using an anthropomorphic phantom. A delayed-coincidence technique was tested as a method for correcting PEM images for the occurre nce of accidental events. Also, a Compton scatter correction algorithm desi gned specifically for PEM was developed and tested using a compressed breas t phantom. Finally, the effect of object size on image counts and a correct ion for this effect were explored. The imager used in this study consisted of two PEM detector heads mounted 20 cm apart on a Lorad biopsy apparatus. The results demonstrated that a majority of the accidental coincidence even ts (similar to 80%) detected by this system were produced by radiotracer up take in the adipose and muscle tissue of the torso. The presence of acciden tal coincidence events was shown to reduce lesion detectability. Much of th is effect was eliminated by correction of the images utilizing estimates of accidental-coincidence contamination acquired with delayed coincidence cir cuitry built into the PEM system. The Compton scatter fraction for this sys tem was similar to 14%. Utilization of a new scatter correction algorithm r educed the scatter fraction to similar to1.5%. Finally, reduction of count recovery due to object size was measured and a correction to the data appli ed. Application of correction techniques for accidental coincidences, Compt on scatter, and count loss due to image size increased target-to-background contrast ratios to approximately the maximum level theoretically achievabl e with this PEM system.