Rr. Raylman et al., Corrections for the effects of accidental coincidences, Compton scatter, and object size in positron emission mammography (PEM) imaging, IEEE NUCL S, 48(3), 2001, pp. 913-923
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.