Scintimammography: better detection of small-sized lesions with tomoscintigraphic than planar images, a phantom study

Planar Tc-99(m)-methoxyisobutylisonitrile (Tc-99(m)-MIBI) scintimammography has been used for several years to detect breast cancer tumours, but with low sensitivity for small lesions. Results of tomoscintimammography studies have not been conclusive. We conducted a phantom study to compare the dete ction of small-sized tumours with planar versus tomoscintigraphic images. W e used a data spectrum anthropomorphic fillable breast phantom with two 9.8 mm and 12.4 mm spheres superficially or deep in the breast compartment wit h sphere/breast activity ratios varying from 3 to 6. We acquired planar and 180 degrees tomoscintigraphic images in each configuration using a double head standard gamma camera. In certain cases we varied different parameters (64 x 64 matrix or 360 degrees rotation) in a second series of tomoscintig raphic acquisitions. We simultaneously used filtered back-projection recons truction (FBP) and iterative reconstruction (IR). Planar images were shown by the sphere in 10 out of 25 cases. Tomoscintigraphic images were shown by the sphere in nine out of 25 cases with FBP and in 18 out of 25 with IR. T here was a significant difference between IR and FBP (P<0.01) and between p lanar and IR images (P<0.01), but no significant difference between planar and IR images. The noise/signal ratio was lower with planar images than wit h the two types of reconstruction (P<0.05) but was not significantly differ ent between the two types of reconstruction. Contrast was lower on planar i mages than on the two types of reconstruction (P<0.05) and was also better on IR than on FBP images (P<0.05). Granularity was lower for planar images than for reconstruction images (P<0.01) and also lower for IR than for FBP (P<0.01). The tomoscintigraphic reconstructions acquired with a 64 x 64 mat rix were only positive in four out of 10 cases, while they were positive in nine out of 10 with a 128 x 128 matrix. We concluded that, in this phantom study, tomoscintimammography with IR provides a significant improvement in the detection of small-sized breast tumours compared with planar images. I n addition, for tomoscintigraphic images, a 128 x 128 matrix is preferable to a 64 x 64 matrix. Those results have, of course, to be confirmed in vivo in a large population of patients with small-sized breast lesions. ((C) 20 01 Lippincott Williams & Wilkins).