Tc-99m-MIBI scintimammography; SPECT versus planar imaging

This study compares single photon emission tomography (SPECT) with planar scintimammography. 16 normal, 54 benign and 80 malignant lesions were studied (total 150). 700 MBq of Tc99m-sestamibi (MIBI) was injected intravenously. Anterior supine, right and left lateral planar images were acquired in prone position at 2 hours post injection. After this a SPECT study (64 projections, 64 x 64 matrix, 30 sec/frame, anterior 180 degrees arc) was acquired in supine position. Attenuation coefficient of 0.12 and Butterworth order 5 Nyquist 0.9 filter was applied for reconstruction. A scoring system for visualization of lesions was devised with scores of 0 or 1 as negative and 2 or 3 as positive for MIBI uptake. Scores for each group of patients were added together and then compared between planar and SPECT studies.

Planar imaging missed 10 malignant lesions while SPECT missed only 4. Ten benign lesions showed uptake of MIBI on planar imaging while 11 showed uptake on SPECT. Cumulative scores for normal and benign groups did not show any significant difference between planar and SPECT imaging. The malignant group showed significant increase in score for SPECT. Specificity, false negative fraction and positive predictive value for planar imaging were 85.7%, 14.3% and 87.5%. These values did not show any significant difference for SPECT (84.5%, 15.5% and 87.4% respectively). Sensitivity, false negative fraction and negative predictive value for planar imaging (87.5%, 12.5% and 85.7%) was significantly different (p < 0.005) than SPECT (95%, 5% and 93.7% respectively). MIBI SPECT scintimammography improves the sensitivity, false negative fraction and negative predictive value of the planar imaging. In the absence of MIBI uptake on SPECT imaging, malignancy can be ruled out with great confidence, while only uptake should be further evaluated.