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

This study compares single photon emission tomography (SPECT) with planar s cintimammography. 16 normal, 54 benign and 80 malignant lesions were studie d (total 150). 700 MBq of Tc99m-sestamibi (MIBI) was injected intravenously . Anterior supine, right and left lateral planar images were acquired in pr one position at 2 hours post injection. After this a SPECT study (64 projec tions, 61 x 64 matrix, 30 sec/frame, anterior 180 degrees are) 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 v isualization 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 a dded together and then compared between planar and SPECT studies. Results: Planar imaging missed 10 malignant lesions while SPECT missed only 4. Ten b enign lesions showed uptake of MIBI on planar imaging while II showed uptak e on SPECT. Cumulative scores for normal and benign groups did not show any significant difference between planar and SPECT imaging. The malignant gro up showed significant increase in score for SPECT. Specificity, false negat ive fraction and positive predictive value for planar imaging were 85.7%, 1 4.3% and 87.5%. These values did not show any significant difference for SP ECT (84.5%, 15.5% and 87.4% respectively). Sensitivity, false negative frac tion 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% res pectively). MIBI SPECT scintimammography improves the sensitivity, false ne gative 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 any uptake should be further evaluated.