Increasing the radiochemical purity of 99mTc sestamibi commercial preparations results in improved sensitivity of dual-phase planar parathyroid scintigraphy.
BACKGROUND
Poor results for dual-phase parathyroid scintigraphy have recently prompted increased use of dual-tracer imaging. We noticed that seminal studies used higher radiochemical purity than provided by current commercial preparations meeting US Pharmacopea (USP) specifications (90% of technetium bound to sestamibi). We surmised that the presence of unbound Tc (non-MIBI tracer) might hamper dual-phase detection that is dependent on rapid wash-out of technetium from thyroid tissue.


OBJECTIVE
To test the hypothesis that reducing non-MIBI tracer will enhance thyroid wash-out and improve sensitivity of dual-phase imaging.


METHODS
Starting in April 2003 we decreased the technetium to sestamibi ratio. This resulted in a significant decrease of non-MIBI tracer from 8.1+/-2.2% (SD) (group 1, n = 42) to 3.5+/-1.1% (group 2, n = 47) (P < 0.05 t-test). We performed a retrospective review of 89 patients with primary hyperparathyroidism who underwent imaging and subsequent surgery. The pathological findings served as the 'gold standard'.


RESULTS
Scanning detected 21/39 diseased glands (sensitivity=54%) in group 1 patients. In group 2 imaging detected 38/45 diseased glands (sensitivity = 84%). An improvement in sensitivity (P < 0.01) was achieved by modifying the radiopharmaceutical preparation.


CONCLUSIONS
Elevated levels of non-MIBI tracer in Tc-MIBI commercial preparations result in persistent thyroid background activity that may interfere with detection of parathyroid pathology. Achieving a higher degree of radiochemical purity (at least 95% bound, 5% impurities) than required by USP may be needed for optimal results. The large variation in sensitivity reported in the literature may be related in part to non-uniform radiopharmaceutical preparation.
Karam
Maroun
M
Department of Radiology, Albany Medical College, Albany, NY, USA. karamm@mail.amc.edu
Dansereau
Raymond N
RN
Dolce
Charles J
CJ
Feustel
Paul J
PJ
Robinson
Lawrence W
LW
D000328:Adult; D000368:Aged; D004345:Drug Industry; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D010279:Parathyroid Diseases / Q000175:diagnosis*; D010282:Parathyroid Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging*; D011877:Radionuclide Imaging / Q000379:methods*; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D017256:Technetium Tc 99m Sestamibi / Q000032:analysis*; D013997:Time Factors
D019275:Radiopharmaceuticals; D017256:Technetium Tc 99m Sestamibi