OPTIMAL TECHNIQUE FACTORS FOR MAGNIFICATION MAMMOGRAPHY

RATIONALE AND OBJECTIVES. Use of small focal spots with low x-ray tube currents may result in very long exposure times and thus result in mo tion blur in magnification mammography, The authors investigated the r eduction in exposure time with increasing x-ray tube kVp and the corre sponding decrease in perceived visibility of low-contrast objects in p hantom images. METHODS. Exposure times required to radiograph an RMI 1 56 phantom in a magnification geometry were measured as a function of x-ray tube kVp when operated under automatic exposure control, Magnifi cation images of the RMI 156 phantom were obtained at x-ray tube volta ges ranging from 28 to 34 kVp, Five radiology residents ranked the vis ibility of two borderline fibers and six borderline microcalcification specks using a 5-point scale ranging from excellent to barely visible . RESULTS. Between 28 and 34 kVp, the density of the RMI phantom image s was nearly constant with a mean value of 1.32 +/- 0.04. Increasing t he x-ray tube voltage from 28 kVp to 34 kVp reduced the exposure time from 1.27 seconds to 0.66 seconds, Image quality at 30 and 32 kVp was not significantly worse than that achieved at 28 kVp, Increasing the x -ray tube voltage to 34 kVp, however, resulted in a statistically sign ificant (P < 0.001) deterioration in the relative visibility of fibers and microcalcification specks. CONCLUSIONS. Magnification mammography performed at 32 kVp will decrease exposure times significantly and re sult in a microcalcification and fiber visibility that is similar to t hat achieved at 28 kVp.