Magnification mammography: a low-dose technique

Film-screen magnification versus electronic magnification and enhancement of digitized contact mammograms in the assessment of subtle microcalcifications

RATIONALE AND OBJECTIVES

To compare information drawn from magnification mammography with that extracted from electronic magnification, processing, and display of the digitized contact images.

METHODS

Contact and magnification images of a mammographic statistical phantom were obtained. The magnification films versus the computer-enhanced, digitized images of the corresponding contact mammograms were separately presented to three observers. Receiver operating characteristic analysis was used to compare lesion detectability. The contact and magnification mammograms of 86 patients with subtle microcalcifications were also studied. The breast imaging reporting and data system (BI-RADS) scheme was used to compare the magnification patient films versus the corresponding digitized contact images. Differences in mammographic assessment were evaluated by using the kappa statistic. The dose to breast tissue from contact and magnification mammography was measured to evaluate dose reduction in instances where magnification mammography was to be avoided.

RESULTS

Lesion detectability was found to be similar when either the digitized film image or the magnification hard-copy film was inspected. Interpretation of patient images by inspection of the contact and magnification screen-film mammograms on a view-box was in excellent agreement with that yielded by inspection of the contact image on a view-box and the computer-enhanced, digitized contact image on a display monitor.

CONCLUSIONS

Electronic magnification and processing of the digitized contact image may provide valuable information concerning subtle microcalcifications, rendering magnification mammography unnecessary for many patients with such lesions.

Image quality in mammography with special reference to anti-scatter grids and the magnification technique

Some of the parameters determining image quality in mammography are analyzed: the effects of primary photon spectra, focal spot size and screen-film systems on spatial resolution are discussed as are scattered radiation, development temperature and absorbed dose. The parameters limiting spatial resolution and contrast are evaluated for the standard and magnification techniques. Methods of reducing scattered radiation to improve contrast are evaluated. Scatter to primary ratios for different scatter reducing methods are compared, using the physical quantity energy imparted. For the standard technique the spatial resolution has been found to be limited by the fluorescent screen. With magnification technique the focal spot is the weakest link for the spatial resolution. The contrast is mainly set by the amount of scatter using the standard technique considering the use of a low tube potential (approximately 25 kVp). Using the magnification technique the amount of scatter is so small, that the tube potential is the limiting factor. We have found the optimized standard mammographic technique to be achieved under the following conditions: 25 kVp, 0.3 to 0.6 mm focal spot, film-focus distance 500 mm, anti-scatter grid, developing temperature 36 to 38 degrees C and 4 minutes total processing time with the screen-film system we have used. In magnification technique an air gap of at least 20 mm is desired. With an FFD of about 500 mm this will give a magnification ratio of 1.8 to 2.0 and a 0.1 mm X 0.1 mm focus spot is mandatory. With this technique, it is necessary to use a faster screen-film system than that used in standard mammography.

Metastatic carcinoma in axillary lymph nodes without pathologic evidence of a primary mammary lesion: a case report

A 56-year-old nullipara presented with a mass in the right axilla. Pathologically, two enlarged lymph nodes were found to contain metastatic adenocarcinoma consistent with a primary from the breast. Clinically, no breast mass was palpable, and xeromammography showed diffuse ductal hyperplasia and a small focus suggestive of malignancy. Modified radical mastectomy was done, and no tumor was found pathologically in the excised breast. The patient received local radiotherapy and is alive and well one year postoperatively. Attention is drawn to this rare occurrence, and patient management is briefly discussed.