Dedicated gamma camera for single photon emission mammography (SPEM)

Prone scintimammography with Tc-99m MIBI has been proposed as a method of detecting breast cancers in women with dense breasts. Clinical reports have shown that this technique lacks sensitivity and specificity for cancers smaller than one cm. This shortcoming is unfortunate, since a patient's prognosis is most favorable when her cancer is discovered at an early stage (i.e., when the cancer is less than one cm in size). The authors explored some of the possible causes for the poor performance of prone scintimammography in this population by performing phantom and clinical studies with several different instruments, including a general-purpose gamma camera, a nonimaging germanium detector with excellent energy resolution, and a dedicated high spatial resolution camera for scintimammography (single photon emission mammography, or SPEM) using breast compression. The authors' results suggest that unlike X-ray mammography, scatter from extramammary sources plays an important role in breast imaging with radiotracers, and is the dominant effect when imaging near the chest wall. Away from the chest wall, and in conjunction with gentle breast compression (depth less than 7 cm), the energy resolution attained with a dedicated SPEM camera employing cesium iodide crystals appears adequate to differentiate between photopeak and Compton counts, with a Compton-to-photopeak ratio of less than six. The authors' preliminary clinical studies suggest that breast compression, good energy resolution and spatial resolution may improve detection of small cancers.