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Positron Emission Mammography Camera with Avalanche Gain
Early diagnosis of breast cancer is crucial for effective treatment and needs greater detection ability and specificity than conventional screening X-ray mammography (currently the primary imaging technique for the detection of breast lesions). Positron Emission Tomography (PET) using F-18-2-deoxy-fluoro-D-glucose (FDG) as a radiotracer can offer a non-invasive, highly sensitive method for the diagnosis of breast cancer. Images from PET contain unique metabolic information not available from anatomical imaging techniques and can aid in establishing the diagnosis of breast cancer.
The aim of the proposed research is to develop an affordable, high-resolution Positron Emission Mammography (PEM) imaging system that maintains the established high specificity of FDG PET while improving spatial resolution and collection efficiency. Thus detection of considerably smaller lesions compared with whole body PET system will be possible. The compact dual-head PEM camera will be based on an amorphous selenium (a-Se) avalanche photodetector and an advanced scintillator lutetium oxyorthosilicate (LSO). Each camera head will have a finely-pixelated LSO array in optical contact with the avalanche a-Se photodetector. The capability for high collection efficiency is achieved by combining the high light yield (~30 photons/keV) and fast scintillation light decay (40 ns) of LSO scintillator with the high quantum efficiency (~95%), extremely high avalanche gain (up to 1000) and fast time response of the a-Se photodetector.
A small PEM camera would allow focused coverage of the breast improving signal-to-noise ratio; in contrast the whole body PET system’s open geometry makes it sensitive to background signal from the chest. In addition, LSO arrays will be engineered to match the pixel layout of the photodetector in order to optimize the light collection and achieve the high resolution (~2 mm) desired. The improved performance of the proposed PEM camera will enable accurate detection and identification of small tumours, which is crucial for early breast cancer diagnosis, initiation of effective treatment, and ultimately a higher survival rate.
One in eight women in North America will develop breast cancer during her lifetime. Breast cancer is the second leading cause of cancer death but early detection can lead to a very high cure rate. Currently, screening X-ray mammography is the primary imaging technique for the detection of breast lesions. Its effectiveness depends on breast density. For younger women (i.e. for women with dense breasts) mammography fails to detect cancer in 30% of cases. Furthermore, in dense breasts the detected tumours are rarely less than 1–2 cm and thus the early stages of the disease may not be detected. Mammography cannot distinguish normal from malignant tissue. Thus, dense glandular tissue, surgical scars, and non-malignant but excessive growth of tough tissue are often mistaken for a malignancy. In fact, up to 85% of prescribed biopsies could be avoided if better detection procedures were available.
There is clearly a need for a much more sensitive and reliable technique for breast cancer detection and diagnosis. Positron emission tomography (PET) has demonstrated encouraging results in patients, including differentiation of normal from malignant tissues in women with dense breasts or excessive growth of tough tissues. Our proposal is to make a Positron Emission Mammography (PEM) camera, i.e. a portable PET device dedicated to breast cancer detection. Compared to whole body PET systems, dedicated equipment can have better spatial resolution. Furthermore, a PEM camera whose field of view is restricted to a single breast allows closer coverage of the region under analysis, leading to better detection.
Our strategy is to combine the unique properties of advanced materials and crystals to develop an affordable high-resolution imaging system that maintains the specificity of PET, but offers improved resolution and efficiency. The increased detection efficiency of the proposed PEM camera will allow more accurate detection and identification of small tumours, which is crucial for early breast cancer diagnosis, initiation of effective treatment and, as a result, increased survival.