How many physicists does it take to test a mammography unit?

Mammography is defined as the X-ray examination of the breast. It is just one of the modalities used for breast imaging; ultrasound and magnetic resonance imaging (MRI) are incredibly valuable adjunct techniques and newer technologies are gradually being adopted, such as molecular breast imaging and dedicated breast computed tomography. Inevitably, we tend to associate the term breast imaging with breast screening. Although breast screening has its critics [3], there can be no doubt that breast cancer is a major health burden on a global scale; it is the second most common cancer in the world and is responsible for more female deaths than any other cancer type [4]. Within Australia, 1 in 8 women will be diagnosed with breast cancer by the age of 85 [5]. However, it is reassuring to note that mortality rates are decreasing despite the fact that incidence rates continue to rise and the diagnosis rates in young women are increasing [6]. Mammography is considered to be the gold standard for breast screening, having an overall sensitivity of about 85% and specificity of 90% [7] in women aged 50–70. Breast imaging is challenging since it is necessary to detect and classify pathological details (microcalcifications and masses) against a background of fibrous tissue, which can vary considerably in radiological appearance depending on breast thickness and composition. Microcalcifications have a relatively high atomic number and density and hence high inherent and subject contrast. Unfortunately they are generally very small in size, ranging from 10 μm through to several mm [8]. Although masses are of moderate size (5–10 mm), detection of carcinoma is difficult since malignant tissue has negligible physical density difference from fibrous breast tissue, a similar attenuation coefficient and therefore low inherent contrast I’m sorry to lure you in with a joke for which I don’t have a punchline; the answer is just one, yet there are 95 physicists in Australia and New Zealand who hold ACPSEM Certification in Mammography Equipment Testing [1]. To put this into perspective, there are only 41 medical physicists who hold ACPSEM Certification in Radiology [2]. This raises the questions of why mammography is the only radiology modality to have its own certification process and why there is so much demand for this qualification. Having spent 12 years specialising in mammography physics, I’ll attempt to answer these questions and look at how mammographic technology has changed over the years and how this has impacted the role of the medical physicist.