Breast cancer is the most common cancer and secondcommonest cause of cancer death after lung and bronchialcancer in women. In Europe, 429,900 cases of breast cancerwere diagnosed in 2006 and 131,900 women died frombreast cancer in the same year [1]. It has been estimated that182,460 new cases of breast cancer will have beendiagnosed and 71,030 patients will have died from breastcancer in United States in 2008 [2]. Early diagnosis andreliable imaging assessment of response to treatment areessential in the clinical management of breast cancer.Conventional imaging modalities such as screen-filmmammography, digital mammography, ultrasonography(USG), and magnetic resonance imaging (MRI), provideonly morphological details and do not provide informationon the metabolic status of a lesion, which is very importantin differentiating a benign from a malignant lesion, andtherefore conventional imaging modalities lack specificity.Since its introduction, positron emission tomography(PET) has been widely shown to be highly useful for thediagnosis of palpable masses, for staging, for obtaininglong-term prognostic information, and for demonstratingtumour response to chemotherapy at an early phase or aftercompletion of treatment in patients with breast cancer.However, PET is not a very useful modality for screeningand early diagnosis of breast carcinoma. The sensitivity ofPET is 92% for lesions >20 mm, but is only 53% forprimary lesions <5 mm [3]. This poor detection of smalllesions is due to partial volume effects and low FDG uptakein the tumour as compared to the background breast tissue[4]. A possible solution to this problem is dual time-pointacquisition which can improve the diagnostic utility of PETin the detection of breast cancer [5]. FDG uptake in densebreast is high as compared to uptake in the fatty breast,which also hampers the detection of small tumours in densebreast [6, 7]. Moreover, the poor anatomical resolution ofPET further worsens the visibility of small tumours. Wehave previously systematically evaluated various clinico-pathological factors that predict false-negative FDG-PETresults in patients with primary breast cancer [8]. Wedemonstrated that smaller tumour size (<10 mm) and lowerhistological grade of the tumour are strong predictors offalse-negative FDG-PET results.With the advances in technology, there is progressiveimprovement in the spatial resolution of PET. The spatialresolution has been further enhanced with the introduction ofthehybridPET/CTscannerwherethePETpartofthescanneris equipped with a high-resolution state-of-the-art multi-detector CT (MDCT) system. The introduction of this hybridPET/CT scanner has led to a paradigm shift in oncologicalimaging, and it can be used as a “one-stop shop” not only todiagnose the involvement of various organs but also poten-tially to characterize the lesions. It is well established thatcombined PET/CT has higher sensitivity and specificity thanPET and CT used separately. The process of malignanttransformation is very complex, involving many alterationsinthemetabolicandfunctionalstatusoftumourcells.PETandPET/CT heavily rely on the metabolic activity of FDGdetected by its PETcomponent. The perfusion component of