We propose to develop and evaluate Magnetic Resonance Imaging (MRI) pulse sequences to detect breast cancer and distinguish it from benign breast disease; and to develop and evaluate MRI-guided biopsy techniques. We will develop and optimize a new, ultra-fast spiral k- space MR pulse sequence that has fat suppression, magnetization transfer, and high resolution, and evaluate it with a pharmokinetic model. We will also optimize an existing high resolution three- dimensional spectral-spatial volume acquisition magnetization transfer (3DSSMT) pulse sequence. MR-compatible biopsy techniques with 14- gauge large core needles will be developed, and MR scan techniques for interactively guiding needle placement optimized. We will study 120 women with the optimized 3DSSMT and dynamic spiral k-space MR sequences to identify and characterize enhancing breast lesions. All lesions will be core biopsied with MRI guidance, a wire placed, and pathology confirmed by surgical excision of the wire localized lesion. We will use receiver operating characteristic (ROC) curves to measure the ability of the new MR technique to detect focal and multicentric breast cancer.