Prostate and breast cancer continues to be the most common cancer among men and women, respectively. The exact assessment of the cancer spread with detection of possible bone metastasis is crucial for treatment decision. In the current study 50 patients with prostate cancer and 50 patients with breast cancer at high risk for bone metastases or with know metastatic disease will be studied with multiple imaging modalities. Patients will be recruited from the Department of Oncology, Turku University Hospital. Planar bone scintigraphy (BS), single photon emission computed tomography combined with low-dose computed tomography (SPECT/CT), 18F-fluoride positron emission tomography computed tomography (PET/CT) and magnetic resonance imaging (MRI) will be performed to all patients. The primary objective is to determine the diagnostic accuracy of the four imaging modalities. The secondary goal is to calculate the sensitivities and specificities of the four imaging modalities on a patient-to-patient and lesion-to-lesion basis. Based on the results of this study an optimal imaging protocol for detection of prostate and breast cancer bone metastasis will be developed and validated.