A diagnostic imaging apparatus for contrast enhanced imaging using a contrast agent, the apparatus comprising: a magnetic resonance portion that includes: a main magnetic coil assembly for generating a main magnetic field in an imaging region of the apparatus; a gradient coil assembly for overlaying gradient magnetic fields on the main magnetic field; an RF coil assembly for at least transmitting RF signals into the imaging region and for receiving magnetic resonance emanating from the imaging region; a positron emission tomography portion that includes: a detector array for detecting radiation indicative of nuclear decay events; at least one reconstruction processor (22, 40) being adapted for producing an image representation from the detected radiation and the magnetic resonance originating from the contrast agent that gathers in the imaging region, wherein the detected radiation and the magnetic resonance are detected simultaneously, and wherein the contrast agent comprises i) a first component that is able to be imaged by a magnetic resonance imaging apparatus, ii) a second component that includes a radiopharmaceutical that is able to be imaged by a nuclear imaging apparatus, and iii) a targeting system being able to take advantage of biological processes to cause the contrast agent to collect in a target region; and a display for displaying the reconstructed image representation, wherein the diagnostic imaging apparatus is adapted to perform: enhancing spatial resolution of a positron emission tomography data set with a simultaneously gathered magnetic resonance data set, wherein the diagnostic imaging apparatus is adapted to calculate an amount of activity Q OBS (t) in a voxel with the relationship: Q OBS t = 1 − β V EES C EES t + C T t + βV EES C P t where V EES is a volume of extracellular, extravascular space within the voxel, β is the blood volume fraction, C T is a concentration of the contrast agent bound in the volume V EES, C EES is a concentration of the contrast agent unbound within the volume V EES, and C P is a plasma input function, wherein β is a known parameter determined separately from the magnetic resonance data set. a magnetic resonance portion that includes: a main magnetic coil assembly for generating a main magnetic field in an imaging region of the apparatus; a gradient coil assembly for overlaying gradient magnetic fields on the main magnetic field; an RF coil assembly for at least transmitting RF signals into the imaging region and for receiving magnetic resonance emanating from the imaging region; a main magnetic coil assembly for generating a main magnetic field in an imaging region of the apparatus; a gradient coil assembly for overlaying gradient magnetic fields on the main magnetic field; an RF coil assembly for at least transmitting RF signals into the imaging region and for receiving magnetic resonance emanating from the imaging region; a positron emission tomography portion that includes: a detector array for detecting radiation indicative of nuclear decay events; at least one reconstruction processor (22, 40) being adapted for producing an image representation from the detected radiation and the magnetic resonance originating from the contrast agent that gathers in the imaging region, wherein the detected radiation and the magnetic resonance are detected simultaneously, and wherein the contrast agent comprises i) a first component that is able to be imaged by a magnetic resonance imaging apparatus, ii) a second component that includes a radiopharmaceutical that is able to be imaged by a nuclear imaging apparatus, and iii) a targeting system being able to take advantage of biological processes to cause the contrast agent to collect in a target region; and a display for displaying the reconstructed image representation, wherein the diagnostic imaging apparatus is adapted to perform: enhancing spatial resolution of a positron emission tomography data set with a simultaneously gathered magnetic resonance data set, wherein the diagnostic imaging apparatus is adapted to calculate an amount of activity Q OBS (t) in a voxel with the relationship: Q OBS t = 1 − β V EES C EES t + C T t + βV EES C P t where V EES is a volume of extracellular, extravascular space within the voxel, β is the blood volume fraction, C T is a concentration of the contrast agent bound in the volume V EES, C EES is a concentration of the contrast agent unbound within the volume V EES, and C P is a plasma input function, wherein β is a known parameter determined separately from the magnetic resonance data set. enhancing spatial resolution of a positron emission tomography data set with a simultaneously gathered magnetic resonance data set, wherein the diagnostic imaging apparatus is adapted to calculate an amount of activity Q OBS (t) in a voxel with the relationship: Q OBS t = 1 − β V EES C EES t + C T t + βV EES C P t where V EES is a volume of extracellular, extravascular space within the voxel, β is the blood volume fraction, C T is a concentration of the contrast agent bound in the volume V EES, C EES is a concentration of the contrast agent unbound within the volume V EES, and C P is a plasma input function, wherein β is a known parameter determined separately from the magnetic resonance data set.