A magnetic resonance imaging system (100, 200) for imaging a subject using arterial spin tagging, wherein the magnetic resonance imaging system comprises: - a memory storing machine executable instructions, wherein the memory further contains tagging pulse sequence commands and control pulse sequence commands, wherein the tagging pulse sequence commands comprise a tagging inversion pulse portion for spin labeling a tagging location (122, 122') within the subject, wherein the tagging pulse sequence commands comprise a phase-contrast readout portion, wherein the phase-contrast readout portion comprises phase-contrast encoding in at least one direction configured to visualize blood flow velocity and direction, wherein the control pulse sequence commands comprise a control inversion pulse portion, wherein the control pulse sequence commands comprise the phase-contrast readout portion; and - a processor configured for controlling the magnetic resonance imaging system, wherein execution of the machine executable instructions causes the processor to: - acquire tagged magnetic resonance data by controlling the magnetic resonance imaging system with the tagging pulse sequence commands; - acquire control magnetic resonance data by controlling the magnetic resonance imaging system with the control pulse sequence commands; - reconstruct a tagged magnitude image using the tagged magnetic resonance data; - reconstruct a control magnitude image using the control magnetic resonance data; - construct an arterial image by subtracting the control magnitude image and the tagged magnitude image; characterised in that execution of the machine executable instructions causes the processor to: - construct an arterial mask using the arterial image by identifying arteries in the arterial image; - reconstruct a phase image (156, 158, 160) using either the tagged magnetic resonance data and/or the control magnetic resonance data at least partially using said phase-contrast encoding in the at least one direction, wherein the phase image is configured to be used for detecting blood flow; and - construct a venous image at least partially by setting voxels within the phase image that are within the arterial mask to the predetermined background value. - a memory storing machine executable instructions, wherein the memory further contains tagging pulse sequence commands and control pulse sequence commands, wherein the tagging pulse sequence commands comprise a tagging inversion pulse portion for spin labeling a tagging location (122, 122') within the subject, wherein the tagging pulse sequence commands comprise a phase-contrast readout portion, wherein the phase-contrast readout portion comprises phase-contrast encoding in at least one direction configured to visualize blood flow velocity and direction, wherein the control pulse sequence commands comprise a control inversion pulse portion, wherein the control pulse sequence commands comprise the phase-contrast readout portion; and - a processor configured for controlling the magnetic resonance imaging system, wherein execution of the machine executable instructions causes the processor to: - acquire tagged magnetic resonance data by controlling the magnetic resonance imaging system with the tagging pulse sequence commands; - acquire control magnetic resonance data by controlling the magnetic resonance imaging system with the control pulse sequence commands; - reconstruct a tagged magnitude image using the tagged magnetic resonance data; - reconstruct a control magnitude image using the control magnetic resonance data; - construct an arterial image by subtracting the control magnitude image and the tagged magnitude image; characterised in that execution of the machine executable instructions causes the processor to: - construct an arterial mask using the arterial image by identifying arteries in the arterial image; - reconstruct a phase image (156, 158, 160) using either the tagged magnetic resonance data and/or the control magnetic resonance data at least partially using said phase-contrast encoding in the at least one direction, wherein the phase image is configured to be used for detecting blood flow; and - construct a venous image at least partially by setting voxels within the phase image that are within the arterial mask to the predetermined background value. - acquire tagged magnetic resonance data by controlling the magnetic resonance imaging system with the tagging pulse sequence commands; - acquire control magnetic resonance data by controlling the magnetic resonance imaging system with the control pulse sequence commands; - reconstruct a tagged magnitude image using the tagged magnetic resonance data; - reconstruct a control magnitude image using the control magnetic resonance data; - construct an arterial image by subtracting the control magnitude image and the tagged magnitude image; - construct an arterial mask using the arterial image by identifying arteries in the arterial image; - reconstruct a phase image (156, 158, 160) using either the tagged magnetic resonance data and/or the control magnetic resonance data at least partially using said phase-contrast encoding in the at least one direction, wherein the phase image is configured to be used for detecting blood flow; and - construct a venous image at least partially by setting voxels within the phase image that are within the arterial mask to the predetermined background value.