1. A method for visualizing a sequence of tomographic volume data records for medical imaging, the tomographic volume data records being recorded in temporal sequence with administration of contrast agents in vessels in an object volume such that at least one temporal sequence of measured signal values is present for each voxel of the object volume, the method comprising: determining at least one extremal value and at least one time value from the temporal sequence of the measured signal values for each voxel, the time value indicating a time lag of the extremal value or of a value derived therefrom compared to a fixed time during the recording of the volume data records; assigning, via a multi-dimensional transfer function, each combination of time value and extremal value or value derived therefrom a color value and an opacity value, the color value being a measure of the magnitude of the time value, and the opacity value being a measure of the magnitude of the extremal value or the value derived therefrom; assigning each voxel of the object volume a color value and opacity value by applying the transfer function to the determined time and extremal values or values derived therefrom; and displaying the voxels with the respective color and opacity values using volume rendering.