A method for rendering an image from a medical scanner, the method comprising: scanning a volume of a patient by the medical scanner, the scanning providing intensities representing voxels of the volume; rendering, by a graphics processing unit, a first two-dimensional image from the intensities representing the voxels, the rendering using a first transfer function; receiving a region of interest determined based on the first two-dimensional image wherein the region of interest is an area on the first two-dimensional image; identifying a subset of the voxels based on the region of interest wherein the subset of voxels is identified from a voxel cache including a depth map, wherein the depth map provides, for each pixel, a depth, at which a first gradient above a threshold in the intensities traveling from a virtual viewer through the volume occurs, wherein the region of interest provides lateral positions for the pixels included in the region of interest and the depth map defines a depth for each lateral position wherein the depth and the lateral position define a voxel and wherein the intensity value from the scan data for the defined voxels are loaded from the voxel cache to determine the intensities for the identified subset of voxels; determining a second transfer function from a distribution of the intensities of the voxels of the subset wherein the distribution is represented by a histogram of intensities, wherein a Gaussian curve is fit to the histogram, wherein a mean and a standard deviation of the Gaussian curve are determined and wherein the mean and the standard deviation of the Gaussian curve are mapped to values for a setting of the second transfer function; and rendering, by the graphics processing unit, a second two-dimensional image using the second transfer function. scanning a volume of a patient by the medical scanner, the scanning providing intensities representing voxels of the volume; rendering, by a graphics processing unit, a first two-dimensional image from the intensities representing the voxels, the rendering using a first transfer function; receiving a region of interest determined based on the first two-dimensional image wherein the region of interest is an area on the first two-dimensional image; identifying a subset of the voxels based on the region of interest wherein the subset of voxels is identified from a voxel cache including a depth map, wherein the depth map provides, for each pixel, a depth, at which a first gradient above a threshold in the intensities traveling from a virtual viewer through the volume occurs, wherein the region of interest provides lateral positions for the pixels included in the region of interest and the depth map defines a depth for each lateral position wherein the depth and the lateral position define a voxel and wherein the intensity value from the scan data for the defined voxels are loaded from the voxel cache to determine the intensities for the identified subset of voxels; determining a second transfer function from a distribution of the intensities of the voxels of the subset wherein the distribution is represented by a histogram of intensities, wherein a Gaussian curve is fit to the histogram, wherein a mean and a standard deviation of the Gaussian curve are determined and wherein the mean and the standard deviation of the Gaussian curve are mapped to values for a setting of the second transfer function; and rendering, by the graphics processing unit, a second two-dimensional image using the second transfer function.