1. Date of download: 6/1/2016 Copyright © 2016 SPIE. All rights reserved. On the left is a 3-D DSA of a canine with all vessels opacified. On the right is a 4-D DSA early time frame before opacification of the venous return vessels. Demonstrated is the ability of 4-D time frames to provide an unobstructed view of arterial vessels. The 3-D DSA contains both arteries and veins, therefore obscuring visualization of the internal carotid arteries (ICAs). The white arrows highlight the course of the right ICA in the 4-D DSA view. The ellipse highlights the distal segments of the ICAs for reference. Both these reconstructions can be viewed from any angle; however, only 4-D DSA can be viewed from any time. Figure Legend: From: Volumetric limiting spatial resolution analysis of four-dimensional digital subtraction angiography J. Med. Imag. 2016;3(1):013503. doi:10.1117/1.JMI.3.1.013503

2. Date of download: 6/1/2016 Copyright © 2016 SPIE. All rights reserved. 4-D reconstruction process illustrating the projection space left of the dashed line and 3-D space on the right. The projections are first acquired in step 1. The volume is then reconstructed from projections as shown in step 2. Constraining image generation by which the 3-D DSA is threholded is shown in step 3. The 2-D blurring kernel is applied to the temporal projections and reprojections (not shown) of the constraining volume in step 4. The blurred temporal projections and reprojections are then divided (not shown). The normalized projections are then backprojected individually to create a weighting volume for each time frame, step 5, and the result is multiplied with the constraining image shown in step 6. Highlighted are steps 3 and 4 as the effect these steps have on the limiting spatial resolution is the focus of this research. Figure Legend: From: Volumetric limiting spatial resolution analysis of four-dimensional digital subtraction angiography J. Med. Imag. 2016;3(1):013503. doi:10.1117/1.JMI.3.1.013503

3. Date of download: 6/1/2016 Copyright © 2016 SPIE. All rights reserved. Resulting geometric and frequency scaling from the image plane to the object plane. Figure Legend: From: Volumetric limiting spatial resolution analysis of four-dimensional digital subtraction angiography J. Med. Imag. 2016;3(1):013503. doi:10.1117/1.JMI.3.1.013503

4. Date of download: 6/1/2016 Copyright © 2016 SPIE. All rights reserved. Image of the physical phantom. The location of the tungsten wire has been highlighted by dark gray box overlaid on the image and is located in the center of the box. Figure Legend: From: Volumetric limiting spatial resolution analysis of four-dimensional digital subtraction angiography J. Med. Imag. 2016;3(1):013503. doi:10.1117/1.JMI.3.1.013503

5. Date of download: 6/1/2016 Copyright © 2016 SPIE. All rights reserved. C-Arm CT and constraining image frequency response curves. Figure Legend: From: Volumetric limiting spatial resolution analysis of four-dimensional digital subtraction angiography J. Med. Imag. 2016;3(1):013503. doi:10.1117/1.JMI.3.1.013503

6. Date of download: 6/1/2016 Copyright © 2016 SPIE. All rights reserved. Frequency response results for the (a) ISPH and (b) PPH. Near-exact results have been grouped for clarity. Figure Legend: From: Volumetric limiting spatial resolution analysis of four-dimensional digital subtraction angiography J. Med. Imag. 2016;3(1):013503. doi:10.1117/1.JMI.3.1.013503

7. Date of download: 6/1/2016 Copyright © 2016 SPIE. All rights reserved. ISPH profiles of the PSF with (a) kernel size 5 and 10% threshold and (b) kernel size 0 and 10% threshold. Figure Legend: From: Volumetric limiting spatial resolution analysis of four-dimensional digital subtraction angiography J. Med. Imag. 2016;3(1):013503. doi:10.1117/1.JMI.3.1.013503

8. Date of download: 6/1/2016 Copyright © 2016 SPIE. All rights reserved. Physical phantom profiles of the PSF with (a) kernel size 5 and 10% threshold and (b) kernel size 0 and 10% threshold. Figure Legend: From: Volumetric limiting spatial resolution analysis of four-dimensional digital subtraction angiography J. Med. Imag. 2016;3(1):013503. doi:10.1117/1.JMI.3.1.013503

9. Date of download: 6/1/2016 Copyright © 2016 SPIE. All rights reserved. ISPH PSF mesh plot with (a) kernel size 5 and 10% threshold representing an unmodulated PSF and (b) kernel size 0 and 10% threshold representing a highly modulated PSF in the direction of the projection angle. Figure Legend: From: Volumetric limiting spatial resolution analysis of four-dimensional digital subtraction angiography J. Med. Imag. 2016;3(1):013503. doi:10.1117/1.JMI.3.1.013503