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Comparing DRRs, kV, and MV images:
- (A) This is a DRR constructed from a CT scan using a bone filter so it displays virtually no soft tissue. DRR’s can be reconstructed using arbitrary parameters in order to display different information. For instance, below is a DRR constructed with a lung filter (of a different patient), and, in it, you can see the soft tissue as well as bone. They are constructed to match what would be expected to be imaged on the machine. This includes the divergence from the source.
- (B) This is a kV image taken of the same patient as the DRR from (A). Notice the excellent bony contrast and the high contrast displayed in the pacemaker. This is due to the presence of photoelectric interactions in the higher Z materials.
- (C) This is an MV image of the same patient as the DRR from (A). Notice now that the ribs are much less defined and the spinous process’ are visualized well. This is due to a lack of enough attenuation in the ribs for good contrast, but the thick process’ attenuate enough for relatively improved contrast. Also, note the fine detail is removed from the pacemaker due to a lack of photoelectric effect interactions.
- It is recommended that pacemakers be removed from MV imaging fields to reduce dose and remove problems with magnetic interference.