Performance of Virtual Unenhanced Images on a Prototype Silicon Photon Counting Detector CT: Preliminary Clinical Results

Background: To compare virtual unenhanced images (VUE) from a prototype deep silicon photon-counting detector computed tomography (PCD-CT) system with true unenhanced images (TUE). Methods: Five subjects including various anatomic structures were scanned on a prototype deep silicon PCD CT at 120 kV across different phases with mA adjusted for anatomy and subject size. Five slices were selected from each image set at two locations to provide a variety of anatomy, including vessels, soft tissue, and adipose. Regions of interest were drawn over the anatomy on both TUE and VUE images. VUE error was defined as VUE CT number in Hounsfield units (HU) minus the VUE CT number. Results: For all tested structures, 82% had a VUE error less than 10 HU, and 62% had a VUE error less than 5 HU. Vessels demonstrated VUE errors less than 10 HU and less than 5 HU for 70.4% and 40.7% of tested structures, respectively. Soft tissue had VUE errors less than 10 HU and 5 HU in 96.9% and 84.4%, and adipose had VUE errors less than 10 HU and 5 HU in 75% and 58.4% of tested structures. Conclusion: With the prototype scanner and VUE algorithm, the majority of tested anatomic structures demonstrated VUE error less than 10 HU. For all but vessels, the majority of structures demonstrated VUE error less than 5 HU. With such small differences in HU between VUE and TUE images, further work may support removing TUEs from scanning protocols.