Fig 1.
The CT images of the CIRS phantom (Model 062M, Sun Nuclear Corp. FL, USA) acquired by the DECT (iQon Spectral CT, Philips, the Netherlands) (A) and planning CT scanner (Brilliance Big Bore (BBB) CT, Philips, the Netherlands) (B). CT, computed tomography; DECT, dual-energy computed tomography.
Table 1.
Mass density, electron density, and relative electron density of tissue equivalent plugs inserted in CIRS electron density reference phantom (Model 062M, Sun Nuclear Corp., FL, USA).
Fig 2.
The model takes contrast enhanced dual-energy CT (CE DECT) images as input and generates virtual non-contrast (VNC) images as output. The numbers denoted below the encoder/decoder blocks represent the number of channels. The bottom of the figure depicts the structure of the down-sampling block of the encoder, which comprises a UnetConv2D block and a max pooling layer. The UnetConv2D component includes two ConvBNReLU blocks, each consisting of a Conv layer that executes 2D convolutional operations, followed by batch normalization and a ReLU activation function.
Fig 3.
This is the tree diagram of the proposed method’s pipeline.
Fig 4.
VNC-Net model results for DECT dataset.
Three samples from the test set are visualized. The rightmost column represents the difference map between the target and model output, and it is overlaid on the model output in the third column to highlight where the anatomy differs from the target. The images in the middle row have the right atrium (marked by the upper left yellow box of each image), the descending aorta (marked by the lower right yellow box of each image), and the rib (marked by the green box of each image) as the ROIs. DECT, dual-energy computed tomography; ROI, region of interest.
Table 2.
CT numbers (HU) of ROIs in the images of test dataset.
CE DECT (denoted as (A)), VNC DECT (denoted as (B)), and VNC-Net (denoted as (C)) were analyzed. Numbers in parentheses are standard deviations. Statistical significance (p-value < 0.05) was assessed by Wilcoxon signed rank test. CE DECT, contrast enhanced dual-energy computed tomography; CT, computed tomography; HU, Hounsfield unit; ROI, region of interest; VNC DECT, virtual non-contrast dual-energy computed tomography.
Fig 5.
Linear relationship between the CT numbers from pCT and DECT.
The linear relationship obtained from the pixel values of the pCT (Brilliance Big Bore (BBB) CT, Philips, the Netherlands) and DECT (iQon Spectral CT, Philips, the Netherlands) images of the CIRS phantom (Model 062M, Sun Nuclear Corp., FL, USA) with all tissue plugs. We obtained two linear equations for values below or equal to 0 HU and above 0 HU. Magenta and blue represent pixel values from the same tissue plug at different locations, while black represents the mean value plotted, with error bars indicating the standard deviation. The error bars are not clearly discerned from the data points due to their small standard deviations. DECT, dual-energy computed tomography; HU, Hounsfield unit; pCT, planning computed tomography.
Table 3.
CT numbers (HU) of a CIRS phantom (Model 062M, Sun Nuclear Corp., FL, USA) with all tissue plugs and CIRS phantom without dense bone plugs.
Numbers in parentheses are standard deviations. CT, computed tomography; DECT, dual-energy computed tomography; HU, Hounsfield unit; pCT, planning CT.
Fig 6.
Conversion between pseudo DECT and pCT.
CE-pCT (A), pseudo DECT (B), pseudo VNC DECT (C), and VNC-pCT (D). To ensure the anatomy is clearly visible, CE-pCT and VNC-pCT were enlarged to match the body size of pseudo DECT and pseudo VNC DECT. CE-pCT, contrast enhanced planning computed tomography; DECT, dual-energy computed tomography; pCT, planning CT; VNC DECT, virtual non-contrast dual-energy CT; VNC-pCT, virtual non-contrast planning computed tomography.
Fig 7.
ROI analysis of the VNC-pCT results.
In the top row, the ROI on the left side of each image is the liver, and the ROI on the right side is the kidney. In the middle row, the ROI in the upper left side of each image is the right atrium, and the ROI in the lower right side is the descending aorta. Lastly, in the bottom row, the ROI marked with a green box represents the ribs, while among the two ROIs marked with yellow boxes, the one on the left is the lung and the one on the right is the breast. ROI, region of interest; VNC-pCT, virtual non-contrast planning computed tomography.
Table 4.
CT number (HU) of ROIs in the images of CE-pCT (denoted as (A)), TNC-pCT (denoted as (B)), and VNC-pCT (denoted as (C)) were analyzed.
Statistical significance (p-value < 0.05) was assessed by Wilcoxon signed rank test. Numbers in parentheses are standard deviations. CE-pCT, contrast enhanced planning computed tomography; CT, computed tomography; HU, Hounsfield unit; ROI, region of interest; TNC-pCT, true non-contrast planning computed tomography; VNC-pCT, virtual non-contrast planning computed tomography.
Table 5.
The dosimetric evaluations for treatment planning on CE-pCT and VNC-pCT for ten breast cancer patients who underwent VMAT.
Numbers in parentheses are standard deviations. CE-pCT, contrast enhanced planning computed tomography; HI, homogeneity index; PTV, planning target volume; VMAT, volumetric modulated arc therapy; VNC-pCT, virtual non-contrast planning computed tomography.
Table 6.
The dosimetric evaluations for treatment planning on CE-pCT and VNC-pCT for ten liver cancer patients who underwent VMAT or SBRT.
CE-pCT, contrast enhanced planning computed tomography; HI, homogeneity index; PTV, planning target volume; SBRT, stereotactic body radiotherapy; VMAT, volumetric modulated arc therapy; VNC-pCT, virtual non-contrast planning computed tomography.