J Korean Soc Radiol.  2018 Aug;79(2):77-87. 10.3348/jksr.2018.79.2.77.

Use of Iterative Reconstruction and a Small Contrast Volume in Rabbit Kidney CT: Comparison with Conventional Protocol

• Kim R
• Kim SY
• Cho JY
• Lee J
• Kim SH

• KMID: 2416392
• DOI: http://doi.org/10.3348/jksr.2018.79.2.77

Abstract

PURPOSE
To investigate the quality of rabbit kidney computed tomography (CT) images obtained using a small contrast volume and iterative reconstruction (IR).
MATERIALS AND METHODS
Twenty sedated rabbits were used. Four milliliters of contrast material and the IR technique were used for the study group. In the control group, 6 mL of contrast and the filtered back projection (FBP) technique were used. The image quality was evaluated by two radiologists in consensus. For qualitative image assessment, the sharpness, noise, texture, and streak artifacts were rated. For quantitative analysis, the CT attenuation values, image noise, signal-to-noise ratios (SNR), contrast-to-noise ratios (CNR), and figures of merit (FOM) were calculated.
RESULTS
Images obtained from the study group were sharper and contained less noise and fewer streak artifacts (all, p < 0.05) compared to those obtained from the control group. However, the texture of images from the study group was worse (p < 0.05). Although the CT attenuation values were comparable between the study and control groups, the image noise was considerably lower for the study group than that for the corresponding control group (all, p < 0.05). Thus, the SNR, CNR, and FOM were higher in the study group (all, p < 0.05) than in the control group.
CONCLUSION
The use of the IR technique and a small volume of contrast material yielded CT images with better qualities compared to those obtained using the FBP technique and conventional contrast volume in a rabbit model.

MeSH Terms

Animals
Artifacts
Consensus
Control Groups
Image Processing, Computer-Assisted
Kidney*
Noise
Rabbits
Signal-To-Noise Ratio
Tomography, X-Ray Computed

Figure

• 

  Fig. 1 Representative axial images showing four region-of-interest circles inside kidney at 35 s (A) and 65 s (B). The CT attenuation values were measured at the renal cortex, outer medulla, inner medulla, and renal pelvis. The 35 s (A) image is displayed at the window width of 900 HU and level of 450 HU and the 65 s (B) image is displayed at the window width of 500 HU and level of 350 HU. HU = Hounsfield units

• 

  Fig. 2. Representative axial images of right kidney obtained at 35 s for each group. Between the groups given the 350 mgI/mL contrast material, the overall quality of the image of the study group (A) is better than that of the control group (B), although the image texture is worse in the study group (blocky appearance). Similarly, between the groups given 240 mgI/mL contrast material, the qualitative image quality of the study group (C) is better than that of the control group (D), despite worse image texture of the study group. All of the images are displayed at the same window width of 900 HU and level of 450 HU settings. HU = Hounsfield units

• 

  Fig. 3 Representative axial images of left kidney obtained at 65 s for each group. The images of the control groups given 350 mgI/mL contrast material (B) and 240 mgI/mL contrast material (D) show noticeable streak artifacts that extend to the periphery of the kidney parenchyma (arrowheads). However, the images of the study groups given 350 mgI/mL contrast material (A) and 240 mgI/mL contrast material (C) depict well-defined boundaries of intrarenal structures and negligible streak artifacts. All of the images are displayed with the same window width of 500 HU and level of 350 HU settings. HU = Hounsfield units

• 

  Fig. 4 Box-and-whisker plots show comparisons of the SNR, CNR, and FOM values of each intrarenal structure according to dynamic phase and contrast material concentration. Ends of boxes are 25th and 75th quartiles and lines across middles of boxes are medians. Maximum and minimum values are displayed with whiskers connecting points to center box. During the corticomedullary phase of 15 s, the median values of SNR (A), CNR (B), and FOM (C) at each intrarenal structure are higher in the study group than in the control group, regardless of contrast material concentration. During subsequent nephrographic phase of 65 s, the quantitative image parameters of SNR (D), CNR (E), and FOM (F) are better in the study group than in the control group for both contrast material concentration. CNR = contrast-to-noise ratio, FOM = figure of merit, SNR = signal-to-noise ratio

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