Korean J Radiol.  2019 Mar;20(3):429-437. 10.3348/kjr.2018.0260.

MRI T2-Weighted Imaging and Fat-Suppressed T2-Weighted Imaging Image Fusion Technology Improves Image Discriminability for the Evaluation of Anal Fistulas

• Feng ST
• Huang M
• Dong Z
• Xu L
• Li Y
• Jia Y
• Cai H
• Shen B
• Li ZP

• KMID: 2438273
• DOI: http://doi.org/10.3348/kjr.2018.0260

Abstract

OBJECTIVE
To explore whether MRI fusion technology (combined T2-weighted imaging [T2WI] and fat-suppressed T2WI [T2WI-(FS)]) improves signal differences between anal fistulas and surrounding structures.
MATERIALS AND METHODS
A total of 32 patients with confirmed diagnoses of anal fistula were retrospectively studied. All available T2WI and T2WI-(FS) images for each patient were used to generate fusion image (T2WI-(Fusion)) based on the addition of gray values obtained from each pixel via an MR post-processing work station. The discriminability of fistula, perianal sphincter, and perianal fat in T2WI, T2WI-(FS), and T2WI-(Fusion) images was quantified with Fisher's scoring algorithm. For subjective visual image assessment by researchers, five-point scale scores were determined using a modified double-stimulus continuous quality-scale test to evaluate T2WI-(FS), T2WI, enhanced axial three-dimensional-volumetric interpolated breath-hold examination (3D-VIBE), and T2WI-(Fusion) sequence images. The differences were subsequently compared.
RESULTS
Mean Fisher scores for fistulas vs. sphincters obtained from T2WI-(Fusion) (F(Fusion-fistula) = 6.56) were significantly higher than those from T2WI (F(T2WI-fistula) = 3.35) (p = 0.001). Mean Fisher scores for sphincters vs. fat from T2WI-(Fusion) (F(Fusion-sphincter) = 10.84) were significantly higher than those from T2WI-(FS) (FS(FS-sphincter) = 2.57) (p = 0.001). In human assessment, T2WI-(Fusion) showed the same fistula discriminability as T2WI-(FS), and better sphincter discriminability than T2WI. Overall, T2WI-(Fusion) showed better discriminability than T2WI, T2WI-(FS), and enhanced 3D-VIBE images.
CONCLUSION
T2WI and T2WI-(FS) fusion technology improves signal differences between anal fistulas and surrounding structures, and may facilitate better evaluation of anal fistulas and sphincters.

Keyword

Anal canal; Magnetic resonance imaging; Fusion technique; Fistula

MeSH Terms

Anal Canal
Diagnosis
Fistula
Humans
Magnetic Resonance Imaging*
Rectal Fistula*
Retrospective Studies

Figure

• 

  Fig. 1 Pixel-based magnetic resonance image fusion.A. T2WI. B. T2WI-FS. C. T2WI-Fusion. A and B were composed of many small pixels; sum of grayscale value in T2WI and T2WI-FS were used in image reconstruction to generate fusion image. T2WI = T2-weighted imaging, T2WI-FS = fat-suppressed T2WI, T2WI-Fusion = fusion image generated from T2WI and T2WI-FS

• 

  Fig. 2 Fisher scores for different scanning sequences.A. T2WI. B. T2WI-FS. C. T2WI-Fusion. Mean scores of signals for fistula, sphincter, and fat in images from three sequences were measured, and Fisher score algorithm then calculated.

• 

  Fig. 3 Image of anal fistulas and perianal structures by T2WI-Fusion.A. On T2WI, fistulas are not clearly shown (arrow). B. On T2WI-FS, fistula with high signal intensity is clearly shown (arrow), but perianal structures are not clear. C. T2WI-Fusion clearly shows fistula (arrow), and structure of internal and external sphincters.

• 

  Fig. 4 Subjective image assessment with five-point scale test.A. T2WI-FS, shows fistula (arrow) with fistula discriminability score of 3 points and sphincter discriminability score of 2 points. B. T2WI shows fistula (arrow) with fistula discriminability score of 2 points and sphincter discriminability score of 4 points. C. E-3D-VIBE shows fistula (arrow) with fistula discriminability score of 3 points and sphincter discriminability score of 4 points. D. T2WI-Fusion shows fistula (arrow) with fistula discriminability score of 5 points and sphincter discriminability score of 5 points. E-3D-VIBE = enhanced three-dimensional volumetric interpolated breath-hold examination with fat suppression

• 

  Fig. 5 Image discriminability of intersphincter anal fistula in different MRI sequences.A. T2WI-FS. B. T2WI. C. E-3D-VIBE. D. T2WI-Fusion. Fistula (arrow) was displayed in 4 images, T2WI-Fusion showed best discriminability (fistula + sphincter) among these four sequences, and fistula (arrow) was displayed well on T2WI-Fusion and T2WI-FS, while it was worse displayed in E-3D-VIBE images than on T2WI-Fusion image. Image discriminability of sphincter on T2WI-Fusion was as good as that of T2WI, but better than that of T2WI-FS.

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