Contrast-Enhanced Perianal Fistula Imaging with Dixon-Based Fat Suppression
Eric G. Stinson1, Joshua D. Trzasko1, Eric A. Borisch1, Phillip M. Young1, Joel G. Fletcher1, and Stephen J. Riederer1

1Radiology, Mayo Clinic, Rochester, MN, United States


Perianal fistula images with high spatial resolution, high SNR, and excellent fat suppression were achieved with a multi-TE interleaved acquisition and a constrained-phase graph cuts-based Dixon fat/water separation.


A perianal fistula is an abnormal connection between the perineum and the anal canal (1). The current clinical protocol for imaging perianal fistulas at our institution consists of multi-planar T2-weighted imaging with and without fat saturation, multi-planar T1-weighted imaging with a gadolinium-based contrast agent (2) with and without fat saturation, and a 3D post-contrast LAVA Flex (2-pt Dixon) sequence. While these techniques have proven satisfactory for identifying tracks not seen surgically, it is also of interest to acquire 3D images with greater spatial resolution for improved treatment of this debilitating disease. However, the product sequence places limits on the spatial resolution and field of view (FOV) due to gradient limitations. The purpose of this work is to demonstrate T1-weighted, contrast-enhanced perianal fistula imaging with an interleaved multi-TE 3D spoiled gradient echo technique that can provide high spatial resolution, excellent fat suppression, and high SNR.


An interleaved multi-TE 3D spoiled gradient echo technique was developed to avoid the gradient limitations of the current (multi-TE in a single TR) clinical sequence. Due to the nature of this research study, post-contrast imaging was performed after completion of the clinical imaging protocol – about 20 minutes after contrast administration. Imaging parameters are shown in Table 1. The study shown here was performed at 3.0T, however, similar studies have been performed at 1.5T with only minor modifications to the pulse sequence and reconstruction to account for the different rate of fat dephasing at the two field strengths. The dual-echo acquisition (with corner cutting in k-space, but no other undersampling) was reconstructed with a Dixon-based fat/water separation with a phase constrained signal model (3) and graph-cuts optimization scheme similar to that in Reference (4). The scheme used here, however, differs from that in (4) in that only 2 echoes are required, and the initial phase of the water and fat signals are constrained to be equal.


Figure 1 shows the acquired axial images and sagittal and coronal reformatted images from a 34 year-old female with a healing perianal fistula. The fistula is well depicted in all images (red arrows), despite the delay between contrast injection and imaging. Good fat suppression was achieved with the phase constrained Dixon technique, and the nearly isotropic resolution allows viewing in all three planes. Compared to the current clinical protocol performed on this patient, (resolution=1.33×1.33×4mm), the high spatial resolution images benefit from improved depiction in reformatted planes and provide the opportunity to better model the fistulas in three dimensions. While previous work has performed high spatial resolution perianal fistula imaging with intermittent fat suppression (5), the Dixon technique provides additional SNR improvement due to the averaging effect of using two appropriately timed echoes (6). As clinical translation continues, the reduced delay between injection of contrast and imaging should further improve the depiction of the perianal fistulas. Future work will aim to further reduce imaging times, particularly through the use of parallel imaging and iterative reconstruction techniques.


Dixon-based CE-MRI has achieved successful imaging of perianal fistulas with high spatial resolution, high SNR, and excellent fat suppression.


Funded by NIH. Grant Numbers: EB000212, RR018898


1. De Miguel Criado J et al. RadioGraphics 2012;32:175–194.

2. Spencer JA et al. Am. J. Roentgenol. 1996;167:735–741.

3. Bydder M et al. Magn. Reson. Imaging 2011;29:216–221.

4. Hernando D et al. Magn. Reson. Med. 2010;63:79–90.

5. Loening AM et al. ISMRM. Milan, Italy; 2014. p. 2126.

6. Stinson EG et al. Magn. Reson. Med. 2015;74:81–92.


Table 1: Imaging parameters for interleaved TE perianal fistula imaging.

Figure 1: Coronal, sagittal, and axial plane images of a perianal fistula (red arrows). Water images from a Dixon-type acquisition and reconstruction depict the contrast-enhanced fistula well in all three planes (reformatted from the axial acquisition) using the proposed method, while the current clinical sequence suffers from reduced through-plane resolution.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)