Does microenema administration improve the quality of DWI sequences in rectal MRI?

Abstract

Purpose: To determine whether the administration of a microenema immediately prior to rectal magnetic resonance imaging (MRI) decreases the level of gas-related artifacts on diffusion-weighted imaging (DWI) sequences.

Methods: This retrospective analysis included 492 (183 baseline and 309 post-total neoadjuvant treatment [TNT]) consecutive MRI scans for rectal cancer from January 2019 to January 2020. Scan-related factors were identified including microenema use (yes or no), field of view (FOV) in DWI (b = 800 or b = 1500), and magnet strength (1.5 T or 3 T). Two readers scored DWI studies for gas-related artifacts and T2-weighted sequences for the amount of intraluminal gas on a 5-point scale. Fisher's exact test and the Rao-Scott Chi-squared test were used to examine associations between microenema use and other factors. Generalized estimating equation and multivariable regression models were performed to examine the effect of microenema use in subgroups of scans for each reader. Cohen's κ was used to assess inter-reader agreement.

Results: Gas-related artifact levels decreased in scans with microenema overall (P < 0.001) as well as when scans were stratified by FOV (P ≤ 0.003). For both readers, post-TNT scans with microenema showed lower artifact levels overall (P < 0.014 and P < 0.001) and in post-TNT subgroups of axial DWI scans (P ≤ 0.006 and P < 0.001) and scans acquired with a 3 T magnet (P ≤ 0.001 for both FOV). No evidence of decreased artifact level was found for baseline studies. Decreased gas was seen with microenema use (P < 0.001 for both readers). Inter-reader agreement on artifact-level and gas-level assessments ranged from slight to substantial (κ = 0.273-0.685).

Conclusion: Microenema use prior to rectal MRI reduces gas-related artifacts on DWI, including both large and small FOV sequences and particularly on post-TNT scans performed at 3 T, and offers a viable solution to improve DWI quality.

Keywords: Diffusion-weighted imaging; Magnetic resonance imaging; Microenema; Rectal neoplasms; Susceptibility artifact.

Fig 1

Flowchart of included MRI rectal scans

Fig 2

Representative axial slices depicting the presence and severity of artifacts within the large field of view axial DWI sequences with b = 800. The scoring system was based on 5-point scale as follows: Score 1 = No artifact (a). Score 2 = Mild artifact (b) (arrow). Score 3 = Moderate artifact (c). Score 4 = Severe artifact (d). Score 5 = Extensive artifact (e)

Fig 3

Representative T2 axial slices depicting the presence and amount of gas within axial T2 sequences. The scoring system was based on a 5-point scale as follows: 1 = No gas (a). 2 = Minimal amount of gas (b). 3 = Small amount of gas (c). 4 = Moderate amount of gas (d). 5 = Large amount of gas (e)

Fig 4

Forest plot on odds ratio estimates of artifact levels for studies performed with microenema (ME) vs without microenema (ME vs No ME) in all post-TNT studies for reader 1 (R1) and reader 2 (R2), as well as stratified first by field of view (axial DWI and FOCUS DWI) followed by magnet strength (1.5T and 3T). Except for studies performed on FOCUS DWI and 1.5 magnet strength for one reader, there was a significant decrease in artifact level for all post-TNT studies.

Fig 5

Forest plot on odds ratio estimates of artifact level for studies performed with microenema (ME) vs without microenema (ME vs No ME) in all baseline studies for reader 1 (R1) and reader 2 (R2), as well as stratified first by field of view (axial DWI and FOCUS DWI) followed by magnet strength (1.5T and 3T). There was no significant decrease in artifact level with microenema use in any baseline group.

Fig 6

Cohen’s κ along with bootstrapping confidence intervals for inter-reader agreement on artifact levels for all studies performed with microenema vs without microenema as well as in all subgroups and for rectal gas.