Benefits and challenges in bowel MR imaging at 3.0 T

Value of high-field magnetic resonance imaging for diagnosis and classification of acute colonic diverticulitis

OBJECTIVES

Due to limited and outdated literature, the role of magnetic resonance imaging (MRI) in the diagnostic work-up of acute colonic diverticulitis (ACD) is still under debate. The purpose of this study was to compare the performance of modern high-field MRI and multidetector computed tomography (MDCT) in the diagnosis and classification of ACD.

METHODS

In our prospective study 24 emergency patients with the clinical diagnosis of ACD received MDCT and high-field MRI. Imaging features of ACD were assessed and categorized according to the classification of diverticular disease (CDD) by three independent readers. Results were matched with the final clinical report.

RESULTS

MRI with a specialized examination protocol clearly depicted all relevant findings of ACD. Statistical analysis resulted in an almost perfect strength of agreement between CT and MRI across all readers for the final CDD category (κ = 0.94) and the stage-related image features (κ = 0.98). Moderate agreement was seen for the detection of micro-abscesses (κ = 0.78), with a slight advantage for MRI.

CONCLUSION

Modern high-field MRI is fully comparable to MDCT in the assessment of ACD and has the potential to serve as a first-line imaging tool.

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

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.

MR imaging of distal ileal and colorectal chronic inflammatory bowel disease--diagnostic accuracy of 1.5 T and 3 T MRI compared to colonoscopy

PURPOSE

The aim of this study was to investigate the diagnostic accuracy of MR enterography (MRE) for detection of distal ileal and colorectal inflammatory bowel disease (IBD) and to evaluate whether 3 T MRI can provide a higher diagnostic performance compared to 1.5 T.

METHODS

A retrospective review of patients with known or suspected IBD who underwent MRE and colonoscopy within 3 months was performed. For analysis, the bowel was divided into six segments. Compared with colonoscopy, the accuracy values for MRI diagnosis of overall and each magnetic field strength were calculated, and the differences between 1.5 T and 3.0 T were compared. The image quality was scored separately for both field strengths and compared.

RESULTS

Eighty-eight patients were included in the study. On a patient basis, MRE had an overall sensitivity of 92.1 % and specificity of 72.0 %. On a segment basis, the sensitivity and specificity were 79.1 % and 93.6 %, respectively. Concerning severely inflamed segments, per-segment sensitivity increased from 79.1 to 94.7 %. The comparison of accuracy values between the two field strengths showed no statistically significant difference. B1 homogeneity and overall artifacts were not significantly different between 3.0 T and 1.5 T imaging. Compared to colonoscopy, MRI found four more fistulas confirmed at subsequent surgery.

CONCLUSIONS

MRI has a high diagnostic accuracy for detection of distal ileal and colorectal IBD. 3 T MRI can be considered equivalent but not superior compared to 1.5 T imaging in this context. In addition, our findings suggest MRE to be a valuable tool in detecting surgically relevant pathologies (fistulas) with higher accuracy than colonoscopy.

Initial experience of MR/PET in a clinical cancer center

Magentic Resonance/positron emission tomography (PET) has been introduced recently for imaging of clinical patients. This hybrid imaging technology combines the inherent strengths of MRI with its high soft-tissue contrast and biological sequences with the inherent strengths of PET, enabling imaging of metabolism with a high sensitivity. In this article, we describe the initial experience of MR/PET in a clinical cancer center along with a review of the literature. For establishing MR/PET in a clinical setting, technical challenges, such as attenuation correction and organizational challenges, such as workflow and reimbursement, have to be overcome. The most promising initial results of MR/PET have been achieved in anatomical areas where high soft-tissue and contrast resolution is of benefit. Head and neck cancer and pelvic imaging are potential applications of this hybrid imaging technology. In the pediatric population, MR/PET can decrease the lifetime radiation dose. MR/PET protocols tailored to different types of malignancies need to be developed. After the initial exploration phase, large multicenter trials are warranted to determine clinical indications for this exciting hybrid imaging technology and thereby opening new horizons in molecular imaging.