Low field magnetic resonance imaging of the equine distal interphalangeal joint: Comparison between weight-bearing and non-weight-bearing conditions

Interobserver agreement during clinical magnetic resonance imaging of the equine foot

BACKGROUND

Agreement between experienced observers for assessment of pathology and assessment confidence are poorly documented for magnetic resonance imaging (MRI) of the equine foot.

OBJECTIVES

To report interobserver agreement for pathology assessment and observer confidence for key anatomical structures of the equine foot during MRI.

STUDY DESIGN

Exploratory clinical study.

METHODS

Ten experienced observers (diploma or associate level) assessed 15 equine foot MRI studies acquired from clinical databases of 3 MRI systems. Observers graded pathology in seven key anatomical structures (Grade 1: no pathology, Grade 2: mild pathology, Grade 3: moderate pathology, Grade 4: severe pathology) and provided a grade for their confidence for each pathology assessment (Grade 1: high confidence, Grade 2: moderate confidence, Grade 3: limited confidence, Grade 4: no confidence). Interobserver agreement for the presence/absence of pathology and agreement for individual grades of pathology were assessed with Fleiss' kappa (k). Overall interobserver agreement for pathology was determined using Fleiss' kappa and Kendall's coefficient of concordance (KCC). The distribution of grading was also visualised with bubble charts.

RESULTS

Interobserver agreement for the presence/absence of pathology of individual anatomical structures was poor-to-fair, except for the navicular bone which had moderate agreement (k = 0.52). Relative agreement for pathology grading (accounting for the ranking of grades) ranged from KCC = 0.19 for the distal interphalangeal joint to KCC = 0.70 for the navicular bone. Agreement was generally greatest at the extremes of pathology. Observer confidence in pathology assessment was generally moderate to high.

MAIN LIMITATIONS

Distribution of pathology varied between anatomical structures due to random selection of clinical MRI studies. Observers had most experience with low-field MRI.

CONCLUSIONS

Even with experienced observers, there can be notable variation in the perceived severity of foot pathology on MRI for individual cases, which could be important in a clinical context.

T2 mapping of cartilage in the equine distal interphalangeal joint with corresponding histology using 0.27 T and 3.0 T magnetic resonance imaging

BACKGROUND

Low-field magnetic resonance imaging (MRI) is widely available to equine veterinarians yet is insensitive at detecting cartilage damage in the distal interphalangeal joint (DIPJ). T2 mapping is a quantitative imaging technique that can detect cartilage damage before morphological change is apparent.

OBJECTIVES

Validation of a T2 mapping sequence on a low-field MR system. Correlation of the mean T2 relaxation time in sections of cartilage with varying levels of pathology using low- and high-field MRI.

STUDY DESIGN

Cross-sectional study.

METHODS

Eight phantoms with known (nominal) T2 values underwent low-field (0.27 T) MRI and 38 ex vivo DIPJs were imaged. A further 9 ex vivo DIPJs were imaged on both the low- and high-field MR systems. Immediately after imaging, the DIPJs were disarticulated and samples collected for histology. Histological sections were graded using the Osteoarthritis Research Society International (OARSI) scoring system. Fiji ImageJ software with the MRIAnalysisPak plugin was used to calculate T2 maps and draw the regions of interest (ROIs).

RESULTS

There was close agreement between the nominal and the measured T2 values in the phantom study. Spearman's rank correlation demonstrated significant positive correlation between low- and high-field T2 measurements, rho 0.644 (p < 0.001). The intrarater agreement for T2 measurements was excellent, intraclass correlation coefficient (ICC) = 0.99 (95% confidence interval [CI] = 0.99-1.00), the inter-rater agreement was excellent, ICC = 0.88 (95% CI = 0.82-0.92) and there was good intrarater agreement for OARSI scores (к = 0.76).

MAIN LIMITATIONS

Only a small number of histological samples were analysed. Both articular cartilage surfaces were measured within the ROI. There were no OARSI grade 0 control samples.

CONCLUSIONS

A T2 mapping sequence on a low-field 0.27 T MR system was validated. There was a positive correlation between low- and high-field T2 measurements. The findings suggest a higher mean T2 relaxation time in pathological cartilage tissue examined in this study compared to normal equine cartilage tissue.

Clinical magnetic resonance image quality of the equine foot is significantly influenced by acquisition system

BACKGROUND

Investigation of image quality in clinical equine magnetic resonance (MR) imaging may optimise diagnostic value.

OBJECTIVES

To assess the influence of field strength and anaesthesia on image quality in MR imaging of the equine foot in a clinical context.

STUDY DESIGN

Analytical clinical study.

METHODS

Fifteen equine foot studies (five studies per system) were randomly selected from the clinical databases of three MR imaging systems: low-field standing (LF St), low-field anaesthetised (LF GA) and high-field anaesthetised (HF GA). Ten experienced observers graded image quality for entire studies and seven clinically important anatomical structures within the foot (briefly, grade 1: textbook quality, grade 2: high diagnostic quality, grade 3: satisfactory diagnostic quality, grade 4: non-diagnostic). Statistical analysis assessed the effect of anaesthesia and field strength using a combination of the Pearson chi-square test or Fisher's exact test and Mann-Whitney test.

RESULTS

There was no difference in the proportion of entire studies of diagnostic quality between LF St (90%, 95% CI 78%-97%) and LF GA (88%, 76-95%, P = .7). No differences were evident in the proportion of diagnostic studies or median image quality gradings between LF St and LF GA when assessing individual anatomical structures (both groups all median grades = 3). There was a statistically significant difference in the proportion of entire studies of diagnostic quality between LF GA and HF GA (100%, 95% CI lower bound 94%, P = .03). There were statistically significant differences in median image quality gradings between LF GA (all median grades = 3) and HF GA (median grades = 1 (5/7 structures) or 2 (2/7 structures) for all individual anatomical structures (all P < .001). The reasons reported for reduced image quality differed between systems.

MAIN LIMITATIONS

Randomised selection of cases from clinical databases. Individual observer preferences may influence image quality assessment.

CONCLUSIONS

Field strength is a more important influencer of image quality than anaesthesia for magnetic resonance imaging of the equine foot in clinical patients.