High resolution morphologic imaging and T2 mapping of cartilage at 7 Tesla: comparison of cartilage repair patients and healthy controls

Object

Our objective was to use 7 T MRI to compare cartilage morphology (thickness) and collagen composition (T2 values) in cartilage repair patients and healthy controls.

Materials and methods

We scanned the knees of 11 cartilage repair patients and 11 controls on a 7 T MRI scanner using a high-resolution, gradient-echo sequence to measure cartilage thickness and a multi-echo spin-echo sequence to measure cartilage T2 values. We used two-tailed t tests to compare cartilage thickness and T2 values in: repair tissue (RT) versus adjacent cartilage (AC); RT versus healthy control cartilage (HC); AC versus HC.

Results

Mean thickness in RT, AC, HC were: 2.2 ± 1.4, 3.6 ± 1.1, 3.3 ± 0.7 mm. Differences in thickness between RT–AC (p = 0.01) and RT–HC (p = 0.02) were significant, but not AC–HC (p = 0.45). Mean T2 values in RT, AC, HC were: 51.6 ± 7.6, 40.0 ± 4.7, 45.9 ± 3.7 ms. Differences in T2 values between RT–AC (p = 0.0005), RT-HC (p = 0.04), and AC–HC (p = 0.004) were significant.

Conclusion

7 T MRI allows detection of differences in morphology and collagen architecture in: (1) cartilage repair tissue compared to adjacent cartilage and (2) cartilage repair tissue compared to cartilage from healthy controls. Although cartilage adjacent to repair tissue may be normal in thickness, it can demonstrate altered collagen composition.     

Subjective perception of safety in healthy individuals working with 7 T MRI scanners: a retrospective multicenter survey

Objective

To retrospectively assess perception of safety of healthy individuals working with human 7 Tesla (T) magnetic resonance imaging (MRI) scanners.

Materials and methods

A total of 66 healthy individuals with a mean age of 31 ± 7 years participated in this retrospective multicentre survey study. Nonparametric correlation analysis was conducted to evaluate the relation between self-reported perception of safety and prevalence of sensory effects while working with 7 T MRI scanners for an average 47 months.

Results

The results indicated that 98.5 % of the study participants had a neutral or positive feeling about safety aspects at 7 T MRI scanners. 45.5 % reported that they feel very safe and none of the participants stated that they feel moderately or very unsafe while working with 7 T MRI scanners. Perception of safety was not affected by the number of hours per week spent in the vicinity of the 7 T MRI scanner or the duration of experience with 7 T MRI. More than 50 % of individuals experienced vertigo and metallic taste while working with 7 T MRI scanners. However, participants’ perceptions of safety were not affected by the prevalence of MR-related symptoms.

Conclusions

The overall data indicated an average perception of a moderately safe work environment. To our knowledge, this study delineates the first attempt to assess the subjective safety perception among 7 T MRI workers and suggests further investigations are indicated.

     

Reliability of velocity pulsatility in small vessels on 3Tesla MRI in the basal ganglia: a test–retest study

Objective

Recent work showed the feasibility of measuring velocity pulsatility in the perforating arteries at the level of the BG using 3T MRI. However, test–retest measurements have not been performed, yet. This study assessed the test–retest reliability of 3T MRI blood flow velocity measurements in perforating arteries in the BG.

Materials and methods

Two-dimensional phase-contrast cardiac gated (2D-PC) images were acquired for 35 healthy controls and repeated with and without repositioning. 2D-PC images were processed and analyzed, to assess the number of detected perforating arteries (N_detected), mean blood flow velocity (V_mean), and velocity pulsatility index (vPI). Paired t-tests and Bland–Altman plots were used to compare variance in outcome parameters with and without repositioning, and limits of agreement (LoA) were calculated.

Results

The LoA was smallest for V_mean (35%) and highest for vPI (79%). Test–retest reliability was similar with and without repositioning of the subject.

Discussion

We found similar LoA with and without repositioning indicating that the measurement uncertainty is dominated by scanner and physiological noise, rather than by planning. This enables to study hemodynamic parameters in perforating arteries at clinically available scanners, provided sufficiently large sample sizes are used to mitigate the contribution of scanner- and physiological noise.