Proprioceptive contribution to oculomotor control in humans.

Stretch receptors in the extraocular muscles (EOMs) inform the central nervous system about the rotation of one's own eyes in the orbits. Whereas fine control of the skeletal muscles hinges critically on proprioceptive feedback, the role of proprioception in oculomotor control remains unclear. Human behavioural studies provide evidence for EOM proprioception in oculomotor control, however, behavioural and electrophysiological studies in the macaque do not. Unlike macaques, humans possess numerous muscle spindles in their EOMs. To find out whether the human oculomotor nuclei respond to proprioceptive feedback we used functional magnetic resonance imaging (fMRI). With their eyes closed, participants placed their right index finger on the eyelid at the outer corner of the right eye. When prompted by a sound, they pushed the eyeball gently and briefly towards the nose. Control conditions separated out motor and tactile task components. The stretch of the right lateral rectus muscle was associated with activation of the left oculomotor nucleus and subthreshold activation of the left abducens nucleus. Because these nuclei control the horizontal movements of the left eye, we hypothesized that proprioceptive stimulation of the right EOM triggered left eye movement. To test this, we followed up with an eye-tracking experiment in complete darkness using the same behavioural task as in the fMRI study. The left eye moved actively in the direction of the passive displacement of the right eye, albeit with a smaller amplitude. Eye tracking corroborated neuroimaging findings to suggest a proprioceptive contribution to ocular alignment.

Body-Mounted Robotic System for MRI-Guided Shoulder Arthrography: Cadaver and Clinical Workflow Studies.

This paper presents an intraoperative MRI-guided, patient-mounted robotic system for shoulder arthrography procedures in pediatric patients. The robot is designed to be compact and lightweight and is constructed with nonmagnetic materials for MRI safety. Our goal is to transform the current two-step arthrography procedure (CT/x-ray-guided needle insertion followed by diagnostic MRI) into a streamlined single-step ionizing radiation-free procedure under MRI guidance. The MR-conditional robot was evaluated in a Thiel embalmed cadaver study and healthy volunteer studies. The robot was attached to the shoulder using straps and ten locations in the shoulder joint space were selected as targets. For the first target, contrast agent (saline) was injected to complete the clinical workflow. After each targeting attempt, a confirmation scan was acquired to analyze the needle placement accuracy. During the volunteer studies, a more comfortable and ergonomic shoulder brace was used, and the complete clinical workflow was followed to measure the total procedure time. In the cadaver study, the needle was successfully placed in the shoulder joint space in all the targeting attempts with translational and rotational accuracy of 2.07 ± 1.22 mm and 1.46 ± 1.06 degrees, respectively. The total time for the entire procedure was 94 min and the average time for each targeting attempt was 20 min in the cadaver study, while the average time for the entire workflow for the volunteer studies was 36 min. No image quality degradation due to the presence of the robot was detected. This Thiel-embalmed cadaver study along with the clinical workflow studies on human volunteers demonstrated the feasibility of using an MR-conditional, patient-mounted robotic system for MRI-guided shoulder arthrography procedure. Future work will be focused on moving the technology to clinical practice.

Effect of allopurinol on phosphocreatine recovery and muscle function in older people with impaired physical function: a randomised controlled trial.

BACKGROUND: Allopurinol has vascular antioxidant effects and participates in purinergic signalling within muscle. We tested whether allopurinol could improve skeletal muscle energetics and physical function in older people with impaired physical performance. METHODS: We conducted a randomised, double blind, parallel group, placebo-controlled trial, comparing 20 weeks of allopurinol 600 mg once daily versus placebo. We recruited community-dwelling participants aged 65 and over with baseline 6-min walk distance of <400 m and no contraindications to magnetic resonance imaging scanning. Outcomes were measured at baseline and 20 weeks. The primary outcome was post-exercise phosphocreatine (PCr) recovery rate measured using 31P magnetic resonance spectroscopy of the calf. Secondary outcomes included 6-min walk distance, short physical performance battery (SPPB), lean body mass measured by bioimpedance, endothelial function and quality of life. RESULTS: In total, 124 participants were randomised, mean age 80 (SD 6) years. A total of 59 (48%) were female, baseline 6-min walk distance was 293 m (SD 80 m) and baseline SPPB was 8.5 (SD 2.0). Allopurinol did not significantly improve PCr recovery rate (treatment effect 0.10 units [95% CI, -0.07 to 0.27], P = 0.25). No significant changes were seen in endothelial function, quality of life, lean body mass or SPPB. Allopurinol improved 6-min walk distance (treatment effect 25 m [95% 4-46, P = 0.02]). This was more pronounced in those with high baseline oxidative stress and urate. CONCLUSION: Allopurinol improved 6-min walk distance but not PCr recovery rate in older people with impaired physical function. Antioxidant strategies to improve muscle function for older people may need to be targeted at subgroups with high baseline oxidative stress.

The Impact of Different Magnetic Resonance Imaging Equipment and Scanning Parameters on Signal Intensity Ratio Measurements in Phantoms and Healthy Volunteers: Implications for Interpreting Gadolinium Signal Changes Within the Brain.

OBJECTIVES: The aim of this study was to examine the variation in signal intensity ratio (SIR) values in Eurospin gel phantoms and healthy volunteer (HV) brain images in response to different magnetic resonance imaging hardware and software settings. MATERIALS AND METHODS: Gel phantoms with T1 relaxation times similar to the dentate nucleus (DN), pons (P), globus palladus (GP), and thalamus (Th) were scanned using a T1-weighted 2-dimensional spin-echo sequence on 2 magnetic resonance imaging scanners (3 T and 1.5 T). Imaging was performed by sequentially altering selected magnetic resonance (MR) parameters relative to a default pulse sequence, and the protocol was implemented repeatedly over 3 months. The experiment was also repeated on a cohort of 15 young HVs. Calculations of DN/P and GP/Th SIR values were derived for the images of the gels (GelDN/P and GelGP/Th) and the HVs (HVDN/P and HVGP/Th). RESULTS: For the default sequence, the mean SIR values of GelDN/P and GelGP/Th varied by ±2.20% and ±0.75%, respectively, when measured over multiple imaging sessions (3 T). Within a single imaging session, these variations were smaller (±0.17% for GelDN/P and ±0.15% for GelGP/Th). At 1.5 T, the equivalent SIR variations for GelDN/P were ±1.41% (multiple sessions) and ±0.41% (single session), and that for GelGP/Th were ±0.47% (multiple sessions) and ±0.33% (single session).Sequential changes to the MR sequence parameters resulted in gel SIR variations as follows: 14.07% ± 2.43% (with/without normalization filters), -7.80% ± 0.28% (different echo times, TE), and -5.06% ± 0.59% (selective activation of RF coil elements). The largest variations were noted when the gels were positioned below the scanner isocenter, where SIR measurements were different by 22%.For the HVs, the SIR values were found to be consistently within 0.64% (single session) for the default sequence. Sequential changes to the MR sequence parameters resulted in SIR variations of -24.47% ± 2.47% (with/without normalization filters), -15.32% ± 7.71% (different echo times, TE), and -2.90% ± 0.78% (selective activation of RF coil elements). CONCLUSIONS: This study has demonstrated that SIR percentage changes from baseline of a similar magnitude to brain gadolinium contrast agent signal hyperintensities can be replicated in phantom models and HVs by altering common MR acquisition parameters and hardware.

Assessment of the accuracy and reproducibility of adrenal volume measurements using MRI and its relationship with corticosteroid phenotype: a normal volunteer pilot study.

OBJECTIVE: The significant role of corticosteroids in hypertension and cardiovascular disease highlights the importance of the adrenal gland in these disorders. The ability to correlate corticosteroid production with adrenal volume offers a novel research tool and intermediate phenotype in cardiovascular disease. The aim of this study was to develop and validate the use of magnetic resonance imaging (MRI) in adrenal volume assessment and investigate whether this associates with corticosteroid production. DESIGN/METHODS: Twenty normotensive men underwent noncontrast 1·5T MRI scanning of adrenals, measurement of blood pressure and plasma corticosteroids. Left adrenal volume was calculated twice using standard segmentation software by four independent observers with differing levels of clinical expertise and segmentation experience. To optimize this process, adrenal 'phantoms' with known fixed volumes underwent MRI scanning and analysis by two observers. RESULTS: Intra-observer coefficients of repeatability (CoRs) in phantoms ranged from 0·23 to 0·43 ml (interobserver CoR 0·48 ml). In the subject group, mean adrenal volumes were 3·99-5·82 ml with intra-observer CoRs 0·27-1·94 ml. Interobserver variability was 2·73 ml. Segmentation expertise was the main factor affecting variability, with experienced observers having the lowest CoRs; clinical knowledge was a factor when combined with segmentation experience. Mean adrenal volume correlated with plasma glucocorticoids (r = 0·523, P < 0·05) and aldosterone (r = 0·515, P < 0·05) for the most experienced observer only. CONCLUSIONS: Measurement of adrenal volume using MRI is challenging; most accurate volumes are achieved using a single observer with both segmentation experience and anatomical knowledge. The data also provide novel preliminary evidence that adrenal gland volume may be associated with plasma corticosteroid concentrations supporting further study of adrenal volume and steroid production across a range of blood pressures.