Interactive Scan Control for Kinematic Study in Open MRI

A pilot trial on kinematic magnetic resonance imaging using a superconducting, horizontally opened, 1.2 T magnetic resonance system

Purpose

This study was performed to introduce and evaluate the potential of kinematic magnetic resonance imaging (KMRI) using a high-field open-magnet magnetic resonance (MR) system.

Methods

We attempted to perform KMRI of healthy volunteers’ lumbar spine and knee in the lateral position and ankle in the supine position utilizing the superconducting, horizontally opened, 1.2 T MR system (OASIS, HITACHI, Tokyo, Japan). For the KMRI of the lumbar spine, the volunteer had to lie on one side while maintaining maximally anteflexed, neutral, and maximally retroflexed positions and remain still for the duration of the acquisition time for each posture. In the same way, KMRI of the knee was performed with the volunteer's knee flexed at 0°, 30°, 60°, 90°, and 120° in the lateral position, and KMRI of the ankle was performed with the volunteer's ankle in maximally dorsiflexed, neutral, and maximally plantarflexed positions while lying in the supine position.

Results

We could acquire higher quality kinematic MR images than those acquired using low-field MR systems. The spinal canal, intervertebral discs and foramina, and facet joints in lumbar spine KMRI; the ligaments, menisci and patellofemoral joint in knee KMRI; and the tibiotalar articulation and peroneal tendon in ankle KMRI were clearly depicted.

Conclusion

The results of our pilot trial indicated that a superconducting horizontally opened, 1.2 T MR system offers high-quality KMRI images and can be utilized for the kinematic diagnosis and evaluation of sports injuries.

Clinical feasibility of a magnetic resonance tracking system to guide the position of the scan plane during physiologic joint motion

PURPOSE

Unrestricted physiologic joint motion results in multidirectional displacement of the anatomic structures. When performing real-time magnetic resonance (MR) imaging of such a joint motion, continuous adjustment of the scan plane position may be required. The purpose of this study was to evaluate the clinical feasibility of a method to guide the scan plane position during dynamic-motion MR imaging of freely moving joints.

MATERIALS AND METHODS

The location of a small tracker device (dedicated hardware) placed on the patient's skin overlying a joint was determined by an ultrashort MR sequence and used to automatically adjust the scan plane position prior to each dynamic-motion MR image. Using a vertically open MR unit, this MR tracking system was applied in ten dynamic-motion MR examinations to evaluate flexion/extension manoeuvres in the weight-bearing knee joint, and in ten dynamic-motion MR examinations of the shoulder joint to evaluate manoeuvres such as internal/external rotation of the humerus, stress testing of the glenohumeral joint and abduction/adduction manoeuvres. Average number of manoeuvre repetitions, total number of images and percentage of useful images per manoeuvre were calculated. Imaging time per scan plane for each manoeuvre was recorded.

RESULTS

Average repetition of manoeuvres varied between 1.6 and 5.8, with an average number of 7 to 18 images per manoeuvre. Average percentage of useful images varied between 61% and 89%. Total imaging time per scan plane ranged between 1 min 10 s and 4 min 51 s.

CONCLUSIONS

The MR tracking system to guide the slice position for each consecutive dynamic-motion MR image of the freely but slowly moving shoulder or knee joint was feasible for clinical use, providing a high percentage of useful images for each manoeuvre within a clinically acceptable time frame.

Quantitative assessment of rotatory instability after anterior cruciate ligament reconstruction

BACKGROUND

Anterior cruciate ligament reconstruction successfully reduces anterior knee instability, but its effect on rotatory stability is not fully understood. In addition, a definitive method for the quantitative evaluation of rotatory instability remains to be established.

HYPOTHESIS

Measurement of anterolateral tibial translation by open magnetic resonance imaging could positively correlate with the clinical grading of the pivot-shift test and would clarify residual rotatory abnormalities not shown by conventional methods for measurement of anterior stability.

STUDY DESIGN

Controlled laboratory study.

METHODS

An anterior cruciate ligament-reconstructed group (n = 21) and an anterior cruciate ligament-deficient group (n = 20) were examined using a Slocum anterolateral rotatory instability test in open magnetic resonance imaging. Anterior tibial translation was measured at the medial and lateral compartments by evaluating sagittal images. Clinical knee stability was evaluated before the above measurement using the pivot-shift test, KT-2000 arthrometer, and stress radiography. A cutoff value for anterolateral tibial translation relating to pivot-shift was determined using a receiver operating characteristic curve.

RESULTS

Side-to-side differences of anterolateral tibial translation correlated with clinical grade of the pivot-shift test and stress radiography but not with KT-2000 arthrometry in both groups. The cutoff value was established as 3.0 mm. Although the mean anterolateral translation showed no difference, 9 reconstructed knees revealed greater than 3 mm of anterolateral tibial translation, whereas only 3 uninjured knees did.

CONCLUSION

Measurement using an open magnetic resonance imaging successfully quantified the remaining rotatory instability in anterior cruciate ligament-reconstructed knees.

CLINICAL RELEVANCE

This method is a useful means for quantifying anterior cruciate ligament function to stabilize tibial rotation.

Parametric characterization of spinal motions in osteoporotic vertebral fracture at level T12 with fluoroscopy

Vertebral fractures due to osteoporosis are a common skeletal disorder affecting the mobility of the patients, although little is known about the relationship between spinal kinematics and osteoporotic fracture. The purpose of this study was to characterize the motions of the thoracolumbar spine affected by osteoporotic vertebral fracture at level T12 and compare the results with those of non-fracture osteoporosis subjects. We examined the continuous segmental kinematics of the vertebrae, and describe the segmental motion of the spine when a fracture at T12 is present. Fluoroscopy sequences of the thoracolumbar spines during sagittal and lateral flexion were collected from 16 subjects with osteoporosis of their spine (6 with vertebral fractures at T12, 10 without a fracture). Vertebrae T10-L2 in each frame of the sequences were landmarked. Kinematic parameters were calculated based on the landmarks and motion graphs were constructed. Compared to the control subjects who did not have a fracture, fracture subjects had a more asymmetric lateral range of motion (RoM) and required a longer time to complete certain phases of the motion cycle which are parameterized as lateral flexion ratio and percentage of motion cycle, respectively. Prolonged deflection was more frequently found from the fracture group. Characterizing the motions of the fractured vertebra together with its neighboring vertebrae with these kinematic parameters is useful in quantifying the dysfunction and may be a valuable aid to tracking progress of treatment.