Ankle laxity: stress investigation under MRI control.

OBJECTIVE: The purpose of this study was to examine the advantages of MRI-guided ankle stress examinations in the detection of chronic ankle instability. SUBJECTS AND METHODS: An MRI-compatible stress device was developed and tested for MRI safety. Bilateral MRI stress examinations were performed on 50 volunteers with and without clinically evident subjective instability of the ankle joints (72 subjective stable ankle joints in 37 subjects, 28 ankles in 15 subjects with chronic ankle instability). Both the inversion test and the anterior drawer test were performed under axial, coronal, 45° paraxial, and sagittal T2-weighted fast spin-echo image control. MR images were assessed for talar tilt, subtalar tilt, anterior talus translation, anterior calcaneus translation, medial talocalcaneal translation, and the diameters of the lateral ankle ligaments (anterior talofibular ligament, calcaneofibular ligament, and posterior talofibular ligament). RESULTS: The MRI stress device was found suitable and safe for use in the MRI environment. The talocrural and subtalar joints could be assessed simultaneously. Significant differences between groups A and B (p≤0.05) were found in talar tilt, subtalar tilt, anterior talus translation, anterior calcaneus translation, medial talocalcaneal translation, and decrease in diameters of calcaneofibular and posterior talofibular ligaments. Also found were sex differences in talar tilt, subtalar tilt, anterior talus translation, and diameters of the anterior talofibular, calcaneofibular, and posterior talofibular ligaments. Significant relations were found between talar tilt and anterior talus translation, subtalar tilt and anterior calcaneus translation, subtalar tilt and medial talocalcaneal translation, and between anterior calcaneus translation and medial talocalcaneal translation in groups A and B. CONCLUSION: Stress examination under MRI control has advantages in the assessment of mechanical ankle instability. Additional diagnostic and clinically relevant information is obtained through direct imaging of the ligaments and assessment of additional parameters of ankle laxity (subtalar tilt, anterior calcaneus translation, medial talocalcaneal translation). The main advantages are objective imaging and measurement of abnormal looseness of the lower ankle joint and its direct simultaneous comparison with the upper ankle joint.

Evaluation of a MR-quadrupole imaging coil for spinal interventions in a vertical 1.0 T MRI.

The in vivo pain treatment was successfully performed with the patient in a prone position. The PD-weighted TSE with echo time = 10 ms rendered contrast-to-noise-ratio values of 27 ± 10 for needle/fat, 1.6 ± 5 for needle/muscle, and 4 ± 4.7 for needle/nerve tissue. The mean diameter of the needle artifact was 1.2 ± 0.2 mm. In the T(1)-weighted gradient echo, the needle's artifact diameter was 6 ± 2 mm; the needle's contrast-to-noise ratio relative to muscle tissue was 4 ± 2, 7.6 ± 1.5 for needle/fat, and 5 ± 1 for needle/nerve tissue. With the PD-weighted TSE (echo time = 10 ms) and the T(1)-weighted gradient echo, the needle was imaged reliably throughout the intervention. The butterfly surface coil is feasible for the guidance of spinal interventions in a prone patient.

The impact of imaging speed of MR-guided punctures and interventions in static organs--a phantom study.

PURPOSE: Verification of MR-guidance with image acquisitions slower than 1 image per second as it is inevitable for some interventions. Therefore, we quantified solely the effect of acquisition-time on the efficiency of MR-guided interventions in a static phantom study. MATERIALS AND METHODS: We measured the duration, accuracy and error rate of simulated interventions for different acquisition-times using a simplified interventional setup. All measurements were performed in a 1.0 T open MRI scanner. Imaging was performed with a gradient-echo sequence (flipangle=20°; TR/TE=12/6 ms; voxelsize=1 mm×1 mm; slicethickness=5 mm; FOV=230 mm×200 mm; acquisition-time=1 s). Variable acquisition times were simulated with intermediate pauses of 0, 1, 2, 3, 4 and 5 s. The interventions were performed by a total of 20 volunteers including 7 experienced interventionalists. RESULTS: The mean duration of the intervention was 2 min. Significant differences between experienced and unexperienced volunteers were limited to the localization of the image plane and corrections made. The mean accuracy was 5.6 mm. The time to localize the image plane increased with deceleration of imaging from 24 s to 49 s. A similar increase was observed for the intervention time (55-108 s). A significant influence of the acquisition-time on durations and corrections was only found with acquisition-times greater than 4s per image. CONCLUSION: Even image rates of several seconds per image are sufficient enough for efficient interventions in static organs. Thus, the main attention has to be turned on the visibility of the needle when sequences are optimized for MR-guidance. The minimization of imaging speed is rather of secondary interest.

Advancements in orthopedic intervention: retrograde drilling and bone grafting of osteochondral lesions of the knee using magnetic resonance imaging guidance.

Computer-assisted surgery is currently a novel challenge for surgeons and interventional radiologists. Magnetic resonance imaging (MRI)-guided procedures are still evolving. In this experimental study, we describe and assess an innovative passive-navigation method for MRI-guided treatment of osteochondritis dissecans of the knee. A navigation principle using a passive-navigation device was evaluated in six cadaveric knee joint specimens for potential applicability in retrograde drilling and bone grafting of osteochondral lesions using MRI guidance. Feasibility and accuracy were evaluated in an open MRI scanner (1.0 T Philips Panorama HFO MRI System). Interactive MRI navigation allowed precise drilling and bone grafting of osteochondral lesions of the knee. All lesions were hit with an accuracy of 1.86 mm in the coronal plane and 1.4 mm the sagittal plane. Targeting of all lesions was possible with a single drilling. MRI allowed excellent assessment of correct positioning of the cancellous bone cylinder during bone grafting. The navigation device and anatomic structures could be clearly identified and distinguished throughout the entire drilling procedure. MRI-assisted navigation method using a passive navigation device is feasible for the treatment of osteochondral lesions of the knee under MRI guidance and allows precise and safe drilling without exposure to ionizing radiation. This method may be a viable alternative to other navigation principles, especially for pediatric and adolescent patients. This MRI-navigated method is also potentially applicable in many other MRI-guided interventions.

Passive navigation principle for orthopedic interventions with MR fluoroscopy.

INTRODUCTION: Of late, computer-assisted surgery has become a novel challenge for orthopedic surgeons. However, for orthopedic interventions magnetic resonance (MR) fluoroscopy is in its early stages of development. The authors have developed an innovative passive navigation concept, which is potentially applicable for many magnetic resonance image (MRI)-guided musculoskeletal interventions. With this method, no switching between different planes is required, since the cross-sectional modality of the MRI is used as a new navigation approach. MATERIALS AND METHODS: This method was mainly evaluated in retrograde drilling of artificial osteochondral lesions of the talus as an example of difficult navigation in drill placement due to poor visualization with X-ray and complex anatomy. To accomplish this objective, a passive navigation device was constructed and evaluated in nine cadaveric ankle joint specimens. Feasibility and accuracy of navigated drillings were evaluated. RESULTS: The interactive high-field MR fluoroscopy and the passive aiming device allow precise drilling of osteochondral lesions of the talus, despite the complex anatomy of the ankle. Drillings could be performed with an accuracy of 1.6 mm. The drilling guide was safe and easy to handle. CONCLUSION: The MR-assisted retrograde drilling of osteochondral lesions may enable precise and safe treatment without radiation exposure. This passive navigation technique for MR fluoroscopy is potentially applicable for many orthopedic interventions and may present an alternative to other navigation methods. Especially, the treatment of pediatric and adolescent patients may benefit from the typical MRI properties.

Osteochondral lesions of the talus: retrograde drilling with high-field-strength MR guidance.

The institutional review board approved the use of cadaveric specimens, and informed consent was obtained from all volunteers. The authors performed and assessed a magnetic resonance (MR)-assisted navigation method for minimally invasive retrograde drilling of talar osteochondral lesions. For this method, a single imaging plane is sufficient for navigation during intervention. To accomplish this objective, a passive MR navigation device was used to evaluate 16 cadaveric ankle joints. Use of this interactive MR-assisted navigation method in combination with a passive aiming device allowed precise and rapid retrograde drilling of talar osteochondral lesions.