Effects of new titanium cerebral aneurysm clips on MRI and CT images

Application of basic principles of physics to head and neck MR angiography: troubleshooting for artifacts

Neurovascular imaging studies are routinely used for the assessment of headaches and changes in mental status, stroke workup, and evaluation of the arteriovenous structures of the head and neck. These imaging studies are being performed with greater frequency as the aging population continues to increase. Magnetic resonance (MR) angiographic imaging techniques are helpful in this setting. However, mastering these techniques requires an in-depth understanding of the basic principles of physics, complex flow patterns, and the correlation of MR angiographic findings with conventional MR imaging findings. More than one imaging technique may be used to solve difficult cases, with each technique contributing unique information. Unfortunately, incorporating findings obtained with multiple imaging modalities may add to the diagnostic challenge. To ensure diagnostic accuracy, it is essential that the radiologist carefully evaluate the details provided by these modalities in light of basic physics principles, the fundamentals of various imaging techniques, and common neurovascular imaging pitfalls.

Quantitative Analysis of Factors Affecting Cobalt Alloy Clip Artifacts in Computed Tomography

Objective

Clip artifacts limit the visualization of intracranial structures in CT scans from patients after aneurysmal clipping with cobalt alloy clips. This study is to analyze the parameters influencing the degree of clip artifacts.

Methods

Postoperative CT scans of 60 patients with straight cobalt alloy-clipped aneurysms were analyzed for the maximal diameter of white artifacts and the angle and number of streak artifacts in axial images, and the maximal diameter of artifacts in three-dimensional (3-D) volume-rendered images. The correlation coefficient (CC) was determined between each clip artifact type and the clip blade length and clip orientation to the CT scan (angle a, lateral clip inclination in axial images; angle b, clip gradient to scan plane in lateral scout images).

Results

Angle b correlated negatively with white artifacts (r=-0.589, p<0.001) and positively with the angle (r=0.636, p<0.001) and number (r=0.505, p<0.001) of streak artifacts. Artifacts in 3-D images correlated with clip blade length (r=0.454, p=0.004). Multiple linear regression analysis revealed that angle b was the major parameter influencing white artifacts and the angle and number of streak artifacts in axial images (p<0.001), whereas clip blade length was a major factor in 3-D images (p=0.034).

Conclusion

Use of a clip orientation perpendicular to the scan gantry angle decreased the amount of white artifacts and allowed better visualization of the clip site.

Ceramic Aneurysm Clips

Objective:

To design and manufacture an aneurysm clip that incorporates ceramic jaws and a titanium spring, thereby decreasing susceptibility artifact at the aneurysm neck and allowing intra- and/or postoperative magnetic resonance (MR) evaluation.

Methods:

A series of aneurysm clips were developed using ceramic jaws and a titanium spring. A corresponding clip applicator with a novel clip-applicator interface was developed to improve ergonomics and visibility during clip placement or removal. Ceramic clips were imaged at 3.0 T in a kiwi fruit phantom model and compared with MR-compatible Yaşargil aneurysm clips (Aesculap, AG & Co., Tuttlingen, Germany). Ceramic clips were subsequently evaluated in a human cadaveric model at 1.5 T.

Results:

Ceramic clips were developed initially using silicon nitride ceramic and subsequently with yttria-stabilized zirconia ceramic. The ceramic clip jaws showed reduced susceptibility artifact compared with MR-compatible Yaşargil clips. Closing pressure was maintained over the course of 50 cycles of clip opening and closing. Aneurysm clip jaw crossing was not observed. The novel clip applicator and enhanced applicator-clip interface improved visibility during clip application and reduced the potential for torque during clip removal.

Conclusion:

The use of ceramic material limited MR imaging susceptibility artifact and image distortion in the area immediately surrounding the ceramic jaws. As expected, image distortion occurred around the titanium spring and pivot. However, in the unique design of this new aneurysm clip, the spring is located far enough from the distal end of the jaws to provide an undistorted image of the clipped area.

Postoperative three-dimensional CT angiography after cerebral aneurysm clipping with titanium clips: detection with single detector CT. Comparison with intra-arterial digital subtraction angiography

AIM

To assess the significance of three-dimensional computed tomography angiography (3D-CTA) in detecting remnant necks after cerebral aneurysm clipping.

MATERIALS AND METHODS

A total of 59 patients (77 aneurysms) underwent surgery using titanium clips. Two blinded observers independently evaluated the presence of neck remnants on shaded-surface display (SSD) imaging, volume rendered (VR) imaging, and intra-arterial digital subtraction angiography (IADSA).

RESULTS

Mean sensitivity and specificity for detecting neck remnants were 50.0 and 74.2% for SSD imaging, 61.5 and 82.8% for VR imaging, and 92.3 and 92.2% for IADSA, respectively. Receiver operating characteristic (ROC) analysis revealed excellent diagnostic performance for IADSA [mean area under ROC curve (Az)=0.97], and good diagnostic performance for 3D-CTA (Az=0.70 and 0.76 for SSD and VR, respectively). Specificity of VR was better than that SSD (p=0.082), however, there was no significant difference between them.

CONCLUSION

Use of 3D-CTA techniques can facilitate postoperative evaluation.

Metal artifact reduction in musculoskeletal magnetic resonance imaging

Many strategies can be employed to reduce the size and scale of metal susceptibility artifacts in the vicinity of orthopedic hardware; factors include selection of metal hardware material, patient positioning, and MRI sequence adjustments and techniques. The adjustments to sequence parameters include high spatial resolution fast spin echo sequences with minimal interecho spacing and increased receiver bandwidth. Frequency and phase encoding gradients can be orientated so misregistration artifacts arising from the metal are directed away from areas of anticipated clinical diagnostic interest. Complications arising in the vicinity of metallic hardware, including loosening, can be assessed after implication of these metal artifact reduction techniques.

MR procedures: biologic effects, safety, and patient care

The technology used for magnetic resonance (MR) procedures has evolved continuously during the past 20 years, yielding MR systems with stronger static magnetic fields, faster and stronger gradient magnetic fields, and more powerful radiofrequency transmission coils. Most reported cases of MR-related injuries and the few fatalities that have occurred have apparently been the result of failure to follow safety guidelines or of use of inappropriate or outdated information related to the safety aspects of biomedical implants and devices. To prevent accidents in the MR environment, therefore, it is necessary to revise information on biologic effects and safety according to changes that have occurred in MR technology and with regard to current guidelines for biomedical implants and devices. This review provides an overview of and update on MR biologic effects, discusses new or controversial MR safety topics and issues, presents evidence-based guidelines to ensure safety for patients and staff, and describes safety information for various implants and devices that have recently undergone evaluation.

Magnetic resonance safety update 2002: implants and devices

The preservation of a safe magnetic resonance (MR) environment requires constant vigilance by MR healthcare professionals, particularly with regard to the management of patients with metallic biomedical implants or devices. The variety and complexity of implants and devices constantly changes, requiring continuous attention and diligence with regard to obtaining the most current and accurate information about these objects relative to the MR environment. This review article discusses MR safety and MR compatibility issues and presents important information for a variety of implants and devices, with an emphasis on those objects that have recently undergone evaluation or that require additional consideration because of existing controversy or confusion.

MRI susceptibility artefacts related to scaphoid screws: the effect of screw type, screw orientation and imaging parameters

Metal implants produce susceptibility artefacts in magnetic resonance imaging. We have explored the effects of scaphoid screw characteristics and orientation on MR susceptibility artefact. Titanium alloy, smallness and longitudinal alignment with the z-axis of the main magnetic field reduce the size of the susceptibility artefact.

MRI assessment of the proximal pole of the scaphoid after internal fixation with a titanium alloy Herbert screw

We report a series of scaphoid fractures fixed with titanium alloy Herbert screws in which postoperative Magnetic Resonance Imaging (MRI) was used to assess the marrow signal in the proximal pole of the scaphoid and thus detect the presence of avascular necrosis. The artefact produced by the titanium alloy Herbert screw did not preclude this assessment.

Virtues and drawbacks of titanium alloy aneurysm clips

This report describes the imaging characteristics of titanium alloy aneurysm clips and our clinical experience with these clips in more than 300 patients. Phantom and clinical investigations showed that clip artifacts on CT and MR are minor as compared to the cobalt alloy clips used previously. Spiral CT angiography (CTA) in combination with titanium alloy clips could be shown to be a feasible mode of postoperative control and can be used to determine completeness of aneurysm elimination, patency of adjacent arteries as well as vasospasm. In contrast, magnetic resonance angiography (MRA) proved to be unfeasible as a method of postoperative vascular imaging since the titanium clips still produce a shadow in the order of size of the entire aneurysm. Therefore, completeness of aneurysm elimination cannot be judged on magnetic resonance angiography. The clinical experience in more than 300 cases showed that the titanium alloy clips essentially performed well. However, the limits of elastic deformation appear to be somewhat inferior to cobalt alloy clips. The standard appliers do not open the blades of the titanium clips quite as far as with the comparable cobalt alloy clips and the corresponding appliers. Therefore the titanium aneurysm clips are not quite as well suited for large broad based aneurysms. Furthermore, the increased susceptibility of the new clips with regard to abuse suggests to follow the recommendations of the manufacturer not to recycle and re-sterilize clips that have been tried but not permanently implanted.

Aneurysm clips: effects of long-term and multiple exposures to a 1.5-T MR system

The authors evaluated the ferromagnetic properties of multiple nonferromagnetic aneurysm clips before and after long-term and multiple exposures to a 1.5-T magnetic resonance system. No alterations in the magnetic properties of these clips was observed. These findings suggest that repeated or chronic exposure of patients with implanted nonferromagnetic aneurysm clips to strong static magnetic fields is unlikely to result in any clinically significant alteration in the magnetic properties of these clips.