Aneurysm clips: evaluation of magnetic field interactions with an 8.0 T MR system

This study was conducted to evaluate magnetic field interactions for aneurysm clips exposed to an 8.0 T magnetic resonance (MR) system. Twenty-six different aneurysm clips were tested for magnetic field translational attraction (deflection angle test) and torque (qualitative assessment method) using previously described techniques. Six of the specific aneurysm clips (i.e. type, model, blade length) made from stainless steel alloy (Perneczky) and Phynox (Yasargil, models FE 748 and FE 750) displayed deflection angles above 45 degrees and torque measurements of +4, indicating that these aneurysm clips maybe unsafe for patients or individuals in an 8.0 T MR environment. The specific aneurysm clips (i.e. type, model, blade length) made from commercially pure titanium (Spetzler), Elgiloy (Sugita), titanium alloy (Yasargil, model FE 750T), and MP35N (Sundt) displayed deflection angles less than 45 degrees and torque that ranged from + 1 to +4. Accordingly, these aneurysm clips are likely to be safe for patients or individuals exposed to an 8.0 T MR system. Depending on the actual dimensions and mass, an aneurysm clip made from Elgiloy may or may not be acceptable for a patient or individual in the 8.0 T MR environment.     

Aneurysm clips: evaluation of magnetic field interactions and translational attraction by use of "long-bore" and "short-bore" 3.0-T MR imaging systems

BACKGROUND AND PURPOSE: The use of 3.0-T MR systems is increasing worldwide. We evaluated magnetic field interactions and translational attraction for 32 aneurysm clips in association with exposure to "long-bore" and "short-bore" 3.0-T MR imaging systems. METHODS: Thirty-two different aneurysm clips were evaluated in this investigation. Each aneurysm clip was qualitatively evaluated for magnetic field interactions and quantitatively assessed for translational attraction by using the deflection angle test. The deflection angle tests were performed at the points of the highest spatial gradients for long-bore and short-bore 3.0-T MR imaging systems. RESULTS: Seventeen of the 32 aneurysm clips showed positive magnetic field interactions. Deflection angles for the aneurysm clips were significantly (P <.001) higher on the short-bore (range, 0-18 degrees) compared with those recorded on the long-bore (range, 0-16 degrees) 3.0-T MR imaging system. Aneurysm clips made from commercially pure titanium and titanium alloy displayed no translational attraction (n = 15), whereas those made from stainless steel alloy, Phynox, and Elgiloy displayed positive deflection angles (n = 17). CONCLUSION: The 32 different aneurysm clips passed (angle <45 degrees) the deflection angle test by using the long- and short-bore 3.0-T MR imaging systems, indicating that they are safe for patients and other persons in these MR environments (ie, immediate area of MR imaging systems). However, only clips made from the titanium and titanium alloy are entirely safe for patients undergoing MR imaging procedures because of the total lack of magnetic field interactions. The remaining clips require characterization of magnetic field-induced torque. Because of possible differences in the points of the highest spatial gradients for different 3.0-T MR imaging systems, the results are specific to the imaging units and bore designs used in this investigation.     

Comparison of MR imaging and CT in patients with intracranial aneurysm clips

CT and MR imaging of the brain were performed without complications in 16 patients who had undergone surgery for a ruptured aneurysm with the use of nonferromagnetic Yasargil 316 or Sugita Elgiloy clips. MR was performed on a 0.3-T Fonar beta-3000M imaging system. The artifacts caused by the clips were smaller on MR than on CT, and, therefore, anatomic structures such as the brainstem and temporal lobes were better visualized on MR. Brain-tissue lesions corresponding to the frontotemporal surgical approach were seen with MR in seven patients and with CT in six. In three patients temporal-lobe lesions seen on MR were not seen on CT because of beam-hardening artifacts. Lesions unrelated to the region of surgery were seen with MR in nine patients and with CT in five. In conclusion, MR was safe and superior to CT both in demonstrating anatomic details and in detecting tissue lesions in patients with aneurysm clips.     

A national survey of attitudes towards the use of MRI in patients known to have intracranial aneurysm clips.

The objective of this study was to determine the attitudes and practice of neuroradiology centres across the UK regarding the use of MRI in patients known to have intracranial aneurysm clips. A postal survey comprising three questions and a comments section was sent to 35 neuroradiology centres across the UK. There were 32 (91%) respondents to the single questionnaire. 16 (50%) respondents said that they would not consider performing MRI on a patient with an intracranial aneurysm clip. Of the remaining 50%, all said that identification of the clip type and assurance of its safety would be needed prior to scanning the patient. The magnetic strength of the system did not appear to affect the decision regarding whether or not to perform MRI on such patients. There was a variation in attitude towards the use of MRI in such patients between different regions. Neuroradiology centres are equally divided in their attitude and practice about whether it is safe to use MR to image a patient known to have an intracranial aneurysm clip. This is most probably due to the conflicting literature, as well as uncertainty about the identification and ferromagnetic properties of individual clips.     

Aneurysm clips made of titanium: magnetic characteristics and artifacts in MR.

PURPOSETo evaluate the magnetic characteristics, artifact formation, and implant safety of titanium aneurysm clips for use in MR imaging.METHODSAneurysm clips made of titanium alloy TiAl6V4 were tested in a magnetometer to determine their magnetic susceptibility and in a 1.5-T MR imager using both a geometric phantom and an animal model. A commercially available alpha-Phynox clip served as the reference standard.RESULTSWe found minimal magnetization and a significant reduction in image artifacts with the titanium clip as compared with the Phynox clip.CONCLUSIONThe titanium clips improve image quality, biocompatibility, and patient safety in medical MR applications.     

High-field-strength MR imaging and metallic biomedical implants: an ex vivo evaluation of deflection forces

Ferromagnetic biomedical implants are considered a contraindication for MR imaging primarily because of the potential hazards associated with their movement or dislodgment. Many metallic biomedical implants are composed of nonferromagnetic materials and do not present a danger to patients during MR imaging. Therefore, to evaluate the ferromagnetic qualities of 36 different metallic biomedical implants (four aneurysm clips, six hemostatic clips, four dental implants, seven prosthetic heart valves, eight orthopedic prostheses, one artificial urinary sphincter, three contraceptive diaphragms, and three cerebral ventricular shunt tube connectors) not previously evaluated with a high-field-strength MR system, we measured deflection forces at the portal of the magnet of a 1.5-T MR system. Fourteen of the 36 metallic biomedical implants were determined to be ferromagnetic as indicated by their deflection in the static magnetic field. However, only the four aneurysm clips (Drake, Mayfield, McFadden, and Sundt-Kees) had sufficient ferromagnetism to warrant exclusion of patients with these implants from imaging with a 1.5-T MR system because of the possibility of movement or displacement. The calculated deflection forces for these aneurysm clips were comparable with previously reported values of certain aneurysm clips that have been designated to present a risk for patients undergoing MR imaging. Patients with 32 of 36 metallic biomedical implants tested can be safely imaged with high-field-strength MR systems.     

Ferromagnetism and MR imaging: safety of carotid vascular clamps

Metallic extracranial carotid vascular clamps of the Selverstone, Crutchfield, Poppen-Blaylock, Salibi, Kindt, and tantalum varieties have been placed for treatment of large, giant, or inoperable intracranial aneurysms. To ascertain what adverse effect, if any, MR imaging would have on these clamps, magnetic deflection at 1.5 T was measured for various carotid clamps. Marked magnetic deflection (and torque) was displayed by stainless steel Poppen-Blaylock clamps. Relatively mild magnetic deflection was displayed by the stainless steel Selverstone, Salibi, Crutchfield, and Kindt clamps. Three patients with previously placed carotid clamps (two Selverstone, one Salibi) and one patient with a nonferromagnetic tantalum carotid clip had cranial or cervical MR studies at field strengths ranging from 0.35 to 0.60 T. No patient experienced any discomfort or neurologic sequelae as a result of MR imaging. Although the ferromagnetic clamps created severe "black-hole" artifacts and image distortion within the cervical and facial regions, no significant image degradation was apparent during spin-echo imaging of the brain. The tantalum clip created a far smaller MR artifact than did ferromagnetic clamps and allowed effective spin-echo and gradient-echo imaging in the cervical region. Our findings indicate that most patients with carotid vascular clamps (and nonferromagnetic clips) can probably be imaged safely with MR.     

Magnetic resonance angiography with ultrashort echo times reduces the artefact of aneurysm clips

We evaluated the ability of an ultrashort echo time (TE) three-dimensional (3D) time-of-flight (TOF) magnetic resonance angiography (MRA) sequence to reduce the metal artefact of intracranial aneurysm clips and to display adjacent cerebral arteries. In five patients (aged 8-72 years) treated with Elgiloy or Phynox aneurysm clips we prospectively performed a conventional (TE 6.0 ms) and a new ultrashort TE (TE 2.4 ms) 3D TOF MRA. We compared the diameter of the clip-induced susceptibility artefact and the detectability of flow in adjacent vessels. The mean artefact diameter was 22.3+/-6.4 mm (range 14-38 mm) with the ultrashort TE and 27.7+/-6.4 mm (range 19-45 mm) with the conventional MRA ( P<0.0001). This corresponded to a diameter reduction of 19.5+/-9.2%. More parts of adjacent vessels were detected, but with less intense flow signal. The aneurysm dome and neck remained within the area of signal loss and were therefore not displayed. Ultrashort TE MRA is a noninvasive and fast method for improving detection of vessels adjacent to clipped intracranial aneurysms, by reducing clip-induced susceptibility artefact. The method cannot, however, be used to show remnants of the aneurysm neck or sac as a result of imperfect clipping.     

Assessment of magnetic field (4.7 T) induced forces on prosthetic heart valves and annuloplasty rings

PURPOSE: To assess the magnetic field interactions on 11 heart valve prostheses and 12 annuloplasty rings subjected to a 4.7 T MR system. MATERIALS AND METHODS: Ex vivo testing was performed to evaluate translational and rotational forces using previously described techniques. RESULTS: Seventeen out of 23 prostheses showed zero interaction with the magnetic field. Translational forces with deflection angles of 2-20 degrees were demonstrated in six prostheses. Only two heart valves and two annuloplasty rings demonstrated rotational forces. The Carpentier Edwards (CE) Physio Ring, which contains Elgiloy, demonstrated deflection angles three times greater than those previously measured at 1.5 T. Furthermore, there was a direct relationship between increasing prosthesis size and increasing translational force. All heart valve prostheses attracted to the magnetic field were slightly paramagnetic/weakly ferromagnetic. CONCLUSION: Twenty-three heart valve prostheses evaluated for MRI are considered safe in static fields up to 4.7 T based on current safety criteria. However, the CE Physio Ring appeared to develop an increasing magnetism upon re-entry into the MR system. We conclude that prostheses made from Elgiloy may not be acceptable for patients in an MR environment of > or =4.7 T. Further investigations are required to confirm the safety of Elgiloy.     

MR imaging of metallic implants and materials: a compilation of the literature

Ferromagnetic metallic implants and materials are regarded as contraindications for MR imaging because of the potential risks associated with their movement or displacement. To date, 14 published articles have evaluated the ferromagnetic qualities of 127 different metallic implants and other materials, including aneurysm and hemostatic clips (32); dental implants and materials (five); intravascular coils, filters, and stents (13); ear implants (14); prosthetic heart valves (29); orthopedic implants and materials (eight); penile implants (nine); and miscellaneous metallic implants and materials (17). All of these materials were evaluated by measuring the deflection forces induced by static magnetic fields at strengths ranging from 0.147 to 4.7 T. This article is a compilation of the results of these studies; it lists all 127 of the materials tested, indicates whether they were found to be deflected by the static magnetic fields, and gives the highest static magnetic field strength at which they were evaluated. Of the metallic implants tested, 66 were nonferromagnetic, and 29 exhibited only minimal deflection relative to their in vivo applications (i.e., the deflection forces were thought to be insufficient to move or dislodge the implant or material in situ). The authors of these studies concluded that patients with these particular metallic implants or materials (95/127, 75%) can be examined safely by MR imaging with scanners having static magnetic field strengths up to and including those used for the specific evaluations. Patients with other ferromagnetic materials or implants may also undergo MR imaging safely; however, both careful consideration of the factors that influence the deflection of metallic implants and prudent clinical judgment are required before patients who have these objects are examined via MR imaging.     

MR imaging artifacts, ferromagnetism, and magnetic torque of intravascular filters, stents, and coils

Experiments were conducted in which various intravascular filters, stents, and coils were imaged using magnetic resonance (MR) spin-echo technique at 0.35 T. These devices were also evaluated for ferromagnetism (at 0.35, 1.5, and 4.7 T), magnetic torque (at 0.35 and 1.5 T), and magnetically induced migration within a plastic tube (at 0.35 and 1.5 T for the Greenfield filter [GF]). The stainless-steel GF was evaluated in vitro for its propensity to perforate canine inferior venae cavae (IVC). Magnetic force and torque at 1.5 T did not dislodge the GF or result in perforation of canine IVC by the GF. Beta-3 titanium alloy (used in a new percutaneous version of the GF) is apparently one of the best-suited metals for use with MR imaging because of its lack of ferromagnetism (up to 4.7 T) and absence of MR imaging artifacts (at 0.35 T). Devices composed of Elgiloy (Mobin-Uddin filter), nitinol, and MP32-N (Amplatz filter) alloys all created mild artifacts. Devices fashioned from 304 and 316L (GF and Palmaz stent) stainless-steel alloys created severe "black-hole" artifacts, with the 304 alloy devices also showing marked image distortion. Generally, the greater the ferromagnetism of a device, the greater its magnetic susceptibility artifact.     

多层螺旋CT三维血管成像在颅内动脉瘤夹闭术后随访中的初步应用

目的探讨多层螺旋CT三维血管成像（MS3D-CTA）在颅内动脉瘤夹闭术后随访中的应用价值。方法回顾性分析16例颅内动脉瘤患者夹闭术前后的MS3D-CTA资料。用16层螺旋CT扫描仪获得原始图像，然后采用容积重组（VR）、薄层最大密度投影（MIP）和多平面重组（MPR）技术对图像进行后处理。结果16例颅内动脉瘤夹闭术后复查共发现17个动脉瘤夹，其中后交通动脉瘤6例，前交通动脉瘤5例，大脑中动脉瘤4例，胼周动脉瘤1例2个动脉瘤夹。MS 3D-CTA检查未见异常7例，动脉瘤残留2例，载瘤动脉局限性狭窄4例，伴有血管痉挛3例，所有患者均未见载瘤动脉闭塞及动脉瘤夹滑脱移位征象。VR上12例清晰显示瘤夹及载瘤动脉的三维空间关系，3例较清晰显示，1例胼周动脉瘤使用2个瘤夹者线束硬化性伪影明显而显示较差；动脉瘤夹的形态及大小在薄层MIP与MPR上均能准确显示，但瘤夹与载瘤动脉的三维空间感较差。结论MS3D-CTA是颅内动脉瘤夹闭术后快捷、安全和有效的随访检查手段，VR与薄层MIP、MPR结合可更好地显示颅内动脉瘤夹闭术后改变。     

MR imaging after surgery for vertebrobasilar aneurysm

We examined the safety and utility of high-field MR in patients who had surgery for cerebral aneurysms of the vertebrobasilar system. Eighteen posterior (and three coincidental anterior) circulation aneurysms were treated. Twenty-one MR scans were obtained at a mean postoperative interval of 7.2 days. The mean size of the preoperative vertebrobasilar aneurysm was 2.2 cm; six were giant (greater than 2.5 cm) and eight were large (greater than 1.5, less than or equal to 2.5 cm). In 17 patients, Sugita nonmagnetic clips were used. In one other, a Drake tourniquet was used. No ill effects occurred from scanning with a high-field imaging unit at 1.5 T. The MR clip artifact was much less obtrusive than that on CT. In 11 cases, the aneurysm could be partially imaged postoperatively, mainly in very large aneurysms or in those treated by clipping the parent vessel. Of these, two revealed residual lumina on MR and nine looked completely thrombosed. Postoperative angiography showed that in four of the thrombosed-appearing aneurysms a residual lumen with a mean diameter of 1.0 cm had been missed. In the patient imaged after application of a Drake tourniquet, no artifact was seen, and a good assessment of progressive partial thrombosis was obtained. Evolution of the signal intensity of new aneurysm thrombus, in those minimally or not obscured by artifact, coincides with patterns previously described for hemoglobin in intracerebral hematomas. The earliest hyperintensity could be seen in either the periphery or the center of the new thrombus. All 15 patients examined with new postoperative deficits showed appropriate lesions, mainly small brainstem ischemic foci. Postoperative CT (performed in all but four of these patients) missed over 80% of these lesions, mainly owing to artifact from clip or bone. We conclude that MR is better than CT in the postoperative assessment of aneurysm patients, particularly in demonstrating small zones of ischemia. High-field MR scanning is safe if nonmagnetic surgical clips are used. MR is not accurate in assessing residual lumina.     

Contrast-enhanced three-dimensional MR angiography with an elliptical centric view for the evaluation of intracranial aneurysms

The purpose of this study was to assess the feasibility of high spatial resolution, selective arterial phase, 3D contrast-enhanced (CE) MR angiography with first pass bolus, software-trigger, elliptical centric view ordering in the detection of intracranial aneurysms. Our study included nine consecutive patients with ten intracranial aneurysms. 3D TOF MR angiography and 3D CE MR angiography were carried out with a 1.5-T MR scanner. 3D CE MR angiography was performed with an automated bolus detection algorithm and elliptical centric view order using ultrafast SPGR with a spatial resolution of 0.63×0.83×0.5 mm and imaging time of 55 s. Observers detected seven of ten aneurysms on 3D TOF MR angiograms and nine of ten aneurysms on 3D CE MR angiograms. 3D CE MR angiography clearly revealed an IC-PC aneurysm with a relatively smaller neck, a broad-based small aneurysm originating from tortuous and dilated MCA bifurcation, and a residual aneurysm and parent vessels adjacent to metallic aneurysmal clips, which had relatively low signal intensities on 3D TOF MR angiograms. 3D CE MR angiography was found to be a good and promising technique for detecting intracranial aneurysms with small necks and slow flow, vasculature with aneurysmal clips and tortuous vasculature with disturbed flow.     

64层螺旋CTA在颅内动脉瘤术前及术后的应用价值

目的：探讨64层螺旋CT血管造影（CTA）对颅内动脉瘤术前诊断及术后评价的应用价值。方法：回顾性分析临床怀疑为颅内动脉瘤患者25例,行64层螺旋CTA检查,其中21例诊断为动脉瘤,并经手术证实,术后亦行CTA复查,通过比较两次CTA结果评价动脉瘤夹闭情况。结果：在25例患者中共发现21例25个动脉瘤,CTA可清楚显示的动脉瘤位置、大小形态及与周围结构的关系,与手术所见一致（符合率100％）;术后CTA能够清楚显示动脉瘤体消失,载瘤动脉与动脉瘤夹之间关系及动脉瘤夹的数量和位置。结论：64层CTA在诊断颅内动脉瘤及动脉瘤术后随访中具有重要临床价值。     

Ligating clips for three-dimensional MR angiography at 1.5 T: in vitro evaluation

Artifact size on three-dimensional (3D) magnetic resonance (MR) angiograms and safety of various vascular clips (15 titanium and three absorbable polydioxanone clips) were assessed. All evaluated clips were completely safe. Biodegradable clips rendered no artifacts; titanium clips were associated with susceptibility effects. Artifact size was dependent on clip size, clip orientation, echo time, and degree of k-space coverage. In the presence of titanium vascular clips, fast 3D MR angiography should be performed with the shortest echo time and full k-space coverage.     

Safety of MR scanning in patients with nonferromagnetic aneurysm clips

The purpose of this study was to report our surveillance of patients with nonferromagnetic aneurysm clips (NFAC) who have undergone magnetic resonance imaging (MRI). Forty-six patients with NFAC underwent MRI over a 7-year period. Medical records were studied for evidence of subjective or objective clinical findings as a result of the MRI scan. In two patients with subjective complaints, computed tomograms (CT) were reviewed and patient interviews conducted. No significant neurologic signs or longterm symptoms were experienced. Two patients did not complete their MRI scans due to transient unilateral head pain in one and head "pressure" in another. CT scans in these patients demonstrated no evidence for hemorrhage or visible change in clip position. We documented no objective adverse outcome of patients undergoing MRI with NFAC, confirming that MRI can be performed safely in patients with nonferromagnetic aneurysm clips. The cause of subjective complaints in two of our patients is unknown.     

Artefact on MRA following aneurysm clipping: an in vitro study and prospective comparison with conventional angiography

Using both an experimental model and clinical cases, we looked at the artefact produced by Aesculap titanium-alloy aneurysm clips on MRA. Experimentally, the volume affected by artefact was 50 % less when the clip was imaged lying parallel to the main ferromagnetic field than when lying perpendicular to it. Clinically, MRA was prospectively compared with digital subtraction angiography (DSA) in nine patients who had undergone aneurysm clipping. One patient with a non-diagnostic MRA due to movement artefact was excluded. In all other cases there was an area of signal loss surrounding the clips, obscuring the immediately adjacent vessel segments. There was good demonstration of the adjacent bifurcations in five cases and the contralateral circulation was seen well in all patients. In three cases in which the adjacent bifurcations were not seen, considerable vasospasm was suggested by MRA and confirmed with DSA. In one patient an unclipped contralateral ophthalmic artery aneurysm was identified using both modalities. In this series there were no adverse events relating to clips in either static or time-varying magnetic fields. Received: 29 November 1998 Accepted: 24 December 1998     

CT angiography in the examination of patients with aneurysm clips.

The use of CT angiography is described in three patients for the evaluation of intracranial clips after surgery for an aneurysm. A postprocessing technique is described in which shaded-surface-display models were superimposed on maximum intensity projection CT angiograms. CT angiograms showed residual aneurysmal filling adjacent to a clip, patency of a vessel thought to be compromised by recent clip placement, and errant position of a clip, which required repeat surgery.     

Even echo MR rephasing in the diagnosis of giant intracranial aneurysm

Blood flow magnetic resonance (MR) imaging has played a significant role in the evaluation and differentiation of vascular from nonvascular lesions, particularly as it applies to the CNS. Even echo rephasing and high velocity signal loss are two phenomena that are useful in differentiating primary vascular lesions that exhibit either slow laminar flow or rapid flow from solid masses or clot-containing vascular lesions. Application of these two basic principles of blood flow imaging with MR aided in establishing the correct diagnosis in a case of giant intracranial aneurysm.