CERAMIC ANEURYSM CLIPS
As published in NEUROSURGERY Magazine
www.neurosurgery-online.com
 Garnette R. Sutherland, M.D.
Department of Clinical Neurosciences,
University of Calgary,
Calgary, Canada
John J.P. Kelly, M.D.
Department of Clinical Neurosciences,
University of Calgary,
Calgary, Canada
David W. Boehm
Concept Solutions, Inc.,
Langley, Canada
James B. Klassen
Concept Solutions, Inc.,
Langley, Canada
Reprint requests:
Garnette R. Sutherland, M.D.,
Department of Clinical Neurosciences,
University of Calgary,
Foothills Medical Centre,
1403 29th Street NW,
Calgary, Alberta, T2N 2T9, Canada.
Email: garnette@ucalgary.ca
Received, November 8, 2007.
Accepted, December 26, 2007.
There have been a number of advances in both design and
material selection for aneurysm clips since Walter Dandy
(3) used a V-shaped malleable silver clip to isolate an
intracranial carotid aneurysm from the cerebral circulation.
Over the past decade, the most significant advancement has
been the development of magnetic resonance (MR)-compatible
clips composed of a titanium alloy, Titanium-6Al-4V (1, 13, 28),
or pure titanium (15). These aneurysm clips allow patients to be
investigated with MR imaging (MRI), but the titanium alloy
results in susceptibility artifact, making subsequent assessment
of the aneurysm site problematic (9, 21, 24, 25, 27, 30). We
describe the development of MR-compatible aneurysm clips
that should not obscure the image of the aneurysm neck or
associated parent and daughter vessels.
Currently, MR-compatible aneurysm clips are constructed
using Titanium-6Al-4V because pure titanium has been
thought to lack the necessary strength (2). This alloy also contains
the elements aluminum and vanadium, together with
trace amounts of carbon, iron, oxygen, and hydrogen (2),
which results in mechanical properties superior to those of
pure titanium. Even pure titanium produces MR susceptibility
artifact, which is similar to that observed with titanium
alloys (17).
Alternative, biocompatible materials have been used in the
production of various medical devices, including joint prostheses
and surgical instruments. One such group of materials is
ceramics (17, 22). Compared with titanium and other metals,
certain ceramics have substantially less MR susceptibility artifact
but equal or greater strength (17, 18).
This report describes the development of an MR-compatible
aneurysm clip composed of ceramic jaws and a small titanium
alloy spring (14). The use of ceramics greatly reduced susceptibility
artifact at the region of interest. The titanium alloy
spring maintained the necessary closing force. Anovel applicator
was developed for use with the ceramic clips. The design of
the clip-applicator interface increased functionality by improving
visibility during clip placement and removal.
MATERIALS AND METHODS
Before the design of the novel aneurysm clip, material selection was
performed based on the goal of MR compatibility with minimal suscep-tibility artifact and in keeping with the American Society for Testing and
Materials Committee F-4.05 guidelines for aneurysm clip biocompatibility
and closing forces (16). Aneurysm clip components include the
spring, pivot, and jaws. Ti 6Al-4V ELI titanium (Ti, 89.4%; Al, 6.08%; V,
4.06%; C, 0.14%; Fe, 0.20%; O, 0.12%; N, 0.006%; Y, 0.005%) was chosen
for the spring and pivot for its biocompatibility and extremely high
modulus of elasticity, or ability to flex without permanent deformation
(2). The extra low interstitial grade provides improved fracture toughness
and ductility over the standard alloy (2).
For the jaws, both silicon nitride ceramic and yttria-stabilized zirconia
ceramic were tested. Silicon nitride is a nonreflective gray color,
making it suitable for intense surgical lighting. Because of its high
strength and hardness, it is widely used in applications such as highspeed
industrial bearings and seals (11). Zirconia is characterized by
extraordinary strength and resistance to crack propagation (8). Among
other applications, yttria-stabilized zirconia is used in the manufacture
of knife blades. It does not have the brittleness characteristic of many
ceramics (6). Silicon nitride approaches the strength of high-grade titanium,
but yttria-stabilized zirconia can even exceed that strength.
Interestingly, although zirconia is stronger and tougher than silicon
nitride, it is more easily prototyped and manufactured. Most varieties
are white in color, but a densification process during fabrication results
in a final beige color, which reduces reflectivity making it suitable for the
microsurgical environment. These materials are biocompatible, which
makes them well suited to medical implant applications (22).
After material selection, computer-aided design (CAD) of the
aneurysm clip was completed using the Solidworks CAD program
(SolidWorks Corp., Concord, MA). Material strength was tested virtually,
using the COSMOSWorks Advanced Professional Finite Element
Analysis program (SolidWorks Corp.), to ensure that the safety factor
was approximately 10 times the maximum force that could be exerted
on the clip during use. Once the design was finalized, clips in an array
of shapes and sizes were machined using a high-precision computer
numerically controlled mill (Model OM2; HAAS Automation, Inc.,
Oxnard, CA) with a high-speed spindle.
In addition to the ceramic clips, a series of Titanium-6Al-4V ELI
temporary clips was constructed. Titanium alloy was chosen for the
temporary clips because they are not imaged, and the alloy is less
expensive than ceramic to prototype and manufacture. The temporary
clips were fitted with a gold-anodized titanium spring that provided a
reduced closing force.
Assorted applicator configurations were also designed and constructed
based on ergonomics, balance, applicator-clip interface, and
maximization of line of sight. Various applicator latching mechanisms
were considered, with the objective of providing the surgeon with certainty
that the latch has become disengaged and, once disengaged, can
not become re-engaged during clip placement. These features were
important in overcoming current limitations in applicator design.
The closing force was measured for both the permanent and temporary
clips using an Imada ZPS-DPU-1 force gauge (IMADA, Inc.,
Northbroook, IL) to measure the closing force. In addition, the effect of
opening and closing the clips for 50 cycles, from fully opened to fully
closed, was determined.
Magnetic resonance imaging was conducted at both 1.5 and 3.0 T on
two silicon nitride clips (one short straight and one short aperture)
and two yttria-stabilized zirconia clips (one long straight and one long
aperture) and Yas¸argil MR-compatible titanium clips (Aesculap, AG &
Co., Tuttlingen, Germany). Initial MRI was performed at 3.0 T using
several different phantom substrates. Akiwi fruit provided the clearest
resolution of the clip jaws and surrounding area. Fast spin echo T1
(repetition time [RT], 500 ms; echo time [TE], 15 ms; flip angle, 90 degrees; bandwidth, 15.6 kHz; slice thickness, 4 mm; field of view,
26 cm; matrix, 256 192; number of excitations, 2) and T2 (TR, 4575 ms;
TE, 102 ms; flip angle, 90 degrees; bandwidth, 31.25 kHz; slice thickness,
4 mm; field of view, 26 cm; matrix, 256 256; number of excitations,
2; echo train length, 12 ms; refocus flip angle, 160 degrees) imaging
sequences were performed at various planes and angles to assess
the artifact characteristics of ceramic jaw clips and Yas¸argil MRcompatible
clips.
A second MRI test was performed at 1.5 Tesla using a cadaveric
head. Before imaging, a right frontal temporal craniotomy was performed.
The right Sylvian fissure was opened, together with the right
carotid cistern. A long apertured ceramic clip was placed across the
right middle cerebral artery, and a long straight clip was positioned
across the right carotid artery. Fast spin echo T1 (TR, 420 ms; TE, 12.1 ms;
flip angle, 90 degrees; bandwidth, 16 kHz; slice thickness, 4 mm; field
of view, 26 cm; matrix, 256 192; number of excitations, 3) and T2 (TR,
4000 ms; TE, 90 ms; flip angle, 90 degrees; bandwidth, 25 kHz; slice
thickness, 4 mm; field of view, 26 cm; matrix, 256 256; number of
excitations, 2; echo train length, 8 ms; refocus flip angle, 180 degrees)
imaging sequences were acquired in both the coronal and axial planes.
RESULTS
CAD drawings were developed based on sizes and shapes of
commercially available aneurysm clips (Fig. 1A). To provide
maximum opening distance and necessary closing force, a
novel spring mechanism was developed based on ceramic
jaws, a titanium spring, and a titanium pivot (Fig. 1A). The
imaging requirement called for positioning the titanium components
away from the section of the jaws used to secure the
aneurysm neck. The configuration allows a compact design
that combines the rigid properties of ceramic with the elastic
properties of titanium. Finite element analysis of the ceramic
jaws showed the highest stress to be located in the midportion
of the jaws, and to be well below the flexural strength of silicon
nitride (Fig. 1B). Finite element analysis of the titanium spring
showed an even distribution of stress, which minimized issues
related to fatigue. Special consideration was given to preventing
jaw crossing. This was accomplished by the geometry of the
ceramic’s contact surface with the pivot and spring. The design
also allowed for component manufacture within an acceptable
range of manufacturing tolerances.
Initially, short straight and short aperture clip jaws were manufactured
from silicon nitride. Because yttria-stabilized zirconia
was more easily prototyped and readily available, all subsequent
clips were manufactured from this ceramic (Fig. 1C). Short
straight, long straight, short aperture, and apertured-T temporary
clip jaws were manufactured from titanium (Fig. 1D). As a
result of the hardness of the ceramic and the minute detail, the
prototyping process required several weeks per clip. Jaw crossing
has not been observed in any of the clips manufactured,
despite their being intentionally applied in a manner that would
cause jaw crossing in conventional clips.
The applicator was constructed from titanium and 301 stainless
steel and includes a novel latching mechanism (Fig. 2). The
latch is constructed from titanium and is designed to withstand
up to 20 pounds of side load without damage. It is
spring-loaded to remain seated against one arm of the applica-tor (Fig. 2, B–E). The latch may be engaged using one hand, and it provides a tactile feedback click to the surgeon when it disengages
(Fig. 2, B–E). Once disengaged, the latch cannot
become unintentionally re-engaged (Fig. 2E, inset).
 
 The new clip design, which incorporates a spring, pivot, and
ceramic jaws, allows the applicator-clip interface to be considerably
reduced in size (Fig. 3). Aball-and-socket interface incorporated
into the design, allowed the applicator to be actuated on the
ceramic jaws rather than encompass the spring, which provided
a clear line of sight along the jaws with no obstruction (Fig. 3A).
In addition, the ball-and-socket interface allows the applicator to
engage the clip at various angles, so that the clip can be removed from the aneurysm or repositioned without applying torque to
the vascular structures (Fig. 3B).
Asilicon nitride short straight clip achieved an effective closing
force of 151 g. With 50 cycles of opening and closing, the closing force stayed within 150 5 g (Fig. 4). The short straight
temporary clip had a closing force of 100 g. Over the course of
50 cycles of opening and closing, there was more variability in
closing force as compared with the permanent clip, ranging
from 98 g to 109 g.
Images obtained from kiwi fruit with implanted aneurysm
clips at 3.0 T showed a susceptibility artifact with the MRcompatible
Yas¸argil clip was several times the diameter of the
cross-section of the jaws (Fig. 5, left). The artifact extending
beyond the end of the titanium jaws did not intersect the jaws
themselves. The titanium spring of the ceramic clip had a sus-ceptibility artifact similar to that of the spring end of the Yas¸argil
clip (not shown). The ceramic jaws were only detectable in the
MRI scan as a void that did not extend outside the width of the
clip (Fig. 5, right). The phantom material directly contacting the
ceramic jaws was completely free of artifact or image distortion.
A right frontotemporal craniotomy was performed, the right
sylvian fissure and carotid cistern opened, and two yttriastabilized
zirconia clips placed across vascular structures (Fig.
6A). The 1.5-T imaging studies obtained from the cadaver shown
in Figure 6A produced minimal susceptibility artifact within the
sylvian or carotid cisterns (Fig. 6, B and C).
DISCUSSION
 The goal of this development
project was to create an
aneurysm clip with a significantly
reduced magnetic susceptibility
artifact. This has
been accomplished through
the use of ceramic jaws. The
imaging benefit was shown in
both phantom and cadaveric
models.
There is a compelling need
to assess patients radiologically
after clipping of cerebral
aneurysms, both perioperatively
and over the long term.
Acutely, it is important to assess
whether the aneurysm has
been obliterated completely,
and often whether vasospasm
involves the parent and daughter
branches in the vicinity of
the clip. Currently, this assessment
requires contrast angiography.
In several reported series,
residual aneurysm has been
observed in up to 14% of cases
(29). Although the natural history
of residual aneurysm has
not been established, aneurysm
regrowth and rupture has been
reported (4, 5). Long-term
assessment would also provide
a comparative data set for coiled
aneurysms. Ceramic aneurysm
clips offer the ability to evaluate
the aneurysm complex, either
intra- or postoperatively, with
MRI (12, 26). This would decrease
the need for x-ray evaluation
and its associated risks (7).
Compared with either pure
titanium or the titanium alloy used for the construction of most MR-compatible aneurysm
clips, ceramics are known to cause significantly less susceptibility
artifact (17). Furthermore, artifact increases with magnet
field strength for most biomaterials other than ceramics (18).
For example, spin echo T1 susceptibility artifact for a 2.0 mmdiameter
sample increases from 8.2 to 12.1 to 19.6 mm as field
strength increases from 0.5 to 1.5 to 3.0 T, respectively, whereas
zirconia values were 2.3, 2.3, and 2.5 mm for the same three
field strengths (18). Other investigators have shown that at
1.5 T, ceramics are not associated with any local temperature
change (23).
 After considering numerous configurations in the CAD modeling
process, it became apparent that a number of secondary
benefits could also be achieved. The pivoting design, which was
necessitated by the use of the rigid ceramic material, also eliminated
the need for the applicators to encompass the spring. In
contrast to conventional clip systems, this design allowed the
applicator tips to be the same width as the aneurysm clip jaws,
providing a significant advantage in visualization of the clip
during placement and removal. This also eliminated the need
for a second set of appliers for removing the clip.
The clip design also reduces or eliminates the possibility of
jaw crossing observed with other MR-compatible titanium
alloy clips, particularly those with longer jaws (10, 19). The
pivoting design of the ceramic clip uses a four-point contact
surface interface between the ceramic jaws and the titanium
pivot and spring. This geometry automatically aligns the jaws
such that jaw crossing requires significant force; it has not been
observed using the clips that have been manufactured to date.
Moving the spring as far from the clipping area of the jaws as
possible decreases the potential for susceptibility artifact at the
aneurysm neck. In addition, it requires a very high spring con-tact force as a result of the low mechanical advantage of the
spring, which was located close to the pivot. This high spring
contact force had the additional benefit of holding the jaws
together securely, preventing the possibility of jaw crossing or
disassembly. The asymmetric side spring, which was necessary
to allow the clip-applicator interface, provided improved
positioning of the applicator tips.
The ball-and-socket design for the clip-applicator interface
allows the clip to stay at the initial grasping angle and allows
application, repositioning, or removal of the clip at various
angles. Conventional applicator latching systems are prone to
damage and/or unintentional re-engagement. This is a problem
because it may prevent the applicator from disengaging from
the clip after placement across the aneurysm. The latch on the
new applicator is designed to give the surgeon a tactile feedback
click when it disengages and it offers a significant safety advantage
in eliminating the possibility of accidental re-engagement.
Prototyping of the ceramic components was extremely
challenging and time-consuming. It is expected, however,
that the assembled nature of this design will provide advantages
in manufacturing. Conventional clips require significant
time and skill to fabricate. In contrast, the titanium and
ceramic components of this new design are well suited to
high-volume production using industry-standard molding
and casting processes. Consistent tolerances from part to part
should lead to consistent closing pressure from clip to clip,
something that has not been observed with other MRcompatible
aneurysm clips (20). Consistency of closing force
has also been proven for 50 cycles. Given its many design
advantages, it is concluded that this new clip will provide
improved performance in addition to its magnetic resonance
imaging advantages.
REFERENCES
1. Bazowski P, Kwiek S, Rudnik A, Wencel T: Own experience with the treatment
of intracranial aneurysms using ’Perneczky’–Zeppelin clips. Neurol
Neurochir Pol 33:1357–1365, 1999.
2. Billinghurst EE Jr: Tensile properties of cast titanium alloys: Titanium-6A1–4V
ELI and titanium-5A1–2.5Sn ELI. NASA Technical Paper 3288:1–16, 1992.
3. Dandy WE: Intracranial aneurysm of internal carotid artery: Cured by operation.
Ann Surg 107:654–659, 1938.
4. David CA, Vishteh AG, Spetzler RF, Lemole M, Lawton MT, Partovi S: Late
angiographic follow-up review of surgically treated aneurysms. J Neurosurg
91:396–401, 1999.
5. Drake CG, Friedman AH, Peerless SJ: Failed aneurysm surgery. Reoperation
in 115 cases. J Neurosurg 61:848–856, 1984.
6. Druschitz AP, Schroth JG: Hot isostatic pressing of a presintered yttria-stabilized
zirconia ceramic. J Am Ceram Soc 72:1591–1597, 1989.
7. Einstein AJ, Henzlova MJ, Rajagopalan S: Estimating risk of cancer associated
with radiation exposure from 64-slice computed tomography coronary
angiography. JAMA 298:317–323, 2007.
8. Gogotsi GA, Galenko VI, Ozerskii BI, Khristevich TA: Fracture resistance of
ceramics: Edge fracture method. Strength Mater 37:499–505, 2005.
9. Grieve JP, Stacey R, Moore E, Kitchen ND, Jäger HR: Artifact on MRA following
aneurysm clipping: An in vitro study and prospective comparison with
conventional angiography. Neuroradiology 41:680–686, 1999.
10. Hirashima Y, Kurimoto M, Kubo M, Endo S: Blade crossing of a pure titanium
clip applied to a cerebral aneurysm. Neurol Med Chir (Tokyo) 42:123–124,
2002.11. Jordi L, Iliev C, Fischer TE: Lubrication of silicon nitride and silicon carbide
by water: Running in, wear and operation of sliding bearings. Tribology
Letters 17:367–376, 2004.
12. Kaibara T, Saunders JK, Sutherland GR: Advances in mobile intraoperative
magnetic resonance imaging. Neurosurgery 47:131–138, 2000.
13. Kato Y, Sano H, Katada K, Ogura Y, Ninomiya T, Okuma I, Kanno T: Effects
of new titanium cerebral aneurysm clips on MRI and CT images. Minim
Invasive Neurosurg 39:82–85, 1996.
14. Klassen J, Boehm D: Surgical clip, applicator, and applicator methods. US
Patent 11742259, 2007.
15. Lawton MT, Heiserman JE, Prendergast VC, Zabramski JM, Spetzler RF:
Titanium aneurysm clips: Part III—Clinical application in 16 patients with
subarachnoid hemorrhage. Neurosurgery 38:1170–1175, 1996.
16. Louw DF, Kaibara T, Sutherland GR: Aneurysm clips. J Neurosurg
98:638–641, 2003.
17. Matsuura H, Inoue T, Konno H, Sasaki M, Ogasawara K, Ogawa A:
Quantification of susceptibility artifacts produced on high-field magnetic resonance
images by various biomaterials used for neurosurgical implants.
Technical note. J Neurosurg 97:1472–1475, 2002.
18. Matsuura H, Inoue T, Ogasawara K, Sasaki M, Konno H, Kuzu Y, Nishimoto
H, Ogawa A: Quantitative analysis of magnetic resonance imaging susceptibility
artifacts cause by neurosurgical biomaterials: Comparison of 0.5, 1.5,
and 3.0 Tesla magnetic fields. Neurol Med Chir (Tokyo) 45:395–399, 2005.
19. Carvi y Nievas MN, Höllerhage HG: Risk of intraoperative aneurysm clip
slippage: Anew experience with titanium clips. J Neurosurg 92:478–480, 2000.
20. Papadopoulos MC, Apok V, Mitchell FT, Turner DP, Gooding A, Norris J:
Endurance of aneurysm clips: Mechanical endurance of Yas¸argil and Spezler
titanium aneurysm clips. Neurosurgery 54:966–972, 2004.
21. Port JD, Pomper MG: Quantification and minimization of magnetic susceptibility
artifacts on GRE images. J Comput Assist Tomogr 24:958–964, 2000.
22. Rahaman MN, Yao AH, Bal BS, Garino JP, Ries MD: Ceramics for prosthetic
hip and knee joint replacement. J Am Ceramic Soc 90:1965–1988, 2007.
23. Shellock FG, Shellock VJ: Ceramic surgical instruments: Ex vivo evaluation of
compatibility with MR Imaging at 1.5 T. J Magn Reson Imaging 6:954–956, 1996.
24. Shellock FG, Shellock VJ: Spetzler titanium aneurysm clips: Compatibility at
MR imaging. Radiology 206:838–841, 1998.
25. Shellock FG, Tkach JA, Ruggieri PM, Masaryk TJ, Rasmussen PA: Aneurysm
clips: Evaluation of magnetic field interactions and translational attraction by
use of ‘long-bore’ and ‘short-bore’ 3.0-T MR imaging systems. AJNR Am J
Neuroradiol 24:463–471, 2003.
26. Sutherland GR, Kaibara T, Louw D, Hoult DI, Tomanek B, Saunders J: A
mobile high-field magnetic resonance system for neurosurgery. J Neurosurg
91:804–813, 1999.
27. Sutherland GR, Kaibara T, Wallace C, Tomanek B, Richter M: Intraoperative
assessment of aneurysm clipping using magnetic resonance angiography and
diffusion-weighted imaging: Technical case report. Neurosurgery 50:893–898,
2002.
28. Takayasu M, Nagatani T, Noda A, Shibuya M, Yoshida J: Clinical safety and
performance of Sugita titanium aneurysm clips. Acta Neurochir (Wein)
142:159–163, 2000.
29. Thornton J, Bashir Q, Aletich VA, Debrun GM, Ausman JI, Charbel FT: What
percentage of surgically clipped intracranial aneurysms have residual necks?
Neurosurgery 46:1294–1300, 2000.
30. Wichmann W, Von Ammon K, Fink U, Weik T, Yas¸argil GM: Aneurysm clips
made of titanium: Magnetic characteristics and artifacts in MR. AJNR Am J
Neuroradiol 18:939–944, 1997.
Acknowledgments
This study was supported by a grant from the Canada Foundation for Innovation
(CFI# 8766).
COMMENTS
The design of aneurysm clips has varied minimally over the past 30
years, except for introduction of titanium clips for magnetic resonance
imaging (MRI) compatibility. Although titanium clips are MRI
safe, they still cause imaging artifact and obscure critical potential MRI and magnetic resonance angiography (MRA) information around the
neck of the clipped aneurysms. In this report, Sutherland et al. propose
an important radical redesign of aneurysm clips. The blades of the clip
are ceramic with only the spring mechanism remaining titanium.
Theoretically, postoperative MRI and MRA images could be obtained
with preserved visualization of the aneurysm neck region. The design
of the clip allowing for a low profile applier is also very appealing. The
clip can apparently be rotated within the applier to achieve the perfect
angle of application. Previous designs along these lines have always
resulted in a more bulky applier.
It remains to be established that the closing forces are comparable to
existing clips in the clinical setting. Also, the lifespan of the clips once
implanted and the shelf-life of the clips previous to implantation are
issues that will be necessary to resolve before widespread clinical use
of the ceramic clips. The design is intriguing, and I look forward to
future clinical trials.
Robert A. Solomon
New York, New York
The golden days of postoperative conventional angiography are
soon expected to be over as noninvasive, safe, and fast methods
such as computed tomographic angiography and MRA are replacing
it in most cases. Complex and giant aneurysms may differ as they
often necessitate even intraoperative angiography to confirm complete
neck occlusion and at the same time the patency of the surrounding
arteries. In less complex ones, direct visualization in combination
with intraoperative indocyanine green angiography and
Doppler ultrasound will enable us to close the wound. However,
unexpected neck remnants and branch occlusions may occur as these
methods are not 100% reliable addressing the importance of postoperative
angiographic control. Dynamic computed tomographic
angiography as a postoperative means necessitates using of titanium clips as otherwise its value is just to see the patency of adjacent
branches. MRA is still slower to perform and often more difficult in
poor condition patients who may need a respirator and extensive
monitoring. Still, any step towards developing clips with less artifact
in MRA and computed tomographic angiography is welcome so that
we may control the quality of clipping with modern methods that
may not even have harmful radiation side effects.
Reza Dashti
Istanbul, Turkey
Mika Niemelä
Riku Kivisaari
Radiologist
Juha A. Hernesniemi
Helsinki, Finland
In modern neurosurgery, the titanium clip is a worthy development
for improving image quality as well as biocompatibility in MRI.
However, the problem remains that titanium clips do not allow us to
inspect clipped aneurysms in detail because of their susceptibility artifact.
In their article, Sutherland et al. introduce an aneurysm clip with
ceramic jaws and a titanium spring to resolve this problem. Their new
clip has decreased susceptibility artifact in comparison with the recent
ordinary titanium-body clip. The authors show beautiful results
demonstrating that their ceramic clip has the potential to improve MR
visualization of the clipped aneurysm. Their clips need to be developed
for clinical use, but we believe that their approach is on the right track.
Yoshiki Arakawa
Kyoto, Japan
Nobuo Hashimoto
Osaka, Japan
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