Key-words:
Coil embolization - intracranial aneurysm - microcatheter - shaping
Introduction
Navigating a microcatheter into an aneurysm is necessary for successful coil embolization;
however, it is often difficult because of the underlying anatomical condition, especially
in paraclinoid internal carotid artery aneurysms.[[1]],[[2]],[[3]],[[4]],[[5]] Recently, we created patient-specific three-dimensional (3-D) vascular models,
using a 3-D printer before performing endovascular operations. However, creating a
suitable catheter shape by tracing the outer surface of the rigid 3-D models is still
challenging.[[6]]
Some authors reported that a spatial augmented reality by a special electrical device
was used for clinical training and simulation.[[7]],[[8]] It allowed insertion of the microcatheter inside the vascular model during its
shaping. We wondered if a classical real image display (RID), which consists of a
couple of concave mirrors, could be used for catheter shaping. Here, we report a novel
microcatheter shaping method using a RID.
Technique
The RID is a classical toy that is available commercially (Opti-Gone International,
Ojai, CA, USA). It consists of two concave mirrors. When a small object is set at
the bottom of the RID, a 3-D spatial augmented image appears beyond the display [[Figure 1]]. The image cannot be touched but can enter inside the object. The theory is shown
in [[Figure 2]]. A parabolic mirror is a special type of curved mirror that looks like a bowl.
It takes incoming light from all directions and reflects it toward a signal focus
point. Parabolic mirrors also reflect light coming out from the focus point outward
in a parallel beam. The RID utilizes these two properties to create the hologram.
The object is at the focus point of the top mirror, and its light is reflected down
onto the bottom mirror. This reflected light is then reflected again upward where
it converges at the focus point recreating the object as a 3-D image. Before endovascular
intervention, a patient-specific 3-D vascular model is made using a 3-D printer. Its
materials and methods are reported in the literature.[[5]]
In the endovascular intervention, the 3-D vascular model was set in the RID. A translucent
sterilized drape was used to cover the RID [[Figure 3]]. The tip of the Headway 17 straight microcatheter (Terumo, Tokyo, Japan) was placed
inside the hologram of the vascular model along with an attached shaping mandrel.
After designing and manually shaping the microcatheter according to the length of
the tip and the sites against the vascular wall, the tip of the microcatheter was
set 3 cm from the nozzle of the hot air gun (BOSCH, Gerlingen, Germany) at 130°C for
30 s. The microcatheter had the ideal shape we were expecting. The shaped microcatheter
could be navigated at the desired position in the aneurysm. Complete obliteration
of the aneurysm was achieved without any trouble among 30 consecutive cases.
Figure 1: Photographs of the real image display. (a) It consists of two concave mirrors. (b)
The vascular model is set at the bottom of the bowl. (c) The three-dimensional hologram
appears at the top of the display. (d) Although we can enter in the three-dimensional
vascular model, we cannot touch it
Figure 2: Schematic illustration of the principal of the real image display. The reflected
parallel lights from the real object then reflected again upward where it converges
at the focus point recreating the object as a real image. We can see the real image
as a hologram
Figure 3: A representative case. (a) A translucent sterilized drape covers the real image display.
(b) The tip of the microcatheter (arrowhead) is bent inside the three-dimensional
hologram. The arrow indicates a shaping mandrel. (c) After heating by a hot air gun,
the tip of the microcatheter shows an ideal shape. (d) An intraoperative road-map
image is shown. The tip of the microcatheter is navigated at the desired position
in the aneurysm (arrow)
Discussion
In coil embolization of cerebral aneurysm, safely guiding the microcatheter to an
appropriate site in the aneurysm and stabilizing it there are extremely important.
Reports have described the characteristics of various microcatheters, differences
in responses to steam shaping, and techniques to guide a microcatheter into the aneurysm.[[1]],[[2]],[[3]],[[4]] In paraclinoid internal carotid aneurysms, complicated shaping of the microcatheter
tip is occasionally required, and various methods, including shaping under 3-D angiographic
guidance and using a 3-D printer, have been reported.[[5]] We agree that the 3-D printer is useful for shaping microcatheters; however, rigid
vascular models prepared with a 3-D printer are not hollow and cannot reproduce the
actual curves of the catheter in the body.[[6]] Therefore, catheters shaped by tracing the outer surface of the rigid vascular
models are considered to not faithfully trail the long axis of the parent artery.
Recently, some authors reported that a spatial augmented reality by a special electrical
device was used for clinical training and simulation.[[7]],[[8]] As it allows the placement of the tip of the microcatheter inside the virtual vascular
model during its shaping, the precise long axis from the parent artery to the inside
of the aneurysm can be traced. However, the virtual reality system for medical use
is expensive. Moreover, virtual sickness cannot be ignored during extremely delicate
neurointerventions.
We discovered that the RID could be used for microcatheter shaping. It is available
commercially as a toy for kids, who enjoy the discrepancy of their feelings between
real and virtual images. However, its cost depends on the diameter, a small RID costs
approximately 10 USD. We have introduced this technique in 30 cases of unruptured
paraclinoid internal carotid artery aneurysms. Using the RID for catheter shaping,
we obtained a more favorable microcatheter shape in our initial attempt than when
tracing the outer surface of rigid 3-D models.
This study has some limitations. First, this was a retrospective analysis conducted
at a single center with only 30 cases. Second, some gap in size was present between
the real object and the hologram. The object is farther away from the bottom of the
RID, and the distortion of the size is >120%. Finally, because this technique requires
a patient-specific vascular model by a 3-D printer, we cannot introduce it in emergency
cases.
We demonstrated the usefulness of the RID for making and navigating a microcatheter
in cases with challenging anatomies. As this method allows placement of the tip of
the microcatheter inside the virtual vascular model during its shaping, the precise
long axis from the parent artery to the inside of the aneurysm can be traced.
