Keywords
computer assisted surgery - video-assisted surgery - tomography - tridimensional image
- endoscopy
Palavras-chave
cirurgia assistida por computador - cirurgia vídeo-assistida - tomografia - imagem
tridimensional - endoscopia
Introduction
The use and application of the three-dimensional (3D) reconstructions generated from
suitable files (DICOMS) of computed tomography (CT) or magnetic resonances (MR) have
been expanding recently. Such reconstructions allow physicians to observe anatomic
cavities and structures of our body with an incredible amount of details and can display
even the textures of different tissues[1]
[2].
The applications of such reconstructions have varied from simple illustrations in
exams up to the help in the diagnosis and preoperative planning in several medical
specialties.
Some examples may be found in the virtual colonoscopies performed by some image centers
in our country and in high resolution CTs for evaluation of the coronary arteries[3].
In our specialty there have been some attempts to carry out virtual endoscopies and
laryngoscopies. However, such application has been practically abandoned due to its
complexity and need for computers with high power of graphic processing[4].
However, with the evolution of proper computers and programs for reading and reconstruction
of the DICOMS files, currently some authors have recovered the use of such 3D reconstructions
for evaluation and preoperative planning specially related to otologic surgeries and
to recess and frontal sinus[5]
[6].
Such 3D reconstructions may offer potentially more usable information than those obtained
with 2D views in the axial, coronal and sagittal plans. These images obtained in the
three different plans: axial, coronal and sagittal are usable in the analysis of the
recess and frontal sinus. However, these two-dimensional images are of more difficult
comprehension for surgeons[7]. Bakker et al. Carried out a research with surgeons on what would be more difficult for learning
and performance of safe nasosinusal endoscopic surgeries[8]. What was considered to be more difficult for the researched surgeons to learn was:
“the spatial guidance, that is, making a 3D mental representation from the 2D computed
tomography”. And what was taken as the second most difficult point was: “understanding
the relationship between the computed tomography with endoscopic actual images”[8].
We live in a three-dimensional world and despite a large part of the endoscopes still
do not allow the performance of 3D stereoscopic surgeries, the images obtained in
the traditional endoscopic surgeries allow us the creation of 3D relationships in
our mind. These relationships may help in the performance of specific tasks and the
excellent preoperative preparation may sometimes prevent generally challenging complications[9].
We have studied the utility of the 3D reconstruction tools for the surgeries of the
ear and of the recess and frontal sinus. In the literature we found since preoperative
planning through other applications such as diseases staging, preoperative measurement
for production of prostheses, air flow analysis and the proper teaching to resident
doctors[5]
[6]
[8]
[10].
The preoperative evaluation for the frontal sinus surgeries through 3D reconstructions
from the proper CT files (DICOMS) may permit the surgeon to acquire more information
than with the traditional two-dimensional images obtained with the three different
plans: axial, coronal and sagittal.
Although it is possible to view all the draining pathway of the frontal sinus and
of its guiding and preoperative planning through the traditional two-dimensional CT
already clearly described by several authors, amongst whom Wormald et al[9]
[11], the use of 3D tools may eliminate the element of uncertainty in the correct finding
of the natural draining pathway of the frontal sinus.
By using such 3D tools, it is possible to view the several holes in the region of
the proper recess and send them for analysis of what is the correct hole for the frontal
sinus draining.
The objective of this work consists of:
-
Demonstrating the production of such 3D reconstruction from CTs of patients submitted
to nasosinusal endoscopic surgeries of the recess region and of the frontal sinus
performed in a personal computer with a specific program.
-
Comparing these virtual images with actual endoscopic images during the surgery.
Method
After authorization of the local ethics committee, DICOM files were obtained from
10 patients taking part in the study. The inclusion criterion was of patients who
were to undergo the paranasal sinuses endoscopic surgery that also included the frontal
sinus. The exclusion criterion was that of patients who would not be submitted to
the frontal sinus endoscopic surgery.
The folders containing files were saved in the personal computer and varied in size
between 150 and 250 Mb. The CTs were requested from patients in the preoperative approach
and they were carried out in different multi-slice equipment. The exams presented
with cuts that varied between 0.5 and 1.3 mm of thickness.
The appropriate files (DICOMS) of the corresponding CTs were reconstructed with the
computer program Intage Realia, version 2009, 0, 0, 702 (KGT Inc., Japan), by using
personal computer with Microsoft Windows 7 operating system ([Figure 1]).
Figure 1. Image of the control screen of the software used.
We used the following tools. The program is in English language, but we translated
the tools into Portuguese for a better understanding.
1) Multiplanar reconstruction: the original DICOM files of the computed tomography are in axial plan. By using
this tool, we created coronal and sagittal reconstructions with well-defined images
([Figure 2]). We call it three-planar or multiplanar reconstruction that is generally used in
the workstations of radiologists or surgical navigators for diagnosis and surgical
guiding. However, these multiplanar reconstructions did not offer 3D viewing and are
generally used for the preoperative planning of patients.
Figure 2. Image captured from the computer screen with the program showing coronal and sagittal
reconstruction, that is, the images in the three plans (triplanar), in 2D though.
2) Control of contrast, shine, shadows and segmentation: the shaded surface displays compose a tool to control shine, contrast and shadows
of the images generated from the DICOM files. The alteration of these parameters enables
the creation of images with different windows, which may facilitate the identification
of bone tissues and soft parts. The work was carried out from the densities of the
tissues and allowed us to mark and color manually or automatically (in areas of mainly
aerial density) regions with osseous and aerial densities and soft parts (diseases).
This segmentation tool was also important to suppress these areas of disease so that
we could have a suitable view of the region studied.
3) Volume rendering: the images generated from DICOM files were transformed into 3D volume ([Figure 3]) that could be rotated at any plan and virtually dissected, by using a cutting tool
that could also be in any plan, direction or angle, depending only on adjustments
done by the computer program operator. We use this tool frequently. The volume created
from the DICOM files was rotated at an angle that was compatible with the entering
of the patient to the surgery. As from this plan, dissections were made by the volume
both in the upper and the lower direction with the densities of the osseous and aerial
areas and soft parts marked with different colors. This allowed us a 3D viewing of
the recess region of the frontal sinus that enables a detailed study of the possible
draining channels of the frontal sinus.
Figure 3. Image of the computer with a program showing 3D volume rendering. In the purple ellipses
we may view the commands for virtual “dissection”, free cuts and controls for rotation
and guiding of this 3D volume. Refer to the yellow ellipsis with commands for selection
(that may be manual or automatic) of areas both in 2D and 3D volume reconstructions,
for further segmentation and/or suppression of some densities.
4) Fly through: this tool allowed us navigation within the volume created, that simulates an endoscopical
image or a virtual endoscopy ([Figure 4]). From commands on the computer program, selecting the option VE (virtual endoscopy),
we obtain an endoscopic viewing of the ostia of the frontal recess. In patients with
less disease in the frontal sinus (mucosa edema, etc.) we could more easily perform
this task in less time because we do not need to segment and/or suppress diseased
areas.
Figure 4. Image showing example of virtual endoscopy, in the VE command. Refer to the possibility
of fly through and different image angles (that may range from 30 to 120 degrees).
With virtual endoscopy it was important to keep a guideline that should be the same
as that used in endoscopic surgeries or actual endoscopies.
The available tools in this program also allowed the moving of the virtual camera
and changing of its angles so that we could reach limited spaces, which would not
be possible with actual endoscopy.
The starting point for fly through virtual endoscopy was the region of the middle
meatus, between the uncinated process, ethmoidal bulla and middle infundibulum. After
this initial layout, the view field was moved upwards the frontal sinus recess. As
we advanced, several apparent holes appeared. We mapped this ostia configuration and
captured the screen to compare the endoscopic view obtained from actual surgeries.
After this 3D reconstruction study, the surgery was digitally performed and stored.
The actual endoscopic images of the recess and frontal sinus region were compared
to images generated from the personal computer to evaluate the likeness.
Results
The 3D reconstruction and the virtual endoscopy were performed in all 10 patients
who were later submitted to the recess and frontal sinus endoscopic surgery.
The images generated in the computer had a large visual resemblance with the images
found in the actual surgeries ([Figures 5], [6] and [7]).
Figure 5. Comparison of real with virtual endoscopy image. A: real endoscopy (30 degrees instrument)
of the left frontal sinus recess region. Cm: middle infundibulum; be: Ethmoidal bulla;
pmo: medial wall of the orbit. B: virtual endoscopy of the same region. Refer to resemblance
of the images.
Figure 6. Comparison of real with virtual endoscopy image. A: real endoscopy (30 degrees instrument)
of the left frontal sinus recess region. Cm: middle infundibulum; pmo: medial wall
of the orbit. B: virtual endoscopy of the same region. Refer to resemblance of the
images.
Figure 7. Comparison of real with virtual endoscopy image. A: real endoscopy (45-degree instrument)
of the frontal sinus (SF) region of the patient after opening. BC: cranial base in
the frontal-ethmoidal angle region. B: virtual endoscopy of the same region. Refer
to resemblance of the images.
Such reconstructions were made without major technical difficulties from a personal
computer, by using the appropriate program for reading and edition of DICOM files.
Discussion
The standard of the holes in the frontal recess area is quite variable and the exact
location of the natural drainage of this sinus is not easily determined by the traditional
two-directional anatomic cuts found in a CT (axial, coronal and sagittal)[7]
[9]
[11]
[12].
In case of an extensive disease this becomes even more difficult. With 3D reconstruction
from the proper CT files of the patients, we could make a virtual map of the frontal
sinus recess region, by evaluating the ostia configuration and the correct pathway
for natural drainage of the frontal sinus. However, in these cases in which we found
very extensive diseases in the sinus and frontal recess region, the identification
of the correct drainage pathway of the frontal sinus was difficult, even with 3D reconstructions,
since for the execution of the virtual endoscopies some presence of air in the cavities
for a better guidance and navigation is required. In these cases, we were guided directly
by the osseous part or used special tools for rendering and suppression of the diseased
areas.
For the correct location of the recess and frontal sinus region, we began by trying
to identify the Agger Nasi that was present in all cases studied and reconstructed.
This is typically the first ethmoidal cell seen in the coronal plan at the antero-posterior
direction and is typically confluent with the uncinated process[12].
The second step was to select the software endoscopic viewpoint with the correct guiding,
that is, the same guiding used for traditional surgeries, for the area between the
uncinated process, the ethmoidal bulla and the middle infundibulum. From this point,
we moved the vision field upwards the frontal sinus and mapped the ostia configuration
so that we could learn in which hole the natural draining of the frontal sinus was.
We had previously attempted to locate the frontal sinus natural draining pathway through
common cuts (2D) of computed tomographies. However, even trying to connect the images
in axial, coronal and sagittal plans, it was too difficult to find the exact way for
natural draining of the frontal sinus.
It is worth remarking that these 3D reconstructions from the CT-proper DICOMS files
of the patients may also be made in other personal computers with another operating
system, such as Macintosh™, of Apple™, in a suitable program called OsiriX™, and the
possible performance of virtual otoscopy and preoperative planning for larynx and
ear surgeries.
Conclusion
With relatively simple tools and personal computer, we demonstrated the possibility
to generate 3D reconstructions and virtual endoscopies from DICOM files of patients'
CP. In these patients submitted to surgery with the study of the previous 3D reconstruction,
the frontal sinus was accessed in all cases. However, it is notorious that we did
not performed comparative studies with a group of patients in which no 3D reconstruction
was made.
The preoperative knowledge of the frontal sinus natural draining path location may
generate significant benefits during the performance of surgeries such as shorter
surgical time and stronger safety for the patients. Nevertheless, it is worth taking
into account that more studies must be developed for the evaluation of the real roles
of such 3D reconstructions and virtual endoscopies.
