Key-words:
Cranial anatomy - microscale - microstructures
Introduction
It is difficult to accurately measure the size of microstructures (perforators, intracranial
nerves, and others) of 1 mm or less in neurosurgical microsurgery. To our knowledge,
a measurement method has never been reported. Intracranial structures are very small
and the field of microsurgical operation is narrow; therefore, it is not possible
to use a ruler. Although we can calculate the size based on surgical tools, this is
not an accurate technique.
In microsurgery, understanding the accurate size of microstructures is essential to
perform operation safely and less invasively. Furthermore, this can provide detailed
information about cranial microanatomy. We here developed a simple method for measuring
the size of microstructures of 1 mm or less with accuracy using a digital image as
a microscale.
Materials and Methods
Initially, the SHEET GAUZE [[Figure 1]] and a paper scale [[Figure 2]] were captured with a scanner as a digital image. The resolution was 1200 dpi. In
the SHEET GAUZE, the minimum scale unit was 0.05 mm and the graphic accuracy was within
±0.004 mm. Next, these digital images were arranged in parallel on the computer to
compare to each scale [[Figure 3]]. This digital image was termed “the microscale.”
Figure 1: The SHEET GAUZE
Figure 2: The paper scale
Figure 3: The microscale
We trimmed the sterilized paper scale to avoid damaging the surrounding brain structures.
We placed the scale on the same plane of the structures, the size of which we wished
to measure [[Figure 4]]. When the depth of the structure is different from that of the paper scale, there
is a difference in scale under the microscope, so it is important to make it in the
same plane. The series of actions were recorded with high-definition video and were
imported as still images into the computer.
Figure 4: Intraoperative view of left vertebral artery aneurysm clipping. The arrow shows the
paper scale placed on the vertebral artery under a surgical microscope
Using image processing software (Adobe Photoshop, San Jose, CA, USA), the still images
and the microscale were aligned on the computer and the scale was adjusted by matching
with each paper scale size [[Figure 5]]. All methods were performed in accordance with the approved guidelines by the Institutional
Review Board (IRB #233) at Showa University Hospital. The patient also gave informed
consent approved by the IRB at Showa University Hospital for study participation.
Figure 5: The size of the microscale was adjusted to the paper scale using zoom function of
computer
Results
We accurately measured the size of the vertebral artery perforator of 1 mm or less
using the adjusted microscale on the computer [[Figure 6]].
Figure 6: The size of the vertebral artery perforator was measured using the adjusted microscale
on the computer. The size of the perforator was 0.4 mm
Discussion
When using a stereomicroscope, the measurement of the object takes place using an
ocular or an objective micrometer.[[1]],[[2]] However, these micrometers cannot be used with a surgical microscope. At the present
time, any surgical microscope company has never built microscales into the view for
precise measurement. Unfortunately, this study was in post hoc processing. We believe
that this report can promote further studies using priori imaging-based segmentation
and measurements.
Our method uses nonspecialized computer and scanner equipment and does not require
an extensive knowledge of computer graphics. It is possible to freely change the size
and angle, making the measurement easier, with digital image processing. Regarding
structures other than objects, it should be noted that even though they appear to
be on the same plane on the digital image, accurate measurements cannot be performed
due to differences in depth. Using this method, it is possible to obtain accurate
measurement data about intracranial microstructures that could be useful in clinical
practice and research.
Conclusions
The development of a microscale is easy and renders the measurement of microstructures,
sized 1 mm or less, feasible, and accurate.
