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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_980_Библиотеки_им_академика_М_И_Перельмана
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CBCT and MRI Data Acquisition as a Basis for Computer-Assisted Maxillofacial…
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Fig. 8 Serial CBCT scans captured form a patient in need of dental implant in the posterior left
maxilla. (a) Preoperative CBCT scan indicated alveolar resorption and sinus pneumatization. The
patient needs sinus lift and bone graft. (b) One-month postoperative CBCT scan from the same
segment after placement of bone graft shows ridge augmentation to 16.68mm, note the presence
of reactive mucosal thickening (arrows). (c) Six-month postoperative CBCT scan shows reduction
in mucosal thickening and slight graft height shrinkage at the same cross-sectional view
Fig. 9 Cone beam computed tomography scan of fully edentulous patient coupled with a 3D
printed denture prosthesis model indicating sites of crowns with radiopaque material. (a) Axial, (b)
reformatted panoramic, (c) cross-sectional, and (d) 3D surface rendering views show virtual
implant insertion in the anterior maxilla and mandible, indicating the possibility of buccal thread
exposure in the maxilla if placed in the ideal inclination, identifying the need for buccal bone
augmentation prior to implant placement
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M. Ghazizadeh Ahsaie
a
c
Fig. 10 Coronal (a), axial (b) and sagittal (c) DICOM data from CBCT is converted to the
Standard Tessellation Language (TSL) format. A 3D model (d) is provided prior to an orbital wall
reconstruction in a patient with severe trauma to the left side of the face, with multiple fractures in
the zygoma, orbit, and frontal bone. The 3D prostheses (pink, orange, and blue) are designed to
reconstruct the traumatic sites. (Mimics research 21.0, Materialise NV, Leuven, Belgium)
b
d
8 Magnetic Resonance Imaging (MRI)
MRI is a revolutionary imaging technique both in terms of lack of any ionizing
radiation and optimum visualization of soft tissues with T1 and T2 relaxation times
varying up to 40% compared to X-ray attenuation coefcients of soft tissue, which
is near 1% [15]. The potential of imaging using resonance was initially introduced
by Paul Lauterbur in 1973. The magnetic eld causes the nuclei of many atoms to
align with the external magnetic eld, particularly hydrogens. In clinical imaging,
the magnetic eld varies between 0.1 and 7T, with 1.5 and 3T being the most common. Application of 3T MRI in dentistry and craniofacial surgeries is getting more
common. Hilgenfeld etal. proposed the potential use of high-resolution MR imaging and indicated that MR-based planning can achieve results comparable to those
with CBCT-based planning [16].
9 Principles ofImage Production
MR images are mostly acquired with spin-echo pulse sequence. In the majority of
cases, both T1-weighted and T2-weighted images are obtained for the assessment
of oral and maxillofacial soft tissues, detection of lesions, their extension, and
effects on adjacent structures. MRI can also be performed with contrast injection
especially in case of presence of tumoral lesions, in which gadolinum is injected
intravenously. T1-weighted images are used for anatomical evaluation and
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T2-weighted images are for the detection of pathological lesions and inammatory reactions. With MRI, direct sagittal, coronal, and oblique images similar to
CBCT are obtained (Fig.11). On the contrary, MDCT, provides axial images and
further reconstruct coronal and sagittal images, which may cause a slight reduction of resolution in reformatted images. Coronal and axial MRI is usually provided for evaluation, and sagittal planes are sometimes added when needed
especially in temporomandibular joint disorders (TMD) and the evaluation of disc
space [17]. In MRI, the spatial resolution depends on the number of frequency
encoding steps (how often the free induction decay is sampled) and the size of the
eld of view [18]. Maxillofacial MRI is usually captured with small FOV; therefore, the frequency of encoding steps mainly affects the resolution. Higher resolution scans provide more anatomical detail and are relatively sharper; however,
these scans are more prone to motion artifacts [19].
Based on the detected signal intensity in T1 and T2MRI images, one can assume
the normal and abnormal anatomy in the maxillofacial region. Tissue intensity can
be categorized into signal void (cortical bone, enamel, dentin, air, metallic artifacts),
low (lower than the intensity of muscles), intermediate (between muscle and fat
signal), and high (same or higher than fat) (Fig.12).
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Fig. 11 MRI imaging. (a) Coronal T1-weighted, (b) sagittal T2-weighted, and (c) axial
T2-weighted images of maxillofacial region. Note that air and cortical bone are signal void
Fig. 12 Sagittal three
Tesla T2MRI.Note that
the air in maxillary sinus,
cortical bone, enamel, and
dentin are presented as
signal voids. The pulp and
root canal system are
presented in higher signal
due to the presence of
vessels and nerves
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Fig. 13 Metallic dental restoration resulted in MRI image artifact. (a) Coronal and (b) axial sec-
tion MRI in a patient. Note the presence of a circular signal void region, causing missing of data in
the vicinity of restoration. (Curtesy Dr. Yaser Sa, Shahid Beheshti University of Medical Sciences,
Tehran, Iran)
M. Ghazizadeh Ahsaie
10 MRI andArtifacts
The resolution of MRI is not solely determined by acquisition factors; rather, it is
also affected by artifacts. In maxillofacial MRI, patient should remove any removable metallic intraoral devices, such as removable orthodontic appliances. Metals in
dental restorations and air-tissue interface can signicantly affect and distort the
images (Fig.13). Artifacts should be detected prior to any image segmentation and
image preparation. Motion artifact can also blur the image and reduce the accuracy
of segmentation process. As previously mentioned, higher resolution scans are more
prone to motion artifacts, and therefore, a balance should be provided between
image voxel size and acquisition time and the possibility of motion in patient [19].
11 Application ofMRI inMaxillofacial Imaging
Indications of MRI in oral and maxillofacial region are broad in diagnosis and
evaluation of benign and malignant tumors of jaw, especially when extension to
adjacent vessels and nerves is suspected. MRI can accurately assess the anatomy
and physiology of salivary glands, pharynx, sinuses, and orbits. Any invasion of
jaw tumors to the cranium and orbit can be astutely assessed. Recent advances in
MR imaging, including volumetric imaging, ow imaging, fast spin imaging, and
diffusion- weighted imaging, have opened new opportunities and potential in
advanced diagnosis. Although MRI is not routinely being used in the eld of
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Fig. 14 Coronal T1 MRI
sections of the mandibular
angle and ramus (a–c). The
cross-sectional
morphology, cortical bone
(white arrow), cancellous
bone (yellow), and position
of the inferior alveolar
nerve (red arrow) are
clearly depicted
a
b
c
dentistry, recent modalities can enhance the quality of patient care in selected
cases. Ultrashort echo time MRI is now being used as an alternative imaging
modality to CBCT for dental implant planning [18, 20, 21]. In addition, MRI can
accurately depict the mandibular nerve, especially when nerve tracing gets complicated in CBCT due to the lack of cortical borders detection, in case of osteoporosis
or malignancies invading through the nerve canal (Fig.14) [22]. Probst etal. indicated that 3T MRI can accurately provide virtual three-dimensional bone surface
models of the mandible equal to CT and CBCT and can be considered as their
alternative in computer-assisted craniomaxillofacial surgery [23]. MRI can clearly
depict soft tissue outline (Fig.15) and properties and is a valuable tool in 3D printing of maxillofacial anatomy, such as the jaw, nose, ear, and orbit [18, 24]. In the
study of Visscher etal. [25], MR images of the nose was used to additively manufacture silicon alar constructs. They suggested that this method can be used to
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Fig. 15 Axial (a) and sagittal (b) T2- and T1-weighted MRI shows the morphology of nose. Note
the presence of a nasal hump and slight deviation of the nasal tip to the left
M. Ghazizadeh Ahsaie
provide patient- specic alar constructs, especially in burn reconstruction or orofacial cleft repair.
12 Conclusion
Advanced three-dimensional imaging, such as CBCT and MRI, has revolutionized
the dental and maxillofacial treatment planning. CBCT is the gold standard for the
imaging of maxillofacial hard tissues prior to most advanced surgeries, while MRI
provides detailed information on soft tissues of this area. Accurate assessment of
head and neck anatomy allows surgeons to plan suitably, operate with condence,
and evaluate results postoperatively. Patients’ imaging scan properties such as FOV
and resolution should be customized based on individual diagnosis and surgical
treatment plan. DICOM images provided can be efciently utilized in third-party
software to manufacture models and prosthesis in maxillofacial reconstructions.
References
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7. Borohovitz CL, Abraham Z, Redmond WR. The diagnostic advantage of a CBCT-derived
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face in OrtogOnBlender for correction of class II dentofacial deformities: an uncontrolled
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13. Sa Y, etal. The occurrence of dental implant malpositioning and related factors: a crosssectional cone-beam computed tomography survey. Imaging Sci Dent. 2021;51(3):251.
14. Zinser MJ, et al. Computer-assisted orthognathic surgery: feasibility study using multiple
CAD/CAM surgical splints. Oral Surg Oral Med Oral Pathol Oral Radiol. 2012;113(5):673–87.
15. White SC, Pharoah MJ.White and Pharoah's oral radiology E-book: principles and interpretation. Amsterdam: Elsevier; 2018.
16. Hilgenfeld T, et al. Use of dental MRI for radiation-free guided dental implant planning: a
prospective, invivo study of accuracy and reliability. Eur Radiol. 2020;30(12):6392–401.
17. Choi B, Yi C, Yoo J.MRI examination of the TMJ after surgical treatment of condylar fractures. Int J Oral Maxillofac Surg. 2001;30(4):296–9.
18. van Eijnatten M, etal. The accuracy of ultrashort echo time MRI sequences for medical additive manufacturing. Dentomaxillofac Radiol. 2016;45(5):20150424.
19. Ripley B, etal. 3D printing from MRI data: harnessing strengths and minimizing weaknesses.
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20. Probst FA, etal. Magnetic resonance imaging based computer-guided dental implant surgery—a clinical pilot study. Clin Implant Dent Relat Res. 2020;22(5):612–21.
21. Aguiar MF, etal. Accuracy of magnetic resonance imaging compared with computed tomography for implant planning. Clin Oral Implants Res. 2008;19(4):362–5.
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3- dimensional bone surface models of the mandible in comparison to computed tomography
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Data Storing andConversion
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inComputer-Assisted Oral
andMaxillofacial Treatments
MitraGhazizadeh Ahsaie andHekmatFarajpour
1 Introduction
Advances in three-dimensional imaging and propriety software have led to vast
improvements in medicine, especially in the diagnosis and treatment planning.
Three-dimensional diagnostic imaging data, whether obtained from cone beam
computed tomography (CBCT), multi-detector computed tomography (MDCT), or
magnetic resonance imaging (MRI), are valuable for presurgical assessment of the
maxillofacial anatomy. Diagnostic imaging enables assessment of presence or
absence of a disease and further temporal changes like disease progression or recurrence and evaluation of outcomes of treatment. Reconstruction of maxillofacial
hard and soft tissue defects requires careful imaging assessment and comprehensive
surgical treatment planning [1]. To assess skeletal and dental anatomy, a number of
applications and software use data obtained from CBCT.The data is segmented to a
specic region of interest (ROI). The ROI may be a potential site for implant insertion, site of pathological lesion or defects, or potential osteotomy sections in orthognathic surgeries. CBCT images provide excellent contrast to segment maxillofacial
bones and therefore facilitate post-processing. Today, medical imaging data is
stored and transmitted in the Digital Imaging and Communications in Medicine
(DICOM) electronic format. DICOM is a common language format and can be easily imported between numbers of software. Several commercial software applications use volumetric data for further computer-aided design and manufacturing
(CAD/CAM) [2]. Three-dimensional printing or rapid prototyping is a novel
M. Ghazizadeh Ahsaie (*)
Department of Oral and Maxillofacial Radiology, School of Dentistry, Shahid Beheshti
University of Medical Sciences, Tehran, Iran
e-mail: mitraghazizadeh@sbmu.ac.ir
H. Farajpour
Department of Tissue Engineering and Applied Cell Sciences, School of Advanced
Technologies in Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023
A. Khojasteh et al. (eds.), Emerging Technologies in Oral and Maxillofacial
Surgery, https://doi.org/10.1007/978-981-19-8602-4_3
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M. Ghazizadeh Ahsaie and H. Farajpour
technology with increasing application in dentistry and maxillofacial surgeries [3,
4]. The entire workow starts from image acquisition, segmenting DICOM images,
and post-processing up to exporting the produced Standard Tessellation Language
(STL) le that is sent to the printer (Fig.1). Close collaboration between radiologists, clinicians, and material scientist is a prerequisite for creating a suitable model.
There are several ways to creating a 3D model, but the best workow mainly
depends on basis images and how one wants the nal model to look like, how the
model will be used, and what printer or printing technology will be used to create
the models.
MDCT, CBCT, MRI
1ststep:Image acquisition
DICOM
2ndstep:Image processing
Primary processing:
Segmentation, thresholding,
Region growing
Secondary processing:
Manual segmentation,
Design segmentation
STL
3rdstep:converting
DICOM toSTL
3D Model
4thstep:Additive
manufacturing
Fig. 1 Image processing steps from image acquisition to nal three-dimensional (3D) printed
model preparation. The DICOM data is processed and further converted to STL to print a 3D
model. DICOM digital images and communications in medicine, STL Standard Tessellation
Language le
Data Storing andConversion inComputer-Assisted Oral andMaxillofacial Treatments
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This chapter provides an overview of the basic steps for generation of a 3D
model from volumetric imaging data. In addition, imaging data storing and conversion in computer-assisted oral and maxillofacial treatments and reconstructions is
presented in detail.
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2 Image Acquisition andDICOM
Volumetric imaging, like CBCT, MDCT, and MRI, provides the basis data for printing a 3D model. Based on the treatment plan, 3D imaging techniques may be fused
and further processed for model preparation. However, in maxillofacial surgeries,
most of the cases are provided with the data obtained by CT [5]. CBCT has sufcient contrast and signal to noise ratio to provide data from maxillofacial skeleton,
while having lower dose in comparison to MDCT.In addition, the relative ease in
image post-processing and automatic bone thresholding further simplies the STL
le construction.
Isotropic voxels are used for reconstruction of CT dataset. Isotropic voxels preserve the anatomic truth without any information loss. Reconstruction of images
with thinner sections provides higher detail and delicate 3D model reconstruction
but consumes more time in processing, artifact removal, segmentation, and printing
time. Anatomical structures, such as orbital oor, lamina papyracea, and anterior
wall of maxillary sinus, need thin-slice imaging reconstruction. Thick section image
reconstruction may compromise accuracy and impact the result of printed model
dimensions. For most applications, reconstruction thickness should be at least
1.25mm [6].
Digital Imaging and Communication in Medicine (DICOM) is an essential step
in oral and maxillofacial radiology. DICOM le format allows digital images to be
stored and transferred electronically. At rst, DICOM was applied to communicate
image data between various systems in clinics. DICOM can be transmitted to a
picture archiving and communication system (PACS) or radiology information system (RIS) and can be stored, encoded, and retrieved upon request [7]. Today, various software import DICOM data from three-dimensional imaging and translate it
to axial, coronal, and sagittal images and manage and analyze this imported data
according to software capabilities. DICOM les from MDCT contain voxels with
gray values that are proportional to the attenuation coefcient in the corresponding
tissue of the patient, ranging from −1000 Hounseld Unit (HU) (air) to +3000 HU
for compact bone. In CBCT, the amount of X-ray attenuation is dened by gray
values, called voxel values. DICOM le manipulation can be efciently done by
CAD software to create highly accurate virtual models of patient-specic anatomy
[8]. In the study of Maureen van etal., STL model accuracy was assessed using
DICOM images from CBCT, MDCT, and dual-energy CT (DECT). The results
showed that MDCT scanners offered the best image quality and STL model [9].
While the majority of models have been created from CT data, there are examples
of models created from MRI data in almost every subspecialty, including neurosurgery, orthopedics, urology, and pediatrics [10]. The DICOM-to-STL conversion
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