Lecture 7: Advanced Imaging in Dentistry PDF

Lecture 7: advanced imaging in dentistry Computed tomography Cone beam computed tomography Magnetic resonance imaging Why do we need 3D imaging? To see extent of etiology When we need to put an implant in Limitation to 2D because we can’t distinguish between the other structure...

Lecture 7: advanced imaging in dentistry Computed tomography Cone beam computed tomography Magnetic resonance imaging Why do we need 3D imaging? To see extent of etiology When we need to put an implant in Limitation to 2D because we can’t distinguish between the other structures ○ Clinical challenges For example: buccal-lingual dimension is not visualized When we take a 3D image we see the implant was implanted in the lingual cortex Lingual inclination and undercut, implant perforates lingual cortex Standard position and orientation The basic of CBCT, there’s a ○ Sagittal view : left and right ○ Coronal view : anterior and posterior ○ Axial view : superior and inferior Computed tomography: CT was the 1st imaging modality invented 1972: invented by Godfred Housfield This technology used image reconstruction mathematics to produce cross-sectional images of the head This form of imaging is called computed tomography or CT Won nobel prize in 1979 Types of CT machines: Helical CT, Multidetector CT, Multislice CT Notes: CBCT → CONE BEAM, just see bone CT → FAN SHAPED, can see soft tissues and bone details Don't generate these numbers for panoramic or periapicals Numbers depends on the content of the tissue Indications: When is 3D images needed (CT) Infections, including osteomyelitis and space infections (osteomyelitis → bone inflammation) Midfacial and mandibular trauma Developmental anomalies of the craniofacial skeleton Benign intraosseous cysts and neoplasms of the jaws Benign and malignant neoplasm that originate in or extend into the orofacial soft tissues Soft tissue cysts → use 3D imaging to see the spread of infection: CT or CBCT → CBCT is not to diagnose any SOFT TISSUE PATHOLOGY (JUST BONE) How does CT work: One rotation per revolution → to generate axial section ○ Acquisition time is longer because it has to X RAY tube and detector needs to rotate around multiple times for image to form ○ Computer generate: sagittal and coronal section ○ Xray does the axial view (DEFAULT) This is for CT imaging: does both soft and bone window (CBCT just does BONE) Soft tissue window: you can visualize things better Bone window: bone looks washed out Soft tissue vs bone window Soft tissue window: CT vs CBCT  CT CBCT More radiation dose (longer exposure) Less radiation dose Has both: soft tissue and bone window Only has bone window → better soft tissue visualization → limited soft tissue visualization Default image : axial sections Default image/Basic projections: multiple sagittal plane Computer does: sagittal and coronal (called basic projections) Multiple rotations → forming axial view →Reconstructions can be done through the basic One slice = one revolution projections by the computer One rotation (360 revolution) (similar to panoramic) Hundreds of revolution in one revolution Beam shaped: Fan shaped Beam shaped: Cone shaped Voxel size and shape: Voxel size and shape Non-isotropic (X=Y but not Z) Isotropic (X=Y=Z) (equal width, length and height) Implications Application of CBCT Pathology: evaluate true lesions extension and the Infections, including osteomyelitis and effect of lesion on surrounding structures space infections (osteomyelitis → bone inflammation) Implants: implant planning, surgical guides Midfacial and mandibular trauma Periodontist: periodontal defects, advanced grafting procedures (sinus lift, block grafts), Developmental anomalies of the maxillary sinus evalitation craniofacial skeleton Endodontics: periapical lesions, certain root Benign intraosseous cysts and fracture, accessory canals neoplasms of the jaws Orthodontics: 3D cephalometry, impacted teeth, Benign and malignant neoplasm that root morphology virtual occlusion, tmj evaluation, originate in or extend into the orofacial cleft palate, airway assessment soft tissues Surgery: 3D surgical assessment, orthognathic Soft tissue cysts surgery planning, a custom-made prosthesis for reconstruction, maxillary sinus evaluation, airway assessment, post-trauma evaluation Cone beam computed tomography (CBCT) An Advanced imaging modality that allows the operator to generate thin sections and 3D reconstruction of the structures of interest by using a cone shape rotating x-ray beam and series of mathematical algorithms How does CBCT WORK? ○ Cone shaped beam pass thru the patient head to generate images Factors affecting image quality: for 3D image (no focal trough in 3D image → bc you see the actual image, no superimposition occurring) Field of view (FOV)→ affects patient dose (look at the table) ○ The smaller the FOV, the higher the image quality (due to less radiation scattering) and the lesser the radiation to the patient A larger FOV and larger detector = more scatter radiation= more noise = decreased image quality (SNR) For CT: Fan shaped (linear detector= more precise) Better signal to noise ratio Less scatter (noise) because it rotates around patients head multiple time For CBCT: Cone beam shaped (less precise) More scatter because it rotates around patients head once Detector is wider: more space for “crappy” information  Voxel size and shape → (in 2D we had pixels, in 3D we use voxel) ○ CBCT (isotropic) X=Y=Z (equal: length, width and height) ○ CT (non-isotropic) X=Y not Z Bit depth → (similar to 2D imaging → usually use 8-bit depth) ○ Can affect image quality.. more bit depth, image (quality) or contrast resolution increases ○ Higher bit depth = more shades of gray, lager the file size ○ Note: human body can see 60 shades of gray ○ 3D detectors: can take 8-10 bit depths, new machines can capture 12 bit depths This means the detector was able to differentiate between muscles, ligaments, tendance to bones, soft tissue Window: adjust shades of gray → what is acceptable to our eyes In CBCT we need high contrast resolution to see different shades of gray High contrast is important to differentiate between structures Our eyes can only accept 60-65 shades of gray ○ Effect of Bit depth on contrast resolution 8 bit vs 12 bit 12 bit image can generate a better image quality (HIGH BIT DEPTH, HIGHER IMAGE QUALITY)  Detector type: (note: remember in in 2D imaging we talked about CCD, CMOS and PSP) ○ In 3D imaging we use Image intensifier Shape of detector: spherical volume (older technology) Flat panel Shape of detector: Cylindrical volume (newer technology) Has better quality image Exposure time (SNR): affects signal to noise ratio signal to noise ratio (less noise, more signals to image a good image quality) ○ MAs from 2D image → same concept for 3D image ○ More mA, more time, more photons → better signal (bc less noise) ○ Higher KVP= better the quality (disadvantage is higher radiation dose to the patient) Need to be in a zone where we are getting an acceptable image quality which is not increasing patient dose Application of CBCT Pathology: evaluate true lesions extension and the effect of lesion on surrounding structures Implants: implant planning, surgical guides Periodontist: periodontal defects, advanced grafting procedures (sinus lift, block grafts), maxillary sinus evalitation Endodontics: periapical lesions, certain root fracture, accessory canals Orthodontics: 3D cephalometry, impacted teeth, root morphology virtual occlusion, tmj evaluation, cleft palate, airway assessment Surgery: 3D surgical assessment, orthognathic surgery planning, a custom-made prosthesis for reconstruction, maxillary sinus evaluation, airway assessment, post-trauma evaluation Not application for CBCT - Caries detection: due image noise and metal artifacts → (periapicals are better for caries detection) - Soft tissue lesion: due to limited soft tissue contrast - TMJ disc: not visualized due to limited soft tissue contrast and resolution - Vertical root fracture: depending on the fracture, even small FOV, high-resolution scans may not be able to detect them Note: CBCT: HAS no units, more scatter Limitations: Artifacts (looks at slides for different types of artifacts) Cupping: distortion of metallic structures ○ Cupping artifact due to huge restoration Scatter and beam hardening: streaks and dark bands Under-sampling Cone beam effect ○ Due to the shape of the cone: you see a artifact at bottom and top of the image REVIEW SLIDES FOR ANATOMICAL STRUCTURES Teeth and supporting structure Pulpal structure Best depicted in the limited field of view and corrected cross sectional images MRI: Magnetic resonance imaging Discovery: 1973 by Paul Lauterbur, but the early 1980s, Peter Mansfield developed it for clinical use Definition: An advanced imaging modality that uses different magnetic moments of protons in the patients tissues to form tomographic images of a specific anatomic site ○ Tomographic mean generating those three different sections: axial, coronal and sagittal Note: in CBCT AND CT: we use x rays which are ionizing In MRI, we use magnetic resonance imaging (using radiofrequency waves, not X RAYS) Unit: Tesla → unit for magnetism Pros of MRI ○ No ionizing radiation involved ○ Excellent soft tissue contrast resolution ○ Intravenous contrast to enhance vascular structures Cons of MRI ○ Long Scan times (patient can stay in the machine as long as 40 minutes) ○ Metal susceptibility artifacts- dental restorations and hardware (artifact will appear as reverse) MRI physics Concept to understand: ○ Body is made up of 75% of water → so there’s lots of hydrogen in our body ○ Scientist use hydrogen molecule to generate images Image #3: hydrogen is randomly orientated in human body Image #4: patient is in the machine (machine has lots of magnetism; in units of TESLA) Tesla units: 3 tesla, 5 tesla: refers to the magnetism of machine Protons are attracted to the magnetism ○ Protons will align in either LOW OR HIGH energy state Most protons have LOW energy state Less protons will align towards high energy state Electromagnetic radiation spectrum: Non-ionizing radiation Longer wavelength Lower frequency ○ Heat up tissues (i.e: putting food in microwave) ○ i.e: MRI has RADIO WAVES to create images (advantage of MRI; using radio waves “safer” ) Ionizing radiation (DAMAGE DNA) Smaller wavelength Higher frequency ○ Actual changes in human body by creating FREE RADICALS (disadvantage; which is why ALARA is required: as low as reasonably achievable) ○ I.e: X RAYS  HOW MRI MACHINE WORKS How MRI works 1. Protons are arranged in low and high energy state (most of them are aligned in low energy state → net magnetization) 2. Radiofrequency coil will release radiofrequency waves which will go to human body (the protons) 3. The protons in the low energy state will go to the high energy state (because they’ve received energy) 4. When they fall back down to low energy state → they generate signals (these are the signals to generate MRI) Note: metals will be attracted to MRI machine (death can occur) T1 vs T2 T1: highlight fats T2: highlights fluid Application of Magnetic resonance imaging in maxillofacial diagnosis MRI: useful in evaluating soft tissue Applications of MRI in dentistry Evaluate the position and integrity of the TMJ articular disk Evaluate neoplasms of oral cavity and jaw to determine soft tissue extent, lymph node involvement and neural invasion Evaluate salivary gland diseases: cysts, neoplasms, infections and obstructions Evaluate vascular lesions in orofacial region Evaluate suspected early osteomyelitis of the jaws to determine edematous changes in the fatty and surround tissue MRI Contraindications (any type of metals are contraindications) Absolute Patient with cerebral aneurysm clips (we don't know the content of the metal) Patient with cardiac pacemakers (pacemaker; made of metallic structures- magnetic can disturb t-waves of the heart) Relative Claustrophobic or uncooperative patients Pregnancy (intravenous agent - those can have harmful effects on fetus) Metallic prosthetic heart valves (can be made with some type of metals No Contraindications Surgical clips outside the brain (not formed of metal) → nowadays these clips are not formed by metal Other metallic prostheses Note: Metals used in dental restorations, implants and orthodontic hardware are SAFE but create artifacts Implants are made of titanium → are safer Orthodontic hardware made up of stainless steel (composition: mixture - but no iron, so relatively safe)