Imaging of Hard and Soft Tissues Dr Dayea Oh Oral and Maxillofacial Radiologist Lecture contents provided through the courtesy of Dr Tom Huang #### Presentation Overview This session covers the diagnostic imaging techniques and interpretations associated with the hard and soft tissues of the maxillofacial region. - **Presenter:** Dr. Dayea Oh, Oral and Maxillofacial Radiologist - **Acknowledgement:** Lecture contents provided through the courtesy of Dr. Tom Huang # **Imaging Modalities** * **– Intraoral radiographs** * **– Extraoral radiographs** * **– Computed tomography** * **– Cone beam computed tomography** * **– Magnetic resonance imaging** * **– Ultrasound** * **– Nuclear medicine** The following imaging modalities are utilized for the assessment of hard and soft tissues: - Intraoral radiographs - Extraoral radiographs - Computed tomography (CT) - Cone beam computed tomography (CBCT) - Magnetic resonance imaging (MRI) - Ultrasound - Nuclear medicine # Intraoral Radiographs - Bitewings - Periapicals - Occlusographs * Two dimensional image of a 3D object. * Limited FOV * **Dental** pathology * i.e. Caries, periodontal disease, peripical inflammatory pathology. * Bony abnormalities ...? * CAN NOT fully exclude presence of disease. #### Common Modalities - Bitewings - Periapicals - Occlusographs #### Diagnostic Characteristics and Limitations - Provides a two-dimensional image of a three-dimensional object. - Features a limited Field of View (FOV). - Primarily used for detecting dental pathology, including: - Caries - Periodontal disease - Periapical inflammatory pathology - Used to assess bony abnormalities. - Important Note: These radiographs cannot fully exclude the presence of disease. “Toothache” <img src="dental_xray_image.jpg" alt="A dental X-ray image showing several posterior teeth with large restorations, possibly indicating decay or pulp involvement causing toothache.">  #### Evaluation of Acute Pain - Investigation of "Toothache" symptoms. A dental X-ray image showing several posterior teeth with large restorations, possibly indicating decay or pulp involvement causing toothache. The image is positioned below the title "Toothache" and illustrates potential sources of dental pain. # Extraoral Radiographs – Panoramic Radiograph (OPG) – Cephalometric Radiograph (Lat / PA) – Other Facial Views – Oblique Lateral – SMV – Waters – Reverse Towne … * Good overview * Large FOV * Two dimensional image of a 3D object * Bony abnormalities * CAN NOT fully exclude presence of disease. #### Common Radiographic Modalities - Panoramic Radiograph (OPG) - Cephalometric Radiograph (Lateral / PA) - Other Facial Views - Oblique Lateral - Submentovertex (SMV) - Waters' View - Reverse Towne's View #### Clinical Utility and Limitations - Provides a good diagnostic overview of the maxillofacial region. - Features a large Field of View (FOV). - Represents a two-dimensional image of a three-dimensional object. - Useful for identifying bony abnormalities. - Important Note: These views cannot fully exclude the presence of disease.  Extraoral radiographs are essential diagnostic tools used when the area of interest is too large to be captured by intraoral films or when a patient cannot open their mouth sufficiently for intraoral sensor placement. #### Clinical Applications - Evaluation of large pathological lesions, such as cysts or tumors. - Assessment of skeletal growth and development. - Examination of impacted teeth and their relationship to surrounding structures. - Evaluation of trauma to the facial bones and jaws. - Assessment of the temporomandibular joint (TMJ). A black and white dental X-ray image showing a full view of the maxilla and mandible, including all teeth and surrounding bone structures. The letter 'R' is visible on the left side, indicating the right side of the patient's mouth. The image reveals detailed dental anatomy, with visible teeth, roots, and jawbone, and appears to be used for diagnostic purposes.  #### Panoramic Radiography Panoramic imaging provides a broad view of the maxilla, mandible, and surrounding structures on a single film. It is the most commonly used extraoral projection in general dentistry. - **Advantages:** - Broad coverage of facial bones and teeth. - Low patient radiation dose compared to a full-mouth intraoral series. - Ease of use for patients with limited opening or gag reflex. - Useful for patient education and visual aids. - **Disadvantages:** - Lower resolution and detail compared to intraoral radiographs. - Magnification and distortion inherent in the technique. - Overlap of structures in the premolar regions. A black and white panoramic X-ray image of a human jaw, showing teeth, dental implants, and surrounding bone structure. The image highlights the alignment and positioning of the teeth and implants within the jawbone.  #### Lateral Cephalometric Projection This projection is primarily used in orthodontics and orthognathic surgery to evaluate the relationship of the teeth to the jaws and the jaws to the rest of the facial skeleton. - **Key Features:** - Standardized positioning using a cephalostat to ensure reproducibility. - Allows for precise measurement of craniofacial growth. - Visualizes soft tissue profiles when a filter is used to attenuate the beam in the anterior region. A black and white dental X-ray image showing a panoramic view of the upper and lower jaws, including teeth, alveolar bone, and surrounding structures. The image includes labels 'R' for the right side and 'L' for the left side, indicating the orientation. The X-ray reveals the arrangement of teeth, root structures, and potential abnormalities such as impacted teeth or cysts.  #### Posteroanterior (PA) Projection The PA projection is used to evaluate the skull for abnormalities, trauma, or developmental progress. Unlike the AP projection, the PA view minimizes magnification of the facial structures by placing them closer to the image receptor. - **Clinical Uses:** - Assessment of facial asymmetry. - Identification of fractures of the mandibular body and ramus. - Evaluation of the frontal and ethmoid sinuses. A black and white dental X-ray image showing the upper and lower teeth, with the letter 'R' indicating the right side. The image displays the dental structure, including teeth, roots, and surrounding bone, with some teeth appearing to be missing or impacted. +  #### Waters' Projection (Occipitomental View) This variation of the PA projection is specifically designed to visualize the paranasal sinuses, particularly the maxillary sinuses. - **Positioning:** The patient's chin touches the receptor, and the nose is positioned approximately 1 to 2 cm away from it. - **Diagnostic Value:** - Best view for detecting sinusitis or fluid levels in the maxillary sinuses. - Visualizes the orbital rims and zygomatic arches. - Identifies fractures of the midface (Le Fort fractures). A panoramic dental X-ray image showing the entire jaw, teeth, and surrounding structures. The image displays the maxillary and mandibular arches with visible teeth, including molars and incisors, as well as the alveolar bone and sinus regions. The grayscale contrast highlights areas of varying density, such as enamel, dentin, and bone, which are essential for diagnosing dental conditions.  #### Submentovertex (SMV) Projection The SMV projection provides a view of the base of the skull and the position of the condyles. - **Indications:** - Evaluation of the sphenoid and ethmoid sinuses. - Assessment of the zygomatic arches (using a reduced exposure). - Identification of the orientation of the mandibular condyles for specialized TMJ imaging. A panoramic dental X-ray image showing the entire jaw, teeth, and surrounding structures. The image reveals multiple teeth, including some with dental restorations or fillings, and highlights the alveolar bone and maxillary sinus regions. The presence of dental implants or crowns is visible on the upper and lower arches.  #### Reverse Towne's Projection This projection is specifically used to visualize the mandibular condyles and the condylar neck. - **Clinical Application:** - Identification of high condylar fractures. - Evaluation of the condylar heads in cases of suspected pathology or displacement. - **Positioning:** The patient's head is tilted down (chin to chest) with the mouth open to bring the condyles out of the glenoid fossa. a black and white dental X-ray image showing the lower jaw with teeth, including a visible dental implant or prosthesis in the lower arch. the image captures the bone structure and surrounding dental anatomy.   #### Cone Beam Computed Tomography (CBCT) While often categorized separately, CBCT is a sophisticated form of extraoral imaging that provides three-dimensional reconstruction of the craniofacial complex. - **Benefits over 2D Imaging:** - Elimination of anatomical superimposition. - Accurate 1:1 measurements for implant planning. - Detailed visualization of the TMJ and airway. - Localization of impacted teeth in three planes of space. black and white medical imaging scan showing a cross-sectional view of a dental structure, likely a CT scan, with visible teeth and surrounding bone tissue. black and white medical imaging scan displaying a detailed view of dental implants or prosthetic teeth, with adjacent bone and soft tissue visible in grayscale. # Computed Tomography Multislice CT AKA Multidetector CT, Sprial CT...   Multislice CT is also known as Multidetector CT (MDCT) or Spiral CT. A diagram illustrating the components of a CT scanner, showing a patient on a CT table with labeled parts including the X-Ray Tube, X-Ray Beam, Detectors, and the CT Table. The diagram is accompanied by a smaller schematic on the left depicting the rotation of the tube/detector assembly around the patient. A schematic diagram of a CT scanner showing the tube/detector assembly rotating around the patient, with the patient table moving into the gantry. The diagram highlights the multiple rows of detectors and the X-ray tube, providing a technical overview of the scanner's structure. **SIEMENS** SOMATOM Force <img src="image_of_ct_scanner_and_diagram.png">   #### Siemens SOMATOM Force The SOMATOM Force represents advanced CT hardware technology used for clinical imaging. A high-resolution photo of the Siemens SOMATOM Force CT scanner, showcasing its sleek design with a large circular opening and a patient bed extending from the base. The machine features a modern interface with a digital display and control panel, emphasizing its advanced medical imaging capabilities. A schematic diagram illustrating the operation of the SOMATOM Force CT scanner. It shows a patient lying on a table being scanned, with an X-ray source emitting radiation that passes through the body and is detected by sensors on the opposite side. The diagram highlights the circular motion of the scanning process and the positioning of the X-ray source and detectors. # Historical Development of CT - **Sixth Generation CT: Helical** (1990's) * Slip-ring technology developed (allows gantry to rotate continuously without wires) * Helical CT scanners acquires data while table is moving c.f. Kalendar WA, Computed Tomography, Second Edition, pg. 79, 2005 **Seventh Generation CT (late** **1990’s – 2000)** * **Multiple Detector Array** c.f. www.impactscan.org   #### Sixth Generation CT: Helical (1990s) - **Slip-ring technology**: Developed to allow the gantry to rotate continuously without the restriction of wires. - **Helical CT scanners**: These systems acquire data while the table is moving. #### Seventh Generation CT (Late 1990s – 2000) - **Multiple Detector Array**: Introduction of systems capable of capturing multiple slices simultaneously. A diagram illustrating the helical CT scanning process, showing the path of a continuously rotating x-ray tube and detector around a patient, with the patient being transported through the scanner. The diagram includes labels for the direction of patient transport, the start of the spiral scan, and the resulting data acquisition in z (mm) and t (s) dimensions. A comparative figure showing two CT scanning methods: on the left, a traditional fan-beam CT with a single x-ray source and detector, and on the right, a multiple detector array CT with a wider array of detectors capturing a broader range of data simultaneously. This illustrates the advancement from single to multiple detector arrays in CT technology.  A diagram illustrating a Dual Source CT system, showing two X-ray sources and two detectors (Detector A and Detector B) arranged around a central object with a 26 cm diameter. The diagram includes a coordinate system (x, y, z) and indicates the rotation direction of the components. # Tomographic Reconstruction – An algorithm is used to produce the CT image (attenuation coefficient map) – Filtered back projection is most widely used in clinical CT scanners  - An algorithm is used to produce the CT image, which serves as an attenuation coefficient map. - Filtered back projection is the most widely used reconstruction method in clinical CT scanners. The diagram illustrates the concept of tomographic reconstruction, showing how attenuation coefficients (μ1 to μ9) are used to calculate line integrals (S1 to S12) in a grid. It demonstrates the process of integrating measurements from different angles to reconstruct an image, which is fundamental to CT imaging.     Axial CT scan showing a cross-sectional view of the jaw and teeth, with visible bone structures and dental implants. The image is labeled 'A' and includes a scale bar indicating 10.00mm/div. Axial CT scan of the lower jaw, displaying the mandible and surrounding soft tissues. The image is labeled 'R' and includes a scale bar indicating 10.00mm/div. Sagittal CT scan of the head and neck, showing the skull, cervical spine, and airway. The image is labeled 'H' and includes a scale bar indicating 10.00mm/div. 3D reconstructed image of a human skull, highlighting the maxilla, mandible, and teeth. The image is labeled 'H' and includes a scale bar indicating 10.00mm/div. # **Hounsfield unit (HU)** – The **Hounsfield unit (HU)** is a quantity commonly used in CT scanning to express CT numbers in a standardised and convenient form. – Hounsfield units, created by and named after Sir Godfrey Hounsfield, are obtained from a linear transformation of the measured attenuation coefficient. – This transformation is based on the arbitrary definitions of air and water. - The Hounsfield unit (HU) is a quantity commonly used in CT scanning to express CT numbers in a standardized and convenient form. - Hounsfield units, created by and named after Sir Godfrey Hounsfield, are obtained from a linear transformation of the measured attenuation coefficient. - This transformation is based on the arbitrary definitions of air and water. CT numbers / Hounsfield Unit <br> <table> <thead> <tr> <td>Substance</td> <td>HU</td> </tr> </thead> <tbody> <tr> <td>Air</td> <td>-1000</td> </tr> <tr> <td>Lung</td> <td>-500</td> </tr> <tr> <td>Fat</td> <td>-100 to -50</td> </tr> <tr> <td>Water</td> <td>0</td> </tr> <tr> <td><span style="font-weight:bold;">CSF</span></td> <td>15</td> </tr> <tr> <td>Kidney</td> <td>30</td> </tr> <tr> <td>Blood</td> <td>+30 to +45</td> </tr> <tr> <td>Muscle</td> <td>+10 to +40</td> </tr> <tr> <td>Grey matter</td> <td>+37 to +45</td> </tr> <tr> <td>White matter</td> <td>+20 to +30</td> </tr> <tr> <td>Liver</td> <td>+40 to +60</td> </tr> <tr> <td>Soft Tissue, Contrast</td> <td>+100 to +300</td> </tr> <tr> <td>Bone</td> <td>+700 (cancellous bone) to +3000 (dense bone)</td> </tr> </tbody> </table>   #### CT Numbers and Hounsfield Units for Various Substances | Substance | HU | | :--- | :--- | | Air | -1000 | | Lung | -500 | | Fat | -100 to -50 | | Water | 0 | | CSF | 15 | | Kidney | 30 | | Blood | +30 to +45 | | Muscle | +10 to +40 | | Grey matter | +37 to +45 | | White matter | +20 to +30 | | Liver | +40 to +60 | | Soft Tissue, Contrast | +100 to +300 | | Bone | +700 (cancellous) to +3000 (dense) | A table listing various substances and their corresponding Hounsfield Unit (HU) values, including air (-1000), lung (-500), fat (-100 to -50), water (0), CSF (15), blood (+30 to +45), muscle (+10 to +40), grey matter (+37 to +45), white matter (+20 to +30), liver (+40 to +60), soft tissue with contrast (+100 to +300), and bone (+700 to +3000). A diagram illustrating CT imaging concepts, showing a cross-sectional image with labeled components such as picture element (pixel), slice width, and volume element (voxel), alongside a grayscale scale from -1000 to 3095 Hounsfield units, representing different tissue densities. c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 359. # Digital Image Display: Window/Level – Computer monitors and laser imagers for printing have about 8 bits of display fidelity ($2^8$=256) – The 12-bit CT images must be reduced to 8 bits to accommodate most image display hardware – The window width (W) determines the contrast of the image, with narrower windows resulting in greater contrast – The level (L) is the CT number at the center of the window | W = 4095, L = 1048 | W = 600, L = -100 | W = 700, L = -650 | |---|---|---| | | | | | CT Number | Display Intensity | |---|---| | -1000 to $P_1$ | black | | $P_1$ to $P_2$ | gray (linearly] | | $P_2$ to +3000 | white | $$\text{P}_1 = \text{L} – \frac{1}{2} \text{W}$$ $$\text{P}_2 = \text{L} + \frac{1}{2} \text{W}$$      #### Image Fidelity and Windowing - Computer monitors and laser imagers for printing typically have about 8 bits of display fidelity (2^8 = 256 levels). - The 12-bit CT images must be reduced to 8 bits to accommodate most image display hardware. - **Window Width (W)**: Determines the contrast of the image; narrower windows result in greater contrast. - **Window Level (L)**: The CT number at the center of the window. #### Display Intensity Mapping | CT Number | Display Intensity | | :--- | :--- | | -1000 to P1 | Black | | P1 to P2 | Gray (linearly) | | P2 to +3000 | White | **Calculation Formulas:** - P1 = L – ½ W - P2 = L + ½ W **Example Settings:** - W = 4095, L = 1048 - W = 600, L = -100 - W = 700, L = -650 A CT scan image with a window width of 600 and level of -100, showing a cross-sectional view of the chest with visible lungs and spinal structures. A CT scan image with a window width of 700 and level of -650, displaying a cross-sectional view of the chest with lungs and spinal structures. A CT scan image with a window width of 4095 and level of 1048, showing a cross-sectional view of the chest with visible lungs and spinal structures. A diagram illustrating the relationship between CT number and display intensity, showing how window width (W) and level (L) determine the contrast and display of image intensities, with P1 and P2 defined as L - 1/2W and L + 1/2W respectively. A chart showing the linear relationship between CT number and display intensity, with black, gray, and white intensity levels corresponding to specific CT number ranges, and formulas for P1 and P2 based on window width and level. Digital Image Display: Window/Level **24** CT value, HU 3000 - 2000 - 1000 - 0 - -1000 - **bone window** **C/W 1000, 2500** **mediastinal** **window** **C/W -50, 400** **lung window** **C/W -600, 1700** +2250 HU -250 HU +150 HU -250 HU +250 HU -1450 HU c.f. Kalendar WA, Computed Tomography, Second Edition, pg. 32, 2005  #### Common Clinical Window Settings 1. **Bone Window** - Center/Width (C/W): 1000, 2500 - Range: +2250 HU to -250 HU 2. **Mediastinal Window** - Center/Width (C/W): -50, 400 - Range: +150 HU to -250 HU 3. **Lung Window** - Center/Width (C/W): -600, 1700 - Range: +250 HU to -1450 HU A diagram illustrating the concept of window/level in digital image display for CT scans, showing a vertical axis labeled 'CT value, HU' ranging from -1000 to 3000. Three horizontal lines represent different window settings: bone window (C/W 1000, 2500), mediastinal window (C/W -50, 400), and lung window (C/W -600, 1700), each corresponding to a CT image slice and its respective HU values. The diagram demonstrates how varying window settings highlight different tissue densities in medical imaging. W:300, L:50 W:3000, L:500  #### Comparative Windowing Examples - **Soft Tissue Focus**: W:300, L:50 - **Bone/Dense Tissue Focus**: W:3000, L:500 Two CT scan images of a human head and neck, labeled A and R, showing cross-sectional views with anatomical structures such as the jaw, teeth, and airway. The images are presented in grayscale with annotations indicating measurement scales of 10.00mm/div. # Contrast Agents – Frequently Iodine – Help better visualize structures <img src="image.png">  - Contrast agents frequently utilize Iodine. - These agents help to better visualize internal structures. The image contains a placeholder for a photo, indicated by the text 'image.png' and a large gray rectangle with a black plus sign in the bottom right corner. This suggests a visual element is intended to be displayed here, but the actual image is not present.  Two axial CT scan images of the head and neck region, labeled A, showing cross-sectional views with anatomical structures such as the skull, mandible, and soft tissues. The images include orientation markers (R for right, L for left) and a scale bar indicating 10.00mm/div, highlighting a lesion or abnormality on the left side of the neck. # MSCT Take Home – 3D Imaging & Dimensionally accurate – Multiplanar reformatting – **Bony pathology** – **Shows soft tissue but not as well as MRI** – Contrast use – Superior Speed – Supine position – Hounsfield Units $\rightarrow$ Tissue density – Air: -1000, Water: 0 - **3D Imaging**: Dimensionally accurate results. - **Multiplanar Reformating**: Ability to view data in different planes. - **Bony Pathology**: Excellent for visualizing bone issues. - **Soft Tissue**: Shows soft tissue, but not as well as MRI. - **Contrast Use**: Enhances visualization of specific structures. - **Superior Speed**: Fast acquisition times. - **Positioning**: Typically performed in the supine position. - **Hounsfield Units (HU)**: Represents tissue density. - Air: -1000 - Water: 0 CONE BEAM VOLUMETRIC TOMOGRAPHY   Cone Beam Volumetric Tomography (CBVT) provides a three-dimensional approach to maxillofacial imaging. A diagram illustrating cone beam volumetric tomography, showing a human head model with a source emitting a cone-shaped beam and a detector capturing the transmitted radiation, labeled as part A. A diagram depicting a cone beam volumetric tomography setup, where a source rotates around a patient's head, emitting a cone-shaped beam that is detected by a detector, labeled as part B.   a medical imaging device with a blue patient seat and control panel, labeled as 'FLX4' on the top right corner. a dental imaging machine with a cylindrical design, featuring a display screen and the label 'GALILEOS' on the side.  A diagram illustrating a CT scanning process, showing an object (a human head) positioned at the center of a circular trajectory. An X-ray source rotates around the object along a defined path, emitting X-rays that pass through the object and are detected by a flat panel detector on the opposite side. The diagram labels key components: 'Axis of rotation,' 'Object,' 'X-ray source,' 'Trajectory,' and 'Flat panel detector,' indicating the setup for tomographic imaging.  The image displays a diagram illustrating the concept of Field of View (FOV) size, with three concentric circles labeled 'Small,' 'Medium,' and 'Large' overlaid on a skull image. The diagram uses the skull as a reference to demonstrate how different FOV sizes affect the visible area, with the largest circle representing the broadest view and the smallest circle indicating the most focused view.  Two side-by-side CT scan images showing cross-sectional views of a bony structure, likely a vertebra or skull base, with high contrast between bone and surrounding soft tissue. The images include measurement scales indicating 10.00mm/div, suggesting a medical imaging context for anatomical analysis. # Radiation Dose Levels <table> <thead> <tr> <th>Type of Examination</th> <th>Effective Dose (ICRP 2007) MICROSIEVERTS</th> </tr> </thead> <tbody> <tr> <td>Bitewing (E)</td> <td>5-9</td> </tr> <tr> <td>OPG</td> <td>4.7-54</td> </tr> <tr> <td>CBCT</td> <td>27-1073</td> </tr> <tr> <td><span style="background-color: yellow;">CT</span></td> <td><span style="background-color: yellow;">180-1160</span></td> </tr> </tbody> </table> Ludlow et al. 2008, Ludlow et al. 2008, Ngan et al. 2003, Loubele et al. 2009, Gavala et all. 2008, Gihbell et al. 2005, Visser et al. 2000, Loubele 2005, Wuomalainen et al. 2009, Okano et al. 2009, Roberts et al. 2009, Kumar et al. 2007, Schultze et al. 2004.  #### Comparative Effective Doses | Type of Examination | Effective Dose (ICRP 2007) Microsieverts (μSv) | | :--- | :--- | | Bitewing (E) | 5-9 | | OPG | 4.7-54 | | CBCT | 27-1073 | | CT | 180-1160 | *Data compiled from Ludlow et al. 2008, Ngan et al. 2003, Loubele et al. 2009, Gavala et al. 2008, Gihbell et al. 2005, Visser et al. 2000, Wuomalainen et al. 2009, Okano et al. 2009, Roberts et al. 2009, Kumar et al. 2007, and Schultze et al. 2004.* Table showing radiation dose levels for various dental imaging examinations, including Bitewing (E), OPG, CBCT, and CT, with effective doses in microsieverts. The table highlights CT doses ranging from 180-1160 microsieverts, which are significantly higher than other procedures. **Table 3** Effective doses for Adult phantom by exposure protocol and field of view - ANOVA p value and Tukey HSD maxilla dentition mandible <table> <thead> <tr> <td rowspan="2"></td> <td rowspan="2">maxila</td> <td rowspan="2">dentition</td> <td rowspan="2">mandible</td> <td rowspan="2">both arches</td> <td rowspan="2">arches + TMJ</td> <td rowspan="2">standard ceph</td> <td rowspan="2">average</td> <td rowspan="2">ANOVA p=.0055 Tukey HSD-*</td> </tr> </thead> <tbody> <tr> <td>Quick Scan +</td> <td>4</td> <td>5</td> <td>8</td> <td>8</td> <td>9</td> <td>11</td> <td>8</td> <td align="center">**C**</td> </tr> <tr> <td>Quick Scan</td> <td>20</td> <td>23</td> <td>34</td> <td>39</td> <td>43</td> <td>54</td> <td>36</td> <td align="center">**BC**</td> </tr> <tr> <td>Standard</td> <td>32</td> <td>44</td> <td>61</td> <td>70</td> <td>79</td> <td>85</td> <td>62</td> <td align="center">**B**</td> </tr> <tr> <td>High Resolution</td> <td>65</td> <td>85</td> <td>127</td> <td>148</td> <td>159</td> <td>171</td> <td>126</td> <td align="center">**A**</td> </tr> <tr> <td>average</td> <td>30</td> <td>39</td> <td>58</td> <td>66</td> <td>73</td> <td>81</td> <td>58</td> <td></td> </tr> <tr> <td>ANOVA p<.0001 - Tukey HSD-*</td> <td align="center">**C**</td> <td align="center">**BC**</td> <td align="center">**ABC**</td> <td align="center">**ABC**</td> <td align="center">**AB**</td> <td align="center">**A**</td> <td></td> <td></td> </tr> </tbody> </table> Ludlow and Walker 2013  #### Effective Doses for Adult Phantom by Exposure Protocol and Field of View | Protocol | Maxilla | Dentition | Mandible | Both Arches | Arches + TMJ | Standard Ceph | Average | Tukey HSD | | :--- | :---: | :---: | :---: | :---: | :---: | :---: | :---: | :---: | | Quick Scan + | 4 | 5 | 8 | 8 | 9 | 11 | 8 | C | | Quick Scan | 20 | 23 | 34 | 39 | 43 | 54 | 36 | BC | | Standard | 32 | 44 | 61 | 70 | 79 | 85 | 62 | B | | High Resolution | 65 | 85 | 127 | 148 | 159 | 171 | 126 | A | | **Average** | **30** | **39** | **58** | **66** | **73** | **81** | **58** | | | **Tukey HSD** | **C** | **BC** | **ABC** | **ABC** | **AB** | **A** | | | *Source: Ludlow and Walker 2013. ANOVA p-values indicate significant variance based on protocol (p < .0001) and region (p = .0055).* Table 3 presents effective doses for an adult phantom by exposure protocol and field of view, showing data for maxilla, dentition, mandible, both arches, arches + TMJ, and standard cephalometric views. The table includes ANOVA p-values and Tukey HSD results, indicating significant differences in dose levels across protocols, with 'High Resolution' having the highest doses and 'Quick Scan +' the lowest. Multislice CT doses are very much protocol dependent –ie Radiologist dependent Multislice CT doses at Envision: 2007 ICRP 103 tissue weights * Mandible: 40-99 $\mu$Sv * Maxilla: 31-77 $\mu$Sv * Orofacial Glabella-chin: 100-180 $\mu$Sv The accuracy and validity of these dose calculations have been confirmed by an independent Qualified Expert as approved by the Radiological Council (Radiation Safety Act 1975) – May 2011 <img src="image_description.png"> COLIN JACOB Compliance Consultancy Service, Medical and Dental Diagnostic X-Ray Equipment ABN 62 612 429 687 PO Box 2177 CLAREMONT NORTH WA 6010 Tel 08 9383 1675 Mob 04 3061 8668 jacobc@bigpond.net.au Bernard Koong Envision Medical Imaging Suite 5/ 178 Cambridge Street WEMBLEY WA 6014 Dear Bernard **RADIATION DOSE CALCULATIONS – Maxillofacial CT** Thank you for sending me the files associated with the *ImPACT CT Patient Dosimetry Calculator* used to calculate doses delivered during typical computed tomography examinations undertaken at your radiology practice. The *ImPACT CT Patient Dosimetry Calculator* calculates the dose in a widely accepted and valid way, based on the ICRP 60 and in this instance, the most recent ICRP 103 tissue weighting factors. It uses Monte Carlo based calculations validated against NRPB SR250 data, which is in turn benchmarked against the results derived from the Monte Carlo code used by the NRPB (UK) from which ICRP 60 and ICRP 103 derived dose data is based. The program offers the further advantage of calculating doses based on both ICRP 60 and ICRP 103 interpretations. In assessing the results I have made the assumption that the primary scan data entered is accurate and appropriate for the Siemens scanner in use. I can confirm that the doses quoted have been calculated correctly. Yours faithfully <img src="signature_image.png"> Colin Jacob Qualified Expert$^1$ 26 May 2011 $^1$ As approved by the Radiological Council, Radiation Safety Act 1975    #### Multislice CT (MSCT) Protocol Variations Multislice CT doses are highly protocol-dependent and vary by radiologist preference. **Calculated Doses at Envision (2007 ICRP 103 tissue weights):** - Mandible: 40-99 μSv - Maxilla: 31-77 μSv - Orofacial (Glabella-chin): 100-180 μSv #### Expert Validation of Dose Calculations The accuracy of these calculations was confirmed by an independent Qualified Expert (Colin Jacob, Compliance Consultancy Service) in May 2011. The assessment utilized the *ImPACT CT Patient Dosimetry Calculator*, which employs Monte Carlo based calculations validated against NRPB SR250 data and benchmarked against ICRP 60 and ICRP 103 tissue weighting factors. The figure is a text-based list titled 'Multislice CT doses at Envision: 2007 ICRP 103 tissue weights', presenting radiation dose values for different anatomical regions: Mandible (40-99 µSv), Maxilla (31-77 µSv), and Orofacial Glabella-chin (100-180 µSv). The figure is a text-based statement confirming the accuracy and validity of the dose calculations, endorsed by an independent Qualified Expert approved by the Radiological Council under the Radiation Safety Act 1975, dated May 2011. The figure is a scanned letter from Colin Jacob, a Qualified Expert, confirming the correctness of radiation dose calculations for maxillofacial CT scans performed at Envision Medical Imaging. The letter includes his signature and contact details. # Radiation Dose Levels **MDCT:** * Variation between different types of scanners * Imaging protocols substantially alter the doses delivered. **CBCT:** * Dependent on the type of unit and the protocols * Not all CBCT scans deliver low radiation dose * A smaller field of view (FOV) in one unit may not necessarily deliver less radiation than a larger FOV in another unit * CBCT may deliver doses greater than low-dose MDCT * Significant challenges in comparisons: * between CBCT units * between the different imaging modalities #### Multidetector Computed Tomography (MDCT) - There is significant variation between different types of scanners. - Imaging protocols substantially alter the doses delivered. #### Comparative Dose Considerations - Radiation dose is highly dependent on the specific CBCT unit and the protocols used. - Not all CBCT scans deliver a low radiation dose; some may deliver doses greater than low-dose MDCT. - A smaller field of view (FOV) in one unit may not necessarily deliver less radiation than a larger FOV in another unit. - Significant challenges exist when comparing doses between different CBCT units or between different imaging modalities. # CBCT Take Home - 3D Morphologic Study - Dimensionally accurate - Multiplanar reformatting - **Dentoalveolar disease** - Bony lesions but CT is preferred - Poor soft tissue depiction - Density measurements **not reliable** - No Hounsfield units - Scattered radiation - Artefacts #### Clinical Applications and Limitations - **3D Morphologic Study:** Provides dimensionally accurate data and allows for multiplanar reformatting. - **Dentoalveolar Disease:** Highly effective for evaluating dental and alveolar structures. - **Bony Lesions:** Useful for assessment, though traditional CT is often preferred for complex cases. - **Soft Tissue:** Poor depiction of soft tissue structures. - **Density Measurements:** Not reliable for quantitative analysis. - No Hounsfield units are available. - Results are affected by scattered radiation and artifacts. # **MAGNETIC RESONANCE IMAGING**  Magnetic Resonance Imaging (MRI) is a sophisticated diagnostic tool utilized for the detailed visualization of internal structures, particularly effective for soft tissue assessment. A cutaway diagram of an MRI scanner showing its internal components, including the patient, patient table, magnet, gradient coils, radio frequency coil, and scanner. The diagram illustrates how the patient is positioned within the scanner for imaging.  This page intentionally left blank in the source material. A high-resolution photograph of a Siemens MAGNETOM Essenza MRI machine, showcasing its sleek white and gray design with a prominent circular scanner and patient bed. The image highlights the modern medical imaging technology against a clean, reflective background. # MRI – **Magnetic field and radiofrequency pulses** – Patient in relatively strong magnetic field – Nuclei of many atoms (**mainly hydrogen**) align with magnetic field – Apply radiofrequency signal – several pulses – protons rotate away from direction induced by imaging magnet – At the end of pulse sequence – relaxation – signal detected by receiver coil – Larger number of nuclei of loosely bound Hydrogen atoms – larger intensity of recovered signal – Fourier transform and reconstruction techniques used to produce images #### Image Generation Process - **Magnetic field and radiofrequency pulses**: The patient is placed in a relatively strong magnetic field. - **Hydrogen alignment**: Nuclei of many atoms, mainly hydrogen, align with the magnetic field. - **Radiofrequency signal**: Several pulses are applied, causing protons to rotate away from the direction induced by the imaging magnet. - **Relaxation and detection**: At the end of the pulse sequence, relaxation occurs, and the signal is detected by a receiver coil. - **Signal intensity**: A larger number of nuclei of loosely bound hydrogen atoms results in a larger intensity of the recovered signal. - **Reconstruction**: Fourier transform and reconstruction techniques are used to produce the final images. # **MRI Applications in DMFR** * **TMJ disorders** * **Tumours and cysts in the head and neck** * Jaw lesions * Salivary gland lesions * Paranasal sinus lesions * **Assessment of IDN** * **Infection / inflammation eg. osteomyelitis** * **Vascular lesions** <table> <tr> <td colspan="2" align="center"><strong>Mouth Closed</strong></td> <td colspan="2" align="center"><strong>Mouth Open</strong></td> </tr> <tr> <td><img src="placeholder_image.png"></td> <td><img src="placeholder_image.png"></td> </tr> <tr> <td>Glenoid fossa</td> <td>EAC</td> <td>Articular eminence</td> <td></td> </tr> <tr> <td>Disc</td> <td>Bilaminar zone</td> <td>A IZ P</td> <td></td> </tr> <tr> <td>Condyle</td> <td></td> <td></td> <td></td> </tr> <tr> <td colspan="2" align="center"><img src="placeholder_image.png" alt="MRI scan of TMJ mouth closed"></td> <td colspan="2" align="center"><img src="placeholder_image.png" alt="MRI scan of TMJ mouth open"></td> </tr> <tr> <td>Disc C</td> <td></td> <td>Disc C</td> <td>EAC</td> </tr> <tr> <td colspan="4" align="right">© Behrang Amini, MD/PhD</td> </tr> </table>   #### Clinical Indications - **TMJ disorders**: Evaluation of the articular disc and surrounding structures. - **Tumours and cysts in the head and neck**: - Jaw lesions - Salivary gland lesions - Paranasal sinus lesions - **Assessment of Inferior Dental Nerve (IDN)** - **Infection / inflammation**: For example, osteomyelitis. - **Vascular lesions** #### TMJ Imaging Anatomy - **Mouth Closed Position**: - Glenoid fossa - External Auditory Canal (EAC) - Articular Disc - Bilaminar zone - Condyle - **Mouth Open Position**: - Articular eminence - Disc (Anterior, Intermediate Zone, Posterior) - Condyle (C) - External Auditory Canal (EAC) A diagram showing the temporomandibular joint (TMJ) in two states: mouth closed and mouth open. The top portion displays anatomical labels such as the glenoid fossa, disc, condyle, and bilaminar zone for the closed mouth, and the articular eminence for the open mouth. The bottom portion shows corresponding MRI scans with labels for the disc and condyle (C), illustrating the joint's structure and movement. Two MRI scans of the TMJ, one with the mouth closed and one with the mouth open, showing the disc and condyle. The images demonstrate the movement of the joint components, with the disc and condyle labeled in both views. Understanding MRI Signals **T1 weighted sequence** | (black) | low SI | intermediate SI | high SI | | :---: | :---: | :---: | :---: | | [Circle representing black] | [Circle representing low SI] | [Circle representing intermediate SI] | [Circle representing high SI] | | air, calcium, cortical bone, rapidly flowing blood | fluid, ligaments/ muscles/tendons, abdominal organs, cartilage | high-protein tissue (abscess, complex cysts, synovial fluid) | fat, blood, gadolinium (= contrast), melanin, protein | **T2 weighted image** | (black) | low SI | intermediate SI | high SI | | :---: | :---: | :---: | :---: | | [Circle representing black] | [Circle representing low SI] | [Circle representing intermediate SI] | [Circle representing high SI] | | air, calcium, cortical bone, rapidly flowing blood | ligaments, tendons, liver, pancreas, adrenals, cartilage | fat, liver, pancreas, adrenals, muscles, cartilage | fluid, CSF, bladder, bile/ gallbladder, kidneys |   #### T1 Weighted Sequence (T1WI) - **Low Signal Intensity (Black)**: Air, calcium, cortical bone, rapidly flowing blood. - **Intermediate Signal Intensity**: Fluid, ligaments, muscles, tendons, abdominal organs, cartilage. - **High-Protein Tissue**: Abscess, complex cysts, synovial fluid. - **High Signal Intensity (Bright)**: Fat, blood, gadolinium (contrast), melanin, protein. #### T2 Weighted Image (T2WI) - **Low Signal Intensity (Black)**: Air, calcium, cortical bone, rapidly flowing blood. - **Intermediate Signal Intensity**: Ligaments, tendons, liver, pancreas, adrenals, cartilage. - **Variable Intermediate/High**: Fat, liver, pancreas, adrenals, muscles, cartilage. - **High Signal Intensity (Bright)**: Fluid, Cerebrospinal Fluid (CSF), bladder, bile/gallbladder, kidneys. A table comparing signal intensities (SI) in T1 and T2 weighted MRI sequences, showing different tissue types associated with black, low SI, intermediate SI, and high SI categories, with corresponding circular icons representing signal levels. Two MRI brain scans labeled T1 and T2, illustrating the differences in signal intensity between the two imaging sequences, with the T2 image showing higher contrast in fluid-filled areas. **T1WI** | **T2WI** ---|--- Fat is bright | Fluid is bright |   #### Primary Signal Differentiators - **T1WI**: Fat appears bright. - **T2WI**: Fluid appears bright. This figure shows a T1WI MRI scan with fat appearing bright, indicated by a yellow arrow pointing to a bright area in the image. The scan displays a cross-sectional view of the head, highlighting anatomical structures where fat is prominently visible. This figure displays a T2WI MRI scan where fluid is bright, as indicated by a yellow arrow pointing to a bright region in the image. The scan provides a cross-sectional view of the head, emphasizing areas with high fluid content. | **DISC** | **DISC** | |---|---| | | | | CLOSED | OPEN |  #### TMJ Disc Visualization - **Closed Position**: Evaluation of the disc relationship to the condyle and glenoid fossa. - **Open Position**: Evaluation of the disc translation and morphology during mandibular excursion. The image displays two MRI scans labeled "CLOSED" and "OPEN," showing the disc in a joint, likely the temporomandibular joint. The left scan (CLOSED) shows the disc in a more anterior position, while the right scan (OPEN) shows the disc moving posteriorly, indicating joint movement. Both images are labeled with "DISC" and arrows pointing to the disc structure.  This page intentionally left blank in the source material. MRI scan showing a sagittal view of the brain with visible anatomical structures, including the cerebellum and brainstem. The image includes technical parameters such as TE 30.0 ms and TI ms, with orientation markers [AL] and [PR] indicating anterior-left and posterior-right directions.  This page intentionally left blank in the source material. A black and white medical imaging scan showing a sagittal view of a human head, likely an MRI or CT scan, with anatomical structures visible including the skull, brain, and nasal cavity. The image includes orientation markers [AL] and [PR] indicating anterior-posterior and posterior-anterior directions, respectively.  This page intentionally left blank in the source material. black and white medical imaging scan showing anatomical structures, with labels [AL] and [PR] indicating left and right sides, and text 'F 4-7' and '3972987x1' visible in the image.    This page intentionally left blank in the source material. black and white medical imaging photo showing a sagittal view of a knee joint with the text "LEFT MEDIAL CLOSED" indicating the medial compartment of the left knee is closed, likely referring to a meniscal tear or joint space narrowing. close-up black and white medical imaging photo of a knee joint, highlighting the femoral condyle and tibial plateau, with visible soft tissue structures and potential signs of degeneration or injury. black and white medical imaging photo displaying a sagittal view of a knee joint, showing the patella, femur, and tibia, with a focus on the articular surfaces and surrounding soft tissues.   This page intentionally left blank in the source material. Two black and white medical images, likely MRI scans, showing cross-sectional views of a joint with visible cartilage and surrounding tissue. The images are presented side-by-side for comparison. A black and white medical image, likely an MRI scan, showing a cross-sectional view of a joint with a highlighted area of interest, possibly indicating a pathological condition or anatomical feature.   This page intentionally left blank in the source material. axial MRI scan showing a cross-sectional view of the head and neck, highlighting a large, well-defined mass with multiple cystic components in the parotid gland region. sagittal MRI scan displaying a longitudinal view of the neck and upper thorax, revealing a large, multiloculated cystic lesion in the parotid region, with surrounding anatomical structures visible.  This page intentionally left blank in the source material. Two axial CT scans of the skull, showing cross-sectional views of the head with visible bone structures, nasal cavities, and sinuses. The images are presented side-by-side, likely for comparison or diagnostic purposes.    This page intentionally left blank in the source material. a black and white medical imaging scan showing a cross-sectional view of a human head, with a bright area indicating a possible lesion or abnormality in the brain region. a black and white MRI scan of a human head, displaying detailed anatomical structures including the nasal cavity, sinuses, and brain, with a prominent bright region suggesting a pathological finding. a black and white MRI scan of a human head, showing a cross-sectional view with visible cranial bones, sinuses, and brain tissue, with a dark area possibly indicating a mass or fluid-filled cavity. # MRI Take Home **Features** * **No ionising radiation** and no known biological side effects * **Superior soft tissue contrast – soft tissue lesions, articular disc of TMJ** * Various sequences can be utilised to visualise different tissues * **IV paramagnetic contrast agents eg. Gadolinium** * Certain anatomical and pathological structures with greater vascularity and permeability can be enhanced. **Weaknesses** * Claustrophobia – “non-claustrophobic” MRI * Long imaging times * Ferromagnetic metals contraindicated eg cardiac pacemakers, cerebral aneurysmal clips * **May not detect osseous changes visualised in CT** * Calcific deposits may be undetected * Can over estimate extent of tumours due to response of adjacent tissues * **Gadolinium-based contrast media must be used with caution in those with renal impairment - has been associated with nephrogenic systemic fibrosis** * **Gadolinium deposition with regions of the brain has recently been discovered and is currently being investigated.** #### Key Features and Advantages - **Safety**: No ionizing radiation and no known biological side effects. - **Contrast**: Superior soft tissue contrast—ideal for soft tissue lesions and the articular disc of the TMJ. - **Versatility**: Various sequences can be utilized to visualize different tissues. - **Contrast Enhancement**: IV paramagnetic contrast agents (e.g., Gadolinium) can enhance anatomical and pathological structures with greater vascularity and permeability. #### Limitations and Contraindications - **Patient Factors**: Claustrophobia (though "non-claustrophobic" MRI options exist) and long imaging times. - **Safety Contraindications**: Ferromagnetic metals are contraindicated (e.g., cardiac pacemakers, cerebral aneurysmal clips). - **Diagnostic Limitations**: - May not detect osseous changes visualized in CT. - Calcific deposits may go undetected. - Can overestimate the extent of tumours due to the response of adjacent tissues. - **Contrast Risks**: - Gadolinium-based contrast media must be used with caution in those with renal impairment; it has been associated with nephrogenic systemic fibrosis. - Gadolinium deposition within regions of the brain has recently been discovered and is currently under investigation. # Ultrasound – Ultrasonic beam **No radiation** – Tissues have different acoustic impedance – Some of the sonic waves will reflect (echo) back to the transducer – Tissues have characteristic echo pattern – Real-time imaging – Soft tissue – **Cystic vs solid** – **Colour Doppler ultrasound – blood flow** – Relatively low cost   Ultrasound imaging utilizes ultrasonic beams to visualize internal structures without the use of ionizing radiation. This modality relies on the principle that different tissues possess unique acoustic impedances. #### Core Principles and Benefits - **Echo Reflection**: Sonic waves reflect back to the transducer based on tissue density and interface. - **Tissue Characterization**: Each tissue type exhibits a characteristic echo pattern, allowing for detailed visualization. - **Real-time Imaging**: Provides immediate, dynamic visual feedback during the examination. - **Cost-Effectiveness**: Offers a relatively low-cost diagnostic solution compared to other advanced imaging modalities. #### Clinical Capabilities - **Soft Tissue Assessment**: Highly effective for evaluating non-mineralized structures. - **Cystic vs. Solid Differentiation**: Capable of distinguishing between fluid-filled cysts and solid masses. - **Hemodynamic Evaluation**: Utilizes Colour Doppler ultrasound to visualize and measure blood flow. A photo of an ultrasound machine with a monitor displaying the text "ACUSON X FAMILY," showing a modern medical device used for imaging. A photo of a patient undergoing an ultrasound examination, with a technician using the ultrasound probe on the patient's neck area. Understanding US Signals "Echogenecity” **Echogenicity** | | | | | |---|---|---|---| | **hyperechoic** | **isoechoic** | | **anechoic** | | O | O | O | O | | | | **hypoechoic** | | | | | | | |---|---|---|---| | **metal** | | **soft tissue** | **air** | | O | O | O | O | | **bone** | | **fat** | |   The interpretation of ultrasound images is based on the concept of echogenicity, which describes how different materials reflect sound waves. #### Degrees of Echogenicity - **Hyperechoic**: Areas that appear bright on the screen due to high reflection (e.g., metal, bone). - **Isoechoic**: Tissues that have the same echogenicity as surrounding structures. - **Hypoechoic**: Areas that appear darker than surrounding tissues due to lower reflection (e.g., certain soft tissues or fat). - **Anechoic**: Areas that appear completely black because they do not reflect sound waves (e.g., air or fluid). #### Material Correlation - **High Reflection (Bright)**: Metal and Bone. - **Intermediate Reflection**: Soft tissue and Fat. - **Minimal/No Reflection (Dark)**: Air. A series of four ultrasound images demonstrating different echogenicity levels: echogenic (bright white), hypoechoic (dark), isoechoic (medium gray), and anechoic (black). Each image is labeled with its corresponding echogenicity type. A diagram illustrating echogenicity in ultrasound imaging, showing a scale from hyperechoic (bright) to anechoic (dark). It categorizes various tissues such as metal, bone, soft tissue, fat, and air, indicating their relative echogenicity levels. # Applications * Soft tissue lumps and swellings * Soft tissue pain/discomfort * Salivary glands * Lymph nodes * Guided FNA and core biopsies   Ultrasound is employed in various clinical scenarios to evaluate head and neck pathologies and assist in diagnostic procedures. #### Diagnostic Indications - **Soft Tissue Evaluation**: Assessment of lumps, swellings, and localized pain or discomfort. - **Glandular and Lymphatic Assessment**: Detailed imaging of the salivary glands and cervical lymph nodes. #### Interventional Guidance - **Biopsy Support**: Provides real-time guidance for Fine Needle Aspiration (FNA) and core biopsies to ensure precision. A photo displaying a collection of ultrasound probes, each labeled with different model numbers such as ML6-15, L8-18i, and M5S, arranged in a row on a white surface. A photo showing a hand holding an ultrasound probe labeled L8-18i, being used on the back of another hand, demonstrating the application of ultrasound for soft tissue examination.   ultrasound image showing a grayscale scan of tissue with a dotted line connecting two points labeled '1' and '2', indicating a measurement or region of interest, with anatomical markers and scale on the right side. ultrasound image with color Doppler overlay, displaying a region with increased blood flow indicated by red and blue hues, suggesting vascular activity, with a zoomed-in inset highlighting the area of interest. # Nuclear Medicine * Functional imaging $\rightarrow$ detects abnormal metabolic processes * Rather than anatomical/morphological changes * May not be discernible in the early stages of some diseases. * Radionuclide imaging: * Radionuclides which emit gamma rays (e.g. Technetium 99m) - combined with a pharmaceutical to form a radiotracer which is distributed to various parts of the body based on their chemical properties. * A gamma camera captures the emitted photons * **Single photon emission computed tomography (SPECT):** * Acquires tomographic slices - gamma camera rotates around the patient detected emitted gamma rays. - similar to multislice CT #### Principles of Functional Imaging - Detects abnormal metabolic processes rather than anatomical or morphological changes. - Useful for identifying pathology that may not be discernible in the early stages of disease through traditional imaging. #### Radionuclide Imaging Process - **Radiotracers:** Radionuclides that emit gamma rays (e.g., Technetium 99m) are combined with a pharmaceutical to form a radiotracer. - **Distribution:** The tracer is distributed to various parts of the body based on specific chemical properties. - **Detection:** A gamma camera captures the emitted photons to create an image. #### Single Photon Emission Computed Tomography (SPECT) - Acquires tomographic slices by rotating a gamma camera around the patient to detect emitted gamma rays. - The process is similar to the acquisition method used in multislice CT.   A panoramic dental X-ray showing the upper and lower jaws with teeth, including a visible tooth extraction site on the lower right side. The image includes anatomical markers such as 'R' for right and 'L' for left. A set of four nuclear medicine bone scan images showing anterior, posterior, left lateral, and right lateral views of the head and neck. The scans highlight areas of increased radiotracer uptake, particularly in the skull and cervical spine regions. SPECT SPECT / CT CT | SPECT | SPECT / CT | CT | |---|---|---| | B | C | A |    #### Comparative Imaging Modalities | SPECT | SPECT / CT | CT | | :--- | :--- | :--- | | B | C | A | SPECT/CT image showing a fused view with blue and yellow regions indicating areas of interest, labeled as C, with red crosshairs for orientation. CT image displaying a grayscale anatomical cross-section, labeled as A, with red crosshairs for orientation. SPECT image showing a blurred, grayscale view with dark regions, labeled as B, with red crosshairs for orientation. Nuclear Medicine: Positron emission tomography (PET): * Positron emitting radionuclides - usually combined with pharmaceuticals such as glucose or amino acids, to assess metabolic processes in the body. * After a set period of time, positron emission decay occurs, and two photons are produced which travel in opposite directions * A PET camera has a ring of detectors which can map the photons that arrive at the same time - produce a functional image of organs and tissues. * Hybrid imaging systems where the nuclear medicine images are co-registered with a CT or MRI images ( ie PET/CT and PET/MRI) allowing for combined morphological and functional imaging. * Very high spatial resolution – detect very small lesions Examples of use * **Cancers** * **Identify viable heart muscle with previous myocardial infarcts** * **Brain – identify epileptic foci, diagnosis of dementia** #### Mechanism of PET Imaging - **Radionuclides:** Uses positron-emitting radionuclides, typically combined with pharmaceuticals such as glucose or amino acids to assess metabolic processes. - **Positron Decay:** After a set period, positron emission decay occurs, producing two photons that travel in opposite directions. - **Detection:** A PET camera utilizes a ring of detectors to map photons that arrive simultaneously, producing functional images of organs and tissues. #### Hybrid Imaging and Resolution - **Co-registration:** Nuclear medicine images can be co-registered with CT or MRI images (e.g., PET/CT and PET/MRI). - **Combined Assessment:** This allows for simultaneous morphological and functional imaging. - **Spatial Resolution:** Offers very high spatial resolution, enabling the detection of very small lesions. #### Clinical Applications - **Oncology:** Detection and monitoring of various cancers. - **Cardiology:** Identification of viable heart muscle following myocardial infarcts. - **Neurology:** Identification of epileptic foci and the diagnosis of dementia.   A CT scan image showing a cross-sectional view of the head and neck, highlighting bone structures and soft tissues with varying densities. An PET scan image displaying metabolic activity in the head and neck region, with areas of high activity indicated by bright yellow and red hues.   3D rendered image of a human skull, showing detailed anatomical features such as the eye sockets, nasal cavity, and teeth, with a metallic texture and a focus on the cranial structure. Medical imaging scan, likely a PET-CT or similar, displaying a cross-sectional view of the pelvic region with highlighted areas in purple and green, indicating abnormal metabolic activity, possibly tumors, within the bladder and surrounding tissues. # **Conclusion** * **Assessment of hard tissue:** Intraoral Radiographs, Extraoral Radiographs, CBCT, MSCT * **Assessment of soft tissues:** MSCT, MRI, Ultrasound * **Functional Imaging Techniques:** SPECT, PET [^1]: Original PDF page 1: [[L4 Imaging of Hard and Soft Tissues.pdf#page=1|L4 Imaging of Hard and Soft Tissues, p.1]] [^2]: Original PDF page 2: [[L4 Imaging of Hard and Soft Tissues.pdf#page=2|L4 Imaging of Hard and Soft Tissues, p.2]] [^3]: Original PDF page 3: [[L4 Imaging of Hard and Soft Tissues.pdf#page=3|L4 Imaging of Hard and Soft Tissues, p.3]] [^4]: Original PDF page 4: [[L4 Imaging of Hard and Soft Tissues.pdf#page=4|L4 Imaging of Hard and Soft Tissues, p.4]] [^5]: Original PDF page 5: [[L4 Imaging of Hard and Soft 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