Computed Tomography Overview
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Questions and Answers

Which factors influence the size of a pixel in imaging?

  • Matrix Size (correct)
  • Slice Thickness
  • Color Depth
  • FOV (correct)

    • What does attenuation refer to in radiology?

  • Reflection of light
  • Absorption of sound waves
  • Reduction of intensity (correct)
  • Increase in intensity

    • What is the maximum range of Hounsfield Units (HU) in modern scanners?

  • 1000 HU
  • 2000 HU
  • 3000 HU
  • 4000 HU (correct)

    • What shade of gray represents water in the Hounsfield scale?

    <p>0 HU</p> Signup and view all the answers

    Which process is used to create an image from calculated Hounsfield units?

    <p>Windowing</p> Signup and view all the answers

    What is a 'narrow window' in imaging?

    <p>A specific HU range centered over a structure's average HU</p> Signup and view all the answers

    Which is NOT a dependent factor for voxel size?

    <p>Color Depth</p> Signup and view all the answers

    Which number represents white on the Hounsfield scale?

    <p>+1000 HU</p> Signup and view all the answers

    What does a narrow window width enhance in a CT image?

    <p>Contrast of the image</p> Signup and view all the answers

    What is the typical range for a liver window in Hounsfield units based on the provided example?

    <p>-15 HU to +155 HU</p> Signup and view all the answers

    Which component is NOT part of a CT scanner?

    <p>Image Display Monitor</p> Signup and view all the answers

    What determines the brightness of a CT image?

    <p>Window level</p> Signup and view all the answers

    What is the typical tilting range of most CT scanners?

    <p>-30 to +30 degrees</p> Signup and view all the answers

    Who was the leader in the introduction of CT scanners in 1971?

    <p>Sir Godfrey Hounsfield</p> Signup and view all the answers

    What does CT stand for in the context of medical imaging?

    <p>Computerized Tomography</p> Signup and view all the answers

    What is the primary advantage of CT over conventional X-ray imaging?

    <p>Good low contrast resolution</p> Signup and view all the answers

    What does the term 'VOXEL' refer to in CT imaging?

    <p>A three-dimensional volume element</p> Signup and view all the answers

    What is the purpose of the matrix in CT imaging?

    <p>To create images of slices</p> Signup and view all the answers

    How is the pixel size in CT imaging determined?

    <p>By dividing FOV by the matrix size</p> Signup and view all the answers

    What is the Field of View (FOV) in CT scanning?

    <p>The diameter of the body region being imaged</p> Signup and view all the answers

    In what way does conventional radiography differ from CT imaging?

    <p>It produces only 2D images and structures overlap</p> Signup and view all the answers

    Which landmark is the articulation between the nasal and frontal bones?

    <p>Nasion</p> Signup and view all the answers

    What is the highest point of the skull in the median sagittal plane called?

    <p>Vertex</p> Signup and view all the answers

    Which line joins the centre of the two orbits when the eyes are looking straight forward?

    <p>Interpupillary line</p> Signup and view all the answers

    What is the lowest point of the inferior rim of the orbit called?

    <p>Infraorbital margin</p> Signup and view all the answers

    Which landmark is found on the occipital bone and usually coincides with the median sagittal plane?

    <p>External occipital protuberance</p> Signup and view all the answers

    Which landmark indicates the point where the upper and lower eyelids meet laterally?

    <p>Outer canthus of the eye</p> Signup and view all the answers

    The angle of the mandible, also known as the gonial angle, is located at which junction?

    <p>Posterior border at the junction of the lower border of the ramus</p> Signup and view all the answers

    What is the term for the line that extends from the outer canthus of the eye to the center of the external auditory meatus?

    <p>Orbito-meatal baseline</p> Signup and view all the answers

    What characterizes a lateral projection in radiology?

    <p>The image receptor is closest to the side of the head the ray exits.</p> Signup and view all the answers

    How is an oblique projection defined?

    <p>The central ray is at an angle to both the median sagittal and coronal planes.</p> Signup and view all the answers

    What is the significance of the 40 degree left anterior oblique (40°LAO) positioning?

    <p>The median sagittal plane is angled 40° to the image receptor.</p> Signup and view all the answers

    What does a complex oblique projection involve?

    <p>Adding cranial or caudal angulation to an oblique projection.</p> Signup and view all the answers

    In a projection designated as 55°RAO35°↓, what does the '35°' refer to?

    <p>The caudal angulation added to the projection.</p> Signup and view all the answers

    Which factors determine how an oblique projection is named?

    <p>Which side of the head is in contact and the part of the head touching the receptor.</p> Signup and view all the answers

    What does raising the chin do in the context of complex oblique projections?

    <p>It causes the baseline to angle with respect to the image receptor.</p> Signup and view all the answers

    In the context of a right lateral projection, where does the central ray enter the skull?

    <p>On the left side of the head.</p> Signup and view all the answers

    What does the median sagittal plane divide the skull into?

    <p>Right and left halves</p> Signup and view all the answers

    Which plane is perpendicular to the anthropological plane?

    <p>Coronal plane</p> Signup and view all the answers

    In an occipto-frontal projection, where does the central ray enter the skull?

    <p>Through the occipital bone</p> Signup and view all the answers

    What is indicated by an FO 30° caudal projection?

    <p>The beam is directed towards the feet</p> Signup and view all the answers

    What anatomical landmarks define the median sagittal plane?

    <p>Nasion and external occipital protuberance</p> Signup and view all the answers

    Why is it important to understand anatomical features in radiographs?

    <p>To make judgements regarding positioning quality</p> Signup and view all the answers

    What does the anthropological plane contain?

    <p>The two anthropological baselines and the infraorbital line</p> Signup and view all the answers

    What type of projection is described when the central ray enters through the frontal bone and exits through the occipital bone?

    <p>Frontal-occipital projection</p> Signup and view all the answers

    Which landmark is located at the highest point of the skull in the median sagittal plane?

    <p>Vertex</p> Signup and view all the answers

    What does the anthropological baseline connect in radiographic positioning?

    <p>The infraorbital point and the upper border of the EAM</p> Signup and view all the answers

    Which line joins the two inferior infraorbital points?

    <p>Inferior orbital line</p> Signup and view all the answers

    What anatomical feature marks the junction of the lower border of the ramus of the mandible?

    <p>Angle of the mandible</p> Signup and view all the answers

    Which of these landmarks is found on the frontal bone just superior to the nasion?

    <p>Glabella</p> Signup and view all the answers

    Which line is defined as joining the center of the two orbits?

    <p>Interpupillary line</p> Signup and view all the answers

    Which landmark is a bony prominence found on the occipital bone often coinciding with the median sagittal plane?

    <p>Inion</p> Signup and view all the answers

    What does the term 'inner canthus' refer to in skull anatomy?

    <p>Junction where the eyelids meet near the nose</p> Signup and view all the answers

    What is a characteristic feature of the median sagittal plane?

    <p>It includes the nasion and the external occipital protuberance.</p> Signup and view all the answers

    In which projection does the central ray enter through the occipital bone and exit through the frontal bone?

    <p>Occipto-frontal projection.</p> Signup and view all the answers

    Which plane is defined as containing the two anthropological baselines and the infraorbital line?

    <p>Anthropological plane.</p> Signup and view all the answers

    What type of angulation implies that the central ray is directed toward the feet in a projection?

    <p>Caudal angulation.</p> Signup and view all the answers

    Which statement is true regarding the relationship between the median sagittal plane and the other planes mentioned?

    <p>It intersects with the coronal plane at right angles.</p> Signup and view all the answers

    What does the term 'FO30°↓' indicate in a projection?

    <p>Frontal occipital projection at 30 degrees caudal.</p> Signup and view all the answers

    What characterizes a right lateral projection in radiology?

    <p>The beam enters from the left side and exits the right side.</p> Signup and view all the answers

    Which option describes the role of anatomical features in evaluating radiographs?

    <p>They enable assessment of the radiograph's quality regarding positioning.</p> Signup and view all the answers

    Which of the following planes is defined to pass through the center of the two external auditory meatuses (EAMs)?

    <p>Auricular plane.</p> Signup and view all the answers

    How is the angle defined in a 40° left anterior oblique (40°LAO) projection?

    <p>The left side of the head is rotated 40° toward the receptor.</p> Signup and view all the answers

    What does a complex oblique projection require regarding additional angles?

    <p>It requires a combination of tube angulation and patient positioning.</p> Signup and view all the answers

    In a projection denoted as 55°RAO35°↓, what does the '35°' specifically indicate?

    <p>The angle of caudal angulation added to the median sagittal plane.</p> Signup and view all the answers

    What is necessary for a projection to be classified as an oblique projection?

    <p>There must be an angle created between the central ray and the projection baseline.</p> Signup and view all the answers

    What impact does raising the chin have in complex oblique projections?

    <p>It alters the baseline's relationship to the image receptor.</p> Signup and view all the answers

    In which scenario is a 55° right anterior oblique (55°RAO) position used?

    <p>When the right side of the face is in contact with the image receptor.</p> Signup and view all the answers

    How is the naming of an oblique projection determined?

    <p>By the part of the head in contact with the receptor and its orientation.</p> Signup and view all the answers

    Which landmark is located at the junction between the nasal and frontal bones?

    <p>Nasion</p> Signup and view all the answers

    What is the function of the infraorbital line in radiographic positioning?

    <p>Connects two inferior infraorbital points</p> Signup and view all the answers

    Which of the following best describes the anthropological baseline?

    <p>Passes from the infraorbital point to the upper border of the external auditory meatus</p> Signup and view all the answers

    What is the highest point of the skull in the median sagittal plane referred to as?

    <p>Vertex</p> Signup and view all the answers

    Which landmark is identified as a bony prominence on the occipital bone?

    <p>Inion</p> Signup and view all the answers

    The angle of the mandible is known as which of the following?

    <p>Gonial angle</p> Signup and view all the answers

    Which line is defined as joining the center of two orbits?

    <p>Interpupillary line</p> Signup and view all the answers

    What anatomical feature is described as the lowest point of the inferior rim of the orbit?

    <p>Infraorbital margin</p> Signup and view all the answers

    In a lateral projection, how is the central ray oriented in relation to the median sagittal plane?

    <p>Along a coronal plane</p> Signup and view all the answers

    What determines how to name an oblique projection?

    <p>The contact point of either anterior or posterior head with the receptor</p> Signup and view all the answers

    In a projection described as a 55° right anterior oblique with a 35° caudal angulation, what does the '55°' specifically indicate?

    <p>The angle of rotation of the head towards the receptor</p> Signup and view all the answers

    What is the significance of a caudal angulation in a complex oblique projection?

    <p>It helps in aligning the median sagittal plane with the image receptor</p> Signup and view all the answers

    When performing oblique projections, how is the side of the head in contact with the cassette determined?

    <p>According to the required projection angle</p> Signup and view all the answers

    What is a complex oblique projection characterized by?

    <p>The addition of cranial or caudal angulation to the projection</p> Signup and view all the answers

    Which positioning technique can achieve a caudal angulation when limited mobility is present?

    <p>Raising the chin or angling the X-ray tube</p> Signup and view all the answers

    In terms of positioning for a right lateral projection, what happens to the beam exit point?

    <p>It exits on the right side of the patient's head</p> Signup and view all the answers

    What is the purpose of the median sagittal plane in skull anatomy?

    <p>To separate the skull into right and left halves.</p> Signup and view all the answers

    Which plane is characterized as an axial plane in cranial positioning?

    <p>Anthropological plane</p> Signup and view all the answers

    In an FO 30° caudal projection, what does the angulation indicate?

    <p>The central ray angles towards the feet.</p> Signup and view all the answers

    What anatomical features are essential for effective evaluation of skull radiographs?

    <p>Identification of positioning relative to the image receptor.</p> Signup and view all the answers

    Which projection has the central ray entering through the occipital bone and exiting through the frontal bone?

    <p>Occipto-frontal (OF) projection</p> Signup and view all the answers

    How does the auricular plane relate to other anatomical planes?

    <p>It is perpendicular to the anthropological plane.</p> Signup and view all the answers

    What does cranial angulation involve during imaging?

    <p>Positioning the beam at an angle towards the head.</p> Signup and view all the answers

    What anatomical landmark is located at the posterior end of the median sagittal plane?

    <p>External occipital protuberance (inion)</p> Signup and view all the answers

    What position is commonly used for lateral projections during flexion and extension of the lumbar region?

    <p>Erect position with the patient seated on a stool</p> Signup and view all the answers

    How should the X-ray beam be directed for lumbar lateral projections?

    <p>Horizontally at right angles to the image receptor</p> Signup and view all the answers

    When performing lateral projections, when should the exposure be made?

    <p>On arrested expiration</p> Signup and view all the answers

    What is an essential characteristic of the image when performing lumbar lateral projections?

    <p>All areas of interest must be included on both projections</p> Signup and view all the answers

    In performing an AP axial projection, what should be avoided to ensure accurate positioning?

    <p>Rotation of the pelvis</p> Signup and view all the answers

    What is the significance of ensuring the posterior ribs are superimposed in an imaging exam?

    <p>It confirms the patient was not rotated too far forwards or backwards.</p> Signup and view all the answers

    Which anatomical landmark corresponds to the sixth cervical vertebra?

    <p>Cricoid cartilage</p> Signup and view all the answers

    What is the preferred positioning of the patient during the imaging process as described?

    <p>Supine with knees and hips flexed</p> Signup and view all the answers

    Why should the central ray (CR) be centered at the level of the lower costal margin?

    <p>To accurately capture lower thoracic vertebrae and sacro-iliac joints.</p> Signup and view all the answers

    What should be considered when evaluating image density for diagnosis?

    <p>Adequate contrast needs to be maintained between upper and lower lumbar vertebrae.</p> Signup and view all the answers

    How can rotation be assessed in an imaging procedure?

    <p>By observing the distance of the sacro-iliac joints from the spine</p> Signup and view all the answers

    What anatomical landmark marks the lower border of the 4th thoracic vertebra?

    <p>Sternal angle</p> Signup and view all the answers

    What is the purpose of placing the patient's feet with their plantar aspect on the tabletop?

    <p>It reduces the lumbar arch for alignment.</p> Signup and view all the answers

    What is the correct position for the patient during a thoracic vertebrae examination?

    <p>Supine with the median sagittal plane perpendicular to the tabletop</p> Signup and view all the answers

    Where should the upper edge of the CR cassette be positioned during the X-ray?

    <p>At a level just below the prominence of the thyroid cartilage</p> Signup and view all the answers

    What is the recommended location for centering the X-ray beam in thoracic imaging?

    <p>2.5 cm below the sternal angle</p> Signup and view all the answers

    What is an essential image characteristic for a thoracic vertebrae X-ray?

    <p>The image should include vertebrae from C7 to L1</p> Signup and view all the answers

    What common fault may occur during the imaging of thoracic vertebrae?

    <p>The image receptor and beam are centered too low</p> Signup and view all the answers

    In a lateral decubitus position X-ray, where should the upper edge of the cassette be placed?

    <p>3–4 cm above the spinous process of C7</p> Signup and view all the answers

    What should the direction of the collimated vertical beam be during thoracic imaging?

    <p>At right angles to the image receptor</p> Signup and view all the answers

    What is a characteristic of high radiographic contrast in imaging?

    <p>It causes high density over vertebrae</p> Signup and view all the answers

    What is the required exposure density for imaging to ensure bony detail can be discerned?

    <p>Sufficient exposure density to visualize all bony structures</p> Signup and view all the answers

    Which positioning fault frequently occurs during the imaging of the sacroiliac joint?

    <p>Missed visualization of the sacroiliac joint</p> Signup and view all the answers

    What is an essential characteristic of the image to ensure proper vertebral alignment?

    <p>The posterior and anterior margins of vertebral bodies must be superimposed</p> Signup and view all the answers

    What positioning adjustment can be made to avoid failure in demonstrating intervertebral disc spaces?

    <p>Ensuring the spine is perfectly perpendicular to the receptor</p> Signup and view all the answers

    What positioning method is used to stabilize the patient during imaging?

    <p>Arms raised and resting on a pillow, with flexed knees and hips</p> Signup and view all the answers

    What is the correct angle for centering the collimated vertical beam during lumbar imaging?

    <p>At right angles to the line of spinous processes anterior to the 3rd lumbar spinous process</p> Signup and view all the answers

    What can result from poor superimposition of vertebral bodies during imaging?

    <p>The patient was rolled too far forward or backward</p> Signup and view all the answers

    What is an indicator of insufficient image density in X-ray imaging?

    <p>High-contrast images</p> Signup and view all the answers

    What is the primary position of the patient when performing lateral projections for lumbar vertebrae evaluation?

    <p>Seated on a stool with either side against the vertical Bucky</p> Signup and view all the answers

    When performing lateral projections, how is the lumbar region positioned during the first exposure?

    <p>Leaning forward with the lumbar region flexed</p> Signup and view all the answers

    Where should the Bucky be centered for the lumbar projection?

    <p>At the level of the lower costal margin</p> Signup and view all the answers

    What is the direction of the X-ray beam during an AP Axial projection?

    <p>Directed cephalad at 5cm below ASIS</p> Signup and view all the answers

    What is a key consideration for achieving quality imaging in lateral projections of the lumbar vertebrae?

    <p>Ensuring all areas of interest are included and using a short exposure time</p> Signup and view all the answers

    What orientation should the patient's coronal plane have in relation to the midline of the Bucky during imaging?

    <p>It should coincide with and be perpendicular to the midline of the Bucky.</p> Signup and view all the answers

    What common fault may occur if the patient is not positioned correctly?

    <p>Exclusion of the spinous processes from the image.</p> Signup and view all the answers

    What is essential for producing sufficient image density for diagnosis from T12 to L5/S1?

    <p>Selecting appropriate imaging factors.</p> Signup and view all the answers

    What should be the position of the patient's arms during the imaging procedure?

    <p>They should be elevated and resting on a pillow in front of their head.</p> Signup and view all the answers

    When should the exposure for an X-ray be made during the imaging process?

    <p>On arrested expiration.</p> Signup and view all the answers

    What might be indicated by poor superimposition of the vertebral body margins?

    <p>The patient was rolled too far forward or backward.</p> Signup and view all the answers

    Where should the collimated vertical beam be centered during the imaging of the lumbar region?

    <p>Anterior to the 3rd lumbar spinous process.</p> Signup and view all the answers

    What is a common solution for high-contrast images resulting in varying image density?

    <p>Adjust the software application for image processing.</p> Signup and view all the answers

    What is the significance of the anterior superior iliac spines being equidistant from the tabletop?

    <p>It helps maintain the patient's lumbar spine alignment.</p> Signup and view all the answers

    Which vertebrae should be included at minimum in a properly centered image of the thoracic region?

    <p>T12 down to the sacro-iliac joints.</p> Signup and view all the answers

    What is the recommended position for patient feet during imaging to reduce lumbar arch?

    <p>Feet should be placed with their plantar aspect on the tabletop.</p> Signup and view all the answers

    How is proper rotation of the patient assessed in imaging?

    <p>By observing the superimposition of the ribs.</p> Signup and view all the answers

    When ensuring adequate image density for diagnosis, what should be avoided?

    <p>Allowing diaphragm movement during exposure.</p> Signup and view all the answers

    Which surface marking is positioned at the level of the 9th thoracic vertebra?

    <p>Xiphisternal joint.</p> Signup and view all the answers

    What method is used to identify the upper and middle thoracic vertebrae in lateral projections?

    <p>Palpating the prominent spinous process of C7.</p> Signup and view all the answers

    What happens if the exposure is made during expiration?

    <p>It creates a large difference in image density.</p> Signup and view all the answers

    What is the appropriate positioning of the patient on the X-ray table for thoracic vertebrae imaging?

    <p>Supine with median sagittal plane perpendicular to the tabletop</p> Signup and view all the answers

    Where should the upper edge of the CR cassette be positioned for optimal imaging of upper thoracic vertebrae?

    <p>Just below the prominence of the thyroid cartilage</p> Signup and view all the answers

    What common issue occurs if the image receptor and beam are centred too low?

    <p>Poor visualization of the lower thoracic vertebrae</p> Signup and view all the answers

    What is the correct angulation of the collimated vertical beam during imaging of the thoracic vertebrae?

    <p>Caudal angulation may be required</p> Signup and view all the answers

    What essential image characteristic should be ensured for thoracic vertebrae imaging?

    <p>Vertebrae from C7 to L1 should be included</p> Signup and view all the answers

    How can the presence of L1 be identified in an X-ray image?

    <p>By the absence of ribs attached to it</p> Signup and view all the answers

    What positioning is typically utilized for a lateral decubitus thoracic vertebrae examination?

    <p>Lateral with arms raised above the head</p> Signup and view all the answers

    What issue might occur due to the superimposition of shoulders during a thoracic vertebrae X-ray?

    <p>Non-visualization of the upper two or three vertebrae</p> Signup and view all the answers

    What should be the positioning of the head in the lateral erect position to avoid superimposition?

    <p>The angle of the mandible should not obscure the anterior cervical vertebra.</p> Signup and view all the answers

    In the lateral erect position, how should the occipital bone be positioned to ensure visibility of the posterior arch of the atlas?

    <p>It should not obscure the posterior arch of the atlas.</p> Signup and view all the answers

    Why is it important for the angle of the mandible not to superimpose over the upper anterior cervical vertebra?

    <p>It ensures accurate diagnosis of vertebral conditions.</p> Signup and view all the answers

    What is a potential consequence of improper head positioning in the lateral erect position?

    <p>Obscured anatomical landmarks.</p> Signup and view all the answers

    What anatomical feature is crucial to avoid overlapping in lateral erect imaging?

    <p>The angle of the mandible.</p> Signup and view all the answers

    What adjustment should be made to the head position to prevent the mandible from superimposing the cervical vertebrae?

    <p>The head should be adjusted so the angle of the mandible is not obscured.</p> Signup and view all the answers

    Which bone should not be obscured by the occipital bone when positioning the head?

    <p>Posterior arch of the atlas</p> Signup and view all the answers

    In the lateral erect position, why is it important to properly orient the head?

    <p>To avoid obscuring the posterior structures of the skull.</p> Signup and view all the answers

    How should the patient's head be positioned during an imaging procedure to avoid superimposition?

    <p>Adjusted to align the mandible angle with the cervical vertebra.</p> Signup and view all the answers

    What anatomical structure is obscured if the head is not positioned correctly?

    <p>Upper anterior cervical vertebra</p> Signup and view all the answers

    Study Notes

    Computed Tomography (CT)

    • CT scanners revolutionized medical imaging in 1971 with the introduction of a single detector for brain studies.
    • CT scanners use X-rays and computer processing to create cross-sectional images of the body.
    • Why CT?
      • CT overcomes limitations of conventional X-ray imaging which only produces 2D images, leading to overlapping structures.
      • CT offers superior low contrast resolution, allowing for the detection of subtle tissue changes.
      • CT provides precise diagnostic information about the distribution of structures within the body.

    Tomography

    • Tomography involves imaging an object by analyzing its slices.
    • Slice Thickness: The thickness of each cross-sectional image.
    • Matrix: A two-dimensional array of numbers representing the image.
    • Voxel: A three-dimensional volume element in the object represented by a number in the matrix.
    • Pixel: A two-dimensional element in the image representing a voxel.
    • Field of View (FOV): The diameter of the body region being imaged.
    • Pixel Size: Determined by dividing FOV by the matrix size.
    • Voxel Size: Dependent on FOV, matrix size, and slice thickness.

    Attenuation

    • Attenuation is the reduction in X-ray beam intensity as it passes through matter.
    • Factors affecting attenuation:
      • Beam energy
      • Atomic number of the absorber

    CT Numbers

    • Each pixel in the image matrix represents a CT number.
    • CT numbers indicate the X-ray attenuation in the corresponding voxel.
    • CT numbers are displayed on a gray scale, with each shade of gray representing a specific attenuation value.
    • Hounsfield Units (HU): A scale used to represent CT numbers, with water assigned an attenuation value of zero.
    • The range of CT numbers is typically 2000 HU, with +1000 (white) and -1000 (black) at the extremes.

    Windowing

    • Windowing utilizes CT numbers to create an image by assigning shades of gray to different attenuation values.
    • Window Level: The CT number selected as the center of the displayed range.
    • Window Width: The total range of values displayed.
    • Narrow Window: Used to highlight variations in a specific structure by focusing on a narrow range of HU values.
    • Wide Window: Used to display a broader range of structures with different densities.

    Imaging System

    • Scanner:
      • Gantry: Houses the X-ray tube, generator, filter, collimators, and detectors.
      • Patient Couch: Supports the patient during the scan.
    • Gantry:
      • Tilting Range: Allows for imaging at different angles.
      • Aperture: The opening through which the patient passes.

    Skull Radiography

    • Skull radiography relies on palpable/visible landmarks and lines and planes of the skull and face.

    • Understanding these landmarks is crucial for radiographers performing skull radiography.

    Landmarks

    • Outer canthus of the eye: The lateral point where the upper and lower eyelids meet.
    • Infraorbital margin/point: The lowest point of the inferior rim of the orbit.
    • Nasion: The articulation between the nasal and frontal bones.
    • Glabella: A bony prominence on the frontal bone, superior to the nasion.
    • Vertex: The highest point of the skull in the median sagittal plane.
    • External occipital protuberance (inion): A bony prominence on the occipital bone, usually coincident with the median sagittal plane.
    • External auditory meatus (EAM): The opening within the ear that leads into the external auditory canal.
    • Inner canthus: The junction where the eyelids meet near the nose.
    • Angle of the mandible (gonial angle): Located at the posterior border, where the lower border of the ramus of the mandible meets.

    Lines

    • Interpupillary (interorbital) line: Joins the centre of the two orbits or the centre of the two pupils when the eyes are looking straight forward.
    • Infraorbital line: Joins the two inferior infraorbital points.
    • Anthropological baseline: Passes from the infraorbital point to the upper border of the EAM.
    • Orbito-meatal baseline (radiographic baseline): Extends from the outer canthus of the eye to the centre of the EAM. This line is angled approximately 10° to the anthropological baseline.

    Planes

    • Median sagittal plane: Divides the skull into right and left halves. Landmarks on this plane are the nasion anteriorly and the external occipital protuberance (inion) posteriorly.
    • Coronal planes: Perpendicular to the median sagittal plane, dividing the head into anterior and posterior parts.
    • Anthropological plane: A horizontal plane containing the two anthropological baselines and the infraorbital line. An example of an axial plane.
    • Auricular plane: Perpendicular to the anthropological plane and passes through the centre of the two EAMs. An example of a coronal plane.

    Positioning Terminology

    • Skull projections are described by stating the relative positions of the skull planes to the image receptor, the central ray relative to skull planes/image receptor, and giving a centring point or area to be included within the collimated X-ray beam.

    Occipto-frontal (OF) Projection

    • The central ray enters the skull through the occipital bone and exits through the frontal bone.

    Fronto-Occipital (FO) Projection

    • The central ray enters the skull through the frontal bone and exits through the occipital bone.

    Beam Angulation

    • OF or FO projections often require the central ray to pass along the sagittal plane at an angle to the orbital-meatal plane.
    • The degree of angulation is stated after the projection name, including the direction:
      • Cranial angulation (↑): beam directed up towards the head.
      • Caudal angulation (↓): beam directed towards the feet.

    Lateral Projection

    • The collimated central ray passes along a coronal plane at right-angles to the median sagittal plane.
    • Named according to the side of the head closest to the image receptor/cassette.

    Oblique Projections

    • The central ray is at an angle to the median sagittal plane and the coronal plane.
    • Named based on whether the anterior or posterior portion of the head is in contact with the receptor/cassette, and whether the left or right side of the head is in contact with the receptor/cassette.
    • Oblique projections can be further complex with the addition of caudal/cranial angulation.

    55 Degree Right Anterior Oblique with 35 Degree Caudal Angulation (55°RAO35°↓)

    • The head is rotated so the right side of the face is in contact with the receptor/cassette, and the median sagittal plane makes an angle of 55° with the image receptor.
    • The central ray has a 35° caudal angulation.

    Complex Oblique Projections

    • This type of oblique projection can be achieved through a combination of tube angulation and raising/lowering the chin to change the baseline angle relative to the image receptor.

    Skull Radiography

    • Skull radiography relies on a series of visible landmarks and recognized lines/planes of the skull and face.
    • Radiographers must understand these landmarks, lines, and planes prior to performing any skull radiographic positioning.

    Landmarks

    • Outer Canthus of the Eye: The lateral point where the upper and lower eyelids meet.
    • Infraorbital Margin/Point: The lowest point of the inferior rim of the orbit.
    • Nasion: The articulation between the nasal and frontal bones.
    • Glabella: A bony prominence found on the frontal bone immediately superior to the nasion.
    • Vertex: The highest point of the skull in the median sagittal plane.
    • External Occipital Protuberance (Inion): A bony prominence found on the occipital bone, usually coincident with the median sagittal plane.
    • External Auditory Meatus (EAM): The opening within the ear that leads into the external auditory canal.
    • Angle of the Mandible: The angle of the mandible (gonial angle) is located at the posterior border at the junction of the lower border of the ramus of the mandible.

    Lines

    • Interpupillary (Interorbital Line): Joins the centre of the two orbits or the centre of the two pupils when the eyes are looking straight forward.
    • Infraorbital Line: Joins the two inferior infraorbital points.
    • Anthropological Baseline: Passes from the infraorbital point to the upper border of the EAM.
    • Orbito-Meatal Baseline (Radiographic Baseline): Extends from the outer canthus of the eye to the centre of the EAM. Angled approximately 10° to the anthropological baseline.

    Planes

    • Median Sagittal Plane: Divides the skull into right and left halves. Includes landmarks such as the nasion anteriorly and the external occipital protuberance (inion) posteriorly.
    • Coronal Planes: Are at right-angles to the median sagittal plane and divide the head into anterior and posterior parts..
    • Anthropological Plane: A horizontal plane that contains the two anthropological baselines and the infraorbital line. It’s an example of an axial plane.
    • Auricular Plane: Perpendicular to the anthropological plane and passes through the centre of the two EAMs. An example of a coronal plane.
    • The median sagittal, anthropological, and coronal planes are at right-angles.

    Positioning Terminology

    • To describe a skull projection, it’s necessary to state:
      • the relative positions of the skull planes to the image receptor
      • the central ray relative to skull planes/image receptor
      • the centring point or area to be included within the collimated X-ray beam.

    Occipto-Frontal Projection

    • The central ray enters the skull through the occipital bone and exits through the frontal bone.

    Frnto-Occipital Projection

    • The central ray enters the skull through the frontal bone and exits through the occipital bone.

    Beam Angulation

    • Many OF or FO projections require the central ray to pass along the sagittal plane at some angle to the orbital-meatal plane.
    • The degree and direction of angulation is stated after the name of the projection.
    • Cranial angulation involves the beam directed upward toward the head (↑).
    • Caudal angulation involves the beam directed toward the feet (↓).

    Lateral Projection

    • The collimated central ray passes along a coronal plane at right-angles to the median sagittal plane.
    • Named according to the side of the head closest to the image receptor/cassette.

    Oblique Projections

    • Obtained when the central ray is at some angle to the median sagittal plane and the coronal plane.
    • Named based on :
      • Whether the anterior or posterior portion of the head is in contact with the receptor/cassette
      • Whether the left or right side of the head is in contact with the receptor/cassette.

    Complex Oblique Projections

    • Oblique projections can be complex with the addition of caudal or cranial angulation in relation to a specified baseline.
    • This additional angle is typically achieved by raising or lowering the chin such that the relevant baseline makes the required angle to the image receptor.
    • Alternatively, the X-ray tube can be angled or a combination of both approaches may be used if the patient has limited mobility.

    Skull Radiography Landmarks

    • Outer canthus of the eye: The point where the upper and lower eyelids meet laterally.
    • Inner canthus: Junction where the eyelids meet near the nose.
    • Infraorbital margin/point: The inferior rim of the orbit, with the point being at its lowest point.
    • Nasion: The articulation point between the nasal and frontal bones.
    • Glabella: A bony prominence on the frontal bone, just above the nasion.
    • Vertex: The highest point of the skull in the median sagittal plane.
    • External occipital protuberance (inion): A bony prominence on the occipital bone, generally aligning with the median sagittal plane.
    • External auditory meatus (EAM): The opening within the ear that leads to the external auditory canal.
    • Angle of the mandible (gonial angle): Located at the posterior border where the lower border of the ramus of the mandible connects.

    Lines and Planes in Skull Radiography

    • Interpupillary (interorbital) line: Connects the centers of the two orbits or pupils when eyes look straight ahead.
    • Infraorbital line: Connects the two inferior infraorbital points.
    • Anthropological baseline: Passes from the infraorbital point to the upper border of the EAM.
    • Orbito-meatal baseline (radiographic baseline): Extends from the outer canthus of the eye to the center of the EAM. This baseline is angled approximately 10° to the anthropological baseline.
    • Median sagittal plane: Divides the skull into right and left halves. Landmarks on this plane include the nasion anteriorly and the external occipital protuberance (inion) posteriorly.
    • Coronal planes: Perpendicular to the median sagittal plane, dividing the head into anterior and posterior parts.
    • Anthropological plane: A horizontal plane containing the two anthropological baselines and the infraorbital line. It's an axial plane.
    • Auricular plane: Perpendicular to the anthropological plane, passing through the center of the two EAMs. It's a coronal plane. The median sagittal, anthropological, and coronal planes are perpendicular.

    Skull Radiography Projection Terminology

    • Occipto-frontal (OF) projection: The central ray enters the skull through the occipital bone and exits through the frontal bone.
    • Fronto-occipital (FO) projection: The central ray enters the skull through the frontal bone and exits through the occipital bone.
    • Beam angulation: Used in many OF or FO projections. The central ray passes along the sagittal plane at an angle to the orbital-meatal plane. Cranial angulation directs the beam up towards the head (written as ↑). Caudal angulation directs the beam toward the feet (written as ↓).
    • Lateral projection: The collimated central ray passes along a coronal plane perpendicular to the median sagittal plane. It's named according to the side of the head closest to the image receptor.
    • Oblique projections: Obtained when the central ray is angled to both the median sagittal plane and the coronal plane. Named based on whether the anterior or posterior portion of the head is in contact with the receptor, and whether the left or right side of the head is in contact.
    • Complex oblique projections: May involve caudal or cranial angulation relative to a specified baseline, often achieved by raising or lowering the chin.

    Examples of Skull Radiographic Projections

    • FO30° caudal projection (FO30°↓): The central ray enters the skull through the frontal bone and exits through the occipital bone, with a 30° caudal angulation.
    • 40° left anterior oblique (40°LAO): The head is rotated to the left, with the median sagittal plane at 40° to the image receptor and the left side of the head in contact with the receptor.
    • 55° right anterior oblique with 35° caudal angulation (55°RAO35°↓): The head is rotated such that the right side of the face is in contact with the receptor, with a 55° angle between the median sagittal plane and the image receptor, and a 35° caudal beam angulation.

    Evaluating Skull Radiographs

    • Understanding the relevant anatomical features demonstrated on standard skull projections is crucial for assessing radiograph quality and positioning.

    Thoracic Vertebrae Radiographic Techniques

    • Patient Positioning (AP): Patient lies supine, median sagittal plane perpendicular to the table, central ray 2.5 cm below sternal angle.
    • Image Receptor (AP): Upper edge at level of thyroid cartilage.
    • X-Ray Beam (AP): Vertical, collimated tightly to spine.
    • Image Characteristics (AP): Should include C7 to L1, sufficient density for bony detail.
    • Common Faults (AP): Centre too low, excluding upper thoracic vertebrae or L1.
    • Patient Positioning (Lateral): Patient lateral decubitus, median sagittal plane parallel to the image receptor, arms raised above head.
    • Image Receptor (Lateral): Upper edge 3-4 cm above spinous process of C7.
    • X-Ray Beam (Lateral): Vertical, caudal angulation, centered below inferior angle of scapula.
    • Image Characteristics (Lateral): Upper two or three vertebrae may be obscured, absence of rib on L1 indicates inclusion of T12.
    • Localised Projections: Anterior surface markings guide centring: cricoid cartilage (C6), sternal notch (T2-T3), sternal angle (T4), xiphisternal joint (T9).
    • Patient Positioning (Lumbar): Patient supine, hips and knees flexed, lower costal margin centered.
    • Image Receptor (Lumbar): Cassette includes lower thoracic vertebrae and sacro-iliac joints.
    • X-Ray Beam (Lumbar): Vertical, exposure done on arrested expiration.
    • Image Characteristics (Lumbar): Should include T12 to sacro-iliac joints, sacro-iliac joints equidistant from spine, density for bony detail.
    • Common Faults (Lumbar): Missing sacro-iliac joints.
    • Patient Positioning (Lateral Lumbar): Patient lateral decubitus, arms raised, knees and hips flexed, non-opaque pads for parallel spine.
    • Image Receptor (Lateral Lumbar): Centered at level of lower costal margin.
    • X-Ray Beam (Lateral Lumbar): Vertical, centered anterior to 3rd lumbar spinous process, exposure on arrested expiration.
    • Image Characteristics (Lateral Lumbar): Includes T12 downwards, posterior and anterior vertebral body margins superimposed, density for diagnostic quality.
    • Common Faults (Lateral Lumbar): High-contrast images, excluded spinous processes, poor superimposition of vertebral body margins, lack of intervertebral disc space.
    • Lateral Projections in Flexion and Extension: Demonstrate mobility and stability of lumbar vertebrae.
    • Patient Positioning (Flexion/Extension): Patient erect, seated on stool, leaning forward for flexion and backward for extension.
    • Image Receptor (Flexion/Extension): Centered at level of lower costal margin, exposure on arrested expiration.
    • X-Ray Beam (Flexion/Extension): Horizontal, centered anterior to 3rd lumbar spinous process.
    • Image Characteristics (Flexion/Extension): All area of interest included, short exposure time.
    • Patient Positioning (AP Axial): Patient supine, no pelvic rotation.
    • X-Ray Beam (AP Axial): Vertical, directed cephalad 5 cm below level of ASIS.

    Thoracic Vertebrae Imaging

    • Positioning for AP Thoracic Vertebrae: The patient lies supine with the center of the X-ray beam directed 2.5 cm below the sternal angle. The upper edge of the image receptor should be positioned just below the thyroid cartilage to ensure that the upper thoracic vertebrae are included. The beam should cover from C7 to L1.
    • Important Features for AP Thoracic Vertebrae Image: Ensure the image includes vertebrae from C7 to L1 with adequate density to show bony detail.
    • Common Positioning Error: The image receptor and beam are often centered too low, excluding the upper thoracic vertebrae. The lower vertebrae can be identified easily by the fact that L1 usually does not have a rib attached to it.
    • Positioning for Lateral Thoracic Vertebrae: Patient lies in lateral decubitus position with the midline of the axilla aligned with the midline of the table. Arms should be raised above the head. The image receptor is positioned 3–4 cm above the spinous process of C7. The beam is directed perpendicular to the long axis of the thoracic vertebrae, which may require a caudal angulation. The beam is centered just below the inferior angle of the scapula.
    • Important Features for Lateral Thoracic Vertebrae Image: Ensure the image includes the upper two or three vertebrae (may not be visible due to shoulder superimposition). Look for the absence of a rib on L1 to confirm T12 is included. The posterior ribs should be superimposed, indicating the patient was not rotated.
    • Localised Projections: Specific projections may be requested depending on the region of interest. The following anatomical landmarks can be used to guide centring points:
      • Cricoid Cartilage: Sixth cervical vertebra.
      • Sternal Notch: 2nd to 3rd thoracic vertebra.
      • Sternal Angle: Lower border of 4th thoracic vertebra.
      • Xiphisternal Joint: 9th thoracic vertebra.
    • Positioning for AP Lumbar Vertebrae: Patient lies supine with hips and knees flexed. The image receptor is centered at the level of the lower costal margin and should encompass the lower thoracic vertebrae and the sacro-iliac joints. The exposure is taken on arrested expiration to reduce diaphragm movement.
    • Important Features for AP Lumbar Vertebrae Image: The image should include T12 down to the sacro-iliac joints. Ensure the sacro-iliac joints are equidistant from the spine to assess for rotation.
    • Common Positioning Error for AP Lumbar Vertebrae: A common error is to miss some or all of the sacro-iliac joint. If this occurs, an additional projection of the sacro-iliac joints should be performed.
    • Positioning for Lateral Lumbar Vertebrae: Patent lies in either lateral decubitus position with arms raised, hips and knees flexed. The image receptor is centered at the level of the lower costal margin. The exposure is taken on arrested expiration, and may be performed upright.
    • Important Features for Lateral Lumbar Vertebrae Image: The image should include T12 downwards, including the lumbosacral junction. Posterior and anterior margins of the vertebral body should be superimposed. The image density should be sufficient to visualize bony detail from T12 to L5/S1.
    • Common Positioning Errors for Lateral Lumbar Vertebrae: High-contrast images may result in insufficient image density. Collimation may exclude spinous processes. Poor superimposition of the anterior and posterior margins of the vertebral bodies suggests the patient was rolled too far forward or backward. A clear intervertebral disc space may be lacking if the spine is not perfectly parallel with the receptor.
    • Positioning for Lateral Lumbar Vertebrae in Flexion and Extension: This projection used to demonstrate mobility and stability of the lumbar vertebrae. The patient leans forward (flexion) and then backward (extension) while maintaining a stable position.
    • Important Features for Lateral Lumbar Vertebrae in Flexion and Extension: Ensure all of the area of interest is included in both projections. A short exposure time is beneficial as the patient may have difficulty maintaining a stable pose.
    • Positioning for AP Axial Lumbar Vertebrae: Patient lies supine with no rotation of the pelvis (ASIS equidistant from the tabletop). The beam is directed cephalad (5cm) below the level of ASIS.

    Lateral Erect (Basic) Position

    • Patient Positioning:
      • Patient stands erect, facing the image receptor.
      • Head Alignment: Head should be adjusted to prevent superimposition:
        • Mandible should not obscure upper anterior cervical vertebrae.
        • Occipital bone should not obscure the posterior arch of the atlas.
    • Image Receptor Positioning: Vertical and perpendicular to the patient's sagittal plane.

    Lateral Erect Position

    • Positioning: The patient should stand or sit erect, facing the image receptor. This is the basic position for a lateral cervical spine radiograph.
    • Head Alignment: It's crucial to ensure the head is correctly aligned. The angle of the mandible should not overlap the upper anterior cervical vertebra. Additionally, the occipital bone should not block the posterior arch of the atlas.
    • Goal: Proper head alignment allows for clear visualization of all cervical vertebrae without any bony obstruction.
    • Image Receptor Placement: The cassette (image receptor) should be placed against the patient's lateral cervical spine, perpendicular to the central ray of the X-ray beam.
    • Patient Position: The patient should be positioned with their shoulders relaxed and their head in a neutral position.

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    Description

    This quiz explores the fundamentals of computed tomography (CT), including its historical significance, advancements in medical imaging, and the basic concepts associated with tomography. Learn about key terms such as slice thickness, matrix, voxel, and pixel, as well as the advantages of CT over conventional X-ray imaging.

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