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Which factors influence the size of a pixel in imaging?
What does attenuation refer to in radiology?
What is the maximum range of Hounsfield Units (HU) in modern scanners?
What shade of gray represents water in the Hounsfield scale?
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Which process is used to create an image from calculated Hounsfield units?
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What is a 'narrow window' in imaging?
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Which is NOT a dependent factor for voxel size?
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Which number represents white on the Hounsfield scale?
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What does a narrow window width enhance in a CT image?
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What is the typical range for a liver window in Hounsfield units based on the provided example?
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Which component is NOT part of a CT scanner?
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What determines the brightness of a CT image?
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What is the typical tilting range of most CT scanners?
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Who was the leader in the introduction of CT scanners in 1971?
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What does CT stand for in the context of medical imaging?
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What is the primary advantage of CT over conventional X-ray imaging?
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What does the term 'VOXEL' refer to in CT imaging?
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What is the purpose of the matrix in CT imaging?
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How is the pixel size in CT imaging determined?
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What is the Field of View (FOV) in CT scanning?
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In what way does conventional radiography differ from CT imaging?
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Which landmark is the articulation between the nasal and frontal bones?
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What is the highest point of the skull in the median sagittal plane called?
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Which line joins the centre of the two orbits when the eyes are looking straight forward?
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What is the lowest point of the inferior rim of the orbit called?
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Which landmark is found on the occipital bone and usually coincides with the median sagittal plane?
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Which landmark indicates the point where the upper and lower eyelids meet laterally?
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The angle of the mandible, also known as the gonial angle, is located at which junction?
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What is the term for the line that extends from the outer canthus of the eye to the center of the external auditory meatus?
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What characterizes a lateral projection in radiology?
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How is an oblique projection defined?
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What is the significance of the 40 degree left anterior oblique (40°LAO) positioning?
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What does a complex oblique projection involve?
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In a projection designated as 55°RAO35°↓, what does the '35°' refer to?
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Which factors determine how an oblique projection is named?
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What does raising the chin do in the context of complex oblique projections?
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In the context of a right lateral projection, where does the central ray enter the skull?
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What does the median sagittal plane divide the skull into?
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Which plane is perpendicular to the anthropological plane?
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In an occipto-frontal projection, where does the central ray enter the skull?
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What is indicated by an FO 30° caudal projection?
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What anatomical landmarks define the median sagittal plane?
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Why is it important to understand anatomical features in radiographs?
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What does the anthropological plane contain?
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What type of projection is described when the central ray enters through the frontal bone and exits through the occipital bone?
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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.
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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
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Scanner:
- Gantry: Houses the X-ray tube, generator, filter, collimators, and detectors.
- Patient Couch: Supports the patient during the scan.
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Gantry:
- Tilting Range: Allows for imaging at different angles.
- Aperture: The opening through which the patient passes.
Skull Radiography
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Skull radiography relies on palpable/visible landmarks and lines and planes of the skull and face.
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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.
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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.
