Basic Principles of CT
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| What is the root term meaning to cut, section, or layer? | Tomo
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| Where did the early acronym CAT (scan) originate from? | Because early scanners did axial cuts and were commonly referred to Computerized Axial Tomography
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| What are possible names of the preliminary image? | Scout (GE), Topogram (Siemens), Scanongram (Toshiba)
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| What are some other terms describing Continuous Acquisition Scanning? | Spiral (Siemens), Helical (GE), or Isotropic (Toshiba)
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| What is the ability of a system to define small objects distinctly? | Spatial Resolution
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| What is the ability of a system to differentiate, on the image, objects with similar densities? | Low-Contrast Resolution
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| What term refers to the speed at which the data can be acquired? | Temporal Resolution
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| What is the thickness of the cross-sectional slice? | Z axis
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| What does the Z axis do? | It works as a collimator and limits the x-ray beam to help with scatter & superimposition
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| The data that form the CT slice (Z axis) are furthered sectioned into what 2 elements? | X (width) & Y (Height)
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| What is each one of these 2-D squares are known as a.... | Pixel (picture element)
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| When the Z Axis is taken into account with X & Y the result is a | Cube
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| What is this Cube referred to as a | Voxel (Volume Element)
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| What is the grid called formed from the rows and columns of pixels? | Matrix
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| What is the most common matrix size? | 512
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| What is the degree to which an x-ray beam is reduced by an object? | Attenuation
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| X-ray photons that pass through objects unimpeded are represented as black on the image and is referred to as having | Low attenuation
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| Objects that absorb the X-ray photon will show as white and is know as having | High Attenuation
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| How is areas of intermediate attenuations represented | with various shades of gray
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| What is the mass of a substance per unit volume? | Density
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| What quantifies the degree that a structure attenuates an x-ray beam? | Hounsfield Units
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| How can the degree of attenuation be measured so that comparisons are possible? | Hounsfield Units
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| What are Hounsfield Units are also referred to as | CT numbers or Density values
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| What are the approximate Hounsfield Units for the following objects..... Bone | 1000
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| Air | -1000
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| Water | 0
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| Blood | 100
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| Brain Matter | 50
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| Fat | -200
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| What makes the ability to measure and compare HU densities important? | By measuring HU of objects the Rad may be able to differentiate if a cyst is fluid based or etc
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| Artifacts that result from absorption of low-energy photons , which leaves higher-intensity photons to strike the detector array is called | beam-hardening artifacts
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| ____________ artifacts appear as dark streaks or vague areas of decreased density. | Beam-hardening
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| What is another term for beam hardening artifacts? | Cupping
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| What is the process in CT in which different tissue attenuation values are averaged to produce one less accurate pixel reading | Volume Averaging
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| What is the thousands of bits of data acquird by each scan is called | raw data
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| What is an interchangeable term for raw data? | Scan Data
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| ___ ____ have not yet been sectioned to create pixels. | Raw data
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| The process of using raw data to create an image is called | image reconstruction.
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| Once raw data has been processed into a pixel, and has been assigned a HU, the data included in the image is known as | Image data
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| The reconstruction that is automatically produced during scanning is often called | Prospective reconstruction
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| What is retrospective reconstruction? | The process in using the same raw data to use later to generate new images.
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| The 80s step & shoot method, limiting rotation to 360 degrees, so that the wires can unwind, is commonly referred to as | Axial scanning, Conventional scanning, or Serial scanning
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| The 90s developed continuous acquisition scanning most often called | Spiral or Helical scanning
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| What changed in 1992? | Scanners were introduced that contained 2 rows of detectors, allowing data for many slices to b acquired w/each gantry rotation.
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| The terms ___ & _____ refer to movement forward. (Toward the face) | Anterior & Ventral
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| What term describes movement towards the back surface of the body? | Posterior & Dorsal
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| What 2 terms describes movement towards the feet or down the body? | Inferior or Caudal
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| What 3 terms describes up, towards head? | Superior, Cephalic, or Cranial
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| What term refers to sides of the body? | Lateral
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| What terms describes the midline of the body? | Medial
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| What term describes away from or movement towards the end? | Distal
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| What term describes close to, or near point of attachment? | Proximal
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| The terms distal and proximal describe ____. | Extremities
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| _____ & ______ planes are parallel to the floor. | Horizontal or transverse
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| _____ & ______ planes are perpendicular to the floor. | Vertical & Longitudinal
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| What plane divides the body into anterior & posterior? | Coronal
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| What plane divides the body into right & left planes? | Sagittal
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| If the sagittal plane is located directly in the center of the body what is it referred to as | Mid-sagittal Plane
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| What is a parasagittal plane? | Located either to the left or right of the midline.
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| What plane divides the body into upper and lower halves? | Axial or cross-sectional planes
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| The plane that describes slanted or at an angle to the standard planes is.... | Oblique
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| What can you change to show the same structures in a different perspective and how is this done? | the imaging plane & by positioning the patient, gantry, or both for scanning in a different plane or by reformatting the image data.
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| Which works better? | Changing the image plane
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| What 2 distinct reasons would you change the scanning plane? | 1) If anatomy of interest lies vertically rather than horizontally
2) To reduce artifacts created by surrounding structures
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| How are x-ray photons created? | When fast moving electrons slam into a metal target.
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| The kinetic energy, the energy of motion, of the electrons is transformed into _______ ________. | electromagnetic energy
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| What does the x-ray tube have that provides the electrons that create the x-ray photons? | A filament
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| How does the filament work? | It heats, until electrons boil off, hovering around the filament.
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| What is the group of electrons surrounding the filament referred to as | Space cloud
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| What does the generator produce and transmit to the tube? | High voltage or kV
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| The high voltage / kV propels the electrons from the filament to the _____ | Anode
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| What is the term to where the electrons hit the anode & produce the x-ray beam? | Focal spot
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| The quantitiy of electrons is propelled and controled by | the tube current or mA (miliamperes)
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| mA is measured in | thousandths
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| Increasing _____ , increases ______, with which the electrons hit the target and increasing the x-ray beam. | voltage, energy
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| What controls the intensity of the xray beam? | kV
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| The ability of the tube to withstand the heat is | heat capacity
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| The ability to rid itself of heat is | heat dissipation
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| Each detector cell is sampled and converted to a digital format by the | Data Acquisition System (DAS)
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| What is considered the brain & receives the transmitted digital data? | Central Processing Unit (CPU)
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| What are the 3 general segments of the CT process? | 1) Data Acquisition
2) Image Reconstruction
3) Image Display
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| What happens in the following stages: Data Acquisition? | Get Data
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| Image Reconstruction? | Use Data
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| Image Display? | Display Data
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| Who invented CT? | Godfrey Hounsfield & Allan Cormack
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