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