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CT
| Question | Answer |
|---|---|
| What Greek term is “tomography” derived from and what does it mean | The term “tomography” is derived from the Greek word “tomos” meaning section or slice |
| Conventional tomography is still used in what specific situations | dental imaging or IVPs |
| Anatomy at the target level remains ........., while structures at different levels are ............. | sharp, blurred |
| Between what years was conventional tomography created by individuals to meet their own needs of 3-dimenstional imaging | Between 1910 and 1940 |
| Who developed and commercialize the first axial computer tomography in 1972 | Hounsfield |
| What was this scanner commonly called | EMI-Scanner or Hounsfield unit |
| True/False: In 1931 Ziedses des Plantes published an extensive and detailed study on tomography | True |
| In the 1940s, what two people would be the first to publish ideas based on the basic principles of axial tomography, even though it would be decades before the necessary developments in electronics would be available to build scanners. | Frank and Takahashi |
| What did the company EMI stand for | Electrical and Musical Industries (famous for recording the Beatles) |
| Who worked for EMI? | Godfrey Hounsfield was an engineer for EMI |
| Who developed the math used to reconstruct CT images? | Alan Cormack |
| True/False: Alan Cormack & Hounsfield shared the Nobel Prize for physics in 1979 | True |
| Summarize how CT occurs- starting with radiation attenuated by pt. | - A portion of radiation is attenuated by the patient and the remnant is measured by detectors. - The attenuated information exits the detectors in analog form. - The analog signal is converted to a digital signal. - The computer uses algorithms to rec |
| CAT Scan provides slices or sections of anatomy what planes | in the axial, sagittal, or coronal planes |
| Most images are axial, but images can be reconstructed in other planes called ....................... | multiplanar reformation |
| What are three advantages of CT over conventional radiography | 1- contrast resolution is superior 2- structures are visualized without superimposition 3- acquired data may be viewed in alternative planes |
| What is the major disadvantage to CT? | Increased patient dose |
| Another disadvantage is in modern helical CT, volume scanning with no inter-slice gap which has the possibility of........ | overlapping scans |
| True/False: The same exposure factors are used for children and adults in CT | True (this leads to unnecessary increased dose to children) |
| The effective dose in chest CT is in the order of ........mSv and in some exams like that of the pelvic region it may be around.......mSv | chest = 8mSv pelvis= 20mSv |
| How much higher is the dose in a CT chest exam compared to a routine CXR? | about 400 times more |
| Breast dose in thorax CT may be as much as, how many mGy? | 30-50mGy |
| True/False: Time and radiation dose are not proportional in modern CT scanners | True: because tubes are becoming more powerful and can give off higher bursts of x-rays to give a satisfactory image in shorter time |
| What does CAT stand for: | computer assisted tomography or Computerized axial tomography |
| What are the three major components of the CT machine: | Gantry, computer, operator console |
| What does the gantry consist of: | x-ray tube, detector array, collimators, high voltage generator, and couch |
| What is the Aperture? | central opening in the gantry |
| What component is electronically linked to the gantry for controlled movement of the scan | Patient couch or table |
| What modifications are made to the tube for CT? | similar to general x-ray tube but modifications to withstand heat capacity from increased exposure times |
| Why do multislice spiral tubes have special requirements? | Because they require high heat capacity that can be engergized up to 60 sec continuously. |
| What is the anode heat storage capacity of a multislice spiral x-ray tube? | 8 MHU or more |
| What is the anode cooling rate of a multislice spiral x-ray unit? why? | 1 MHU because the node disc has a large diameter, thicker, resulting in greater mass |
| Does a multislice spiral tube have a small or large focal spot size? why? | Small focal spot size for high spacial resolution |
| Why does a multislice spiral tube have high speed rotors? | for heat dispersion |
| Define: Detector Array | Detectors are solid-state (no moving parts) composed of photodiodes coupled with scintillation crystal materials |
| Define: photodiode | A photodiode is a type of photo detector which converts light into either current or voltage depending on the mode of operation |
| Define: Scintillation material | A scintillation material exhibits the property of luminescence when excited by ionizing radiation. Cadnium tungstate and special ceramics are current choice of crystals |
| What do solid-state detectors do? | Solid-state detectors convert transmitted x-ray energy into light, which is then converted into electrical energy and into a digital signal. |
| what does the detector array affect? | the detector array affects the patient dose and the efficiency of the CAT scan unit. |
| True/False: Scintillation is preferred to reduce dose | True |
| where is the pre-patient collimator? | at the x-ray tube |
| where is the post-patient collimator and what does it do? | at the detector, it shapes and limits beam. This collimator determines slice thickness. |
| What is the difference between analog and digital? | Analog measures data by means of physical properties along a continuous scale. Digital expresses numerical forms relating to a computer. |
| Name Three attributes of a First Generation Scanner: | - used pencil thin x-ray beam with one detector - required a 4.5 minute exposure time to gather enough info for one slice from at 180* rotation - Could only do Head Scans |
| Name Three attributes of a Second Generation Scanner: | - Greatly improved over 1st generation - produced a fan shaped xray beam with 30 or more detectors - exposure times were 15 seconds per slice or 10 minutes for a 40-slice exam |
| Name two attributes of a 3rd generation scanner: | -included a bank of 960 detectors opposite the xray tube that together rotate around the pt. in a complete 360 -scanning times were reduced significantly compared to 1st and 2nd generation |
| Name three attributes of a 4th generation scanner: | - developed in 1980's with fixed ring of 4800+ detectors surrounds pt. in full circle within gantry - single xray tube rotates around the pt. 360* - short bursts of radiation by a pulsed, rotating anode tube providing shorter scan times as little as 1 m |
| True/False: A 4th generation scanner is more advanced than a 3rd generation scanner | False: 4th is not more advanced than 3rd just different |
| What did slip-ring technology allow CAT scans to do? | to move beyond single slice acquisition. |
| What is a slip-ring? | metal rings that provide a continuous electrical connection through brushes on stationary contacts. |
| What did slip-rings replace? | High tension cables to allow for continuous rotation of the tube while pt. moves in/out of aperture |
| How is a slip-ring configured? | Its configuration is column type. Each ring lies along the drum axis. |
| True/False: the terms Helical or Spiral (vendor specific) are often used instead of volume CT | True |
| Volume CT are considered what generation scanners? | 3rd and 4th |
| Name 3 advantages of volume scanning: | - multiplanar reconstruction (MPR) - Shorter scan times -Artifacts reduced (less pt. movement) |
| True/False: Scanners developed before 1992 were single-slice scanners allowing for only one slice at a time. As technology advances multislice scanners can now slice 64 slices per tube rotation. | True |
| 4 Advantages of multislice scanners: | - Shorter times - decreased amount of IV contrast due to increased speed - improved spacial resolution - improved image quality |
| 2 disadvantages of multislice scanners: | - increased cost - reviewing and archiving large volume cases |
| True/False: images not stored in PACS may be stored on optical discs and hard drives as well as hard copies such as laser sensitive film | True |
| In image reconstruction incident radiation and remnant radiation is measured by detectors in analog form and then converted to digital signal by what? | analog-to-digital converter (ADC) |
| Digital values are used in the reconstruction process using a series of what? | a series of algorithms |
| The display matrix is composed of pixels. Each pixel is a ...... representation of a ......volume of tissue in the CT slice. | 2-D representation of a 3-D volume of tissue |
| What is a voxel? | 3-D tissue volumes with height, width and depth. |
| How is the depth of a voxel determined? | The slice thickness |
| What are CT numbers | Shades of gray that are assigned a numerical value |
| What is the baseline CT number? and what does it represent? | 0 which is water |
| What is the CT value for cortical bone | 1,000 to 3,000 |
| What is the CT number for air? | 1,000 |
| what is between these given CT number? | varying degrees of attenuation |
| What refers to the range of CT numbers that are displayed as shades of gray? | Window width |
| Do wide or narrow windows have more CT numbers | wide |
| what do wide windows represent? | long scale contrast or more greys |
| Define pitch: | the amount of anatomy covered during an exam. It is a ratio reflecting the relationship between table speed and slice thickness |
| what does a 15:1 pitch ratio mean? | 15mm per second with a slice thickness of 10mm |
| what does a 2:1 ratio run the risk of? | Missing pathology |
| What would a 5:1 ratio do? | increase patient dose |
Created by:
rachelreilly
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