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Questions and Answers
What factor determines the radiodensity of each chosen body plane in a CT scan?
What factor determines the radiodensity of each chosen body plane in a CT scan?
- Temperature of the body
- Amount of air, water, fat, or bone in that element (correct)
- Distance from the X-ray tube
- The speed of rotation of the X-ray tube and detector
In a CT scan, how are areas of great absorption and areas with little absorption generally represented?
In a CT scan, how are areas of great absorption and areas with little absorption generally represented?
- Areas of great absorption are black, and areas with little absorption are white
- Both areas of great and little absorption are black
- Areas of great absorption are relatively white, and areas with little absorption are black (correct)
- Both areas of great and little absorption are white
Which imaging technique is faster than MRI according to the text?
Which imaging technique is faster than MRI according to the text?
- PET scan
- X-ray
- Ultrasound
- CT scan (correct)
What is a significant disadvantage of CT scans compared to plain films?
What is a significant disadvantage of CT scans compared to plain films?
Which factor makes CT scans less effective in providing good tissue definition compared to MRI?
Which factor makes CT scans less effective in providing good tissue definition compared to MRI?
What allows CT scans to image bony features effectively according to the text?
What allows CT scans to image bony features effectively according to the text?
Which term is used to describe tissues that appear bright on MRI images?
Which term is used to describe tissues that appear bright on MRI images?
What is a disadvantage of MRI compared to other imaging techniques?
What is a disadvantage of MRI compared to other imaging techniques?
Which imaging technique has tracers with a very short half-life that emit positrons?
Which imaging technique has tracers with a very short half-life that emit positrons?
What is a characteristic of SPECT scans in comparison to PET scans?
What is a characteristic of SPECT scans in comparison to PET scans?
In MRI imaging, what term is used for tissues that appear darker than the surrounding tissues?
In MRI imaging, what term is used for tissues that appear darker than the surrounding tissues?
Which imaging technique shows areas of high metabolic rate in tissues after administration of 18-fluorodeoxy-D-glucose?
Which imaging technique shows areas of high metabolic rate in tissues after administration of 18-fluorodeoxy-D-glucose?
What is the main advantage of MRI compared to CT imaging?
What is the main advantage of MRI compared to CT imaging?
Why can moving fluids like blood appear black on T1-weighted MRI images?
Why can moving fluids like blood appear black on T1-weighted MRI images?
Which of the following is NOT a disadvantage of MRI imaging?
Which of the following is NOT a disadvantage of MRI imaging?
What is a significant drawback of MRI compared to CT imaging in terms of patient experience?
What is a significant drawback of MRI compared to CT imaging in terms of patient experience?
Which of the following is NOT an advantage of MRI imaging?
Which of the following is NOT an advantage of MRI imaging?
Why can MRI not image patients with metallic implants or foreign bodies effectively?
Why can MRI not image patients with metallic implants or foreign bodies effectively?
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Study Notes
Computed Tomography (CT) Scan
- A beam of X-rays passes through the body as the X-ray tube and detector rotate around the body
- The energy absorptions are measured, recorded, and analyzed by a computer to determine the radiodensity of each body plane
- Radiodensity is determined by factors such as the amount of air, water, fat, or bone in that element
- The computer produces a planar image displayed on the monitor
Image Display
- CT scans are displayed as if the viewer were standing at a supine patient's feet, looking at the patient from an inferior view
- Areas of great absorption are relatively white, and those with little absorption are black
Advantages and Disadvantages of CT
- Advantages: lower costs than MRI, availability, 3-D capabilities, ability to image bony features, and faster than MRI
- Disadvantages: high dose of X-rays, artifacts (motion, scattering), and poor tissue definition compared to MRI
Magnetic Resonance Imaging (MRI)
- Based on three properties of protons in a particular region: T1 and T2 relaxation, and proton density
- T1 and T2 relaxation produce T1- and T2-weighted images
- Moving fluids tend to appear black on T1-weighted images despite high proton density
Advantages and Disadvantages of MRI
- Advantages: lack of ionizing radiation, ability to image all planes, and high-resolution imaging of soft tissues
- Disadvantages: high cost, inability to image patients with metallic implants or foreign bodies, inability to image bone well, longer procedure time, and potential for claustrophobia and artifacts
Nuclear Medicine Imaging
- Provides information about the concentration of trace amounts of radioactive substances introduced into the body
- Substances can be introduced intravenously or orally
- Radionuclide is usually tagged with a compound that is selectively taken up by the organ of study
Positron Emission Tomography (PET) Scanning
- Uses cyclotron-produced isotopes with very short half-life that emit positrons
- Evaluates the physiologic function of organs on a dynamic basis
- Glucose uptake in tissues after administration of 18-fluorodeoxy-D-glucose shows areas of high metabolic rate
Single-Photon Emission Computed Tomography (SPECT) Scans
- Similar to PET scan, but uses tracers with longer half-life
- Less costly, requires more time, and has lower resolution than PET scans
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