RAD 111 Test 3 Study Guide
Intercepts the x-ray photons that are able to exit the patient (remnant radiation). Converts the energy of x-rays into an image.
Image receptor (IR)
IR system that uses photostimulable storage phosphor (PSP) technology . Uses a cassette with imaging plate (IP) and creates an image through computer software. The IP is reusable.
Digital Receptor (DR) Systems
Classes of Diagnostic Radiographic Imaging.
- Computed Radiography (CR)
- Digital Radiography (DR)
- Fluoroscopic imaging
(NOTE: there are also cassette-based and cassette-less systems)
Requirements for x-ray production.
- Vacuum inside x-ray tube
- Source of electrons
- Method to accelerate electrons to great speed
- Method to stop electrons
Source of electrons.
- Filament (Within the cathode)
What is the method to accelerate electrons?
Method to stop electrons.
Target (Anode is the target)
How x-rays are produced.
When fast electrons hit matter. Fast electrons are produced in a high vacuum tube by setting them free from the cathode, accelerating them through a high voltage, and having them hit the metal anode.
What is the reason an x-ray tube must have a vacuum?
The vacuum removes all of the air so gas molecules will not interfere with the production of x-rays
When electrons strike a target, x-ray photons are produced. What percentage of this production is actually x-rays and what percentage is heat?
(This x-ray beam is controlled by technical factors set by the radiographer)
- Less than 1% x-rays
- Remaining 99% heat
The radiation (beam of photons) before it interacts with a patient's body.
(Leaves the tube)
Type of radiation that provides little diagnostic information to image. Detracts from image quality with the creation of 'fog'.
Used to reduce scatter. It intercepts a portion of the remnant radiation and improves image quality. Requires higher exposure technique when used.
Radiation that does not exit the patient.
Radiation that exits the patient and creates an image in the IR. Creates chemical changes within the receptor that are invisible.
Loss of radiation energy as a result of passing through an absorbing material (body).
Degree of attenuation that occurs in radiopaque matter. (X-rays cannot pass through.)
Degree of attenuation that occurs in radiolucent matter.
Invisible image created after exposure but before processing.
(It must be processed to convert it to a visible image)
Prime technical exposure factors that a radiographer has direct control over.
- Milliampere-second (mAs)
- Kilovoltage peak (kVp)
- Source-to-image distance (SID)
Determines how many x-rays are produced by the x-ray tube.
(It directly controls the quantity of x-ray photons produced)
Measure of the electrical pressure forcing the current through the tube. It controls penetrating ability of the beam.
(It affects the quality and quantity of x-ray photons produced)
Distance between point of x-ray emission in the x-ray tube (focal spot) and the IR.
(It affects intensity of radiation that reaches the IR as well as the geometric properties of the image)
A proper balance between __________ and __________ is required for optimum image quality.
- Photographic qualities
- Geometric qualities
Affects visibility of the image.
Contribute to image quality by affecting image resolution, size, and shape. Affect sharpness and accuracy of the image. Also known as recorded detail, sharpness of detail, and definition.
Factors affecting recorded detail
- Object unsharpness
- Focal spot size
- Material unsharpness
The two primary image photographic quality factors.
- IR exposure/Density
Most common cause of image unsharpness.
(Caused by voluntary and involuntary patient motion)
Loss in resolution caused by the inherent shape of the patient's anatomic structures relative to the divergence of the x-ray beam.
Optimum use of __________, __________, and __________ can lessen object unsharpness.
- Focal point size
- SID (Increased SID makes image sharper)
The smaller the focal spot size, the __________ the detail.
Overall darkness or blackness of an image. It is directly related to x-ray exposure hitting the IR.
Image density is referred to as __________ in the digital world.
Primarily affects image density/IR exposure.
- mA (milliamperage)
- S (exposure time)
There is a __________ relationship between mAs and density.
(Doubling mAs will double density)
mAs is the product of __________ and __________.
(mA X time=mAs)
- Increasing kVp 15% will __________ IR exposure.
- Decreasing kVp 15% will __________ IR exposure.
What must you do to MAINTAIN IR exposure if you increase kVp by 15%?
Must half mAs
To maintain the original IR exposure, what new value of mAs is necessary when changing from 75 kVp and 50 mAs to 86 kVp?
(Example in book pg. 74)
(Because the kVp was increased 15% the mAs must be halved to maintain the IR exposure)
Relationship between distance and intensity.
(Intensity increases; distance decreases)
Law that deals with intensity.
Inverse Square Law
Inverse Square Law formula.
I1 / I2 = D2 2 / D1 2
Formula used when dealing with mAs and distance.
Direct Square Law
Direct Square Law formula.
mAs1 / mAs2 = D1 2 / D2 2
Can improve image quality and reduce dose as well as control scatter.
Two types of primary beam modification.
- Beam limitation
Beam modification that involves use of attenuating material (aluminum) and removes low energy x-ray photons to decrease patient exposure. The more __________ used, the less intense the beam.
Beam modification that decreases patient dose as well as improving image quality.
Beam limitation (collimation)
Term used for the amount of absorbing material that will reduce the intensity of the x-ray beam to half its original value. It is a way to express x-ray beam quality.
Two methods of digital image capture. Both use thin-film tansistor (TFT) technology.
Type capture that x-ray photons are immediately converted into an electrical signal.
Type capture that x-ray photons are converted to light and then converted into an electronic signal.
Determines image quality in digital cassette-less systems.
Possess greater exposure latitude than conventional film-screen systems.
A numeric representation of total x-ray exposure to the receptor. It is not an indicator of the patient's absorbed dose.
Exposure Index (EI)
Digital radiography key features.
- Uses no cassettes
- Image is displayed in seconds
- Detectors can be direct or indirect
- Uses thin-film transistors (TFT)
- Image brightness is not the same as radiographic density and is not related to exposure
Any misrepresentation of the true size or shape of the patient's anatomy.
Two types of distortion.
Size distortion is minimized by using _________ and __________.
- Longer SIDs
- Minimum OIDs
Distortion controlled by alignment of central ray, patient's anatomy, and IR. It is also called 'true distortion'.
Accomplished by angling or rotating the patient relative to the central ray. Helps overcome superimposition of anatomic structures.
During __________, x-ray exposures are much less than radiographic exposures. Can observe the body's physiologic actions. Images taken are digital images and can be played back for review or sent to an archival system for long term storage (PACs)