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Chapter 6 & 7

Key Words

Anatomically programmed radiography a programmable chart within the computer of the x-ray machine in which techniques for each body part and technique is programmed in to the machine
Automatic exposure control an electronic circuit within the x-ray machine that automatically terminates the exposure when predetermined quantity of x-rays has been detected
Autotransformer a single coil transformer that serves three functions, provides the means for kVp selection, provides for fluctuation in the incoming line, supplies power to the other parts of the x-ray circuit
Back-up timer a timer that backs up the AEC, to ensure that the patient does not get overexposed
Diode an electronic device that permits current to flow in one direction only; prevents back flow. When one used is placed between the anode and the transformer and when two is used the second is placed between the cathode and anode
Electric ground a wire is connected to the mA meter that absorbs or drain off excess electric charges
Electronic timer capable of ultrashort exposure times and are designed for 3 phase and high frequency ge nerators
Exposure switch completes the circuit so that x-rays are made
Exposure time the time in which x-rays are being made
Full wave rectification utilizes the entire electric cycle, the use of 4 diodes in a circuit and redirecting the current during the negative half of the electric cycle so that current will flow in the same direction during both halves of the cycle
Heat unit (HU) the measurement of heating in the x-ray tube, all tubes have a maximum heat limit
High frequency x-ray generator a unit that employ special inverter circuit that convert rectified AC into a series of square pulse that results in even less exposure time and lower patient dose
Ionization chamber a chamber enclosed volume of dry air connected into the circuit, the air is ionized by remnant radiation, a minute amount of current flows through the circuit when a specific quantity of current has been measured the exposure is terminated
Phototimer a fluorescent screen under the Bucky tray that gives off light when exposed to radiation that has passed through the patient and IR that terminates the exposure after a specific amount of light has been detected
Rectifier a unit that makes the current flow in one direction
Rheostat (mA selector) varies the resistance in a circuit
Rotor/prep/ready/standby switch the button in which starts the rotor to heat the filament in preparation for exposure
Self – rectification primitive and inefficient form of rectification in which the x-ray tube itself controls the direction of current flow
Single phase current a current in which is only using one phase of the alternating current results in a pulsating x-ray beam
Synchronous timer controlled by a small electric motor rotating at 60 revolutions/sec time settings will be stated as fractions and multiples of 1/60 second the duration of an electric impulse
Three phase current alternating current is generated in 3 overlapping cycles that produce a more constant & efficient voltage and when rectified is in a waveform that has the appearance of a ripple with no real low points
Tube rating chart a graph that is made by the company that is used to determine if the mA and time chosen will be a safe exposure
Line meter a voltmeter wired to measure the incoming voltage
Rectification – to make right; the process of changing alternating current into direct current so the current flows only in one direction
Contrast the difference in radiographic density between any two adjacent portions of the image
Density (radiographic) the overall blackness or darkness of the radiograph
Distortion difference between the actual subject and its radiographic image
Elongation projects the object so it appears longer than it really is
Foreshortening projects the part so it appears shorter than it really is
Involuntary motion movements of the body in which the patients has no control over such as tremors, peristalsis and heart beat
Magnification result of the geometry of the image set up
Object-image distance the relationship between the distance of the subject and the IR
Over exposed a film that is too dark
Penetrometer (step-wedge) a solid piece of aluminum with steps of varying thickness
Fog unwanted exposure to the film
Penumbra the unsharp edges of an image; the blur; geometric unsharpness
Quantum mottle a grainy or mottled (spotty) appearance of the image usually caused by the use of an insufficient radiation exposure for the boy part or for the requirement of the image receptor. Not desirable in creating x-ray
Radiographic contrast the overall contrast seen in the radiographic image
Recorded detail the sharpness of the structures in the image the terms detail, sharpness and resolution are sometimes used to refer to recorded detail
Shape distortion result in unequal magnification of the actual shape of the structure
Short scale contrast range of densities are few (short) (shades of gray are few)
Size distortion form of magnification
Source-image distance the distance between the x-ray tube and the IR
Subject contrast the range of differences in the intensity of the x-ray beam after it exits the patient
Tissue density the mass density of the body part
Umbra the actual anatomic area, body part or structure
Underexposed a film that is too light
Voluntary motion motion that is normally controllable
Long scale contrast has many densities (shade of gray)
Inverse square Law the relationship between SID & beam intensity; A law that states the x-ray intensity is inversely proportional to the square of the distance from the source I1/I2 = SID22/ SID12
Control console the part of the x-ray equipment where the factors are set to take a radiograph and is behind a lead barrier
Filament circuit the subcircuit of the circuit that supplies and controls the heat required by the x-ray tube filament for thermionic emissionbefore processing; used to measure contrast
Low voltage circuit the circuit between the alternating current (AC) power supply and the primary (input) side of the high voltage (step-up) transformer
High voltage circuit subcircuit of the x-ray circuit that begins and ends with the secondary side of the step up transformer, it increases the voltage to make x-rays
Line voltage compensator a device that ensures that the outgoing voltage is accurate regardless of fluctuations in the incoming line
kVp meter device that measures the voltage output from the autotransformer
Milliammeter device that is connected midpoint of the secondary side of the step-up transformer that measures the current flowing in the high-voltage circuit during exposure
Alternating current the polarity of the power source reverses at regular intervals
Direct current current that flows only in one direction
Falling load generator x-ray units that begin at the highest mA compatible with the desired filament and focal spot selection. mA decreases during exposure if necessary to avoid over heating
Film screen contact uniform tight contact with two intensifying screens with the film between them
Created by: mdtodd