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Eq Op & Qc
equipment operation and quality control
| Question | Answer |
|---|---|
| Safe principles of operation RTs should practice | preventive maintenance and quality control (pg. 495) |
| This is required by hospital accrediting agencies | Quality QC program-properly documented, ongoing, effective (pg. 495) |
| QC program team should include these people | radiographers, a designated QC technologist, service engineer, and a medical physicist (pg. 495) |
| Serves as a guide to good medical radiation practices by describing federal regulations on equipment design, performance, and use. | National Council on Radiation Protection and Measurements (NCRP) Report No. 102 (pg. 495) |
| Responsibilities of the QC technologist, medical physicist, and service engineer for quality control. | equipment testing, correlation of test results, any necessary corrections, accurate documentation of activities (pg. 496) |
| Kilovoltage | -Controls contrast -Selected and actual values should not differ by more than 4 kV for general diagnostic equipment -Should not differ by 5% for mammography equipment (pg. 496) |
| Milliampere | -Controls density -Tested with an aluminum step wedge -Shows RECIPROCITY LAW -LINEARITY can be tested using a digital dosimeter (pg. 496) |
| mA | related to patient dose |
| What is timer accuracy related to? | patient dose and density (pg. 497) |
| Timer QC | -Spinning top test, annually -Selected exposure time should be within 5% of actual time (pg. 497) |
| What is the focal spot size related to? | the degree of geometric blur, also known as edge gradient or penumbra(pg. 497) |
| Manufacturer tolerance for focal spot size | -50% (pg. 497) -size increases with age -Test equipment when new and annually |
| Focal spot QC tests | -Pinhole camera-difficult -Slit camera-measures length and width -Star-pattern type resolution device (pg. 498) |
| What is used to clean an intensifying screen? | nonabrasive, lint-free cloth with a special antistatic screen cleaner (pg. 499) |
| What does poor screen contact do for an image? | gives poor recorded detail (pg. 498) |
| T/F Lead aprons and gloves should be hung appropriately when not in use and cleaned with a damp cloth when soiled. | True (pg. 499) |
| T/F When one bulb in a bank of illuminators requires changing, all the bulbs should be changed to guarantee uniform brightness. | True (pg. 499) |
| PSPs should be cleaned how often? What with? | -Monthly -anhydrous ethanol (pg. 499) |
| The typical PSP lasts how long? | 10,000 exposures (pg. 500) |
| How often is the laser on a CR sytem checked? | Monthly for signs of jitter (pg. 499) |
| What does contrast evaluation do for a CR/digital system? | confirms the consistency of x-ray exposure, CR reader, workstation display, and hardcopy printer (pg. 499) |
| What does a sharpness test evaluate for CR/digital systems? | x-ray tube performance, CR reader optics, monitor display, and hardcopy printer (pg. 499) |
| Define reproducibility | consistency of x-ray tube output )pg 497) |
| Reproducibility test | a group of technical factors is selected and a series of at least 5 exposures is made, digital radiation meter should not vary more than 5% (pg 497) |
| Half-value layer | -provide beam quality information different from the kV testing -the thickness of any absorber that will reduce x-ray beam intensity to 1/2 the original value (pg 497) |
| How is HVL determined? | measure the beam intensity without an absorber and then record the intensity as successive millimeters of aluminum are added to the radiation field (pg. 497) |
| What does it mean if HVL decreases? | indication of decrease in actual kV (pg 497) |
| What does it mean if HVL increases? | indicates the deposition of vaporized tungsten on the inner surface of the glass envelope (as a result of tube aging) or an increase in the actual kV (pg 497) |
| What is HVL influenced by? | type of rectification, total filtration, and kV (pg 497) more kV=more energy=greater HVL thickness required to cut intensity in half |
| 3 common examples of digital imaging | MRI, CT, and CR (pg 290) |
| 3 components of CT | -Gantry- x-ray tube, detector array, high voltage generator -Operating console -Computer (pg. 290) |
| Transformer law | Vs/Vp=Ns/Np also may be helpful to know: Ns/Np=Ip/Is (pg. 291) |
| What is the difference between a motor, stator, rotor, and generator? | Motor-used to convert electrical energy to mechanical energy Stator and Rotor-two parts of induction motor Generator-converts mechanical energy to electrical energy )pg 294) |
| Components of digital imaging include: 1.computer manipulation 2.formation of electronic image on radiation detector 3.formation of x-ray image on IR A. 1 only B. 1 and 2 C. 2 and 3 D 1, 2, 3 | B. 1 and 2 only 3 is right for traditional x-ray with film (pg. 278) |
| Properties of x-rays | -travel in straight lines -travel at the speed of light -electronically neutral -have a penetrating effect on all matter -have a physiological effect on living tissue -have an ionizing effect on air -have a photographic effect on film emulsion |
| Properties of x-rays continued | -cannot be focused -have a spectrum of energies -are unaffected by a magnetic field -not perceptible by the senses (pg 300) |
| T/F In order for the projected light beam to be the same size as the x-ray beam, the focal spot and the light bulb must be exactly the same distance from the center of the mirror. | True (pg 302) |
| Rectifiers are _________ made of semi-conductive materials such as silicon, selenium, and germanium that conduct electricity in only one direction. | solid-state diodes (pg 302) |
| Spinning top test | checks for timer accuracy or rectifier failure, series of black dots (pg 302) |
| Total brightness gain is the product of | minification gain and flux gain Flux gain-ratio of the number of x-ray photons at the input phosphor compared to the number of light photons at the output phosphor Minification gain-decrease in image size from input phosphor to output phosphor (pg 302 |
| T/F Each time an x-ray exposure is made, less than 1% of the total energy is converted to x-rays and the rest is converted to heat. | True (pg 303) |
| Define current and voltage | Current-amount of electric charge flowing per second Voltage-potential difference existing between two points (pg 303) |
| Define resistance and capacitance | Resistance-property of a circuit that opposes current flow Capacitance-quantity of stored electricity (pg 303) |
| Rare earth phosphors used in intensifying screens | gadolinium oxysulfide lanthanum oxybromide cesium iodide-preferred for input phosphor of II (pg 304) |
| Formula for heat units (HU) | mA x kVp x time -single phase mA x kVp x time x 1.35 -3 phase 6 pulse mA x kVp x time x 1.41 -3 phase 12 pulse (pg 304) |
| A technique chart is strongly recommended for use with AEC. What should be indicated? | Optimal kVp, which photocells should be selected, and backup time that should be set (pg 305) |
| Define minimum response time | minimum reaction time, length of the shortest exposure possible with a particular AEC (pg 306) |
| Capacitor-discharge mobile x-ray unit | -use direct current -x-ray tube is grid controlled, permitting very fast and short exposure times -permit only limited mAs values per charge -has a capacitor, or condenser, which is given a charge and then stores energy until used to produce xrays (pg |
| battery powered mobile x-ray unit | -very heavy -carries its heavy duty power source -capable of storing a large mAs capacity for extended periods of time -12 hours required for a full charge (pg 306) |
| How is mA increased? | As heat is increased, more electrons are released, and mA increases. (pg 307) |
| Minification radiography may be used to show small, delicate structures that are difficult to image with conventional radiography. What is needed to maintain image sharpness? | a fractional focal spot .3mm or smaller (pg 307) |
| What is the difference in transformers and resistors? | Transformers (mutual induction) change voltage and current to useful levels. Resistors (rheostats or choke coils) circuit devices used to vary voltage or current. (pg 307) |
| What are rectifiers and solid-state diodes? | Rectifiers-change AC to unidirectional current by allowing current to flow through them in only one direction Solid-state diodes-types of rectifiers used in today's x-ray equipment (pg 307) |
| Rheostat | type of variable resistor that is used to change voltage or currant value (pg 308) |
| Fuse | device used to protect the circuit elements from overload by opening the circuit in the event of a power surge |
| Cassette front material | Bakelite and magnesium -sturdy material with a low atomic number (pg 310) |
| List the voltage ripple percentages | 100% single phase half wave 100% single phase full wave 13% 3 phase 6 pulse 4% 3 phase 12 pulse <1% high frequency |
| define thermoionic emission | when the cathode filament is heated to incandescence and releases electrons |
| isotropic emission | electrons being released in all directions |
| List how xrays, light and electrons flow through image intensifier | At input phosphor xrays are converted to light. At photo cathode light is converted to electrons. At the output phosphor electrons are converted to light. |
| AEC differences ionization chamber | Ionization chamber-under tabletop above IR, part is centered over this and radiographed, exposure terminates after a predetermined amount of ionization has occured |
| AEC differences phototimer | Phototimer-fluorescent screen, under cassette, exposure terminates after a predetermined amount of fluorescent light has been seen by the photocell |
| How are images displayed from an image intensifier? | series of lenses or fiberoptic link TV camera tube(Plumbicon or Vidicon) converts output phosphor image to electrical signal. TV monitor(cathode-ray tube) converts electrical signal to visible light image. |
| Spinning top test numbers | single phase-120 useful xray impulses per second. 1/4 second=30 dots. minor discrepency means timer malfuction. exactly 1/2 correct number of dots means rectifier problem. Half wave rectified=60 pulses |
| synchronous timers for 3 phase equipment | 1 second should be 360 degree arc |
| Primary components of xray circuit | main switch/circuit breaker, autotransformer, kV selector switch, line voltage compensator, timer, primary coil of HV transformer(step up), exposure switch, kV meter |
| Secondary components of xray circuit | mA meter(grounded at midpoint of secondary coil), rectifiers, x-ray tube, secondary coil of HV transformer |
| Filament circuit components of xray circuit | mA selector, focal spot selector, step down transformer |
| The _______ the focal spot, the more limited the anode is with respect to the quantity of heat it can safely accept. | Smaller. Actual focal spot can be increased while still maintaining a small effective focal spot. Steep angle and large focal spot=greatest heat-loading potential |
| Compton scatter | high energy, outer shell electron, retains most of its energy, image fog and occupational exposure (esp in fluroscopy) |
| Photoelectric effect | low energy, inner shell electron, uses all its energy, more likely to occur in absorbers with high atomic number (bones), patient dose |
| Characteristic xrays | 10-30% of xrays,electron fills vacancy and releases energy |
| Bremsstrahlung xrays | 70-90% of xrays, braking, attracted to nucleus, slows down and changes direction |
| Image intensifier's input phosphor is generally composed of | Cesium iodide used to be zinc cadmium sulfide Calcium tungstate was in cassette intensifying screens. |
| Xray tubes used in CT imaging systems must be capable of 1.high short-exposure rating 2.tolerating millions of heat units 3.high-speed anode rotation a.1 only b.1 and 2 c.1 and 3 d. 1, 2, 3 | D, all of the above |
| The total number of xray photons produced at the target is contingent on the 1.tube current 2.target material 3.square of teh kilovoltage a.1 only b.1 and 2 c.2 and 3 d. 1,2, and 3 | D all of the above |
| QA being performed on a 3 phase full rectified unit. Synchronous spinning top test performed using 300 mA, 60 ms, 22 degree arc is observed. What should the arc angle be? | 360 degree x .06 seconds=21.6 degrees |
| Which of the following statements regarding dual x-ray absorbtiometry is true? 1.it is a low dose procedure 2.two x-ray photon energies are used 3.photon attenuation by bone is calculated a.1 only b.1 and 2 c.1 and 3 d.1,2, and 3 | D. All of the above DXA scans |
Created by:
mmarnold2
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