Mobile Radiography Flashcards
List 4 factors that affect the resultant image quality?
- Contrast
- Dynamic range
- Spatial resolution
- Noise
- Artifacts
What is the process of Photostimulabe Luminescence?
It is when the image receptor (photostimulable phosphor) absorbs the radiation and traps electrons at high energy levels under exposure.
What are the two methods of image acquisition in DR?
Direct & Indirect
True or False?
In DR image acquisition, the imaging ‘plate’ is read by a laser which releases high energy electrons to their original state ready for the next exposure.
False.
This is part of the image acquisition process in CR.
Explain the difference between Mobile Radiography and Portable X-rays
Mobile radiography equipment is motor driven and too heavy to move. It requires a mains input to charge and is for hospital use only.
Portable X-rays, however, can be carried or set up and produce a low exposure output. This is why they are used for home visits, veterinary work and the military.
What are 3 disadvantages of portable X-ray units.
- Low kV which requires high mAs
- Short exposure times
- Cannot be used for a long period of time without causing damage
- Restricted exposure factors
List the 5 features of a high frequency generator and their functions.
- Mains AC
- Rectifier (converts AC to DC)
- Inverter (‘chopper’ converts DC/HF)
- High energy voltage transformer (steps up AC then converts back to DC)
- X-ray tube
List 3 advantages & disadvantages of digital mobile X-ray.
+Images available within 5 seconds
+Uses PACS
+Images and patient data combined in same file
+Image transmission via DICOM interfaces
- Operator fatigue due to device weight
- Requires battery recharging
- Can raise body temperature (Thermal effect)
- Needs often disinfection
SNR is a measure of true signal to noise, what factors affect it and how?
- Increasing the mAs improves SNR
- Improved by using high quality sensors that transfer X-ray photons into light photons
- A low SNR results in a grainy appearance
Explain the process of indirect image acquisition in DR.
- X-ray photons encounter a Caesium Iodide (CsI) scintillator which converts them into light
- The needle-like CsI structure minimises scatter at this step
- The light reaches a low noise photodiode array and is converted into electrical charge
- Each photodiode represents a single pixel and produces an electrical charge that is read out digitally before being sent to the image processor
Name the 4 components of mobile X-ray equipment.
- High frequency generator
- Drive unit
- Tube support
- Collimator
With restricted X-ray tube movement…
- ..The patient to be confined in small cubicles
- ..Infection control is difficult to observe
- ..Can damage furniture
- ..Is challenging with ‘no touch’ patients
Describe direct DR image acquisition.
Directly converts the absorbed X-ray into a proportionally sized electrical charge with no intermediate scintillating step using semiconductor material, Amorphous Selenium.
List the 6 features of a DR mobile unit.
- Soft drive control
- Collapsible column
- Front bumper sensor
- Flat panel detector
- Touch screen monitor
- Image processing ( brightness, contrast, edge enhancement)
List 4 advantages of portable units.
- Speed
- Reduces transport and extra patient movement
- Cost effective
- Radiation safety
