Chapter 8: Radiographic and Fluoroscopic Equipment

The x-ray tube has a positive and negative side to its operation. Because of this, the x-ray tube is considered to electrically be a

• diode

• tetrode

• microprocessor

• invertor

Answer explanation

By design, x-ray tubes possess electrical polarity in that one side of the tube is positive (anode) and the other negative (cathode). This diode polarity is critical to its operation as a large electrical potential is created between its poles during exposure.

Newer fluoroscopic system designs utilize flat-panel digital detectors for both static and dynamic imaging. Depending upon the design, the X-ray tube can be positioned above or below the patient. If the X-ray tube is above the patient during fluoroscopy, a key point to remember is that

• 
  

  • there is an increase in image resolution because of tighter collimation.

• the x-ray tube can be disengaged from the detector to permit angled fluoroscopy.

• there is a loss of resolution due to the increased SID.

• the scatter radiation is more intense to the operator at the waist and trunk level.

Answer explanation

An alternative R/F system design positions the X-ray tube above the patient and fluoroscopic detector below. An important consideration with this design, is the scatter radiation coming from the patient during fluoroscopy since it is more intense at the operator’s waist and head level. Because of this, persons standing next to the patient during fluoroscopy should be aware of exposure to their necks and eyes particularly and use appropriate lead protection.

Another term for automatic collimation is

• positive beam limitation.

• electronic masking.

• coning.

• electronic shuttering.

Answer explanation

Most X-ray machines are equipped with an automatic collimation system that performs positive beam limitation (PBL). This feature allows the X-ray unit to detect the size of the image receptor the radiographer is using and automatically collimates to a size not larger than the image receptor.

A popular feature on X-ray generators that reduces repeat exposures caused by inaccurate exposure technique selection by technologists is

• pulse progressive radiography (PPR).

• automatic exposure control (AEC).

• positive exposure limitation (PEL).

• anatomically programmed radiography (APR).

Answer explanation

For many procedures, exposures are terminated using automatic exposure control (AEC) circuitry. The technology of AEC has simplified exposure technique selection and improved the consistency of image quality

What does mA stand for?

(a)  

All of the following are required features of a modern mammography unit except

• low kVp generation (20-40 kVp) to optimize breast tissue visualization.

• a large x-ray tube focal spot to permit field coverage.

• right-angle breast compression.

• 
  AEC.

Answer explanation

Mammography machines are designed with several unique x-ray system features. The x-ray tube uses a rotating molybdenum/rhodium anode with a very small, fractional focal spot and because breast tissue is easy to penetrate, kVp values are typically in the range of 20-40 kVp. Breast compression is at a right-angle to the chest wall and operator-controlled with a foot switch and manual adjustment.

A key distinctive characteristic of MR scanning is that the source of the MR signal to create the image is the

• external coil.

• gantry coil.

• 
  gradient coil.

• 
  patient.

Answer explanation

A key distinction with MR when compared to x-ray is that with MR, the patient is the source of the signal used to create an image. With x-ray, the x-ray tube is the source and it relies upon the process of differential absorption, as x-ray energies are transmitted through tissues and detected.

Portable digital DR detectors are very popular for portable radiographic imaging. It is important to remember that

• wireless detectors use batteries for charging.

• a communication connection must exist between the detector and X-ray generator.

• 
  they must have a small electrical charge applied to the TFT layer.

• All of the these.

Answer explanation

DR detectors require the application of electricity in preparation for an x-ray exposure. To achieve this, manufacturers have designed DR panels that are electrically connected to a power source through a hard-wired connection flexible cable (tether) or rechargeable battery pack. The charge is placed on the TFT layer just prior to and during the X-ray exposure and an electronic communication between the panel and generator is required.

Images acquired in a CT scan are obtained in the patient’s ____________ plane.

• mid-sagittal

• axial

• coronal

• 
  sagittal

Answer explanation

CT scanners acquire hundreds of projections (views) as an x-ray tube and x-ray detector on a ring assembly, rotates around a recumbent patient. Images are acquired in a transverse (axial) plane and the data sets can be reconstructed in any body plane desired through the power of sophisticated computers and software programs.

The latent image in computed radiography is actually _____ within the barium fluorohalide material.

• sensitivity specks

• silver halide specks

• electron traps

• detector elements

Answer explanation

PSP detectors (CR) capture the energy of the remnant beam and store it for a period of time in “electron traps.” These electron traps represent the latent image.