Challenge questions for Digital Fluoro

Question 1

Define Digital subtraction angiography

Answer 1

Method of temporal subtraction that results in successive subtraction images of contrast-filled vessels.

Question 2

Define registration.

Answer 2

Matching two or more images in space.

Question 3

Define interrogation time

Answer 3

Time required for the x-ray tube to be switched on and reach the selected level of kVp and mA.

Question 4

Define hybrid subtraction

Answer 4

Temporal subtraction refers to a number of computer-assisted techniques whereby an image obtained at one time is subtracted from an image obtained at a later time. Energy subtraction uses two x-ray beams alternately to provide a subtraction image resulting from differences in photoelectric interaction. Hybrid subtraction combines temporal and energy-subtraction techniques.

Question 5

Define CCD

Answer 5

Charge-coupled device. Sensitive component is a layer of crystalline silicon, which generates an electrical charge.

Question 6

Define FPIR

Answer 6

Flat panel image receptor. Composed of cesium iodide (CsI)/amorphous silicon (a-Si) pixels. They are lighter and easier to manipulate than CCD image intensifiers.

Question 7

Define Progressive video scan

Answer 7

One line at a time, sequential instead of interlaced.

Question 8

Define duty cycle.

Answer 8

The fraction of time that an x-ray tube is energized.

Question 9

Define ABS

Answer 9

Automatic Brightness Stabilization. With a lens-coupled CCD, a sample of light is measured and used to drive the ABS. When the CCD is directly coupled to the page intensifier, the entire CCD signal is sampled and drives the ABS system.

Question 10

Define flat panel image display

Answer 10

A digital display device as compared with a cathode ray tube.

Question 11

What are the principal advantages of DF over conventional fluoroscopy?

Answer 11

Improved contrast resolution because of postprocessing procedures, instant access to spot films, signal-to-noise improvement by frame averaging, and instant image subtraction for contrast studies.

Question 12

Describe the sequence of image acquisition in mask-mode fluoroscopy?

Answer 12

The acquisition of a series of images is followed by contrast administration, followed by another series of images. The precontrast and postcontrast images can be summed to improve the signal-to-noise ratio and then subtracted from one another to produce an angiogram or other such image of contrast-filled anatomy.

Question 13

Describe the differences between a view system operating in the interlace mode and one operating in the progressive mode.

Answer 13

Interlaced = alternate video lines. Progressive = sequential video lines.

Question 14

Why are all electronic devices inherently noisy?

Answer 14

There are spurious electrical signals resulting from small stray electrical current and thermally induced stray currents. Cooling electronics always reduces electronic noise.

Question 15

Describe the process of energy subtraction.

Answer 15

Subtraction of two images at different kVp.

Question 16

What determines the spatial resolution of a DF system?

Answer 16

Spatial resolution is determined both by the image matrix and by the size of the image intensifier.

Question 17

A DF system is operated in a 512x512 image mode with a 23-cm image intensifier. What is the size of each pixel?

Answer 17

Pixel size = 0.45 mm × 0.45 mm (230 mm/512 =0.45 mm).

Question 18

The dynamic range of some DF systems is descried as 12 bits deep. What does this mean?

Answer 18

That each pixel can contain up to 4096 values, each value representing a different shade of gray.

Question 19

What principally determines spatial resolution in digital fluoroscopy?

Answer 19

The spatial resolution of all digital images is pixel limited. We cannot image something smaller than a pixel. Theoretically, therefore, for digital fluoroscopy a limited spatial resolution is field of view divided by matrix size.

Question 20

How is automatic brightness stabilization implemented with FPIR fluoroscopy?

Answer 20

ABS using FPIR is accomplished by controlling the duty cycle of x-ray exposure.

Question 21

What is the pixel size of a 1000-line video system when the DF image intensifier is operated in the 12-cm mode?

Answer 21

0.12 mm.

Question 22

How does a fluoroscopic image captured by FPIR differ from that captured with an II-CCD?

Answer 22

The image is immediate and the response to varying anatomy quicker.

Question 23

What additional equipment is required to progress from conventional fluoroscopy to DF?

Answer 23

A computer, an analog-to-digital converter (ADC), and a digital-to-analog converter (DAC). Both are special computer systems.

Question 24

Discuss the pt dose implications associated with DF compared with conventional fluoroscopy.

Answer 24

Dose should be the same or lower with digital fluoroscopy, but experience shows it to be somewhat higher because of ease of image acquisition.

Question 25

What is image-guided catheter navigation?

Answer 25

Manipulation of a magnetized catheter with external controlled magnetic fields. Such is not possible with a CRT fluoroscopic system, because the magnetic field would interfere with CRT.

Question 26

What X-ray energy (keV) would result in greatest contrast in digital subtraction angiography when an iodinated contrast agent is used?

Answer 26

34 keV. Approximately 90 kVp.

Question 27

What are some advantages associated with the use of a CCD instead of a TV camera tube?

Answer 27

Direct digital, no lag, long life.

Question 28

How can misregistration artifacts be corrected?

Answer 28

Postprocessing to reregister the image.

Question 29

Why is SNR ratio important in DF?

Answer 29

High SNR results in better contrast.