< Basic Physics of Digital Radiography

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Technology of Radiographic Imaging

  

1 The phosphor most likely to be used in indirect digital radiography is:

BaFlBr:Eu.
CsI:Tl.
NaI:Tl.
a-Se.

2 With regard to computed radiographic (CR) imaging:

Images with the same CR exposure index are all obtained with the same radiation dose to the patient.
An automatic exposure control (AEC) is not required.
Unlike photographic film, CR plates are impervious to “fogging” by background radiation during storage.
Good quality diagnostic images can be acquired with radiation exposures which are similar to those required for film/screen imaging.

3 A radiographic image is acquired using a 42 cm x 30 cm CR plate. The scanned digital image obtained from this plate has an effective pixel size of 0.2 mm. The image is acquired at 80 kVp, 30 mAs. A 3 megapixel (2,100x1,500) display will be therefore be required to display this image. Is this statement:

TRUE.
FALSE.

4 A patient undergoes two AP radiographic examinations of the abdomen on the same high frequency X-ray unit. The settings are: (1) 85 kV, 350 mA and 0.2s; (2) 85 kV, 600 mA and 0.15s. The entrance skin dose of examination (2) relative to that of the first examination is about:

30% less.
10% less.
the same.
10% greater.
30% greater.

5 Pulsed fluoroscopy is generally used to:

reduce motion blur.
reduce patient dose.
reduce the effective focal spot size.
increase kVp stabilization.

6 A radiologist wants to improve the spatial resolution of the anatomy being examined. The change most likely to lead to this is:

increased field of view, same matrix size.
selection of a smoothing algorithm.
increased matrix size, same field of view.
decreased collimation.

7 An 8:1 grid is replaced with a 12:1 grid. This will have the effect of:

Increasing contrast and patient radiation dose.
Increasing contrast with no change in patient radiation dose.
Increasing contrast and reducing patient radiation dose.
Decreasing contrast and patient radiation dose.

8 Scattered radiation arising in a patient increases sharpness in the resulting image. Is this statement:

TRUE.
FALSE.

9 In an X-ray tube, the actual anode focal area for a 17.5º anode angle is 4 mm (length) by 1.2 rnm (width). What is the effective focal spot size at the central axis in the X-ray field (Note: sine 17.5º is ~0.3.)?

4 mm (length) by 1.2 mm (width).
4 mm (length) by 0.4 mm (width).
1.2 mm (length) by 4 mm (width).
1.2 mm (length) by 1.2 mm (width).

10 The fluoroscopy factors displayed on a monitor are 120 kV and 20 mA. Which one of the following statements is true?

the display is wrong.
the XII is too close to the patient.
the skin entrance dose rate is normal.
the skin entrance dose rate is extremely high.
the skin entrance dose rate is too low.

11 The gamma of an Antimony Trisulphide target video camera is generally:

Less than 1.
Equal to 1.
Greater than 1.
Variable.

12 Scattered radiation arising in a patient decreases contrast in the resulting radiographic image. Is this statement:

TRUE.
FALSE.

13 Increasing the filtration of an 80 kV X-ray beam from 2 to 3 mm Al will:

increase the intensity.
soften the beam.
decrease the effective beam energy.
none of the above.

14 In digital subtraction angiography (DSA), video cameras are generally used in the progressive scan mode. This implies:

Repeated scanning of the same video image to improve signal-to-noise ratio.
Scanning adjacent raster lines sequentially after termination of the X-ray exposure.
Scanning the video camera target at appropriate intervals during the X-ray exposure.
Use of a double interlaced vidicon beam.

15 All other factors remaining unchanged, the signal -to-noise ratio in digitally subtracted images can be increased by summing several frames for both mask and contrast image. Is this statement:

TRUE.
FALSE.

16 Patient skin dose rate will decrease with kV only when:

the pulse rate is increased.
the tube current is reduced.
the grid is removed.
the collimators are fully open.

17 The image file format widely used thoughout digital medical imaging is:

JPEG.
TIFF.
DICOM.
HDR.

18 Scattered radiation arising in a patient is more penetrating than the primary radiation. Is this statement:

TRUE.
FALSE.

19 A 22 cm multi-mode image intensifier is switched to the 11 cm mode. As a result, the image will be _________ and the automatic brightness control system will _________ the exposure to the image intensifier and the patient:

Magnified; decrease.
Minified; decrease.
Magnified; increase.
Magnified; not change.

20 DSA images are generally transformed logarithmically prior to subtraction in order to:

reduce scatter effects.
eliminate motion artefacts.
correct for exponential attenuation.
sharpen vessel edges.

21 All other factors remaining unchanged, the signal -to-noise ratio in digitally subtracted images can be increased by increasing the exposure per frame. Is this statement:

TRUE.
FALSE.

22 For a pixel size of 0.64 mm, 50% of the Nyquist frequency is:

0.16 LP/mm.
0.32 LP/mm.
0.39 LP/mm.
0.64 LP/mm.

23 Which one of the following is not evidence of good radiation dose management?

moving the XII as close to the patient as practicable.
collimating the field of view as tightly as possible.
monitoring screening time and dose-area product (DAP) for each procedure.
always using a grid.

24 A radiographic image is acquired using a 42 cm x 30 cm CR plate. The scanned digital image obtained from this plate has an effective pixel size of 0.2 mm. The image is acquired at 80 kVp, 30 mAs. The Nyquist frequency is therefore 2.5 LP/mm. Is this statement:

TRUE.
FALSE.

25 Processing a digital radiograph using Unsharp Masking increases the:

patient dose.
image magnification.
landmarking.
visualisation of edges.

26 Scattered radiation arising in a patient increases with increasing irradiated volume. Is this statement:

TRUE.
FALSE.

27 Fluorography typically:

results in dose rates which are much less than in fluoroscopy.
uses the same dose rate as fluoroscopy.
uses dose rates 10-50 times greater than in fluoroscopy.
produces images of far inferior quality to fluoroscopy.

28 In an X-ray image intensifier, X-rays are converted into light at the:

Photo-cathode.
Anode.
Input phosphor.
Output phosphor.

29 All other factors remaining unchanged, the signal -to-noise ratio in digitally subtracted images can be increased by increasing the matrix size from 512x512 to 1024x1024 pixels. Is this statement:

TRUE.
FALSE.

30 The binding energies of the K, L, and M shell electrons in tungsten are 69.5, 11.0 and 2.5 keV, respectively. What photon energies will be present in its characteristic X-ray spectrum?:

67.0, 58.5, 8.5 keV.
80.5, 72.0, 13.5 keV.
69.5, 11.0, 2.5 keV.
Continuous spectrum from 2.5 to 69.5 keV

31 The magnification mode of an image intensifier is switched from 15 cm to 30 cm. In order to maintain the same image brightness, the exposure at the image intensifier input phosphor must roughly:

halve.
remain the same.
double.
quadruple.

32 In Computed Radiography, photostimulable luminance is stimulated by:

microwaves.
red light.
ultraviolet.
ultrasound.

33 A radiographic image is acquired using a 42 cm x 30 cm CR plate. The scanned digital image obtained from this plate has an effective pixel size of 0.2 mm. The image is acquired at 80 kVp, 30 mAs. Increasing the mAs to 90 will therefore result in a much darker image. Is this statement:

TRUE.
FALSE.

34 In an X-ray image intensifier, the overall gain in image brightness is of the order 5000:1 but the gain in brightness due to acceleration of electrons is only about 50:1. The other contribution to brightness gain is the:

Preamplifier gain.
Conversion efficiency.
Video camera.
Minification gain due to the reduction of image size.

35 All other factors remaining unchanged, the signal -to-noise ratio in digitally subtracted images can be increased by processing the subtracted image with an edge sharpening filter. Is this statement:

TRUE.
FALSE.

36 Which ONE of the following will increase subject contrast in a CR imaging system?

Selecting a narrower window for display.
Increasing x-ray beam filtration
Decreasing the kV.
Decreasing the Grid Ratio.

37 The storage required on an optical disk for 2000 images of size 1024 x 1024 and depth 8 bits is approximately?

1 MByte.
1 GByte.
2 GByte.
16 MByte.

38 The input phosphor material in a modern X-ray image intensifier is typically:

CdWO4.
CsI:Na.
LaOBr.
A rare earth material.

39 A kilobyte is equal to:

1000 bytes.
1024 bytes.
A quarter of a megabyte.
0.1% of a megabyte.

40 The contrast of DSA images can be increased by:

using a higher kVp.
reducing the intensity of detected scattered radiation.
increasing the intensity of detected scattered radiation.
reducing the air gap.

41 A radiograph is acquired using a 25 cm square image receptor and is digitised to a 512x512 matrix. The spatial resolution is:

0.5 LP/mm.
1.0 LP/mm.
2.0 LP/mm.
4.0 LP/mm.

42 The most commonly used reconstruction technique in Cone-Beam CT is called:

Algebraic Reconstruction.
Filtered Back Projection.
Fourier Reconstruction.
Iterative Reconstruction.

43 All other factors remaining unchanged, the signal -to-noise ratio in digitally subtracted images can be increased by increasing the sensitivity of the image receptor. Is this statement:

TRUE.
FALSE.

44 Which one of the following would most likely be used in a DR image receptor?

CsI:Tl.
LiF
CaWO4.
NaI:Tl.

45 Scattered radiation arising in a patient decreases with increasing kV applied to the X-ray tube. Is this statement:

TRUE.
FALSE.

46 A Charge-Coupled Device can be used in digital fluoroscopy:

In lieu of a conventional video camera to look at the output of the image intensifier.
For filtration of the X-ray beam.
As a mechanism to reduce scattered radiation.
As a collimation device.

47 In analogue to digital conversion, a memory 10 bits deep allows how many grey levels?

10.
128.
512.
1024.

48 With regard to TV cameras which statement is false?

Video tubes vary in contrast depending on the type of target used.
A vidicon has more lag than a plumbicon.
The Australian TV scanning standard is 625 lines, interlaced.
A low bandpass system is required for best spatial resolution.

49 To reproduce a square wave with a Fourier series ideally:

Requires up to 3 component frequencies.
Requires an infinite number of component frequencies.
Is theoretically impossible.
Requires one component frequency.

50 When two images are subtracted, the noise is:

increased by about 40%.
unchanged.
decreased by about 40%.
decreased by a factor of 2.

51 The heel effect is caused by:

Operating the X-ray tube with the beam horizontal.
Placing wedge filters in the X-ray beam.
Different path lengths of electrons in the anode.
Misaligned collimation.

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