ABSTRACT
X-ray photons d. The photocathode is attached to the output screen e. The potential difference across the intensifier of about 25 kV
accelerates electrons towards the photocathode
2. More structure of the image intensifier: a. The output screen is normally about 15-40 cm in diameter b. A layer of aluminium is placed over the inner surface of the output
phosphor to improve its mechanical strength c. Focusing electrodes use positive potentials to concentrate the
path of the electron beam d. One of the functions of the intensifier housing is to prevent
light from entering the intensifier e. The output screen is normally made of sodium iodide (NaI)
3. Gain and magnification: a. Gain is the ratio of the brightness of the output phosphor over
that of the input phosphor b. Overall gain is the sum of the flux gain and the minification gain c. An increase in gain increases the signal to noise ratio (SNR) d. By changing the voltages on the focusing electrodes the focal
electron crossover point is moved closer to the input screen to magnify the image
e. Magnification uses a smaller area of the output screen to increase the minification gain
4. Automatic brightness control and dose control curves: a. Automatic brightness control adjusts the gain automatically to
keep the monitor image at the same level of brightness b. Automatic brightness control is normally set by the brightness
at the centre of the image or the set region of interest c. Dose control curves always increase kV in preference to
mA to keep patient dose as low as is reasonably practicable (ALARP)
d. Dose control curves can be selected by the operator depending on the quality of image required
e. Modern image intensifiers use charge coupled device (CCD) cameras to acquire the image displayed on the output phosphor
5 . F lu o ro sc o p y : Q u e stio
n s
5. exceed 100 mGy per minute fluoroscopy than for continu-
ous fluoroscopy c. A typical effective dose for a barium meal would be 2.5 mSv d. A typical equivalent dose for a barium enema would be 7 mSv e. Screening times for a barium enema are typically in the range
of 1-3 min
6. Safety in fluoroscopy screening: a. Staff members who do not have to be next to the patient should
stand back to take advantage of the inverse square law b. Under couch tubes result in more radiation exposure to an
operator standing next to the patient than over couch tubes c. Most scatter is from the point where the beam exits the patient d. The lead shielding around the intensifier provides adequate
protection from the primary beam e. A lead apron combined with a thyroid shield provides adequate
protection from the primary beam
7. Image quality and noise in image intensifiers: a. Noise in fluoroscopy is predominantly electrical noise caused
by minification gain b. SNR can be increased by increasing the kV across the intensifier c. SNR can be increased by frame averaging d. Typical resolution on the monitor of a fluoroscopy system is
1.2-3 lp/mm depending on magnification e. Veiling glare and geometrical distortion are common artefacts
in fluoroscopy
8. In traditional fluoroscopic image intensifiers: a. Brightness gain increases with increasing voltage across the
intensifier b. Brightness gain increases with the use of magnification c. Brightness gain is increased when the exposure to the input
phosphor is increased d. Vignetting causes the periphery of the image to be brighter than
the centre e. Geometrical distortion may cause the periphery of the image to
be distorted
5 . F lu o ro sc o p y : Q u e stio
n s
9. needs to be taken after
b. DSA cannot be viewed in realtime because the images need
to be processed in the computer before the subtracted image can be displayed
c. Slight movements between the mask and subtracted images may produce dark or light lines along high contrast structures such as bones
d. DSA requires at least two frames per second to image arteries, with slower frame rates being used for venous structures
e. Subtracted images have a decreased SNR
10. Flat plate detectors: a. Contrast using a flat plate detector is much better than traditional
fluoroscopy b. Flat plate detectors do not suffer from veiling glare or
geometric distortion c. Spatial resolution is not as good using digital flat plate
detectors when compared with traditional fluoroscopy d. Flat plate X-ray photon detection efficiency is comparable to
traditional fluoroscopy e. Flat plate detectors can be made much smaller compared with
image intensifier explorators
5 . F lu o ro sc o p y : Q u e stio
n s
1a. True This size difference contributes towards the intensification via minification gain.
