Fluoroscopy Q&A Robert L. Metzger, Ph.D.

RAPHEX Diagnostic Question 2001 D23: A fluoroscope is switched to the magnification mode (9” to 6” II). This will INCREASE all of the following EXCEPT: A. Conversion gain B. Quantum mottle C. Patient dose D. Spatial resolution

RAPHEX Answer to 2001 Question D23 B. Quantum mottle Conversion gain is related to brightness gain which is the product of mnification gain and flux gain. In the 6” mode, the minification gain decreases. Quantum mottle remains about the same. The automatic brightness control boosts the radiation level in magnification mode, to maintain brightness, and in doing so boosts the patient dose. Spatial resolution improves because of apparent magnification.

RAPHEX Diagnostic Question 2001 D30: The reason for overframing in cine filming is to: A. Improve spatial resolution B. Increase the field of view C. Reduce patient dose D. Change the shape of the cine image E. Increase the framing rate

RAPHEX Answer for 2001 Question D30 A. Improve spatial resolution The FoV is decreased and the patient dose is increased. Overframing has no clinical effect on shape or framing rate.

RAPHEX Diagnostic Question 2002 D36: The fluoroscopic operating factors displayed on a monitor are 120 kVp and 10 mA. Which of the following is true? A.The skin entrance dose is unusually low B. The five-minute timer is broken C. The skin entrance dose is extremely high D. The display must be wrong E. The anti-scatter grid is not in the beam

RAPHEX Answer to 2002 Question D36 C. The skin entrance dose is extremely high. As the fluoroscopic beam is positioned over thick or more dense areas of a patient, the penetration of x-rays decreases. The factors of 120 kVp and 10 mA indicate that the image intensifier is not receiving enough transmitted radiation through the patient. At such high technique factors the patient’s skin entrance exposure is extremely high. A broken timer will not affect the technique, and a missing grid would tend to decrease the factors.

RAPHEX Diagnostic Question 2002 D37: The maximum vertical resolution in 1p/mm for 23-cm diameter image intensifier coupled to a 1024 line TV system is _____. A. 0.8 B. 1.5 C. 2.2 D. 3.1 E. 4.0

RAPHEX Answer to 2002 Question D37 B. 1.5 Of the 1024 lines in standard TV only about 980 lines are used to actually trace out the image. It takes two lines to make a line pair, so there are 980/2 =4 490 line pairs. However, small objects are generally not perfectly aligned between the TV lines, so the effective resolution is obtained by multiplying by the Kell factor, which takes into account the random positioning of small objects in the TV field. The Kell factor is generally about 0.7, so the effective resolution is about 490 X 0.7 = 343 line pairs. For a 23-cm (230 mm) input, the resolution would be 343/230 =1.5 lp/mm.

RAPHEX Diagnostic Question 2003 D40: _____ is the persistence of an image on the fluoroscopic TV monitor. With motion, the image becomes blurred because of this persistence. A. Lag B. Vignetting C. Flare D. Veiling glare E. Blooming

RAPHEX Answer for 2003 Question D40 A. Lag Vignetting is the brightness change from the center to the edge of the II. The center is brighter than the edge. Flare and veiling glare are related parameters that indicate a degradation in contrast due to light scattering in the image intensifier. Blooming is the excessive brightness that occurs at the outside edge of a highly attenuation object.

RAPHEX Diagnostic Question 2003 D39: In cardiac catheter procedures, all of the following changes would reduce the patient’s dose EXCEPT: A. Reducing the frame rate B. Increasing the f number of the lens C. Increasing the aperture of the lens D. Increasing conversion gain of the II E. Increasing the source-to-image receptor distance (SID)

RAPHEX Answer for 2003 Question D39 B. Increasing the f number of the lens. Dose is directly proportional to frame rate. Large f-number lenses are less efficient at gathering light. Larger apertures permit more light to reach the cine film. A higher conversion gain produces more light for less radiation. Larger SIDs utilize geometry to reduce the patient’s radiation dose.