Perception of fluoroscopy last-image hold

Area of Science:

• Medical Imaging Physics
• Human Visual Perception
• Radiological Imaging

Background:

• Last-image hold (LIH) is a feature in x-ray fluoroscopy for convenience and dose reduction.
• The human visual system (HVS) temporally filters noise in image sequences, reducing perceived noise.
• Single, static fluoroscopy frames lack this temporal filtering, appearing noisier and obscuring low-contrast details.

Purpose of the Study:

• To compare the perceived image quality of single LIH frames with continuous fluoroscopy.
• To determine the "equivalent-perception dose" for LIH by varying its dose against a fixed continuous fluoroscopy dose.
• To investigate how object shape and size influence this equivalent-perception dose.

Main Methods:

• Stationary cylinder and disk phantoms with low contrast were used in a noisy environment.
• Perception of single LIH frames was compared to continuous fluoroscopy (30 frames/s) using a paired-comparison task.
• The dose for LIH was adjusted to find the dose yielding equivalent perception to continuous fluoroscopy (fixed dose Q/acq).

Main Results:

• Equivalent-perception dose is dependent on object shape and size.
• For cylinders, equivalent-perception dose decreased from 4.6 to 2.8 Q/acq as diameter increased from 1 to 21 pixels.
• A 10-pixel diameter cylinder was perceptually equivalent to a 20-pixel diameter disk at equal doses.

Conclusions:

• HVS processing effectively reduces noise variance by a factor of 3.5 for LIH, equivalent to 120 ms of averaging.
• An average equivalent-perception dose of ~3.5 Q/acq is predicted for single-frame LIH in interventional angiography.
• Techniques to reduce variance in LIH frames are suggested to match the perceptual quality of continuous fluoroscopy sequences.