An adaptive reference/test paradigm: Application to pulsed fluoroscopy perception

Abstract

Wedeveloped an adaptive forced-choice method whereby reference and test presentations were alternated in order to minimize effects from variables such as subject attention level. In our demonstration example of an X-rayfluoroscopy perception study, we measured detectability of low-contrast objects in noisy image sequences and determined X-raydose levels for equivalent detectability of identical contrasts for a new test acquisition method (fluoroscopy at 15 acq/sec) as compared with a reference (conventional fluoroscopy at 30acq/sec). In preliminary experiments, we found a dose savings with the test method. We derived parameter uncertainties for the adaptive procedure and demonstrated their applicability with Monte Carlo simulations. Repeated experiments on a single subject demonstrated reduced standard errors due to the reduction of day-to-day variations. It is believed that the method can be applied in a variety of situations in which one needs to compare perception measurements.We have developed a new experimental method that addresses issues in human perception studies. First, a subject's response can vary due to fatigue, a lapse in attention, or possible physiological changes. Kahneman (1973) discussed the importance of attention in perception experiments, indicating that attention may affect the sensory mechanism as well as the decision mechanism. Taylor (1967) observed variation in performance from one day to the next, and others (Hall, 1981;Madigan & Williams, 1987) reported variations within single experiments. This variation complicates comparison of results. For example, in our experiments in medical X-ray fluoroscopy, we compared new test acquisition methods with an established reference technique. Some of the effects that we wished to measure are comparable to day-to-day variations, and our solution was to alternate reference and test presentations over a time scale of seconds and obtain responses under identical conditions. Second, variability between subjects also presents a dilemma. For an independent variable such as image contrast, many trial-and-error presentations are required to arrive at display conditions that match the floor and ceiling responses of all subjects. This problem is well known, and adaptive techniques can solve the problem (

Perceived noise versus display noise in temporally filtered image sequences

“…Other details, including methods for determining the uncertainty of u and EDVR estimates, are described elsewhere. 15 …”

“…10,15 It assumes a continuous decision variable internal to the human observer with Gaussian probability density functions for the choices ''object present'' and ''no object present.'' There is a distance dЈ between the means of the two overlapping distributions, and we hypothesize that dЈ is proportional to image CNR.…”

“…15 Briefly, we use a 9-alternative forcedchoice ͑9-AFC͒ paradigm where a low-contrast object is placed in the center of one of nine noisy squares, and the subject rightly or wrongly chooses the position where he ͑she͒ thinks the object resides. Our method is adaptive.…”

“…It can also be incorporated into other applications such as perception-based video compression. 14 In this paper, we measure detectability of low-contrast objects using a new adaptive forced-choice procedure 15 and compare temporally filtered and unfiltered image sequences. We find the noise level of the unfiltered sequence that gives the same detectability as the filtered sequence.…”

Quantitative fluoroscopic dose saving in cardiovascular imaging with a novel motion discriminating temporal filter

“…We employed a 4-AFC detection paradigm [2] to measure the necessary x-ray dose for observers to correctly detect the presence of a moving guide-wire 80 percent of the time for the unfiltered and filtered image sequences.…”