Evaluating interaction techniques for stack mode viewing

Abstract

Three interaction techniques were evaluated for scrolling stack mode displays of volumetric data. Two used a scroll-wheel mouse: one used only the wheel, while another used a "click and drag" technique for fast scrolling, leaving the wheel for fine adjustments. The third technique used a Shuttle Xpress jog wheel. In a within-subjects design, nine radiologists searched stacked images for simulated hyper-intense regions on brain, knee, and thigh MR studies. Dependent measures were speed, accuracy, navigation path, and user preference. The radiologists considered the task realistic. They had high inter-subject variability in completion times, far larger than the differences between techniques. Most radiologists (eight out of nine) preferred familiar mouse-based techniques. Most participants scanned the data in two passes, first locating anomalies, then scanning for omissions. Participants spent a mean 10.4 s/trial exploring anomalies, with only mild variation between participants. Their rates of forward navigation searching for anomalies varied much more. Interaction technique significantly affected forward navigation rate (scroll wheel 5.4 slices/s, click and drag 9.4, and jog wheel 6.9). It is not clear what constrained the slowest navigators. The fastest navigator used a unique strategy of moving quickly just beyond an anomaly, then backing up. Eight naïve students performed a similar protocol. Their times and variability were similar to the radiologists, but more (three out of eight) students preferred the jog wheel. It may be worthwhile to introduce techniques such as the jog wheel to radiologists during training, and several techniques might be provided on workstations, allowing individuals to choose their preferred method.

Fig 1

The Contour Design Shuttle Xpress jog and shuttle wheel used in our experiments.

Fig 2

Consecutive image slices containing an artificial anomaly.

Fig 3

A typical navigation chart (P7, Trial 13, wheel technique). The locate pass takes the first 11.1 s, followed by a 0.5-s pause, and then the review pass takes 3.8 s.

Fig 4

The same stimulus as in Figure 3, with the drag/wheel technique (P5, Trial 13). Forward speed is 4.3 slices/s, backward is 8.6 slices/s. Thinking time to confirm the anomaly is 9.0 s.

Fig 5

The same stimulus as in Figures 3 and 4, with the jog technique (P9, Trial 13). Forward speed is 8 slices/s, backward speed is 11 slices/s. Thinking time to confirm the anomaly is 5.2 s.

Fig 6

Mean thinking and forward navigation times per trial, for each participant.

Fig 7

Mean rate of forward navigation in slices/second, for each participant. Sorted by mean rate.

Fig 8

Slow navigator P6 on Trial 5 using the wheel technique. Forward rate = 3.2 slices/s, backward rate = 6.7 slices/s.

Fig 9

Fast navigator P2 using wheel, Trial 10. Rate of forward navigation = 17.7 slices/s. Note the absence of a review pass.

Fig 10

Fast navigator P2 using jog, Trial 11. Rate of forward navigation = 13.0 slices/s, backward navigation = 16.5 slices/s.