Medical Image Perception & Performance

Film vs. Monitor Search

Rationale

  • Radiology departments increasingly going film-less with introduction of PACS and teleradiology
  • CRT monitors present images very differently than film
  • Display differences could influence scanning strategies
  • Monitors generally have an image processing menu, presenting more information to radiologists than film
  • Monitor viewing times are generally longer for film - why?

Dwell Time Differences

  • [20] Compared film vs. monitor search for signs of trauma in skeletal computed radiography images
  • CRT viewing times about 60 sec longer than film
  • Time to first fixate the lesion is significantly longer on CRT (4.67 sec) than film (2.35 sec)
  • Readers generated more clusters (31.98 vs. 27.55; p <.05) with longer dwell times (892 msec vs. 816 msec; p < .05) on diagnostic areas of images on the monitor than on film images

Table : Median dwell times (msec) for decisions made during search of skeletal images for trauma on film vs. a CRT monitor (6 readers). Only true-negatives differ significantly.

Decision CR Film CRT Monitor
True-Positive 1206 1286
False-Negative 1204 938
False-Positive 896 895
True-Negative 358 532

Scan Pattern Differences 

  • Search patterns for film vs. monitor are comparable on diagnostic image areas
  • Scanning on non-image areas differ significantly
  • Radiologists generally scan to menu within first 10 sec of search after only about 3 fixations on diagnostic image

Table: Mean percentages of image areas receiving fixation clusters during search for CRT monitor vs. film viewing of skeletal radiographs.

Image Area Film Monitor
Diagnostic Image  95 78
Background 3  3
Image Processing Menu 0 20

Possible Explanations

  • Difficult to make every image on monitor appear the way every radiologist wants it to
  • Radiologist must adjust image using image processing menu
  • Spending time on menu increases overall viewing times
  • Long true-negative dwells suggest readers require more visual processing time to classify normal anatomic areas as normal than on film
  • Radiologists scan to the menu extremely early in search (after only about 3 fixations to the diagnostic image)
  • This early scanning away from diagnostic image may cause a disruption in initial global perception of image
  • This disruption causes lesions to be found later in search than with film 
  • Differences in brightness on resolution between monitor & film may contribute to the greater number of clusters with greater dwell times on film than on the monitor (especially for determination of true-negative status of image areas as reflected in significantly longer true-negative dwell times on the monitor than on film).

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