CRT compensation tool aids detection performance

Those interested in improving radiology reading variables still face the problem of nonisotropic MTF (modulation transfer function) characteristic of CRT displays, according to a scientific paper presented Friday at the SCAR meeting.

"The degradation of MTF is different in the horizontal than vertical direction, and the overall result is that images displayed on CRTs are degraded in both spatial and contrast resolution, especially at the higher spatial frequencies to which the human eye is sensitive," said Elizabeth Krupinski, Ph.D., of the University of Arizona.

Krupinski presented a way to use an image-processing technique to compensate for this MTF degradation.

The study found that an MTF compensation tool can be used to compensate for limitations in the MTF of CRT monitors to improve the detection of microcalcifications, and thus should be considered as a standard image processing tool, she said.

The MTF compensation processing involves two one-dimensional Fourier transform filters using measured vertical and horizontal MTF functions as the bases for constructing filters, she said.

The study used mammographic images with microcalcifications as targets of detection since microcalcifications are typically high spatial frequency objects.

"We demonstrated the utility of using a vision model to accurately predict human detection performance on images that have been processed to compensate for CRT limitations," Krupinski said.

Both human and model observers performed better than without MTF compensation, suggesting that display properties should be carefully analyzed if they are to be used for interpreting radiographic images, she said.

"Subtle variables such as the nonisotropic nature of monitor MTF can affect observer detection performance," she said.

Further work is underway to determine if such MTF compensation methods are useful for other types of targets, such as masses in mammograms, that do not have high spatial resolution properties.

"We are also investigating the use of interactive MTF compensation for use with full mammographic images instead of the small regions of interest here," she said.