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1.  Differential Use of Image Enhancement Techniques by Experienced and Inexperienced Observers 
Journal of Digital Imaging  2005;18(4):311-315.
Full-field digital mammography (FFDM) systems are currently being used to acquire mammograms in digital format, but digital displays are less than ideal compared to traditional film-screen display. Certain physical properties of softcopy displays [e.g., modulation transfer function (MTF)] are less than optimal compared to film. We developed methods to compensate for some of these softcopy display deficiencies, based on careful physical characterization of the displays and image-processing software. A series of 100 FFDM and 60 digitized images was shown to six observers—half experienced (mammographers) and half inexperienced (radiology residents). The observers had to decide if a mass or microcalcification cluster was present and classify it as benign or malignant. A window could be activated that brought the image detail within the window to full resolution and corrected for the nonisotropic MTF of the Cathode Ray Tube (CRT) display. Experienced readers had better diagnostic performance and took less time to view the images. Experienced readers used window/level more than inexperienced readers, but inexperienced readers used magnification and the MTF compensation tool more often. Use of the magnification and the MTF tool increased reader decision confidence. Experienced and inexperienced readers use image-processing tools differently, with certain tools increasing reader confidence. Understanding how observers use image-processing tools may help in the development of better and more automated user interfaces.
PMCID: PMC3046729  PMID: 16142436
Observer performance; mammography; softcopy display; optimization
2.  Determining the MTF of Medical Imaging Displays Using Edge Techniques 
Journal of Digital Imaging  2005;18(4):296-310.
The modulation transfer function (MTF) of a medical imaging display is typically determined by measuring its response to square waves (bar patterns), white noise, and/or line stimuli. However, square waves and white noise methods involve capture and analysis of multiple images and are thus quite tedious. Measurement of the line-spread function (LSF) offers a good alternative. However, as previously reported, low-frequency response obtained from the LSF method is not as good as that obtained from measurement of edge-spread function (ESF). In this paper, we present two methods for evaluating the MTF of a medical imaging display from its ESF. High degree of accuracy in the higher frequency region (near the Nyquist frequency of the system) was achieved by reducing the noise. In the first method, whichis a variant of the Gans' original method, the periodic raster noise is reduced by subtracting a shifted ESF from the ESF. The second method employs a low-pass differentiator (LPD). A novel near maximally flat LPD with the desired cut-off frequency was designed for this purpose. Noise reduction in both the methods was alsoachieved by averaging over large portions of the image data to form the ESF. Experimental results show that the MTF obtained by these methods is comparable to that obtained from the square wave response. Furthermore, the MTFs of rising and falling edges of a cathode ray tube (CRT) were measured. The results show that the rising and falling vertical MTFs are practically the same, whereas the rising horizontal MTF is poorer than the falling horizontal MTF in the midfrequency region.
PMCID: PMC3046730  PMID: 16132485
Cathode ray tube (CRT); liquid crystal display (LCD); modulation transfer function (MTF); edge-spread function (ESF); line-spread function (LSF); Gans' method; low-pass differentiator; image quality
3.  Use of a Human Visual System Model to Predict Observer Performance with CRT vs LCD Display of Images 
Journal of Digital Imaging  2004;17(4):258-263.
This Project evaluated a human visual system model (JNDmetrix) based on just noticeable difference (JND) and frequency-channel vision-modeling principles to assess whether a Cathode ray tube (CRT) or a liquid crystal display (LCD) monochrome display monitor would yield better observer performance in radiographic interpretation. Key physical characteristics, such as veiling glare and modulation transfer function (MTF) of the CRT and LCD were measured. Regions of interest from mammographic images with masses of different contrast levels were shown once on each display to six radiologists using a counterbalanced presentation order. The images were analyzed using the JNDmetrix model. Performance as measured by receiver operating characteristic (ROC) analysis was significantly better overall on the LCD display (P = 0.0120). The JNDmetrix model predicted the result (P = 0.0046) and correlation between human and computer observers was high (r2 (quadratic) = 0.997). The results suggest that observer performance with LCD displays is superior to CRT viewing, at least for on-axis viewing.
PMCID: PMC3047185  PMID: 15692869
Vision model; observer performance; digital display

Results 1-3 (3)