Thomas S. Chang

Computed radiography versus screen-film mammography in detection of simulated microcalcifications: a receiver operating characteristic study based on phantom images.

RATIONALE AND OBJECTIVES The authors compare a 43-micron computed radiographic system with a mammographic screen-film system for detection of simulated microcalcifications in an observer-performance study. MATERIALS AND METHODS The task of detecting microcalcifications was simulated by imaging aluminum wire segments (200-500 microns in length; 100, 125, or 150 microns in diameter) that overlapped with tissue background structures produced by beef brisket. A total of 288 such simulations were generated and examined with both computed radiography and conventional screen-film mammography techniques. Computed radiography was performed with high-resolution plates, a 43-micron image reader, and a 43-micron laser film printer. Computed radiographic images were printed with simple contrast enhancement and compared with screen-film images in a receiver operating characteristic study in which experienced readers detected and scored the simulated microcalcifications. Observer performance was quantitated and compared by computing the area under the receiver operating characteristic curve. RESULTS Although the resolution of the computed radiography system was better than that of commercial systems, it fell short of that of screen-film systems. For the 100-micron microcalcifications, the difference in the average area under the curve was not statistically significant, but it was significant for the larger simulated microcalcifications: the average area under the curve was 0.58 for computed radiography versus 0.76 for screen-film imaging for the 125-micron microcalcifications and 0.83 versus 1.00, respectively, for the 150-micron microcalcifications. CONCLUSION Observer performance in the detection of small simulated microcalcifications (100-150 microns in diameter) is better with screen-film images than with high-resolution computed radiographic images.

Selection of processing algorithms for digital image compression: a rank-order study.

RATIONALE AND OBJECTIVES We investigated non-receiver operating characteristic (non-ROC) methods for the selection of processing algorithms for digital image compression. METHODS We performed a multipoint, rank-order study with 20 posteroanterior chest images, each processed using four different algorithms. Seven radiologists reviewed these alongside the digitized noncompressed image. Observers were forced to rank order the similarity and/or difference of the processed images to the nonprocessed image in each case. RESULTS A two-way analysis of variance of the rankings was statistically significant (p = .025), indicating that one processing scheme yielded images that were clearly perceived as the most similar to the nonprocessed images. The selected processing scheme was not the one that yielded the lowest quantitative difference from the nonprocessed images as measured by root mean square error. CONCLUSION Non-ROC study designs that are highly sensitive to small differences among similar images can be used to select processing algorithms.

Can a limited double reading/second opinion of initially recalled breast ultrasound screening examinations improve radiologists' performances?

Interpretations of breast ultrasound screening examinations result in high recall rates and large inter-radiologist variability, frequently leading to “conservative” recommendations. Double reading of all breast ultrasound screening examinations is cost prohibitive, but double reading of only “initially recalled” cases may prove efficacious. We assessed changes in recommendations, if any, by providing a consensus second opinion in a limited subset of examinations initially recommended for recall. We performed a retrospective reader study with 197 ultrasound examinations (97 not recalled and 100 recalled clinically). First, we generated a consensus “second opinion” consisting of the majority vote of three independent readings of each case by experienced ultrasound interpreters. During the reader study that followed, if the reader recommended a “recall” and the “consensus second opinion” did not, a message to that effect was displayed and the reader was asked to re-review the exam and re-assess if, knowing the second opinion, a re-rating of the case was warranted. We compared performance levels pre- and post- the second opinion. The second opinion resulted in “no recall” recommendations of 141 cases in the entire set, including four cancer cases missed by all three readers. On average, radiologists received “warning” messages in 30 cases (range 15-50), or in ~15% of cases. Rating changes (downgrades to no recall) occurred in 36 of these cases. These changes resulted in a possible recall rate reduction of 28% in prompted cases or 14% overall recall reduction, while increasing the false negative rate by only one case missed by 2 readers (~1%).