Tamara Miner Haygood

Humans are very adept at extracting the "gist" of a scene in a fraction of a second. We have found that radiologists can discriminate normal from abnormal mammograms at above-chance levels after a half-second viewing (d' ∼ 1) but are at chance in localizing the abnormality. This pattern of results suggests that they are detecting a global signal of abnormality. What are the stimulus properties that might support this ability? We investigated the nature of the gist signal in four experiments by asking radiologists to make detection and localization responses about briefly presented mammograms in which the spatial frequency, symmetry, and/or size of the images was manipulated. We show that the signal is stronger in the higher spatial frequencies. Performance does not depend on detection of breaks in the normal symmetry of left and right breasts. Moreover, above-chance classification is possible using images from the normal breast of a patient with overt signs of cancer only in the other breast. Some signal is present in the portions of the parenchyma (breast tissue) that do not contain a lesion or that are in the contralateral breast. This signal does not appear to be a simple assessment of breast density but rather the detection of the abnormal gist may be based on a widely distributed image statistic, learned by experts. The finding that a global signal, related to disease, can be detected in parenchyma that does not contain a lesion has implications for improving breast cancer detection.

OBJECTIVE: Our purpose was to determine interobserver variability in the interpretation of the shape of the acromion on sagittal oblique MR images and conventional radiographs. The shape of the acromion was defined according to a previously described classification scheme. MATERIALS AND METHODS: We reviewed 26 sets of sagittal oblique MR images and corresponding conventional Y- or outlet-view radiographs of the shoulder. The shape of the acromion was graded for each study independently by four reviewers. Interobserver agreement was measured by using the kappa statistic. Analysis of variance and the chi 2-test were used for univariate analysis. RESULTS: The acromion was interpreted most often as being curved. The observers scored 9% of MR images and 28% of conventional radiographs as nondiagnostic (p < .001) (41% of transscapular Y views and 3% of supraspinatus outlet views were also considered nondiagnostic [p < .0001]). Kappa values were .23 for MR images and .43 for conventional radiographs. Variability in interpretation between techniques when controlled for observer was not statistically significant. CONCLUSION: Although sagittal oblique MR images were significantly more likely than conventional radiographs to be considered diagnostic by observers, interobserver agreement for MR examinations was poor. There was moderate agreement with conventional radiographs. This calls into question the usefulness of the previous system of interpretation and suggests that it might be more applicable with conventional radiographs than with MR images.

Soft-tissue masses caused by long-standing foreign bodies in the extremities: MR imaging findings.J U Monu, C M McManus, W G Ward, T M Haygood, T L Pope, Jr and S P BohrerAudio Available | Share