Experiments were conducted on a series of chest radiographs to evaluate the effects of mean film density on reader performance. It was found that the false negative is not measurably affected, in agreement with earlier published data. It was also found, however, that the false positive rate increases with increasing film density. The causes and implications of these results are discussed.

False Negative Reactions↗

PubMedDate not supplied

Contrast gradient and the detection of lung nodules.

The effects of edge gradient and blur on the detection pulmonary nodules were studied, using a test series of 175 artificial nodules on 30 chest films. The nodules were of homogeneous texture, about 1 cm in diameter and had a mean contrast of .12. Six observers viewed the film set, scoring both location and confidence. The sensitivity or the probability of a true-positive response was linearly related to the blur and a modified ROC analysis resulted in a family of ROC curves with the index of detectability monotonically decreasing with increased blur.

Evaluation Studies as Topic↗

PubMedDate not supplied

Densitometric measurements of lung nodules on chest radiographs.

A technique is described whereby embedded nodular densities appearing on chest radiographs can be densitometrically measured without the obscurring effects of anatomic structures. The technique consists of rear-projecting a light beam into a chest radiograph and an observe adjusting this beam until the lucency matches that of the nodule's appearance. The radiography is then removed, and the lucency is scanned and analyzed with a microcomputer. Calibration data using simulated nodules show a good accuracy in measuring size, contrast, and edge gradient.

Absorptiometry, Photon↗

PubMedDate not supplied

The effect of verification on the assessment of imaging techniques.

In order to measure the accuracy of a diagnostic imaging technique, the correctness of each observer decision must be determined. This is often difficult in clinical cases, and various strategies are frequently used to approximate the truth. Experiments using chest radiographs as an example are reported to show the pitfalls in those strategies. To assess relative accuracies of three different radiographic techniques, chest radiographs were taken of 66 patients with each of the three techniques, and the films were evaluated by six radiologists. Their findings were then scored by comparing them with the correct decision defined by each of the following methods: majority vote, consensus opinion, expert judgment, feedback review, and clinical/pathologic proof. The findings showed that any one of the techniques could be shown to be better than the other, depending on how the truth was defined. It is concluded, therefore, that strategies that define the presence or absence of disease only by the diagnostic tests under evaluation are inadequate. The truth must be determined by clinical or pathologic proof and follow-up data.

Decision Making↗

PubMedDate not supplied

Femoral neck torsion angle measurement by computed tomography.

To establish the accuracy and reproducibility of measuring femoral neck torsion angles (FNTA) on CT images, this angle was measured on 12 dry femora directly on the gross specimens, on plain radiographs, and on CT images. The selection of the CT level, both at the femoral neck and the condyles, that may affect the measurement of FNTA was analyzed. The CT measurements of FNTA were found to have a reproducibility of 2.5 and 0 degrees mean offset error when compared with readings on plain radiographs. A new CT method was developed to measure this angle particularly in patients with coxa valga in whom this measurement is difficult if not impossible to accomplish by current methods. For this purpose composite CT images were made of the femoral head and the femoral shaft, immediately below the lesser trochanter. On these images the line connecting the centers of the femoral head and shaft were inferred to represent the cervical plane. In comparison with the standard CT method, this new method had the same reproducibility, although it slightly overestimated this angle by 2 degrees. This degree of error is negligible when compared with the normal variations of this angle, which ranges from -20 to +38 degrees. Furthermore, it compares favorably with the limited accuracy of derotational osteotomy surgery.

Adult↗

PubMedDate not supplied

Clinical significance of increased density in the proximal femoral marrow detected by visual inspection on abdominopelvic postcontrast CT examination.

PURPOSE: The purpose of this study was to ascertain the clinical significance of increased density of the proximal femoral diaphyseal marrow when incidentally detected on postcontrast abdominopelvic CT examinations. METHOD: The proximal femoral marrow of 63 patients was classified as normal or abnormal based on visual inspection by three attending radiologists. Abnormal density was defined as attenuation greater than that of adjacent musculature. The attenuation of the marrow was also measured. All patient medical records were reviewed for pertinent laboratory and clinical data. RESULTS: Increased marrow density had a low sensitivity for anemia (28%) but a high specificity and positive predictive value (100%) for anemia. Three of these patients had unilaterally increased attenuation associated with local pathology. Visual inspection was adequate for identifying abnormalities in instances of underlying malignancy. CONCLUSION: Increased density of the proximal femoral diaphysis is a highly specific finding for a marrow replacement process. Anemia was the most common clinical diagnosis in our series of patients with abnormal marrow density. Although the sensitivity for increased bone marrow attenuation is low, the extremely high specificity and positive predictive value of this finding for marrow reconversion and/or replacement suggest that even if detected incidentally, it should not be disregarded and, in the absence of a preexisting causative diagnosis, warrants further evaluation. The specific pattern of marrow abnormality may be helpful in differentiating localized processes from other processes that may affect hematopoietic function in a more widespread or global distribution. In particular, visual inspection of marrow density was more specific for identifying asymmetric marrow density in localized processes than was a quantitative measure of difference between the two femurs (>20 HU).

Adult↗