Forced choice and ordinal discrete rating assessment of image quality: a comparison.

This study compared a five-category ordinal scale and a two-alternative forced-choice subjective rating of image quality preferences in a multiabnormality environment. 140 pairs of laser-printed posteroanterior (PA) chest images were evaluated twice by three radiologists who were asked to select during a side-by-side review which image in each pair was the "better" one for the determination of the presence or absence of specific abnormalities. Each pair included one image (the digitized film at 100 microns pixel resolution and laser printed onto film) and a highly compressed (approximately 60:1) and decompressed version of the digitized film that was laser printed onto film. Ratings were performed once with a five-category ordinal scale and once with a two-alternative forced-choice scale. The selection process was significantly affected by the rating scale used. The "comparable" or "equivalent for diagnosis "category was used in 88.5% of the ratings with the ordinal scale. When using the two-alternative forced-choice approach, noncompressed images were selected 66.8% of the time as being the "better" images. This resulted in a significantly lower ability to detect small differences in perceived image quality between the noncompressed and compressed images when the ordinal rating scale is used. Observer behavior can be affected by the type of question asked and the rating scale used. Observers are highly sensitive to small differences in image presentation during a side-by-side review.

Choroid plexus metastasis: CT appearance.

Tumors of the choroid plexus are rare, and included among the list of such tumors is metastasis. We report a case of lung carcinoma metastasizing to the choroid plexus of the lateral ventricle. This mass was isodense on unenhanced CT and demonstrated moderate to marked enhancement after intravenous contrast medium administration. Follow-up studies over the course of 2 1/2 months showed hemorrhage into the mass and periventricular enhancement. Confirmation of the diagnosis was made by stereotactic biopsy. The differential diagnosis of choroid plexus masses is reviewed.

Hydromediastinum after aberrant central venous catheter placement.

After central venous catheter placement via the right subclavian route, a hydromediastinum was produced. Aberrant placement of the catheter was undiscovered for 13-1/2 hours despite clinical and radiographic signs. Careful interview of the patient and analysis of postcatheterization chest radiographs are imperative in order to avoid catastrophic consequences of aberrant catheter placement.