Many important applications of DNA sequence-dependent hybridization reactions have recently emerged. This has sparked a renewed interest in analytical calculations of sequence-dependent melting stability of duplex DNA. In particular, for many applications it is often desirable to accurately predict the transition temperature, or tm of short duplex DNA oligomers (approximately 20 base pairs or less) from their sequence and concentration. The thermodynamic analytical method underlying these predictive calculations is based on the nearest-neighbor model. At least 11 sets of nearest-neighbor sequence-dependent thermodynamic parameters for DNA have been published. These sets are compared. Use of the nearest-neighbor sets in predicting tm from the DNA sequence is demonstrated, and the ability of the nearest-neighbor parameters to provide accurate predictions of experimental tm's of short duplex DNA oligomers is assessed.

Nonenhanced helical CT is a highly accurate technique for diagnosing or excluding acute appendicitis. Developing experience with the technique and understanding the subtleties of interpretation can further improve diagnostic accuracy.

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OBJECTIVE. The objectiveof our studywas to determinethe value of usingcolor and power Doppler sonography to reveal extrathyroidal feeding arteries in the detection of abnor mal parathyroid glands. SUBJECTSAND METHODS.Forty-four patients withprimaiy hyperparathyroidism wereimaged prospectively with high-resolution gray-scale,color flow, and power Doppler sonogra phy. The presence of extrathyroidal arteries supplying the adenomas was noted. All patients un derwent subsequent neck exploration. The locations of the abnormal glands were recorded. RESULTS. At surgery, 51abnormal parathyroid glands wereremoved inthe44patients.Sonography correctly revealed an adenomain 40 of the 44 patients. Likewise, sonography re vealed 42 of the 51 adenomas. Nine false-negative and two false-positive interpretations of the sonograms were made. Thus, overall sensitivity was 83%, specificity was 98%, and accu racy was 94%. Three of the false-negative interpretations were ectopic glands within the supe nor mediastinum. Excluding thesethree glands from analysis, the sensitivity for detection of adenomas within the neck was 88%, specificity was 98%, and accuracy was 95%. An ex trathyroidal artery leading to a parathyroid adenoma was seen in 35 of the 42 adenomas re vealed by sonography. The presenceof an extrathyroidal artery leading to an adenoma was found to aid in the detection of an otherwise inconspicuous parathyroid gland in five patients, which improved sensitivity from 73% to 83%. CONCLUSION. Prominent vessels supplying parathyroid adenomas arefrequently revealed by color flow and power Doppler sonography.These vesselscan serve as â€oe¿ road maps― to abnormal parathyroid glands.

AAS is an insensitive technique in the evaluation of nontraumatic acute abdominal pain in adults. Unenhanced helical CT is an accurate technique in the evaluation of adult patients with nontraumatic acute abdominal pain and should be considered as an alternative to radiography as the initial imaging modality.

Based on the limited reports of arterial extravasation in the nonhelical CT literature, the percentage (18%) of clinically stable patients in our study with CT scans showing arterial extravasation was higher than anticipated. This finding likely reflects the improved diagnostic capability of helical CT. Although the spleen and liver were the organs most commonly associated with arterial extravasation, radiologists should be aware that arterial extravasation may be associated with several other visceral injuries.

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