Carotid artery stenosis: a prospective comparison of CT angiography and conventional angiography.

OBJECTIVE: The purpose of this study was to prospectively compare CT angiography with conventional angiography for detecting stenosis at the carotid bifurcation. SUBJECTS AND METHODS: Thirty-five patients referred for evaluation of carotid artery disease were studied with conventional angiography followed by CT angiography 4-24 hr later. Seventy carotid arteries were studied. CT angiograms were acquired by using 40-sec spiral scans with a 2-mm/sec table speed, 2-mm beam collimation, and IV iodinated contrast material injected at 2.5 ml/sec. Studies were interpreted on the CT workstation by using three-dimensional shaded surface objects and multiplanar reformations requiring 10-15 min per artery. The conventional and CT angiograms were interpreted by separate observers who did not know the results of the other imaging study. The degree of stenosis was determined by using the guidelines of the North American Symptomatic Carotid Endarterectomy Trial collaborators. Each artery was categorized as normal, mildly stenosed (1-29%), moderately stenosed (30-69%), severely stenosed (70-99%), or occluded. RESULTS: The degree of carotid artery stenosis on the CT angiograms correlated well with that seen on the conventional angiograms (r = .928, p < .001). With CT angiography, all occluded internal carotid arteries were correctly identified, and no arteries were wrongly classified as occluded. The degree of stenosis was overestimated on CT angiograms by greater than 10% in 16 arteries, especially when calcified atherosclerotic plaque was present. In some of these cases, the severity of the stenosis was underestimated on the conventional angiograms. All arteries, except one, with severe disease seen on conventional angiograms were correctly classified on the basis of the results of CT angiography. CONCLUSION: Results of CT angiography had a high degree of correlation with results of conventional angiography in the evaluation of carotid artery stenosis. CT angiography is multiplanar and allows differentiation of calcified plaque from contrast material, which provides information about plaque calcification, ulceration, and size that cannot be obtained with conventional angiography.

Islet cell tumors: comparison of dynamic contrast-enhanced CT and MR imaging with dynamic gadolinium enhancement and fat suppression.

Ten patients with 11 islet cell tumors underwent dynamic contrast material-enhanced computed tomography (CT) and magnetic resonance (MR) imaging within a 1-month period. MR imaging depicted all 11 tumors, and CT depicted seven of the 11 tumors. CT did not depict four of seven tumors that measured 2.5 cm in diameter or less. Islet cell tumors had low signal intensity on T1-weighted fat-suppressed MR images, and gastrinomas were best shown with this technique. Two of three insulinomas less than 1.5 cm in diameter were best shown on dynamic contrast-enhanced fast low-angle shot (FLASH) images as uniform areas of high signal intensity. Hepatic metastases were seen in five patients and showed peripheral ringlike enhancement best demonstrated on dynamic gadolinium-enhanced FLASH images. Hepatic lesions were most conspicuous on T2-weighted fat-suppressed spin-echo images. MR imaging with dynamic gadolinium enhancement and fat suppression is a promising tool in the investigation of islet cell tumors.

Leaf water balance during oscillation of stomatal aperture.

Continuous transpiration and beta-guage measurements were made on cotton plants, the stomatal apertures of which had been induced to oscillate, thus allowing a water balance to be made, and leaf potential to be measured as functions of time.Analyses showed phase differences between the water entering and leaving the leaf. Also, from the phase relationship between the flow into the leaf and the water potential in the leaf it was shown that the water potential in the xylem of the plant also oscillated. This is proposed as a necessary condition for the stomates of all the leaves of a plant to oscillate in phase.It is convenient to describe the dynamics of the phenomena using a simple electrical analogue, and the usefulness and limitations of the model are discussed.