Robert L. Siegle

THE USE OF IOHEXOL IN PATIENTS WITH PREVIOUS REACTIONS TO IONIC CONTRAST MATERIAL : A MULTICENTER CLINICAL TRIAL

Patients who have had prior reactions to iodinated contrast material have increased risk for repeat reactions. Nonionic contrast agents have been reported to reduce the risk of contrast reactions. A multicenter study was undertaken to determine the repeat reaction rate using iohexol. Two hundred ninety-one repeat reactors were included in the study, of whom one-third received premedication. Sixteen patients (5.5%) experienced repeat reactions; none was severe, and only one was more serious than the prior reaction. This is in contrast to the reported 16% to 44% repeated reaction rate for ionic agents. We conclude that iohexol is effective in reducing the occurrence of repeat reactions from the level observed with ionic agents without premedication. Iohexol appears to be as effective as ionic agents plus premedication in this high-risk group of patients.

New magnetic resonance imaging techniques for the detection of breast cancer

SummaryThe importance of contrast agents in enhancing diagnoses from magnetic resonance images has been established in numerous cases. However, the development of a potent tissue-specific contrast agent, as a sensitive probe for early detection and investigation of the physiological characteristics of a tumor, has not yet been realized in MR imaging (MRI). In nuclear scintigraphy the technique has been demonstrated; however, the poor spacial resolution inherent to the modality and the substantial dose of radioactivity administered to the patient has hindered its widespread use. This article will review the different classes of contrast agents in MRI, with special focus on the strategies involved in the development of targeted tissue-specific MRI contrast agents for the early detection of breast cancer. The features of a new class of contrast agents for targeted MR imaging will be described. Gadolinium-containing melanin polymers (GMPs) have been synthesized as MR contrast agents in our laboratory. These GMPs demonstrate significantly higher relaxivities than any other paramagnetic contrast agents reported; consequently, they are extremely effective contrast enhancing, imaging agents by themselves. The successful coupling of these potent GMPs to a monoclonal antibody specific for breast carcinoma, the 323/A3 monoclonal antibody, suggests thatin vivo tissue-specific MR imaging, at the receptor level, will become feasible in the near future.

The hemodynamic effects of the administration of ionic and nonionic contrast materials into the pulmonary arteries of a canine model of acute pulmonary hypertension

Clinical studies have shown pulmonary and right ventricular hypertension to be important factors increasing the risk to patients during pulmonary angiography. This experiment was undertaken to define the hemodynamic changes induced by the administration of contrast material into the pulmonary arteries of dogs with embolic pulmonary hypertension, and to compare the effects of ionic and nonionic agents. Ten closed-chest dogs under light halothan anesthesia were subjected to pulmonary embolization with sephadex microspheres until severe pulmonary hypertension occurred and the cardiac output decreased to 50%-60% of the pre-embolization baseline. Intra-pulmonary injections of contrast material were performed in eight animals while hemodynamic indices were measured. Sodium methylglucamine diatrizoate induced severe, transient, hypotension associated with a large decrease in systemic vascular resistance and little change in the cardiac output. Hypotension is especially undesirable in the presence of pulmonary hypertension because it worsens the preexisting coronary ischemia and compromised right ventricular function. No elevation in mean pulmonary artery pressure was seen, and pulmonary vascular resistance decreased. Iohexol induced milder effects, perhaps because it exerts a less severe systemic vasodilatory effect and is not a negative inotrope. These findings suggest iohexol may be safer in the high risk patient, however, these data may not be directly applied to unanesthetized humans.

Rates of idiosyncratic reactions. Ionic versus nonionic contrast media.

RATIONALE AND OBJECTIVES. Nearly 40 years ago, investigators began collecting data regarding idiosyncratic reactions to iodinated contrast agents. The rates of idiosyncratic reactions in patients receiving ionic contrast agents are compared with those found in patients receiving nonionic agents.METHODS. A comprehensive literature review was conducted. Retrospective and prospective studies were included, as well as recent analytical multistudy reviews.RESULTS. For conventional hypermolar agents, rates are estimated to be 5% and the rate of repeat reactions, greater than 20%. Large comparative studies conducted in the late 1980s found significantly lower rates of idiosyncratic reactions with the newer, nonionic agents than with conventional agents. The results of studies evaluating the use of routine administration of steroids before the use of ionic agents have been contradictory. Two analytical reviews of earlier research find fault with the methodology of most studies, but the reviewers supported the increased safety of nonionic agents.CONCLUSIONS. All iodinated contrast media have excellent safety records. Most evidence, however, demonstrates that nonionic agents are safer than ionic agents.

Changing roles: The radiologist in management

RATIONALE AND OBJECTIVES Radiologists have rarely had direct administrative control of the hospital departments in which they practice. Several years ago, the administration of the medical school at the University of Texas Health Science Center at San Antonio and its county-owned principal teaching hospital agreed to integrate the physician and administrative management of the radiology department in an attempt to improve operations and reduce expenses. This integration is a pilot plan that will eventually be extended to most departments. MATERIALS AND METHODS The authors have collected data that measure department function for the seven quarters of physician management and compared these data with those of the previous four quarters prior to physician management. RESULTS There are substantial increases in department activity, together with reductions in expenses and waiting time for procedures. These changes have occurred while overall hospital activity has decreased. Bench-marking studies show favorable comparison with comparable radiology departments. CONCLUSION Radiologists can have an important effect on department operations when given the responsibility and authority for managing these affairs.

Development of a model using polypeptide antibodies for scintigraphy of the pancreas.

A study was designed to develop an agent for pancreatic scintigraphy with greater specificity for the pancreas than selenomethionine. A series of successful experiments was performed using rabbit-produced antibodies to the recently discovered hormone, pancreatic polypeptide. Via hemagglutination and radiolabeled hemagglutination studies, the antibody activity was demonstrated. Gel diffusion studies showed selective uptake by the rat pancreas of intravenously injected antibody and no uptake by the liver and spleen. Immunocytochemical studies on human tissue demonstrated the same selectivity for the pancreas. Also, the titers of different batches of rabbit-produced antibody were quantitated by the enzyme-linked immunospecific assay system. These studies indicate that polypeptide antibody has the potential for carrying a radionuclide selectively to the pancreas.

Comparison of iodixanol with iohexol in excretory urography

RATIONALE AND OBJECTIVES We compared the safety and efficacy of iodixanol, a nonionic, dimeric, iodinated contrast agent, with that of iohexol, a monomeric agent, in adult excretory urography. METHODS The study used a randomized, double-blind, parallel-comparison design to evaluate image quality, vital signs, laboratory values, and adverse reactions. Seventy-five patients from each of two centers were included. One third received iodixanol at 270 mg I/ml, one third received iodixanol at 320 mg I/ml, and one third received iohexol at 300 mg I/ml. The dose for every patient was 1 ml/kg of body weight. The radiographs were interpreted and evaluated for quality by the primary investigator at each center. There were no important differences among the three groups in terms of demographics. RESULTS Evaluation of each phase of the radiographic study showed almost uniform good-to-excellent opacification, with no significant differences among the three agents. No significant differences existed for the three groups in terms of vital signs, hematology, blood and urine chemistry, and injection discomfort. There were no deaths or serious reactions during the study, nor was there a statistically significant difference among the number of adverse events for the three agents. CONCLUSION Iodixanol at both 270 and 320 mg I/ml proved to be a safe and effective contrast material for intravenous urography. In this study, its profile was essentially indistinguishable from that of iohexol at 300 mg I/ml.

Contrast Agent Reactions and Free Will

As part of the quality assurance/risk management process of the Department of Radiology at the University of Texas Health Science Center, we continually monitor the number of contrast reactions and their severity and outcome. The process had been in place for many years and showed a constancy that usually allowed it to be ignored. A period with unexpected gyrations in these numbers caused the risk management monitor to bring it to my attention as department director. I then sought the cause for these unexpected numbers.

Effect of oral metrizamide on hematocrit and serum osmolality in the neonate

Sixteen newborns and young infants, weighing between 800 and 5200 grams, received orally administered metrizamide for evaluation of suspected gastrointestinal pathology. Images were judged good to excellent in 14 cases. No effect of metrizamide on hematocrit and serum osmolality was noted. Metrizamide appears to be a relatively safe and effective agent for examination of the neonatal gastrointestinal tract.