The risks to patients with metal surgical implants who are undergoing nuclear magnetic resonance (NMR) imaging and the artifacts caused by such implants were studied. Twenty-one aneurysm and other hemostatic clips and a variety of other materials (e.g., dental amalgam, 14 karat gold) were used. Longitudinal forces and torques were found to be exerted upon 16 of the 21 clips. With five aneurysm clips, forces and torques sufficient to produce risk of hemorrhage from dislocation of the clip from the vessel or aneurysm, or cerebral injury by clip displacement without dislodgement were identified. The induced ferromagnetism was shown to be related to the composition of the alloys from which the clips were manufactured. Clips with 10-14% nickel are evidently without sufficient induced ferromagnetism to cause hazard. The extent of NMR imaging artifacts was greater for materials with measurable ferromagnetic properties, but metals without measurable ferromagnetism in our tests also resulted in significant artifacts. Dental amalgam and 14 karat gold produced no imaging artifacts, but stainless steels in dentures and orthodontic braces produced extensive artifacts in the facial region.

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SUMMARY Determination of myocardial infarct size is important for clinical management of patients with ischemic heart disease and for research on limiting infarct size. Nuclear magnetic resonance (NMR) imaging permits tomographic depiction of the distribution of mobile tissue protons. NMR images have demonstrated high spatial resolution and contrast. To evaluate the potential of this technique in measuring myocardial infarct size, NMR imaging was performed in six canine hearts excised 24 hours after circumflex coronary artery ligation. Before sacrifice, the dogs received i.v. manganous chloride (0.05 mmol/kg). After NMR imaging, the hearts were sectioned and the myocardial slices were stained with triphenyl tetrazolium chloride. The pathologically determined infarct size was compared with the infarct size measured by NMR imaging. The correlation was good (regression line slope 1.06; r = 0.94). We conclude that NMR imaging with paramagnetic contrast agents can be used to determine infarct size in excised hearts.THE ACCURATE determination of myocardial infarct size has been a topic of major interest over the past decade. Previous work has demonstrated that prognosis depends upon infarct size."A Careful measurement of infarct size is important in determining the efficacy of interventions designed to limit infarction. Methods used clinically to quantify infarct size rely on assessment of wall motion (radionuclide angiography or ultrasound), myocardial perfusion (thallium-201), radioisotopic labeling of necrotic myocardium (technetium-99m stannous pyrophosphate), or release of intracellular enzymes into the bloodstream (CK-MB). Nuclear magnetic resonance (NMR) imaging is a noninvasive, high-resolution technique that uses no ionizing radiation and allows tomographic depiction of the distribution of mobile tissue protons. Image contrast can be enhanced by using paramagnetic substances that are markers of myocardial blood flow and alter NMR properties of tissue in their distribution. We have used NMR imaging with paramagnetic ion contrast enhancement to detect acute myocardial infarction in excised canine hearts.5 To evaluate the potential utility of NMR imaging in quantifying myocardial infarction, we studied a canine model of myocardial infarction with paramagnetic ion contrast enhancement using manganous ion. Methods Infarct ProductionSix adult mongrel dogs of either sex that weighed 15-20 kg were anesthetized with intravenous pentobarbital, 60 mg/kg (Veterinary Lab Inc.), intubated, and ventilated with 100% oxygen by positive pressure ventilator (Bird Corp.). The pericardium was opened through a left lateral thoracotomy, and the left circumflex coronary artery was isolated and ligated with 3-0 silk suture. The thoracotomy was closed and pleural air was evacuated. One gram of cephaloridine (Eli Lilly and Co.), and 1 g of procainamide (E.R. Squibb and Sons) were administered intramuscularly. The dogs were allowed to recover. Twenty-four hours after coronary ligation, the dogs were reanesthetized with i.v. pentobarbita...

In a study to evaluate the potential of proton nuclear magnetic resonance (NMR) imaging with and without manganese contrast with and without manganese contrast enhancement for detecting acute myocardial infarction, 12 dogs underwent 90-minute occlusion of the left circumflex coronary artery. Transverse-section NMR images of the excised, nonbeating heart were obtained at 1-cm intervals using the steady-state-free-precession (SSFP) technique. All NMR images revealed detailed structure of the heart. The three hearts without manganese showed no difference in intensity between the normal and the ischemic posterior regions, whereas those with manganese demonstrated a clearly demarcated zone of reduced signal intensity consistent with the ischemic zone. It is concluded that high-resolution tomograms of the excised canine myocardium can be obtained using proton NMR imaging. With the SSFP imaging technique, proton signal enhancement with manganese infusion is necessary to differentiate between ischemic and nonischemic myocardium after 90 minutes of coronary occlusion.

Background:This systematic review combines data from multiple papers on contrast media extravasation to identify factors contributing to increased extravasation risk.Methods:Data were extracted from 17 papers reporting 2191 extravasations in 1,104,872 patients (0.2%) undergoing computed tomography (CT) or magnetic resonance imaging (MRI).Results:Extravasation rates were 0.045% for gadolinium-based contrast agents (GBCA) and nearly 6-fold higher, 0.26% for iodinated contrast agents. Factors associated with increased contrast media extravasations included: older age, female gender, using an existing intravenous (IV) instead of placing a new IV in radiology, in-patient status, use of automated power injection, high injection rates, catheter location, and failing to warm up the more viscous contrast media to body temperature.Conclusion:Contrast media extravasation is infrequent but nearly 6 times less frequent with GBCA for MRI compared with iodinated contrast used in CT.

Continent urinary diversions are currently gaining wide acceptance as alternatives to the ileal conduit following cystectomy for neoplasm or bladder dysfunction. Clean, intermittent catheterization of the reservoir (pouch) at regular intervals obviates the inconvenience of wearing an external stomal appliance. A variety of surgical techniques have been described for continent pouches. These techniques make use of the small bowel alone (Camey and Kock techniques) or a combination of cecum and terminal ileum (Indiana, Mainz, Penn, and King techniques). The optimum pouch protects the upper tracts by prevention of reflux, provides urinary continence, and has sufficient capacity to require catheterization no more frequently than every 3-6 hours. Simplified construction techniques for the commonly encountered pouches are graphically presented, and a method is suggested for the study of continent diversions.

Proton nuclear magnetic resonance (NMR) images of cat heads were obtained using a small, experimental imaging system. As a prelude to the study of experimental ischemic brain infarction, the normal cat head was imaged for identification of anatomical features. Images of one cat which had undergone ligation of the middle cerebral artery three weeks previously showed brain changes associated with chronic ischemic stroke and compared favorably with findings on computed tomography (CT). The NMR images have millimetric spatial resolution. NMR parameters inherent in the tissues provide intensity variations and are sufficiently sensitive to yield contrast resolution surpassing that of CT.

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