Synthesized MR images: comparison with acquired images

Synthesized and directly acquired spin-echo images were compared in order to assess the validity of magnetic resonance (MR) image synthesis as a method enabling retrospective formation of images by interactive manipulation of scan parameters. Synthetic images subjectively compared favorably in both accuracy and precision with acquired images when formed for the same values of echo (TE) and repetition times (TR) and for interpolated and extrapolated values of both TE and TR. Plots of synthetic and acquired signals within the same pixel sectors quantitatively showed comparable values for several regions of interest in the brain. Percent error and noise-normalized differences between acquired and synthetic images were tested as a quantitative measure of accuracy. Percent error was consistently less than 5% for brain parenchyma, and synthetic signals were accurate to within four times the noise level at acquisition. The apparent signal-to-noise ratio of synthetic images was comparable, superior, or inferior to similar acquired images, depending on the values of TE and TR. Total acquisition time required for synthetic formation of images for arbitrary values of TE and TR was equivalent to that of a single direct acquisition with a TR of 2,500 msec.     

Use of CO2 to move structures as an aid to percutaneous procedures

By injecting small amounts of CO2 through a needle, one can move bowel or bladder from the intended path of instruments during interventional procedures. The technique worked well in six of seven cases in the pelvis and retroperitoneum; it was not effective in the mediastinum or midabdomen (n = 6).     

Limitations of the Countershock Dose Response: A Study of Transthoracic Current

Dose response assessment of Countershock efficacy has been widely determined with respect to energy but not current. The purpose of this study was to examine the utility of the dose response method in a current-based model of trunsthoracic defibrillalion (penlobarbital anesthetized dogs, n = 8). Ventricular fibrillation induction lasting 15 seconds was separated by 5-minute intervals. Current defibrillation threshold (DFT: the lowest current that successfully defibrillated) was determined by decreasing current on successive trials. Energy DFT equaled the energy value of the corresponding current DFT. Subsequent data were expressed in normalized terms with each DFT assigned a normalized value of 1.00. Three shocks were delivered in random order at each of seven normalized current nodes (total of 21 shocks); 0.55, 0.70, 0.85, 1.00, 1.15, 1.30, and 2.00 × DFT (early testing). Randomization was repeated, and a second set of 21 trials were performed (late testing). Composite plots were made relating normalized current and energy to the percent successful defibrillation. The dose response expressed in normalized energy demonstrated an overall shift to the left compared to current. The difference was significant at every node value below the estimated DFT. Ninety percent of successful trials with respect to current and energy occurred at or above 0.85 DFT and 0.55 DFT, respectively. Significant changes in impedance occurred between early testing (60 ± 6 ohms) and late testing (47 ± 5 ohms), n = 8, mean ± SD. Current, compared to energy, is a more accurate parameter in the dose response assessment of transfhoracic defibrillation. This phenomenon is largely secondary to a time-dependent fall in impedance that results in lower delivered voltage and energy for a fixed delivered current. Energy should not be used as a parameter of Countershock efficacy.     

Postoperative ileus

Postoperative ileus follows any operation. Although worsened if the peritoneum is entered, the length and duration of surgery does not influence the severity of postoperative ileus. Inhibitory alpha 2-adrenergic reflexes with peptidergic afferents contribute to postoperative ileus. Clinically, treatment of ileus centers around symptomatic relief with nasogastric suction. Trials of adrenergic blockade combined with cholinergic stimulation have met with limited success. Prokinetic drugs have not been proved effective in the treatment of this disorder. Two types of ileus exist: postoperative and paralytic. Postoperative ileus resolves spontaneously after two to three days, and probably reflects inhibition of colonic motility. Paralytic ileus is more severe, last more than three days, and seems to represent inhibition of small bowel activity. No discrete structural changes cause postoperative ileus and the role of peptidergic neuronal systems of the enteric nervous system has not been elucidated. Possible central or humoral mechanisms have not been studied extensively. The possible direct inhibition of enteric or spinal nerves by anesthetic agents not cleared from these tissues remains to be studied. Also in need of study is the potential alteration of neurotransmitter receptor activity within the enteric nervous plexus after manipulation of the bowel.     

Doppler Echocardiography in Pulmonary Stenosis

Doppler ultrasound has dramatically improved the accuracy of noninvasive detection of pulmonary stenosis. Combined with careful two-dimensional imaging, the site and severity of obstruction to pulmonary flow can be detected and quantified. Although there are some limitations to the technique, interpretive errors are avoidable with an understanding of the method and careful attention to detail during the performance of the examination. Doppler echocardiography has become a valuable adjunct to the nonsurgical treatment of valvular pulmonary stenosis and promises to provide more information for developing new management schemes in congenital heart disease.     

Congestive cardiomyopathy in association with AIDS

During a 10-month period in 1985 and 1986, three cases of acquired immunodeficiency syndrome (AIDS) and a rapidly progressive fatal cardiomyopathy were encountered. All three patients originally presented with common opportunistic infections and later experienced marked congestive heart failure associated with echocardiographic and radiologic findings consistent with four-chamber cardiomyopathy. Diffuse cardiomyopathy was confirmed postmortem, but in each case a specific cause was not found.