Optical mode solving for complex waveguides using a finite cloud method.

A meshless method for the solution of full vectorial optical mode fields has been applied to micro-structured optical waveguides. The Finite Cloud Method is used to approximate the solution using a point distribution and material definitions. Presented are two methods of defining material interfaces, one which implements a step index and a second which uses a graded index. Coupled field equations are used to solve for both transverse components of the magnetic field as well as the guided wavelength and effective index of refraction. Comparing results for a ridge waveguide, solid core, micro-structured and air core structures with commercial FEM solvers highlight the methods versatility, accuracy and efficiency.

An upgraded x-ray spectroscopy diagnostic on MST.

An upgraded x-ray spectroscopy diagnostic is used to measure the distribution of fast electrons in MST and to determine Z(eff) and the particle diffusion coefficient D(r). A radial array of 12 CdZnTe hard-x-ray detectors measures 10-150 keV Bremsstrahlung from fast electrons, a signature of reduced stochasticity and improved confinement in the plasma. A new Si soft-x-ray detector measures 2-10 keV Bremsstrahlung from thermal and fast electrons. The shaped output pulses from both detector types are digitized and the resulting waveforms are fit with Gaussians to resolve pileup and provide good time and energy resolution. Lead apertures prevent detector saturation and provide a well-known etendue, while lead shielding prevents pickup from stray x-rays. New Be vacuum windows transmit >2 keV x-rays, and additional Al and Be filters are sometimes used to reduce low energy flux for better resolution at higher energies. Measured spectra are compared to those predicted by the Fokker-Planck code CQL3D to deduce Z(eff) and D(r).

Biliary and other gastrointestinal interventions.

Over the past several years, renewed interest in biliary endoprostheses has developed among interventional radiologists. The experimental, technical, and clinical progress that produced this enthusiasm is reviewed, with emphasis on recently published reports. The application of percutaneous enterostomy for gastric decompression or feeding has become widely practiced, and recent reports of percutaneous and endoscopic gastrostomy are compared, with emphasis on controversial points. The technique of percutaneous enterostomy has been adapted for jejunal and colonic application, and these technical modifications, as well as miscellaneous biliary and gastrointestinal interventions, comprise the remainder of the review.

Assessment of heparin anticoagulation during peripheral angioplasty.

The amount of heparin administered during peripheral angioplasty procedures is controversial and varies greatly among angiographers. Complications may result from both excessive and insufficient anticoagulation. The authors characterized the anticoagulant response to heparin in patients undergoing angioplasty by means of the activated clotting time (ACT). The ACT was measured in 64 patients who underwent lower extremity angioplasty. There was a linear relationship between heparin dose and ACT (P = .0001), but the slope of this relationship varied from patient to patient (R2 = .232). The response to heparin was blunted in one patient with thrombosis, but it was not exaggerated in patients with hematomas. Heparin anticoagulant response is highly variable, and heparin administration should be individualized according to ACT to produce a desired level of anticoagulation. Use of the ACT is a convenient and reproducible means of monitoring heparin administration and may increase safety and efficacy during peripheral angioplasty.

Percutaneous extraction of gallstones in 20 patients.

Percutaneous cholecystolithotomy (PCL) was accomplished successfully without general anesthesia in 17 of 20 consecutive symptomatic patients from an outpatient gallstone center who were at risk for or had refused cholecystectomy. The other three patients underwent cholecystectomy because of a gallbladder collapse before admission, a tight stone-bearing phrygian cap, and a cannula slippage, respectively. A subhepatic approach was preferentially used after the fundus of the gallbladder was stabilized with a percutaneous anchor to prevent invagination and bile leakage. Retrograde slippage of the anchor into the tract in the first six patients was remedied by elongating the anchor from 2 to 3 cm. Calculi were removed in one session (11 patients) or two consecutive sessions (six patients). Morbidity included rehospitalization for stitch infection (n = 1) and dehydration (n = 1), cannula slippage (n = 1), broken guide wire (n = 1), vasovagal reaction (n = 1), and unextractable anchors (n = 3). Gallbladder endoscopy enabled identification of stones not visible at cholecystography. Hospitalization lasted 3-5 days; outpatient gallbladder drains were removed in 2-3 weeks in 10 patients and 4-6 weeks in seven (older) patients. No retained stones were seen at 6 months. The authors recommend PCL for patients at risk for surgery.

Angioplasty-induced dissections in human iliac arteries: management with Palmaz balloon-expandable intraluminal stents.

Intravascular stent placement may be an effective treatment for percutaneous transluminal angioplasty (PTA)-induced dissection. Among the first 228 patients treated with Palmaz balloon-expandable intraluminal stents (BEISs) for iliac artery stenosis, stents were used to treat PTA-induced dissection in at least 12 iliac arteries in 11 patients. All 12 vessels were shown by angiography to be severely dissected. Stents were placed at the time of PTA in six vessels and as a separate procedure in the other six. An average of three stents per vessel were employed. All arteries showed marked improvement at angiography. Angiographic follow-up was obtained for eight vessels in seven patients at a mean follow-up time of 12.9 months. All had patent stent lumens with neointima formation, although one stented lumen had narrowed, and another clinical failure occurred despite a patent stented vessel and an ankle-arm index (AAI) of 1.35. With a mean clinical follow-up of 9.5 months, the mean AAI for the stented extremities in the nine remaining patients is 0.91 +/- 0.15. Palmaz BEISs are effective in the management of PTA-induced human iliac artery dissection.

Angiography in poor-risk patients with massive nonvariceal upper gastrointestinal bleeding.

The purpose of this retrospective study was to determine the diagnostic and therapeutic usefulness of gut angiography in patients with massive upper gastrointestinal bleeding from a nonvariceal source. All patients (n = 64) in this category who underwent a gut angiogram between 1980 and 1986 were studied. Pre-angiogram endoscopy was attempted in all patients and was nondiagnostic in 14 (22%). Contrast extravasation at angiography was seen in 25 of 64 patients (39%), and in over half of these patients endoscopy was nondiagnostic (n = 11) or wrong (n = 3). Attempts to control bleeding in this group by selective arterial embolization (n = 14) or intra-arterial vasopressin (n = 11) successfully averted operation in 13 of 25 patients (52%) and was associated with a 50% reduction in mortality (83% versus 38%). Selective embolization of vessels thought to be bleeding on clinical grounds without evidence of contrast extravasation (i.e., "blind" embolization) was not helpful in controlling hemorrhage. Urgent gut angiography in patients with massive upper gastrointestinal bleeding of arteriocapillary source is a useful diagnostic and therapeutic maneuver and warrants continued application in this group of poor-risk patients.

Obstructions of the hepatic duct confluence: internal drainage of bilateral lesions with a single catheter.

Strictures at the confluence of the right and left hepatic ducts are difficult to treat surgically, endoscopically, or percutaneously. Percutaneous decompression techniques previously described involved separate transhepatic catheterizations of the isolated right and left ducts. In the present study, modifications of existing self-retaining loop drainage catheters allowed bilateral internal biliary drainage of isolated right and left hepatic ductal systems with a single catheter in three patients. The technique can be used for primary palliation and for recurrent strictures after hepaticojejunostomy.

Role of endoprostheses in the management of malignant biliary obstruction.

Therapeutic and palliative procedures for treating biliary obstruction can be surgical, percutaneous, or endoscopic. Incurable malignancies can be palliated by each of these three approaches. None of these has an advantage in terms of longevity over the others. Choosing the procedure which offers the best quality of life for the individual patient is complex. The virulence of the underlying tumor, the anatomic location within the biliary tree, and the availability of expertise in each of the alternative methods must be considered. For the group of patients whose conditions are palliated with transhepatic biliary drainage, the choice between chronic indwelling internal-external catheter versus endoprosthesis placement involves questions of utility, patient acceptance, and the geometry of the obstructed biliary tree. Each of these must be considered before deciding on the approach which offers the best compromise of the technical preferences of the physician, the psychological preferences of the patient, and the limitations imposed by the level and number of obstructions. Research by radiologists and gastroenterologists has resulted in improved endoprosthesis function. Current research aimed at improving stability and patency promises further improvements in endoprosthesis efficacy.

Malignant jejunal strictures after Whipple procedure: stenting with large-bore tubes and use of combined transhepatic and peroral approach.

Malignant strictures of the afferent jejunal limbs are difficult to treat. Surgical revision and chronic external drainage, two commonly used palliative procedures, have significant associated morbidity. A combined transhepatic and peroral approach was used to stent malignant jejunal strictures in two patients, allowing antegrade internal drainage of biliary and pancreatic secretions. Excellent palliation was achieved, and there were no associated complications.

Percutaneous drainage of abscesses in patients with Crohn's disease.

The hospital courses of 9 patients with intraabdominal abscesses and Crohn's disease who underwent abscess drainage utilizing percutaneous techniques were reviewed. Percutaneous methods brought about resolution of fever, leukocytosis, and the abscess cavity in 8 patients. In 5 of these, definitive cure was achieved with percutaneous drainage. In 3, single-stage bowel surgery and fistulectomy were performed following resolution of the abscess cavities and improvement of clinical signs and symptoms. All patients had uncomplicated postoperative courses. Percutaneous drainage should be the initial drainage procedure in treating postoperative abscesses, and, when performed preoperatively, can diminish surgical morbidity.