Recanalization of completely occluded superficial femoral or popliteal arteries was attempted in 18 patients with use of an Argon laser-mediated thermal probe. The length of the occluded segments varied between 0.5 and 26.0 cm, but 67% of the occlusions were greater than 9 cm long. The initial success rate was 67%. Arterial perforation occurred in six patients but was not associated with major complications. To study the mechanism of the laser-mediated thermal probe, thermal recanalization was performed on 11 human arterial segments in vitro obtained after amputation, and mechanical recanalization was performed in vitro in 10 human peripheral arteries with use of a guide wire and catheter technique. An additional four arteries were studied with the laser probe as a non-heated mechanical device. Both the mechanical and thermal devices appear to follow a similar pathway through a complete obstruction. These studies suggest that the thermal probe burns through soft fibrous tissue but is mechanically deflected away from hard fibrocalcific plaque. The probe then advances along the plane between the intimal plaque and the media for a variable length before perforating through the adventitia. These observations suggest that the major mechanism of thermal probe recanalization may be a mechanical process. It appears that thermal probe devices do not inherently seek the true lumen of an occluded artery and that better guidance systems need to be developed.

Digftal subtraction techniquesused in the examination of eight patients with salivary and nasolacrimal disease are described. Materials and MethodsThe theory and technology of digital video subtraction imaging has been described in detail [11. Eight consecutive patients referred for evaluation of suspected salivary or nasolacrimal pathology were examined using digital techniques. Our patients were examined using a dedicated Xonics digital DA-20 system. A 9-inch (23-cm) image intensifier (6-inch [1 5-cm] and 4.5-inch [1 1-cm] field sizes also available) is coupled to an Amperex Plumbicon-based television camera. Analog-to-digital conversion is performed with 1 0 bits of resolution, and video images are stored in a 51 2 x 51 2 x 8-bit-deep memory. The system is based on a PDP LSI 1 1/23 computer and a 184 Mbyte disk; image acquisition protocol programming, mask/image reregistration, and video window control are among the available facilities. For digital sialography, a 0 or 00 cannula was inserted into Stensen's duct, and meglumine iothalamate 60% (4-6 ml) was injected by hand. Video images were acquired at 1 frame/sec. The procedure was performed first in thelateral and then in the posteroanterior (PA) projection.Typical exposure values per frame were 90 kVp, 25 mAs. Each projections required a total of 1 0-25 frames per patient examined.For dacryocystography, a 00 cannula was inserted into the punctum of the inferior canaliculus, and 4 ml of meglumine iothalamate was hand-injected. Digital image acquisition was performed in the PA projection at a 1/sec frame rate for a total of five exposures. Technical factors used were 99 kVp and 64 mAs.Image selection, subtraction, and reregistration are performed by the radiologist. Hardcopy images are recorded by standard multiformat camera.Radiation exposure of the lens of the eye was estimated using a standard phantom and an MDH IOI5C x-ray probe for both procedures.

The solution casting of films of common plastics on water can provide a simple, rapid method for a classroom demonstration of the formation of transparent films.

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