Comparative effects of stimulation of the trigeminal ganglion and the superior sagittal sinus on cerebral blood flow and evoked potentials in the cat

The superior sagittal sinus (SSS) and the trigeminal ganglion (Vg) of anesthetized cats were stimulated electrically and field potentials in the upper cervical spinal cord and regional cerebral blood flow were recorded. Stimulation of the entire ganglion produced smaller field potential changes in two regions (medioventral area (MVA); dorsolateral area (DLA] of the upper spinal cord than did stimulation of the sagittal sinus (Vg/SSS response ratio = 17% for the MVA and 48% for the DLA). Stimulation of the trigeminal ganglion increased blood flow in only the frontal and parietal cortices (+93% and +33%), whereas stimulation of the sinus produced both larger changes in these areas (+137% and +139%) and also produced changes in regional cerebral blood flow in the thalamus (+122%).     

Insulin degradation: mechanisms, products, and significance

Although much remains to be learned, our understanding of the mechanisms and processes by which insulin is degraded has advanced considerably over the past few years. The roles of receptor binding and internalization in mediating insulin degradation have been clarified, and the endosomal pathway for intracellular insulin degradation has been established and partially characterized. The importance of IP (IDE) in cellular insulin degradation has been established and the importance of lysosomal degradation questioned. Studies on IP have identified the degradation products resulting from insulin metabolism by this enzyme and shown that the degradation products by IP are identical with those produced by isolated hepatocytes. A major remaining question for future investigation is the potential role of insulin degradation and intracellular processing in insulin action.     

Thermoluminescent dosimetry of the SourceTech Medical model STM1251 125I seed

Many new models of 125I seeds are being introduced, mainly due to the increase in prostate seed implants. We have evaluated the SourceTech Medical (STM), model STM1251, 125I seed using thermoluminescent dosimeters (TLDs) in a solid water phantom. TLD cubes, LiF TLD-100, with dimension 1 mm on each edge, were irradiated at various distances, 1, 2, 3, and 5 cm, at angles ranging from 0 degrees to 90 degrees in 10 degrees increments. Sensitivity calibration of the TLDs was achieved by irradiation to 10 cGy with 6 MV x rays from a clinical linear accelerator, Clinac 600C. Concurrent with the 125I seed exposures, several TLDs were also exposed to 10 cGy with the 600C as a control set. Dose rates per unit air kerma strength were determined based on the 1999 NIST traceable standard for the STM1251 seed. They are presented as a function of distance r and angle theta. The TG-43 parameters, including the dose rate constant, lambda, anisotropy function, F(r,theta), radial dose function, g(r), anisotropy factor, phian(r), and anisotropy constant, phi, were obtained for use in radiation treatment planning software. The value of lambda was determined as 1.07 +/- 5.5% cGy U(-1) h(-1), which is comparable to model 6702 and to the value determined using the point extrapolation method by Kirov and Williamson. We also find agreement between our TLD data and their Monte Carlo results for g(r), F(r,theta), phian(r), and phi. Additionally, agreement is found with the TLD data of Li and Williamson for lambda and g(r).     

Verification of Ir-192 near source dosimetry using GAFCHROMIC film

Intravascular brachytherapy treatments of in-stent restenosis have been performed extensively using Ir-192 ribbon. Task Group 60 of the American Association of Physicists in Medicine (AAPM) recommends a dose reference point at 2 mm from the source center for these treatments. However, it is known that the source can be as close as 0.5 mm to the arterial wall if not centered in the lumen. Therefore, the source dosimetry needs to be characterized at these close distances to accurately determine the amount of dose delivered for noncentered cases. In this paper, we report the verification of the dose distributions around Ir-192 seed sources at radial distances from 0.5 mm to 6 mm using GAFCHROMIC film. We evaluated an Ir-192 single seed source and a train of 6 seeds spaced 1 mm apart enclosed in a nylon ribbon. Each source was placed in a homogeneous solid water phantom directly below a stack of GAFCHROMIC films (MD-55-2). The calibration curve of the lot of films used in the experiment was established for Ir-192 by exposing a set of calibration films, one at a time, to an Ir-192 high dose rate (HDR) source. All films were scanned 5 or more days after exposure with a Lumisys Model 150 microdensitometer. The data were acquired and evaluated using RIT113 (Radiological Imaging Technology) software and analyzed using Excel and IDL (Interactive Data Language) software. Isodose curve plots in the plane containing the source's longitudinal axis and dose rate plots in the radial direction were obtained. For both configurations, the dose rates along the transverse axes agree to within the margin of error with previous Monte Carlo results. The isodose curve plots display hot spots near the seed ends, which is consistent with the leakage of beta particles and electrons from the unsealed seed ends as predicted with Monte Carlo calculations.     

Spinal cord dysfunction in Paget's disease of bone. Has medical treatment a vascular basis?

The medical treatment of eight patients with paraparesis associated with Paget's disease of the vertebrae is described. Treatment, for 3 to 87 months, with calcitonin or with diphosphonates produced marked clinical improvement in seven of these patients. From this series and a review of 19 additional case reports it is concluded that favourable clinical response is seen in about 90 per cent of patients, and that this may occur very rapidly. Results are as good or better than those obtained by surgical decompression. It seems possible that paraparesis in some cases may be due to diversion of blood supply from the spinal cord to the highly vascular Pagetic bone giving rise to a vascular "steal" syndrome. It is suggested that medical treatment should be used more widely to avoid or delay the need for operation and reduce the risks of recurrence. These patients, however treated, require lifelong follow-up because relapses are common.