A Monte-Carlo code for the detailed simulation of electron and light-ion tracks in condensed matter.

In an effort to understand the basic mechanism of the action of charged particles in solid radiation dosimeters, we extend our Monte-Carlo code (MC4) to condensed media (liquids/solids) and present new track-structure calculations for electrons and protons. Modeling the energy dissipation process is based on a model dielectric function, which accounts in a semi-empirical and self-consistent way for condensed-phase effects which are computationally intractable. Importantly, these effects mostly influence track-structure characteristics at the nanometer scale, which is the focus of radiation action models. Since the event-by-event scheme for electron transport is impractical above several kilo-electron volts, a condensed-history random-walk scheme has been implemented to transport the energetic delta rays produced by energetic ions. Based on the above developments, new track-structure calculations are presented for two representative dosimetric materials, namely, liquid water and silicon. Results include radial dose distributions in cylindrical and spherical geometries, as well as, clustering distributions, which, among other things, are important in predicting irreparable damage in biological systems and prompt electric-fields in microelectronics.

Synthesis and study of glutaryl-S-(omega-aminoalkyl)-L-cysteinylglycines as inhibitors of glyoxalase I.

Glutaryl-S-(8-aminooctyl)-L-cysteinylglycine and glutaryl -S-(10-aminodecyl)-L-cysteinylglycine have been prepared by a seven-step procedure as potential ligands for affinity chromatography purification of mouse liver glyoxalase I. Both compounds exhibited nonlinear, mixed-type inhibition of the enzyme. The decyl derivative was a more effective inhibitor than was the octyl analog.

Immunoelectron microscopy of acetylcholine receptors and 43 KD protein after rapid freezing, freeze-substitution, and low-temperature embedding in lowicryl K11M.

To label intracellular determinants of the acetylcholine receptor and associated cytoplasmic proteins while preserving optimal ultrastructure, we developed a post-embedment labeling technique that uses rapid-frozen specimens and freeze-substitution without chemical fixatives. This procedure has been made possible through the use of a low-temperature resin (Lowicryl K11M) that can be polymerized with UV light at -60 degrees C. Rapid-frozen muscle cells were used to evaluate the preservation of structure, and Torpedo electroplaque cells and purified postsynaptic membranes were used to quantitatively evaluate the labeling specificity, efficiency, and resolution of the technique. The labeling efficiency of seven different monoclonal antibodies (MAb) to the acetylcholine receptor varied from 3-13%; there was a correlation between the degree of efficiency and the number of epitopes with which the antibodies reacted. The resolution of the technique was not sufficient to determine whether the anti-acetylcholine receptor MAb were bound to the cytoplasmic or the extracellular surface, but was sufficient to correctly determine the location of the receptor-associated 43 KD protein on the cytoplasmic surface.

Recurrent groin varicose veins: an assessment by descending phlebography.

Descending phlebography was performed in 24 legs with groin recurrence following previous long saphenous vein surgery. Recurrence was demonstrated in 20 legs (83%) and the value of this technique in patient assessment is discussed.

Radiation dosimetry using three-dimensional optical random access memories.

Three-dimensional optical random access memories (3D ORAMs) are a new generation of high-density data storage devices. Binary information is stored and retrieved via a light induced reversible transformation of an ensemble of bistable photochromic molecules embedded in a polymer matrix. This paper describes the application of 3D ORAM materials to radiation dosimetry. It is shown both theoretically and experimentally, that ionizing radiation in the form of heavy charged particles is capable of changing the information originally stored on the ORAM material. The magnitude and spatial distribution of these changes are used as a measure of the absorbed dose, particle type and energy. The effects of exposure on 3D ORAM materials have been investigated for a variety of particle types and energies, including protons, alpha particles and 12C ions. The exposed materials are observed to fluoresce when exposed to laser light. The intensity and the depth of the fluorescence is dependent on the type and energy of the particle to which the materials were exposed. It is shown that these effects can be modeled using Monte Carlo calculations. The model provides a better understanding of the properties of these materials. which should prove useful for developing systems for charged particle and neutron dosimetry/detector applications.

Radiation dosimetry using three-dimensional optical random access memories.

The ability to determine particle type and energy plays an important role in the dosimetry of heavy charged particles (HCP) and neutrons. A new approach to radiation dosimetry is presented, which is shown to be capable of particle type and energy discrimination. This method is based on utilising radiation induced changes in the digital information stored on three-dimensional optical random access memories (3D ORAM). 3D ORAM is a small cube (a few mm3) composed of poly(methyl methacrylate) doped with a photochromic dye. and it was originally proposed as a memory device in high speed parallel computers. A Nd:YAG laser system is used to write and read binary information (bits) on the ORAM, which functions as a charged particle detector. Both the read and the write processes use two laser beams that simultaneously strike the material to cause a colour change at their intersection (similar to the darkening of light-sensitive sunglasses when exposed to sunlight.) The laser produces colour changes in the ORAM, which then reverts to the original colour ('bit-flips') at sites where energy is deposited from interaction with incident HCP or neutron-recoil protons. The feasibility of this approach was demonstrated both theoretically and experimentally. Calculations based on track structure theory (TST) predict that when HCP interact with the ORAM material, the local energy deposition is capable of inducing measurable 'bit-flips'. These predictions were recently confirmed experimentally using two types of ORAM systems, one based on spirobenzopyran and the other on anthracene, as the photochromic dyes.

Feasibility of a neutron detector-dosemeter based on single-event upsets in dynamic random-access memories.

The feasibility was investigated of a solid-state neutron detector/dosemeter based on single-event upset (SEU) effects in dynamic random-access memories (DRAMs), commonly used in computer memories. Such a device, which uses a neutron converter material to produce a charged particle capable of causing an upset, would be light-weight, low-power, and could be read simply by polling the memory for bit flips. It would have significant advantages over standard solid-state neutron dosemeters which require off-line processing for track etching and analysis. Previous efforts at developing an SEU neutron detector/dosemeter have suffered from poor response, which can be greatly enhanced by selecting a modern high-density DRAM chip for SEU sensitivity and by using a thin 10B film as a converter. Past attempts to use 10B were not successful because the average alpha particle energy was insufficient to penetrate to the sensitive region of the memory. This can be overcome by removing the surface passivation layer before depositing the 10B film or by implanting 10B directly into the chip. Previous experimental data show a 10(3) increase in neutron sensitivity by chips containing borosilicate glass, which could be used in an SEU detector. The results are presented of simulations showing that the absolute efficiency of an SEU neutron dosemeter can be increased by at least a factor of 1000 over earlier designs.

Review of arterial vascular ultrasound.

Duplex ultrasound (US) is established as having a major role in the assessment of both extracranial carotid disease and lower limb graft surveillance. It is also of considerable value in the assessment of lower limb ischemia when used in conjunction with clinical and pressure measurements, and in the monitoring of abdominal aneurysms. Its many other arterial applications are of interest but are currently less well defined. The impact of power Doppler, contrast agents, harmonic imaging, and 3-dimensional reconstruction techniques is yet to be fully appreciated.

Review of venous vascular ultrasound.

Duplex ultrasound (US) has become the new gold standard in the assessment of acute deep vein thrombosis. In view of the large number of cases with persistent changes, all cases should be reassessed at 6 months to document the extent of residual disease. The role of duplex US in chronic venous disease is less well established but it is evolving as the single most useful examination and is likely to supplant other noninvasive methods in the near future.

Chondrosarcoma presenting as an anterior mediastinal mass.

We describe a chondrosarcoma presenting as an anterior mediastinal mass. The tumour was unusual in that it simulated more commonly occurring mediastinal tumours. There was relatively little destruction of the anterior chest wall and very little calcification within the lesion.

Relation of infant heart to sternum: its significance in cardiopulmonary resuscitation.

In a radiographic study of 55 infants with an age-range of 27 weeks' gestation to 13 months post-term, the centre of the heart was positioned under the lower third of the sternum in 48 cases. In 4 infants the position was slightly more cephalad, but still below the lower half of the sternum. In 3 infants, the position was below the xiphisternal junction. Present guidelines for infant resuscitation should be revised in view of these findings.

Chaotic phasic pattern as sole ultrasound evidence of extensive post-thrombotic change.

We report three cases of extensive post-thrombotic change confirmed at ascending venography but which did not demonstrate the currently accepted duplex ultrasound criteria for post-thrombotic change. We also document a new ultrasound finding which we describe as a chaotic phasic pattern of deep venous flow which was the only duplex evidence of post-thrombotic change in two of the cases. We suggest that its routine inclusion in duplex ultrasound assessment of the deep veins should be considered.

The value of ultrasound in the assessment of incompetent perforating veins.

To determine the value of ultrasound in identifying significant perforator disease we assessed 121 perforators in 90 legs of 61 consecutive patients referred for assessment of varicose veins over a 6 month period. Perforators greater than 4mm in diameter demonstrated reflux in approximately 60% of cases, perforators 3-4 mm in diameter demonstrated reflux in approximately 45% and perforators less than 3 mm in diameter demonstrated reflux in approximately 25% of cases. From correlation with previous published data we recommend that all perforators greater than 4 mm in diameter be considered incompetent regardless of whether reflux is demonstrated.

Gallstone dissolution by methyl-tert-butyl ether (MTBE) via percutaneous transhepatic cholecystostomy.

Dissolution of gallbladder stones with MTBE appears to be an effective and safe treatment for patients with symptomatic gallstones who are unfit for surgery. However, the procedure is tedious and the stone recurrence rate is as yet unknown.

A comparison of colour duplex ultrasound with venography and varicography in the assessment of varicose veins.

Ninety-three legs in 68 consecutive patients presenting for preoperative assessment of varicose veins were examined by a combination of ascending venography with varicography and also by colour duplex ultrasound. Ninety-one to ninety-two per cent of incompetent sapheno-femoral and sapheno-popliteal communications were demonstrated by ascending venography/varicography and 92-95% by ultrasound. Ascending venography/varicography demonstrated 83-90% of incompetent perforators whilst ultrasound demonstrated only 40-63%. We conclude that ultrasound is an accurate method of assessing primary and recurrent sapheno-femoral and sapheno-popliteal incompetence but is of limited value in assessing perforator incompetence. This is a significant limitation of ultrasound in view of the importance of perforator disease, and it is likely that this technique can only be used in combination with other venographic methods.