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A device was developed for mapping left ventricular endocardial activation through the aortic valve during surgery. It uses an exploring electrode at the tip of a hand-held probe that is mounted on a mechanical arm with six joints whose movements are digitized by a computer while the position of the probe tip is calculated continuously. The probe is inserted by the surgeon into the left ventricle retrogradely through the aortic valve after the patient is on total cardiopulmonary bypass, the aorta has been opened and the coronary arteries cannulated.

The target of the X-ray tube is enclosed in a massive lead cone at the open end of which are placed two sets of 2-inch thick blocks mounted at right angles (Fig. 2). These blocks form the usual type of adjustable diaphragm device for square and rectangular fields. The original ones were of lead which transmitted approximately 7 per cent. of the primary beam, and even more in places where they had brass inserts. They were replaced by blocks of G.E.C. heavy alloy (95 per cent. tungsten), and the method of mounting was modified to avoid brass inserts. The radiation escaping the outside edges of the blocks was lessened by reducing the maximum aperture, limiting the field to 22 × 18 cm. at 100 cm. focus-skin distance.A steel holder was added in which heavy alloy inserts could be fitted for defining circular fields (Fig. 3A) and grid fields (Fig. 3B). Thin perspex plates incorporated in these inserts removed the electrons produced by the X-ray beam glancing on their tapered apertures. These fields are used at two focus-skin distances (67 cm. and 100 cm.) in order to increase the number of available field sizes. In practice the diaphragms for defining square and oblong fields are closed until they just obscure parts of the circle and are then opened slightly. This stops radiation escaping around the outside of the circular insert. For grid fields the adjustable diaphragm is used to define the superficial field size.

An account is given of the construction and use of a comparatively inexpensive whole-body counting room, designed primarily for clinical applications. Bulk shielding is provided by about 16 tons of chalk, loaded into polythenelined paper bags, to form a layer 2 ft. thick, the room being lined inside with 0·25 thick aged lead sheets. Comparative studies of the background of scintillation counters in this room, and in other shielded rooms, are presented; it is noted that for ? energies > 250 keV the background was reduced from 50 to 4·2 cps when a particular counter was taken from a brick-walled laboratory into the chalk-bag shielded room, but only by a further 2·6 cps if instead the counter was shielded by 4 in. of lead. Illustrations of clinical applications of the room are given, these, using three 3 in. diameter × 2 in. long NaI (TI) crystals as detectors, including studies of the retention and redistribution of 47Ca following the administration of about 1 µc of this nuclide, and measurements of the retention of 131I several weeks after therapeutic administration to patients. Examples are also given of measurement of low-level contamination due to the administration of Thorotrast, and to the ingestion of 131I from radioactive fallout during a period of nuclear weapon tests.

The technique of scanning automatically with a scintillation detector for the localisation of radioactive isotopes in vivohas been in use for many years at the Institute of Cancer Research (Mayneord, Evans and Newbery, 1955). The apparatus described here, the prototype of which was constructed in 1955, was designed for large-area scanning with a non-adjustable mechanical movement, readily interchangeable collimators, and pulse-height analysis. The mechanical system was built on to a diagnostic X-ray set couch with the detector head moving in an undercouch plane. The alternative system in which the patient moves while the detector head remains stationary has been adopted in other designs (Mallard and Peachey, 1959). The final version of this scanner has been in use since October, 1958, and has proved satisfactory for several of the clinical investigations in hand which require the scanning of large areas.The mechanical movement was designed to produce a square-wave motion of the detector head with a width of scan of 18¾ in., a line separation of ? in., and a length of frame of 12½ in. for each setting of the instrument. The line movement is produced by a reciprocating Archimedean screw, i.e., one having both right-hand and left-hand threads linked at each end of the screw to make a continuous screw-form, which moves the detector head at a speed of 1½ in./second. The line-spacing is produced by a screw with a square-cut thread synchronised to the line screw by a Geneva movement and worm and wheel drive.

Several instruments have been designed for implanting radon seeds, all of which seem to us to have serious disadvantages. The chief difficulty in producing a satisfactory type has been the variation in size and shape of the seeds supplied. Radon seeds themselves have other disadvantages, the chief of which are difficulties in protecting those engaged in their preparation and the expense and waste involved when they are ordered and not used. This waste is considerable if seeds are to be available at the time of exploratory operations for use only should the condition prove to be inoperable. Such considerations have been responsible for the neglect of a valuable method of treatment in some centres, for there are many occasions in the treatment of patients with cancer when it would be a great advantage to have a precision instrument available for the speedy implantation of multiple small sources of radiation.We have attempted to overcome these difficulties by using short sections (“grains”) of radioactive gold wire encased in platinum, which serves to filter the primary β radiation from Au198(see preceding paper, page 417.) The overall dimensions of the grains are: length 2·5 mm., diameter 0·8 mm., and they can be accurately machined, with the result that a precision introducer may be designed for them.A schematic diagram of the introducer, or “gun”, is shown in Fig. 1. The duralumin magazine (A) is loaded with 15 inactive gold grains and the end caps are screwed on.

The chair illustrated in Figs. 1 and 2 was designed to meet the need for accurate adjustment and rigid but comfortable support of patients undergoing radiotherapy—particularly of the head and neck—by a 60Co teletherapy beam. It differs from chairs previously described (e.g.Wiernik, 1961) in that the castors are used only to bring the chair into approximately the correct position relative to the treatment head. The chair is then immobilized by pressure pads on the floor and the final accurate adjustments made on guide rails built into the chair itself. Each of these movements is controlled by a lead screw. The seat is supported on two tubular arcs (Fig. 2) resting on nylon rollers and its angle can be varied smoothly with the patient sitting in the chair, from horizontal to about 45 deg. by means of the large handwheel at the back of the chair.