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Magnetic resonance force microscopy (MRFM) is a scanning probe technique capable of detecting MRI signals from nanoscale sample volumes, providing a paradigm-changing potential for structural biology and medical research. Thus far, however, experiments have not reached sufficient spatial resolution for retrieving meaningful structural information from samples. In this work, we report MRFM imaging scans demonstrating a resolution of 0.9 nm and a localization precision of 0.6 nm in one dimension. Our progress is enabled by an improved spin excitation protocol furnishing us with sharp spatial control on the MRFM imaging slice, combined with overall advances in instrument stability. From a modeling of the slice function, we expect that our arrangement supports spatial resolutions down to 0.3 nm given sufficient signal-to-noise ratio. Our experiment demonstrates the feasibility of subnanometer MRI and realizes an important milestone toward the three-dimensional imaging of macromolecular structures.

Internationally agreed standards for radiation measurements applied to medicine underpin the application of scientific methods to both therapeutic and diagnostic radiological practices. Equally it is recommended that these standards should underpin radiation measurements within the fields of nuclear energy and industrial applications of ionizing radiations. Such measurements should also apply to all exposed groups: patients, workers and members of the general public. It would appear that the underlying philosophy as well as measurement methods, including units, employed in the therapeutic and diagnostic domains have developed separately and independently over the past 30 years. Similarly, although radiological imaging methods are fundamental to both domains, a similar situation appears to apply to the assessment of image quality. This letter attempts to highlight the present situation regarding the role and relevance of dosimetric methods applied in both therapeutic and diagnostic radiological practices. In particular the present situation is discussed in relation to the primary objectives of the International Commission on Radiological Units and Measurements (ICRU). Scope for harmonization and unification of scientific methods applied in therapy and diagnosis is highlighted.

Preliminary images produced by a prototype digital radiographic imaging system are presented. These images indicate the potential of this technique and also highlight the interplay between hardware and software developments in digital imaging. The existing imaging performance, approximately 1% large area threshold contrast and 2 lp/mm resolution, compares quite favourably with screen/film performance for the same total absorbed X-ray energy. At present the resolution limit is set by the electrometer probe and ionographic. chamber design. It seems quite probable that systems can be designed with resolutions exceeding the limit. However, other factors will then begin to play a more noticeable role, for instance:—(i) The accuracy with which the heads can be incremented at the end of each scan line;(ii) The foil-to-probe separation;(iii) Factors inherent in the ionography.Similarly, for large image fields the interplay between resolution, the rate of data collection, image memory size, display characteristics, and image processing facilities will all need to be considered. Nevertheless it appears that digital radiographic systems with large field sizes, satisfactory digital image characteristics and radiographic factors can be produced with existing technology.

Educational software has been designed and developed for training within the field of diagnostic radiography and is particularly concerned with the science and technology of diagnostic X-rays. The material has been structured into hypertext networks and as such allows interactive exploration of the available information. The courseware development platform was Microsoft Windows and authoring was accomplished using the constructional tool kit ToolBook. The resulting CAL package is highly graphical in nature with a user interface designed to meet the ‘friendliness’ demands of the end user group. Mechanisms for navigation through, and orientation within, the hypertext have also been established which support two levels of user activities. By changing the level of user freedom, students using the system as a learning tool are restricted to more structured routes than experienced staff using the courseware as an information resource. An aim of this work has been to provide interactive educational activities to support the main courseware, and consequently a novel application has been developed using dynamic data exchange (DDE) and the spreadsheet software Excel. Through a ToolBook front end students can interactively alter an X-ray spectrum by changing the operating conditions of a simulated X-ray tube.

Lithium fluoride (LiF) thermoluminescent dosemeters (TLD) have been employed to measure the radiation dose distribution within a phantom and the central axis dose in air. Results are presented for seven (four EMI CT1010, one EMI CT5005, one EMI CT7070 and one Siemens DR2) different machines. Organ doses for four different computed tomography (CT) investigations (head, lung, liver and pelvis) have been estimated from previously published tables and the central axis dose in air in 3 CT units. These estimated organ doses were used in turn to deduce the somatic and genetic risks for the four types of CT examination. These calculations indicate that for an ‘average’ male patient undergoing a CT examination corresponding to the average conditions encountered, the total somatic risks are 3.15 10-4, 1.98 10-4, 2.31 10-4, and 1.38 10-4for head, lung, liver and pelvis scans, respectively. The corresponding figures for female patients are 3.39 10-4, 3.95 10-4, 2.73 10-4, and 1.60 10-4. The risk from head scanning is approximately 250 times that of a dental pantomograph. Somatic and genetic risks will be approximately twice as high for contrast examinations.

Measurements of scattered radiation were made on two fluoroscopic installations, one with an overcouch tube and one with an undercouch tube. The annual doses to staff involved in a fluoroscopic procedure undertaken on both types of unit were estimated using measured dose rates and weighting factors referred to in ICRP 26.Environmental monitoring at the protective barrier was performed for various room layouts to determine the effect of both equipment and room design on the annual dose received by staff at the control panel. In all circumstances the annual dose to staff inside the control cubicle was negligible.

In order to investigate the levels of radiation exposure resulting from fluoroscopic examinations, area–exposure product measurements were performed on 6532 patients whilst undergoing a variety of examinations at a large district general hospital. Results for both the same and different types of examinations, performed in two different X-ray rooms by a number of different radiologists, are compared in order to highlight some of the factors which influence the wide variations in patient exposure which frequently occur in radiological examinations. Variations in exposure of patients of different weights are also presented.

Lithium fluoride (LiF) thermoluminescent dosemeters (TLD) have been employed to measure the radiation dose distribution within a phantom and the central axis dose in air. Results are presented for seven (four EMI CT1010, one EMI CT5005, one EMI CT7070 and one Siemens DR2) different machines. Organ doses for four different computed tomography (CT) investigations (head, lung, liver and pelvis) have been estimated from previously published tables and the central axis dose in air in 3 CT units. These estimated organ doses were used in turn to deduce the somatic and genetic risks for the four types of CT examination. These calculations indicate that for an ‘average’ male patient undergoing a CT examination corresponding to the average conditions encountered, the total somatic risks are 3.15 10−4, 1.98 10−4, 2.31 10−4, and 1.38 10−4for head, lung, liver and pelvis scans, respectively. The corresponding figures for female patients are 3.39 10−4, 3.95 10−4, 2.73 10−4, and 1.60 10−4. The risk from head scanning is approximately 250 times that of a dental pantomograph. Somatic and genetic risks will be approximately twice as high for contrast examinations.

The purpose of this study was to assess the suitability of different radiation dosimetry methods and record radiation exposures during paediatric catheterization. Three methods of dosimetry were employed: thermoluminescent dosimetry (TLD), dose-area product and calculation of entrance surface dose from calibrated exposure factors. Examinations included bi-plane fluoroscopy, and cineangiography for diagnosis and treatment of congenital heart disease. The most suitable method of radiation dosimetry for cardiac catheterization is the use of calculated entrance dose or a dose-area product meter. Children were exposed to high levels of radiation during cardiac catheterization but there was a wide variation in radiation dosage. Careful consideration should be given to the suitability of radiation dosimetry for cardiac catheterization.

Radiation dose levels in xeromammography were measured both on entry and exit surfaces of the breast. The mean skin dose in the upper inner quadrant was 2.4 rad for a complete examination. The addition of 1 mm aluminium filtration reduced this dose to 1.6 rad. The mean dose to the breast tissues is, however, a more meaningful indication of potential hazard from mammographic investigations and entrance and exit dose measurements enable this to be assessed.

A number of image-processing techniques have been applied to a digital ionographic chest image in order to evaluate their possible effects on this type of image. In order to quantify any effect, a simulated lesion was superimposed on the image at a variety of locations representing different types of structural detail. Visualization of these lesions was evaluated by a number of observers both pre- and post-processing operations. The operations employed included grey-scale transformations, histogram operations, edge-enhancement and smoothing functions. The resulting effects of these operations on the visualization of the simulated lesions are discussed.

A test phantom containing simulated micro-calcifications was constructed. This was imaged by seven systems suitable for use in mammography, firstly in scatter-free conditions and secondly with the addition of tissue-equivalent scattering material. The ability of the systems to resolve micro-particles of known size was assessed using the techniques of signal detection theory. The resultant receiver operating characteristic curves separated the systems into three major groups. Firstly, high resolution systems requiring high radiation dose techniques; secondly at the other extreme, a mediocre imaging system producing its results at low radiation levels; and thirdly a larger middle group producing intermediate resolution of fine particles at similar, acceptable dose levels. The ability to image small particles does not increase linearly with the radiation dose. Scatter did not affect all of the systems to the same extent.

Eye dose measurements have been performed when using medium speed conventional and rare-earth screen-film combinations during tomography of the para-nasal sinuses. The measurements show that using conventional intensifying screens with the A.P. view a total eye dose of about 20 rad may be given during an examination. This eye dose can be reduced by 98% using the P.A. position. If rare-earth screen/film combinations are employed the eye dose measured in the A.P. view was reduced by 75% of that obtained with conventional screens without detectable loss of image quality. A total eye dose reduction of about 99·5% was measured in the P.A. view with the rare-earth systems.

There are currently two groups of individuals studying assossment of work-load. Thousands of work study officers are performing this task, generally as a basis for payment purposes, using techniques relatively unchanged for 40 years. Work physiologists are also concerned with examining the same problem with a different set of motives and methods.An attempt is made here to compare the two assessments on four arduous operations. The physiological evaluations were those of energy expenditure, whilst the work study officers' assessment was achieved by showing films of the operations to 105 practising observers throughout the country.The two final sots of values disagree alarmingly. Naturally, the work physiologist feels the work study officer is expecting too much, whilst he, in turn, before contemplating changing his methods, requires more justification for the physiological norms,

A programme has been set up to monitor the exposure of personnel during specific diagnostic procedures. This programme includes the investigation of radiation hazard associated with the operation of computed tomography scanners.The first-generation CT scanners employed a rotatetranslate geometry where both the detectors and the X-ray tube moved around the patient. Since then, there have been many advances in the design of CT scanners, such as the introduction of a fan-beam geometry coupled with a multi-detector array. These design changes have had little effect on the number of photons employed in producing an image; any reduction in exposure time in later-generation units is balanced by an increase in beam size. However, the decrease in time of exposure and picture reconstruction has enabled the number of tomographic sections in any given period of time to be increased. This increase allows either a larger throughput of patients and/or more slices per patient. Consequently, the total magnitude of scattered radiation will increase.

The possibility of employing ionography as a digital radiographic imaging system and the preliminary results produced by a laboratory prototype system have recently been presented (Moores et al, 1984; 1985). This work demonstrated the feasibility of employing digital ionography clinically. Given the potential for technical improvements in most aspects of the design, it seems quite possible with this approach to meet many of the requirements of a digital radiographic transducer.The laboratory prototype unit employed an ionography chamber which had been designed for mammorgraphy (Moores et al, 1980). Consequently the limited field size and sensitivity of this system make it unsuitable for more general radiographic applications.

Electrostatic X-ray image forming systems have received a great deal of attention over the past decade due to their potential as a replacement for conventional screen/film systems. Initially, the most promising approach was xeroradiography and a commercial unit manufactured by Xerox Corporation has been employed routinely in mammography. However, owing to its relative insensitivity it has not found widespread use in radiology.An alternative approach, ionography, employing a layer of gas to achieve X-ray absorption and charge generation has also received a great deal of attention by both commercial (Muntz et al, 1975; Proudian et al, 1974) and a number of research groups (Johns et al, 1974; Seelentag & Boag, 1979; Fenster et al, 1974). All of this work has been undertaken with gas under high pressures to ensure sufficient X-ray absorption. This approach does, however, suffer from two main problems:—(a) relatively thick front plates must be employed on the chamber to withstand high gas pressures. This can lead to significant X-ray absorption in the front plate with corresponding increase in patient exposure,(b) the routine use of high pressure gas containers in the vicinity of patients may not have zero risk, particularly when producing large area full field X-ray images.In order to try and overcome these problems whilst at the same time investigating its potential for use in radiology, an atmospheric pressure ionography system was designed and constructed.

We wish to raise a number of issues concerning radiation protection aspects associated with well women breast cancer screening programmes now established throughout the UK.Does irradiation of well women for screening purposes constitute a medical exposure and, therefore, fall within the terms of the 1988 Ionizing Radiation (Protection of Persons Undergoing Medical Examination or Treatment) Regulations? If so, then according to section 4 part 3, persons physically directing a medical exposure shall select procedures such as to ensure a dose of ionizing radiation to the “patient” as low as reasonably parcticable in order to achieve the required diagnostic or therapeutic purpose.

We would like to thank all those who responded to our letter (Moores & Henshaw, 1992). We are fully conversant with the views expressed in all of the replies but unfortunately we feel that none address the fundamental operational radiation protection issues raised in our letter. Therefore, we would like to make the following comments to these replies.1. Law et al quite rightly point out that: “Screening programmes… should be undertaken only if the expected medical benefits to the individuals examined and to the population as a whole exceed the economic and social costs, including the risks associated with the radiation involved. Since benefits are not always the same for all members of the population screening should be limited normally to particular groups”. The main elements of this statement are:(a) A screening programme has responsibilities to the individual as well as to the population.(b) Since well women participating in a breast screening programme are volunteers all those participating should be provided with information appropriate to their own circumstances if they are expected to give informed consent.(c) Particular groups may need to be considered separately, particularly if items (a) and (b) are to be effectively implemented.

In order to ensure the widespread application of information technology to departments of medical imaging, there is a real need to develop a digitally compatible, film-replacement, radiographic imaging system. The feasibility of employing digital ionography in this capacity has been demonstrated Moores et al, 1984, 1985) using a laboratory prototype system.We wish to present preliminary results produced by the clinical prototype digital ionography system in order to demonstrate its imaging capability as well as indicate the overall potential of this technology.

In a recent publication (Robinson and Grimshaw, 1975) a comparison was made of the pinhole and star-pattern methods of focal spot size determinations. The authors highlighted the practical difficulties associated with the pinhole technique and also the fact that this method does not take into account the effect on resolution of the focal spot intensity distribution. The star-pattern technique which could provide a quantitative measure of the radiographic properties of the focal spot was proposed as an alternative to the pinhole method.

The phosphorus halides PX3(X: F, Cl, Br) all form molecular complexes with ozone in solid argon.

This report presents the proceedings of a meeting that was held in Bilthoven in October, 1982 concerning a radiation protection dosimeter intercomparison programme, initiated in 1979 and completed in 1982. There were 48 participants in attendance at the meeting, originating from 9 European states. The largest contingents came from Germany, Holland and the United Kingdom but the proceedings do provide an overall perspective of European scientific involvement in personal dosimetry.

The major reaction products between stibine and ozone, which are codeposited with excess argon at 12 K, are shown to be stibylene ozonide, HSbO3, and hydroxystibine, H2SbOH.

I wish to comment on the paper entitled “A new phantom for mammography” by J. Law (1991). In this paper the author compares the performance of a mammographic test phantom from Du Pont with the Bart's phantom (White & Tucker, 1980) by measuring the numbers of image details visible in images of each phantom for different radiographic factors; kV, focal-spot size, screen/film combination and processing. Unfortunately the comparison as presented is quite inconsistent and highlights the need for great care when attempting to compare the performance of test phantoms.In the case of the Bart's phantom six images were produced for each set of radiographic conditions. A “global” image-detail score was then measured for each image and the average of the six images formed. Thus, for this phantom the average global score per single image was the measure of performance for a particular set of radiographic conditions.

Digital radiography as a subject area is beginning to show rapid growth, and this book is an indication of this. It presents the proceedings of a summer school held in 1984 and organised by the American Association of Physicists in Medicine.

This book is intended to be an up-to-date text dealing with equipment employed in X-ray medical imaging and aimed at radiographers and radiologists in training. The book is 588 pages long and is divided into three parts: A, B and C.Part A is divided into two sections, A and B, with Section A itself divided into 10 chapters and two parts. Part B, comprising four chapters, is divided into Sections C and D whilst Part C is Section E. Having unravelled the structure of the book it is then possible to consider the content. Part A, Section A covers X-ray tubes and generators, including timers, tables and tube supports, tomographic equipment, portable/dental units and other techniques including mammography, high-kV techniques and photofluorography. Part A, Section B deals with image intensifier/TV systems.

The title of this book should more correctly read ‘digital information processing in radiology’, since parts of it deal with the calculation and measurement of quantities that arise from a database which can be used, although not always necessarily, to produce images. Nuclear medicine has long realised this distinction but then the level of image quality produced by this modality more easily engenders this philosophy. The book highlights again the less than clear situation which already exists in digital radiology concerning the structural philosophy of the subject and the nomenclature employed.