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Contrast agents based on the lanthanide elements gadolinium and holmium have recently been developed for magnetic resonance imaging (MRI). Because of the increased atomic number of these elements relative to iodine, these new compounds, used as x-ray contrast agents, may yield higher radiographic contrast, and hence improved x-ray image quality, relative to conventional iodinated compounds, for clinically useful x-ray spectra. This possibility has been investigated, in independent experimental and theoretical studies, for two x-ray imaging systems: a digital radiographic system, using an x-ray image intensifier (XRII) and charge-coupled device (CCD) detector; and a conventional screen/film system, using a Lanex Regular screen. Iodine, gadolinium, and holmium contrast agents were investigated over a wide range of concentration-thickness products (0.1-0.6 M cm) and diagnostic x-ray spectra (60-120 kVp). A simple theoretical model of x-ray detector response predicts the experimental radiographic contrast measurements with a mean absolute error of 8.0% for the XRII/CCD system and 5.9% for the screen/film system, and shows that the radiographic contrast for these two systems is representative of all XRII and screen/film systems. An index of image quality is defined, and its dependence on radiographic contrast, x-ray fluence per unit dose, and detective quantum efficiency (DQE) is shown. Theoretical values of the index, predicted by our model, are then used to compare the performance of the three contrast agents for the two systems investigated. In general, iodine performance decreases steadily with increasing kVp, gadolinium performance has a broad maximum near 85 kVp, and gadolinium outperforms holmium. Gadolinium outperforms iodine for spectra above (and vice versa below) about 72 kVp, depending slightly on spectrum filtration, object thickness, and detector type. Thus, raising the kVp to shorten exposure times or reduce x-ray tube heat loading results in a loss of image quality with iodine, but not with gadolinium. Similarly, beam-hardening artifacts in performing video densitometry with iodine would be reduced with gadolinium. Gadolinium-based contrast agents are thus shown to offer several practical advantages over conventional iodinated contrast agents.

A retrospective study of severe adverse reactions to intravenous contrast agents used for intravenous pyelography and enhanced CT scans is reported. There was no difference between large and small hospitals in the incidence and management of serious reactions to these agents. In spite of 81 cardiac or respiratory arrests during over 450,000 intravenous urograms in Ontario, only five deaths occurred.

A digital x-ray imaging system for quantitative arterial imaging and blood flow characterization has been developed in our laboratory and evaluated with a phantom study. The system consists of a low noise photo-diode array detector optically coupled to an x-ray image intensifier. The diode array can be considered as an "add-on" to an existing conventional XRII system to produce high quality images of small regions of interest selected from a larger field of view in fluoroscopy mode. X-ray collimation is used to reduce scatter and veiling glare to increase contrast, reduce a non-linear effect in logarithmically subtracted images, and minimize noise.

Flow alterations to give complete filling of the lymphatic sinusoidal system and saccular lymph spaces around the germinal centers were demonstrated during a primary immune reaction. By contrast, in delayed hypersensitivity, saccules were not seen although there was marked enlargement of individual follicular units.

The speeds of screen -film combinations available in Canada have been measured at 75 kVpwith appropriately filtered beams. The influence on speeds of kVp, attenuation of thefront of the cassette, age and use of screens, reciprocity failure and film variations frombatch to batch is surveyed. The significance of the observed variations in speed (inselecting screen -film combinations) is considered. A set of radiographs of head and bodyphantoms has been used to examine the criteria which radiologists use in defining a 'good'radiograph and from this a qualitative assessment has been made of the priorities inselection of screen -film combinations.IntroductionThe selection of screen -film combinations involves a choice between several conflictingfactors, such as eye appeal of the radiograph, accuracy of diagnosis, dose to the patient,and efficiency and economy of operation of a radiology department. In helping radiologistsand technologists to make a selection we have attempted to answer their questions about thephysical properties of screens and films. Examples of our measurements and results arereported here and their significance to the radiologist is considered. In return radiol-ogists have shown us from sets of test radiographs of phantoms what they consider to be'good' radiographs and have tried to define the parameters they consider important in imagequality. From this we have obtained a qualitative assessment of the relative prioritiesgiven to these parameters in selecting a screen -film combination for general radiography.MethodsSpeeds of screen -film combinations (defined here as the reciprocal of the exposure inmR needed to produce a density of 1.0) were measured using a calibrated three -phase 12pulse generator. Water, lucite and TEMEX water -equivalent rubber phantoms (J. Girdler andSons Ltd., London, U.K.) were used to simulate clinical conditions and provide a suitablyfiltered beam. A simple jig was used to ensure consistent collimation of the X -ray beam.The X -ray exposure of the cassette was measured directly above the front face of thecassette using a pancake -type calibrated ionisation chamber dosimeter. The speeds measuredusing this arrangement were the same as those obtained when the cassette was used with amoving grid in a Bucky tray.Films were processed in DuPont XMD chemistry in a Kodak M6AN processor at 92` F.

Efficient use of low-osmolar contrast media is essential, owing to their cost and increasing substitution for conventional agents. A study was undertaken in three radiology departments to examine use of intravascular contrast media. Over a one-month period in the summer of 1987, the amount of intravascular contrast medium used and discarded was measured in one community hospital and two university-affiliated hospitals in southwestern Ontario. The major part of the waste occurred in the angiography suite, while minimal wastage was recorded in computed tomography. Much less contrast was wasted in the community hospital than in the teaching hospitals. Thirteen percent of all contrast material used by the three hospitals was discarded. Some wastage appears inevitable. Multidose dispensing systems as well as variety in bottle sizes have been proposed to reduce waste. Individual departments need to be aware of the problem and analyze their own patterns of contrast use.

The use of narrow x -ray spectra to produce the radiographic image allows a reduction in patient exposurewithout any appreciable degradation in image quality. When this method is combined with the use of rare -earthintensifying screens, the performance of the screens is improved primarily in terms of patient exposure. A number of screens have been tested in a case of bone imaging with aluminum filtered beams and with ytterbium filtered beams. A summary of the results in terms of radiation doses and image quality is presented. Introduction The idea of using a narrow interval of x -ray energies to produce the radiographic image has been discussedby several authors, and it has been in the literature for about twenty years (5). However, it was only veryrecently that applications of this idea in clinical work have been reported (10). At present the most con-venient method to obtain narrow x -ray spectra is by filtering the output of a tungsten anode tube, withelements of relatively high atomic number. Narrow x -ray spectra obtained by this method have been used inclinical experiments in which the use of holmium filter for intravenous pyelograms reduced patient skin ex-posure by approximately 65%, and the use of an ytterbium filter in lumbar spine examinations resulted in areduction of skin exposure by an average of 35% (10). These results have been obtained using only calciumt_ungstate screens, and the reductions in exposure have been achieved without any detectable image degradation.The x -ray spectrum used for the intravenous pyelograms was mostly contained within the range between 33 keVand 56 keV, and the interval of energies used for lumbar spine studies was between approximately h0 keV and

A total digital teleradiology system using a prototype DuPont laser beam scanner (DTR 2000) and a Bell Canada digital transmission network was evaluated. A total of 489 radiographic and ultrasonographic examinations were transmitted for interpretation from a 41-bed rural community hospital in Seaforth to the University Hospital in London, Ontario, 80 km away. There was concurrence in 98% of these examinations, i.e. the laser-sensitive facsimile film clearly duplicated the original film findings and allowed a confident interpretation to be made. We conclude that this system could readily serve the needs of family physicians in rural communities for radiologic consultation, diagnosis, management, and triage of patients 24 hours per day.

A new x-ray imaging system is being developed for angiographic imaging and blood flow measurments. The system makes use of an x-ray image intensifier optically coupled to a multi-element solid-state photo-detector (Reticon diode array RL1024S). We describe the design of the system and its use in two modes of operation. The first mode is used to produce low noise images by imaging only small regions of interest at a time, thereby reducing noise from the detection of scattered radiation, and by making use of the very large dynamic range (8000:1) of the solid-state detector. The second mode of operation is used to obtain information on the flow of an injected bolus of contrast material through a region of interest. This is accomplished by determining the mean concentration of dye in each 0.33 mm section along the length of an arterial phantom as a function of time over a period of several seconds while the bolus passes through. This data is used to determine areas of flow separation and turbulence due to the presence of simulated stenoses ranging in size from 10% to 84% cross-sectional area reduction. Information on the flow conditions through an artery may be useful for chararterising stenoses or for investigating the conditions associated with the development of atherosclerotic disease.

The authors have developed a new x-ray imaging system for quantitative arterial imaging and blood flow measurements. The system is based on the scanned projection technique and employs an x-ray beam collimated into a fan of radiation and an x-ray image intensifier optically coupled to a 1024-element linear photo-diode detector array. The system has two modes of operation: quantitative projection imaging and blood flow measurements. In the first mode of operation, low-noise, quantitative images are obtained by irradiating small regions of interest to minimize the detection of scattered radiation and intensifier tube veiling glare. System performance is optimized by making use of the large dynamic range (8,000:1) and response linearity of the solid-state photo-detector. In the second mode of operation, flow information is obtained by detecting the passage of a small bolus of iodine contrast agent.

Low osmolar contrast media have been available in Canada for several years. Their introduction has lead to considerable controversy because of the substantive increase in costs compared to conventional ionic media. This increased cost is in the order of 13 times per gram of iodine. There is extensive scrutiny by both the medical profession and Government because of this added cost, estimated to be +17 million annually for cardiology. A challenge is presented to Canadian cardiology to help solve this problem.

An x-ray imaging system is described that can be used for obtaining arterial blood flow information. The system consists of a linear photodiode array image detector, simple optical and mechanical components, and a data acquisition microcomputer that connect to a conventional x-ray image intensifier based fluorography system. Flow information is obtained by detecting the movement of a small, locally injected bolus of radio-opaque contrast agent. This is done by determining the bolus mass, integrated over the cross-sectional area, at each of 1024 positions along the length of the artery with a sampling rate of up to 200 samples per s. It is shown in a phantom study that the peak flow velocity can be measured with an accuracy of +/- 5% by detecting the bolus arrival times at each of the 1024 positions. The mean velocity is obtained with similar accuracy using a cross-correlation technique and a modified form of the Stewart-Hamilton principle. In addition, it is shown that the separation and reattachment points resulting from flow separation near a stenosis can be determined from the bolus clearance times. The locations of these points are consistent with theoretical values for the cosine shaped symmetric 89% stenosis used in this study.

Between June 1, 1976 and Apr. 30, 1981, 157 patients were treated for inoperable cancer of the liver by intermittent percutaneous infusion of chemotherapeutic agents into the hepatic artery. The majority of these patients had metastatic colorectal cancer. The regimen of chemotherapeutic infusion evolved during the study and is described. The survival of the total group of patients is analysed according to type of cancer, extent of disease, dosage and combination of drugs. This therapeutic modality appears to benefit patients with metastases from colorectal cancer confined to the liver. The complication rate for this procedure is relatively low. The results from this study suggest that intermittent percutaneous infusion of cytotoxic agents into the hepatic artery is worthwhile for selected patients and should be studied further in combination with other forms of therapy.

Dose and quality control in diagnostic radiology can play an important role in reducing x-ray exposure and costs whilst maintaining a high level of imaging quality and diagnostic benefit. It can also become very costly. Current government regulations demand unnecessary accuracy in the measurement and performance of certain parameters of x-ray generators whilst ignoring others which are more important. They totally neglect imaging systems. We urge a more critical approach to the requirements for dose and quality control programs. We propose the exchange of information through a user's club and a less regulatory but equally important role for government.

Six cases of cystic hydatid disease of the liver studied by selective angiography are described. In three of these a very characteristic triad of signs was demonstrated. In the fourth case, where the cysts were relatively small and restricted to the left lobe of the liver, no angiographic abnormality and could be found although the diagnosis was strongly suspected clinically. In the fifth case, where the cyst had virtually extruded itself from the liver and had undergone chronic leakage, the findings were atypical. The sixth patient had an old heavily calcified, non-symptomatic cyst, and here the angiographic findings were unremarkable. We believe that these cases illustrate the great value of selective angiography in this condition and some of its limitations.