The flow of blood to lymph nodes and its relation to lymphocyte traffic and the immune response.

The blood flow to individual lymph nodes of sheep and rabbits has been determined with 85Sr-labeled microspheres. A popliteal node of the sheep received 0.014% of the cardiac output and a comparable node in the rabbit 0.011%. A sheep lymph node weighing 1 g received an average of 24 ml/h of blood. It was calculated that there was a highly selective removal of lymphocytes by the node and that an equivalent to one in every four lymphocytes that entered a normal lymph node migrated out of the blood, through the substance of the node, and into the efferent lymph. During the immune response to either allogeneic lymphocytes or tuberculin, the blood flow to sheep lymph nodes, even without considering the increase in node weight, increased an average of fourfold. During the primary immune response in the rabbit to keyhole limpet hemocyanin, the blood flow increased threefold. The increase in blood flow preceded the antigen-induced increase in lymphocyte traffic recorded in the efferent lymph. The early phase of increased blood flow was considered to be due to hyperemia, whereas the latter phase had a significant angiogenesis component. It was calculated that an equivalent to 60% of the entire mobilizable pool of lymphocytes could pass through an average lymph node in the blood during an immune response lasting 5 days.

A new system for quantitative arterial imaging and blood flow measurements.

A new x-ray imaging system is being developed for quantitative arterial imaging and blood flow measurements. The system consists of an x-ray image intensifier optically coupled with a 1024-element photo-diode detector array. Low-noise, quantitative images are obtained by irradiating small regions of interest to minimize the detection of scattered radiation and intensifier tube veiling glare, and by making use of the large dynamic range (8000:1) and response linearity of the solid-state photo-detector. In the first of two modes of operation, low-noise scanned projection images are produced. Stenosis size (reduction of lumen area) in phantoms is determined with a maximum uncertainty of 10% over a range of iodine contrast agent concentrations of 4 to 100 mg/ml in a 1.0 cm2 cross-sectional area tube, independent of stenosis orientation and size. In the second mode, flow information is obtained by detecting the movement of a small, locally injected iodine bolus. Peak flow velocity and locations of flow separation and turbulence resulting from simulated stenoses are determined with stenosis sizes ranging from 0 to 84% area reduction.

A comparison of three radionuclide techniques for measuring blood flow to rat extremities.

A detailed comparison of three radionuclide techniques to estimate blood flow was done in the rat hind limb under reduced, normal and increased blood flow. The techniques compared were the washout of intra-arterial and intra-muscular Xenon-133 and the accumulation of radioactive microspheres in the reference organ technique. There was no significant difference between the three techniques at each of the three flow states. This confirmed that the simpler I.M. Xenon technique is a useful and accurate technique in estimating low blood flow rates in small animals. It was found that the skin puncture had to be sealed after the intra-muscular injection of Xenon to obtain valid results.

Arterial flow characterization with a photodiode array based imaging system.

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.

Experimental and theoretical x-ray imaging performance comparison of iodine and lanthanide contrast agents.

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.

Low osmolar contrast media--a challenge for cardiology.

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.

The microcirculation of the mammalian lymph node.

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.

Adverse reactions to intravenous contrast agents in Ontario, 1975 - 1979.

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.

Selective angiography in the diagnosis of hydatid disease of the liver.

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.

Contrast use: waste not--want not.

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.

A scanning x-ray imaging system for quantitative arteriography and blood flow measurements.

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.

Abdominal bruits. Clinical and angiographic correlation.

The results of abdominal auscultation were correlated with abdominal angiograms in 503 patients. Bruits were heard in 106 (21%). The majority of bruitswere in the epigastrium, mainly because of a high incidence of celiac artery stenosis usually of the extrinsic compression type. Sixty-seven patients had stenoses or occlusions of one or more renal arteries and 27 (40%) had bruits. Most of these patients, however, had other possible causes for their bruits, usually related to atherosclerosis of coincidental celiac compression. Collateral channels were considered to be the cause of epigastric bruits in eight of ten patients with complete occlusion of the celiac artery and in two patients with spelic artery occlusions. Collateral channels may be partly responsible for bruits in many patients with celiac artery stenosis.

Reduction of patient exposure by use of heavy elements as radiation filters in diagnostic radiology.

The effect on patient exposure of x-ray filters made of heavy elements has been studied in excretory urography and lumbar spine examinations. Several elements with atomic numbers between 62 and 74 were tested in experiments using radiographic phantoms and in patient studies. A holmium filter reduced skin exposure by more than 50% in excretory urography. Similar results were obtained with ytterbium and tungsten in lumbar spine studies.

Detection accuracy in chest radiography.

The detection accuracy of the diagnostic radiologist is important in everyday medical decision making. However, little work has been done relating the detection accuracy of the radiologist to the quality of the image. This study, using a thorax and lung phantom, simulated tissue-equivalent 6.4 mm lesions, and a 183 cm source-to-image distance, shows that the detection accuracy is not dependent on the focal spot size (over a range of 0.3-2.0 mm). However, the false positive rate increases when using small focal spots. In addition, the detection accuracy decreases with increasing root-mean-square (RMS) noise (a measure of the amount of quantum mottle in the image), while the false positive rate and intraobserver disagreement increase with increasing RMS noise. It is also shown that the nonradiologist responds to changes in noise in exactly the same way as the radiologist.

Dose and quality control (DQC) in diagnostic radiology.

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.

The role of hyperemia in cellular hypersensitivity reactions.

The three physiological processes vascular permeability, blood flow and lymphocyte migration were all enhanced in tuberculin reactions induced in guinea pigs and sheep and also in normal lymphocyte transfer reactions in sheep. Microspheres labelled with 85Sr were used to measure blood flow to dermal sites and it was found that cellular hypersensitivity reactions had blood flows 7-25 times that of normal skin at the reaction peak. Vascular permeability was measured as an increase in the flow rate of afferent lymph or, in guinea pigs, as the enhanced leakage of intravascular 125I-albumin. When the permeability-inducing peptide bradykinin was injected directly into tuberculin reaction, the resulting permeability was greater than the sum of the tuberculin and bradykinin permeability taken individually and it was concluded that the hyperemia enhanced the permeability-inducing capacity of bradykinin. When the traffic of lymphocytes through hypersensitivity lesions was measured in sheep by cannulating the regional afferent lymph vessels and continuously collecting the lymph, the increase in lymphocyte traffic was of the same order of magnitude as the increase in blood flow. It is suggested than the antigen-induced enhancement of blood flow caused the increase in lymphocyte traffic and that the mechanism was similar to that occurring within lymph nodes during the immune response to all antigens.

Need for radiologists to interpret orthopedic total joint radiographs.

We applaud the aim of Nayak and colleagues: to use our scarce economic resources as judiciously as possible. We have suggested several alternatives that would save more of our scarce health care dollars. We would be delighted to take part in a properly designed prospective randomized trial to address the issues presented in this paper. We believe the literature would be strengthened by the publication of a collegial paper, coauthored by orthopedic and radiology departments, addressing the issue of saving health care dollars by omitting unnecessary or redundant procedures.