Eric N. C. Milne

Left Ventricular Filling and Diastolic Pressure-Volume Relations in the Conscious Dog

In 7 conscious dogs, left ventricular diastolic volume (V) was estimated by taking biplane cineradiographs with the left ventricular cavity previously outlined by permanent radiopaque markers. Left ventricular pressure (P) was measured with an implanted miniature transducer. There were two rapid filling periods during early and late diastole; little filling occurred during the middle third of diastole (diastasis). The diastolic pressure-volume relationship was approximately exponential and was fitted by the equation P=−a+becv, where, a, b, and c are positive constants; the relationship appeared to be determined principally by the elastic properties. The effects of infusions of saline, isoproterenol, calcium gluconate, and methoxamine suggested that viscous and inertial properties are also important determinants of diastolic left ventricular mechanics. No significant series viscosity was observed. Plastic properties were not detected. The elastic properties were not affected by agents having a positive inotropic effect. End-diastolic pressure often differed from that predicted by the exponential equation above, suggesting that it is not a reliable index of enddiastolic volume and left ventricular compliance.

Effect of Changes in Heart Rate on Left Ventricular Performance in Conscious Dogs

An increase in heart rate produced in 12 conscious dogs by right atrial pacing resulted in a fall of end-diastolic volume, stroke volume, stroke work and end-diastolic pressure. Stroke power and the maximum rate of increase of left ventricular pressure (LV dP/dt max) were affected only slightly. Sudden large changes of rate produced transient changes in LV dP/dt max typical of the positive and negative inotropic effects of activation, but steady-state LV dP/dt max was not affected; these effects persisted after autonomic blockade with propranolol and atropine. Postural changes produced no change in LV dP/dt max even after autonomic blockade. We conclude that in this preparation, the interval-strength relationship has a plateau at the physiologic range of heart rate, i.e., myocardial contractility is unaffected by change in heart rate over the range 90 to 190 beats/min.

Development of a radiographic chest phantom with disease simulation.

An anthropomorphic chest phantom with realistic disease simulation is described with a review of previously available chest phantoms. The need for subjective image analysis is discussed and compared with the existing physics parameters as a means of evaluating image quality in chest radiology. An introduction to the use of such a radiographically realistic chest phantom with lung parenchymal detail and disease simulation is illustrated.

Histologic type-specific vascular patterns in rat tumors

There has been some debate as to whether the vascular pattern of a tumor reflects its histology or that of the stroma of its tissue of origin and also whether the vascular pattern of a metastasis imitates the pattern of its primary lesion. To study these questions, the authors transplanted a Walker 256 sarcoma and a fibrosarcoma into 70 rats and successfully induced pulmonary metastases in 30 of these. The circulation of both the primaries and the metastases was then studied by “lethal” microangiography. The study has shown that the vascular pattern does reflect the histology of the tumor itself and not the stroma of its tissue of origin and that metastatic tumors do not have the same circulatory pattern as their primary tumor.

Characterizing Focal Spot Performance

The pinhole technique measures the physical dimensions of the focal spot (effective size or Feff) but ignores the intensity distribution (ID). Resolution chart methods do not measure physical size but provide an “index of resolution,” expressed as the size of a homogeneously irradiating focal spot having the same resolving power (equivalent size or Feq). F values indicate resolving power and are of value to the practicing radiologist, while Feff measurements are required to calculate the heat load and magnification of small objects. Since most focal spots enlarge with increasing mA, manufacturers must supply purchasers with standardized Feq values for the mA range of that tube.

Relationship between specific dynamic pulmonary compliance and diaphragmatic excursion.

The level to which the diaphragm descends on inspiration is dictated by the opposing forces of muscular inspiratory effort and elastic recoil of the lungs, best measured and expressed as its reciprocal; compliance. The level to which the diaphragm ascends on expiration is not dictated by muscular effort but by the elasticity of the chest wall and again by the pulmonary compliance. We theorized therefore that, if there is no change in inspiratory effort or chest wall tonus, the diaphragmatic excursion must be related to the functional or dynamic compliance of the lung. To test this theory inspiratory/expiratory roentgenograms have been taken at total lung capacity and functional residual capacity, respectively, and pulmonary function studies including mechanics (compliance studies) performed on 250 patients. Of these, 130 had chronic obstructive pulmonary disease, 50 had sarcoidosis, 20 renal failure, 40 rheumatic valvular disease, and 10 were controls. A further 900 patients had inspiratory/expiratory roe...

A Highly Accurate Focal Spot Camera—Laboratory and Field Model

A device has been developed to determine accurately and quickly the shape, size, and intensity distribution of an x-ray tube focal spot. The pinhole device weighs only 1 kg and is portable, enabling it to be used either as a field unit or in a laboratory. The special design obviates any risk of irradiation danger to the investigator, or thermal overloading of the x-ray tube under investigation. The degree of accuracy with which the central beam can be located is better than +/-250 micron, well beyond the requirements of the latest NEMA standards regarding dimensional measurements of diagnostic x-ray tube focal spots. A star test pattern picture may be taken instead of the pinhole picture if required. The device is described and areas of application are discussed.

The Diagnostic Quality of Optically Processed Radiographs

The diagnostic quality of optically processed radiographs was compared with that of unprocessed radiographs, using the number of lesions detected as a criterion. It was found that merely removing phase-shifted information with either a binary or focal spot filter alone did not improve image quality, however, use of the focal spot filter plus removal of all phase-shifted frequencies did lead to the detection of an increased number of lesions. The authors suggest that currently available optical filtration techniques should be evaluated with caution, as they may actually degrade diagnostic quality by increasing the visibility of phase-shifted information.

Electronic Magnification of the X-Ray Image

Physical factors in production of a magnified radiographic image include size and intensity distribution of the focal spot and divergence of its rays, secondary radiation, object motion, and the transfer function of the recording medium. Each of three main approaches to magnification—geometric, optical, and electronic—overcomes one or more of the image-degrading factors but has limited application. Electronic magnification with an x-ray-sensitive Vidicon tube permits magnification of dynamic subjects up to 60×, but presently high radiation dose prevents its clinical use. Several methods of reducing radiation to acceptable levels are pointed out. The technique has great potential.

DETERMINANTS AND INDICES OF FOCAL SPOT PERFORMANCE-THE CONCEPT OF THREE-DIMENSIONALITY.

Determinants of performance: There are four major factors which affect the imaging performance of a focal spot. I. Size. Intensity distribution. III . Shape. IV. Off-focus irradiation.