Effect of background correction on left ventricular ejection fraction calculation through analysis of a simple cardiac model.

The dependence of the left ventricular ejection fraction calculation on the background correction in gated cardiac blood pool studies is examined by analyzing a simple cardiac model. It is shown that the ejection fraction is relatively insensitive to the background correction when an accurately determined variable region of interest is used, but that with a fixed region of interest the background correction must be accurately estimated. A similar ejection fraction-background correction relationship is obtained in the analysis of clinical cardiac data. Based on the cardiac model, two methods are suggested which, with further investigation and refinement, may lead to a more accurate and consistent technique for determining ejection fraction and background.

Linearity and contrast scale control in computed tomography.

The aim of this paper is to present linearity studies and quality control charts for changes in the computed tomography (CT) number of water and contrast scales for two CT scanners over one year. Linear regression relates the attenuation coefficient to CT number. The CT number for water and the contrast scale values as obtained from the fit are: CT1 = (-0.13 +/- 1.3) Hounsfield units (HU), CT2 = (-1.8 +/- 1.6) HU and contrast scale (CS)1 = (1.80 +/- 0.03) 10(-4) cm-1 HU-1, CS2 = (1.82 +/- 0.02) 10(-4) cm-1 HU-1 for Picker International scanner models 600SE and 1200SX, respectively. Direct measurements of CT numbers are compared with fitted results, providing a necessary preliminary steps in the development of objective CT interpretation.

Lung ventilation model for radioactive tracer itdal breathing.

A mathematical lung ventilation model for radioactive tracer tidal breathing is developed on the basis of the previously established simple mathematical lung model for quantitative regional ventilation measurements. In the present model, the periodicity of breathing is completely taken into account. A precise definition of the effective specific ventilation is given. This was found to be related to the ratio of tidal volume (TV) and functional residual capacity (FRC). The determination of the regional effective specific ventilation is reduced to a simple fitting to a straight line. A description is given of the method of measurement (in the framework of radioisotope dynamic studies) that makes it possible to use the mathematical model for the actual determination of lung ventilation and volume parameters. The model is experimentally verified on healthy subjects, and the value of the effective specific ventilation obtained is in agreement with comparable parameters in the literature. Furthermore, the value for TV/FRC is comparable with that determined by classical spirometrical methods.

A mathematical model for the quantitative study of left to right cardiac shunt.

Non-invasive radioisotope cardiographic techniques have become a useful tool for studying the anatomy and function of the heart. The mathematical model described justifies the phenomenological analysis of pulmonary time-activity histograms and was invented for quantitative study of left to right cardiac shunt. The model also gives a theoretical insight into such an empirically proposed diagnostic method and represents an adequate framework for the understanding of other possible approaches to the problem of left to right shunt.

Double peak attenuation method for estimating organ location.

Radioactive sources of finite volume containing 133Xe, 67Ga, 99Tcm and 111In were used to measure the attenuation coefficient, mu, in water at six different energies in the range 80-296 keV using an Anger camera. The experimental accuracy was about 7% for the volume range from 40-225 ml when corrections were made for background. The same radioactive sources were used to measure zero attenuation count rates per unit of activity. The theoretical basis was also derived, which confirms our experimental findings, i.e. the measurement of the thickness of the attenuator using a dual energy method. The determination of the linear attenuation coefficient in the broad-beam geometry situation is possible by accounting for cross-talk, scatter and out-of-target activity. By correcting for the broad-beam geometry, agreement with the narrow-beam geometry linear attenuation coefficient was obtained. We also demonstrate the use of the technique to accurately determine the depth of the organ using two separate energies. This methodology is independent of the organ volume for determination of the depth. It is hoped that our findings will provide a better understanding of the photon interactions when extended sources are used. Such a knowledge can also be applied to organ volume measurements.

Functional imaging of lung ventilation using the concept of mean transit time.

This paper describes a new way of expressing local ventilation using a scintillation gamma camera interfaced to a digital computer. From the ratio of the first to the zeroth moment of the lung clearance curve for 13N gas, a mean transit time is calculated and displayed for different regions of the lung. Lung clearance curves following intravenously administered 13N solutions, or after equilibration with 13N gas, are measured during normal breathing. Describing regional ventilation by mean transit time during clearance uses all the counts in the lung clearance curve and the improvement in statistical accuracy compared with the height over area method using a Stewart-Hamilton equation is significant. In normal subjects the average mean transit time for clearance from the total lung field is t = (61 +/- 4) s, from the upper zone tuz = (64 +/- 4) s and from the lower zone tlz = (54 +/- 5) s. These results show uneven ventilation between regions of the normal lung in general agreement with that described by previous authors. In addition, the functional image gives the mean transit time for each cell of the 64 X 64 matrix of the computer display. The fractional error in mean transit time is 3% for an area of 2-2 cm2 corresponding to 12 cells in the display. This display provides a sensitive method, functionally and spatially, of investigating local differences in ventilation, including vertical and horizontal gradients in narrow strips of lung.

The use of 81mKr gas for the measurement of absolute regional lung ventilation.

In this paper a new method of using 81mKr for the measurement of specific absolute regional lung ventilation is described. Experimental data suitable for the calculation of quantitative regional ventilation are provided using an adequate respiratory system for 81mKr dosage and a scintillation gamma camera interfaced to a digital computer. A simple mathematical lung model for the inhalation of 81mKr is used to determine the specific ventilation and the parameters proportional to the ventilation for the whole lung and different lung regions in patients and in healthy subjects. The lung count rate for a given region correlated well with the ventilation of that region. Clinical examples are given and discussed.

Toward quantitative characterization of the caudate nucleus through CT image enhancement.

Dilated lateral cerebral ventricles have been reported in association with psychiatric disorders. The dilatation is likely secondary to changes in anatomically related centers in the brain. Our attention is focused on the caudate nucleus and the need to develop quantitative characterization of it in psychiatric research. A computer method is described for accurately detecting the edges of the caudate nuclei in CT scans. The method consists of a two-dimensional filtering step to reduce image noise, followed by gradient computation for edge enhancement, and then an edge detection step to identify and record the caudate nuclei cross sections. Results from both head scans and synthetic images indicate that the method is successful even for low-contrast edges where the standard deviation of image noise approaches the difference in mean HU across the edge. The availability of an automated method of delineating the caudate nucleus permits the cross-sectional area and shape to be determined, the density to be estimated, and, from a set of closely spaced slices, volume information to be obtained.

Uneven perfusion and ventilation within lung regions studied with nitrogen-13.

The clearance of nitrogen-13 (13N) from the upper, mid and lower zones was measured with a gamma camera during spontaneous breathing in 10 seated subjects. The clearance was monitored after (a) an intravenous injection of 13N dissolved in saline and (b) equilibration with 13N gas in closed circuit. Subjects breathed air first, and then a 30 or 11% oxygen mixture. For any region, the time for 90% elimination (T90) was related to the volume expired by the whole lung during that time (VE90). For the mid and lower zones, the clearance was faster (VE90 smaller) after intravenous 13N than after equilibration with 13N gas. This difference persisted when 30% or 11% oxygen was inspired. For the lung overall, the physiological dead space for a mean tidal volume of 884 ml was 277 ml for intravenous 13N clearance, and 384 ml for 13N clearance after equilibration. The conclusions drawn for this study are (1) ventilation in relation to volume is uneven within lung regions (2) intraregional perfusion in relation to volume is also uneven (3) at a local level the well-ventilated units are better perfused (4) these inhomogeneities are not affected by raising or lowering the inspired oxygen concentration.

Digital diagnostic imaging with a comprehensive PACS: hypothetical economic evaluation at a large community hospital.

Since 1983, the 422-bed Victoria General Hospital (VGH) and Siemens Electric Limited have been piloting the implementation of digital medical imaging, including digital acquisition of diagnostic images, in British Columbia. Although full PACS is not yet in place at VGH, experience to date has been used to project annual cost figures (including capital replacement) for a fully digital department. The resulting economic evaluation has been labeled hypothetical to emphasize that some key cost components were estimated rather than observed; this paper presents updated cost figures based on recent revisions to proposed departmental equipment configuration. Compared with conventional diagnostic imaging, digital imaging appears to raise overall annual costs at VGH by nearly $0.7 million, (Canadian currency) or 11.6%; this is more favorable than the previous results, which indicated extra annual costs of $1 million (16.9%). Sensitivity analysis still indicates that all reasonable changes in the underlying assumptions result in higher costs for digital imaging than for conventional imaging. Digital imaging appears likely to offer lower radiation exposure to patients, shorter waiting times, and other potential advantages, but as yet the price of obtaining these benefits remains substantial.