Methods for detection of left ventricular edges

Application of mathematical methods in dynamic nuclear medicine studies

Dynamic nuclear medicine studies can generate large quantities of data, and their analysis consists essentially of a reduction of these data to a small number of relevant parameters which will assist in clinical decision making. This review examines some of the mathematical techniques that have been used in the process of data reduction and attempts to explain the principles behind their application. It particularly identifies the techniques that have stood the test of time and demonstrated their usefulness, many of which are now available as standard tools on nuclear medicine processing computers. These include curve processing tools such as smoothing, fitting and factor analysis, as well as tools based on empirical models, such as the Patlak/Rutland plot and deconvolution. Compartmental models and vascular models are also examined and the review finishes with a summary of some functional images and condensed images. It is concluded that an appreciation of the principles and limitations of these mathematical tools is valuable for their correct usage and interpretation of the results produced.

Validation of a knowledge-based boundary detection algorithm: a multicenter study

A completely operator-independent boundary detection algorithm for multigated blood pool (MGBP) studies has been evaluated at four medical centers. The knowledge-based boundary detector (KBBD) algorithm is nondeterministic, utilizing a priori domain knowledge in the form of rule sets for the localization of cardiac chambers and image features, providing a case-by-case method for the identification and boundary definition of the left ventricle (LV). The nondeterministic algorithm employs multiple processing pathways, where KBBD rules have been designed for conventional (CONV) imaging geometries (nominal 45 degrees LAO, nonzoom) as well as for highly zoomed and/or caudally tilted (ZOOM) studies. The resultant ejection fractions (LVEF) from the KBBD program have been compared with the standard LVEF calculations in 253 total cases in four institutions, 157 utilizing CONV geometry and 96 utilizing ZOOM geometries. The criteria for success was a KBBD boundary adequately defined over the LV as judged by an experienced observer, and the correlation of KBBD LVEFs to the standard calculation of LVEFs for the institution. The overall success rate for all institutions combined was 99.2%, with an overall correlation coefficient of r=0.95 (P<0.001). The individual success rates and EF correlations (r), for CONV and ZOOM geometers were: 98%, r=0.93 (CONV) and 100%, r=0.95 (ZOOM). The KBBD algorithm can be adapted to varying clinical situations, employing automatic processing using artificial intelligence, with performance close to that of a human operator.

Computation of left ventricular volume curves from gated blood pool studies without explicit use of edge detection algorithms: concise communication

A new technique has been developed to compute left ventricular (LV) time activity curves from gated blood pool (GBP) studies without the use of manual, semiautomated or fully automated edge detection algorithms. The method utilizes the correlation of entropy calculated from the counts of a fixed region of interest covering the left ventricle during a cardiac cycle to compute the LV volume curve for a new patient. The new LV volume curve is obtained through interpolation of those volume curves of a data base which are associated with the closest variations in normalized entropy to the new one. The computed LV time activity curves agree with those obtained from manual or fully automated outlines of the left ventricle within 9 percent for the selected set of 67 patients demonstrating the potential of the method. The accuracy of calculated LV volume curves can be improved theoretically to any degree by increasing the number of cases in the data base of known statistical feature vectors associated with the LV images and LV volume curves. The new method for computation of LV curves is very efficient and robust when compared to traditional techniques.

A semi-automated method for edge detection in the evaluation of left ventricular function using ECG-gated single-photon emission tomography

Thallium-201 gated single-photon emission tomography (GSPET) of myocardium was performed at rest in 18 patients. Images were reconstructed to obtain end-diastolic (ED) and end-systolic (ES) images. The endocardial and epicardial edges of the left ventricle (LV) for the ED and ES images were defined for the mid-ventricular images of the short-axis slices, using a semi-automated method. LV wall thickness was measured for ED and ES images at 10 degrees intervals. Mean LV thickness was derived as the mean of the LV thickness for the three mid-ventricular slices. The systolic thickening (ST) was derived as: mean LV thickness (ES)--mean LV thickness (ED). The systolic thickening ratio (STR) was defined as: ST/mean LV thickness (ED). LV cavity area was measured. The dilation ratio (DR) was defined as: [mean cavity area (ED)--mean cavity area (ES)]/mean cavity area (ED). LV ejection fraction (LVEF) was estimated using technetium-99m gated blood pool study. There was a linear correlation between LVEF and ST (r = 0.85), LVEF and STR (r = 0.77) and LVEF and DR (r = 0.81). There was a strong correlation (r = 0.85) between regional STR and regional percent count increase in 52 segments which did not have perfusion defects. As well as for the evaluation of myocardial perfusion, GSPET images can be of use for the assessment of LV function using an appropriate method for LV edge detection.

A consideration of current clinical options for stress imaging in the diagnosis and evaluation of coronary artery disease

The evolution of technology and our health care system, tinctured by advocacy groups for specific imaging modalities, has produced controversy, relating to the optimal stress imaging method for coronary disease evaluation. Stress perfusion scintigraphy and stress echocardiography advocates seem to make claims that each nullify the other. This extensive, in-depth review of the subject presents facts as well as opinion and experience in an effort to assess the full portrait of the issue for consideration by advocates as well as those many yet undecided. The issue is an evolving one, affected strongly by the reader's own experience. The presentation is not meant to be the final word. Rather, it seeks to present a basis for understanding and progress in both fields.

Using mathematical morphology to determine left ventricular contours

The aim of this study is to investigate the use of mathematical morphology for the determination of left ventricular contours in scintigraphic images using multigated radionuclide angiography. We have developed a completely automatic method that first restores the image with a Wiener filter, then finds the region where the left ventricle is contained, and finally segments the left ventricle contour and a background zone. The contours depend on the values of the parameters that appear in the mathematical morphology method, which are related to the height and the slope of the count distribution. Results obtained with this method are compared with the contours and the background zones outlined by experts on the basis of the number of counts. We study the values of the parameters with which the optimum correlation is obtained.

A three-dimensional second-derivative surface-detection algorithm for volume determination on SPECT images

Most existing techniques for determining volumes on single-photon-emission computed tomography (SPECT) data employ thresholding, two-dimensional edge detection, or manual delineation of edges. These methods, however, are limited in both accuracy and applicability. In seeking to overcome these limitations, a truly three-dimensional (3D) second-derivative-based algorithm which can be implemented with relative ease has been developed. The method incorporates 3D matrix operators; these are convoluted with the SPECT count data in order to produce a 3D voxel map whose data elements correspond to the second derivative of counts in the image. This map is then searched, a suitable derivative-based edge-defining criterion being applied to each voxel position, in order to locate the derivative surface boundary which defines the volume. Validation is obtained using phantom data from 99Tcm-filled bottles of volumes 200, 580 and 2500 cm3 placed within a body-sized tank containing background activities set to give a range of contrasts between 1.00 and 0.75 (i.e. background 0% to 25%). The performance of the algorithm is encouraging: the volumes of the two larger bottles are determined to within a 3% accuracy without the need for any prior calibration, and the results obtained over all bottle sizes are found to be contrast independent to within approximately 4%.

Automated detection of the left ventricular region of interest by means of the extraction of typical behaviors in cardiac radionuclide angiographies

An automated process for the detection of the left ventricular end diastolic contour is defined. The extraction of a pure left ventricular behavior, obtained by the application of the Gram-Schmidt orthogonalization process on a set of vectors representing the three main typical behaviors present in the scintigraphic sequence, yields the synthesis of a new factorial image particularly matched for the extraction of the left ventricular region of interest (ROI). An edge following technique with conditional dilation applied simultaneously on the two binary images resulting from processing the new left ventricular factorial and the average images with a Laplacian operator gives a robust method for the detection of the left ventricular ROI.

Automatic ventricular edge detection for determination of left ventricular volumes, ejection fraction and regional ejection fractions from first pass radioisotope angiography

An automated method for detection of left ventricular (LV) outline (including the aortic and mitral valve planes) was developed for measurements of end-diastolic volume (EDV), end-systolic volume (ESV), global ejection fraction (EF), and regional EFs from first pass radioisotope ventriculography. The procedure includes: (1) interpolative background subtraction, (2) construction of gradient images, (3) automatic detection of valve planes, and (4) automatic radial search of LV outlines. The correlation between contrast angiography and Tc-99m first pass study was r = 0.84 (SEE = 23.4) for EDV, r = 0.93 (SEE = 12.8) for ESV, r = 0.84 (SEE = 6.91) for EF (via counts) and r = 0.80 (SEE = 8.56) for EF (via area-length method). Tests of intra-observer, inter-observer and inter-study variability revealed low level of variability. The results showed the potential of the automation of data processing for first pass radioisotope ventriculography.

Quantitative radionuclide angiocardiography

Quantitation of cardiac pump function using radionuclide angiocardiography provides objective information for the management of patients with heart disease. Left and right ventricular ejection fraction, stroke volume ratio, ejection rate, diastolic function, ventricular volume, parametric imaging, amplitude and phase analysis, and shunt quantification can be measured from the radionuclide angiocardiogram at rest, during exercise, and during pharmacologic interventions. This review describes these methods and discusses their reliability and their role in the clinical assessment of patients with cardiac disease.

Short- and long-term dobutamine treatment in chronic ischemic heart failure

This study was undertaken in order to characterize the short-term (1 hour) and long-term (72 hours) effect of dobutamine on hemodynamic and regional ejection fraction parameters measured by radionuclear angiography in patients with chronic congestive heart failure due to coronary artery disease. Baseline hemodynamic and radionuclear parameters were measured and then intravenous dobutamine (8.5 mu/kg/min) was administered. The above parameters were determined again after 1 hour and 72 hours of continuous dobutamine administration. Sixty minutes (short-term) after dobutamine administration heart rate and cardiac index increased significantly (p less than 0.001 for both) and peripheral resistance decreased concomitantly (p less than 0.005). Global left ventricular ejection fraction (LVEF) as measured by multigated equilibrium nuclear angiography (MUGA) increased from 21.8 +/- 10.6% to 25 +/- 13.5 (p less than 0.02). Count-based mean regional ejection fraction in the septal, inferoapical, posterolateral (45 degrees left anterior oblique view) and inferior apical and anterolateral (30 degree right anterior oblique gated first pass) regions increased also. At 72 hours (long-term) after continuous dobutamine infusion, heart rate and cardiac index were still significantly higher and peripheral resistance lower than in the control study. However, global and count-based regional ejection fraction decreased to control values in the right anterior oblique view (first-pass analysis) and the left anterior oblique view (MUGA). Global LVEF measured in the right anterior oblique view by first-pass technique was significantly higher than control in the long-term study (23 +/- 9.7 vs. 27.8 +/- 2.4; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Dual isotope (81Krm and 99Tcm) SPECT in lung function diagnosis

A method is presented for deriving regional values for lung volume, ventilation, perfusion and dV/dQ ratios suitably plotted for clinical interpretation. Necessary data are obtained from a 12 min dual-head, dual isotope (81Krm and 99Tcm) SPECT acquisition and subsequent graphics and image processing. Computed histograms make possible a detailed quantitative impression of lung function.

Diagnostic radiology and nuclear cardiology. Their use in assessment of equine cardiovascular disease

Survey thoracic radiography, although limited by physical considerations in the adult horse, can supply clinically useful information about changes in cardiac size and function. The radiographic features of cardiomegaly, altered pulmonary circulation, pulmonary edema, and pleural effusion as manifested in the horse are discussed. Nuclear cardiology can be performed in the standing horse. The initial transit of a radioactive tracer through the central circulation provides information about cardiac chamber size, efficiency of ventricular contraction, valvular competence, and presence of intracardiac or extracardiac shunts. Computer analysis of similar studies allows quantitation of several useful cardiac parameters including ventricular ejection fraction and shunt size (QP/QS). Gated blood pool nuclear studies are better suited to evaluate cardiac response to stress but are difficult to perform in the conscious horse with standard imaging equipment.

A simplified QRS scoring system for the estimation of the severity of acute inferior wall myocardial infarction

Electrocardiographic assessment of the R/Q wave ratio (lead 2) of patients with a first acute inferior wall myocardial infarction (IWMI) offers important indirect quantitative information regarding the severity and extent of the myocardial damage. Eighty-eight consecutive patients with IWMI were investigated by echocardiography and radionuclear angiography. After measuring the R/Q ratio in lead 2 during the ST-wave stabilized stage of myocardial infarction, patients were separated into three groups--group 1 with an R/Q ratio greater than 2; group 2 with an R/Q ratio between 1 to 2; and group 3 with an R/Q ratio less than 1. Utilizing the information thus gathered from the electrocardiogram (ECG) offers a simple and efficient method for early prognosis which merits further investigation.

Right ventricular dysfunction in acute inferoposterior myocardial infarction. An echocardiographic and isotopic study

We analyzed right ventricular (RV) regional wall motion by two-dimensional echocardiographic (2D echo) and multigated acquisition radionuclear (MUGA) studies in 104 patients with acute inferoposterior myocardial infarction (AIPMI). Sixty-eight patients (65 percent) had 2D echo RV regional wall motion abnormalities (RV dysfunction(RVD) group) while 36 patients showed no 2-D echo RV regional wall motion abnormalities (no-RVD group). The RVD group had a higher incidence of jugular venous engorgement (p less than 0.05), Kusmaul's sign, (p less than 0.05) complete atrio-ventricular block (p less than 0.05), and in-hospital death (p less than 0.02). The RVD group had significantly higher 2-D echo RV end-systolic dimensions (p less than 0.005) and lower values of percentage of fractional shortening (%FS) (p less than 0.005) in the long and short axis of the RV four-chamber view than patients in the no-RVD group and a control group of 20 patients with normal hearts. There was no statistical significant difference in the 2-D echo RV end-diastolic dimensions among the three groups. Patients in the RVD group had a lower MUGA derived RV ejection fraction (EF) than patients in the no-RVD and control groups (26.5 +/- 13.2 vs. 46.3 +/- 7 and vs. 50.6 +/- 4, respectively; p less than 0.05). RVD was diagnosed by both 2-D echo and MUGA in 60 of 104 patients (57.7 percent) with a sensitivity for 2-D echo of 92 percent and 79 percent specificity (when compared to the MUGA study). The predictive value for a positive test was 88 percent and for a negative test 86 percent. The accuracy was 87.5 percent. Recognition of regional wall motion abnormalities by 2-D echo permits a prompt and accurate bedside identification of right ventricular dysfunction (RVD) within the first 72 hours of clinical onset. An enlarged RV 2D echo end-diastolic dimension was not a sensitive parameter for the diagnosis of this pathology, whereas an increased end-systolic RV diameter and decreased RV %FS were better indicators of RV dysfunction in patients with acute inferoposterior wall myocardial infarction.

Sectoranalysis of left ventricular function by fully automated equilibrium radionuclide ventriculography

We describe a fully automated method for quantification of left ventricular performance by equilibrium radionuclide ventriculographic studies, based on subdivision of the left ventricular region into 9 equiangular sectors. The precise identification of the left ventricular contours is achieved by the use of morphological and functional criteria in a sequential edge detection algorithm with a success rate of 96%. In addition to left ventricular global and sectorial ejection fraction the first harmonic of the corresponding Fourier spectrum is approximated to each sectorial time-activity curve and to the global one. Sectorial phase is calculated as the difference between the phase of the sectorial and global first Fourier component. Computerized comparison between the sectorial parameters at rest and during peak exercise localizes and classifies the degree of global and regional impairment in response to exercise. The processing time of 60 sec makes this method suitable for routine use. The validity of our procedure has been tested in 34 patients before and after successful transluminal coronary angioplasty. In these patients, 73% of the stenosed vessels before dilatation were localized by sectorial ejection fraction, 77% by sectorial phases, and 88% by the combination of both.

Fully automated sectorial equilibrium radionuclide ventriculography. Proposal of a method for routine use: exercise and follow-up

A fully automated computer program is described for processing equilibrium radionuclide ventriculography data with regard to global and sectorial left ventricular ejection fraction. The precise identification of the left ventricular outline, a prerequisite for reproducible determination of sectorial ejection fraction, was achieved by using morphological and functional criteria in a sequential edge detection technique. The high reproducibility of this method (correlation coefficient r: global ejection fraction r = 0.96, sectorial ejection fraction r = 0.82-0.97) allows the evaluation of a mean normal sectorial ejection fraction profile and its adaptation to the individual left ventricle. Computerized comparison between individual and adjusted normal sectorial ejection fraction permits quantitation of the degree and localization of functional impairment at rest, sectorial comparison between ejection fraction at rest and during peak exercise is used for the detection of ischemic functional impairment. The success rate of end diastolic left ventricular edge detection of 96% and the processing time of 150 s makes this method suitable for routine use.

Phase analysis of the first pass radionuclide angiocardiogram

Fifty-two subjects with suspected coronary artery disease were studied by first pass radionuclide angiocardiography using a single crystal gamma camera. Phase analysis, a new technique which can detect ventricular regions with abnormal emptying patterns, was applied to the resulting left ventricular radionuclide angiocardiograms. Eighteen turned out be normal and in these subjects the variation of phase values in each of eight ventricular segments was established. Thirty-four had coronary artery disease. By comparison with the normal subjects, 21 had at least one segment with an abnormally high phase value. Such high values were associated with low values of ejection fraction, as determined by a radionuclide technique, total occlusion of a major coronary artery and significant wall motion abnormalities on the radiographic ventriculogram. A comparison between phase analysis and wall motion on a regional basis disclosed progressively high phase values with increasing severity of wall motion abnormality. Particularly high values were found in association with ventricular aneurysm. Phase analysis of first pass radionuclide angiocardiograms is a valid method for the detection of regional abnormalities of ventricular contraction in coronary artery disease.

Evaluating the performance of an edge detection algorithm for use in radioisotope imaging

The criteria are presented for establishing how an edge detection algorithm (EDA) will respond under a variety of imaging situations. Several parameters have been defined to allow comparison of the processed image under varying conditions of count density, target to background ratio, depth of organ, scatter and intra-image motion. These parameters could also be used for intercomparison of EDAs.