Esophageal source measurement of Tc-99m attenuation coefficients for use in left ventricular volume determinations

A linear attenuation coefficient for water (mu = .15 cm-1) at 140 keV has been used in the determination of left ventricular volumes (LVV) by attenuation-corrected equilibrium methods. This theoretical value ignores the effect of Compton scatter and thus may be too high for human LVV determinations. The effective attenuation coefficient, mu', of the human chest was determined in ten normal volunteers using a Tc-99m esophageal source imaged with a gamma camera. Values for mu' at 30 degrees LAO in end-expiration, quiet breathing, and end-inspiration were .125 +/- .006 cm-1, .125 +/- .005 cm-1, and .113 +/- .007 cm-1, respectively (95% confidence interval). Values of mu' at 45 degrees LAO were .122 +/- .006 cm-1, .119 +/- .007 cm-1, and .099 +/- .009 cm-1, respectively, for the same conditions. The measured value of mu' for the source in a water phantom was .127 +/- .001 cm-1. This suggests that a value of mu' of .125 cm-1 may be appropriate for use in determining LVV in patients.     

Direct determination of the attenuation coefficient for radionuclide volume measurements

Correcting for the attenuation of photons between the cardiac chambers and chest surface is crucial for accurate nongeometric ventricular volume determinations from equilibrium radionuclide angiograms. Previous techniques have assumed that the attenuation coefficient of water for 99mTc (0.15/cm) should be used for this correction. In this study, this assumption was tested directly by measuring attenuation of the activity of a radioactive source within the right and left cardiac chambers. The balloon of a flow-directed catheter, filled with 99mTc, was used as a source and its depth within the body was measured with biplane fluoroscopy. In ten patients, a total of 36 measurements of attenuation were made. With linear regression analysis, the overall calculated attenuation coefficient, mu, was 0.12/cm (standard error of slope = 0.01, R = 0.93). Although the mean value of mu varied from 0.08 to 0.13 for four different intracardiac locations these differences were not significant. These direct measurements indicate that the attenuation of photons in the heart is not equivalent to that of water and suggest that an attenuation coefficient of 0.12/cm should be used in analyzing ventricular activity.     

Left ventricular volume determination by first-pass radionuclide angiocardiography using a semi-geometric count-based method]

A new radionuclide technique for the calculation of left ventricular (LV) volume by the first-pass (FP) method was developed and examined. Using a semi-geometric count-based method, the LV volume can be measured by the following equation: CV = CM/(L/d). V = (CT/CV) x d3 = (CT/CM) x L x d2. (V = LV volume, CV = voxel count, CM = the maximum LV count, CT = the total LV count, L = LV depth where the maximum count was obtained, and d = pixel size.) This theorem was applied to FP LV images obtained in the 30-degree right anterior oblique position. Frame-mode acquisition was performed and the LV end-diastolic maximum count and total count were obtained. The maximum LV depth was obtained as the maximum width of the LV on the FP end-diastolic image, using the assumption that the LV cross-section is circular. These values were substituted in the above equation and the LV end-diastolic volume (FP-EDV) was calculated. A routine equilibrium (EQ) study was done, and the end-diastolic maximum count and total count were obtained. The LV maximum depth was measured on the FP end-diastolic frame, as the maximum length of the LV image. Using these values, the EQ-EDV was calculated and the FP-EDV was compared to the EQ-EDV. The correlation coefficient for these two values was r = 0.96 (n = 23, p less than 0.001), and the standard error of the estimated volume was 10 ml.(ABSTRACT TRUNCATED AT 250 WORDS)     

Left ventricular volume calculation using a count-based ratio method applied to multigated radionuclide angiography

The purpose of this study was to investigate the accuracy of a new count-proportional method for the measurement of left ventricular volume when applied to gated equilibrium blood-pool imaging. An equation is developed that relates total chamber volume, Vt, to the area of a pixel (M) and the ratio (R) of total counts within the chamber to the counts within the hottest pixel in the chamber such that Vt = 1.38 M3R3/2. The value of M is a constant for the particular scintillation camera-collimator system and R is obtained from observed count rates. All calculated volumes were compared to volumes measured using biplane contrast ventriculography. In 25 patients, the method for ventricular volumes gave an r of 0.95 and an s.e.e. of 23 ml [Volume (nuclear) = 0.94 Volume (cath) + 1.3]. Endsystolic volume was best calculated from end-diastolic volume and ejection fraction. Manual regions of interest were more accurate than automated regions of interest. This method appears to be as accurate as more complex approaches and has the advantage of not requiring attenuation correction or blood sampling.     

Left ventricular volume calculation using a count-based ratio method applied to first-pass radionuclide angiography.

Most count-based radionuclide methods for calculating left ventricular volume rely on measurement of radioactivity in a peripheral blood sample and a measurement of ventricle to collimator distance. We have developed a method which requires neither a blood sample nor a distance measurement and which is applicable to first-pass radionuclide angiography. The parameters used to calculate volume are the area of pixel, the total counts in the left ventricle and the maximum pixel count. The equation was used to calculate the volumes in 50 patients who had both resting first-pass radionuclide angiography (25 patients with a single crystal and 25 patients with a multicrystal camera) and contrast ventriculography on the same day. Correlation coefficients for end-diastolic and end-systolic volumes showed r ranging 0.93-0.98 and standard error of estimate ranging 23-35 ml for end-diastolic volume (14%-17% of mean end-diastolic volume) and 16-23 ml for end-systolic volume (18%-21% of mean end-systolic volume). Image processing software for extracting the needed values is generally available on most commercial nuclear medicine imaging systems and the additional time for the calculations is short. Although the theory is based on multiple assumptions, the volume calculation appears to be reasonably accurate and clinically applicable.     

Stability of radionuclide left ventricular volume measurements

Left ventricular volume measurements are useful in the evaluation of cardiac function and are important in the long-term management of patients with various cardiac diseases. Although there are many methods of measuring left ventricular volumes, a non invasive and reproducible method relies on radionuclide techniques. The errors in estimation of left ventricular volumes have previously been well studied. To date there is little information on the reproducibility of left ventricular volume measurements made by this technique at different points in time. This study evaluated 61 patients with stable coronary artery disease over a period of approximately 1 year. All patients had two resting radionuclide gated blood pool studies. Patients had no changes in symptoms, electrocardiographic findings or medication between studies. Using +/- 2 SD as 95% confidence limits for a true change, an end diastolic volume index change greater than -34 ml m-2 and +38 ml m-2 or an end systolic volume index change greater than -24 ml m-2 and +26 ml m-2 are required to state with confidence that a change has occurred between two examinations. These data provide guidelines to assess whether interval changes in left ventricular volumes are real or are due to variations within the technique.     

Left ventricular diastolic function in systemic sclerosis: assessment by radionuclide angiography.

The aim of this study was to assess left ventricular function in subjects with systemic sclerosis. Twenty-four women with systemic sclerosis (mean age 48 +/- 11 yr) and 14 age- and sex-matched normal subjects were studied by radionuclide angiography performed at rest with a temporal resolution of 20 msec/frame. Left ventricular volume curves were generated and indices of systolic and diastolic function were computed. Left ventricular diastolic asynchrony was evaluated by dividing the left ventricle into five regions and then computing the time-to-peak filling rate for each region. After excluding the valvular region, the coefficient of variation of this index was obtained. The isovolumic relaxation period was prolonged in systemic sclerosis patients in comparison to normal subjects (127 +/- 39 msec versus 87 +/- 44 msec, p less than 0.05). Moreover, 38% of the systemic sclerosis patients had a subnormal peak filling rate. Left ventricular diastolic asynchrony was increased in the systemic sclerosis group, as expressed by a higher coefficient of variation of the regional time to peak filling rate (27.9% +/- 11.5% versus 14.5% +/- 8.6%, p less than 0.05). Our results indicate an impaired relaxation and an increased diastolic asynchrony in patients with systemic sclerosis.     

Left ventricular end-diastolic volume is decreased at maximal exercise in athletes with marked repolarisation abnormalities: a continuous radionuclide monitoring study

Purpose Although marked repolarisation abnormalities (MRAs) are considered innocuous in trained athletes, their functional significance awaits clarification. The aim of this study was to further evaluate the pathophysiological implications of such MRAs.Methods We compared left ventricular (LV) functional response to exhausting exercise in 39 male athletes with (n=22) or without (n=17) MRAs and with no structural cardiac abnormalities, by means of a portable radionuclide monitoring system (Vest, Capintec, Inc., Ramsey, NJ). MRAs were defined by the presence of negative T waves 2 mm in three or more rest ECG leads. The Vest data were averaged for 30 s and analysed at baseline and at different heart rate (HR) values (50%, 75%, 85%, 95% and 100% of peak HR), as well as at 2, 5 and 10 min of recovery.Results There were no significant differences in the effect of exhausting exercise between athletes with and athletes without MRAs. However, there was a significant difference in the trend in end-diastolic volume (EDV) during exercise depending upon the group of athletes considered (p=0.05). EDV differed significantly between the two groups of athletes at peak HR (p=0.031). EDV in athletes with MRAs was lower than that in athletes without MRAs (102%±7% vs 107%±8%, p=0.034).Conclusion EDV is decreased at peak HR in athletes with MRAs. Such high HR values are infrequently achieved or maintained during sporting activities; therefore, in the absence of structural heart disease, MRAs should not preclude physical training and competitive availability.     

Validation of left ventricular volume measurements by radionuclide angiography

A nongeometric, attenuation-corrected technique to quantitate left ventricular volumes using equilibrium radionuclide angiography was validated in vitro and in vivo. In vitro experiments were performed to derive a linear attenuation coefficient, which was then employed in the volume determinations using balloons in a water bath. Good in vitro correlation was found between radionuclide and actual volumes (r = 0.99, p less than 0.0001), over a wide range (5 to 400 ml). In vivo validation was done by comparing the nuclear technique to contrast angiography in 29 patients: Good correlations were found for end-diastolic volume (r = 0.98), end-systolic volume (r = 0.95), stroke volume (r = 0.96), and ejection fraction (r = 0.85). When the conventional linear attenuation coefficient was used, the radionuclide technique consistently overestimated volumes in vitro and in vivo. Although high intraobserver and interobserver correlation coefficients were found (r from 0.88 to 0.93), significant individual variability existed, particularly in the interobserver data. Our data provide unique validation of radionuclide volume determinations, using an experimentally determined attenuation coefficient, which results in improved accuracy.     

An intravenous radionuclide method for repeated shunt determinations

Using a subtraction technique, repeated shunt determinations were successfully performed on 25 patients with a high degree of correlation.     

Measurement of absolute left ventricular volume by radionuclide angiography: a technical review

Absolute left ventricular volumes have important clinical implications in the evaluation of cardiac performance. Several invasive and noninvasive techniques have been reported, none of which can be considered ideal for this purpose. Contrast angiography, echocardiography and radionuclide ventriculography are open to criticism. Different radioisotopic approaches are described with emphasis on the importance of accurate separation of left ventricular activity, the selection of background activity, and the correction for photon attenuation by body tissues. Improper use of statistics and validation techniques have obscured the value of these techniques. In the absence of a 'gold standard' there should be a 'radioisotopic' left ventricular volume with established independent characteristics, repeatability and reproducibility by which new approaches can be judged.     

Left ventricular function evaluation using radionuclide methods in the intensive coronary care unit

We describe an adapted first-transit (FT) technique to perform left ventricular ejection fraction (LVEF) measurements on patients with Swan-Ganz catheters in the intensive cardiac care unit (ICCU). The radionuclide is introduced directly into the right pulmonary artery through the catheter. High-quality images of the left ventricle are obtained owing to minimal activity in the right ventricle and left lung. LVEF measurements obtained by FT compared well with measurements obtained from gated blood pool studies (r = 0.91) but gave consistently lower values. The adapted FT method improves LVEF determination and left-ventricular wall motion evaluation in the ICCU patient.