Accurate estimates of absolute left ventricular volumes from equilibrium radionuclide angiographic count data using a simple geometric attenuation correction

To simplify and clarify the methods of obtaining attenuation-corrected equilibrium radionuclide angiographic estimates of absolute left ventricular volumes, 27 patients who also had biplane contrast cineangiography were evaluated. Background-corrected left ventricular end-diastolic and end-systolic counts were obtained by semiautomated variable and hand-drawn regions of interest and were normalized to cardiac cycles processed, frame rate and blood sample counts. Blood sample counts were acquired on (d°) and at a distance (d′) from the collimator. A simple geometric attenuation correction was performed to obtain absolute left ventricular volume estimates.Using blood sample counts obtained at d° or d′, the attentuation.corrected radionuclide left ventricular end-diastolic volume estimates using both region of interest selection methods correlated with the cineangiographic end-diastolic volumes (r = 0.95 to 0.96). However, both mean radionuclide semiautomated variable left ventricular end-diastolic volumes (179 ± 100 [± 1 standard deviation] and 185 ± 102 ml, p < 0.001) were smaller than the average cineangiographic end-diastolic volume (217 ± 102 ml), and both mean hand-drawn left ventricular end-diastolic volumes (212 ± 104 and 220 ± 106 ml) did not differ from the average cineangiographic end-diastolic volume. Using the blood sample counts obtained at d° or d′, the attenuation-corrected radionuclide left ventricular end-systolic volume estimates using both region of interest selection methods correlated with the cineangiographic end-systolic volumes (r = 0.96 to 0.98). Also, using blood sample counts at d°, the mean radionuclide semiautomated variable left ventricular end-systolic volume (116 ± 98 ml, p < 0.05) was less than the average cineangiographic end-systolic volume (128 ± 98 ml), and the other radionuclide end-systolic volumes did not differ from the average cineangiographic end-systolic volume.Therefore, it is concluded that: 1) a simple geometric attenuation-correction of radionuclide left ventricular end-diastolic and end-systolic count data provides accurate estimates of biplane cineangiographic end-diastolic and end-systolic volumes; and 2) the hand-drawn region of interest selection method, unlike the semiautomated variable method that underestimates end-diastolic and end-systolic volumes, provides more accurate estimates of biplane cineangiographic left ventricular volumes irrespective of the distance blood sample counts are acquired from the collimator

Accurate estimates of absolute left ventricular volumes from equilibrium radionuclide angiographic count data using a simple geometric attenuation correction

To simplify and clarify the methods of obtaining attenuation-corrected equilibrium radionuclide angiographic estimates of absolute left ventricular volumes, 27 patients who also had biplane contrast cineangiography were evaluated. Background-corrected left ventricular end-diastolic and end-systolic counts were obtained by semiautomated variable and hand-drawn regions of interest and were normalized to cardiac cycles processed, frame rate and blood sample counts. Blood sample counts were acquired on (d°) and at a distance (d′) from the collimator. A simple geometric attenuation correction was performed to obtain absolute left ventricular volume estimates.Using blood sample counts obtained at d° or d′, the attentuation.corrected radionuclide left ventricular end-diastolic volume estimates using both region of interest selection methods correlated with the cineangiographic end-diastolic volumes (r = 0.95 to 0.96). However, both mean radionuclide semiautomated variable left ventricular end-diastolic volumes (179 ± 100 [± 1 standard deviation] and 185 ± 102 ml, p < 0.001) were smaller than the average cineangiographic end-diastolic volume (217 ± 102 ml), and both mean hand-drawn left ventricular end-diastolic volumes (212 ± 104 and 220 ± 106 ml) did not differ from the average cineangiographic end-diastolic volume. Using the blood sample counts obtained at d° or d′, the attenuation-corrected radionuclide left ventricular end-systolic volume estimates using both region of interest selection methods correlated with the cineangiographic end-systolic volumes (r = 0.96 to 0.98). Also, using blood sample counts at d°, the mean radionuclide semiautomated variable left ventricular end-systolic volume (116 ± 98 ml, p < 0.05) was less than the average cineangiographic end-systolic volume (128 ± 98 ml), and the other radionuclide end-systolic volumes did not differ from the average cineangiographic end-systolic volume.Therefore, it is concluded that: 1) a simple geometric attenuation-correction of radionuclide left ventricular end-diastolic and end-systolic count data provides accurate estimates of biplane cineangiographic end-diastolic and end-systolic volumes; and 2) the hand-drawn region of interest selection method, unlike the semiautomated variable method that underestimates end-diastolic and end-systolic volumes, provides more accurate estimates of biplane cineangiographic left ventricular volumes irrespective of the distance blood sample counts are acquired from the collimator

Cardiac angiotensin-(1-12) expression and systemic hypertension in rats expressing the human angiotensinogen gene

Angiotensin-(1-12) [Ang-(1-12)] is processed into Ang II by chymase in rodent and human heart tissue. Differences in the amino acid sequence of rat and human Ang-(1-12) renders the human angiotensinogen (hAGT) protein refractory to cleavage by renin. We used transgenic rats harboring the hAGT gene [TGR(hAGT)L1623] to assess the non-renin dependent effects of increased hAGT expression on heart function and arterial pressure. When compared to Sprague Dawley (SD) control rats (n=11), male homozygous TGR(hAGT)L1623 (n=9) demonstrated sustained day and night-time hypertension associated with no changes in heart rate but increased heart rate lability. Increased heart weight/tibial length ratio and echocardiographic indices of cardiac hypertrophy were associated with modest reduction of systolic function in hAGT rats. Robust human Ang-(1-12) immunofluorescence within myocytes of TGR(hAGT)L1623 rats was associated with a 4-fold increase in cardiac Ang II content. Chymase enzymatic activity, using the rat or human Ang-(1-12) as a substrate, was not different in the cardiac tissue of SD and hAGT rats. Since both cardiac ACE and ACE2 activities were not different among the two strains, the changes in cardiac structure and function, blood pressure, and left ventricular Ang II content might be a product of an increased cardiac expression of Ang II generated through a non-renin dependent mechanism. The data also underscores the existence in the rat of alternate enzymes capable of acting on hAGT protein. Homozygous transgenic rats expressing the human AGT gene represent a novel tool to investigate the contribution of human relevant renin-independent cardiac Ang II formation and function