F. Cauwe

Area-at-risk determination by technetium-99m-hexakis-2-methoxyisobutyl isonitrile in experimental reperfused myocardial infarction.

In a canine model of reperfused myocardial infarction, we tested the hypothesis that after reperfusion, technetium-99m-hexakis-2-methoxyisobutyl isonitrile (Tc-MIBI) tomographic imaging still reflects occlusion blood flow when the tracer is injected before reperfusion. Nine anesthetized dogs underwent 2 hours of coronary occlusion followed by 3 hours of reperfusion ending by being killed. Reference coronary blood flow was determined by radioactive microspheres injected during occlusion and after reperfusion. Biopsies in normal and ischemic myocardium and single photon emission computed tomography were obtained during occlusion and after reperfusion. Circumferential profiles were applied to axial slices divided into 5-degree sectors. The sectors were divided into 3 groups selected on the occlusion acquisition (normal, mildly reduced, and severely reduced) and compared with the postreperfusion acquisition. Tissular Tc-MIBI kinetics was assessed both by Tc-MIBI time-activity curves of normal and ischemic tissue obtained by biopsy and by the relative gradient between normal, ischemic, and necrotic postmortem tissue samples. In biopsy samples, Tc-MIBI content remained unchanged during occlusion and after reperfusion in normal as well as in ischemic tissue (4,662 +/- 2,237 counts/min/mg vs. 4,599 +/- 1,577 counts/min/mg in normal tissue, NS; 941 +/- 903 counts/min/mg vs. 1,087 +/- 721 counts/min/mg in ischemic tissue, NS). In postmortem tissue samples, there was a good correlation between occlusion microsphere blood flow and Tc-MIBI activity (r = 0.91). In the necrotic samples, mean normalized Tc-MIBI activity (10 +/- 17%) was slightly higher than the normalized microsphere blood flow (3 +/- 3%, p less than 0.001) but markedly lower than the normalized microsphere reperfusion blood flow (63 +/- 31%, p less than 0.001). Comparing the single photon emission computed tomographic acquisitions before and after reperfusion, Tc-MIBI activity remained unchanged in normal as well as in mildly reduced or severely reduced segments. Thus, our data are consistent with the hypothesis that Tc-MIBI traces blood flow, does not redistribute significantly despite reperfusion, and can be used for imaging the area at risk.

Quantitative organ-uptake measurement with a gamma camera.

A study was carried out to investigate the use of a gamma camera for quantitative measurement of the absolute radioactivity in internal organs. Phantoms simulating different patient conditions were used to derive the attenuation correction factor and the conversion factor which relates a known radioactive dose to organ activity. The delimitation of the source image was established by means of an isocontour of maximum count rate. A mathematical approach was used for achievement of isosensitivity with depth of the organ and for correction for background. The accuracy of the procedure was proven by the recovery over the stomach area of the ingested activity. The method is applied to the quantitative assessment of the splenic red-cell volume.

Effect of exercise on plasma atrial natriuretic factor and cardiac function in men and women.

Abstract In order to provide an integrated view of the physiology of atrial natriuretic factor (ANF) during exercise, we studied changes of its plasma concentrations in 13 normal subjects (seven males, six females) during three graded exercise levels and two periods of recovery (5 and 30 min), concomitantly with an assessment of cardiac function and ventricular volumes by multigated radionuclide angiography. Mean ANF levels (± SEM) increased in all patients at the second (P < 0·002) and third (P < 0·002) exercise levels, and after 5‐min recovery (P < 0·01): in males from 16 ± 7 to 30 ± 11 pg ml‐1at the third level, in females from 27 ± 12 to 61 ± 33 pg ml‐1. Normal values were observed after 30‐min recovery. Even if mean ANF levels were all higher in females, this difference did not reach statistical significance (P= 0·06). Significant decreases of ventricular volumes, as well as increases of ejection fraction and rate pressure product, were noted during exercise and were similar in both sexes. The kinetics of plasma ANF concentrations, compared with the increase of rate pressure product, was characterized by a latency and a remanence in recovery. This remanence, also present in the changes of ventricular volumes, supports the hypothesis that other factor(s) like catecholamines might still exert their influence after the exercise stops.

Clinical Usefulness of Tc-99m Hmpao Spect Imaging To Map the Ischemic Lesion in Acute Stroke - a Reevaluation

To address the issue of whether single-photon emission computed tomography (SPECT) may add useful topographic information to neurologic examination in clinical practice, we compared technetium-99m hexamethyl propyleneamine oxime (HMPAO) SPECT and brain CT in 100 consecutive stroke patients involving the following clinical vascular territories: cortical middle cerebral artery (CMCA), 52; deep, 39; anterior cerebral artery(ACA), 3; posterior cerebral artery (PCA), 7. SPECT and CT sensitivity were calculated as the percentage of patients with respectively focal hypoperfusion or hypodensity related to the index event. The overall sensitivity of SPECT was not significantly different from CT (69 vs. 73%). The sensitivity of SPECT was not significantly dependent on the time of investigation (72% within 24 h, 50% on day 2, and 71% after day 3). Compared with CT, the sensitivity of SPECT was statistically significantly higher in CMCA infarcts (89 vs. 71%; p = 0.027) and lower in deep infarcts (40 vs. 69%; p = 0.024). The degree of hypoperfusion was significantly higher in cortical lesions than in deep lesions (27 vs. 9%; p < 0.001). Crossed cerebellar diaschisis seemed less frequent in patients with clinical lesion in the ACA and PCA territory (respectively 30 and 40%) and was not significantly different when the ischemic lesion involved the CMCA (56%) or deep territories (50%). No significant difference was found when SPECT took place within or after 48 h. Thus, the selective SPECT sensitivity according to the site of lesion and the degree of hypoperfusion may help to determine stroke subtypes in the acute phase. In contrast, in the subacute phase, SPECT is as sensitive as CT in mapping the ischemic lesion and should not be recommended for this purpose.

Effect of beta-adrenergic blockade on plasma atrial natriuretic factor and cardiac volumes during exercise in normal men.

Abstract Exercise stimulates the release of the atrial natriuretic factor (ANF). 1–3 The principal determinant of ANF release is atrial distension, 4 although adrenergic stimulation has also been implicated in the direct release of ANF. 5,6 Both of these mechanisms could account for the release of ANF during exercise. To elucidate the relative roles of these mechanisms, we determined the plasma ANF concentrations and cardiac volumes during exercise before and after β-adrenergic blockade with propranolol.

Measurement of Erythropoiesis using 52Fe

Summary A method for determining erythropoiesis quantitatively with 52Fe has been applied to 25 patients with anaemia. The data were derived from quantitative scanning of the erythropoietic areas and the measurement of the plasma iron turnover. We have assessed this 52Fe measurement of erythropoiesis by comparing it with total marrow iron turnover studies. Both methods give similar estimates of erythropoiesis except in patients with severe ineffective erythropoiesis and in a patient with significant peripheral haemolysis, when erythropoiesis as measured with the 52Fe technique gave higher results. In these conditions, the estimate of total erythropoiesis might be more reliable using the 52Fe quantitative scanning technique. However, the measurement of erythropoiesis with 52Fe does not distinguish effective from ineffective erythropoiesis and cannot be applied to patients with extramedullary erythropoiesis.

Assessment of the Sites of Red-cell Destruction Using Quantitative Measurements of Splenic and Hepatic Red-cell Destruction

Red cell survival, surface counting indices, the splenic and hepatic contribution to red cell destruction and the rate of splenic and hepatic red cell destruction were measured in 29 patients. Splenectomy was performed in 14. No correlation could be found between the splenic excess count index and both the amount and rate of red cell destruction in the spleen, but the rate of splenic and hepatic red cell destruction was related to the rate of disappearance of red cells from the circulation. The mean fractions of red cell destruction in spleen and liver were 46.1%± 20.5 (SD) and 11.7%± 4.2 (SD) respectively. After splenectomy, the haematocrit returned to normal in all patients despite fractions of red cell destruction in the spleen not exceeding 60%. Although the measurements of the splenic red cell destruction rate and of the fraction of red cell destruction in the spleen provide more precise information on the role of the spleen in red cell destruction, their prognostic value in patients who underwent splenectomy was not obvious.

Exercise gated planar myocardial perfusion imaging using technetium-99m sestamibi for the diagnosis of coronary artery disease: an alternative to exercise tomographic imaging.

Single-photon emission tomography (SPET) using technetium-99m labelled myocardial tracers (e.g.99mTc-sestamibi) has become one of the most popular myocardial imaging methods for the diagnosis of coronary artery disease (CAD). This prospective study was designed to evaluate the diagnostic performance of99mTc-sestamibi exercise gated planar myocardial imaging by comparison with both visual and quantitative analyses of SPET. The study was conducted in 115 consecutive patients with known or suspected CAD, including 54 patients with a previous myocardial infarction (MI), referred for exercise testing prior to coronary angiography. Multi-gated planar imaging and SPET were performed after bicycle exercise. The end-diastolic (ED) and SPET images were visually scored (SVi). Myocardial uptake was quantitated on SPET slices using maximum count circumferential profiles (SQu) and defect extent was measured by comparison with gender-matched data sets obtained from 27 controls (<5% likelihood of CAD). CAD was defined as coronary artery stenosis >50% and/or regional wall motion abnormality. The cut-off criteria for positivity of the three procedures were determined from receiver operating characteristic (ROC) curves derived from the data of patients without previous MI. The area under the ROC curves was similar for ED, SVi and SQu. This was confirmed by the analysis of sensitivity performed using the ROC curve-derived cut-off criteria, in patients with or without previous MI. SVi was more sensitive than ED in identifying the diseased vessel(s) (ED: 41% vs SVi: 80%;P<0.0005) but ED was more specific in this respect (ED: 79% vs SVi: 61%;P<0.0005). We conclude that visual analysis of ED images obtained from gated99mTc-sestamibi stress planar imaging is a valuable alternative to SPET imaging for the diagnosis of CAD. SPET is, however, more accurate for the evaluation of the disease extent and localization and therefore remains the method of choice for the assessment of myocardial perfusion.