Search PubMed⌕ Search

Biomedical subjects

P Rigo

Publications and source records attributed to P Rigo.

At least 73 records · Page 4Linked to original sources
PubMed1990

Use of technetium-99m sestamibi to determine the size of the myocardial area perfused by a coronary artery.

The value of the new radionuclide tracer, technetium-99m (Tc-99m) sestamibi, to demonstrate myocardial perfusion in areas supplied by specific coronary arteries was evaluated in patients injected with the agent during cardiac catheterization. Tc-99m sestamibi differs from thallium-201 in its physical characteristics (photon energy 140 keV), half-life (6 hours) and lack of significant redistribution, allowing its administration during an episode of chest pain or ischemia occurring outside the nuclear medicine laboratory with later imaging to visualize the distribution. In 13 patients Tc-99m sestamibi was administered intravenously during balloon-occlusion angioplasty. In 11 of 13 patients, defects of the single photon emission computed tomography images corresponded to the area made ischemic during angioplasty. In the remaining 2 patients, abundant collateral flow was present and no defects were seen. In a second study, 15 patients had Tc-99m sestamibi selectively injected into a coronary artery during angiography. Later imaging identified the area supplied by the artery injected. Tc-99m sestamibi imaging can detect perfusion defects associated with short episodes of ischemia, and the area supplied by the different coronary arteries.

Adult↗
PubMed1990

Imaging of myocardial metabolism by positron emission tomography.

Tracer techniques have provided new insight in cardiology by allowing noninvasive studies of myocardial perfusion, function, metabolism, and, more recently, ligand-receptor interaction. Positron emission tomography allows accurate quantification and the use of natural substrates labelled with 11C, 13N, or 15O. Myocardial metabolism is complex and utilizes a number of substrates, primarily fatty acids. Fatty acids utilization can be studied with 11C palmitate, while 11C acetate more selectively traces TCA cycle activity and reflects myocardial oxygen utilization. Glucose uptake can be traced using 18F deoxyglucose, a glucose analog that is a substrate for hexokinase but is not further metabolized. Flow and oxidative glucose metabolism are usually coupled, and thereby the uptake of FDG and perfusion tracers are usually similar. In myocardial ischemia, however, glucose utilization can persist due to anaerobic glycolysis, and its uptake is frequently enhanced. Clinical applications of the use of metabolic studies in patients with ischemic heart disease are presented.

Amino Acids↗
PubMed1990

99mTc-MIBI (RP-30) to define the extent of myocardial ischemia and evaluate ventricular function.

99mTc-MIBI, a new myocardial perfusion agent, is a technetium labeled isonitrile derivative. We have taken advantage of the physical characteristics of 99mTc to combine at rest, post infarction, ventricular function studies with analysis of perfusion. We have studied at rest and at stress, 22 patients with coronary artery disease selected on the basis of an abnormal coronary angiogram or on the basis of a positive exercise ECG stress test for symptomatic angina. We have also studied, at rest only, 20 patients with a previous myocardial infarction. A comparative thallium planar scintigraphy was obtained for all patients. The sensitivity of 99mTc-MIBI scintigraphy for detecting individual vessel lesions at stress was 88% as compared with 83% for 201Tl. Sensitivity was higher in patients with previous myocardial infarction (93% for the 2 isotopes) than in patients without (85% for 99mTc-MIBI versus 81% for 201Tl). Segmental myocardial correspondence between 99mTc-MIBI and 201Tl was very close (92%). The overall sensitivity for the detection of acute myocardial infarction reached respectively 91% for 99mTc MIBI and 87% for 201Tl. The specificity in the regions corresponding to arteries not involved was excellent for both tracers as we did not observe any false positive result. This is important information but it does not correspond to the specificity to detect coronary artery disease in the overall patient population. The correlation between first pass left ventricular ejection fraction obtained with 99mTc-MIBI and equilibrium left ventricular ejection fraction obtained with 99mTc red cells was excellent (r = 0.96). It was not as good but was still satisfactory for the right ventricle (r = 0.75).(ABSTRACT TRUNCATED AT 250 WORDS)

Contrast Media↗
PubMed1990

Identification of viable myocardium by echocardiography during dobutamine infusion in patients with myocardial infarction after thrombolytic therapy: comparison with positron emission tomography.

To assess the presence of viable myocardium salvaged by coronary artery reperfusion, 17 patients with acute anterior myocardial infarction were studied. Each received intravenous thrombolysis within the first 3 h of symptoms and underwent two-dimensional echocardiography before and during dobutamine infusion (10 micrograms/kg per min) 7 +/- 4 days after admission and positron emission tomography 9 +/- 5 days after admission. Echocardiography and positron emission tomography were again performed 9 +/- 7 months later. Six comparable segments specific for the territory of the left anterior descending artery were selected for comparison of the two techniques. Wall thickening was evaluated by using an echocardiographic score index. Segmental perfusion and glucose uptake were measured and normalized to the peak activity. A ratio of glucose uptake to perfusion was calculated for each segment. Concordant interpretation of the two techniques was found in 79% of affected segments for both acute and follow-up studies. Positron emission tomography revealed the presence of viable myocardium in 11 patients (group 1); perfusion was within normal limits in 5 of these (group 1A). Myocardial thickening improved with dobutamine infusion in these five patients, the echocardiographic score index decreasing from 12 +/- 2 at rest to 7.8 +/- 1.3 during dobutamine infusion (p = 0.003). Functional recovery was demonstrated in all five patients (follow-up score index 7.4 +/- 1.7). Six patients exhibited decreased perfusion but an abnormally high glucose to perfusion ratio (group 1B); their score index improved with dobutamine from 14.8 +/- 2.2 to 12 +/- 2.1 (p = 0.05), but late functional recovery was found in only one of the six patients (mean follow-up score index in group 1B 16 +/- 1.7). In the six remaining patients in whom no viable myocardium was detected with positron emission tomography (group 2), the echocardiographic score index did not change with dobutamine (15 +/- 0.9 to 14.7 +/- 0.8, p = NS) and there was no functional recovery (follow-up score index 15.5 +/- 1.0). Echocardiography during dobutamine infusion is a promising method to unmask viable myocardium in acute myocardial infarction. Early recovery of perfusion in the area at risk is associated with a good functional outcome, whereas a high glucose to perfusion ratio indicates jeopardized myocardium that frequently loses viability.

Adult↗
PubMed1989

Myocardial perfusion imaging with a new radiotracer, technetium-99m-hexamibi (methoxy isobutyl isonitrile): comparison with thallium-201 imaging.

Technetium-99m-hexamibi (methoxy isobutyl isonitrile) is a Tc-99m-hexakis analog that can be used as a myocardial perfusion imaging agent. This is a report of an initial study that was performed in four institutions to assess the feasibility of Tc-99m-hexamibi myocardial imaging for the detection of coronary artery disease in patients undergoing treadmill stress test. Thirty-three patients referred for evaluation of chest pain had two exercise stress tests, one with Tl-201 and at least 24 hours after, and a second one with Tc-99m-hexamibi. Myocardial planar imaging started 60 minutes after injection at stress of 10-20 mCi of Tc-99m-hexamibi. Because this agent does not redistribute in myocardium after a stress injection, a second injection of 10-20 mCi of Tc-99m-hexamibi was performed with the patient at rest a few days later. Qualitative assessment of both Tl-201 and Tc-99m-hexamibi myocardial distribution was performed in 297 left ventricle segments (three segments of each of three views). There was a good correlation for the presence of normality, scar, or ischemia with the two radiopharmaceuticals, both on a segment by segment (259/297, or 87.2%) and patient-by-patient basis (29/33, or 87.9%). The number of segments found ischemic with Tl-201 and with Tc-99m-hexamibi were nearly equal, as were the number that were normal with one radiopharmaceutical and ischemic by the other. This initial study demonstrates that it is possible to detect stress-induced abnormalities of myocardial perfusion with Tc-99m-hexamibi similar to Tl-201 imaging.

Adult↗
PubMed1989

Characterization of technetium-99m-L,L-ECD for brain perfusion imaging, Part 2: Biodistribution and brain imaging in humans.

The safety, biodistribution and kinetics of a new perfusion imaging agent [99mTc-L,L]-ethyl cysteinate dimer (ECD) was evaluated in normal volunteers. Technetium-99m-L,L-ECD is a neutral, lipophilic complex, which is radiochemically pure and stable. Twelve healthy adults were injected with 25-30 mCi of 99mTc-L,L-ECD and imaged periodically for up to 24 hr. Planar imaging showed rapid brain uptake with a peak concentration of 4.9% injected dose and very slow brain washout (approximately 6% per hour during the first 6 hr). Repeat or dynamic tomographic imaging of the brain using either a rotating gamma camera or a multidetector system was performed up to 6 hr postinjection. The distribution of 99mTc-L,L-ECD in the brain did not change and was similar to the pattern seen with other perfusion agents. Background facial areas and lungs cleared rapidly. Peak blood activity was below 10% injected dose at all times and 99mTc-L,L-ECD cleared rapidly through the kidneys. Vital signs, blood and urine chemistries were normal in all volunteers and no adverse reactions were noted. These results suggest that 99mTc-L,L-ECD should be useful for routine assessment of cerebral perfusion in humans.

Adult↗
PubMed1988

Automated production of potassium-38 for the study of myocardial perfusion using positron emission tomography.

The 35Cl(alpha, n)38K nuclear reaction was developed for the routine cyclotron production of repeated multimillicurie batches of 38K for dynamic studies of regional tissue perfusion with positron emission tomography. The objective is to make this isotope available as an alternative to the use of [13N]NH3 and 82Rb for the investigation of flow in experimental and clinical use. A sodium chloride powder target mounted on a water-cooled nickel backing is bombarded with 26 MeV helium-4 ions at a maximum beam current of 25 microA. The target is remotely disconnected from the bombardment port, transported to a hot cell and entirely processed by a computer-controlled system within a total time of less than 4 min. The final pyrogen-free isotonic and sterile solution of 38K has a radionuclidic purity of more than 99.99%. A typical yield of 19 +/- 2 mCi of 38K is obtained at the end of a 30 min bombardment at 10 microA. The production rate at saturation can therefore be estimated to 2.05 +/- 0.2 mCi/microA.

Coronary Circulation↗
PubMed1987

Usefulness of thromboendarterectomy in association with coronary artery bypass grafting.

Thromboendarterectomy is sometimes performed in association with coronary artery bypass graft surgery (CABG). Right coronary arteries and severely narrowed coronary arteries mainly undergo thromboendarterectomy, but perioperative acute myocardial infarctions (AMI) are possible complications. One hundred seventy-six consecutive patients with rest and stress thallium-201 scintigraphy and angiography were studied before and after surgery. To compare patients with and without thromboendarterectomy, 48 patients who had undergone thromboendarterectomy and whose characteristics matched closely those of patients who had not were selected. Twenty patients had previous AMI before CABG in each group. Analysis accounted for the severity of vessel lesion (complete or incomplete) and for the patency of the graft and of the native coronary artery. In these 96 patients, graft patency was lower than in the overall group and similar among patients with and without thromboendarterectomy among the 56 patients without previous AMI. In patients with previous AMI and thromboendarterectomy, however, reperfusion was achieved more often through the native vessel than through the graft. New AMI or residual ischemia occurred in 32% of the areas undergoing thromboendarterectomy and in only 5% of the standard grafts (p less than 0.001). Best results were obtained in patients with incomplete occlusion after AMI. Patients without previous AMI had worse results. Thus, thromboendarterectomy can yield 64 to 75% good results in selected subgroups when CABG is otherwise impossible, but should be avoided in mildly or moderately stenotic arteries perfusing noninfarcted myocardium.

Coronary Artery Bypass↗
PubMed1987

Preparation and evaluation of a hydrous tin(IV) oxide 82Sr/82Rb medical generator system for continuous elution.

Hydrous tin(IV) dioxide in the Na+-form appears to be the most efficient inorganic exchanger for a reliable and versatile clinical 82Rb generator. Continuous elution with a commercial physiological NaCl solution yields 82Rb ranging between 10 and 40% at a flow rate as low as 3 to 10 mL/min respectively. At the same time the Sr breakthrough is less than 1.6 10(-6)%/mL. A clinical generator loaded with 100 mCi 82Sr (150 mCi 85Sr) and continuously eluted for 3 min at a typical flow rate of 5 mL/min yields 40 mCi of 82Rb, 8 nCi of 82Sr and 11 nCi of 85Sr. The total absorbed radiation dose for 40 mCi 82Rb administered is primarily due to 82Rb and has been estimated for the three principal target organs as 760 mrad for the kidneys, 520 mrad for the heartwalls and 276 mrad for the lungs. The 82,85Sr contribution to the dosimetry has been shown to be negligible. The absence of radiolysis with generators loaded with high level of 82Sr was demonstrated by the excellent reproductibility of continuous elution properties of the generator during its practical shelf-life estimated to 5-6 weeks of clinical use which would require more than 30 L of eluent.

Humans↗
PubMed1987

Quantification of valvular regurgitation using radioisotopes.

Mitral and aortic regurgitations impose an abnormal volume overload on the left ventricle. Recent advances in radionuclide angiographic measurements of all cardiac volumes have made this a practical technique for the detection, quantification and functional assessment of valvular regurgitations and shunts. The method is based on the comparative evaluation of total and effective left ventricular stroke volume. In the radionuclide technique, the right ventricular stroke volume is most frequently used to represent the effective left ventricular stroke volume although techniques have been presented which used as reference the left ventricular stroke volume calculated from measurements of heart rate and cardiac output (Fick method or dye dilution or scintigraphic techniques). The technique can be performed either during first-pass or at equilibrium. Equilibrium measurements are performed in the left anterior oblique position. The stroke volume ratio and the regurgitant fraction are calculated. This technique has been shown to provide adequate quantitative measurements of mitral and aortic regurgitations. Its specificity is adequate with careful positioning and if regions of interest are determined and care is taken to exclude inadequate studies (as these can be prospectively recognized). The technique can separate moderate from severe regurgitation, provide follow-up values for both left ventricular volume and regurgitant fraction, and assess the effect of interventions on the amount of regurgitation. The technique is, however, not adequate to detect mild or minimal regurgitation. In conclusion, equilibrium scintigraphic measurement of valvular regurgitation is an attractive new technique for measuring valvular regurgitation. Its clinical value lies in its simplicity, its reproducibility and its wide applicability. Its accuracy will be improved by performance of gated tomographic acquisitions.

Adaptation, Physiological↗
PubMed1987

Value, sensitivity and specificity of stroke volume ratio in routine equilibrium gated scintigraphy.

The stroke volume ratio (SVR) is a new, non invasive method to quantify ventricular volume overload (VVO). We have analyzed its value, sensitivity and specificity in routine clinical practice. The results of 238 consecutive patients (pts) were analysed prospectively within a 3 months period. The SVR was expressed as the ratio of left ventricular (LV) stroke counts over the right ventricular (RV) stroke counts measured on the time-activity curves. One region of interest was drawn per ventricle on the phase and amplitude images. Values above 1.6 were considered as LVVO and below 0.9 as RVVO. Fifty-one patients had VVO due to valvular regurgitation or left-to-right shunt; 187 patients had no evidence of VVO. Mean value obtained for 23 normal subjects with adequate positioning was 1.27 +/- 0.14 (MV +/- SD), ranging from 0.9 to 1.47. Among patients with adequate positioning, no difference was observed in subgroups with dilated cardiopathy (DC) or anteroseptal aneurysm (AA) despite a low EF. MV for patients with LV or RV hypertrophy (H) were statistically different. Sensitivity was 82% for the 51 patients with VVO. False negatives were due to biventricular overload or mild VVO. Specificity evaluated in the 187 patients without VVO was 76%. The 45 false positives were due to poor separation of the right cardiac chambers and/or of the 2 ventricles. They were observed in 4 patients with AA, 3 patients with DC, 7 patients with LVH, 4 patients with RVH and 24 patients with inadequate positioning. No explanation was found in 3 patients. We conclude that cardiac equilibrium blood pool scintigraphy has an adequate sensitivity and specificity to evaluate patients with VVO.

Cardiomegaly↗
PubMed1987

Prevention of aorta-coronary bypass graft occlusion. Beneficial effect of ticlopidine on early and late patency rates of venous coronary bypass grafts: a double-blind study.

The efficacy of coronary bypass grafting obviously being linked to graft patency, it is compulsory to look for any innovation that could improve the patency rate. Ticlopidine, an antiplatelet drug, was tested against placebo in a double-blind trial: 173 patients (475 grafts) subjected to venous coronary artery bypass grafting were randomly treated with ticlopidine (250 mg twice daily) or placebo from the second postoperative day for 12 months. Graft patency was assessed by digital angiography on days 10 (99.4% of the patients), 180 (98.2%), and 360 (91.7%). The effect of treatment on platelet aggregation and bleeding time were measured concomitantly; a clear-cut effect was demonstrated at each interval. Intention-to-treat graft-by-graft analysis shows that ticlopidine significantly reduced the graft occlusion rate on day 10 (7.1% versus 13.4%, p less than 0.05), day 180 (15.0% versus 24.0%, p less than 0.02), and day 360 (15.9% versus 26.1%, p less than 0.01). Sequential grafts to the left anterior descending coronary artery, with side-to-side anastomosis to diagonal branch(es), are less frequently occluded than individual grafts. On the contrary, grafts to endarterectomized vessels occlude more frequently. Individual patient-by-patient analysis shows that patency of all grafts at each study time, is more frequent in the ticlopidine group. The difference is significant when one considers patients without sequential or endarterectomized grafts. The difference is also present at each study time: day 10 (84.4% versus 66.7%, p less than 0.05), day 180 (74.4% versus 52.3%, p less than 0.05) and day 360 (75.0% versus 52.5%, p less than 0.05). Results are even more impressive if one excludes from analysis the four patients in the ticlopidine group in whom administration of the drug was delayed. This supports previous suggestions that early therapy is necessary. These results show that graft occlusion occurs mainly in the first 6 postoperative months. The incidence of occlusion is significantly reduced by ticlopidine therapy.

Angiography↗
PubMed1987

Rapid method for the measurement of differential renal function: validation.

The precise measurement of glomerular filtration rate (GFR) and renal plasma flow (ERPF) usually requires continuous intravenous administration of adequate substances, with multiple blood and urine analysis, and does not allow measurement of separate renal function. Schlegel et al. and Gates described isotopic methods for the measurement of global and unilateral GFR and ERPF based on the determination by scintillation camera of the fraction of the injected dose ([99mTc]DTPA-[131I]hippuran) present in the kidneys 1-3 min after its administration. These methods require counting of the injected dose and correction for attenuation, but no blood or urine sampling. We have validated these techniques by simultaneous infusion of inulin and PAH in patients with various levels of global renal function (anuric to normal). To better define unilateral renal function we have also studied nine kidneys in patients either nephrectomized or with a nephrostomy enabling unilateral function measurement. A good correlation between inulin or PAH clearances and fractional uptake of [99mTc]DTPA or [131I]hippuran by the kidney was observed. Very good reproducibility of both isotopic techniques was shown. We conclude that determination of the fractional uptake of [99mTc]DTPA and [131I]hippuran between 1 and 3 min allows good and reproducible prediction of global and especially of unilateral kidney function with great rapidity and simplicity, rendering this technique suitable for clinical practice.

Adult↗
PubMed1986

[Cardiac radionuclide tomography with gamma emitters].

Two types of radioisotope tomography have been developed: single photon emission computed tomography and positron emission tomography. Tomography of the heart meets with several problems due to the mobility and obliquity of that organ and to the heterogeneity of surrounding tissues. Compared with planar tomography, myocardial tomography with thallium 201 improves the detection of ischaemic and sub-ischaemic areas in myocardial infarction and chronic coronary disease. In spite of some technical limitations, tomography with labelled red cells is very helpful to determine pre-operative size and location of aneurysms.

Coronary Disease↗