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R Itti

Publications and source records attributed to R Itti.

98 records · Page 6Linked to original sources
PubMedDate not supplied

Single photon emission computed tomography of the heart: a functional image?

Images of radioactive tracer uptake are mainly functional images since the tracer distribution may directly be related to the regional variations in function, such as myocardial perfusion in the case of thallium-201 single photon tomography. Combination of pictures obtained in different physiological conditions (stress-rest, for instance) enhance the functional aspects of these studies. For gated cardiac blood pool images, on the contrary, labelling of the circulating blood pool using technetium-99m provides morphological pictures of the heart chambers and function can only be derived from the dynamic analysis of the image sequence recorded at the successive phases of the cardiac cycle. The technique of 'thick slice' tomography preserves the relationship between count rates and local volumes of radioactive blood. Parametric imaging therefore applies to tomography as well as to plane projections. In the simplest case reconstruction of the extreme phases of the heart beat, end-diastole and end-systole may be sufficient. But to achieve more sophisticated functional analysis such as Fourier phase mapping, reconstruction of the whole cardiac cycle is necessary.

Erythrocytes↗
PubMedDate not supplied

Myocardial single-photon emission computed tomographic imaging with technetium 99m tetrofosmin: stress-rest imaging with same-day and separate-day rest imaging.

BACKGROUND: Technetium 99m tetrofosmin is a new ethylene diphosphine ligand for myocardial perfusion imaging and has unique properties. We have compared stress-rest single-photon emission computed tomographic (SPECT) imaging with 99mTc tetrofosmin with same-day and separate-day rest imaging to detect myocardial perfusion defects. METHODS AND RESULTS: Myocardial SPECT imaging was performed in 22 patients with coronary artery disease who had undergone planar thallium 201 imaging and coronary angiography. Single-day (stress-rest) and separate-day rest 99mTc tetrofosmin SPECT protocols were compared in the same patient. Images were assessed by a blinded panel to identify myocardial infarction, ischemia, or normal scans. Overall sensitivity for identification of patients with coronary artery disease was 86% (19/22) by both same-day stress-rest and separate-day rest protocols with 99mTc tetrofosmin (p = NS). Of a total of 396 segments studied, 107 abnormal segments were identified at exercise and 76 and 81 at the same-day and separate-day rest tests, respectively (p = NS). Same-day stress-rest and separate-day rest 99mTc tetrofosmin SPECT protocols were also useful for detecting individual coronary stenosis with a greater than 50% lesion: 80% of the left anterior descending, 93% of the right coronary, and 75% of the left circumflex coronary arteries were detected. CONCLUSION: Excellent images were obtained with 99mTc tetrofosmin during both stress and rest. 99mTc tetrofosmin imaging with the same-day stress-rest and separate-day rest imaging protocols have similar diagnostic sensitivities for detection of coronary heart disease.

Aged↗
PubMedDate not supplied

Theoretical model for myocardial functional characterization: application to a group of patients evaluated before and after surgical revascularization.

BACKGROUND: The functional improvements resulting from coronary revascularization (CABG) in patients with depressed ventricular function may be described by the use of a model combining global or local quantification of myocardial perfusion, viability, and contraction. An illustration of this model, with data provided by conventional radionuclide studies as they are performed routinely in many centers, is presented and the limitations of this approach for predicting the results of CABG are discussed. METHODS AND RESULTS: The model is based on three independent variables, which can be approximated in this preliminary study by parameters derived from standard stress and redistribution/reinjection thallium-201 single-photon emission computed tomography (SPECT) acquisitions with quantification of the tracer uptake defects and from a planar gated blood pool left ventricular ejection fraction (LVEF) measurement: Perfusion is assumed to correspond to 100-stress defect (in percentage), viability is 100-redistribution/reinjection defect, and contraction is 100(LVEF/70), assuming that a normal 70% LVEF corresponds to 100% contraction. In a group of 30 patients prospectively evaluated with this protocol and included in the study on the basis of a pre-CABG LVEF <40%, a significant improvement in LVEF was demonstrated (28.2% +/- 8.5% before CABG vs 35.8% +/- 7.3% after CABG), which is accompanied by a significant decrease of the stress thallium defects (34.8% +/- 13.8% vs 25.6% +/- 10.6%), whereas the average (but not the individual) redistribution/reinjection defects remain almost stable (27.7% +/- 10.9% vs 25.7% +/- 10.1%). As reported in the three-dimensional model, pre-CABG and post-CABG representative points clearly demonstrate the functional improvements for the main variables, but there is a large spectrum of responses to revascularization. It appears that the border between reversible and nonreversible thallium defects does not match the limit between ischemic myocardium (with no contraction alteration and therefore without contraction improvement potential) and hibernating myocardium, which is able to recover mechanical function and therefore is responsible for the improvement of global LVEF. CONCLUSIONS: Thallium SPECT is far from ideal for use as an independent characterization of perfusion and viability because hibernating myocardium may be present in both the fixed and reversible parts of thallium defects. Prediction of functional recovery is conditioned by an accurate identification of viable but underperfused and noncontracting myocardium. In the future, with the use of adequate study protocols that are able to measure viability without interference of perfusion and perfusion independent of viability, the proposed model may be able to characterize regional function as a cluster of representative points for each territory and to delineate areas of the theoretical volume corresponding to a potentially recoverable situation.

Adult↗
PubMedDate not supplied

Effects of subcortical cerebrovascular lesions on cortical hemodynamic parameters assessed by perfusion magnetic resonance imaging.

A simultaneous decrease of cerebral blood volume (CBV) and cerebral blood flow (CBF) has been described after subcortical stroke with positron emission tomography. However, this imaging modality cannot be applied routinely to stroke patients. Dynamic susceptibility contrast-enhanced MRI techniques (DSC-MRI) might be interesting in the assessment of these effects. Dynamic T2-weighted echo planar imaging was used to produce DSC-MR images during an intravenous bolus injection of gadopentetate dimeglumine in 9 patients who experienced a subcortical stroke involving thalamus or basal ganglia and in 8 control subjects. A series of 50 consecutive images at 1-second intervals was acquired at the anatomic level of the centrum semiovale quite distant from the subcortical lesion, rCBF and rCBV were determined over frontal and parietal regions of interest and through the entire cortical mantle. DSC-MRI enabled the detection of hemodynamic changes induced by subcortical stroke. Analysis of rCBV and rCBF values showed that the hemodynamic parameters were significantly decreased on the affected side. In controls mean rCBF and rCBV values recorded over the whole cortical mantle of each hemisphere showed no significant interhemispheric asymmetry.

Adult↗