Ugo Meldolesi

Single photon emission computed tomography with technetium-99m hexakis 2-methoxyisobutyl isonitrile in acute myocardial infarction before and after thrombolytic treatment : assessment of salvaged myocardium and prediction of late functional recovery

Single photon emission computed tomography (SPECT) with technetium-99m hexakis 2-methoxyisobutyl isonitrile was investigated as a method to evaluate the results of intravenous thrombolytic treatment in 14 patients (11 men and 3 women) with acute myocardial infarction admitted to the coronary care unit within 4 h of the onset of symptoms. All patients received an injection of 740 MBq of the tracer before starting the thrombolytic therapy, and isonitrile tomography was performed 3 to 4 h later. The tomographic study was repeated 5 days after the acute event. The results of thrombolytic treatment were independently evaluated taking into account the clinical, electrocardiographic (ECG) and enzymatic data and the findings of left ventricular and coronary angiography. Furthermore, all patients were studied with two-dimensional echocardiography on admission, 5 days later and 1 month later. The site and extent of the perfusion defects on admission scintigraphy were consonant with the ECG and echocardiographic findings. A good correlation could be established between the 5 day scintigraphic estimate of infarct dimension and the enzymatic infarct size (r = 0.907, p less than 0.00002). The comparison between pre- and postthrombolytic treatment images enabled the identification of successful and unsuccessful reperfusion even in patients whose other noninvasive findings were inconclusive. Finally, the reduction in defect size predicted late functional improvement that was demonstrated by echocardiography performed 1 month later (r = 0.89, p less than 0.00005). The results of the study suggest the feasibility and the possible usefulness of isonitrile tomography in demonstrating the presence and size of myocardial damage and in assessing the extent of myocardial salvage after thrombolytic therapy in acute myocardial infarction.

Excessive vasoconstriction after stress by the aging kidney: Inadequate prostaglandin modulation of increased endothelin activity

The adaptive capacity of the aging kidney to stimulation of the sympathetic nervous system, as induced by a 30-minute mental stress (MS), was assessed in 8 elderly healthy women (68 to 82 years of age) and compared with that of 8 younger women (24 to 40 years of age). The study encompassed 4 consecutive 30-minute periods (baseline, mental stress, recovery 1, and recovery 2). In the elderly subjects, baseline effective renal plasma flow (ERPF)(iodine 131-labeled hippurate clearance) was lower and glomerular filtration rate (GFR)(iodine 125-labeled iothalamate clearance) was proportionally less reduced than in the younger group; the filtration fraction (FF) was higher. The elderly group excreted more endothelin 1 (ET-1) (P < .05), prostaglandin E2 (PGE2), and 6-keto-prostaglandin F1alpha (6-keto PGF1alpha)(P < .001 for both)(radioimmunoassay). Mental stress induced similar increases in blood pressure, heart rate, and plasma catecholamines in the 2 age groups, limited to the stimulation period. In the elderly group, mental stress caused a prolonged decrease in ERPF that reached its maximum 60 minutes after mental stress (-33%, P < .05), while GFR remained constant during the whole experiment, so that FF increased. In the younger subjects, renal hemodynamic changes were limited to the mental stress period. ET-1 increased during mental stress and the first recovery period in the elderly group (+50% and +25%, P < .05) as it did in the younger group, but the elderly group differed from the younger in that vasodilating prostaglandins increased only during mental stress. In conclusion, the aging kidney reacts to adrenergic stimulation with more-pronounced and -prolonged vasoconstriction that is probably caused by a defect in prostaglandin modulation of endothelin activity. Autoregulation of GFR is maintained at the expense of increased intraglomerular pressure.

Physical modelling (geometrical system response, Compton scattering and attenuation) in brain SPECT using the conjugate gradients reconstruction method

A technique for the simultaneous compensation of spatial system response, Compton scattering and attenuation in brain SPECT using 99Tcm is described here. The procedure involves the acquisition of experimental information relative to spatial response, attenuation and scatter from capillary sources as well as by means of a special experimental set-up. The latter has been accurately designed to isolate the Compton scattering part of the point spread function, by blocking the acquisition of primary gamma rays. The formulation of a physical model allowed a set of weighting factors, which were stored in a disk file, to be calculated. Data were then reconstructed by means of the conjugate gradients iterative least-squares technique, with the system matrix modified by the incorporation of the precalculated weighting factors. Experimental projection data relative to phantoms with constant activity along the rotation axis as well as experimental projection data relative to one phantom with variable axial activity, were acquired. Reconstruction of these data shows that a high degree of compensation for attenuation and scatter in brain SPECT is achieved. With respect to the reconstruction algorithms based upon the backprojection of analytically filtered experimental projections, higher spatial resolution together with very good quantitative activity ratios are the main accomplishments of this reconstruction technique. The method has also been applied to in vivo study reconstructions.

High-performance computing and networking as tools for accurate emission computed tomography reconstruction.

It is well known that the quantitative potential of emission computed tomography (ECT) relies on the ability to compensate for resolution, attenuation and scatter effects. Reconstruction algorithms which are able to take these effects into account are highly demanding in terms of computing resources. The reported work aimed to investigate the use of a parallel high-performance computing platform for ECT reconstruction taking into account an accurate model of the acquisition of single-photon emission tomographic (SPET) data. An iterative algorithm with an accurate model of the variable system response was ported on the MIMD (Multiple Instruction Multiple Data) parallel architecture of a 64-node Cray T3D massively parallel computer. The system was organized to make it easily accessible even from low-cost PC-based workstations through standard TCP/IP networking. A complete brain study of 30 (64×64) slices could be reconstructed from a set of 90 (64×64) projections with ten iterations of the conjugate gradients algorithm in 9 s, corresponding to an actual speed-up factor of 135. This work demonstrated the possibility of exploiting remote high-performance computing and networking resources from hospital sites by means of low-cost workstations using standard communication protocols without particular problems for routine use. The achievable speed-up factors allow the assessment of the clinical benefit of advanced reconstruction techniques which require a heavy computational burden for the compensation effects such as variable spatial resolution, scatter and attenuation. The possibility of using the same software on the same hardware platform with data acquired in different laboratories with various kinds of SPET instrumentation is appealing for software quality control and for the evaluation of the clinical impact of the reconstruction methods.

A brain phantom for studying contrast recovery in emission computerized tomography

A brain phantom is described that is characterized by a high anatomical definition and by the possibility of varying the internal contrast with the use of a single radioactive solution. The experimental work was done with a single-photon emission computerized tomographic (SPET) rotating camera. The phantom was used to study the contrast recovery of both the filtered back-projection and an iterative reconstruction algorithm. Moreover, it was also used to find a cross-calibration factor between activity concentrations in the SPET slices and an external reference.

Use of technetium-99m hexamethylpropylene amine oxime SPET for the study of cerebral blood flow reactivity after acetazolamide infusion in patients with Behçet's disease

Abstract.The purpose of this study was to characterise the nature of the baseline perfusion defects found in patients with Behçet’s disease using hexamethylpropylene amine oxime single-photon emission tomography in conjunction with acetazolamide test (Acz SPET). Eleven patients underwent both baseline and Acz SPET. Regions of interest (ROIs) were drawn on the areas with decreased perfusion (D-ROI) and, in the same section, on areas with normal perfusion (N-ROI). The ROIs were then repositioned on the corresponding section on Acz SPET. The mean ROI counts were then transformed into a perfusion index value (PIV) with reference to the global brain counts. In total we found 24 D-ROIs (17 in the cortical and 7 in subcortical grey matter). The influence of Acz infusion was selectively registered in the D-ROIs, where PIVs changed from 1.23±0.17 (baseline SPET) to 1.63±0.23 (Acz SPET) (P<0.001). No significant difference was seen in the N-ROIs (1.46±0.21 and 1.40±0.17, respectively, on baseline SPET and Acz SPET). Our results demonstrate that Acz infusion increases the regional cerebral blood flow within baseline grey matter perfusion defects. This finding suggests that baseline perfusion abnormalities could reflect a disconnection rather than local vasculitic involvement.

Comparison of tomographic and planar imaging for the evaluation of thrombolytic therapy in acute myocardial infarction using pre- and post-treatment myocardial scintigraphy with technetium-99m sestamibi

Pre- and post-treatment myocardial scintigraphy with technetium-99m hexakis 2-methoxy-isobutyl-isonitrile (Tc-99m sestamibi) was performed in patients who underwent thrombolytic therapy for acute myocardial infarction comparing planar imaging and single-photon emission computed tomography (SPECT). Twenty-one patients were injected with Tc-99m sestamibi before thrombolytic treatment. SPECT and planar imaging were acquired after completion of the treatment. The scintigraphy was repeated 5 days later in 20 subjects. Planar and SPECT studies were evaluated using an uptake score. Patients were divided according to the status of the infarct-related vessel (patent in 13 patients, group 1, and occluded in seven, group 2) and to the presence of functional recovery in serial echocardiographic controls (present in 10 patients, group A, and absent in 10, group B). The scintigraphic defect extent in the 5-day images correlated with the enzymatic infarct size: SPECT: r = 0.75, p less than 0.0002; planar: r = 0.68, p less than 0.002. The decrease of the uptake defects correlated with the reduction of the left ventricular wall asynergy (admission versus 1 month echocardiogram): SPECT: r = 0.92, p less than 0.000001; planar: r = 0.82, p less than 0.00001. The percent decrease of the uptake defects was significantly higher in patients in group 1 and group A compared with group 2 and, respectively, group B--SPECT: group 1: 51.4 +/- 27.7 versus group 2: 13.1 +/- 8.6, p less than 0.02; group A: 64.2 +/- 15.3 versus group B: 11.9 +/- 8.1, p less than 0.0002; planar group 1: 41 +/- 30.4 versus group 2: 7.7 +/- 6.2, p less than 0.05; group A: 52.5 +/- 24.3 versus group B: 6.1 +/- 6, p less than 0.0002. This study confirms the reliability of pre- and post-treatment myocardial scintigraphy with Tc-99m sestamibi for evaluating the outcome of thrombolytic treatment in myocardial infarction. The results seems slightly more accurate using SPECT, but a simple three-view planar study also gives useful data.

Validation of a New Method for Quantifying Renal Function

In this study we evaluated a further refinement of the background subtraction technique and the introduction of correction factors for the influences produced by kidney depth and surface dimensions on the system counting efficiency

Evaluation of technetium 99m cyclobutylpropylene amine oxime as a potential brain perfusion imaging agent for SPET

Technetium 99md,l-cyclobutylpropylene amine oxime (99mTc-CBPAO) has been developed as a brain-imaging agent for single photon emission tomography (SPET).99mTc-CBPAO can be prepared using a simple labelling procedure suitable for routine clinical use. It has a high in vitro stability, as has been demonstrated by high-pressure liquid chromatography (HPLC) analysis. This shows that 3 h after labelling, less than 5% of the primary lipophilic complex which is capable of crossing the blood-brain barrier (BBB) converts to a secondary hydrophilic complex. Brain uptake (% dose/g wet tissue) of99mTc-CBPAO, determined at 5 and 30 min after injection in two groups of six adult male Sprague-Dawley rats, was found to be 0.74±0.06 and 0.73±0.13 (mean ± SD), respectively. These values are not significantly different from those obtained repeating the experiment with99mTc-labelled hexamethylpropylene amine oxime (99mTc-HMPAO) (0.72±0.15 at 5 min and 0.88 ± 0.24 at 30 min after injection). Since the rat brain uptake of99mTc-CBPAO remained unchanged for a period of time suitable for tomographic study, the comparison of the two tracers was extended to two groups of ten patients. The latter were affected by neurological and psychiatric disorders and were studied with SPET. Human brain uptake (% dose/cc cortical grey matter) of99mTc-CBPAO and99mTc-HMPAO were 3.04±0.57 and 4.22±0.46 (mean × 10−3 ± SD × 10−3), respectively, with a 32% significant difference. In two other groups of five patients, the first transit time-activity curves of the two tracers were compared. From the analysis of these curves we suggest that99mTc-CBPAO has a higher binding effect on blood components and/or a higher degradation rate in blood than that of99mTc-HMPAO. This may account for the reduced human brain uptake. In conclusion, SPET images of99mTc-CBPAO reflect blood perfusion, and they have a good diagnostic quality. The main advantage of99mTc-CBPAO is its in vitro stability; however,99mTc-HMPAO is a superior imaging agent.

Prognostic value of the 131I whole‐body scan in postsurgical therapy for differentiated thyroid cancer

Seventy‐two patients affected by differentiated thyroid cancer underwent whole‐body scan seven days after the postsurgical thyroablative treatment with 131I. In 40 patients this scanning did not reveal any area of 131I uptake outside the residual thyroid parenchyma. During the follow‐up period, no signs of functioning tumors were detected in these patients and therefore, there was no need for further therapeutic treatment with radioiodine. From this results it is legitimate to conclude that whole‐body scan control can be significantly postponed without diagnostic inaccuracy for those patiants whose postthyroablative scans do not reveal diffuse tumor localizations.