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.     

Study of myocardial perfusion at rest using technetium Tc 99m methoxy-isobutylisonitrile: comparison with labeled microspheres and thallium 201

In order to evaluate the potential usefulness of 99m technetium (Tc)-methoxy-isobutyl-isonitrile (MIBI) as a myocardial perfusion tracer in man, its myocardial distribution at rest was compared with that of 201thallium (TI). Perfusion images obtained with 99mTc-labelled microspheres, whose myocardial distribution is exclusively coronary flow dependent, were used as reference. The study was performed on twelve patients (10 males and 2 females, mean age 55.4 +/- 6.4) with suspected effort angina and without a history of previous myocardial infarction. In the space of two weeks patients underwent rest and exercise 99mTc-MIBI myocardial scintigraphy, exercise-redistribution 201TI myocardial scintigraphy, 99mTc-labelled microsphere scintigraphy after microsphere injection in the left ventricle at rest during catheterization before performing left ventriculography and coronary angiography. The comparison with microsphere distribution was limited to rest 99mTc-MIBI scintigraphy and redistribution 201TI images. Single photon emission tomography (SPECT) was employed. SPECT was performed using a double-head Rotacamera with a 360 degrees rotation arc. Ninety projections of 20 seconds each were acquired; subsequently image reconstruction was performed using an iterative algorithm. To evaluate regional perfusion the left ventricular wall was divided into 18 segments; the uptake pattern of each segment was graduated according to a qualitative score (0: severe defect; 1: moderate defect; 2: normal uptake). The quality of tomographic myocardial 99mTc-MIBI and 99mTc-microspheres images was higher than that of 201TI tomograms in account of the different physical characteristics of the two radionuclides.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rethinking on the concept of biomarkers in preclinical Alzheimer’s disease

The neuropathological processes eventually leading to Alzheimer’s disease (AD) are thought to start decades before the appearance of clinical symptoms and the clinical diagnosis of AD dementia. The term “preclinical AD” has been recently introduced to identify this “silent stage” of AD, when the disease is already present, but symptoms are not yet clinically evident. Advances in AD biomarkers have dramatically improved the ability to detect AD pathological processes in vivo in cognitively intact subjects, thus demonstrating the presence of AD pathology in the preclinical phase. This review focuses on the recent advances in the field of neuroimaging and CSF AD biomarkers specifically in the preclinical phase of AD, and aims to discuss the significance that such biomarkers could have in cognitively intact subjects. Even though the use of such biomarkers in AD preclinical phase has contributed to improve our understanding of AD early pathological processes, it raised also a number of new challenges that still remain to be overcome, such as a better definition of the clinical and individual significance of currently known biomarkers in preclinical stages and the development of novel biomarkers of different early AD-related events.     

Influence of the postexercise acquisition delay on the detection of functional abnormalities in sestamibi-gated SPECT.

BACKGROUND: Gated single photon emission computed tomography (SPECT) identifies functional changes produced by ischemia, but the influence of acquisition delay on their detection is not established. METHODS AND RESULTS: In 80 patients with known or suspected coronary artery disease, gated SPECT was acquired twice: first, less than 30 minutes after peak exercise (stress 1), and second, more than 45 minutes after peak exercise (stress 2). End-diastolic volume (EDV), end-systolic volume (ESV), and ejection fraction (EF) were compared with perfusion. The relationship between the DeltaEF (stress EF - resting EF) and the summed difference score (SDS) was -0.443 (P < .0001) for stress 1 and -0.416 (P < .0001) for stress 2. In stress 1, EF increased in patients without inducible ischemia (SDS = 0) (57% +/- 10% vs 54% +/- 9% at rest, P < .02) and decreased in those with an SDS of 1 or greater (53% +/- 10.8% vs 55% +/- 9.6% at rest, P < .05). In stress 2, EF was unchanged in patients without ischemia (55.8% +/- 9.7%, P = .06) and decreased in the other patients (52.8% +/- 10.2%, P < .01). In patients without ischemia, both the EDV and ESV decreased significantly in stress 1 and were unchanged in stress 2. In patients with an SDS of 1 or greater, the EDV remained unchanged and the ESV minimally decreased in stress 1, whereas both volumes clearly and significantly increased in stress 2. CONCLUSIONS: The early acquisition of postexercise gated SPECT is slightly more effective in detecting ischemia-related functional changes; however, a delayed acquisition within 60 minutes still permits the detection of functional abnormalities in most patients.     

Predicting revascularization outcome in patients with coronary artery disease and left ventricular dysfunction (data from the SEMINATOR study)

A main goal of revascularization in patients with chronic ischemic cardiomyopathy is to improve global left ventricular (LV) function. This study aimed to verify whether it is possible to predict an increase in LV ejection fraction (EF) after revascularization on the basis of the extent of LV asynergy, myocardial viability, and revascularization completeness. We studied 77 patients with chronic LV ischemic dysfunction using baseline resting and nitrate-enhanced technetium-99m sestamibi single-photon emission computed tomography. Regional wall motion and global LVEF were assessed with echocardiography before and after revascularization, which was complete in 51 patients and incomplete in 26. The number of viable asynergic segments included in revascularized coronary artery territories was the strongest predictor of significant (≥5 EF U) functional improvement in univariate discriminant analysis. According to multivariate stepwise discriminant analysis, this parameter, together with the number of baseline asynergic segments, allowed the detection of patients with significant LVEF improvement with 75% accuracy. With use of a multivariate regression model, including the 2 mentioned variables, the measure of postrevascularization LVEF increase could be accurately quantified (R² 0.43, p <0.000001). In conclusion, this study suggests that the severity of baseline asynergy, the extent of myocardial viability, and the completeness of revascularization are the main determinants of postrevascularization functional recovery in patients with LV ischemic dysfunction, and that on the basis of these variables it is possible to predict the measure of LVEF increase.     

A sampling epidemiological study of infant health in relation to the type of feeding]

An epidemiological study has been carried out an the scholastic population of L'Aquila (Abruzzo). This study had the aim of verifying possible correlations between feeding procedures and the outbreak of illnesses whose causes are unknown. The information was registered with the collaboration of the Medical Scholastic Service, in the period of May-June in 1988-1989, interviewing four hundred and seventy-seven mothers of students, the information regards the temporary period of 1973-1985. The results of their elaboration are as follows: 75.9% of babies took breast milk at birth and in following months breast feeding was the most frequent (34.8%). The procedure breast feeding-bottle feeding was carried out in 30.4% of cases and exclusively bottle feeding in 22.4%. The study has permitted to discover thirteen cases of illnesses whose cause are unknown among which a case of SIDS (sudden infant death syndrome) in a newborn baby fed till eighteen weeks with breast milk and through twenty days before dying with undiluted cows milk. These illnesses happened in 13.4% of babies fed by bottle milk and diluted with running water; in 7.7% by cow's milk diluted with running water and in 4.3% by undiluted cow milk. Some Authors have suspected a relationship between bacterial endotoxin introduced by diet and baby illnesses whose causes are unknown. For this a quantitative determination of such substances is necessary in baby diets.     

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.     

The role of whole body scan and skeletal radiography in the preoperative staging of breast cancer

442 patients with breast cancer were studied by means of radiologic and scintigraphic examination of the skeleton to detect the presence of bone metastases. All the patients have been clinically followed-up for a mean period of 22 months. The overall prevalence of bone metastases at staging was 4.5%. Bone scan showed a higher sensitivity in detecting bone metastases (90% vs 45%) and a lower positive predictive value (60% vs 75%) with respect to X-ray examination. In the presence series no asymptomatic case with bone metastases was found in limited stages (T1-T2 N0-N1). The authors suggest that the bone scan be routinely included in the staging of advanced breast cancer cases and that the use of this procedure be restricted to the symptomatic patients in the more limited stages.     

Evaluation of the influence of age and gender on the relationships between infarct size,infarct severity,and left ventricular ejection fraction in patients successfully treated with primary percutaneous coronary intervention

Background  

Female sex and advanced age have adverse prognostic meaning in acute myocardial infarction. Whether gender and/or age influence the relationship between infarct size, infarct severity, and left ventricular ejection fraction (LVEF) is unclear.