Evaluation of myocardial perfusion defects by means of "bull's eye" images

Imaging Regional Metabolic Changes in the Ischemic Rat Heart In Vivo Using Hyperpolarized [1-13C]Pyruvate

We evaluated the use of hyperpolarized ¹³C magnetic resonance imaging (MRI) in an open-chest rat model of myocardial infarction to image regional changes in myocardial metabolism. In total, 10 rats were examined before and after 30 minutes of occlusion of the left anterior descending coronary artery using hyperpolarized [1-¹³C]pyruvate. Cardiac metabolic images of [1-¹³C]pyruvate and its metabolites [1-¹³C]lactate, [1-¹³C]alanine, and [¹³C]bicarbonate were obtained before and after ischemia. Significant reduction in the [1-¹³C]alanine and [1-¹³C]lactate signals were observed in the ischemic region post ischemia. The severity of the ischemic insult was verified by increased blood levels of troponin I and by using late contrast-enhanced MRI that showed enhanced signal in the ischemic region. This study shows that hyperpolarized MRI can be used to image regional metabolic changes in the in vivo rat heart in an open-chest model of ischemia reperfusion. Hyperpolarized MRI enables new possibilities for evaluating changes in cardiac metabolism noninvasively and in real time, which potentially could be used for research to evaluate new treatments and metabolic interventions for myocardial ischemia and to apply knowledge to future application of the technique in humans.

Stent Maps--Comparative Visualization for the Prediction of Adverse Events of Transcatheter Aortic Valve Implantations

Transcatheter aortic valve implantation (TAVI) is a minimally-invasive method for the treatment of aortic valve stenosis in patients with high surgical risk. Despite the success of TAVI, side effects such as paravalvular leakages can occur postoperatively. The goal of this project is to quantitatively analyze the co-occurrence of this complication and several potential risk factors such as stent shape after implantation, implantation height, amount and distribution of calcifications, and contact forces between stent and surrounding structure. In this paper, we present a two-dimensional visualization (stent maps), which allows (1) to comprehensively display all these aspects from CT data and mechanical simulation results and (2) to compare different datasets to identify patterns that are typical for adverse effects. The area of a stent map represents the surface area of the implanted stent - virtually straightened and uncoiled. Several properties of interest, like radial forces or stent compression, are displayed in this stent map in a heatmap-like fashion. Important anatomical landmarks and calcifications are plotted to show their spatial relation to the stent and possible correlations with the color-coded parameters. To provide comparability, the maps of different patient datasets are spatially adjusted according to a corresponding anatomical landmark. Also, stent maps summarizing the characteristics of different populations (e.g. with or without side effects) can be generated. Up to this point several interesting patterns have been observed with our technique, which remained hidden when examining the raw CT data or 3D visualizations of the same data. One example are obvious radial force maxima between the right and non-coronary valve leaflet occurring mainly in cases without leakages. These observations confirm the usefulness of our approach and give starting points for new hypotheses and further analyses. Because of its reduced dimensionality, the stent map data is an appropriate input for statistical group evaluation and machine learning methods.

Cardiac MR perfusion image processing techniques: a survey

First-pass cardiac MR perfusion (CMRP) imaging has undergone rapid technical advancements in recent years. Although the efficacy of CMRP imaging in the assessment of coronary artery diseases (CAD) has been proven, its clinical use is still limited. This limitation stems, in part, from manual interaction required to quantitatively analyze the large amount of data. This process is tedious, time-consuming, and prone to operator bias. Furthermore, acquisition and patient related image artifacts reduce the accuracy of quantitative perfusion assessment. With the advent of semi- and fully automatic image processing methods, not only the challenges posed by these artifacts have been overcome to a large extent, but a significant reduction has also been achieved in analysis time and operator bias. Despite an extensive literature on such image processing methods, to date, no survey has been performed to discuss this dynamic field. The purpose of this article is to provide an overview of the current state of the field with a categorical study, along with a future perspective on the clinical acceptance of image processing methods in the diagnosis of CAD.

Usefulness of rapid low-dose/high-dose 1-day 99mTc-sestamibi ECG-gated myocardial perfusion single-photon emission computed tomography

BACKGROUND

The clinical usefulness of a rapid rest low-dose/stress high-dose (dose ratio =1:5) (99m)Tc-sestamibi myocardial perfusion single-photon emission computed tomography (SPECT) protocol for the detection of coronary artery disease was evaluated.

METHODS AND RESULTS

In 89 patients, rest images were obtained immediately after the injection of (99m)Tc-sestamibi (256.1+/-28.4 MBq) followed by drinking water (400 ml). Exercise or vasodilator stress test was performed immediately after the completion of rest imaging with the injection of (99m)Tc-sestamibi (1312.3 +/-167.6 MBq). Prior to the post-stress imaging, patients were asked again to drink water (400 ml) in order to eliminate subdiaphragmatic tracer activity. The myocardial count ratio (stress/rest) of (99m)Tc-sestamibi was calculated. Image quality was scored using a 4-point scale system (4= excellent, 3= good, 2= poor, 1= unacceptable). Coronary angiography was performed in 56 patients within 1 month of the SPECT scan. All patients successfully performed the protocol and total examination time was 108+/-7 min. The myocardial count ratio of (99m)Tc-sestamibi was always greater than 6. The image quality was satisfactory both at rest (3.4+/-0.9) and after stress (3.9+/-0.2). The sensitivity and specificity to detect coronary artery stenosis >50% was 84% and 97%, respectively.

CONCLUSIONS

This rapid one-day (99m)Tc-sestamibi protocol provides adequate image quality and diagnostic accuracy for detecting coronary artery disease.

Identification of proximal left anterior descending artery stenosis with thallium-201 defect patterns in patients with angina pectoris

We determined the accuracy of perfusion defect patterns in predicting the presence of proximal left anterior descending (LAD) artery stenosis in patients with angina pectoris. The development population consisted of 80 patients with single-vessel LAD stenosis and reversible LAD territory defects on thallium-201 tomography. The types of defect patterns associated with angiographic proximal LAD stenosis in this population were categorized as "proximal LAD patterns." The accuracy of these patterns for identifying proximal LAD stenosis was evaluated in a separate validation population of 152 patients with angina pectoris. The development population demonstrated LAD territory defects of type I (most of the LAD territory; n = 12); type II (apex, apicoanterior, and most of the septum; n = 26), type III (septum; n = 19); type IV (anteroseptum; n = 6); type V (apex; n = 10); and type VI patterns (anterolateral wall; n = 7). Patients with type I, II, and IV patterns were highly associated with proximal LAD stenosis (38 of 44 segments), whereas those with type III, V, and VI patterns were mostly related to distal LAD disease (29 of 36 segments). In the validation population, proximal LAD patterns had a sensitivity, specificity, and accuracy of 72%, 95%, and 91%, respectively, for identifying patients with proximal LAD stenosis. Test sensitivity was 86% when patients without LAD territory defects were excluded from analysis. Results were virtually identical in the subgroup of 84 patients with stable angina. Thus, recognition of LAD territory thallium defect patterns is useful for identifying patients with angina who are likely to have proximal LAD stenosis.

Anatomy of a meta-analysis: a critical review of "exercise echocardiography or exercise SPECT imaging? A meta-analysis of diagnostic test performance"

BACKGROUND

Accurate diagnosis of coronary heart disease has the potential to contribute substantially to cost-effective delivery of health services. Recent work by Fleischmann et al (JAMA 1998;280:913-20) represents an effort to summarize the accuracy of exercise echocardiography and exercise single photon emission computed tomography (SPECT).

METHODS AND RESULTS

A critique of the previous work was constructed, obtaining the 44 articles used. These articles were reviewed and summarized with established techniques for meta-analysis. The studies summarized by Fleischmann et al were found to be significantly heterogeneous (echocardiography and SPECT, both P<.001). In the SPECT cohort, combination of different radioisotopes and reading techniques, and inclusion of reports using experimental techniques, were sources of heterogeneity. In the echocardiography cohort, experimental techniques and an individual series were identified. When the sample was stratified for sources of heterogeneity, it was found that there was no significant difference in diagnostic accuracy between the echocardiography and SPECT techniques used in current clinical practice. Meta-regression with summary receiver operating characteristic curve techniques, after adjustment of the model for multicolinearity and outliers, revealed that there were no significant differences between SPECT as used in current clinical practice and echocardiography.

CONCLUSION

The report by Fleischmann et al contains serious flaws that limit its validity and generalizability.

Myocardial SPET: artificial neural networks describe extent and severity of perfusion defects

Artificial neural networks are computer programs that learn from examples. They have been successfully used to detect coronary artery disease from myocardial perfusion images. The purpose of the present study was to develop neural networks that could classify myocardial scintigrams regarding reversibility, localization, severity and extent of perfusion defects. Rest/exercise technetium-99m sestamibi scintigrams from 338 patients were studied. The classifications of two experts were employed as the gold standard. Artificial neural networks were trained to classify both reversible (ischaemia) and non-reversible (infarct) defects in three vascular territories, corresponding to the main coronary arteries. The extent (small or large) and severity (mild or severe) of the defects were described by the networks. After the training process, separate test sets were used to compare the neural networks with one of the experts who reclassified the scintigrams two months later. The neural networks made correct classifications in 71% of the test cases and the human expert in 70% (P=0.10). It was concluded that artificial neural networks can be trained to make clinical interpretations of myocardial perfusion scintigrams. The results indicate that networks can assist physicians in achieving correct interpretations and thereby improve the diagnostic accuracy of medical imaging.

Scintigraphic diagnosis of coronary artery disease: myocardial bull's-eye images contain the important information

The bull's-eye image, also called polar map image, has been developed as an important display for the visual and quantitative analysis of myocardial perfusion scintigrams. Quantitative analysis can be performed for example by comparing areas in the bull's-eye image with normal limits or by processing it using artificial neural networks. The usefulness of such methods is highly dependent on the information content of the bull's-eye image. The purpose of this study was to investigate whether there is more diagnostically important information in a set consisting of the myocardial bull's-eye image plus tomographic slice image than in the bull's-eye image alone. A population of 135 patients who had undergone both myocardial scintigraphy and coronary angiography, with no more than 3 months elapsing between the two examinations, was studied retrospectively. Four experienced observers independently classified visually all scintigrams regarding the presence/absence of coronary artery disease in two vascular territories using a four-grade scale. The observers classified the scintigrams once viewing bull's-eye images only, and once viewing tomographic slices and bull's-eye images. Coronary angiography was used as gold standard. The classifications were evaluated using the areas under the receiver operating characteristics (ROC) curves. The classifications based on bull's-eye images only were slightly more accurate than those based on tomographic slices and bull's-eye images in one of the two vascular territories (ROC areas of 0.66 vs. 0.64). The opposite relationship was found in the other vascular territory (0.78 vs. 0.81). None of the differences was statistically significant. In conclusion, the diagnostically important information for the diagnosis of coronary artery disease by myocardial perfusion scintigraphy is present in the bull's-eye image.

d-alpha-tocopherol inhibition of vascular smooth muscle cell proliferation occurs at physiological concentrations, correlates with protein kinase C inhibition, and is independent of its antioxidant properties

d-alpha-Tocopherol, but not d-beta-tocopherol, negatively regulates proliferation of vascular smooth muscle cells at physiological concentrations. d-alpha-Tocopherol inhibits protein kinase C (PKC) activity, whereas d-beta-tocopherol is ineffective. Furthermore d-beta-tocopherol prevents the inhibition of cell growth and of PKC activity caused by d-alpha-tocopherol. The negative regulation by d-alpha-tocopherol of PKC activity appears to be the cause and not the effect of smooth muscle cell growth inhibition. d-alpha-Tocopherol does not act by binding to PKC directly but presumably by preventing PKC activation. It is concluded that, in vascular smooth muscle cells, d-alpha-tocopherol acts specifically through a nonantioxidant mechanism and exerts a negative control on a signal transduction pathway regulating cell proliferation.