Correction of partial volume effects in myocardial SPECT

BACKGROUND

Marked partial volume effects occur in myocardial single photon emission computed tomographic (SPECT) studies because of limited resolution in imaging the myocardial wall and contractile motion of the heart. Little work has been undertaken to develop correction techniques for SPECT except for efforts to improve the reconstructed resolution. Our purpose was to examine the extent of the problem and propose a correction method.

METHODS AND RESULTS

A potential correction method, developed initially for positron emission tomography, involved estimation of extravascular density by means of subtracting vascular density derived in a blood pool study from total density derived from a transmission study. Provided partial volume errors are the same for transmission and emission data, activity per gram of extravascular tissue can be obtained by means of dividing the perfusion regional data by extravascular density for the same region. Simulations were designed to assess the importance of partial volume errors and the use of extravascular density to correct the errors. Recovery coefficients for the myocardium were estimated by means of simulation of the beating heart on the basis of published values for ventricular dimensions. Resolution for transmission with a scanning line source system was compared with emission resolution. The effect of spillover on measured partial volume losses was assessed, and a method for matching spillover for emission and extravascular density was demonstrated. Correction for partial volume effects was demonstrated for a phantom with variable wall thickness. Significant variation in recovery coefficient was demonstrated between posterior and septal walls for individual patients independent of heart size. Filtering was necessary to account for the difference in transmission resolution measured in the axial direction. Spillover effects had a significant influence on the measured recovery for small objects; however, for a specific reconstruction algorithm and defined region size, correction was implemented to match the spillover effects for emission and extravascular density. Use of extravascular density for correction of partial volume loss, for ordered subsets expectation maximization reconstruction with compensation for resolution, was demonstrated to be accurate to within 10%.

CONCLUSIONS

The feasibility of correcting partial volume effects with extravascular density was demonstrated. Correction is effective provided care is taken to match both resolution and spillover for emission and extravascular density.

Transmission-based scatter correction of 180 degrees myocardial single-photon emission tomographic studies

Meaningful comparison of single-photon emission tomographic (SPET) reconstructions for data acquired over 180 degrees or 360 degrees can only be performed if both attenuation and scatter correction are applied. Convolution subtraction has appeal as a practical method for scatter correction; however, it is limited to data acquired over 360 degrees. A new algorithm is proposed which can be applied equally well to data acquired over 180 degrees or 360 degrees. The method involves estimating scatter based on knowledge of reconstructed transmission data in combination with a reconstructed estimate of the activity distribution, obtained using attenuation correction with broad beam attenuation coefficients. Processing is implemented for planes of activity parallel to the projection images for which a simplified model for the scatter distribution may be applied, based on the measured attenuation. The appropriate broad beam (effective) attenuation coefficients were determined by considering the scatter buildup equation. It was demonstrated that narrow beam attenuation coefficients should be scaled by 0.75 and 0.65 to provide broad beam attenuation coefficients for technetium-99m and thallium-201 respectively. Using a thorax phantom, quantitative accuracy of the new algorithm was compared with conventional transmission-based convolution subtraction (TDCS) for 360 degrees data. Similar heart to lung contrasts were achieved and correction of 180 degrees data yielded a 10.4% error for cardiac activity compared to 5.2% for TDCS. Contrast for myocardium to ventricular cavity was similarly good for scatter-corrected 180 degrees and 360 degrees data, in contrast to attenuation-corrected data, where contrast was significantly reduced. The new algorithm provides a practical method for correction of scatter applicable to 180 degrees myocardial SPET.

Cardiomyopathy Associated with Right Ventricular Apical Pacing-Systematic Review and Meta-Analysis

AIMS

Bradyarrhythmias are potentially life-threatening medical conditions. The most widespread treatment for slow rhythms is artificial ventricular pacing. From the inception of the idea of artificial pacing, ventricular leads were located in the apex of the right ventricle. Right ventricular apical pacing (RVAP) was thought to have a deteriorating effect on left ventricular systolic function. The aim of this study was to systematically assess results of randomized controlled trials to determine the effects of right ventricular apical pacing on left ventricular ejection fraction (LVEF).

METHODS

we systematically searched the Cochrane Central Register of Controlled Trials, PubMed, and EMBASE databases for studies evaluating the influence of RVAP on LVEF. Pooled mean difference (MD) with a 95% confidence interval (CI) was estimated using a random effect model.

RESULTS

14 randomized controlled trials (RCTs) comprising 885 patients were included. In our meta-analysis, RVAP was associated with statistically significant left ventricular systolic function impairment as measured by LVEF. The mean difference between LVEF at baseline and after intervention amounted to 3.35% (95% CI: 1.80-4.91).

CONCLUSION

our meta-analysis confirms that right ventricular apical pacing is associated with progressive deterioration of left ventricular systolic function.

Cardiomyopathy associated with right ventricular apical pacing – systematic review and meta-analysis

Aims

Bradyarrhythmias are potentially life threatening medical conditions. The most widespread type of treatment of slow rhythms is artificial ventricular pacing. From the inception of the idea of artificial pacing, ventricular lead was located in the apex of the right ventricle. Right ventricular pacing (RVP) was thought to have deteriorating effect on left ventricular systolic function. The aim of this study was to systematically assess results of randomized controlled trials of the right ventricular pacing on left ventricular ejection fraction (LVEF).

Methods

We systematically searched the Cochrane Central Register of Controlled Trials, PubMed, and EMBASE databases for studies evaluating the influence of the RVP on the LVEF. Pooled mean difference (MD) with a 95% confidence interval (CI) was estimated using a random effect model.

Results

15 randomized controlled trials (RCTs) comprising 951 patients were included. The mean follow-up in the included studies ranged between 6 to 24 months. In our meta-analysis, RV pacing was associated with statistically significant (MD 2.91; 95% confidence interval (CI): 1.07–4.75) left ventricular systolic function impairment measured by LVEF.

Conclusion

Our meta-analysis confirms, that the right ventricular pacing is associated with progressive deterioration of the left ventricular systolic function.

Funding Acknowledgement

Type of funding sources: None.

Arrhythmias and conduction disorders in patients with viral heart disease

Viral heart disease comprises of two cardiovascular entities being evoked by viral infection: acute viral myocarditis and viral cardiomyopathy. Viral myocarditis may completely resolve leaving no traceable sign or cause ongoing inflammation with subsequent development of hypokinetic dilated/non-dilated cardiomyopathy. The exact epidemiology of viral myocarditis remains unknown due to its sometimes asymptomatic course, but according to the Global Burden of Disease Study 2019, the prevalence of myocarditis in young adults is estimated to range between 6.1 per 100,000 in men and 4.4 per 100,000 in women, with the most common viral etiology. According to the literature viral genome can be found in considerable percentage (up to 67,4%) of endomyocardial biopsy specimens obtained from patients with idiopathic left ventricular dysfunction- suggesting viral etiology of the cardiomyopathy. In this review we would like to enlighten most common types of arrhythmias and conduction disorders as well as their prevalence in patients with viral heart disease. Moreover, our paper depicts probable pathological mechanisms in which viruses induce arrhythmias and cardiac conduction system disease in both, acute viral infection and chronic viral disease. We would also like to highlight unresolved problem of sudden death protection in the course of acute myocarditis.

Relationship between Copper, Zinc, and Copper-to-Zinc Ratio in Hair and Severity of Coronary Artery Disease according to the SYNTAX Score

Coronary artery disease (CAD) continues to be a foremost contributor to global mortality, and the quest for modifiable risk factors could improve prophylactic strategies. Recent studies suggest a significant role of zinc (Zn) and copper (Cu) deficiency in atheromatous plaque formation. Furthermore, hair was previously described as a valuable source of information on elemental burden during the 6-8 week period before sampling. The aim of this study was to investigate the possibility of correlation between the extent of CAD evaluated with the SYNergy Between PCI With TAXUS and the Cardiac Surgery (SYNTAX) score with Cu and Zn content in hair samples, as well as with the Cu/Zn ratio in a cohort of 130 patients. Our findings describe a statistically significant inverse correlation between Cu content and the Cu/Zn ratio in hair samples and the extent of CAD. In contrast, no significant correlation was found between Zn content and the extent of CAD. Considering the scarcity of existing data on the subject, the analysis of hair samples could yield a novel insight into elemental deficiencies and their potential influence on CAD extent.