Dysfunctional but viable myocardium - ischemic heart disease assessed by magnetic resonance imaging and single photon emission computed tomography

The assessment of ischemic heart disease (IHD) often focuses on the detection of dysfunctional but viable myocardium which may improve in function following revascularization. Dysfunctional but viable myocardium is identified by distinct characteristics with regards to function, perfusion and viability. Therefore, in Paper I we developed a method for quantitative polar representation of left ventricular myocardial function, perfusion and viability using single photon emission computed tomography (SPECT) and cardiac magnetic resonance (CMR). Polar representation of these parameters was feasible, and the quantitative method agreed with visual assessment. Paper II showed that wall thickening decreases with increasing infarct transmurality. However, the variation in wall thickening was large, and importantly, influenced more so by the function of adjacent myocardium than by infarct transmurality. This underscores the difficulty of using resting function alone to accurately assess myocardial infarction in revascularized IHD. In Paper III we assessed the relationship between left ventricular ejection fraction (LVEF) and infarct size and found that LVEF cannot be used to estimate infarct size, and vice versa. However, the study showed that LVEF can be used to estimate a maximum predicted infarct size, and that infarct size can be used to estimate a maximum predicted LVEF. These results emphasize the importance of direct infarct imaging by CMR when attempting to estimate the size of infarction in patients with IHD. Paper IV was designed to assess the time course of recovery of myocardial perfusion and function after revascularization. The recovery of perfusion was found to occur in the first month, while the recovery of function was delayed in segments with non-transmural infarction. In summary, the presented studies emphasize the importance of direct infarct imaging by CMR for the accurate identification of infarction in the assessment of dysfunctional myocardium. Neither regional nor global myocardial function have a close correlation to infarction, but the presence of non-transmural infarction is a marker for delayed recovery of function following revascularization

Pulmonary intravascular blood volume changes through the cardiac cycle in healthy volunteers studied by cardiovascular magnetic resonance measurements of arterial and venous flow

BACKGROUND: This study aims to present a novel method for using cardiovascular magnetic resonance (CMR) to non-invasively quantify the variation in pulmonary blood volume throughout the cardiac cycle in humans. METHODS: 10 healthy volunteers (7 males, 3 female, age range 21-32 years) were studied. The blood flow in the pulmonary artery and all pulmonary veins was quantified during free breathing using phase contrast velocity encoded CMR. The difference in flow between the pulmonary artery and the pulmonary veins was integrated to calculate the change in pulmonary blood volume throughout the cardiac cycle. RESULTS: The stroke volumes in the pulmonary artery and the sum of the pulmonary veins were (mean +/- SEM) 103 +/- 6 ml and 95 +/- 6 ml, respectively. The pulmonary blood volume variation (PBVV) was 48 +/- 5 ml, and the PBVV expressed as percent of the pulmonary artery stroke volume was 46 +/- 3%. The maximum increase in pulmonary blood volume occurred 310 +/- 12 ms after the R-wave from the ECG (32 +/- 2% of the cardiac cycle). PBVV did not correlate to change in cross-sectional area in the pulmonary artery (R2 = 0.03, p = 0.66). CONCLUSION: It is feasible to non-invasively quantify the change in pulmonary blood volume during the cardiac cycle in humans using CMR. The average pulmonary blood volume variation in healthy volunteers was approximately 50 ml and this was approximately 50% of the stroke volume. Further studies are needed to assess the utility of the pulmonary blood volume variation as a measure for identifying cardiac and pulmonary vascular disease

Counterfactual Evaluation of Peer-Review Assignment Policies

Peer review assignment algorithms aim to match research papers to suitable expert reviewers, working to maximize the quality of the resulting reviews. A key challenge in designing effective assignment policies is evaluating how changes to the assignment algorithm map to changes in review quality. In this work, we leverage recently proposed policies that introduce randomness in peer-review assignment--in order to mitigate fraud--as a valuable opportunity to evaluate counterfactual assignment policies. Specifically, we exploit how such randomized assignments provide a positive probability of observing the reviews of many assignment policies of interest. To address challenges in applying standard off-policy evaluation methods, such as violations of positivity, we introduce novel methods for partial identification based on monotonicity and Lipschitz smoothness assumptions for the mapping between reviewer-paper covariates and outcomes. We apply our methods to peer-review data from two computer science venues: the TPDP'21 workshop (95 papers and 35 reviewers) and the AAAI'22 conference (8,450 papers and 3,145 reviewers). We consider estimates of (i) the effect on review quality when changing weights in the assignment algorithm, e.g., weighting reviewers' bids vs. textual similarity (between the review's past papers and the submission), and (ii) the "cost of randomization", capturing the difference in expected quality between the perturbed and unperturbed optimal match. We find that placing higher weight on text similarity results in higher review quality and that introducing randomization in the reviewer-paper assignment only marginally reduces the review quality. Our methods for partial identification may be of independent interest, while our off-policy approach can likely find use evaluating a broad class of algorithmic matching systems

Dark blood late enhancement imaging.

Background Bright blood late gadolinium enhancement (LGE) imaging typically achieves excellent contrast between infarcted and normal myocardium. However, the contrast between the myocardial infarction (MI) and the blood pool is frequently suboptimal. A large fraction of infarctions caused by coronary artery disease are sub-endocardial and thus adjacent to the blood pool. It is not infrequent that sub-endocardial MIs are difficult to detect or clearly delineate. Methods In this present work, an inversion recovery (IR) T2 preparation was combined with single shot steady state free precession imaging and respiratory motion corrected averaging to achieve dark blood LGE images with good signal to noise ratio while maintaining the desired spatial and temporal resolution. In this manner, imaging was conducted free-breathing, which has benefits for image quality, patient comfort, and clinical workflow in both adults and children. Furthermore, by using a phase sensitive inversion recovery reconstruction the blood signal may be made darker than the myocardium (i.e., negative signal values) thereby providing contrast between the blood and both the MI and remote myocardium. In the proposed approach, a single T1-map scout was used to measure the myocardial and blood T1 using a MOdified Look-Locker Inversion recovery (MOLLI) protocol and all protocol parameters were automatically calculated from these values within the sequence thereby simplifying the user interface. Results The contrast to noise ratio (CNR) between MI and remote myocardium was measured in n = 30 subjects with subendocardial MI using both bright blood and dark blood protocols. The CNR for the dark blood protocol had a 13 % loss compared to the bright blood protocol. The CNR between the MI and blood pool was positive for all dark blood cases, and was negative in 63 % of the bright blood cases. The conspicuity of subendocardial fibrosis and MI was greatly improved by dark blood (DB) PSIR as well as the delineation of the subendocardial border. Conclusions Free-breathing, dark blood PSIR LGE imaging was demonstrated to improve the visualization of subendocardial MI and fibrosis in cases with low contrast with adjacent blood pool. The proposed method also improves visualization of thin walled fibrous structures such as atrial walls and valves, as well as papillary muscles