Inter-observer Variability of Expert-derived Morphologic Risk Predictors in Aortic Dissection

OBJECTIVES: Establishing the reproducibility of expert-derived measurements on CTA exams of aortic dissection is clinically important and paramount for ground-truth determination for machine learning. METHODS: Four independent observers retrospectively evaluated CTA exams of 72 patients with uncomplicated Stanford type B aortic dissection and assessed the reproducibility of a recently proposed combination of four morphologic risk predictors (maximum aortic diameter, false lumen circumferential angle, false lumen outflow, and intercostal arteries). For the first inter-observer variability assessment, 47 CTA scans from one aortic center were evaluated by expert-observer 1 in an unconstrained clinical assessment without a standardized workflow and compared to a composite of three expert-observers (observers 2-4) using a standardized workflow. A second inter-observer variability assessment on 30 out of the 47 CTA scans compared observers 3 and 4 with a constrained, standardized workflow. A third inter-observer variability assessment was done after specialized training and tested between observers 3 and 4 in an external population of 25 CTA scans. Inter-observer agreement was assessed with intraclass correlation coefficients (ICCs) and Bland-Altman plots. RESULTS: Pre-training ICCs of the four morphologic features ranged from 0.04 (-0.05 to 0.13) to 0.68 (0.49-0.81) between observer 1 and observers 2-4 and from 0.50 (0.32-0.69) to 0.89 (0.78-0.95) between observers 3 and 4. ICCs improved after training ranging from 0.69 (0.52-0.87) to 0.97 (0.94-0.99), and Bland-Altman analysis showed decreased bias and limits of agreement. CONCLUSIONS: Manual morphologic feature measurements on CTA images can be optimized resulting in improved inter-observer reliability. This is essential for robust ground-truth determination for machine learning models. KEY POINTS: • Clinical fashion manual measurements of aortic CTA imaging features showed poor inter-observer reproducibility. • A standardized workflow with standardized training resulted in substantial improvements with excellent inter-observer reproducibility. • Robust ground truth labels obtained manually with excellent inter-observer reproducibility are key to develop reliable machine learning models

Registry of Aortic Diseases to Model Adverse Events and Progression (ROADMAP) in Uncomplicated Type B Aortic Dissection: Study Design and Rationale

PURPOSE To describe the design and methodological approach of a multicenter, retrospective study to externally validate a clinical and imaging-based model for predicting the risk of late adverse events in patients with initially uncomplicated type B aortic dissection (uTBAD). MATERIALS AND METHODS The Registry of Aortic Diseases to Model Adverse Events and Progression (ROADMAP) is a collaboration between 10 academic aortic centers in North America and Europe. Two centers have previously developed and internally validated a recently developed risk prediction model. Clinical and imaging data from eight ROADMAP centers will be used for external validation. Patients with uTBAD who survived the initial hospitalization between January 1, 2001, and December 31, 2013, with follow-up until 2020, will be retrospectively identified. Clinical and imaging data from the index hospitalization and all follow-up encounters will be collected at each center and transferred to the coordinating center for analysis. Baseline and follow-up CT scans will be evaluated by cardiovascular imaging experts using a standardized technique. RESULTS The primary end point is the occurrence of late adverse events, defined as aneurysm formation (≥6 cm), rapid expansion of the aorta (≥1 cm/y), fatal or nonfatal aortic rupture, new refractory pain, uncontrollable hypertension, and organ or limb malperfusion. The previously derived multivariable model will be externally validated by using Cox proportional hazards regression modeling. CONCLUSION This study will show whether a recent clinical and imaging-based risk prediction model for patients with uTBAD can be generalized to a larger population, which is an important step toward individualized risk stratification and therapy.Keywords: CT Angiography, Vascular, Aorta, Dissection, Outcomes Analysis, Aortic Dissection, MRI, TEVAR© RSNA, 2022See also the commentary by Rajiah in this issue

Neuronal Assembly Detection and Cell Membership Specification by Principal Component Analysis

In 1949, Donald Hebb postulated that assemblies of synchronously activated neurons are the elementary units of information processing in the brain. Despite being one of the most influential theories in neuroscience, Hebb's cell assembly hypothesis only started to become testable in the past two decades due to technological advances. However, while the technology for the simultaneous recording of large neuronal populations undergoes fast development, there is still a paucity of analytical methods that can properly detect and track the activity of cell assemblies. Here we describe a principal component-based method that is able to (1) identify all cell assemblies present in the neuronal population investigated, (2) determine the number of neurons involved in ensemble activity, (3) specify the precise identity of the neurons pertaining to each cell assembly, and (4) unravel the time course of the individual activity of multiple assemblies. Application of the method to multielectrode recordings of awake and behaving rats revealed that assemblies detected in the cerebral cortex and hippocampus typically contain overlapping neurons. The results indicate that the PCA method presented here is able to properly detect, track and specify neuronal assemblies, irrespective of overlapping membership

Selective interhemispheric circuits account for a cardinal bias in spontaneous activity within early visual areas

Ongoing brain activity exhibits patterns resembling neural ensembles co-activated by stimulation or task performance. Such patterns have been attributed to the brain's functional architecture, e.g. selective long-range connections. Here, we directly investigate the contribution of selective connections between hemispheres to spontaneous and evoked maps in cat area 18 close to the 17/18 border. We recorded voltage-sensitive dye imaging maps and spiking activity while manipulating interhemispheric input by reversibly deactivating corresponding contralateral areas. During deactivation, spontaneous maps continued to be generated with similar frequency and quality as in the intact network but a baseline cardinal bias disappeared. Consistently, neurons preferring either horizontal (HN) or vertical (VN), as opposed to oblique contours, decreased their resting state activity. HN decreased their rates also when stimulated visually. We conclude that structured spontaneous maps are primarily generated by thalamo- and/or intracortical connectivity. However, selective long-range connections through the corpus callosum - in perpetuation of the long-range intracortical network - contribute to a cardinal bias, possibly, because they are stronger or more frequent between neurons preferring horizontal and/or cardinal contours. As those contours are easier perceived and appear more frequently in natural environment, long-range connections might provide visual cortex with a grid for probabilistic grouping operations in a larger visual scene

Callosal Influence on Visual Receptive Fields Has an Ocular, an Orientation-and Direction Bias

One leading hypothesis on the nature of visual callosal connections (CC) is that they replicate features of intrahemispheric lateral connections. However, CC act also in the central part of the binocular visual field. In agreement, early experiments in cats indicated that they provide the ipsilateral eye part of binocular receptive fields (RFs) at the vertical midline (Berlucchi and Rizzolatti, 1968), and play a key role in stereoscopic function. But until today callosal inputs to receptive fields activated by one or both eyes were never compared simultaneously, because callosal function has been often studied by cutting or lesioning either corpus callosum or optic chiasm not allowing such a comparison. To investigate the functional contribution of CC in the intact cat visual system we recorded both monocular and binocular neuronal spiking responses and receptive fields in the 17/18 transition zone during reversible deactivation of the contralateral hemisphere. Unexpectedly from many of the previous reports, we observe no change in ocular dominance during CC deactivation. Throughout the transition zone, a majority of RFs shrink, but several also increase in size. RFs are significantly more affected for ipsi- as opposed to contralateral stimulation, but changes are also observed with binocular stimulation. Noteworthy, RF shrinkages are tiny and not correlated to the profound decreases of monocular and binocular firing rates. They depend more on orientation and direction preference than on eccentricity or ocular dominance of the receiving neuron's RF. Our findings confirm that in binocularly viewing mammals, binocular RFs near the midline are constructed via the direct geniculo-cortical pathway. They also support the idea that input from the two eyes complement each other through CC: Rather than linking parts of RFs separated by the vertical meridian, CC convey a modulatory influence, reflecting the feature selectivity of lateral circuits, with a strong cardinal bias

Spatial clustering of orientation preference in primary visual cortex of the large rodent agouti

All rodents investigated so far possess orientation-selective neurons in the primary visual cortex (V1) but – in contrast to carnivores and primates – no evidence of pe- riodic maps with pinwheel-like structures. Theoretical studies debating whether phylogeny or universal principles determine development of pinwheels point to V1 size as a critical constraint. Thus, we set out to study maps of agouti, a big diurnal rodent with a V1 size comparable to cats’. In electrophysiology, we detected inter- spersed orientation and direction-selective neurons with a bias for horizontal con- tours, corroborated by homogeneous activation in optical imaging. Compatible with spatial clustering at short distance, nearby neurons tended to exhibit similar orientation preference. Our results argue against V1 size as a key parameter in determining the presence of periodic orientation maps. They are consistent with a phylogenetic influence on the map layout and development, potentially reflecting distinct retinal traits or interspecies differences in cortical circuitry

Minimally Invasive Versus Transcatheter and Surgical Aortic Valve Replacement: A Propensity Matched Study

An increasing number of options exist for the treatment of severe symptomatic aortic stenosis. The study aim was to compare short-term outcomes in patients undergoing surgical aortic valve replacement (SAVR), minimally invasive aortic valve replacement (MIAVR), and transcatheter aortic valve replacement (TAVR). A multi-institutional retrospective review of 2,571 patients undergoing SAVR (n = 842), MIAVR via right anterior thoracotomy (n = 699) and TAVR (n = 1,030) between 2011 and 2014 was conducted. TAVR patients were further stratified as either transfemoral (TF) or transapical (TA). Propensity matching was performed between MIAVR and SAVR (384 pairs), MIAVR and TA-TAVR (115 pairs), and MIAVR and TF-TAVR (247 pairs). Total numbers of AVR increased between 2011 and 2014. When stratified by procedure type, MIAVR and TF-TAVR accounted for most of the growth, while TA-TAVR and SAVR each experienced a decreased volume. Propensity matched comparisons of SAVR, TF-TAVR, and TA-TAVR versus MIAVR revealed no difference in 30-day mortality. TF-TAVR versus MIAVR revealed that MIAVR had a decreased rate of stroke (0.4% versus 3.6%, p = 0.02) and increased atrial fibrillation (AF; 19.4% versus 4%, p <0.01). When compared to SAVR, MIAVR had a lower incidence of AF (19% versus 32.6%, p <0.01). MIAVR exhibited decreased ventilation time (27.2 versus 134 h, p = 0.03) and intensive care unit time (63.7 versus 92.7 h, p = 0.02) compared to TA-TAVR. During recent years, MIAVR and TFTAVR have experienced significant growth in volume with near-comparable short-term outcomes, while SAVR and TA-TAVR volumes have declined. These results underscore the importance of surgeons adopting MIAVR and TF-TAVR techniques in order to offer patients optimal outcomes

Traditional Sternotomy Versus Minimally Invasive Aortic Valve Replacement in Patients Stratified by Ejection Fraction

Low ejection fraction (EF < 40%) portends adverse outcomes in patients undergoing valvular heart surgery. The role of traditional median sternotomy aortic valve replacement (SAVR) compared with minimally invasive aortic valve replacement (MIAVR) in this cohort remains incompletely understood. A multi-institutional retrospective review of 1503 patients who underwent SAVR (n = 815) and MIAVR via right anterior thoracotomy (n = 688) from 2011 to 2014 was performed. Patients were stratified into two groups: EF of less than 40% and EF of 40% or more. In each EF group, SAVR and MIAVR patients were propensity matched by age, sex, body mass index, race, diabetes, hypertension, dyslipidemia, dialysis, cerebrovascular disease, cardiovascular disease, cerebrovascular accident, peripheral vascular disease, last creatinine level, EF, previous MI and cardiogenic shock, and the Society for Thoracic Surgeons (STS) score. Among patients with an EF of 40% or more (377 pairs), patients who underwent MIAVR compared with SAVR had decreased intensive care unit hours (56.8% vs 84.6%, P < 0.001), postoperative length of stay (7.1 vs 7.9 days, P = 0.04), incidence of atrial fibrillation (18.8% vs 38.7%, P < 0.001), bleeding (0.8% vs 3.2%, P = 0.04), and a trend toward decreased 30-day mortality (0.3% vs 1.3%, P = 0.22). The STS scores were largely equivalent in patients undergoing MIAVR compared with SAVR (2.4% vs 2.6%, P = 0.09). In patients with an EF of less than 40% (35 pairs), there was no difference in intensive care unit hours (69% vs 72.6%, P = 0.80), postoperative length of stay (10.3 vs 7.2 days, P = 0.13), 30-day mortality (3.8% vs 0.8%, P = 0.50), or the STS score (3.3% vs 3.2%, P = 0.68). Minimally invasive aortic valve replacement in patients with preserved EF was associated with improved short-term outcomes compared with SAVR. In patients with left ventricular dysfunction, short-term outcomes between MIAVR and SAVR are largely equivalent