Mohammed Sm ElBaz

Vortex flow during early and late left ventricular filling in normal subjects: Quantitative characterization using retrospectively-gated 4D flow cardiovascular magnetic resonance and three-dimensional vortex core analysis

BackgroundLV diastolic vortex formation has been suggested to critically contribute to efficient blood pumping function, while altered vortex formation has been associated with LV pathologies. Therefore, quantitative characterization of vortex flow might provide a novel objective tool for evaluating LV function. The objectives of this study were 1) assess feasibility of vortex flow analysis during both early and late diastolic filling in vivo in normal subjects using 4D Flow cardiovascular magnetic resonance (CMR) with retrospective cardiac gating and 3D vortex core analysis 2) establish normal quantitative parameters characterizing 3D LV vortex flow during both early and late ventricular filling in normal subjects.MethodsWith full ethical approval, twenty-four healthy volunteers (mean age: 20±10 years) underwent whole-heart 4D Flow CMR. The Lambda2-method was used to extract 3D LV vortex ring cores from the blood flow velocity field during early (E) and late (A) diastolic filling. The 3D location of the center of vortex ring core was characterized using cylindrical cardiac coordinates (Circumferential, Longitudinal (L), Radial (R)). Comparison between E and A filling was done with a paired T-test. The orientation of the vortex ring core was measured and the ring shape was quantified by the circularity index (CI). Finally, the Spearman’s correlation between the shapes of mitral inflow pattern and formed vortex ring cores was tested.ResultsDistinct E- and A-vortex ring cores were observed with centers of A-vortex rings significantly closer to the mitral valve annulus (E-vortex L=0.19±0.04 versus A-vortex L=0.15±0.05; p=0.0001), closer to the ventricle’s long-axis (E-vortex: R=0.27±0.07, A-vortex: R=0.20±0.09, p=0.048) and more elliptical in shape (E-vortex: CI=0.79±0.09, A-vortex: CI=0.57±0.06; <0.001) compared to E-vortex. The circumferential location and orientation relative to LV long-axis for both E- and A-vortex ring cores were similar. Good to strong correlation was found between vortex shape and mitral inflow shape through both the annulus (r=0.66) and leaflet tips (r=0.83).ConclusionsQuantitative characterization and comparison of 3D vortex rings in LV inflow during both early and late diastolic phases is feasible in normal subjects using retrospectively-gated 4D Flow CMR, with distinct differences between early and late diastolic vortex rings.

Active shape model with inter-profile modeling paradigm for cardiac right ventricle segmentation

In this work, a novel active shape model (ASM) paradigm is proposed to segment the right ventricle (RV) in cardiac magnetic resonance image sequences. The proposed paradigm includes modifications to two fundamental steps in the ASM algorithm. The first modification includes employing the 2D-principal component analysis (PCA) to capture the inter-profile relations among shapes neighboring landmarks and then model the inter-profile variations between the training set. The second modification is based on using a multi-stage searching algorithm to find the best profile match based on the best maintained profiles relations and thus the best shape fitting in an iterative manner. The developed methods are validated using a database of short axis cine bright blood MRI images for 30 subjects with total of 90 images. Our results show that the segmentation error can be reduced by about 0.4 mm and contour overlap increased by about 4% compared to the classical ASM technique with paired Students t-test indicates statistical significance to a high degree for our results. Furthermore, comparison with literature shows that the proposed method decreases the RV segmentation error significantly.

Assessment of viscous energy loss and the association with three-dimensional vortex ring formation in left ventricular inflow: In vivo evaluation using four-dimensional flow MRI.

To evaluate viscous energy loss and the association with three‐dimensional (3D) vortex ring formation in left ventricular (LV) blood flow during diastolic filling.

Comparison of fast acquisition strategies in whole‐heart four‐dimensional flow cardiac MR: Two‐center, 1.5 Tesla, phantom and in vivo validation study

To validate three widely‐used acceleration methods in four‐dimensional (4D) flow cardiac MR; segmented 4D‐spoiled‐gradient‐echo (4D‐SPGR), 4D‐echo‐planar‐imaging (4D‐EPI), and 4D‐k‐t Broad‐use Linear Acquisition Speed‐up Technique (4D‐k‐t BLAST).

Unravelling cardiovascular disease using four dimensional flow cardiovascular magnetic resonance

Knowledge of normal and abnormal flow patterns in the human cardiovascular system increases our understanding of normal physiology and may help unravel the complex pathophysiological mechanisms leading to cardiovascular disease. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has emerged as a suitable technique that enables visualization of in vivo blood flow patterns and quantification of parameters that could potentially be of prognostic value in the disease process. In this review, current image processing tools that are used for comprehensive visualization and quantification of blood flow and energy distribution in the heart and great vessels will be discussed. Also, imaging biomarkers extracted from 4D flow CMR will be reviewed that have been shown to distinguish between normal and abnormal flow patterns. Furthermore, current applications of 4D flow CMR in the heart and great vessels will be discussed, showing its potential as an additional diagnostic modality which could aid in disease management and timing of surgical intervention.

Clinical applications of intra-cardiac four-dimensional flow cardiovascular magnetic resonance: A systematic review

Background Four-dimensional flow cardiovascular magnetic resonance (4D flow CMR) is an emerging non-invasive imaging technology used to visualise and quantify intra-cardiac blood flow. The aim of this systematic review is to assess the literature on the current clinical applications of intra-cardiac 4D flow CMR. Methods A systematic review was conducted to evaluate the literature on the intra-cardiac clinical applications of 4D flow CMR. Structured searches were carried out on Medline, EMBASE and the Cochrane Library in October 2016. A modified Critical Skills Appraisal Programme (CASP) tool was used to objectively assess and score the included studies. Studies were categorised as ‘highly clinically applicable’ for scores of 67–100%, ‘potentially clinically applicable’ for 34–66% and ‘less clinically applicable’ for 0–33%. Results Of the 1608 articles screened, 44 studies met eligibility for systematic review. The included literature consisted of 22 (50%) mechanistic studies, 18 (40.9%) pilot studies and 4 (9.1%) diagnostic studies. Based on the modified CASP tool, 27 (62%) studies were ‘highly clinically applicable’, 9 (20%) were ‘potentially clinically applicable’ and 8 (18%) were ‘less clinically applicable’. Conclusions There are many proposed methods for using 4D flow CMR to quantify intra-cardiac flow. The evidence base is mainly mechanistic, featuring single-centred designs. Larger, multi-centre studies are required to validate the proposed techniques and investigate the clinical advantages that 4D flow CMR offers over standard practices. PROSPERO = CRD42016051438.

In-scan and scan–rescan assessment of LV in- and outflow volumes by 4D flow MRI versus 2D planimetry

To evaluate the in‐scan and scan–rescan consistency of left ventricular (LV) in‐ and outflow assessment from 1) 2D planimetry; 2) 4D flow magnetic resonance imaging (MRI) with retrospective valve tracking, and 3) 4D flow MRI with particle tracing.

Three dimensional right ventricular diastolic vortex rings: characterization and comparison with left ventricular diastolic vortex rings from 4D flow MRI

Background Efficient right ventricular (RV) pumping function requires optimal blood flow dynamics. In the left ventricle (LV), diastolic vortex ring formation distal to the mitral valve (MV) has been reported to be an important mechanism for such blood flow optimization. Earlier work based on computational fluid dynamic s( CFD) simulations using simplified RV geometry modeling have reported vortex ring formation in the RV during the early filling phase and its breakdown at the late diastolic phase. However, neither those CFD studies have characterized vortex rings nor have they been confirmed by 4D flow MRI. The purpose of this study was to investigate and characterize the formation of vortex rings during diastolic filling in the RV and to compare them with those of LV in healthy volunteers.

Automatic Extraction of the 3D Left Ventricular Diastolic Transmitral Vortex Ring from 3D Whole-Heart Phase Contrast MRI Using Laplace-Beltrami Signatures

In this work, a new method is proposed for automatic extraction of the left ventricular diastolic transmitral vortex ring from 3D whole-heart three directional Phase Contrast MRI. The proposed method consists of two parts, training and extraction. In the training step, an average reference signature of the complex transmitral vortex ring is captured from training subjects using Laplace- Beltrami spectrum and the Lambda2 method. In the vortex extraction step, the trained signature is used to identify the vortex ring by performing an iterative search for the vortex object with minimum distance from the trained signature. The proposed method is validated on a dataset of 8 healthy volunteers with 32 observed diastolic vortex rings. The method was able to successfully extract 27 diastolic vortex rings from a total of 32. Furthermore, the conducted experiments showed the capability of the proposed method in dealing with vortex shape changes that occur between the phases of early and late diastolic filling.

Biventricular vortex ring formation corresponds to regions of highest intraventricular viscous energy loss in a Fontan patient: analysis by 4D Flow MRI

(Fig. 1b). Mathematical identification of vortex core structures from 4D Flow MRI [2] showed a large 3D ring-like vortex formation filling the common biventricular region at the level of the ventricular septal defect, with protrusion in both ventricles (Fig. 1c). To assess the regions of highest EL in this patient, a map of EL inside the ventricle was made in the cross-sectional four-chamber view (Fig. 1d). In Fig. 1e, regions of the identified 3D vortex structure associate with the highest EL levels in the EL map. These high EL levels anatomically correspond to the region of the ventricular septal defect and part of the remaining septum. Knowledge on the consequences of intracardiac deformations on hemodynamic vortex formation and viscous energy loss might be useful in unraveling the pathophysiological mechanisms leading to circulatory failure, one of the main causes of morbidity and mortality in Fontan patients. Image focus