Left atrial structure and functional quantitation using cardiovascular magnetic resonance and multimodality tissue tracking: validation and reproducibility assessment

Background

Left atrium (LA) strain, volume and function are important markers of cardiovascular disease and myocardial impairment. We aimed to assess the accuracy of LA biplane volume and function measured by Multimodality Tissue Tracking (MTT). Also we assessed the inter-study reproducibility for cardiovascular magnetic resonance (CMR) derived LA volume and function parameters.

Methods

Thirty subjects (mean age: 71.3 ± 8.7, 87 % male) including twenty subjects with cardiovascular events and ten healthy subjects, with CMR were evaluated in the Multi-Ethnic Study of Atherosclerosis (MESA). LA volumes were computed by the modified biplane method from 2- and 4-chamber projections and the Simpson’s method from short-axis slices using both methods - manual and semi-automated delineation using MTT. LA total, active and passive ejection fractions were calculated. Pearson’s correlation and Bland-Altman analysis were used to compare the measurements. In a second sample of 25 subjects (age: 65.7 ± 7.1, 72 % males) inter study, intra and inter reader reliability analysis was performed. The intra-class correlation coefficient (ICC) was evaluated.

Results

Left atrial MTT structural and functional parameters were not different from manual delineation, yet image analysis was only half as time consuming on average with MTT. Maximal volume MTT was not different between the Simpson’s and Biplane methods, functional parameters, however were different. MTT allowed us to measure multiple LA parameters with good-excellent (ICC; 0.88– 0.98, p < 0.001) intra-and inter reader reproducibility and fair-good (ICC; 0.44–0.82, p < 0.05–0.001) inter study reproducibility.

Conclusions

MTT derived LA biplane volume and function is accurate and reproducible and is suited for use in longitudinal studies.     

Dual-contrast agent photon-counting computed tomography of the heart: initial experience

To determine the feasibility of dual—contrast agent imaging of the heart using photon-counting detector (PCD) computed tomography (CT) to simultaneously assess both first-pass and late enhancement of the myocardium. An occlusion-reperfusion canine model of myocardial infarction was used. Gadolinium-based contrast was injected 10 min prior to PCD CT. Iodinated contrast was infused immediately prior to PCD CT, thus capturing late gadolinium enhancement as well as first-pass iodine enhancement. Gadolinium and iodine maps were calculated using a linear material decomposition technique and compared to single-energy (conventional) images. PCD images were compared to in vivo and ex vivo magnetic resonance imaging (MRI) and histology. For infarct versus remote myocardium, contrast-to-noise ratio (CNR) was maximal on late enhancement gadolinium maps (CNR 9.0?±?0.8, 6.6?±?0.7, and 0.4?±?0.4, p?<?0.001 for gadolinium maps, single-energy images, and iodine maps, respectively). For infarct versus blood pool, CNR was maximum for iodine maps (CNR 11.8?±?1.3, 3.8?±?1.0, and 1.3?±?0.4, p?<?0.001 for iodine maps, gadolinium maps, and single-energy images, respectively). Combined first-pass iodine and late gadolinium maps allowed quantitative separation of blood pool, scar, and remote myocardium. MRI and histology analysis confirmed accurate PCD CT delineation of scar. Simultaneous multi-contrast agent cardiac imaging is feasible with photon-counting detector CT. These initial proof-of-concept results may provide incentives to develop new k-edge contrast agents, to investigate possible interactions between multiple simultaneously administered contrast agents, and to ultimately bring them to clinical practice.     

Left Atrial structure and function in hypertrophic cardiomyopathy sarcomere mutation carriers with and without left ventricular hypertrophy

Background

Impaired left atrial (LA) function is an early marker of cardiac dysfunction and predictor of adverse cardiac events. Herein, we assess LA structure and function in hypertrophy in hypertrophic cardiomyopathy (HCM) sarcomere mutation carriers with and without left ventricular hypertrophy (LVH).

Method

Seventy-three participants of the HCMNet study who underwent cardiovascular magnetic resonance (CMR) imaging were studied, including mutation carriers with overt HCM (n =?34), preclinical mutation carriers without HCM (n =?24) and healthy, familial controls (n =?15).

Results

LA volumes were similar between preclinical, control and overt HCM cohorts after covariate adjustment. However, there was evidence of impaired LA function with decreased LA total emptying function in both preclinical (64?±?8%) and overt HCM (59?±?10%), compared with controls (70?±?7%; p =?0.002 and p =?0.005, respectively). LA passive emptying function was also decreased in overt HCM (35?±?11%) compared with controls (47?±?10%; p =?0.006). Both LAtotal emptying function and LA passive emptying function were inversely correlated with the extent of late gadolinium enhancement (LGE; p?=?0.005 and p <?0.05, respectively), LV mass (p =?0.02 and p <?0.001) and interventricular septal thickness (p?<?0.001 for both) and serum NT-proBNP levels (p?<?0.001 for both).

Conclusion

LA dysfunction is detectable by CMR in preclinical HCM mutation carriers despite non-distinguishable LV wall thickness and LA volume. LA function appears most impaired in subjects with overt HCM and a greater extent of LV fibrosis.

     

Human peripheral arteries: feasibility of transvenous intravascular MR imaging of the arterial wall

Feasibility of in vivo transvenous intravascular magnetic resonance (MR) imaging of the human arterial wall was determined. All subjects provided written informed consent, and institutional review board approved the study. Six arteries in six patients were imaged with a guidewire placed in the iliac vein (n = 5) or left renal vein (n = 1). Pre- and postcontrast T1-weighted and T2-weighted transvenous MR imaging were performed. An atherosclerotic plaque with a fibrous cap was identified on 27 (42%) of 64 images of veins without stents; intimal hyperplasia in a renal artery with a stent was identified on 12 images. Contrast-to-noise ratios (CNRs) on arterial wall postcontrast T1-weighted images were superior to those on images obtained with other sequences (P < .001), and the postcontrast images demonstrated the greatest number of plaques with a low-signal intensity core and fibrous cap. Preliminary results show that transvenous MR imaging is feasible for high-spatial-resolution imaging of the arterial wall and atherosclerotic plaque. Postcontrast T1-weighted imaging affords greatest CNR for the arterial wall.