John Paul Finn

Left ventricular shape variation in asymptomatic populations: the multi-ethnic study of atherosclerosis

BackgroundAlthough left ventricular cardiac geometric indices such as size and sphericity characterize adverse remodeling and have prognostic value in symptomatic patients, little is known of shape distributions in subclinical populations. We sought to quantify shape variation across a large number of asymptomatic volunteers, and examine differences among sub-cohorts.MethodsAn atlas was constructed comprising 1,991 cardiovascular magnetic resonance (CMR) cases contributed from the Multi-Ethnic Study of Atherosclerosis baseline examination. A mathematical model describing regional wall motion and shape was used to establish a coordinate map registered to the cardiac anatomy. The model was automatically customized to left ventricular contours and anatomical landmarks, corrected for breath-hold mis-registration between image slices. Mathematical techniques were used to characterize global shape distributions, after removal of translations, rotations, and scale due to height. Differences were quantified among ethnicity, sex, smoking, hypertension and diabetes sub-cohorts.ResultsThe atlas construction process yielded accurate representations of global shape (errors between manual and automatic surface points in 244 validation cases were less than the image pixel size). After correction for height, the dominant shape component was associated with heart size, explaining 32% of the total shape variance at end-diastole and 29% at end-systole. After size, the second dominant shape component was sphericity at end-diastole (13%), and concentricity at end-systole (10%). The resulting shape components distinguished differences due to ethnicity and risk factors with greater statistical power than traditional mass and volume indices.ConclusionsWe have quantified the dominant components of global shape variation in the adult asymptomatic population. The data and results are available at cardiacatlas.org. Shape distributions were principally explained by size, sphericity and concentricity, which are known correlates of adverse outcomes. Atlas-based global shape analysis provides a powerful method for quantifying left ventricular shape differences in asymptomatic populations.Trial registrationClinicalTrials.gov NCT00005487

Cardiovascular MRI with ferumoxytol

The practice of contrast-enhanced magnetic resonance angiography (CEMRA) has changed significantly in the span of a decade. Concerns regarding gadolinium (Gd)-associated nephrogenic systemic fibrosis in those with severely impaired renal function spurred developments in low-dose CEMRA and non-contrast MRA as well as efforts to seek alternative MR contrast agents. Originally developed for MR imaging use, ferumoxytol (an ultra-small superparamagnetic iron oxide nanoparticle), is currently approved by the US Food and Drug Administration for the treatment of iron deficiency anaemia in adults with renal disease. Since its clinical availability in 2009, there has been rising interest in the scientific and clinical use of ferumoxytol as an MR contrast agent. The unique physicochemical and pharmacokinetic properties of ferumoxytol, including its long intravascular half-life and high r1 relaxivity, support a spectrum of MRI applications beyond the scope of Gd-based contrast agents. Moreover, whereas Gd is not found in biological systems, iron is essential for normal metabolism, and nutritional iron deficiency poses major public health challenges worldwide. Once the carbohydrate shell of ferumoxytol is degraded, the elemental iron at its core is incorporated into the reticuloendothelial system. These considerations position ferumoxytol as a potential game changer in the field of CEMRA and MRI. In this paper, we aim to summarise our experience with the cardiovascular applications of ferumoxytol and provide a brief synopsis of ongoing investigations on ferumoxytol-enhanced MR applications.

Improved left ventricular mass quantification with partial voxel interpolation: in vivo and necropsy validation of a novel cardiac MRI segmentation algorithm.

Background— Cardiac magnetic resonance (CMR) typically quantifies LV mass (LVM) by means of manual planimetry (MP), but this approach is time-consuming and does not account for partial voxel components— myocardium admixed with blood in a single voxel. Automated segmentation (AS) can account for partial voxels, but this has not been used for LVM quantification. This study used automated CMR segmentation to test the influence of partial voxels on quantification of LVM. Methods and Results— LVM was quantified by AS and MP in 126 consecutive patients and 10 laboratory animals undergoing CMR. AS yielded both partial voxel (ASPV) and full voxel (ASFV) measurements. Methods were independently compared with LVM quantified on echocardiography (echo) and an ex vivo standard of LVM at necropsy. AS quantified LVM in all patients, yielding a 12-fold decrease in processing time versus MP (0:21±0:04 versus 4:18±1:02 minutes; P <0.001). ASFV mass (136±35 g) was slightly lower than MP (139±35; Δ=3±9 g, P <0.001). Both methods yielded similar proportions of patients with LV remodeling ( P =0.73) and hypertrophy ( P =1.00). Regarding partial voxel segmentation, ASPV yielded higher LVM (159±38 g) than MP (Δ=20±10 g) and ASFV (Δ=23±6 g, both P <0.001), corresponding to relative increases of 14% and 17%. In multivariable analysis, magnitude of difference between ASPV and ASFV correlated with larger voxel size (partial r =0.37, P <0.001) even after controlling for LV chamber volume ( r =0.28, P =0.002) and total LVM ( r =0.19, P =0.03). Among patients, ASPV yielded better agreement with echo (Δ=20±25 g) than did ASFV (Δ=43±24 g) or MP (Δ=40±22 g, both P <0.001). Among laboratory animals, ASPV and ex vivo results were similar (Δ=1±3 g, P =0.3), whereas ASFV (6±3 g, P <0.001) and MP (4±5 g, P =0.02) yielded small but significant differences with LVM at necropsy. Conclusions— Automated segmentation of myocardial partial voxels yields a 14–17% increase in LVM versus full voxel segmentation, with increased differences correlated with lower spatial resolution. Partial voxel segmentation yields improved CMR agreement with echo and necropsy-verified LVM.Background— Cardiac magnetic resonance (CMR) typically quantifies LV mass (LVM) by means of manual planimetry (MP), but this approach is time-consuming and does not account for partial voxel components— myocardium admixed with blood in a single voxel. Automated segmentation (AS) can account for partial voxels, but this has not been used for LVM quantification. This study used automated CMR segmentation to test the influence of partial voxels on quantification of LVM. Methods and Results— LVM was quantified by AS and MP in 126 consecutive patients and 10 laboratory animals undergoing CMR. AS yielded both partial voxel (ASPV) and full voxel (ASFV) measurements. Methods were independently compared with LVM quantified on echocardiography (echo) and an ex vivo standard of LVM at necropsy. AS quantified LVM in all patients, yielding a 12-fold decrease in processing time versus MP (0:21±0:04 versus 4:18±1:02 minutes; P<0.001). ASFV mass (136±35 g) was slightly lower than MP (139±35; &Dgr;=3±9 g, P<0.001). Both methods yielded similar proportions of patients with LV remodeling (P=0.73) and hypertrophy (P=1.00). Regarding partial voxel segmentation, ASPV yielded higher LVM (159±38 g) than MP (&Dgr;=20±10 g) and ASFV (&Dgr;=23±6 g, both P<0.001), corresponding to relative increases of 14% and 17%. In multivariable analysis, magnitude of difference between ASPV and ASFV correlated with larger voxel size (partial r=0.37, P<0.001) even after controlling for LV chamber volume (r=0.28, P=0.002) and total LVM (r=0.19, P=0.03). Among patients, ASPV yielded better agreement with echo (&Dgr;=20±25 g) than did ASFV (&Dgr;=43±24 g) or MP (&Dgr;=40±22 g, both P<0.001). Among laboratory animals, ASPV and ex vivo results were similar (&Dgr;=1±3 g, P=0.3), whereas ASFV (6±3 g, P<0.001) and MP (4±5 g, P=0.02) yielded small but significant differences with LVM at necropsy. Conclusions— Automated segmentation of myocardial partial voxels yields a 14–17% increase in LVM versus full voxel segmentation, with increased differences correlated with lower spatial resolution. Partial voxel segmentation yields improved CMR agreement with echo and necropsy-verified LVM.

Accelerated ferumoxytol-enhanced 4D multiphase, steady-state imaging with contrast enhancement (MUSIC) cardiovascular MRI: validation in pediatric congenital heart disease: Accelerated 4D MUSIC

The purpose of this work was to validate a parallel imaging (PI) and compressed sensing (CS) combined reconstruction method for a recently proposed 4D non‐breath‐held, multiphase, steady‐state imaging technique (MUSIC) cardiovascular MRI in a cohort of pediatric congenital heart disease patients. We implemented a graphics processing unit accelerated CS‐PI combined reconstruction method and applied it in 13 pediatric patients who underwent cardiovascular MRI after ferumoxytol administration. Conventional breath‐held contrast‐enhanced magnetic resonance angiography (CE‐MRA) was first performed during the first pass of ferumoxytol injection, followed by the original MUSIC and the proposed CS‐PI MUSIC during the steady‐state distribution phase of ferumoxytol. Qualities of acquired images were then evaluated using a four‐point scale. Left ventricular volumes and ejection fractions calculated from the original MUSIC and the CS‐PI MUSIC were also compared with conventional multi‐slice 2D cardiac cine MRI. The proposed CS‐PI MUSIC reduced the imaging time of the MUSIC acquisition to 4.6 ± 0.4 min from 8.9 ± 1.2 min. Computationally intensive image reconstruction was completed within 5 min without interruption of sequential clinical scans. The proposed method (mean 3.3–4.0) provided image quality comparable to that of the original MUSIC (3.2–4.0) (all P ≥ 0.42), and better than conventional breath‐held first‐pass CE‐MRA (1.1–3.3) for 13 anatomical structures (all P ≤ 0.0014) with good inter‐observer agreement (κ > 0.46). The calculated ventricular volumes and ejection fractions from both original MUSIC (r > 0.90) and CS‐PI MUSIC (r > 0.85) correlated well with 2D cine imaging. In conclusion, PI and CS were successfully incorporated into the 4D MUSIC acquisition to further reduce scan time by approximately 50% while maintaining highly comparable image quality in a clinically practical reconstruction time.

CMR tagging in the polar coordinate system

Strain of the myocardium is conventionally presented in the polar coordinate system since it adapts best to the morphology of the heart. Strain calculation would be facilitated considerably if the CMR tagging patterns were in the radial or circumferential direction. However, the CMR tagging is implemented mostly in the Cartesian coordinate system as it is prescribed by SPAMM technique in which the gradient fields create only parallel taglines. Radial tagging is not used widely due to SAR problem for tight radial pattern. Implementation of circular tagging, to the best of our knowledge, has not been reported yet. Here we introduce an approach that makes both patterns possible for tagging based on off-resonance excitation. Its theoretical basis and practical details as well as initial results in phantoms and human hearts are presented.

Geometry-Independent Inclusion of Basal Myocardium Yields Improved Cardiac Magnetic Resonance Agreement with Echocardiography and Necropsy Quantified Left Ventricular Mass

Objectives: Left-ventricular mass (LVM) is widely used to guide clinical decision-making. Cardiac magnetic resonance (CMR) quantifies LVM by planimetry of contiguous short-axis images, an approach dependent on reader-selection of images to be contoured. Established methods have applied different binary cut-offs using circumferential extent of left-ventricular myocardium to define the basal left ventricle (LV), omitting images containing lesser fractions of left-ventricular myocardium. This study tested impact of basal slice variability on LVM quantification. Methods: CMR was performed in patients and laboratory animals. LVM was quantified with full inclusion of left-ventricular myocardium, and by established methods that use different cut-offs to define the left-ventricular basal-most slice: 50% circumferential myocardium at end diastole alone (ED50), 50% circumferential myocardium throughout both end diastole and end systole (EDS50). Results: One hundred and fifty patients and 10 lab animals were studied. Among patients, fully inclusive LVM (172.6 ± 42.3 g) was higher vs. ED50 (167.2 ± 41.8 g) and EDS50 (150.6 ± 41.1 g; both P < 0.001). Methodological differences yielded discrepancies regarding proportion of patients meeting established criteria for left-ventricular hypertrophy and chamber dilation (P < 0.05). Fully inclusive LVM yielded smaller differences with echocardiography (&Dgr; = 11.0 ± 28.8 g) than did ED50 (&Dgr; = 16.4 ± 29.1 g) and EDS50 (&Dgr; = 33.2 ± 28.7 g; both P < 0.001). Among lab animals, ex-vivo left-ventricular weight (69.8 ± 13.2 g) was similar to LVM calculated using fully inclusive (70.1 ± 13.5 g, P = 0.67) and ED50 (69.4 ± 13.9 g; P = 0.70) methods, whereas EDS50 differed significantly (67.9 ± 14.9 g; P = 0.04). Conclusion: Established CMR methods that discordantly define the basal-most LV produce significant differences in calculated LVM. Fully inclusive quantification, rather than binary cut-offs that omit basal left-ventricular myocardium, yields smallest CMR discrepancy with echocardiography-measured LVM and non-significant differences with necropsy-measured left-ventricular weight.

CMR in pediatric patients with congenital heart disease: comparison at 1.5T and at 3.0T

Author(s): Nguyen, Kim-Lien; Khan, Sarah; Moriarty, John; Mohajer, Kiyarash; Renella, Pierangelo; Satou, Gary; Ayad, Ihab; Patel, Swati; Boechat, Ines; Finn, J

Improved 4D cardiac functional assessment for pediatric patients using motion-weighted image reconstruction

ObjectiveOur aim was to develop and evaluate a motion-weighted reconstruction technique for improved cardiac function assessment in 4D magnetic resonance imaging (MRI).Materials and methodsA flat-topped, two-sided Gaussian kernel was used to weigh k-space data in each target cardiac phase and adjacent two temporal phases during the proposed phase-by-phase reconstruction algorithm. The proposed method (Strategy 3) was used to reconstruct 18 cardiac phases based on data acquired using a previously proposed technique [4D multiphase steady-state imaging with contrast enhancement (MUSIC) technique and its self-gated extension using rotating Cartesian k-space (ROCK-MUSIC) from 12 pediatric patients. As a comparison, the same data set was reconstructed into nine phases using a phase-by-phase method (Strategy 1), 18 phases using view sharing (Strategy 4), and 18 phases using a temporal regularized method (Strategy 2). Regional image sharpness and left ventricle volumetric measurements were used to compare the four reconstructions quantitatively.ResultsStrategies 1 and 4 generated significantly sharper images of static structures (P ≤ 0.018) than Strategies 2 and 3 but significantly more blurry (P ≤ 0.021) images of the heart. Left ventricular volumetric measurements from the nine-phase reconstruction (Strategy 1) correlated moderately (r < 0.8) with the 2D cine, whereas the remaining three techniques had a higher correlation (r > 0.9). The computational burden of Strategy 2 was six times that of Strategy 3.ConclusionThe proposed method of motion-weighted reconstruction improves temporal resolution in 4D cardiac imaging with a clinically practical workflow.

Magnetic resonance angiography in paced complex heterotaxy syndrome with Fontan conduit obstruction and venovenous collateral decompression.

Imaging of complex congenital heart diseases (CHDs) in children is challenging. This article reviews the complementary role of high temporal and high spatial resolution magnetic resonance (MR) angiographic imaging techniques in evaluation of a patient with complex congenital cardiovascular disease and related postsurgical complications. A 4-year-old female patient with complex CHD and multiple previous palliative surgical procedures underwent MR angiography to evaluate the cause of refractory hypoxia. High-resolution MR angiography demonstrated the complex postsurgical cardiovascular anatomy and also assisted in the evaluation of cavopulmonary shunt patency and secondary venovenous shunt formation. Time-resolved MR angiography evaluated pulmonary perfusion and demonstrated a significant pulmonary arteriovenous malformation. This information guided physicians in planning further managements, which resulted in a satisfactory clinical outcome.

Detection and correction of regional shape bias arising from imaging protocol: differences between GRE and SSFP

Summary We present a methodology to detect and correct shape bias arising from imaging protocol in an atlas of the left ventricle. We show how it can be used to correct the differences between GRE and SSFP shapes and volumes. Background