Magnetic resonance tissue phase mapping: analysis of age-related and pathologically altered left ventricular radial and long-axis dyssynchrony

Purpose:

To employ magnetic resonance tissue phase mapping (TPM) for the assessment of age‐related left ventricular (LV) synchrony of radial and long‐axis motion in healthy volunteers and in hypertensive heart disease, dilated cardiomyopathy (DCM), and left bundle branch block (LBBB).

Materials and Methods:

TPM (spatial/temporal resolution = 1.3 × 2.6 mm²/13.8 msec) was employed to measure radial and long‐axis myocardial velocities in 58 healthy volunteers of three age groups and 37 patients (hypertensive, n = 18; DCM, n = 12; DCM and LBBB n = 7). Regional times‐to‐peak velocities (TTP) in systole and diastole were derived for all LV segments. Four measures of dyssynchrony were defined as the standard deviation of systolic and diastolic TTP for radial and long‐axis motion.

Results:

Systolic radial and diastolic long‐axis dyssynchrony was increased (P < 0.01) in all patient groups compared to controls. Multiple regressions revealed a significant relationship of dyssynchrony with LV ejection fraction and mass for systolic radial (P < 0.001 resp. P = 0.02), diastolic radial (P < 0.001 resp. P < 0.05), and long‐axis (P < 0.001 resp. P = 0.001) motion. Diastolic dyssynchrony correlated with the LV remodeling index (P < 0.05) and increased with age (P < 0.03). Systolic long‐axis dyssynchrony was not influenced by disease or LV function.

Conclusion:

Radial systolic and long‐axis diastolic dyssynchrony were the most sensitive markers for altered dyssynchrony in hypertensive heart disease or DCM. Future studies are needed to evaluate the diagnostic value of TPM‐derived dyssynchrony parameters. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Hypertensive heart disease: MR tissue phase mapping reveals altered left ventricular rotation and regional myocardial long-axis velocities

Objectives

The aim of this study was the evaluation of left ventricular (LV) segmental 3D velocities in patients with hypertensive heart disease using magnetic resonance (MR) tissue phase mapping (TPM).

Methods

LV radial, long-axis and rotational myocardial velocities were assessed by TPM in patients with LV hypertrophy and preserved EF (n?=?18, age = 53?±?12 years) and volunteers (n?=?20, age = 51?±?4 years). Systolic and diastolic peak and time-to-peak velocities were mapped onto a 16-segment LV model. 3D myocardial motion was displayed on an extended visualisation model. Correlation coefficients were calculated to investigate differences in regional dynamics.

Results

Patients revealed diastolic dysfunction as expressed by decreased peak long-axis velocities in all (except apical) segments (basal, P?≤?0.01; two midventricular segments, P?=?0.02, P?=?0.03). During systole, hypertrophy was associated with heterogeneous behaviour for long-axis velocities including an increase in anteroseptal apical and midventricular regions (P?=?0.001), a reduction in mid-inferior segments (P?=?0.03) and enhanced septal velocities (P?<?0.05). Segmental correlation analysis revealed altered dynamics of LV base rotation and increased dyssynchrony of lateral long-axis motion.

Conclusions

Patients with hypertensive heart disease demonstrated alterations in systolic long-axis motion, basal rotation and dyssynchrony. Longitudinal studies are needed to investigate the value of regional wall motion abnormalities regarding disease progression and outcome.

Key Points

? Magnetic resonance tissue phase mapping enables segmental evaluation of 3D myocardial velocities. ? Patients with hypertensive heart disease demonstrated new alterations in systolic long-axis motion. ? Correlation analysis revealed left ventricular long-axis dyssynchrony and an altered rotation. ? MR may provide new, sensitive diagnostic markers concerning hypertensive heart disease.     

Rapid and accurate left ventricular chamber quantification using a novel CMR segmentation algorithm: A clinical validation study

Purpose:

To evaluate the clinical performance of a novel automated left ventricle (LV) segmentation algorithm (LV‐METRIC) that involves no geometric assumptions.

Materials and Methods:

LV‐METRIC and manual tracing (MT) were used independently to quantify LV volumes and LVEF (ejection fraction) for 151 consecutive patients who underwent cine‐CMR (steady‐state free precession). Phase contrast imaging was used to independently measure stroke volume.

Results:

LV‐METRIC was successful in all cases. Mean LVEF was within 1 point of MT (Δ 0.6 ± 2.3%, P < 0.05), with smaller differences among patients with (0.5 ± 2.5%) versus those without (0.9 ± 2.3%; P = 0.01) advanced systolic dysfunction (LVEF ≤ 35% by MT). LV volumes by LV‐METRIC were slightly smaller than MT during end‐diastole (3.9 ± 6.8 mL, P < 0.001) and end‐systole (1.4 ± 5.5 mL, P < 0.01). Mean processing time was 22 ± 13 seconds for LV‐METRIC and 4:59 ± 1:56 minutes for MT (P < 0.001). Processing time correlated with LV blood volume by MT (r = 0.43) and LV‐METRIC (r = 0.55), but slope was 10‐fold steeper for MT (0.02 vs. 0.001), indicating greater proportionate time increases in relation to chamber dilation. Compared to stroke volume by phase contrast, LV‐METRIC yielded smaller differences (0.3 ± 18.3 mL) than MT (2.5 ± 17.2 mL; P < 0.001).

Conclusion:

Among a broad series of consecutive patients undergoing CMR, automated LVEF by LV‐METRIC was within 1 point of MT with processing time reduced 14‐fold. Stroke volume by LV‐METRIC yielded improved agreement with an independent standard of phase contrast imaging. J. Magn. Reson. Imaging 2010;31:845–853. ©2010 Wiley‐Liss, Inc.     

Visualization of multidirectional regional left ventricular dynamics by high‐temporal‐resolution tissue phase mapping

Purpose

To apply high‐temporal‐resolution tissue phase mapping (TPM) to derive a detailed representation of normal regional myocardial motion in a large cohort of 58 normal subjects (three age groups) and one patient with dilated cardiomyopathy.

Materials and Methods

Analysis included transformation of the acquired myocardial velocities into radial, circumferential, and long‐axis motion components representing left ventricular (LV) function with a spatiotemporal resolution of 1.3 × 2.6 × 8 mm³ and 13.8 msec, respectively. To compare multidirectional regional myocardial velocities between groups of subjects, a multisegment and multislice visualization model was employed. Regional myocardial motion was mapped onto the visualization model to display the current status of myocardial motion from base to apex as in‐plane velocity vector fields in conjunction with color‐coded long‐axis plane motion. Moreover, correlation analysis was used to investigate regional differences in myocardial dynamics.

Results

Age‐related changes in LV myocardial velocities resulted in significant differences of peak and time‐to‐peak velocities in the radial and long‐axis directions. Correlation analysis revealed clearly visible regional differences in the temporal evolution of long‐axis and circumferential velocities, particularly between the youngest and oldest age groups. Comparison of pathological LV motion with age‐matched volunteers indicated marked regional alterations in myocardial velocities and dynamics.

Conclusion

High‐temporal‐resolution TPM in combination with a schematic visualization model and correlation analysis permits the identification of local changes in myocardial velocities associated with different age groups and a common LV pathology. J. Magn. Reson. Imaging 2009;29:1043–1052. © 2009 Wiley‐Liss, Inc.     

Sites of latest mechanical activation as assessed by SPECT myocardial perfusion imaging in ischemic and dilated cardiomyopathy patients with LBBB

Objective

Sites of latest mechanical activation (SOLA) have been recognized as optimal left-ventricular (LV) lead positions for cardiac resynchronization therapy (CRT). This study was aimed to investigate SOLA in ischemic cardiomyopathy (ICM) and dilated cardiomyopathy (DCM) patients with left bundle branch block (LBBB).

Methods

Sixty-four consecutive LBBB patients (47 DCM, 17 ICM), who met the standard indications for CRT and underwent resting SPECT myocardial perfusion imaging (MPI), were selected. Phase analysis was used to assess LV dyssynchrony and SOLA. The Emory Cardiac Toolbox was used to measure perfusion defects. LV dyssynchrony and SOLA were compared between the DCM patients with wide (≥150 ms) and moderate (120-150 ms) QRS durations (QRSd). The relationship between SOLA and perfusion defects was analyzed in the ICM patients.

Results

The DCM patients with wide QRSd had significantly more LV dyssynchrony than those with moderate QRSd. Lateral SOLA were significantly more frequent in the DCM patients with wide QRSd than those with moderate QRSd (96 % vs. 62 %, p?=?0.010). In the ICM patients, SOLA were either in the scar segments (82 %) or in the segments immediately adjacent to the scar segments (18 %), regardless of QRSd.

Conclusion

Lateral SOLA were more frequent in the DCM patients with wide QRSd than those with moderate QRSd. Such relationship was not observed in the ICM patients, where SOLA were associated with scar location rather than QRSd. These findings support the use of SPECT MPI to aid the selection of potential CRT responders and guide LV lead placement.     

Ischemic extent as a biomarker for characterizing severity of coronary artery stenosis with blood oxygen-sensitive MRI

Purpose:

To investigate whether a statistical analysis of myocardial blood‐oxygen‐level‐dependent (mBOLD) signal intensities can lead to the identification and quantification of the ischemic area supplied by the culprit artery.

Materials and Methods:

Cardiac BOLD images were acquired in a canine model (n = 9) with controllable LCX stenosis at rest and during adenosine infusion on a 1.5T clinical scanner. Statistical distributions of myocardial pixel‐intensities derived from BOLD images were used to compute an area metric (ischemic extent, IE). True myocardial perfusion was estimated from microsphere analysis. IE was compared against a standard metric (segment‐intensity‐response, SIR). Additional animals (n = 3) were used to investigate the feasibility of the approach for identifying ischemic territories due to LAD stenosis from mBOLD images.

Results:

Regression analyses showed that IE and myocardial flow ratio between rest and adenosine infusion (MFR) were exponentially related (R² > 0.70, P < 0.001, for end‐systole and end‐diastole), while SIR and MFR were linearly related to end‐systole (R² = 0.51, P < 0.04) and unrelated to end‐diastole (R² ≈ 0, P = 0.91). Receiver‐operating‐characteristic analysis that IE was superior to SIR for detecting critical stenosis (MFR ≤2) in end‐systole and end‐diastole. Feasibility studies on LAD narrowing demonstrated that the proposed approach could also identify oxygenation changes in the LAD territories.

Conclusion:

The proposed evaluation of cardiac BOLD magnetic resonance imaging (MRI) offers marked improvement in sensitivity and specificity for detecting critical coronary stenosis at 1.5T compared to the mean segmental intensity approach. Patient studies are now warranted to determine its clinical utility. J. Magn. Reson. Imaging 2012;35:1338–1348. © 2012 Wiley Periodicals Inc.     

Systolic and diastolic cardiac function time intervals and exercise capacity in women

PURPOSE: To determine the relationship between exercise capacity and resting cardiac function time intervals in women. METHODS: The noninvasive method of seismocardiography was used to measure resting cardiac intervals in 12 female subjects. On the basis of maximal treadmill time (Bruce protocol), two groups were studied and categorized as long duration runners (LDR; N = 6) or short duration runners (SDR, N = 6). The following resting atrial and left ventricular (LV) cardiac function time intervals were determined: atrial systole, LV systole, LV diastole, LV isovolumetric contraction, LV isovolumetric relaxation, LV ejection, LV preejection, LV filling, LV rapid filling, and Tei index. RESULTS: Heart rate (HR) (65+/-3 vs 61+/-4 b x min(-1) for LDR and SDR, respectively; P = NS) and atrial systolic time (75+/-6 vs 81+/-5 ms for LDR and SDR, respectively; P = NS) were similar between groups. LV systole (348+/-15 vs 302+/-8 ms for LDR and SDR, respectively; P < 0.05) and LV ejection (297+/-13 vs 247+/-7 ms for LDR and SDR, respectively; P < 0.01) were longer in LDR, despite a similar LV isovolumetric contraction time. There was a general trend for a shortened LV diastole in LDR with a significantly shortened LV isovolumetric time in LDR (80+/-8 vs 107+/-8 ms for LDR and SDR, respectively; P < 0.05). LV preejection was shorter in LDR versus SDR (LDR; 114+/-6 vs SDR; 130+/-3 ms, P < 0.05), and the Tei index was less in LDR versus SDR. CONCLUSIONS: Independent of HR, increased treadmill time in young women is associated with greater resting systolic time intervals and decreased diastolic cardiac function time intervals.     

Arterial flow characteristics in the presence of vascular disease and implications for fast spin echo-based noncontrast MR angiography

Purpose:

To investigate arterial flow characteristics in the setting of vascular disease, and examine their effect on the performance of fast spin‐echo (FSE)‐based noncontrast MR angiography (NC‐MRA).

Materials and Methods:

Seventeen patients were recruited from among those scheduled for routine contrast‐enhanced MR angiography (CE‐MRA) of the lower extremities at 1.5 Tesla. The research portion of the exam was performed before the clinically‐indicated protocol and included phase‐contrast imaging at multiple levels in the legs and FSE‐based NC‐MRA in the calf and thigh, using a three‐dimensional ECG‐gated technique that exploits differences in arterial flow velocity between diastole and systole.

Results:

Vascular occlusions were associated with reduced systolic velocity, a delayed systolic peak, and, in two middle‐aged patients, an increase in diastolic velocity. Elevated systolic and diastolic velocities were observed in a subject with a nonhealing ulcer. NC‐MRA allowed visualization of arteries with systolic velocities as low as 3 cm/s, and exhibited comparable depiction to CE‐MRA for diastolic velocities as high as 6 cm/s. At the highest diastolic velocities observed (15 cm/s) arterial depiction was severely degraded.

Conclusion:

FSE‐based NC‐MRA as presently implemented performs successfully over a wide range of flow patterns, but does not accommodate extremely low systolic velocities or very high diastolic velocities. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Comparison of four-dimensional flow parameters for quantification of flow eccentricity in the ascending aorta

Purpose:

To compare quantitative parameters for assessing the degree of eccentric systolic blood flow in the ascending thoracic aorta (AsAo).

Materials and Methods:

Forty‐one patients were studied with three‐dimensional (3D), cine phase‐contract MRI (4D Flow). Analysis was performed at peak systole for a cross‐sectional plane in the AsAo just distal to the sinotubular junction. AsAo flow was graded as normal, mildly, or markedly eccentric based on qualitative visual assessment. For quantitative analysis, flow jet angle and normalized flow displacement from the vessel center were calculated.

Results:

Patients with normal AsAo systolic flow (n = 25) had an average flow jet angle of 13.7 degrees and flow displacement 0.04. These parameters were significantly elevated for patients with mild eccentric systolic flow (n = 6): 24.6 degrees (P = 0.012) and 0.12 (P = 0.001), respectively. However, for patients with marked eccentric flow (n = 10), only flow displacement was significantly elevated compared with the mild eccentric group (0.18; P = 0.04); flow angle was 25.7 degrees.

Conclusion:

Flow displacement is a more reliable quantitative parameter for measuring eccentric AsAo systolic flow than flow jet angle, and should be evaluated in studies investigating the role of eccentric flow in the promotion of aortic pathology. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Quantitative assessment of systolic and diastolic left ventricular twist using Fourier Analysis of Stimulated echoes (FAST) and CSPAMM

Purpose:

To evaluate Fourier Analysis of Stimulated echoes (FAST) and CSPAMM for the quantification of left ventricular (LV) systolic and diastolic function and compare it with the previously validated FAST+SPAMM technique.

Materials and Methods:

LV short‐axis tagged images were acquired with CSPAMM and SPAMM in healthy volunteers (n = 13). The FAST method was used to automatically estimate LV systolic and diastolic twist parameters from rotation of the stimulated echo and stimulated anti‐echo about the middle of k‐space subsequent to ～3 min of user interaction.

Results:

There was no significant difference between measures obtained for FAST+CSPAMM and FAST+SPAMM for mean peak twist (13.5 ± 2.7° versus 11.9 ± 4.0°), torsion (3.4 ± 0.8°/cm versus 2.9 ± 1.0°/cm), twisting rate (76.8 ± 22.2°/s versus 68.2 ± 23.4°/s), untwisting rate (?102.7 ± 24.6°/s versus ?106.6 ± 32.4°/s), normalized untwisting rate (?7.9 ± 2.2/s versus ?9.9 ± 4.4/s), and time of peak twist (279 ± 23 ms versus 293 ± 25 ms) (all P > 0.01). FAST+CSPAMM also provided measures of duration of untwisting (148 ± 21 ms) and the ratio of rapid untwist to peak twist (0.8 ± 0.3). Bland‐Altman analysis of FAST+CSPAMM and FAST+SPAMM twist data demonstrates excellent agreement with a bias of 1.1° and 95% confidence intervals of [?3.3°, 5.2°].

Conclusion:

FAST+CSPAMM is a semi‐automated method that provides a quick and quantitative assessment of LV systolic and diastolic twist and torsion. J. Magn. Reson. Imaging 2013;37:678–683. © 2013 Wiley Periodicals, Inc.

     

Quantification of left ventricular indices from SSFP cine imaging: Impact of real‐world variability in analysis methodology and utility of geometric modeling

Purpose:

To assess the impact of “real‐world” practice variation in the process of quantifying left ventricular (LV) mass, volume indices, and ejection fraction (EF) from steady‐state free precession cardiovascular magnetic resonance (CMR) images. The utility of LV geometric modeling techniques was also assessed.

Materials and Methods:

The effect of short‐axis‐ versus long‐axis‐derived LV base identification, simplified versus detailed endocardial contouring, and visual versus automated identification of end‐systole were evaluated using CMR images from 50 consecutive, prospectively recruited patients. Additionally, the performance of six geometric models was assessed. Repeated measurements were performed on 25 scans (50%) in order to assess observer variability.

Results:

Simplified endocardial contouring significantly overestimated volumes and underestimated EF (–6 ± 4%, P < 0.0005) compared to detailed contouring. A mean difference of –34g (P < 0.0005) was observed between mass measurements made using short‐axis‐ versus long‐axis‐derived LV base positioning. A technique involving long‐axis LV base identification, signal threshold‐based detailed endocardial contouring, and automated identification of end‐systole had significantly higher observer agreement. Geometric models showed poor agreement with conventional analysis and high variability.

Conclusion:

Real‐world variability in CMR image analysis leads to significant differences in LV mass, volume and EF measurements, and observer variability. Appropriate reference ranges should be applied. Use of geometric models should be discouraged. J. Magn. Reson. Imaging 2013;37:1213–1222. © 2012 Wiley Periodicals, Inc.     

Cyclic CINE-balanced steady-state free precession image intensity variations: implications for the detection of myocardial edema

Purpose

To evaluate the dependence of CINE‐balanced steady‐state free precession (bSSFP) image intensities on spatial location, cardiac phase, and disease state.

Materials and Methods

Eight subjects with recent myocardial infarctions and eight age‐ and sex‐matched normal volunteers were studied using CINE‐bSSFP imaging to describe cyclic image intensity variations as a function of the cardiac cycle and to optimize and assess the ability of CINE‐bSSFP imaging to depict myocardial edema. Signal intensities of the left ventricular (LV) bloodpool and myocardium were measured using region‐of‐interest analysis across the cardiac cycle. The magnitude and time course of the cyclic variations were evaluated. Mixed‐model analysis of variance was used to examine the influence of physical location, cardiac phase, and presence of myocardial infarction.

Results

The LV bloodpool and myocardial CINE‐bSSFP signal intensities varied significantly with spatial location, cardiac phase, and disease (P < 0.001). Cardiac phase had a significant effect on the signal intensities after adjustments for spatial location. The LV bloodpool signal decreased slowly during systole and rose sharply during LV filling. There were two distinct myocardial intensity peaks, one occurring at peak systole and the other at the end of the LV rapid inflow phase. Myocardial edema was seen as a hyperintense region. Image contrast with adjacent myocardium was the greatest at the end of systole.

Conclusion

Detection of myocardial edema using the conventional CINE‐bSSFP technique is feasible, but is complicated by normal cyclic changes in myocardial image intensities during the cardiac cycle. J. Magn. Reson. Imaging 2011;33:573–581. © 2011 Wiley‐Liss, Inc.     

Flow‐sensitive 4D MRI of the thoracic aorta: Comparison of image quality,quantitative flow,and wall parameters at 1.5 T and 3 T

Purpose:

To evaluate the effect of field strength on flow‐sensitive 4D magnetic resonance imaging (MRI) of the thoracic aorta. A volunteer study at 1.5 T and 3 T was conducted to compare phase‐contrast MR angiography (MRA) and 3D flow visualization quality as well as quantification of aortic hemodynamics.

Materials and Methods:

Ten healthy volunteers were examined by flow‐sensitive 4D MRI at both 1.5 T and 3 T MRI with identical imaging parameters (TE/TR = 6/5.1 msec, spatial/temporal resolution ≈2 mm/40.8 msec). Analysis included assessment of image quality of derived aortic 3D phase contrast (PC) angiography and 3D flow visualization (semiquantitative grading on a 0–2 scale, two blinded observers) and quantification of blood flow velocities, net flow per cardiac cycle, wall shear stress (WSS), and velocity noise.

Results:

Quality of 3D blood flow visualization (average grading = 1.8 ± 0.4 at 3 T vs. 1.1 ± 0.7 at 1.5 T) and the depiction of aortic lumen geometry by 3D PC‐MRA (1.7 ± 0.5 vs. 1.2 ± 0.6) were significantly (P < 0.01) improved at 3 T while velocity noise was significantly higher (P < 0.01) at 1.5 T. Velocity quantification resulted in minimally altered (0.05 m/s, 3 mL/cycle and 0.01 N/m²) but not statistically different (P = 0.40, P = 0.39, and P = 0.82) systolic peak velocities, net flow, and WSS for 1.5 T compared to 3 T.

Conclusion:

Flow‐sensitive 4D MRI at 3 T provided improved image quality without additional artifacts related to higher fields. Imaging at 1.5 T MRI, which is more widely available, was also feasible and provided information on aortic 3D hemodynamics of moderate quality with identical performance regarding quantitative analysis. J. Magn. Reson. Imaging 2012;36:1097–1103. © 2012 Wiley Periodicals, Inc.     

Time‐resolved analysis of coronary vein motion and cross‐sectional area

Purpose:

To quantify periods of low motion and cross‐sectional area changes of the coronary veins during the cardiac cycle for planning magnetic resonance coronary venograms (MRCV).

Materials and Methods:

Images were acquired from 19 patients with coronary artery disease (CAD) and 13 patients scheduled for cardiac resynchronization therapy (CRT). The displacement and cross‐sectional area of the coronary sinus was tracked, and periods of low motion were defined as consecutive time points during which the position of the coronary sinus remained within a 0.67‐mm diameter region. Patients were classified as systolic dominant or diastolic dominant based on the relative duration of their low motion periods.

Results:

All CRT patients were classified as systolic dominant, and 32% of these had no separate diastolic rest period. All CAD patients with ejection fraction < 35% were classified as systolic dominant, while all CAD patients with ejection fraction > 35%were diastolic dominant. In 77% of all subjects, the cross‐sectional area of the coronary sinus was larger in systole than in diastole.

Conclusion:

The movement of the coronary sinus can be used to classify patients as either having a longer systolic or diastolic rest period. The classification of the CRT patients as systolic dominant suggests that MRCVs be acquired in systole for CRT planning; however, each patient's low motion periods should be categorized to ensure the correct period is being used to minimize motion artifacts. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Systolic 3D first‐pass myocardial perfusion MRI: Comparison with diastolic imaging in healthy subjects

Three‐dimensional (3D) first‐pass myocardial perfusion imaging (MPI) is a promising alternative to conventional two‐dimensional multislice MPI due to its contiguous spatial coverage that is beneficial for estimating the size of perfusion defects. Data acquisition at mid‐diastole is a typical choice for 3D MPI yet is sensitive to arrhythmia and variations in R‐R interval that are common in cardiac patients. End systole is the second longest quiescent cardiac phase and is known to be less sensitive to the R‐R variability. Therefore, 3D MPI with systolic acquisition may be advantageous in patients with severe arrhythmia once it is proven to be comparable to diastolic MPI in subjects with negligible R‐R variation. In this work, we demonstrate the feasibility of 3D MPI with systolic data acquisition in five healthy subjects. We performed 3D MPI experiments in which 3D perfusion data were acquired at both end‐systole and mid‐diastole of every R‐R interval and analyzed the similarity between resulting time intensity curves (TIC) from the two data sets. The correlation between systolic and diastolic TICs was extremely high (mean = 0.9841; standard deviation = 0.0166), and there was a significant linear correlation between the two time intensity curve upslopes and peak enhancements (P < 0.001). Magn Reson Med 63:858–864, 2010. © 2010 Wiley‐Liss, Inc.     

Shorter difference between myocardium and blood optimal inversion time suggests diffuse fibrosis in dilated cardiomyopathy

Purpose:

To find evidence of diffuse fibrosis in dilated cardiomyopathy (DCM) patients by comparing measurements on clinical late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) studies between DCM and healthy subjects.

Materials and Methods:

LGE‐CMR and the Look–Locker images from 20 DCM patients and 17 healthy controls were analyzed. Blood signal‐to‐noise ratio (SNR), myocardium SNR, and blood‐to‐myocardium contrast‐to‐noise ratio (CNR) were measured on the LGE‐CMR images. The optimal inversion time (TI) to null blood and myocardium was determined on the Look–Locker images. The postcontrast T₁ was estimated using a phantom study that correlated optimal TI and heart rate to T₁.

Results:

The blood SNR was lower, myocardium SNR was higher, and the blood‐to‐myocardium CNR was lower (6.6 ± 0.7 vs. 10.3 ± 0.9, P = 0.004) on DCM LGE‐CMR images as compared to controls. The blood‐myocardium optimal TI difference (ΔTI) was lower (38 ± 2 msec vs. 55 ± 3 msec, P < 0.001) in DCM, and the estimated blood‐myocardium T₁ difference (ΔT₁) (116 ± 6 msec vs. 152 ± 8 msec, P = 0.001) was also lower.

Conclusion:

DCM patients have reduced blood‐myocardium ΔTI and ΔT₁, and lower CNR as compared to controls, suggesting the presence of diffuse fibrosis. This may impact the interpretation of LGE data. J. Magn. Reson. Imaging 2009;30:967–972. © 2009 Wiley‐Liss, Inc.     

Does the amplatzer septal occluder device alter ventricular contraction pattern? A ventricular motion analysis by MR tagging

Purpose:

To assess by cardiovascular magnetic resonance (CMR) and CMR tagging if the Amplatzer Septal Occluder affects right ventricular (RV) and left ventricular (LV) motion pattern.

Materials and Methods:

Sixteen consecutive patients with significant atrial septal defect (ASD) and nine consecutive patients with persistent foramen ovale (PFO) as controls were studied before and a median of 14 days after defect closure by an Amplatzer occluder. By CMR end‐diastolic (EDV) and end‐systolic (ESV) RV and LV volumes were determined. Aortic and pulmonary artery flow was measured for assessment of left‐to‐right shunt (Qp/Qs). By CMR tagging circumferential strain and radial shortening, maximal rotation and torsion were measured,

Results:

In ASD patients RV‐EDV and RV‐ESV decreased (P < 0.05). LV‐EDV and LV‐ESV increased after ASD closure (P < 0.005). Qp/Qs dropped from 1.8 to 1.0 (P < 0.001). PFO patients showed no ventricular volume change after PFO closure. In ASD patients circumferential strain and radial shortening and maximal rotation of the RV decreased by ASD closure (P < 0.01). In LV only maximal rotation at the base and apex decreased significantly (P < 0.05). Torsion remained constant. In PFO patients no tagging parameter changed after defect closure.

Conclusion:

The Amplatzer occluder itself does not change the ventricular contraction pattern. All volume and myocardial deformation changes were caused by ventricular loading shifts. J. Magn. Reson. Imaging 2012;35:949–956. © 2012 Wiley Periodicals, Inc.     

Optimization of single injection liver arterial phase gadolinium enhanced MRI using bolus track real-time imaging

Purpose:

To measure contrast agent enhancement kinetics in the liver and to further evaluate and develop an optimized gadolinium enhanced MRI using a single injection real‐time bolus‐tracking method for reproducible imaging of the transient arterial‐phase.

Materials and Methods:

A total of 18 subjects with hypervascular liver lesions were imaged with four dimensional (4D) perfusion scans to measure time‐to‐peak (TTP) delays of arterial (aorta‐celiac axis), liver parenchyma, liver lesion, portal, and hepatic veins. Time delays were calculated from the TTP‐aorta signal, and then related to the gradient echo (GRE) k‐space acquisition design, to determine optimized timing for real‐time bolus‐track triggering methodology. As another measure of significance, 200 clinical patients were imaged with 3D‐GRE using either a fixed time‐interval or by individualized arterial bolus real‐time triggering. Bolus TTP‐aorta was calculated and arterial‐phase acquisitions were compared for accuracy and reproducibility using specific vascular enhancement indicators.

Results:

The mean bolus transit‐time to peak‐lesion contrast was 8.1 ± 2.7 seconds following arterial detection, compared to 32.1 ± 5.4 seconds from contrast injection, representing a 62.1% reduction in the time‐variability among subjects (N = 18). The real‐time bolus‐triggered technique more consistently captured the targeted arterial phase (94%), compared to the fixed timing technique (73%), representing an expected improvement of timing accuracy in 28% of patients (P = 0.0001389).

Conclusion:

Our results show detailed timing window analysis required for optimized arterial real‐time bolus‐triggering acquisition of transient arterial phase features of liver lesions, with optimized arterial triggering expected to improve reproducibility in a significant number of patients. J. Magn. Reson. Imaging 2011;33:110–118. © 2010 Wiley‐Liss, Inc.     

3D left ventricular strain from unwrapped harmonic phase measurements

Purpose:

To validate a method for measuring 3D left ventricular (LV) strain from phase‐unwrapped harmonic phase (HARP) images derived from tagged cardiac magnetic resonance imaging (MRI).

Materials and Methods:

A set of 40 human subjects were imaged with tagged MRI. In each study the HARP phase was computed and unwrapped in each short‐axis and long‐axis image. Inconsistencies in unwrapped phase were resolved using branch cuts manually placed with a graphical user interface. 3D strain maps were computed for all imaged timeframes in each study. The strain from unwrapped phase (SUP) and displacements were compared to those estimated by a feature‐based (FB) technique and a HARP technique.

Results:

3D strain was computed in each timeframe through systole and mid‐diastole in ≈30 minutes per study. The standard deviation of the difference between strains measured by the FB and the SUP methods was less than 5% of the average of the strains from the two methods. The correlation between peak circumferential strain measured using the SUP and HARP techniques was over 83%.

Conclusion:

The SUP technique can reconstruct full 3D strain maps from tagged MR images through the cardiac cycle in a reasonable amount of time and user interaction compared to other 3D analysis methods. J. Magn. Reson. Imaging 2010;31:854–862. ©2010 Wiley‐Liss, Inc.     

Transthoracic Doppler echocardiography to predict optimal tube pulsing window for coronary artery CT angiography

Rationale and objective

To evaluate the feasibility of transthoracic Doppler echocardiography to determine the optimal pulsing windows for CT coronary angiography to narrow the pulsing windows further, especially in higher heart rate.

Materials and methods

Doppler was performed on 135 patients before CT scanning. For Doppler, the intervals with minimal motion were evaluated during both systole and diastole integrating electrocardiogram (ECG) intervals. For CT scanning, the retrospective ECG-gating was applied and the optimal reconstruction intervals were determined. The accuracy of Doppler analysis to predict the optimal reconstruction intervals was tested. The predicted length of pulsing windows was compared between Doppler analysis and traditional prospective ECG-gating protocol (heart rate ≦ 65 bpm, 60–76%; 66–79 bpm, 30–77%; ≧80 bpm, 31–47%).

Results

According to Doppler analysis, the mean length of intervals with minimal motion in systole was 106.4 ± 39.2 ms and 125.2 ± 92.0 ms in diastole. When the intervals with minimal motion during diastole > 90 ms, the optimal reconstruction intervals were located at diastole; otherwise, at systole (P < 0.001). The optimal reconstruction intervals in 93.8% (132/135) patients could be predicted accurately by Doppler analysis. If the optimal reconstruction intervals predicted by Doppler were applied as the exposure windows, the mean length of pulsing windows should has been 105.2 ± 69.4 ms (range: 26.9–510.3 ms), which was significantly shorter than that of traditional prospective ECG-gating protocol (232.0 ± 120.2 ms, range: 93.2–427.3 ms, P < 0.001).

Conclusion

Doppler can help detecting the optimal pulsing windows accurately. Prospective ECG-gating incorporating Doppler analysis may narrow pulsing windows significantly while maintaining image quality.