Quantitative Assessment of Regional Pulmonary Transit Times in Pulmonary Hypertension.

BACKGROUND: Pulmonary hypertension (PH) contributes to restricted flow through the pulmonary circulation characterized by elevated mean pulmonary artery pressure acquired from invasive right heart catheterization (RHC). MRI may provide a noninvasive alternative for diagnosis and characterization of PH. PURPOSE: To characterize PH via quantification of regional pulmonary transit times (rPTT). STUDY TYPE: Retrospective. POPULATION: A total of 43 patients (58% female); 24 controls (33% female). RHC-confirmed patients classified as World Health Organization (WHO) subgroups 1-4. FIELD STRENGTH/SEQUENCE: A 1.5 T/time-resolved contrast-enhanced MR Angiography (CE-MRA). ASSESSMENT: CE-MRA data volumes were combined into a 4D matrix (3D resolution + time). Contrast agent arrival time was defined as the peak in the signal-intensity curve generated for each voxel. Average arrival times within a vessel region of interest (ROI) were normalized to the main pulmonary artery ROI (t0 ) for eight regions to define rPTT for all subjects. Subgroup analysis included grouping the four arterial and four venous regions. Intraclass correlation analysis completed for reproducibility. STATISTICAL TESTS: Analysis of covariance with age as covariate. A priori Student's t-tests or Wilcoxon rank-sum test; α = 0.05. Results compared to controls unless noted. Significant without listing P value. ICC ran as two-way absolute agreement model with two observers. RESULTS: PH patients demonstrated elevated rPTT in all vascular regions; average rPTT increase in arterial and venous branches was 0.85 ± 0.15 seconds (47.7%) and 1.0 ± 0.18 seconds (16.9%), respectively. Arterial rPTT was increased for all WHO subgroups; venous regions were elevated for subgroups 2 and 4 (group 1, P = 0.86; group 3, P = 0.32). No significant rPTT differences were found between subgroups (P = 0.094-0.94). Individual vessel ICC values ranged from 0.58 to 0.97. DATA CONCLUSION: Noninvasive assessment of PH using standard-of-care time-resolved CE-MRA can detect increased rPTT in PH patients of varying phenotypes compared to controls. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 3.

Pilot Tone-Triggered MRI for Quantitative Assessment of Cardiac Function, Motion, and Structure.

OBJECTIVE: The aim of this study was to test the hypothesis that there are good agreements between cardiac functional and structural indices derived from magnetic resonance imaging (MRI) sequences triggered with pilot tone (PT) and electrocardiogram (ECG). MATERIALS AND METHODS: Sixteen healthy volunteers (11 male, age 21-76 years) underwent a cardiac MRI scan. Cine MRI, T1, and T2 mapping were acquired by using PT and ECG triggering. Quantitative measurements, including left and right ventricular end-diastolic volume, end-systolic volume, stroke volume, ejection fraction, longitudinal strain, left ventricular T1 and T2 values, left and right atrial longitudinal strain, and maximal/minimal volumes, were measured. The interclass correlation coefficient, coefficient of variation, and Bland-Altman plots were used to evaluate the agreements between measurements derived by MRI sequences triggered with 2 methods. RESULTS: There were no significant differences among end-diastolic volume, end-systolic volume, stroke volume, ejection fraction, left ventricle mass, T1 and T2 values, or longitudinal strains acquired using PT and ECG. There were good agreements and low variations between the levels of these indices acquired with PT and ECG. Interclass correlation coefficients mainly ranged from 0.73 to 0.98. The coefficients of variation ranged from 1.4% to 22.6%. CONCLUSIONS: Pilot tone-triggered MRI provides comparable measurements of cardiac function, motion, and structure as ECG-triggered MRI. Pilot tone has the potential to become a backup of ECG gating in cardiovascular imaging.

Left Ventricular Fibrosis Assessment by Native T1, ECV, and LGE in Pulmonary Hypertension Patients.

Cardiac magnetic resonance imaging (MRI) is emerging as an alternative to right heart catheterization for the evaluation of pulmonary hypertension (PH) patients. The aim of this study was to compare cardiac MRI-derived left ventricle fibrosis indices between pre-capillary PH (PrePH) and isolated post-capillary PH (IpcPH) patients and assess their associations with measures of ventricle function. Global and segmental late gadolinium enhancement (LGE), longitudinal relaxation time (native T1) maps, and extracellular volume fraction (ECV) were compared among healthy controls (N = 25; 37% female; 52 ± 13 years), PH patients (N = 48; 60% female; 60 ± 14 years), and PH subgroups (PrePH: N = 29; 65% female; 55 ± 12 years, IpcPH: N = 19; 53% female; 66 ± 13 years). Cardiac cine measured ejection fraction, end diastolic, and end systolic volumes and were assessed for correlations with fibrosis. LGE mural location was qualitatively assessed on a segmental basis for all subjects. PrePH patients had elevated (apical-, mid-antero-, and mid-infero) septal left ventricle native T1 values (1080 ± 74 ms, 1077 ± 39 ms, and 1082 ± 47 ms) compared to IpcPH patients (1028 ± 53 ms, 1046 ± 36 ms, 1051 ± 44 ms) (p < 0.05). PrePH had a higher amount of insertional point LGE (69%) and LGE patterns characteristic of non-vascular fibrosis (77%) compared to IpcPH (37% and 46%, respectively) (p < 0.05; p < 0.05). Assessment of global LGE, native T1, and ECV burdens did not show a statistically significant difference between PrePH (1.9 ± 2.7%, 1056.2 ± 36.3 ms, 31.2 ± 3.7%) and IpcPH (2.7 ± 2.7%, 1042.4 ± 28.1 ms, 30.7 ± 4.7%) (p = 0.102; p = 0.229 p = 0.756). Global native T1 and ECV were higher in patients (1050.9 ± 33.8 and 31.0 ± 4.1%) than controls (28.2 ± 3.7% and 1012.9 ± 29.4 ms) (p < 0.05). Cardiac MRI-based tissue characterization may augment understanding of cardiac involvement and become a tool to facilitate PH patient classification.

Doppler assessment of the ratio of the systolic to diastolic duration in normal children: relation to heart rate, age and body surface area.

BACKGROUND: It has been shown that the ratio of systolic duration to diastolic duration (S/D) is a valuable global index of ventricular dysfunction in pediatric dilated and restrictive cardiomyopathy and is also a valuable index of the ventricular function of single systemic right ventricles in children who have undergone palliation of hypoplastic left-heart syndrome. The purposes of this study were to establish normal values for the S/D ratio in children without heart disease and to investigate its variation with heart rate (HR), age, and body surface area. METHODS: Of 752 children found to have functional murmurs by clinical means, 179 (24% of the total database) had trace holosystolic tricuspid regurgitation. These patients ranged in age from 0.02 months to 19 years. For this study, the diastolic interval was defined as the period of right ventricular filling (ie, the period between 2 tricuspid regurgitant jets) and the systolic interval as the remainder of the cardiac cycle corresponding to the duration of holosystolic tricuspid regurgitation, including the periods of isovolumic contraction and relaxation. The relations between the systolic and diastolic periods and their ratio (S/D ratio) and HR, age, and body surface area were evaluated using univariate and multivariate linear regression analysis. RESULTS: Patient's age ranged from 0.02 months to 19 years (mean, 70.18+/-65.12 months), body surface area from 0.11 to 2.51 m2 (mean, 0.85+/-0.55 m2), and HR from 50 to 156 beats/min (mean, 96.72+/-23.19 beats/min). The systolic period ranged from 208.5 to 467 ms (mean, 314.08+/-52.57 ms) and the diastolic period from 166.5 to 809 ms (mean, 341.34+/-129.61 ms), yielding a S/D ratio ranging from 0.397 to 1.62 (mean, 0.995+/-0.23). Systolic period duration showed a linear negative decrease with increasing HR (y=1.9228x+500.05, r=-0.85). Diastolic duration decreased in an exponential fashion as HR increased (y=130,679x(-1.3232), r=-0.88). The S/D ratio correlated positively with HR (y=-1.656+0.0265 HR-0.000954 HR2, r=76). On multivariate analysis, no significant correlations of S/D ratio with age or body surface area were found. CONCLUSIONS: The results of this study provide useful reference values for the S/D ratio across a wide range of HRs in children, adolescents, and young adults.