CT-determined pulmonary artery diameters in predicting pulmonary hypertension

This study was to determine if the diameters of pulmonary arteries measured from computed tomographic (CT) scans could be used 1) as indicators of pulmonary artery hypertension and 2) as a reliable base for calculating mean pulmonary artery pressure. The diameters of the main, left, proximal right, distal right, interlobar, and left descending pulmonary arteries were measured from CT scans in 32 patients with cardiopulmonary disease and in 26 age- and sex-matched control subjects. Diameters were measured using a special computer program that could display a CT density profile of the artery and its adjacent tissues. The upper limit of normal diameter for the main pulmonary artery was found to be 28.6 mm (mean + 2 SD). In the patient group, the diameters were correlated with data from cardiac catheterization. In these patients, a diameter of the main pulmonary artery above 28.6 mm readily predicted the presence of pulmonary hypertension. The calculated cross-sectional areas of the main and interlobar pulmonary arteries (normalized for body surface area [BAS]) were found to give the best estimates of mean pulmonary artery pressure (r = 0.89, P less than 0.001 and r = 0.66, P less than 0.001). Multiple regression analysis gave the useful equation: mean pulmonary artery pressure = -10.92 + 0.07646 X area of main pulmonary artery/BSA + 0.08084 X area of the right interlobar pulmonary artery/BSA (r = 0.93, P less than 0.0001). Because CT allows precise, noninvasive measurement of the diameter of pulmonary arteries, it can be of value in detecting pulmonary hypertension and estimating mean pulmonary artery pressure.     

Early onset of retrograde flow in the main pulmonary artery is a characteristic of pulmonary arterial hypertension

Purpose:

To evaluate if early onset of retrograde flow in the main pulmonary artery is a characteristic of pulmonary arterial hypertension (PAH).

Materials and Methods:

Fifty‐five patients with suspected pulmonary hypertension (PH) underwent right‐sided heart catheterization and retrospectively ECG‐gated MR phase‐contrast velocity quantification in the main pulmonary artery. Pulmonary hypertension was defined by a mean pulmonary artery pressure being larger than 25 mmHg. The onset time of the retrograde flow relative to the cardiac cycle duration (Relative Onset Time = ROT) was compared with mean pulmonary artery pressure.

Results:

By the catheterization, 38 patients were identified as having PAH. The ROT for these PAH patients was significantly different from those found in the 17 non‐PH subjects (0.14 ± 0.06 versus 0.37 ± 0.06, P < 0.001). The mean pulmonary artery pressure was related to the ROT (r² = 0.62, P < 0.001) and could be estimated from the ROT with a standard deviation of 11.7 mmHg. With a cutoff value of 0.25, the ROT distinguished PAH patients from non‐PH subjects.

Conclusion:

Early onset of retrograde flow in the main pulmonary artery is a characteristic of pulmonary arterial hypertension and is visible by standard MR phase‐contrast velocity quantification. J. Magn. Reson. Imaging 2011;33:1362–1368. © 2011 Wiley‐Liss, Inc.     

Evaluation of a resistance-based model for the quantification of pulmonary arterial hypertension using MR flow measurements

PURPOSE: To establish an estimate for the mean pulmonary arterial pressure (mPAP) derived from noninvasive data acquired with magnetic resonance (MR) velocity-encoded sequences. MATERIALS AND METHODS: In seven sedated pigs synchronous catheter-based invasive pressure measurements (IPM) and noninvasive MR were acquired in the main pulmonary artery (MPA) at different severities of pulmonary arterial hypertension (PAH) that were caused by infusion of thromboxane A2 (TxA2). The invasively measured mPAP was correlated with the noninvasive MR velocity data and linear combination equations (LCE) were computed. RESULTS: Intravenously applied TxA2 induced a dose dependent level of severity of PAH with an mPAP of up to 54 mmHg without systemic effects. The acceleration time (AT) measured with MR demonstrated the best correlation with the mPAP (r(2) = 0.75). The LCE with the highest correlation (R = 0.945, alpha < 0.01) between IPM and MR revealed a mean difference of 0, a SD of s = 4.66 and a maximal difference of 12.2 mmHg using the Bland-Altman analysis. CONCLUSION: Applying the identified LCE allowed the estimation of the mPAP in an acute and resistance-based model of PAH with high accuracy using noninvasive MR velocity-encoded sequences.     

Pulmonary artery and right ventricle assessment in pulmonary hypertension: correlation between functional parameters of ECG-gated CT and right-side heart catheterization

Background Right ventricular function predicts outcome in patients with pulmonary hypertension (PH). Therefore accurate assessment of right ventricular function is essential to graduate severity, assess follow-up, and response to therapy. Purpose To evaluate whether PH severity could be assessed using electrocardiography-gated CT (ECG-gated CT) functional parameters. A further objective was to evaluate cardiac output (CO) using two ECG-gated CT methods: the reference Simpson technique and the fully automatic technique generated by commercially available cardiac software. Material and Methods Our institutional review board approved this study; patient consent was not required. Twenty-seven patients who had undergone ECG-gated CT and right heart catheterization (RHC) were included. Two independent observers measured pulmonary artery (PA) diameter, PA distensibility, aorta diameter, right ventricular cardiac output (CT-RVCO) and right ventricular ejection fraction (CT-RVEF) with automatic and Simpson techniques on ECG-gated CT. RHC-CO and mean pulmonary arterial pressure (mPAP) were measured on RHC. Relationship between ECG-gated CT and RHC measurements was tested with linear regression analysis. Results Inter-observer agreement was good for all measurements (r > 0.7) except for CT-RVCO calculated with Simpson's technique (r = 0.63). Pulmonary artery (PA) distensibility was significantly correlated to mPAP (r = -0.426, P = 0.027). CT-RVEF was correlated with mPAP only when issued from Simpson technique (r = -0.417, P = 0.034). CT-RVEF was not significantly correlated to RHC-CO (P > 0.2). CT-RVCO measured with Simpson technique (r = 0.487, P = 0.010) and automatic segmentation (r = 0.549, P = 0.005) correlated equally with RHC-CO. Conclusion CT-RVEF and CT-RVCO measured on ECG-gated CT are significantly correlated, respectively, to mPAP and RHC-CO in this population with severe reduction of the right ventricular ejection fraction and could be useful for evaluating and following patients with PH.     

Pulmonary arterial hypertension: noninvasive detection with phase-contrast MR imaging

PURPOSE: To retrospectively identify pulmonary arterial (PA) flow parameters measured with phase-contrast magnetic resonance (MR) imaging that allow noninvasive diagnosis of chronic PA hypertension (PAH). MATERIALS AND METHODS: The study was HIPAA compliant and was approved by the institutional review board; a waiver of informed consent was obtained. Fifty-nine patients (49 female patients; mean age, 46 years; range, 16-85 years) known to have or suspected of having PAH underwent breath-hold phase-contrast MR imaging and right-sided heart catheterization (RHC). The presence of PAH (mean pulmonary artery pressure [mPAP], >25 mm Hg) was confirmed in 42 patients. Parameters, including PA areas, PA strain, average velocity, peak velocity, acceleration time, and ejection time, were measured in each patient by investigators blinded to RHC results. These measurements were correlated with mPAP, systolic pulmonary artery pressure (sPAP), and pulmonary vascular resistance index (PVRI). The diagnostic ability of phase-contrast MR imaging to depict PAH was quantified. Statistical tests included Spearman rho coefficients, receiver operating characteristic curve analysis, and Bland-Altman plots. RESULTS: Results showed average velocity to have the best correlation with mPAP, sPAP, and PVRI (r = -0.73, -0.76, and -0.86, respectively; P < .001). Average velocity (cutoff value = 11.7 cm/sec) revealed PAH with a sensitivity of 92.9% (39 of 42) and a specificity of 82.4% (14 of 17). Sensitivity and specificity for the minimum PA area (cutoff value = 6.6 cm(2)) were 92.9% (39 of 42) and 88.2% (15 of 17), respectively. CONCLUSION: The average blood velocity throughout the cardiac cycle is strongly correlated with pulmonary pressures and resistance.     

Flow characteristics of the proximal pulmonary arteries and vena cava in patients with chronic thromboembolic pulmonary hypertension: correlation between 3.0 T phase-contrast MRI and right heart catheterization

PURPOSE

We aimed to determine the correlation between flow characteristics of the proximal pulmonary arteries and vena cava obtained by 3.0 T phase-contrast magnetic resonance imaging (MRI) and hemodynamic characteristics by right heart catheterization in patients with chronic thromboembolic pulmonary hypertension.

MATERIALS AND METHODS

Twenty consecutive patients with chronic thromboembolic pulmonary hypertension and 20 sex- and age-matched healthy volunteers were included prospectively. All patients and controls underwent phase-contrast MRI to determine the flow characteristics including peak velocity, mean velocity, and mean blood flow of the proximal pulmonary artery and vena cava. All patients underwent right heart catheterization to determine the hemodynamics.

RESULTS

Peak velocity and mean velocity of the proximal pulmonary artery were significantly lower in the patient group. In patients, both peak velocity and mean blood flow were sequentially decreased in the main pulmonary artery, left and right pulmonary arteries, and left and right interlobar pulmonary arteries. Inferior vena cava had higher peak velocity, mean velocity, and mean blood flow than superior vena cava. Peak velocity of the main pulmonary artery correlated with mean and diastolic pulmonary artery pressure. Peak velocity of both inferior and superior vena cava strongly correlated with the pulmonary vascular resistance index (PVRI) (r=−0.68, P < 0.001 and r=−0.74, P < 0.001, respectively). Mean velocity of the main pulmonary artery and right pulmonary artery strongly correlated with PVRI and mean pulmonary artery pressure. Mean velocity of the superior vena cava and mean blood flow of the main pulmonary artery strongly correlated with PVRI and right cardiac work index.

CONCLUSION

Blood flow in the proximal pulmonary artery and vena cava evaluated by phase-contrast MRI correlate with hemodynamic parameters of right heart catheterization and can be used to noninvasively evaluate the severity of chronic thromboembolic pulmonary hypertension and, potentially, to follow up the treatment response.Chronic thromboembolic pulmonary hypertension (CTEPH) develops as a result of obstruction of pulmonary arterial vessels by organized thromboembolic material and subsequent vascular remodeling in small unobstructed vessels, and it is associated with significant morbidity and mortality (1). Right heart catheterization remains the reference standard to diagnose CTEPH, assess the hemodynamic disturbance, and follow up the treatment response; but it is invasive, delivers radiation, and is associated with recognized complications (2, 3).Magnetic resonance imaging (MRI) is considered not only as the reference standard for evaluation of ventricular function, but it also provides a reproducible and noninvasive assessment of hemodynamics changes in pulmonary hypertension (4). In a separate validation study, cardiac MRI-derived parameters showed a strong correlation with invasive determinations (5).In a study by Mohiaddin et al. (6), phase-contrast MRI was used to confirm reduced diastolic peak velocity of the inferior vena cava (IVC) in patients with pulmonary hypertension. Only one study reported blood flow conditions in the proximal pulmonary arteries and vena cava in healthy children (7). To our knowledge, no study has assessed proximal pulmonary artery and vena cava flow or evaluated correlation of the flow determined by phase-contrast MRI and hemodynamics by right heart catheterization in CTEPH.We performed a prospective study to observe the flow change in the proximal pulmonary artery, superior vena cava (SVC) and inferior vena cava (IVC) in patients with CTEPH by phase-contrast MRI, and to evaluate the correlation of the proximal pulmonary artery and vena cava flow with hemodynamics derived by right heart catheterization in patients with CTEPH.     

CT肺动脉成像评价慢性血栓栓塞性肺动脉高压栓塞指数及右心功能

目的：以选择性肺动脉造影及右心导管为标准,探讨多层螺旋计算机断层肺动脉成像（CTPA）评价慢性血栓栓塞性肺动脉高压（CTEPH）及右心功能的价值。方法：回顾性收集确诊CTEPH的患者24例,均行右心导管及肺动脉造影、CTPA及超声心动图检查。结果：CT Qanadli栓塞指数为（37.16±8.77）%,CT Mastora栓塞指数为（38.14±21.56）%,Qanadli栓塞指数高于Mastora栓塞指数（Z=-4.107,P=0.000）,且二者正相关（r=0.734,P=0.000）。CTPA测得主肺动脉/升主动脉直径比与右心导管测定肺动脉平均压（mean pulmonary arterial pressure,mPAP）正相关（r=0.461,P=0.036）。CTPA测定右心室前壁厚度与mPAP成正相关（r=0.515,P=0.018）。CTPA测得肺动脉直径大于超声测肺动脉内径（t=3.485,P=0.002）,且正相关（r=0.588,P=0.002）。CTPA测得右心室最大短轴直径大于超声测右室横径（t=2.647,P=0.016）,且正相关（r=0.429,P=0.031）。CTPA测定右室前壁厚度小于超声测值（t=3.768,P=0.001）,且成正相关（r=0.551,P=0.004）。CTPA测室间隔厚度略低于超声测室间隔厚度（t=2.941,P=0.007）,两组资料正相关（r=0.751,P=0.000）。Qanadli栓塞指数和Mastora栓塞指数与肺动脉压、主肺动脉直径、肺动脉/主动脉直径比、右室横径、右室前壁厚度等参数均无相关性（P〉0.05）。结论：CT肺动脉造影不仅能够明确诊断慢性血栓性肺栓塞,而且能够提供肺动脉树的阻塞程度、右心功能改变信息,为临床决策和治疗提供更多的信息,但慢性血栓性肺动脉高压肺栓塞程度与右心功能无关。     

Validation of magnetic resonance phase-contrast flow measurements in the main pulmonary artery and aorta using perivascular ultrasound in a large animal model

OBJECTIVES: Phase-contrast flow magnetic resonance imaging (pc-MRI) measurements are an established technique for noninvasive assessment of hemodynamics. However, in vivo validation data on the accuracy of pc-flow especially for nonphysiologic hemodynamic conditions are missing. The goal of our work was 1) to validate pc-flow with perivascular ultrasound in different hemodynamic conditions in the main pulmonary artery (MPA) and ascending aorta (AO) and 2) to investigate the relation between pc-MRI and invasive pressure measurements. MATERIALS AND METHODS: Five healthy pigs with opened chest were investigated. Ultrasound measurements were performed outside the MRI unit using a detachable MR-table. Parallel to ultrasound flow measurements, invasive pressure measurements were performed. PC-MRI (1.5 T MRI) measurements were done using a FLASH 2-dimensional sequence. First the animals were examined in normotonia, followed by hypertension (infusion of Arterenol) and hypotension (infusion of Sodiumnitropussid). RESULTS: Flow measurements acquired in normotonia were 2.7 +/- 0.6 L/min (ultrasound) and 2.8 +/- 0.6 L/min for pc-MRI (not significantly different, P = 0.17). During hypertonia, the blood flow increased to 3.1 +/- 0.7 and 2.7 +/- 0.8 L/min, respectively (P = 0.01). During hypotension, the blood flow decreased to 1.7 +/- 0.5 and 1.7 +/- 0.5 L/min, respectively (P = 0.7). An excellent linear correlation (taking all measurements together) between the ultrasound and pc-MRI measurements was found (r = 0.89). 95% Limits of intraindividual agreement correspond to relative differences of -36 to 44%. Systolic pressure measurements in the AO were 91 mm Hg (normotonic), 111 mm Hg (hypertonic), and 64 mm Hg (hypotonic) and in the MPA 23 mm Hg (normotonic), 29 mm Hg (hypertonic), and 20 mm Hg (hypotonic). Systolic pressure measurements showed good linear correlation with pc-MRI average flow per minute and peak velocity (AO: r = 0.79, MPA: r = 0.66). CONCLUSION: MRI pc-flow measurements are a reliable tool for noninvasive assessment of blood flow. Hemodynamic parameters derived by MRI demonstrate good linear correlations with the pressure in the systemic and pulmonary arterial circulation.     

MRI和心导管检查对肺动脉血流动力学的对比性研究

目的　评价磁共振血流分析技术无创性检测肺动脉血流动力学的价值。材料与方法　应用MR相位速度图测量 45例患者的主肺动脉直径、流速及其最大返流速度并与右心导管检查进行比较。通过直线相关分析评判MRI测量结果的敏感性和特异性。结果　 45例患者中 40例存在返流 ,占 88.89%。 2 5例肺动脉高压 (PAH)组主肺动脉的流速及其肺血管的顺应性均低于非PAH组 ,而返流的百分比也显著增高 (P <0 .0 5 ) ,且返流量与肺动脉平均压呈正相关 (r=0 .89,P <0 .0 1) ,与肺动脉峰值流速呈负相关 (r =-0 .82 ,P <0 .0 1)。结论　MR相位速度图是评价肺动脉血流动力学变化一种新的可靠技术     

MRI和心导管检查同步测定肺动脉舒张压的相关性研究

目的　探索MRI无创性测量肺动脉舒张压 (PADP)的新途径。材料与方法　应用MR相位速度图测量 40例具有肺动脉瓣返流 (PR)患者的最大返流速度并计算出舒张末期肺动脉与右心室间的压差 (PVDG) ,同时 ,与右心导管检查结果进行比较 ,通过直线相关与回归分析MRI测量PADP的敏感性和特异性。结果　MRI测定的PADP为 4.82± 1.2 4mmHg(1mmHg =0 .133kPa) ,右心导管的测值为 4.5 2± 2 .0 0mmHg ,二者之间无明显差异 (t=1.45 ,P >0 .0 5 ) ,但具有高度相关性 (r =0 .94,P <0 .0 1)。回归方程y =0 .82x + 4.5 8,其敏感性和特异性高达 90 %。结论　MRI是评价PR患者PADP的较可靠的新技术。     

Assessment of pulmonary hypertension what CT and MRI can provide

RATIONALES AND OBJECTIVES: Pulmonary hypertension (PH) is a life-threatening condition, characterized by elevated pulmonary arterial pressure, which is confirmed based on invasive right heart catheterization (RHC). Noninvasive examinations may support diagnosis of PH before proceeding to RHC and play an important role in management and treatment of the disease. Although echocardiography is considered a standard tool in diagnosis, recent advances have made computed tomography (CT) and magnetic resonance (MR) imaging promising tools, which may provide morphologic and functional information. In this article, we review image-based assessment of PH with a focus on CT and MR imaging. CONCLUSIONS: CT may provide useful morphologic information for depicting PH and seeking for underlying diseases. With the accumulated technological advancement, CT and MRI may provide practical tools for not only morphologic but also functional assessment of patients with PH.     

Estimation of pulse wave velocity in main pulmonary artery with phase contrast MRI: preliminary investigation

PURPOSE: To assess the feasibility and reproducibility of a noninvasive MRI method to measure pulse wave velocity (PWV) in the main pulmonary artery (MPA). MATERIALS AND METHODS: A total of 17 subjects without history of pulmonary diseases (38.2 +/- 18.4 years) participated in this study. Series of MR velocity maps of the MPA were acquired at 2 cm above the pulmonary valves using a two-dimensional phase-contrast sequence. Effective temporal resolution was 11 msec after interleaving two dynamic series with different values of electrocardiograph (ECG) trigger delay. PWV was derived as the rate of MPA flow variations per unit change in MPA cross-sectional area, during early systole. Seven healthy subjects underwent three repetitive examinations to investigate intrascan and interscan reproducibility. RESULTS: Flow vs. area was highly linear in the MPA during early systole, with Pearson's coefficients ranging from 0.982 to 0.999, rendering derivation of PWV with little difficulty. Average value of PWV in MPA was 1.96 +/- 0.27 m/second, in good agreement with literature values measured using invasive means. The percentage intra- and interscan differences were 5.46% and -10.86%, respectively. CONCLUSION: Phase-contrast MRI to noninvasively measure PWV in the MPA is feasible with good reproducibility.     

Simultaneous assessment of right ventricular function and hypertrophy by Tc-99m MIBI

PURPOSE: Tc-99m MIBI allows the simultaneous performance of cardiac blood pool scintigraphy and myocardial SPECT. The authors performed studies to determine whether right ventricular function and hypertrophy can be evaluated simultaneously using Tc-99m MIBI in patients with right heart disease. METHODS: Using right heart catheterization, several parameters of pulmonary circulation were measured, including right ventricular ejection fraction, in 23 patients with chronic pulmonary disease and pulmonary vascular disease. Within 1 week, right heart blood pool scintigraphy was performed using the first-pass method using Tc-99m MIBI. The right ventricular ejection fraction calculated from right heart blood pool scintigraphy was compared with that measured using right heart catheterization. Myocardial SPECT was performed 1 hour after right heart blood pool scintigraphy. On the short axis images, which allowed optimal visualization of the right ventricle, the right and left ventricular free walls were established as regions of interest. Myocardial wall counts were determined. The right ventricular uptake: left ventricular uptake ratio was calculated to study the relation of that ratio to mean pulmonary artery pressure and total pulmonary resistance. RESULTS: A significant correlation was observed between the right ventricular ejection fraction calculated on right heart catheterization and that calculated on right heart blood pool scintigraphy. The right ventricular uptake:left ventricular uptake ratio correlated positively with pulmonary artery pressure and total pulmonary resistance. CONCLUSION: These results suggest that Tc-99m MIBI allows simultaneous noninvasive evaluation of cardiac function and structure, which previously was considered impossible in patients with right heart disease.     

Diving-induced venous gas emboli do not increase pulmonary artery pressure

Venous gas emboli are frequently observed in divers even if proper decompression procedures are followed. This study was initiated to determine if pulmonary artery pressure increases in asymptomatic divers, which could increase the risk of arterial embolization due to passage of venous gas emboli from the right to the left side of the heart. Recordings of venous gas emboli and estimation of pulmonary artery pressure by non-invasive transthoracic echocardiography were applied in 10 recreational scuba diving volunteers before and 20, 40, 60, and 80 min after simulated dives to 18 m (80 min bottom time) in a hyperbaric chamber. The ratio between pulmonary artery acceleration time and right ventricular ejection time was used as an estimate of pulmonary artery pressure. None of investigated divers had signs of decompression sickness. Despite the post-dive presence of the venous gas emboli, measured in the region of the pulmonary valve annulus (mean=1.71 bubbles.cm-2, 40 min after dive), the ratio between pulmonary artery acceleration time and right ventricular ejection time did not decrease, but actually increased (from 0.43+/-0.06 to 0.49+/-0.06, 40 min after dive; p<0.05), suggesting a decrease in pulmonary artery pressure after the dive. We conclude that diving-induced venous gas bubbles do not cause significant changes in the central circulation which could increase the risk of arterial embolization.     

汉族人群移居高原后其心脏结构、心功能和肺动脉压等变化的研究

目的：研究汉族人群移居高原后其心脏结构、心功能、肺动脉压变化。方法：随机选取从内地平原移居至西藏高原多年（移居高原时间：28．88年±9．76年）的汉族人群,经病史及相关检查排除其他原因引起疾病共67例为移居高原组,并随机选取内地平原健康者61例为平原对照组。分别检测其心脏结构、心脏功能、肺动脉压和瓣膜口血流速度等指标,并进行统计分析探讨高原心血管适应问题。结果：移居高原组右心房、右心室和左心房内径;肺动脉收缩压、肺动脉内径、右肺动脉内径,均显著大于平原对照组（P〈0．001）,而且移居高原组内肺动脉收缩压与右心房、右心室内径存在正相关关系（r=0．370,P=0．011;r=0．403,P=0．005）。移居高原组左室射血分数显著高于平原对照组（P=0．018）、而心脏指数明显低于平原对照组（P=0．036）、每搏输出量和心输出量值两组无明显差异。移居高原组二尖瓣舒张期血流E峰、二尖瓣舒张期血流A峰、三尖瓣舒张期血流E峰、三尖瓣舒张期血流A峰均明显高于平原对照组（P=0．000）。结论：本研究表明,汉族人群移居高原多年后其心脏结构、心功能、肺动脉压、瓣口血流速度等指标均发生了显著的高原适应性变化;而且研究表明移居高原者心脏增大与肺动脉收缩压升高之间存在关联。     

Relationship between pulmonary artery volumes at computed tomography and pulmonary artery pressures in patients with- and without pulmonary hypertension

OBJECTIVES: This study was designed to determine the relationship between pulmonary artery (PA) volumes at computed tomography (CT) and PA pressures at right-sided heart catheterization in patients with and without pulmonary hypertension (PAH) to develop a noninvasive CT method of PA pressure quantification. MATERIALS AND METHODS: Sixteen patients with chronic sleep apnea syndrome underwent contrast enhanced helical CT (slice thickness 3mm; pitch 2; increment 2mm) at inspiration. Eight patients had PAH while cardiopulmonary disease has been excluded in eight other patients. Vascular volumes were determined using a 3D technique (threshold seeded vascular tracing algorithm; thresholds -600H [lower] and 3000H [upper]). Right-sided heart catheterization measurements were available for linear regression analysis of PA volumes and pressures. RESULTS: Correlation between PA pressures and volumes (normalized for BMI), was high in both groups (without PAH: r=.85; with PAH .90, Pearson). Compared to elevated PA pressures in patients with pulmonary hypertension (p<.005), PA volumes also were significantly increased (p<.05) among the groups. CONCLUSIONS: High correlation was found between PA volumes and mean PA pressures in patients with- and without PAH. Significant differences in PA volumes at CT-volumetry may admit non-invasive determination of pulmonary hypertension.     

Clinical Application of 4D Flow MR Imaging to Pulmonary Hypertension

Pulmonary hypertension (PH) is characterized by elevated pulmonary arterial pressure (PAP). Although right-heart catheterization is the gold standard method for the diagnosis of PH by definition, various less-invasive imaging tests have been used for screening, detection of underlying diseases-causing PH, and monitoring of diseases. Among them, 4D flow MRI is an emerging and unique imaging test that allows for comprehensive visualization of blood flow in the right heart and proximal pulmonary arteries. The characteristic blood flow pattern observed in patients with PH is vortical flow formation in the main pulmonary artery. Recent studies have proposed the use of these findings to determine not only the presence of PH but also estimate the mean PAP. Other applications of 4D flow MRI for PH include measurement of wall shear stress, helicity, and 3D flow balance in the pulmonary arteries. It is worth noting that 4D flow has also the potential for longitudinal follow-ups. In this review, the clinical definition of PH, summary of conventional imaging tests, characteristics of pulmonary arterial flow as shown by 4D flow MRI, and clinical application of 4D flow MRI in the management of patients with PH will be discussed.     

Pulmonary hypertension: pulmonary flow quantification and flow profile analysis with velocity-encoded cine MR imaging.

Velocity-encoded cine magnetic resonance (MR) imaging provides two-dimensional velocity maps of a cross-sectional area of a vessel. Pulmonary flow and flow patterns in the main pulmonary artery were analyzed with velocity-encoded cine MR imaging and Doppler echocardiography in 10 patients with pulmonary hypertension (PH), one patient with a dilated main pulmonary artery, and 10 healthy subjects, and these findings were compared. Peak systolic velocity measured with velocity-encoded cine MR imaging was similar to that measured with Doppler echocardiography in healthy subjects and in patients with PH. Velocity-encoded cine MR imaging demonstrated substantial differences in velocity across the vascular lumen in PH. The flow pattern in healthy subjects was different than that in patients with PH; the latter had lower peak systolic velocity and greater retrograde flow after middle to late systole. The retrograde flow observed in patients with PH reflected hemodynamic events, since it was inversely proportional to pulmonary flow volume and directly proportional to pulmonary resistance and cross-sectional area of the vessel. Velocity-encoded cine MR imaging demonstrates an inhomogeneous flow profile in PH and may serve as a noninvasive method to estimate pulmonary vascular resistance.     

Utility of phase contrast MR imaging for assessment of pulmonary flow and pressure estimation in patients with pulmonary hypertension: Comparison with right heart catheterization and echocardiography

Purpose:

To compare the utility of phase contrast MR imaging (PC‐MRI) for assessment of pulmonary flow and pressure estimation with that of right heart catheterization and echocardiography (cardiac US) in patients with pulmonary arterial hypertension (PAH).

Materials and Methods:

Twenty consecutive patients with suspected PAH underwent PC‐MRI, cardiac US, and right heart catheterization. In each patient, PC‐MRI was acquired by cine 2D‐PC method on a 1.5 Tesla scanner, and stroke volume (SV) and pulmonary arterial systolic pressure (PASP) were assessed by using the modified Bernoulli's equation. To evaluate the agreements of SV and PASP among the three methods, correlations and limits of agreement among the three methods were statistically assessed by using the Bland‐Altman's analyses.

Results:

The correlations and limits of agreement for SV and PASP between PC‐MRI and catheterization (r = 0.96, r² = 0.94, 1.1 ± 6.9 mL and r = 0.94, r² = 0.88, ?3.2 ± 14.5 mmHg, respectively) were better than between cardiac US and catheterization (r = 0.01, r² < 0.01, 8.9 ± 42.1 mL and r = 0.86, r² = 0.72, ?5.9 ± 27.7 mmHg, respectively).

Conclusion:

PC‐MRI is more compatible with right heart catheterization than cardiac US in pulmonary flow and pressure estimation. J. Magn. Reson. Imaging 2009;30:973–980. © 2009 Wiley‐Liss, Inc.

     

MRI evaluation of right ventricular pressure overload in chronic obstructive pulmonary disease

In chronic obstructive pulmonary disease (COPD), the development of pulmonary hypertension is common. This study was performed to assess the signs of right ventricular (RV) pressure overload and RV failure in COPD. In 8 COPD patients without primary cardiac disease, RV wall thickness, mass, and end-diastolic volume were measured by cardiac-triggered cine MRI. MR phase-contrast velocity quantification was used to measure stroke volume and the patterns of flow into and out of the RV. Data of patients were tested versus those of a control group matched for age (n = 8). Results showed that the RV wall thickness was increased (.6 ± 0.1 vs 0.4 ± 0.1 cm, P < .001). RV mass was increased (67 ± 11 vs 57 ± 5 g, P < .005). RV stroke volume was decreased (57 ± 13 vs 71 ± 13 ml, P < .01), but RV ejection fraction was not different. In the main pulmonary artery flow, the quotient of acceleration time divided by ejection time was decreased (33 ± 5% vs 38 ± 4%, P < .05), which is indicative of pulmonary hypertension. In conclusion, this MRI protocol provides a tool to assess the effects of RV pressure overload in COPD before heart failure has become manifest.