Central thrombi in pulmonary arterial hypertension detected by MR imaging

Differentiation of thrombi from slow flow in the pulmonary arteries, sometimes observed in the presence of pulmonary arterial hypertension, can be equivocal. Magnetic resonance (MR) imaging was performed in a patient with chronic pulmonary thromboembolism and pulmonary arterial hypertension using an electrocardiographically gated technique that allowed visualization of the pulmonary arteries at the end of diastole and multiple times during systole. These images were compared with those of a patient with primary pulmonary hypertension and those of healthy subjects. Thrombi were discrete structures, seen throughout the cardiac cycle on both the first and second spin-echo images, and decreased in signal intensity on the second image. Slow flow increased in signal intensity and changed in structure during the cardiac cycle and was seen best on the second image. MR may play an important role in excluding large central thrombi as the cause of pulmonary arterial hypertension. It is a noninvasive method for defining pulmonary arterial wall thickness and for direct visualization of chronic pulmonary thrombus.     

Estimation of pulmonary vascular resistance by MRI in patients with congenital cardiovascular shunt lesions

The intensity of the magnetic resonance signal in the pulmonary arteries was assessed in 15 patients with congenital left to right shunts and in 10 normal volunteers, using an ECG-gated multislice spin-echo technique. In normal subjects, magnetic resonance signal was only observed in great vessels of the thorax on images acquired near end-diastole; they disappeared in systole. Among the group of 15 patients, 10 had severe pulmonary hypertension (systolic pressures greater than 80 mm Hg) with severe elevation of pulmonary vascular resistances (greater than 787 dynes cm sec-1). The magnetic resonance signal persisted in systole in all 10 patients, and its intensity could be quantitatively assessed. On the other hand, in one other patient with high pulmonary artery pressure but only moderate elevation of pulmonary vascular resistance, and in patients with moderate pulmonary hypertension and normal pulmonary vascular resistance, the intravascular signal was minimal and no different from the signal recorded in normal subjects. A direct linear relationship was found between the pulmonary vascular resistance and the intensity of the magnetic resonance signal in the right pulmonary artery during systole (r = 0.84). An even closer correlation was found for the linear relationship between the ratio pulmonary vascular resistance/systemic resistance and the magnetic resonance signal in the right pulmonary artery (r = 0.93). Thus, magnetic resonance, with its sensitivity to slow-flow conditions, can potentially provide physiological information in congenital cardiovascular disease.     

Pulmonary vascular cine MR imaging: a noninvasive approach to dynamic imaging of the pulmonary circulation

Cine gradient-recalled magnetic resonance (MR) imaging, which has flow sensitivity and high temporal resolution, may potentially yield both morphologic and dynamic flow-related information in the pulmonary vasculature. The authors used this modality to evaluate pulmonary vessels in 12 healthy subjects and in 14 patients with a variety of cardiopulmonary disorders. Normal pulmonary arteries and veins were characterized by distinctive signal intensity and diameter variations as well as motion of the vessels during the cardiac cycle. Patients with pulmonary arterial hypertension demonstrated loss of the normal pulsatile systolic increase and diastolic decline in velocity-related signal intensity and in diameter of the proximal pulmonary arteries. Disorders of pulmonary venous signal and diameter profiles during the cardiac cycle, which show a characteristic biphasic pattern in healthy subjects, were identified in five patients with mitral valvular disease. These initial results indicate that cine MR imaging techniques hold promise in the evaluation of pathophysiologic conditions in the pulmonary circulation.     

Assessment of pulmonary perfusion using a subtracted HASTE image between diastole and systole

The MR signal intensity change in the pulmonary parenchyma during the cardiac cycle was studied using HASTE sequence in volunteers. In addition, the potential to assess pulmonary perfusion abnormality by subtraction between diastolic and systolic HASTE images was tested in a pig model of pulmonary embolism. Signal intensity decreased in systole while it increased gradually in diastole. In a pig model with pulmonary embolism, subtracted images could identify the perfusion abnormality. Thus, subtraction of diastolic and systolic HASTE images has the potential to detect pulmonary perfusion abnormality. The technique may provide a new simple method for evaluating pulmonary perfusion.     

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.     

Fresh blood imaging of the peripheral vasculature: an emerging unenhanced MR technique

OBJECTIVE: There is an increasing demand for MR angiography (MRA) techniques that do not require the administration of exogenous contrast material. Fresh blood imaging utilizes an ECG-gated fast spin-echo sequence to acquire images in both the systolic and diastolic phases of the cardiac cycle. Fast systolic arterial flow is differentiated from slower diastolic flow and a subtraction technique is used to produce angiographic images. We describe the technical aspects of performing lower extremity MRA and illustrate some sample cases. CONCLUSION: Fresh blood imaging is an emerging unenhanced MRA technique that has recently become commercially available. Early clinical trials appear promising and it is anticipated that fresh blood imaging will become invaluable, particularly in patients with impaired renal function. Technical refinements are still required to perfect this novel MR application, particularly for the assessment of distal calf and pedal vessels and for the evaluation of patients with arrhythmias and those with impaired cardiac function.     

Mechanical thrombectomy of major and massive pulmonary embolism with use of the Amplatz thrombectomy device.

RATIONALE AND OBJECTIVES: To evaluate the feasibility of mechanical thrombectomy with the Amplatz thrombectomy device (ATD) in restoring patency of acutely thrombosed pulmonary arteries resulting from pulmonary embolism for the improvement of patient outcome. METHODS: Mechanical thrombectomy with the ATD (8F) was performed in nine consecutive patients with angiographically documented thrombus in the left or right pulmonary artery resulting from deep vein thrombosis (n = 4) or unknown cause (n = 5). RESULTS: The Miller index decreased from 18 to 11. In all patients, the majority of the thrombus in the pulmonary artery was cleared after a mean activation time of the ATD of 367 seconds. Thrombectomy was performed with the ATD alone (n = 4) or with additional long-term fibrinolysis therapy (n = 5) with infusion of recombinant tissue-type plasminogen activator. Pulmonary arterial pressure decreased from a mean of 57 mm Hg before mechanical thrombectomy to 55 mm Hg directly after the procedure and to 39 mm Hg after termination of the recombinant tissue-type plasminogen activator infusion. CONCLUSIONS: Mechanical thrombectomy with the ATD in patients with minor and major pulmonary embolism is technically feasible and safe. It is a potential alternative to drug-mediated thrombolysis and surgery. However, the incremental benefit of the ATD over conventional treatments could be shown only in a randomized controlled study.     

ECG-gated multislice spiral CT for diagnosis of acute pulmonary embolism

AIM: The purpose of this study was to determine the feasibility of echocardiogram (ECG)-gated multi-slice CT angiography (MCTA) in patients with clinical suspicion of acute venous thromboembolism (VTE), to investigate the effect of ECG-gating on cardiac motion artefacts, and to determine the diagnostic reader agreement of ECG-gated MCTA in comparison with conventional MCTA. MATERIALS AND METHODS: Forty-eight consecutive patients were prospectively enrolled and randomly underwent ECG-gated (n=25, group 1) or non-ECG-gated (n=23, group 2) eight-slice pulmonary MCTA. Image data were evaluated by three independent chest radiologists with respect to the presence or absence of emboli at different arterial levels (main, lobar, segmental, and subsegmental arteries), and with regard to cardiac motion artefacts. Statistical tests used to calculate inter-observer agreement were weighted kappa statistics, extended kappa statistics and confidence indices indicating three-reader agreement accuracy. RESULTS: Twenty-seven patients (56.3%) were diagnosed to have pulmonary embolism (13 from group 1, 14 from group 2). Cardiac motion artefacts were significantly more frequent in group 2 (70% in group 2 versus 13% in group 1, p=0.0001). The overall diagnostic agreement was excellent with both MCTA techniques (three-reader confidence index for all vascular territories: 0.76 and 0.84 for groups 1 and 2, respectively (extended kappa=0.69 and 0.78, respectively); three-reader confidence index for diagnosis of VTE: 0.94 and 0.85 for groups 1 and 2, respectively (extended kappa=0.91 and 0.73, respectively), weighted kappa=0.81-0.83 and 0.92-0.95 for groups 1 and 2, respectively, and did not differ significantly between the two groups. In addition there was no significant difference of inter-observer agreement in either group at any assessed pulmonary arterial level. CONCLUSION: ECG-gated pulmonary MCTA is feasible in patients with clinical suspicion of VTE. However, ECG-gated image acquisition did not influence the diagnostic reader agreement accuracy and inter-observer agreement of MCTA. Hence, it does not appear to be advantageous for the MCTA diagnosis of pulmonary embolism.     

Pulmonary perfusion patterns and pulmonary arterial pressure

PURPOSE: To use artificial intelligence methods to determine whether quantitative parameters describing the perfusion image can be synthesized to make a reasonable estimate of the pulmonary arterial (PA) pressure measured at angiography. MATERIALS AND METHODS: Radionuclide perfusion images were obtained in 120 patients with normal chest radiographs who also underwent angiographic PA pressure measurement within 3 days of the radionuclide study. An artificial neural network (ANN) was constructed from several image parameters describing statistical and boundary characteristics of the perfusion images. With use of a leave-one-out cross-validation technique, this method was used to predict the PA systolic pressure in cases on which the ANN had not been trained. A Pearson correlation coefficient was determined between the predicted and measured PA systolic pressures. RESULTS: ANN predictions correlated with measured pulmonary systolic pressures (r = 0.846, P <.001). The accuracy of the predictions was not influenced by the presence of pulmonary embolism. None of the 51 patients with predicted PA pressures of less than 29 mm Hg had pulmonary hypertension at angiography. All 13 patients with predicted PA pressures greater than 48 mm Hg had pulmonary hypertension at angiography. CONCLUSION: Meaningful information regarding PA pressure can be derived from noninvasive radionuclide perfusion scanning. The use of image analysis in concert with artificial intelligence methods helps to reveal physiologic information not readily apparent at visual image inspection.     

电子束CT在肺动脉栓塞治疗中的应用评价(附五例报告)

目的探讨肺动脉栓塞（ＰＥ）溶栓或手术治疗前后电子束ＣＴ（ＥＢＣＴ）检查的临床价值。方法３例急性ＰＥ行静脉溶栓治疗,２例慢性ＰＥ行肺动脉血栓及内膜清除术,所有病例均在治疗前１周及治疗后２周内行ＥＢＣＴ增强连续容积扫描,慢性ＰＥ尚作ＥＢＣＴ心脏电影。结果３例急性ＰＥ中２例在溶栓后ＥＢＣＴ复查示病灶基本消失,另１例首次溶栓后ＥＢＣＴ示病变无显著变化,遂更改治疗方案而奏效,血栓消失;２例慢性ＰＥ经手术治疗,ＥＢＣＴ证实病灶基本清除,心功能明显改善。结论ＥＢＣＴ对ＰＥ溶栓及手术治疗有重要的诊断和指导治疗价值,也是治疗后随访的可靠方法。     

Peripheral MR angiography: separation of arteries from veins with flow-spoiled gradient pulses in electrocardiography-triggered three-dimensional half-Fourier fast spin-echo imaging

The authors evaluated a nonenhanced magnetic resonance (MR) angiographic technique that allows separation of arteries from veins. In 15 healthy subjects, peripheral MR angiography was performed with readout flow-spoiled gradient pulses in electrocardiography-triggered three-dimensional half-Fourier fast spin-echo MR imaging. Appropriate flow-spoiled gradient pulses were measured and applied in the three-dimensional acquisition to differentiate arteries and veins in the peripheral vasculature. Subtraction of the diastolic bright-blood arteries from the systolic black-blood arteries allowed visualization of the arteries by cancelling the veins, which are constantly depicted as bright blood throughout the cardiac cycle. Stronger flow-spoiled gradient pulses improved the depiction of slow-flow arteries even in the distal foot and hand vessels.     

Congenital heart disease: gated MR imaging in 72 patients

Seventy-two patients (aged 2 months to 75 years; mean 23 years) with a variety of congenital anomalies of the heart and great vessels underwent ECG-gated magnetic resonance (MR) imaging using the multisectional spin-echo technique (0.35 Tesla). The ability to define segmental anatomy and intracardiac anomalies on transverse, sagittal, and coronal images was evaluated. MR images were graded as excellent, diagnostic, or nondiagnostic, and MR findings were corroborated by angiography and/or two-dimensional echocardiography. Studies that were considered to be excellent or diagnostic were obtained in 96% of the cases. Visceroatrial situs, the type of ventricular loop, and the relationship of the great vessels could be identified in all patients with studies encompassing the entire heart. Forty-four of 47 abnormalities at the level of the great vessels were identified with MR, including coarctation of the aorta and vascular rings. MR showed 32 of 35 ventricular abnormalities; 2 small ventricular septal defects and 1 Ebstein anomaly were not demonstrated. All of the abnormalities at the atrial level and those of systemic and pulmonary venous return were seen on MR images. Complex cardiac anomalies, such as single ventricles, and the status of the pulmonary arteries were clearly demonstrated, and a good assessment of total and palliative postoperative anatomy was provided.     

Cine-gradient-refocused MR imaging of central pulmonary emboli

We studied the use of MR imaging with a limited-flip-angle, gradient-refocused pulse sequence to show central pulmonary emboli in 11 patients and to distinguish acute from chronic emboli. The central pulmonary vasculature was imaged by using a cine-limited-flip-angle (cine-MR) pulse sequence with 63/13 (TR/TE) and a 30 degrees flip angle (theta), as well as standard spin-echo sequences. Patients were selected on the basis of suspicion of central pulmonary embolism and correlative studies done within 24 hr of the MR examination. Correlations with other studies were based on the original MR report and blinded review of the MR images by two observers in consensus. Emboli were shown in all cases by cine-MR, and they corresponded to the locations of angiographic abnormalities and mismatched perfusion defects on scintigraphy. In three patients considered to have acute pulmonary embolus on the basis of angiography, the cine-MR studies were consistent with acute pulmonary embolus in two patients and chronic pulmonary embolus in one patient (however, in that patient pathologic examination showed chronic embolism). In one case in which angiography led to the diagnosis of acute and chronic pulmonary embolism, the cine-MR study showed acute embolism. In three patients thought to have chronic pulmonary embolus on the basis of angiography, the cine-MR study was interpreted as representing acute embolus in one patient and chronic embolus in two patients. In this highly selected, small group of patients, cine-MR imaging was accurate in showing central pulmonary embolism.     

Pulmonary embolism, right ventricular strain, and intracardiac thrombus-in-transit: Evaluation using comprehensive cardiothoracic computed tomography

A 67-year-old woman presented with symptoms of exertional chest discomfort and dyspnea that had been progressive over the past few days. Her initial evaluation was significant of a mildly elevated troponin-T level and T-wave inversion in leads V₁-V₂ on an electrocardiogram (ECG). Initial suspicion was for acute coronary syndrome. However, a transthoracic echocardiogram showed normal left ventricular systolic function, moderate right ventricular enlargement with moderate decrease in systolic function, possible left atrial mass or thrombus, and a possible right atrial mass or thrombus versus a prominent Chiari network. ECG-gated comprehensive cardiothoracic computed tomography (CT) with a 64-slice multidetector CT was done to assess for pulmonary embolism or acute coronary syndrome and to further evaluate the possible right and left atrial masses. This showed large bilateral pulmonary embolism, interatrial thrombus in transit through a patent foramen ovale, and minimal coronary atherosclerosis. Dynamic imaging showed right ventricular enlargement with severe systolic dysfunction. The patient underwent successful pulmonary thromboembolectomy, removal of intracardiac thrombus, and closure of patent foramen ovale.     

Assessment of lung perfusion impairment in patients with pulmonary artery-occlusive and chronic obstructive pulmonary diseases with noncontrast electrocardiogram-gated fast-spin-echo perfusion MR imaging

PURPOSE: To evaluate the ability of noncontrast electrocardiogram (ECG)-gated fast-spin-echo (FSE) perfusion MR images for defining regional lung perfusion impairment, as compared with technetium (Tc)-99m macroaggregated albumin (MAA) single-photon emission computed tomography (SPECT) images. MATERIALS AND METHODS: After acquisition of ECG-gated multiphase FSE MR images during cardiac cycles at selected lung levels in nine healthy volunteers, 11 patients with pulmonary artery-occlusive diseases, and 15 patients with chronic obstructive pulmonary diseases (COPD), the subtracted perfusion-weighted (PW) MR images were obtained from the two-phase images of the minimum lung signal intensity (SI) during systole and the maximum SI during diastole, and were compared with SPECT images. RESULTS: ECG-gated PW images showed uniform but posture-dependent perfusion gradient in normal lungs and visualized the various sizes of perfusion defects in affected lungs. These defect sites were nearly consistent with those on SPECT images, with a significant correlation for the affected-to-unaffected perfusion contrast (r = 0.753; P < 0.0001). These MR images revealed that the pulmonary arterial blood flow in the affected areas of COPD was relatively preserved as compared with pulmonary artery-occlusive diseases, and also showed significant decrease in blood flow, even in the areas with homogeneous perfusion on SPECT images in patients with focal pulmonary emphysema. CONCLUSION: This noninvasive MR technique allows qualitative and quantitative assessment of lung perfusion, and may better characterize regional perfusion impairment in pulmonary artery-occlusive diseases and COPD.     

Bronchial artery dilatation on MDCT scans of patients with acute pulmonary embolism: comparison with chronic or recurrent pulmonary embolism

OBJECTIVE: The purpose of our study was to compare the bronchial arteries of patients with acute pulmonary embolism with those of patients with chronic or recurrent pulmonary embolism. MATERIALS AND METHODS: Twenty-seven patients with acute pulmonary embolism and 14 patients with chronic or recurrent pulmonary embolism were retrospectively identified from 700 consecutive patients with suspected pulmonary embolism. The case data for the patients were assessed by two thoracic radiologists whose final judgments were reached by consensus. On the MDCT pulmonary angiograms obtained in these patients, the bronchial arteries were assessed by finding enhancing, small, round or curvilinear structures within the mediastinum and tracing their paths along the bilateral main bronchi. Bronchial arteries with a diameter greater than 1.5 mm were considered to be dilated. RESULTS: The diameters of the bronchial arteries in the group with chronic or recurrent pulmonary embolism were significantly larger than diameters of the bronchial arteries in the group with acute pulmonary embolism (p = 0.0002). Dilatation of bronchial arteries was observed in two of the 27 patients with acute pulmonary embolism and in seven of 14 patients with chronic or recurrent pulmonary embolism. This difference was statistically significant (p = 0.004). No dilated bronchial arteries were seen in patients who had acute pulmonary embolism but had no a history of deep venous thrombosis. CONCLUSION: Acute pulmonary embolism did not appear to cause dilatation of bronchial arteries, whereas chronic or recurrent pulmonary embolism was frequently associated with dilated bronchial arteries. In patients in whom the distinction between acute and chronic or recurrent pulmonary embolism on MDCT pulmonary angiography is clinically unclear and in whom the bronchial arteries are dilated, a diagnosis of chronic or recurrent pulmonary embolism should be favored.     

Interventricular septal configuration at mr imaging and pulmonary arterial pressure in pulmonary hypertension

PURPOSE: To investigate whether a relationship exists between septum shape and systolic pulmonary arterial pressure (PAP) in patients with pulmonary hypertension. MATERIALS AND METHODS: Study protocol was approved by institutional ethics review committee; all patients gave informed consent. Right-sided heart catheterization with vasodilator testing was performed in 39 adult subjects suspected of having pulmonary hypertension. There were 11 men and 28 women, aged 21-75 years (mean, 46 years). Only two patients showed favorable response to vasodilators, defined by a decrease in PAP of more than 20%. Synchronous right- and left-ventricular pressure measurements and four-chamber magnetic resonance (MR) imaging were used to identify timing of maximal leftward ventricular septal bowing within cardiac cycle. Septal bowing was evaluated with MR, measured on short-axis cine heart images, and expressed as curvature (reciprocal of radius). Curvature was quantified on one image (the one that showed the most severe distortion of normal septal shape). The relationship between systolic PAP and septal curvature was tested with linear regression analysis. P <.05 was considered to indicate a statistically significant difference. RESULTS: Of 39 subjects, 37 had pulmonary hypertension. Maximal distortion of normal septal shape was found during right ventricular relaxation phase. Systolic PAP was proportional to septal curvature: r=0.77 (P < .001), slope=-114.7, and intercept=67.2. In the two vasodilator responsive subjects, a significant reduction of leftward ventricular septal bowing was observed in response to reduction of right ventricular pressure. CONCLUSION: In 37 patients with pulmonary hypertension, systolic PAP higher than 67 mm Hg may be expected when leftward curvature is observed.     

Assessment of carotid artery patency on routine spin-echo MR imaging of the brain

We retrospectively reviewed the routine spin-echo MR studies of the brain in 12 patients with 13 angiographically demonstrated occlusions and in 14 patients with 16 high-grade stenoses of the carotid arteries. Intraluminal signal that was isointense with adjacent brain on long TR/short TE and long TR/long TE images was 100% specific for atherosclerotic occlusion. Of the 13 proved occlusions, six (46%) had significant degrees of hyperintense intraluminal signal indistinguishable from that observed consequent to slow flow distal to high-grade stenoses. MR detected only five (31%) of the 16 proved high-grade stenoses. Normal flow void does not exclude significant extracranial carotid stenosis. Occlusion cannot always be distinguished from high-grade stenosis when hyperintense intraluminal signal is encountered. However, a reliable diagnosis of atherosclerotic occlusion can be made when isointense intraluminal signal is observed.     

Dynamic contrast-enhanced MR tomoangiography of major pulmonary arteries

We evaluated the use of contrast-enhanced MR tomoangiography of the major pulmonary arteries in patients with suspected pulmonary embolism and hilar lung carcinoma. Patients with acute pulmonary emboli of the major pulmonary arteries, pulmonary hypertension (n = 11), and hilar lung carcinoma with suspected infiltrated pulmonary artery (n = 4), underwent MRI after selective digital subtraction pulmonary angiography (DSA). Subsecond contrast-enhanced MR tomoangiograms were obtained in the long axis of each pulmonary artery after bolus injection of a paramagnetic MR contrast agent. All proximal thrombi visualized using DSA (n = 13) were depicted using contrast-enhanced MR tomoangiography. Pulmonary artery obstruction (n = 2) or stenosis (n = 2) by the tumor were similarly assessed by DCMRA and DSA. Contrast-enhanced MR tomoangiography allows a reproducible, fast, dynamic, and multiplanar good quality imaging of the major pulmonary arteries and their proximal branches. This technique may be useful in patients with pulmonary hypertension for whom DSA is dangerous, and in the diagnosis of malignant involvement of central pulmonary arteries.     

基于肺部血流MRI信号在心动周期内变化的灌注成像技术研究

目的探讨血流变化对肺部MRI信号的影响，并研究1种新的MR肺血流灌注成像方法。方法对健康志愿者15例，采用相位对比电影MRI技术测量大肺动脉血流速度和流量在心动周期内的变化；并选用单次激发半傅立叶变换超快速自旋回波序列观察肺实质MR信号的相应改变，评价其相关性；根据不同心动期相肺实质MR信号的差异进行图像减影。结果肺实质．MRI信号表现为心脏收缩期降低，舒张期升高。大肺动脉的瞬时速度、瞬时流量与其呈负相关(r=-0．878、-0．770，P=0，002、0．015)。经肺部MRI信号差异最大的舒张末期和收缩中期的MRI减影可获得肺灌注像。结论肺实质MRI信号的改变与肺血流模式和速度有关。该技术是1种简便易行的非对比剂性的MR肺灌注评价新方法。