Fetal lung volume: estimation at MR imaging-initial results

PURPOSE: To plot normal fetal lung volume (FLV) obtained with fast spin-echo magnetic resonance (MR) images against gestational age; to investigate the correlation between lung growth and fetal presentation, sex, and ultrasonographic (US) biometric measurements; and to investigate its potential application in fetuses with thoracoabdominal malformations. MATERIALS AND METHODS: In a prospective multicenter study, 336 fetuses suspected of having central nervous system disorders underwent fast spin-echo T2-weighted lung MR imaging. Data obtained at 21-38 weeks gestation in 215 fetuses without thoracoabdominal malformations and with normal US biometric findings were selected for an FLV normative curve. FLV measurements obtained at pathologic examination with an immersion method were compared with MR FLV measurements in 11 fetuses. MR FLV values in 16 fetuses with thoracoabdominal malformations were compared with the normative curve. RESULTS: Normal FLV increased with gestational age as a power curve; the spread of values increased with age. Interobserver correlation was excellent (R(2) = 0.96). FLV measurements at MR imaging were 0.90 times those at pathologic examination. A constant ratio (0.78) between FLV on the left and right sides was observed. No significant difference in FLV was observed between fetal presentations. Normal FLV was observed in all fetuses with cystic adenomatoid malformations and in four of six with oligohydramnios. Lowest FLV values were observed in fetuses with diaphragmatic hernia. CONCLUSION: In fetuses with normal lungs, FLV distribution against gestational age is easily assessed in utero with fast spin-echo T2-weighted MR imaging. These preliminary findings illustrate the potential for comparing FLV measurements in fetuses at risk of lung hypoplasia with normative values.     

Fetal relative lung volume: quantification by using prenatal MR imaging lung volumetry

PURPOSE: To retrospectively determine a biometric algorithm for calculating relative lung volume in fetuses with normal lungs and of a wide range of gestational ages by using proved independent variables and to retrospectively investigate the use of this algorithm in fetuses with pulmonary hypoplasia. MATERIALS AND METHODS: Total lung volume (TLV) was measured by using planimetry on single-shot rapid acquisition with relaxation enhancement magnetic resonance (MR) images obtained in 91 fetuses with ultrasonographically (US) normal chests and 28 fetuses with US-determined pulmonary hypoplasia. All fetuses were aged between 18 and 38 weeks gestation. Analysis of covariance was used to identify parameters that were not different between the fetuses with US-determined normal and those with US-determined abnormal chests, and these variables were used to construct an algorithm for calculating predicted lung volume. The relative lung volume-that is, the observed lung volume expressed as a percentage of the predicted lung volume-was then calculated in fetuses with pulmonary hypoplasia. RESULTS: There was no significant difference in mean maternal or gestational age between the two fetus groups. Stepwise regression analysis was used to generate the following equation for predicting fetal lung volume on the basis of independent biometric indexes, with a correlation coefficient of 0.93: TLV = (0.52 . LV) + (0.33 . BD) - (0.06 . FL) - 13.7, with TLV and liver volume (LV) in milliliters and biparietal diameter (BD) and femoral length (FL) in centimeters. In the fetuses with normal chests, relative lung volume varied between 51% and 134%. In the fetuses with pulmonary hypoplasia, relative lung volume varied between 6% and 70%. CONCLUSION: The predicted lung volume in fetuses of a wide range of gestational ages can be calculated with a high degree of accuracy, enabling prenatal MR imaging lung volumetry in which relative lung volume is used to quantify fetal pulmonary hypoplasia.     

Fetal posterior fossa volume: assessment with MR imaging

PURPOSE: To retrospectively determine the relationship between posterior fossa volume (PFV) and estimated gestational age (EGA) and/or femur length (FL) during pregnancy for the purpose of developing a normal growth curve. MATERIALS AND METHODS: Advance institutional review board approval was obtained for this HIPAA-compliant study, and the need for parent informed consent was waived. A cross-sectional retrospective study was performed to measure PFV on in vivo magnetic resonance (MR) images obtained in 76 fetuses of 18-36 weeks gestation who had a morphologically normal CNS. Because this was a retrospective series, MR imaging techniques varied slightly, but all fetuses underwent imaging at contiguous 3-5-mm intervals in at least two orthogonal planes, with repetition time msec/echo time msec, 5-12/62-95; number of signals acquired, one; flip angle, 150 degrees -180 degrees; and matrix, 128-192 x 256. Posterior fossa areas were manually traced on half-Fourier rapid acquisition with relaxation enhancement in utero fetal MR images by one observer. PFVs were then calculated by manually summing areas from the contiguous sections and multiplying the total area by the section thickness. An average PFV (APFV) across orthogonal planes was calculated for each fetus, and the relationship between APFV and EGA was mathematically modeled. Coronal, transverse, and sagittal views were compared with correlations and Bland-Altman plots. Two additional observers repeated the measurements for a small subset of fetuses (n = 5). Paired t test analyses were also performed to determine significant differences between sagittal, transverse, and coronal measurements, as well as to determine preliminary intraobserver and interobserver variability of measurements in a subset of cases. RESULTS: The relationship between APFV (in cubic centimeters) and EGA (in weeks) was well described by a single exponential function [APFV = 0.689 exp(EGA/9.10)]. APFV doubling time was 6.31 weeks. Root-mean-square variation of values around the model line was 1.63 cm(3). There was no statistically significant intra- or interobserver variation (P > .16 for all fetuses) at preliminary analysis. No correlation between APFV and FL could be found. CONCLUSION: The normal fetal PFV growth curve generated in this study may have potential as a model for clinical application.     

Fetal body volume: use at MR imaging to quantify relative lung volume in fetuses suspected of having pulmonary hypoplasia

PURPOSE: To retrospectively determine an algorithm based on fetal body volume (FBV) by using magnetic resonance (MR) imaging to calculate relative lung volume in fetuses with normally developed lungs and prospectively assess the use of this algorithm in predicting pulmonary hypoplasia in the late second and early third trimesters for fetuses at risk for pulmonary hypoplasia. MATERIALS AND METHODS: Oral informed consent was obtained for the prospective component of this ethics committee-approved study. MR imaging lung volumetry was performed in 36 fetuses with normally developed lungs between 18 and 39 weeks gestational age by using T2-weighted single-shot fast spin-echo imaging in fetal transverse and sagittal planes. Findings were then correlated with biometric variables and gestational age. The best-performing algorithm was applied to 37 fetuses (between 18 and 29 weeks gestational age) at risk for pulmonary hypoplasia to determine observed-expected lung volume ratio. This group was stratified according to pregnancy management, and observed-expected ratios were correlated with outcome. In fetuses with isolated congenital diaphragmatic hernia (CDH) (n = 19), observed-expected ratio was correlated with lung-head ratio, neonatal survival in pregnancies managed expectantly (n = 13), and/or lung-body weight ratio at necropsy (n = 9). For that purpose, linear regression correlation was used with the Pearson correlation coefficient; P < .05 was considered to indicate a significant difference. RESULTS: Total fetal lung volume correlated best with total FBV (r = 0.96, P < .05). Observed-expected ratio based on FBV correlated with lung-head ratio in patients with CDH (r = 0.71, P < .001) and with lung-body weight ratio at necropsy (r = 0.68, P < .05) and could be used to help predict neonatal survival. CONCLUSION: FBV measured with MR imaging can be used as a single parameter in an algorithm and showed closest correlation with normal total fetal lung volume. In the transition from second to third trimester, this algorithm enabled calculation of the observed-expected ratio and prediction of outcome in fetuses at risk for pulmonary hypoplasia.     

Temporal lobe seizures: lateralization with MR volume measurements of the hippocampal formation

A retrospective magnetic resonance (MR) imaging study was performed in 41 right-handed patients with presumed mesial sclerosis who underwent surgery for medically intractable, complex partial seizures of temporal lobe origin. The ability of each of five different MR imaging-based tests to lateralize the seizure disorder was determined. In order of decreasing usefulness the tests were (a) hippocampal formation (HF) volume measurements, (b) visual grading of MR images for unilateral HF atrophy, (c) anterior temporal lobe (ATL) volume measurements, (d) visual grading of MR images for unilateral ATL atrophy, and (e) evidence of unilateral medial temporal lobe signal intensity abnormalities on long repetition time MR images. A right-side minus left-side volume (designated DHF) was obtained to quantify unilateral HF atrophy with a single number. Patients with right-sided seizures had a median DHF of -0.4 cm3, while those with left-sided seizures had a median DHF of 0.8 cm3, consistent with atrophy of the HF ipsilateral to the seizure disorder. Conservative volumetric threshold values (-0.2 cm3 and 0.6 cm3), separating individual DHF measurements into right-side abnormal, indeterminate, and left-side abnormal, allowed DHF measurements to be 76% sensitive and 100% specific for correct seizure lateralization.     

Estimating splenic volume: sonographic measurements correlated with helical CT determination

OBJECTIVE: The purpose of this study was to determine which sonographic measurements of the spleen most closely correlate with splenic volume as determined on helical CT. MATERIALS AND METHODS: From October 17, 2000, to April 27, 2001, 142 consecutive patients prospectively underwent abdominal helical CT and sonography as part of an evaluation for liver disease. Calculations of splenic volumes were based on 10-mm unenhanced images. Maximum length (ML) and width (W), thickness (T), and craniocaudal length (CCL) were measured sonographically. Standard ellipsoid volume formulas (with the addition of new ellipsoid coefficients) and linear regression formulas were calculated for 117 patients whose examinations were performed within 30 days of each other. Mean percent differences, standard deviations, and 95% confidence intervals (CI) were calculated. RESULTS: We calculated the average difference between sonography- and CT-measured volume and the 95% CI for each of the four initial sonographic volume estimates with the ellipsoid method using two lengths and linear regression using two lengths and compared them to CT-determined volume. The ellipsoid formulas were then adjusted for bias. Linear regression formulas were derived in which splenic volumes were separately calculated on the basis of each of the two lengths. Mean percent differences and standard deviations for ellipsoid formulas with varying coefficients using the three length measurements were also calculated. CONCLUSION: Sonographic measurements allow accurate determination of splenic volume. Estimating splenic volume with the formula 0.524 x W x T x (ML + CCL) / 2 provides the greatest overall accuracy.     

Fetal sheep with tracheal occlusion: monitoring lung development with MR imaging and B-mode US

PURPOSE: To assess the accuracy of magnetic resonance (MR) imaging in determining fetal lung volume (FLV) and to observe fetal lung development with B-mode ultrasonography (US) and MR imaging. MATERIALS AND METHODS: Seven sheep fetuses between 92 and 141 gestational days (term, 145 days) with and without tracheal occlusion (controls) underwent serial MR imaging and US. FLV at MR imaging was measured with true fast imaging with steady-state precession in coronal and transverse planes. The combined cross-sectional left- and right-lung area was measured with US at three transverse levels. FLV was measured at autopsy. Statistical evaluations included linear regression analysis and calculation of the mean and 95% CI. RESULTS: No differences in FLV were observed on coronal or transverse MR images (r2 = 0.98; slope = 0.91; 95% CI: 0.82, 1.01). FLV at MR imaging at termination of the experiment was significantly related to FLV at autopsy (r2 = 0.96; slope = 1.27; 95% CI: 0.97, 1.57; n = 6). FLV at MR imaging increased more rapidly with gestational age in fetuses with tracheal occlusion (21.0 mL/d; 95% CI: 10.7, 31.3) than in controls (4.7 mL/d; 95% CI: 1.7, 7.7). Increase in left- and right-lung area at US was accelerated in fetuses with tracheal occlusion (1.60 cm2/d; 95% CI: 1.3, 1.9) compared with controls (0.38 cm2/d; 95% CI: 0.23, 0.53). Left- and right-lung area at US and FLV at MR imaging were significantly correlated (r2 = 0.82). CONCLUSION: FLV can be measured with moderate accuracy at MR imaging on both coronal and transverse images. MR imaging and B-mode US are useful tools for monitoring and quantifying tracheal occlusion-stimulated fetal lung growth in sheep fetuses.     

Comparison of skull circumference and linear measurements with CSF volume MR measurements in hydrocephalus.

In children with hydrocephalus, accurate and reproducible estimation of the presence, severity, and course of the condition is of paramount importance for both clinical and scientific purposes. In this study, 30 hydrocephalic patients were assessed with a number of commonly used methods, such as occipitofrontal skull circumference (SC) measurements, Evans ratio (ER), and bicaudate index (BCI), as well as, for comparison, another ratio of linear measurements [ventricle-skull ratio (VSR)] and MR measurements of total intracranial CSF volume. In repeated CSF volume measurements in healthy volunteers, the MR method appeared to be accurate and reproducible. This technique was simpler and easier in application, requiring less interaction than comparable MR techniques described by others. The variation coefficients were within the same range. In increased CSF volumes, our technique can be recommended; in very small CSF volumes, another technique is more adequate. Direct assessment of CSF volume as a measure of hydrocephalus was preferable over derived estimations for scientific purposes and may function as a gold standard against which to evaluate other techniques that are easier to apply clinically. In comparison, SC measurements were poor; CSF volume changes were not reflected in SC changes. VSR was preferable over ER and BCI, because it correlated more closely with CSF volume.     

Repetitive MR measurements of lung volume in fetuses with congenital diaphragmatic hernia: individual development of pulmonary hypoplasia during pregnancy and calculation of weekly lung growth rates

Objective

To investigate individual changes in fetal lung volume (FLV) in fetuses with isolated congenital diaphragmatic hernia (CDH) and to calculate weekly growth rates of the FLV using serial MR examinations during pregnancy.

Methods

MR-FLV was measured in 89 fetuses with CDH. All fetuses received two MRIs. A mean weekly growth rate of the FLV was determined for each fetus and compared with the growth rate of healthy fetuses.

Results

Mean observed-to-expected MR-FLV (o/e MR-FLV) measured at the first MRI was 33.3?±?12.2 % and 29.5?±?10.9 % at the second MRI. In 61 % of all fetuses (54/89) the o/e MR-FLV decreased during pregnancy, 26 % (23/89) showed an increase in the o/e MR-FLV and 13 % (12/89) had stable values. First and last o/e MR-FLV values were significantly associated with mortality and neonatal extracorporeal membrane oxygenation (ECMO) requirement with a higher prognostic accuracy of MR-FLV measurements near delivery. Patients with CDH had lower weekly lung growth rates than healthy fetuses. There was a significant difference in the mean weekly growth rate between survivors and non-survivors and patients with and without ECMO requirement.

Conclusion

Individual development of FLV in patients with CDH during pregnancy is extremely variable. Follow-up MR-FLV measurements are advisable before deciding upon pre- and postnatal therapeutic options.

Key points

? Lung development in congenital diaphragmatic hernia (CDH) during pregnancy is extremely variable. ? MRI demonstrates that lung growth rate is reduced in fetuses with CDH. ? The final observed-to-expected fetal lung volume provides the best prognostic information. ? Follow-up measurements are advisable before deciding upon therapeutic options.     

Liver volume measurements and three-dimensional display from MR images

A method was investigated for measuring the volumes of human livers in vivo from magnetic resonance images and subsequently displaying these livers in three dimensions. Volumetric image sets of phantoms, healthy volunteers, and patients with cirrhotic livers were processed. Two image-processing approaches were compared for accuracy of liver measurements, intrasubject and interobserver variation, and speed of processing. Results indicated that both processing methods had a high degree of volume-measuring accuracy (within 8%), the interobserver measurements had a high coefficient of correlation (r = .9994), the intrasubject measurements had a low coefficient of variation (1.8%), and one method was four to five times faster than the other. The faster and easier of the two image-processing approaches provided satisfactory results for measuring liver volumes, but the slower approach provided more realistic-looking three-dimensional images of the liver.     

Renal volume measurements: accuracy and repeatability of US compared with that of MR imaging.

PURPOSE: To determine the accuracy and repeatability of ultrasonography (US) with the ellipsoid formula in calculating the renal volume. MATERIALS AND METHODS: The renal volumes in 20 volunteers aged 19-51 years were determined by using US with the ellipsoid formula and magnetic resonance (MR) imaging with the voxel-count method by two independent observers for each modality. The observers performed all measurements twice, with an interval between the first and second examinations. The voxel-count method was the reference standard. Repeatability was evaluated by calculating the SD of the difference (method of Bland and Altman). RESULTS: Renal volume was underestimated with US by 45 mL (25%) on average. A comparable underestimation was found when the ellipsoid formula was applied to MR images. This indicates that the inaccuracy of US renal volume measurements (a) occurred because the kidney does not resemble an ellipsoid and (b) was not primarily related to the imaging modality. Intra- and interobserver variations in US volume measurements were poor; the SD of the difference was 21-32 mL. For comparison, the SD of the difference in reference-standard measurements was 5-10 mL. CONCLUSION: Use of US with the ellipsoid formula is not appropriate for accurate and reproducible calculation of renal volume.     

Dynamic susceptibility contrast MR imaging: correlation of signal intensity changes with cerebral blood volume measurements

Cerebral blood volume (CBV) maps derived from dynamic susceptibility contrast (DSC) magnetic resonance (MR) imaging provide valuable information regarding intracranial micro-hemodynamics and have been helpful in characterizing primary brain tumors and guiding stereotactic biopsy. Another parameter, the maximum signal drop (MSD) during the first pass of intravascular contrast bolus due to T2* effect, can also be measured directly without extensive post-processing and data manipulation. The purpose of our study is to determine whether MSD maps provide information similar to CBV maps in patients presenting with intracranial mass lesions. Twenty-nine patients with various intracranial mass lesions were studied with DSC MR imaging prior to stereotactic biopsy or volumetric resection. Maps of both CBV and MSD are calculated on a pixel-by-pixel basis and displayed as color overlays over the raw images. Relative CBV (rCBV) and MSD (rMSD) values were measured in regions of interest (ROIs) within areas of abnormality and compared. In addition, computer-generated noise was added to the data to estimate the sensitivity of each measurement to noise. The rMSD values were strongly correlated with rCBV values (r = 0.87, P = 0.0001). CBV values were much more sensitive to added noise than MSD values (P < 0.01). MSD maps derived from DSC MR imaging provide information similar to CBV maps in patients with intracranial mass lesions. MSD maps are a simple and reliable indicator of vascularity that can easily be incorporated into routine MR imaging.     

MR microimaging of the lung using volume projection encoding

Radial acquisition (RA) techniques have been extended to produce isotropic, three-dimensional images of lung in live laboratory animals at spatial resolution down to 0.013 mm³ with a signal-to-noise ratio of 30:1. The pulse sequence and reconstruction algorithm have been adapted to allow acquisition of image matrices of up to 256³ in less than 15 min. Scan-synchronous ventilation has been incorporated to limit breathing motion artifacts. The imaging sequence permits randomizing and/or discarding selected views to minimize the consequences of breathing motion. The signal in lung parenchyma was measured as a function of flip angle (α) for different repetition times and found to follow the predictions for which there is an optimum excitation (Ernst) angle. A single T₁, relaxation value of 780 ± 54 ms fits all data from six guinea pigs at 2.0 T. This T₁, value parameterizes the signal and allows for a priori optimization, such as calculation of the Ernst angle appropriate for lung imaging.     

Motion measurements from individual MR signals using volume localization.

A novel method is presented for measuring motion using individual magnetic resonance (MR) signals. This method uses a volume-localized excitation with reduced spatial encoding to measure displacement with a temporal resolution of several milliseconds. The trajectory of the excited volume is derived from the time-dependent frequency of the MR signal, which changes as the volume moves through a magnetic-field gradient. Phantom and in vivo experiments confirm that this method can monitor the trajectory of plug-like structures accurately, with T2* decay limiting the measurement period. The displacement of flowing blood in a human aorta has been measured for 65 msec from one MR signal, with a theoretical accuracy of 0.25 mm and an effective time resolution of 2 msec. The high temporal resolution of this method is useful for capturing rapid motions. An interesting property of this method is that it measures motion from the reference frame of the moving anatomy.     

Validation of volume flow measurements with cine phase-contrast MR imaging for peripheral arterial waveforms

A flow phantom was used to study MR volume flow measurements for monophasic and triphasic waveforms over the flow range expected in peripheral arteries at rest and with exercise (2–24 mL/sec, n = 50). The improvement in accuracy with phase-correction image processing to eliminate errors caused by eddy currents was measured. Volume flow estimates with Doppler sonography were also measured. MR volume flow measurements correlated with volume collection with r = 0.996 and mean error = 4.6%. Phase–correction processing decreased mean error from 12.6% to 4.6% (P <.001, paired t-test). Doppler sonography had a higher mean error of 10.3% (P <.001, unpaired t-test). Cine phase-contrast MR imaging provides accurate estimates of volume blood flow for waveforms and flow ranges expected in peripheral arteries.     

Fetal thoracic abnormalities: MR imaging

PURPOSE: To elucidate the appearance of fetal thoracic abnormalities at prenatal magnetic resonance (MR) imaging and determine whether MR imaging yields information additional to that obtained with ultrasonography (US). MATERIALS AND METHODS: US and MR imaging data from 83 MR examinations of 74 fetuses with thoracic abnormalities and confirmatory US performed within 1 week before MR imaging were compared with respect to resulting changes in patient counseling and/or care. Lung parenchyma and lesion signal intensities and vascularity, airway, esophagus, and diaphragm appearances were reviewed retrospectively on MR images. Student t tests and analyses of variance were performed. RESULTS: MR imaging yielded information additional to that acquired with US in 28 (38%) of 74 fetuses. The additional findings were confirmed in 19 of the 28 fetuses at postnatal follow-up; no follow-up data were available for the other nine fetuses. Thoracic MR information affected care with regard to six (8%) of 74 fetuses. Mean gestational age of 15 fetuses with lung signal intensity (SI) slightly lower than that of amniotic fluid (28.4 weeks +/- 6.8 [SD]) at T2-weighted MR imaging was significantly older than that of 18 fetuses with intermediate SI (21.3 weeks +/- 4.3) (P <.05). Mean SI of 13 congenital cystic adenomatoid malformations (CCAMs) and/or sequestrations (1.74 +/- 1.05) at T2-weighted MR imaging was significantly higher than that of the normal lungs of 33 fetuses (2.63 +/-.63) (P <.001). Among nine studies in which vessels were visualized in CCAMs and/or sequestrations, six involved a normal vascular branching pattern. Portions of the esophagus were seen in 31 (36%) of 85 fetuses. Nonvisualization of a major airway was not sufficient for diagnosis of pulmonary atresia. Visualization of a portion of the esophagus did not correlate with esophageal atresia. In all except one fetus, who had anhydramnios and pulmonary hypoplasia, and the fetuses with congenital diaphragmatic hernia, at least a portion of the diaphragm was visualized at MR imaging. CONCLUSION: MR imaging yields information additional to that yielded with US in fetuses with thoracic abnormalities.     

Impact of lung volume on MR signal intensity changes of the lung parenchyma

PURPOSE: To test the hypothesis that, in magnetic resonance (MR) imaging of healthy individuals, equal relative changes in lung volume cause equal relative changes in MR signal intensity of the lung parenchyma. MATERIALS AND METHODS: In two experimental runs, 10 volunteers underwent spirometrically monitored MR imaging of the lungs, with MR images acquired at 10 incremental lung volumes ranging from total lung capacity to 10% above residual volume. Average signal intensity, signal variability, and signal intensity integrals were calculated for each volunteer and for each lung volume. The effect of lung volume on signal intensity was quantified using linear regression analysis complemented by the runs test. Slopes and intercepts of regression lines were compared with an analysis of covariance. Slopes of the lines of best fit for lung volumes and signal intensities from the two runs were compared to the slope of the line of identity. Comparisons between the two runs were visualized using Bland and Altman plots. RESULTS: The slopes of the 10 individual regression lines yielded no significant differences (F = 1.703, P = 0.101; F = 1.321, P = 0.239). The common slopes were -0.556 +/- 0.027 (P = 0.0001) for the first and -0.597 +/- 0.0031 (P = 0.0001) for the second experimental run. Both slopes displayed no significant nonlinearity (P = 0.419 and P = 0.067). There was a strong association between changes in lung volumes (rs = 0.991, P = 0.0001) and changes in signal intensity (rs = 0.889, P = 0.0001) in the two experimental runs. Lines of best fit for lung volume and signal intensities were not significantly different from the slope of the line of identity (P = 0.321 and P = 0.212, respectively). CONCLUSION: Equal changes in lung volume cause equal changes in MR signal intensity of the lung parenchyma. This linear and reproducible phenomenon could be helpful in comparing pulmonary MR signal intensity between individuals.     

重力和肺容积对MR肺灌注的影响

目的 用血流敏感性交替反转恢复(FAIR)序列评价重力和肺容积对MR肺灌注血流分布的影响.方法 应用GE 1.5 T MR系统,10名健康志愿者取仰卧位呼气末屏气时,用FAIR序列自背侧至腹侧每隔3 cm依次进行5个冠状面(依次标记为P3、P6、P9、P12、P15)扫描,之后再对P3层面在吸气末屏气时扫描.对5个冠状面的相对肺血流量(rPBF)进行方差分析,同一层面左、右肺rPBF间进行配对t检验,并对5个层面和rPBF进行线性回归分析;分析P3层面在不同呼吸相时反转脉冲标记前、后双肺信号强度变化率(⊿SI%)、rPBF及P3层面肺面积(Area)的变化情况,并进行配对t检验.结果 (1)5个不同冠状面:在重力方向上,右肺由后至前的rPBF依次为:100.57±18.22、79.57±12.36、61.65±11.15、48.92±9.96、41.20±9.88;左肺为:106.61±26.99、78.89±11.98、64.00±13.64、51.27±8.95、43.04±12.18;除P12与P15间差异无统计学意义外(P＞0.05),其余两两之间差异均有统计学意义(F值分别为27.43、15.83,P值均＜0.05),rPBF由后至前是逐渐减小的;在非重力方向上,即同一冠状面,左、右肺rPBF之间差异无统计学意义(P＞0.05);回归系数(r值)右肺为-4.98,左肺为-5.16.(2)P3层面在不同呼吸相时:右肺呼气相和吸气相的⊿SI%、rPBF、Area分别为1.12±0.31和0.71±0.18、90.78±17.35和52.85±8.75、(12.59±3.23)×103mm2和(17.77±4.24)×103mm2;左肺呼气相和吸气相的⊿SI%、rPBF、Area分别为1.01±0.24和0.70±0.11、91.08±18.68和54.58±10.70、(12.34±3.08)×103mm2和(17.34±4.98)×103mm2.不同呼吸相时⊿SI%、rPBF、Area间差异均有统计学意义(P＜0.05),呼气末的⊿SI%及rPBF明显高于吸气末;吸气末Area明显大于呼气末.结论 FAIR评价肺灌注在重力方向的灌注梯度是比较敏感的,不同呼吸相时肺灌注之间存在差异,所以检查时将感兴趣区置于重力依赖性区域,并在呼气末屏气可以提高灌注缺损的检出率.