Pulmonary Perfusion Imaging Research Articles

Real-time in-vivo imaging of pulmonary capillary perfusion using probe-based confocal laser scanning endomicroscopy in pigs: An interventional laboratory study.

Little is known about real-time in-vivo microscopy of pulmonary capillary perfusion because current microscopy requires direct access to lung tissue with surgical intervention such as the thoracic-window technique and open-lung model. To evaluate if probe-based confocal laser scanning endomicroscopy (pCLE) via the trachea allows for real-time in-vivo visualisation of pulmonary capillary density and red blood cell (RBC) velocity in pigs. An interventional animal study. European University Hospital. Nine female domestic pigs (50 to 60 kg) were used. A pCLE probe was positioned in non-dependent, central and dependent lung zones in nine anaesthetised pigs (Alveoflex, Cellvizio, Maunakea, France). After intravenous administration of fluorescein isothiocyanate dextran as contrast agent repetitive pCLE videos were recorded during pressure-controlled ventilation (PCV) or continuous positive airway pressure for 3 min each. Using fluorescein isothiocyanate-labelled RBC erythrocyte velocities in pulmonary capillaries were quantified. Data are expressed as mean ± SD or median with interquartile range (IQR). Capillary density was greater in dependent and central as compared with non-dependent lung zones [[32 (29 to 34) %] and 32 (30 to 34) % vs. 28 (26 to 28) %, respectively, P < 0.05]. During PCV, RBC velocities were higher in larger lung capillaries [diameter >20 μm, 309 μm s(-1) (209 to 397)] than intermediate [diameter 10.1 to 20 μm, 146 μm s(-1) (118 to 235)] and small [diameter <10 μm, 153 μm s(-1) (117 to 236), P < .05]. During continuous positive airway pressure of 1.5 kPa, RBC velocities in dependent lung areas decreased to 47 μm s(-1) (30 to 82) compared with 198 μm s(-1) (148 to 290) during PCV (P < 0.05). pCLE allows endoscopic real-time in-vivo imaging of pulmonary capillary morphology and perfusion. Alterations in pulmonary capillary blood flow induced by different ventilator regimens can be detected. This minimally invasive approach via the endotracheal route is feasible in an experimental setting and may help to understand changes in regional pulmonary capillary perfusion.

TU‐CD‐BRA‐08: Single‐Energy Computed Tomography‐Based Pulmonary Perfusion Imaging: Proof‐Of‐Principle in a Canine Model

Purpose:Pulmonary perfusion imaging has provided significant insights into pulmonary diseases, and can be useful in radiotherapy. The purpose of this study was to prospectively establish proof‐of‐principle in a canine model for single‐energy CT‐based perfusion imaging, which has the potential for widespread clinical implementation.Methods:Single‐energy CT perfusion imaging is based on: (1) acquisition of inspiratory breath‐hold CT scans before and after intravenous injection of iodinated contrast medium, (2) deformable image registration (DIR) of the two CT image data sets, and (3) subtraction of the pre‐contrast image from post‐contrast image, yielding a map of Hounsfield unit (HU) enhancement. These subtraction image data sets hypothetically represent perfused blood volume, a surrogate for perfusion. In an IACUC‐approved clinical trial, we acquired pre‐ and post‐contrast CT scans in the prone posture for six anesthetized, mechanically‐ventilated dogs. The elastix algorithm was used for DIR. The registration accuracy was quantified using the target registration errors (TREs) for 50 pulmonary landmarks in each dog. The gradient of HU enhancement between gravity‐dependent (ventral) and non‐dependent (dorsal) regions was evaluated to quantify the known effect of gravity, i.e., greater perfusion in ventral regions.Results:The lung volume difference between the two scans was 4.3±3.5% on average (range 0.3%–10.1%). DIR demonstrated an average TRE of 0.7±1.0 mm. HU enhancement in lung parenchyma was 34±10 HU on average and varied considerably between individual dogs, indicating the need for improvement of the contrast injection protocol. HU enhancement in ventral (gravity‐dependent) regions was found to be greater than in dorsal regions. A population average ventral‐to‐dorsal gradient of HU enhancement was strong (R2=0.94) and statistically significant (p&lt;0.01).Conclusion:This canine study demonstrated relatively accurate DIR and a strong ventral‐to‐dorsal gradient of HU enhancement, providing proof‐of‐principle for single‐energy CT pulmonary perfusion imaging. This ongoing study will enroll more dogs and investigate the physiological significance.This study was supported by a Philips Healthcare/Radiological Society of North America (RSNA) Research Seed Grant (RSD1458).

Quantitative assessment of pulmonary perfusion using dynamic contrast-enhanced CT in patients with chronic obstructive pulmonary disease: correlations with pulmonary function test and CT volumetric parameters.

Pulmonary function test (PFT) is commonly used to help diagnose chronic obstructive pulmonary disease (COPD) and other lung diseases. However, it cannot be used to evaluate regional function and morphological abnormalities. To quantitatively evaluate pulmonary perfusion imaging using dynamic contrast-enhanced (DCE) computed tomography (CT) and observe its correlations with PFT and CT volumetric parameters in COPD patients. PFT and CT pulmonary perfusion examination were performed in 63 COPD patients. Perfusion defects were quantitated by calculating the CT value ratio (RHU) between perfusion defects (HUdefect) and normal lung (HUnormal). Volumetric CT data were used to calculate emphysema index (EI), total lung volume (TLV), and total emphysema volume (TEV). Emphysematous parenchyma was defined as the threshold of lung area lower than -950 HU. Correlations between RHU and TLV, TEV, EI, and PFT were assessed using Spearman correlation analysis. The positive rate of perfusion defects on CT perfusion images was higher than that of emphysema on CT mask images (χ(2) = 17.027, P < 0.001). The Spearman correlation test showed that RHU was positively correlated with FEV1 (R = 0.59, P < 0.001), FEV1% Predicted (R = 0.61, P < 0.001), FVC (R = 0.47, P = 0.002), and FEV1/FVC (R = 0.65, P < 0.001), and negatively correlated with EI (R = -0.67, P < 0.001). CT perfusion imaging is more sensitive in detecting emphysema that is inconspicuous on CT images. RHU is correlated with PFT and CT volumetric parameters, suggesting that it is more sensitive in detecting early COPD changes and may prove to be a potential predictor of focal lung function.

Three-dimensional pulmonary perfusion MRI with radial ultrashort echo time and spatial-temporal constrained reconstruction.

To assess the feasibility of spatial-temporal constrained reconstruction for accelerated regional lung perfusion using highly undersampled dynamic contrast-enhanced (DCE) three-dimensional (3D) radial MRI with ultrashort echo time (UTE). A combined strategy was used to accelerate DCE MRI for 3D pulmonary perfusion with whole lung coverage. A highly undersampled 3D radial UTE MRI acquisition was combined with an iterative constrained reconstruction exploiting principal component analysis and wavelet soft-thresholding for dimensionality reduction in space and time. The performance of the method was evaluated using a 3D fractal-based DCE digital lung phantom. Simulated perfusion maps and contrast enhancement curves were compared with ground truth using the structural similarity index (SSIM) to determine robust threshold and regularization levels. Feasibility studies were then performed in a canine and a human subject with 3D radial UTE (TE=0.08 ms) acquisition to assess feasibility of mapping regional 3D perfusion. The method was able to accurately recover perfusion maps in the phantom with a nominal isotropic spatial resolution of 1.5 mm (SSIM of 0.949). The canine and human subject studies demonstrated feasibility for providing artifact-free perfusion maps in a simple 3D breath-held acquisition. The proposed method is promising for fast and flexible 3D pulmonary perfusion imaging. Magn Reson

Simultaneous MRI of lung structure and perfusion in a single breathhold

To develop and demonstrate a breathheld 3D radial ultrashort echo time (UTE) acquisition to visualize co-registered lung perfusion and vascular structure. Nine healthy dogs were scanned twice at 3 Tesla (T). Contrast-enhanced pulmonary perfusion scans were acquired with a temporally interleaved three-dimensional (3D) radial UTE (TE = 0.08 ms) sequence in a breathhold (1 s time frames over a 33 s breathhold). The 3D breathheld volume was reconstructed into time-resolved perfusion datasets, and a composite vascular structure dataset. For structural comparison, a 5 min respiratory-gated 3D radial UTE scan was acquired. Data were analyzed by quantitative metrics and radiologist scoring. Appropriate time-course of contrast was seen in all subjects. Right ventricle to aorta transit times were 7.4 ± 2.0 s. Relative lung enhancement was a factor of 8.4 ± 1.5. Radiologist scoring showed similarly excellent visualization of the pulmonary arteries to the subsegmental level in breathheld (94% of cases) and respiratory-gated (100% of cases) acquisitions (P = 0.33) despite the aggressive under sampling in the breathheld scan. Similarly, differentiation of lung tissue and airways was achieved by both acquisition methods. A time-resolved 3D radial UTE sequence for simultaneous imaging of pulmonary perfusion and co-registered vascular structure is feasible.

High-resolution imaging of pulmonary ventilation and perfusion with 68Ga-VQ respiratory gated (4-D) PET/CT

Our group has previously reported on the use of (68)Ga-ventilation/perfusion (VQ) PET/CT scanning for the diagnosis of pulmonary embolism. We describe here the acquisition methodology for (68)Ga-VQ respiratory gated (4-D) PET/CT and the effects of respiratory motion on image coregistration in VQ scanning. A prospective study was performed in 15 patients with non-small-cell lung cancer. 4-D PET and 4-D CT images were acquired using an infrared marker on the patient's abdomen as a surrogate for breathing motion following inhalation of Galligas and intravenous administration of (68)Ga-macroaggregated albumin. Images were reconstructed with phase-matched attenuation correction. The lungs were contoured on CT and PET VQ images during free-breathing (FB) and at maximum inspiration (Insp) and expiration (Exp). The similarity between PET and CT volumes was measured using the Dice coefficient (DC) comparing the following groups; (1) FB-PET/CT, (2) InspPET/InspCT, (3) ExpPET/Exp CT, and (4) FB-PET/AveCT. A repeated measures one-way ANOVA with multiple comparison Tukey tests were performed to evaluate any difference between the groups. Diaphragmatic motion in the superior-inferior direction on the 4-D CT scan was also measured. 4-D VQ scanning was successful in all patients without additional acquisition time compared to the nongated technique. The highest volume overlap was between ExpPET and ExpCT and between FB-PET and AveCT with a DC of 0.82 and 0.80 for ventilation and perfusion, respectively. This was significantly better than the DC comparing the other groups (0.78-0.79, p < 0.05). These values agreed with a visual inspection of the images with improved image coregistration around the lung bases. The diaphragmatic motion during the 4-D CT scan was highly variable with a range of 0.4-3.4cm (SD 0.81cm) in the right lung and 0-2.8cm (SD 0.83cm) in the left lung. Right-sided diaphragmatic nerve palsy was observed in 3 of 15 patients. (68)Ga-VQ 4-D PET/CT is feasible and the blurring caused by respiratory motion is well corrected with 4-D acquisition, which principally reduces artefact at the lung bases. The images with the highest spatial overlap were the combined expiration phase or FB PET and average CT. With higher resolution than SPECT/CT, the PET/CT technique has a broad range of potential clinical applications including diagnostic algorithms for patients with suspected pulmonary embolism, preoperative evaluation of regional lung function and improving assessment or understanding of pulmonary physiology in the vast range of pulmonary diseases.

Comparative study of three dimensional dynamic contrast-enhanced MR perfusion imaging in healthy volunteers and patients with chronic obstructive pulmonary disease

Objective To prospectively compare MR pulmonary perfusion imaging with quantitative HRCT for the detection of mild chronic obstructive pulmonary disease (COPD) and classification of COPD. Methods Sixty-two consecutive patients with COPD and 17 healthy volunteers underwent pulmonary function test (PFT),HRCT and MR perfusion imaging on the same day.According to the Global Initiative for Chronic Obstructive Lung Disease (GOLD),all COPD patients were classified into 4 stages:stageⅠ (n=19),stageⅡ (n=17),stageⅢ (n=14),stageⅣ Key words: Pulmonary disease,chronic obstructive; Respiratory function tests; Magnetic resonance imaging; Tomography,X-ray computed

Preliminary Results on Different Impedance Contrast Agents for Pulmonary Perfusion Imaging with Electrical Impedance Tomography

Recent studies in animal models suggest that the use of small volume boluses of NaCl as an impedance contrast agent can significantly improve pulmonary perfusion imaging by Electrical Impedance Tomography (EIT). However, these studies used highly concentrated NaCl solution (20%) which may have adverse effects on the patients. In a pilot experiment, we address this problem by comparing a number of different Impedance Contrast Boluses (ICBs). Conductivity changes in the lungs of a sheep after the injection of four different ICBs were compared, including three NaCl-based ICBs and one glucose-based ICB. The following procedure was followed for each ICB. Firstly, ventilation was turned off to provide an apneic window of approximately 40s to image the conductivity changes due to the ICB. Each ICB was then injected through a pig-tail catheter directly into the right atrium. EIT images were acquired throughout the apnea to capture the conductivity change. For each ICB, the experiment was repeated three times. The three NaCl-based ICB exhibited similar behaviour in which following the injection of each of these ICBs, the conductivity of each lung predictably increased. The effect of the ICB of 5% glucose solution was inconclusive. A small decrease in conductivity in the left lung was observed in two out of three cases and none was discernible in the right lung.

Pulmonary perfusion MRI using interleaved variable density sampling and HighlY constrained cartesian reconstruction (HYCR)

To demonstrate the feasibility of performing single breathhold, noncardiac gated, ultrafast, high spatial-temporal resolution whole chest MR pulmonary perfusion imaging in humans. Eight subjects (five male, three female) were scanned with the proposed method on a 3 Tesla clinical scanner using a 32-channel phased-array coil. Seven (88%) were healthy volunteers, and one was a patient volunteer with sarcoidosis. The peak lung enhancement phase for each subject was scored for gravitational effect, peak parenchymal enhancement and severity of artifacts by three cardiothoracic radiologists independently. All studies were successfully performed by MR technologists without any additional training. Mean parenchymal signal was very good, measuring 0.78 ± 0.13 (continuous scale, 0 = "none" → 1 = "excellent"). Mean level of motion artifacts was low, measuring 0.13 ± 0.08 (continuous scale, 0 = "none" → 1 = "severe"). It is feasible to perform single breathhold, noncardiac gated, ultrafast, high spatial-temporal resolution whole chest MR pulmonary perfusion imaging in humans.

Cardiac mapping of electrical impedance tomography by means of a wavelet model

To improve the identification of cardiac regions in Electrical impedance tomography (EIT) pulmonary perfusion images, a model of wavelet transform was developed. The main goal was to generate maps of the heart using EIT images in a controlled animal experiment using a healthy pig and in two human volunteers. The model was capable of identifying the heart regions, demonstrated robustness and generated satisfactory results. The pig images were compared to perfusion images obtained using injection of a hypertonic solution and achieved an average area of the ROC curve of 0.88. The human images were qualitatively compared with Computerized Tomography scan (CT-scan) images.

Capability of differentiating smokers with normal pulmonary function from COPD patients: a comparison of CT pulmonary volume analysis and MR perfusion imaging

To compare CT volume analysis with MR perfusion imaging in differentiating smokers with normal pulmonary function (controls) from COPD patients. Sixty-two COPD patients and 17 controls were included. The total lung volume (TLV), total emphysema volume (TEV) and emphysema index (EI) were quantified by CT. MR perfusion evaluated positive enhancement integral (PEI), maximum slope of increase (MSI), maximum slope of decrease (MSD), signal enhancement ratio (SER) and signal intensity ratio (RSI) of perfusion defects to normal lung. There were 19 class I, 17 class II, 14 class III and 12 class IV COPD patients. No differences were observed in TLV, TEV and EI between control and class I COPD. The control was different from class II, III and IV COPD in TEV and EI. The control was different from each class of COPD in RSI, MSI, PEI and MSD. Differences were found in RSI between class I and III, I and IV, and II and IV COPD. Amongst controls, MR detected perfusion defects more frequently than CT detected emphysema. Compared with CT, MR perfusion imaging shows higher potential to distinguish controls from mild COPD and appears more sensitive in identifying abnormalities amongst smokers with normal pulmonary function (controls). • Detailed information is needed to diagnose chronic obstructive pulmonary disease. • High-resolution CT provides detailed anatomical and quantitative information. • Magnetic resonance imaging is demonstrating increasing potential in pulmonary function imaging. • MR perfusion can distinguish mild COPD patients from controls. • MRI appears more sensitive than CT in identifying early abnormalities amongst controls.

Application of dual-energy scanning technique with dual-source CT in pulmonary mass lesions

Objective To explore the feasibility of DSCT dual-energy technique in pulmonary mass lesions.Methods A total of 100 patients with pulmonary masses underwent conventional plain CT scan and dual-energy enhanced CT scan.The virtual non-contrast (VNC) images were obtained at post-processing workstation.The mean CT value,enhancement value,signal to noise ratio (SNR),image quality and radiation dose of pulmonary masses were compared between the two scan techniques using F or t test and the detectability of lesions was compared using Wilcoxon test. Results There was no statistically significant difference among VNC ( A ) ( 32.89 ± 12.58 ) HU,VNC (S) ( 30.86 ± 9.60) HU and conventional plain images (35.89 ± 9.99 ) HU in mean CT value of mass ( F =2.08,P ＞ 0.05 ).There was statistically significant difference among VNC ( A ) ( 3.29 ± 1.45 ),VNC (S) ( 3.93 ± 1.49 ) and conventional plain image (4.61 ± 1.50) in SNR ( F =6.01,P ＜ 0.05 ),which of conventional plain scan was higher than that of VNC.The enhancement value of mass in conventional enhanced scan(60.74 ± 13.9)HU and distribution of iodine from VNC (A) ( 58.26 ± 31.99 ) HU was no statistically significant difference ( t =0.48,P ＞ 0.05 ),but there was a significant difference between conventional enhanced scan (56.51 ± 17.94 ) HU and distribution of iodine from VNC (S) (52.65 ± 16.78 ) HU (t =4.45,P ＜ 0.05 ).There was no statistically significant difference among conventional plain scan ( 4.69 ± 0.06 ) and VN C ( A ) ( 4.60 ± 0.09 ),VNC (S)(4.61 ±0.11 ) in image quality at mediastinal window ( F =3.014,P ＞ 0.05 ).The appearance,size,internal features of mass (such as necrosis,calcification and cavity) were showed the same in conventional plain scan,VNC (A) and VNC (S).Of 41 patients with hilar mass,18 patients were found to have lobular and segmental perfusion decrease or defect. Perfusion defect area was found in 59 patients with peripheral lung mass. The radiation dose of dual-energy enhanced scan was lower than that of conventional scan.Conclusion The virtual non-contrast,distribution of iodine and pulmonary virtual perfusion images can be obtained by DSCT dual-energy technique in one scan,which has a potential clinical value in the thorax. Key words: Lung,neoplasms; Tomography,X-ray computed; Radiation dosage

Pulmonary arterial hypertension: an imaging review comparing MR pulmonary angiography and perfusion with multidetector CT angiography

Pulmonary hypertension (PH) is a progressive disease that leads to substantial morbidity and eventual death. Pulmonary multidetector CT angiography (MDCTA), pulmonary MR angiography (MRA) and MR-derived pulmonary perfusion (MRPP) imaging are non-invasive imaging techniques for the differential diagnosis of PH. MDCTA is considered the gold standard for the diagnosis of pulmonary embolism, one of the most common causes of PH. MRA and MRPP are promising techniques that do not require the use of ionising radiation or iodinated contrast material, and can be useful for patients for whom such material cannot be used. This review compares the imaging aspects of pulmonary MRA and 64-row MDCTA in patients with chronic thromboembolic or idiopathic PH.

Optimization of the scanning technique and diagnosis of pulmonary nodules with first-pass 64-detector-row perfusion VCT

ObjectiveThe aims of this study were to optimize the scanning technique of first-pass 64-detector-row perfusion volume computed tomography imaging, to evaluate the effectiveness and stability of this scan protocol, and lastly to evaluate the differential diagnosis ability of perfusion imaging in solitary pulmonary nodules (SPNs). MethodsA total of 144 patients with SPNs underwent perfusion scan with 64-slice spiral CT scanner. The CT perfusion imaging was analyzed for time–density curve, perfusion parametric maps, and the respective perfusion parameters. We then analyzed the main factors concerning the imaging quality and evaluated the effectiveness of scan protocol by determining the receiver operating characteristic (ROC) curve, diagnostic efficacy, and odds ratio as well as the stability of scan protocol by consistency analysis. Immunohistochemical findings of microvessel density measurement and vascular endothelial growth factor expression were evaluated. ResultsThe total sensitivity, specificity, accuracy, positive predictive value, negative predictive value, likelihood ratio, and the area under ROC curve during 5–45-s scan period were 78.95%, 82.4%, 80.6%, 83.3%, 77.8%, 4.620, 0.280, and 0.840, respectively, and Kappa value was 0.894. The diagnostic efficacy of CT pulmonary perfusion was significantly higher than during 0–40-s scan period. The parameter values in different nodules were different. ConclusionThe optimized 5–45-s scan period of CT pulmonary perfusion imaging is effective in pathologic diagnosis and has good stability, worthy of being popularized. Lung perfusion CT could be a promising and feasible method for differentiation of SPNs.

Application value of pulmonary perfusion and ventilation imaging during diagnosis and treatment of pulmonary embolism

肺通气灌注(V/Q)显像于20世纪60年代末进入临床,是成熟的诊断肺栓塞影像学检查.它通过直接显示肺动脉阻塞导致的肺组织血流灌注缺损而诊断肺栓塞,确定肺栓塞的部位、范围.和传统平面V/Q显像相比,新近发展的V/Q断层显像(V/QSPECT)诊断肺栓塞的准确性更高,定位、定量更精确,可发现更多的外周型肺栓塞病灶;其诊断肺栓塞的敏感度为96％～99％,特异度为91％～98％[1-4]。

Quantitative pulmonary perfusion imaging at 3.0 T of 2-year-old children after congenital diaphragmatic hernia repair: initial results

To investigate whether dynamic contrast-enhanced MR imaging of the lung following congenital diaphragmatic hernia repair is feasible at 3.0 T in 2-year-old children and whether associated lung hypoplasia (reflected in reduced pulmonary microcirculation) can be demonstrated in MRI. Twelve children with a mean age 2.0 ± 0.2 years after hernia repair underwent DCE-MRI at 3.0 T using a time-resolved angiography with stochastic trajectories sequence. Quantification of lung perfusion was performed using a pixel-by-pixel deconvolution approach. Six regions of interest were placed (upper, middle and lower parts of right and left lung) to assess differences in pulmonary blood flow (PBF), pulmonary blood volume (PBV) and mean transit time (MTT) while avoiding the inclusion of larger pulmonary arteries and veins. The difference in PBF and PBV between ipsilateral and contralateral lung was significant (P < 0.5). No significant differences could be detected for the MTT (P = 0.5). DCE-MRI in 2-year-old patients is feasible at 3.0 T. Reduced perfusion in the ipsilateral lung is reflected by significantly lower PBF values compared with the contralateral lung. DCE-MRI of the lung in congenital diaphragmatic hernia can help to characterise lung hypoplasia initially and in the long-term follow-up of children after diaphragmatic repair. Congenital diaphragmatic hernia often leads to lung hypoplasia and secondary pulmonary hypertension. Dynamic contrast-enhanced 3-T magnetic resonance can assess these complications in 2-year-olds. The affected ipsilateral lung shows reduced perfusion and lower pulmonary blood flow. Thoracic DCE-MRI helps characterise lung hypoplasia in children after hernia repair.

Dynamic pulmonary perfusion imaging in patients with idiopathic pulmonary arterial hypertension

Objective To investigate the value of dynamic PPI in patients with IPAH.Methods Twenty consecutive patients with IPAH underwent dynamic PPI and right ventricular catheterization.Ten healthy volunteers were also recruited in this study as control.Total lung ROI was drawn to calculate time-activity curves from dynamic PPI.Lung equilibrium time (LET),the duration from 99Tcm-MAA entering the lungs to equilibrium,was measured.Comparisons between two groups were carried out using t-test.Correlations between LET and hemodynamic parameters were determined by Pearson correlation analysis.Results LET was significantly prolonged in IPAH patients over the control group ( (33.9 ± 15.5) s vs ( 14.4 ± 3.7) s,t =5.340,P ＜0.001).Significant correlations were found between LET and mPAP(r =0.566,P ＜0.01) and between LET and total pulmonary resistance (TPR) measured by right heart catheterization (r =0.688,P ＜0.05).LET had a negative linear relationship with CI (r=-0.480,P ＜0.05).Conclusion Dynamic PPI is a practical and noninvasive method for evaluating the haemodynamic function of right heart in patients with IPAH. Key words: Hypertension, pulmonary; Radionuclide imaging; MAA

In vivo MR imaging of pulmonary perfusion and gas exchange in rats via continuous extracorporeal infusion of hyperpolarized 129Xe.

BackgroundHyperpolarized (HP) 129Xe magnetic resonance imaging (MRI) permits high resolution, regional visualization of pulmonary ventilation. Additionally, its reasonably high solubility (>10%) and large chemical shift range (>200 ppm) in tissues allow HP 129Xe to serve as a regional probe of pulmonary perfusion and gas transport, when introduced directly into the vasculature. In earlier work, vascular delivery was accomplished in rats by first dissolving HP 129Xe in a biologically compatible carrier solution, injecting the solution into the vasculature, and then detecting HP 129Xe as it emerged into the alveolar airspaces. Although easily implemented, this approach was constrained by the tolerable injection volume and the duration of the HP 129Xe signal.Methods and Principal FindingsHere, we overcome the volume and temporal constraints imposed by injection, by using hydrophobic, microporous, gas-exchange membranes to directly and continuously infuse 129Xe into the arterial blood of live rats with an extracorporeal (EC) circuit. The resulting gas-phase 129Xe signal is sufficient to generate diffusive gas exchange- and pulmonary perfusion-dependent, 3D MR images with a nominal resolution of 2×2×2 mm3. We also show that the 129Xe signal dynamics during EC infusion are well described by an analytical model that incorporates both mass transport into the blood and longitudinal relaxation.ConclusionsExtracorporeal infusion of HP 129Xe enables rapid, 3D MR imaging of rat lungs and, when combined with ventilation imaging, will permit spatially resolved studies of the ventilation-perfusion ratio in small animals. Moreover, EC infusion should allow 129Xe to be delivered elsewhere in the body and make possible functional and molecular imaging approaches that are currently not feasible using inhaled HP 129Xe.

Hemodynamic changes vs pathologic foundation in rabbit models of radiation-induced lung injury: a preliminary study

Objective To study the hemodynamic changes and pathologic foundation of rabbit models of radiation-induced lung injury (RILI) via 64-slice CT pulmonary perfusion imaging ( CTPI),in order to seek the correlation between the alterations of the hemodynamic parameters and pathophysiology.Methods Seventy-two healthy New Zealand rabbits were randomly classified into two groups:test group ( n =36),received 25 Gy with single fraction irradiation in a whole unilateral lung; control group ( n =36),received sham-irradiation.Each group was divided into 12 subgroups respectively according to post- and pseudo-irradiation time points (1,6,12,24,48,72 h and 1,2,4,8,16,24 w).Each rabbit underwent HRCT and CTPI at every pre- and post-radiation time point.All rabbits were sacrificed,and morphology of specimens was observed using light- and electron microscope. The changing regularity of HRCT,CTPI parameters and pathology were analyzed and compared with each other in order to find the correlation among them.The CTPI parameters of the test and control groups were compared using t test.The CTPI parameters and pathological values were analyzed using linear correlation with two variables,the detection rates of RILI by CTPI and HRCT was compared using Chi-square test.Results ( 1 ) The changes of CTPI parameters from control group after irradiation was relatively stable,but in test group those parameters including rBF,rBV and rPS,at pre- and post-irradiation time points (0,72 h and 2 w),were respectively 1.01 ± 0.09,1.86 ± 0.20,1.43 ±0.12,1.03 ±0.08,1.63 ±0.19,1.56±0.14,0.96±0.12,1.54 ±0.17 and 1.83 ±0.24.The corresponding parameters before and after irradiation were significantly different ( t =2.90-6.37,P ＞ 0.05).(2)In test group,capillary endothelial cells,basement membrane and alveolar epithelial cells,as the main injury targets,showed certain alterations in pathology.There was a significant correlation between the changes of CTPI parameters ( rBF and rBV) and pathophysiology in control group ( r =0.74,0.83,P ＜0.05 ),with the dependent relationship between rPS and the amounts of RBC outside the capillary and the destruction of basement membrane( r =0.87,0.88,P ＜ 0.01 ).(3)The detection rate of RILI with CTPI (72.2％,26/36) was obviously higher than that with HRCT( 16.7％,6/36,x2 =4.37,P =0.036).Conclusions CTPI parameters is capable of revealing the rule of hemodynamic process and reflecting the pathophysiologic state of different stages of RILI.By the time of detecting RILI,the detection rate of CTPI is clearly superior to that of HRCT,which yields potential value in predicting RILL Key words: Radiation pneumonitis ; Hemodynamic processes ; Tomography,X-ray comPuted; Pathology

Pulmonary perfusion imaging using MRI: clinical application

BackgroundLung perfusion is one of the key components of oxygenation. It is hampered in pulmonary arterial diseases and secondary due to parenchymal diseases.MethodsAssessment is frequently required during the workup of a patient for either of these disease categories.ResultsThis review provides insight into imaging techniques, qualitative and quantitative evaluation, and focuses on clinical application of MR perfusion.ConclusionThe two major techniques, non-contrast-enhanced (arterial spin labeling) and contrast-enhanced perfusion techniques, are discussed.